26720 lines
1002 KiB
Plaintext
26720 lines
1002 KiB
Plaintext
@c Copyright (C) 1988-2017 Free Software Foundation, Inc.
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@c This is part of the GCC manual.
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@c For copying conditions, see the file gcc.texi.
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@ignore
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@c man begin INCLUDE
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@include gcc-vers.texi
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@c man end
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@c man begin COPYRIGHT
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Copyright @copyright{} 1988-2017 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``GNU General Public License'' and ``Funding
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Free Software'', the Front-Cover texts being (a) (see below), and with
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the Back-Cover Texts being (b) (see below). A copy of the license is
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included in the gfdl(7) man page.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development.
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@c man end
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@c Set file name and title for the man page.
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@setfilename gcc
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@settitle GNU project C and C++ compiler
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@c man begin SYNOPSIS
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gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
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[@option{-g}] [@option{-pg}] [@option{-O}@var{level}]
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[@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}]
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[@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}]
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[@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}]
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[@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}]
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[@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
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Only the most useful options are listed here; see below for the
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remainder. @command{g++} accepts mostly the same options as @command{gcc}.
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@c man end
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@c man begin SEEALSO
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gpl(7), gfdl(7), fsf-funding(7),
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cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1)
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and the Info entries for @file{gcc}, @file{cpp}, @file{as},
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@file{ld}, @file{binutils} and @file{gdb}.
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@c man end
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@c man begin BUGS
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For instructions on reporting bugs, see
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@w{@value{BUGURL}}.
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@c man end
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@c man begin AUTHOR
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See the Info entry for @command{gcc}, or
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@w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}},
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for contributors to GCC@.
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@c man end
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@end ignore
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@node Invoking GCC
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@chapter GCC Command Options
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@cindex GCC command options
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@cindex command options
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@cindex options, GCC command
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@c man begin DESCRIPTION
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When you invoke GCC, it normally does preprocessing, compilation,
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assembly and linking. The ``overall options'' allow you to stop this
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process at an intermediate stage. For example, the @option{-c} option
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says not to run the linker. Then the output consists of object files
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output by the assembler.
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@xref{Overall Options,,Options Controlling the Kind of Output}.
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Other options are passed on to one or more stages of processing. Some options
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control the preprocessor and others the compiler itself. Yet other
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options control the assembler and linker; most of these are not
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documented here, since you rarely need to use any of them.
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@cindex C compilation options
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Most of the command-line options that you can use with GCC are useful
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for C programs; when an option is only useful with another language
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(usually C++), the explanation says so explicitly. If the description
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for a particular option does not mention a source language, you can use
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that option with all supported languages.
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@cindex cross compiling
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@cindex specifying machine version
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@cindex specifying compiler version and target machine
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@cindex compiler version, specifying
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@cindex target machine, specifying
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The usual way to run GCC is to run the executable called @command{gcc}, or
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@command{@var{machine}-gcc} when cross-compiling, or
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@command{@var{machine}-gcc-@var{version}} to run a specific version of GCC.
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When you compile C++ programs, you should invoke GCC as @command{g++}
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instead. @xref{Invoking G++,,Compiling C++ Programs},
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for information about the differences in behavior between @command{gcc}
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and @code{g++} when compiling C++ programs.
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@cindex grouping options
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@cindex options, grouping
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The @command{gcc} program accepts options and file names as operands. Many
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options have multi-letter names; therefore multiple single-letter options
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may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d
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-v}}.
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@cindex order of options
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@cindex options, order
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You can mix options and other arguments. For the most part, the order
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you use doesn't matter. Order does matter when you use several
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options of the same kind; for example, if you specify @option{-L} more
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than once, the directories are searched in the order specified. Also,
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the placement of the @option{-l} option is significant.
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Many options have long names starting with @samp{-f} or with
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@samp{-W}---for example,
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@option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of
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these have both positive and negative forms; the negative form of
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@option{-ffoo} is @option{-fno-foo}. This manual documents
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only one of these two forms, whichever one is not the default.
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@c man end
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@xref{Option Index}, for an index to GCC's options.
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@menu
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* Option Summary:: Brief list of all options, without explanations.
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* Overall Options:: Controlling the kind of output:
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an executable, object files, assembler files,
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or preprocessed source.
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* Invoking G++:: Compiling C++ programs.
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* C Dialect Options:: Controlling the variant of C language compiled.
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* C++ Dialect Options:: Variations on C++.
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* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
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and Objective-C++.
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* Diagnostic Message Formatting Options:: Controlling how diagnostics should
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be formatted.
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* Warning Options:: How picky should the compiler be?
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* Debugging Options:: Producing debuggable code.
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* Optimize Options:: How much optimization?
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* Instrumentation Options:: Enabling profiling and extra run-time error checking.
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* Preprocessor Options:: Controlling header files and macro definitions.
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Also, getting dependency information for Make.
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* Assembler Options:: Passing options to the assembler.
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* Link Options:: Specifying libraries and so on.
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* Directory Options:: Where to find header files and libraries.
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Where to find the compiler executable files.
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* Code Gen Options:: Specifying conventions for function calls, data layout
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and register usage.
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* Developer Options:: Printing GCC configuration info, statistics, and
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debugging dumps.
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* Submodel Options:: Target-specific options, such as compiling for a
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specific processor variant.
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* Spec Files:: How to pass switches to sub-processes.
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* Environment Variables:: Env vars that affect GCC.
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* Precompiled Headers:: Compiling a header once, and using it many times.
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@end menu
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@c man begin OPTIONS
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@node Option Summary
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@section Option Summary
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Here is a summary of all the options, grouped by type. Explanations are
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in the following sections.
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@table @emph
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@item Overall Options
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@xref{Overall Options,,Options Controlling the Kind of Output}.
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@gccoptlist{-c -S -E -o @var{file} -x @var{language} @gol
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-v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help --version @gol
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-pass-exit-codes -pipe -specs=@var{file} -wrapper @gol
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@@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol
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-fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}}
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@item C Language Options
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@xref{C Dialect Options,,Options Controlling C Dialect}.
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@gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol
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-fpermitted-flt-eval-methods=@var{standard} @gol
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-aux-info @var{filename} -fallow-parameterless-variadic-functions @gol
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-fno-asm -fno-builtin -fno-builtin-@var{function} -fgimple@gol
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-fhosted -ffreestanding -fopenacc -fopenmp -fopenmp-simd @gol
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-fms-extensions -fplan9-extensions -fsso-struct=@var{endianness} @gol
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-fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol
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-fsigned-bitfields -fsigned-char @gol
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-funsigned-bitfields -funsigned-char}
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@item C++ Language Options
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@xref{C++ Dialect Options,,Options Controlling C++ Dialect}.
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@gccoptlist{-fabi-version=@var{n} -fno-access-control @gol
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-faligned-new=@var{n} -fargs-in-order=@var{n} -fcheck-new @gol
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-fconstexpr-depth=@var{n} -fconstexpr-loop-limit=@var{n} @gol
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-ffriend-injection @gol
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-fno-elide-constructors @gol
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-fno-enforce-eh-specs @gol
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-ffor-scope -fno-for-scope -fno-gnu-keywords @gol
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-fno-implicit-templates @gol
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-fno-implicit-inline-templates @gol
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-fno-implement-inlines -fms-extensions @gol
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-fnew-inheriting-ctors @gol
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-fnew-ttp-matching @gol
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-fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol
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-fno-optional-diags -fpermissive @gol
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-fno-pretty-templates @gol
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-frepo -fno-rtti -fsized-deallocation @gol
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-ftemplate-backtrace-limit=@var{n} @gol
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-ftemplate-depth=@var{n} @gol
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-fno-threadsafe-statics -fuse-cxa-atexit @gol
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-fno-weak -nostdinc++ @gol
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-fvisibility-inlines-hidden @gol
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-fvisibility-ms-compat @gol
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-fext-numeric-literals @gol
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-Wabi=@var{n} -Wabi-tag -Wconversion-null -Wctor-dtor-privacy @gol
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-Wdelete-non-virtual-dtor -Wliteral-suffix -Wmultiple-inheritance @gol
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-Wnamespaces -Wnarrowing @gol
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-Wnoexcept -Wnon-virtual-dtor -Wreorder -Wregister @gol
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-Weffc++ -Wstrict-null-sentinel -Wtemplates @gol
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-Wno-non-template-friend -Wold-style-cast @gol
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-Woverloaded-virtual -Wno-pmf-conversions @gol
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-Wsign-promo -Wvirtual-inheritance}
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@item Objective-C and Objective-C++ Language Options
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@xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
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Objective-C and Objective-C++ Dialects}.
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@gccoptlist{-fconstant-string-class=@var{class-name} @gol
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-fgnu-runtime -fnext-runtime @gol
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-fno-nil-receivers @gol
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-fobjc-abi-version=@var{n} @gol
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-fobjc-call-cxx-cdtors @gol
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-fobjc-direct-dispatch @gol
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-fobjc-exceptions @gol
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-fobjc-gc @gol
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-fobjc-nilcheck @gol
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-fobjc-std=objc1 @gol
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-fno-local-ivars @gol
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-fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} @gol
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-freplace-objc-classes @gol
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-fzero-link @gol
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-gen-decls @gol
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-Wassign-intercept @gol
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-Wno-protocol -Wselector @gol
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-Wstrict-selector-match @gol
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-Wundeclared-selector}
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@item Diagnostic Message Formatting Options
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@xref{Diagnostic Message Formatting Options,,Options to Control Diagnostic Messages Formatting}.
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@gccoptlist{-fmessage-length=@var{n} @gol
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-fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol
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-fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]} @gol
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-fno-diagnostics-show-option -fno-diagnostics-show-caret @gol
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-fdiagnostics-parseable-fixits -fdiagnostics-generate-patch @gol
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-fno-show-column}
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@item Warning Options
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@xref{Warning Options,,Options to Request or Suppress Warnings}.
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@gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol
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-pedantic-errors @gol
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-w -Wextra -Wall -Waddress -Waggregate-return @gol
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-Walloc-zero -Walloc-size-larger-than=@var{n}
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-Walloca -Walloca-larger-than=@var{n} @gol
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-Wno-aggressive-loop-optimizations -Warray-bounds -Warray-bounds=@var{n} @gol
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-Wno-attributes -Wbool-compare -Wbool-operation @gol
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-Wno-builtin-declaration-mismatch @gol
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-Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat @gol
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-Wc++-compat -Wc++11-compat -Wc++14-compat -Wcast-align -Wcast-qual @gol
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-Wchar-subscripts -Wclobbered -Wcomment -Wconditionally-supported @gol
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-Wconversion -Wcoverage-mismatch -Wno-cpp -Wdangling-else -Wdate-time @gol
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-Wdelete-incomplete @gol
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-Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol
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-Wdisabled-optimization @gol
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-Wno-discarded-qualifiers -Wno-discarded-array-qualifiers @gol
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-Wno-div-by-zero -Wdouble-promotion -Wduplicated-cond @gol
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-Wempty-body -Wenum-compare -Wno-endif-labels -Wexpansion-to-defined @gol
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-Werror -Werror=* -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol
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-Wno-format-contains-nul -Wno-format-extra-args @gol
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-Wformat-nonliteral -Wformat-overflow=@var{n} @gol
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-Wformat-security -Wformat-signedness -Wformat-truncation=@var{n} @gol
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-Wformat-y2k -Wframe-address @gol
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-Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol
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-Wignored-qualifiers -Wignored-attributes -Wincompatible-pointer-types @gol
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-Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=@var{n} @gol
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-Wimplicit-function-declaration -Wimplicit-int @gol
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-Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context @gol
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-Wno-int-to-pointer-cast -Winvalid-memory-model -Wno-invalid-offsetof @gol
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-Winvalid-pch -Wlarger-than=@var{len} @gol
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-Wlogical-op -Wlogical-not-parentheses -Wlong-long @gol
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-Wmain -Wmaybe-uninitialized -Wmemset-elt-size -Wmemset-transposed-args @gol
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-Wmisleading-indentation -Wmissing-braces @gol
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-Wmissing-field-initializers -Wmissing-include-dirs @gol
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-Wno-multichar -Wnonnull -Wnonnull-compare @gol
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-Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol
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-Wnull-dereference -Wodr -Wno-overflow -Wopenmp-simd @gol
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-Woverride-init-side-effects -Woverlength-strings @gol
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-Wpacked -Wpacked-bitfield-compat -Wpadded @gol
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-Wparentheses -Wno-pedantic-ms-format @gol
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-Wplacement-new -Wplacement-new=@var{n} @gol
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-Wpointer-arith -Wpointer-compare -Wno-pointer-to-int-cast @gol
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-Wno-pragmas -Wredundant-decls -Wrestrict -Wno-return-local-addr @gol
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-Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar @gol
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-Wshadow=global, -Wshadow=local, -Wshadow=compatible-local @gol
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-Wshift-overflow -Wshift-overflow=@var{n} @gol
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-Wshift-count-negative -Wshift-count-overflow -Wshift-negative-value @gol
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-Wsign-compare -Wsign-conversion -Wfloat-conversion @gol
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-Wno-scalar-storage-order @gol
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-Wsizeof-pointer-memaccess -Wsizeof-array-argument @gol
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-Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol
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-Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=@var{n} @gol
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-Wstringop-overflow=@var{n} @gol
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-Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol
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-Wsuggest-final-types @gol -Wsuggest-final-methods -Wsuggest-override @gol
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-Wmissing-format-attribute -Wsubobject-linkage @gol
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-Wswitch -Wswitch-bool -Wswitch-default -Wswitch-enum @gol
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-Wswitch-unreachable -Wsync-nand @gol
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-Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs @gol
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-Wtype-limits -Wundef @gol
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-Wuninitialized -Wunknown-pragmas -Wunsafe-loop-optimizations @gol
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-Wunsuffixed-float-constants -Wunused -Wunused-function @gol
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-Wunused-label -Wunused-local-typedefs -Wunused-macros @gol
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-Wunused-parameter -Wno-unused-result @gol
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-Wunused-value -Wunused-variable @gol
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-Wunused-const-variable -Wunused-const-variable=@var{n} @gol
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-Wunused-but-set-parameter -Wunused-but-set-variable @gol
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-Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol
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-Wvla -Wvla-larger-than=@var{n} -Wvolatile-register-var -Wwrite-strings @gol
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-Wzero-as-null-pointer-constant -Whsa}
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@item C and Objective-C-only Warning Options
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@gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol
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-Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol
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-Wold-style-declaration -Wold-style-definition @gol
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-Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol
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-Wdeclaration-after-statement -Wpointer-sign}
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@item Debugging Options
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@xref{Debugging Options,,Options for Debugging Your Program}.
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@gccoptlist{-g -g@var{level} -gcoff -gdwarf -gdwarf-@var{version} @gol
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-ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol
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|
-gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol
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-gvms -gxcoff -gxcoff+ -gz@r{[}=@var{type}@r{]} @gol
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|
-fdebug-prefix-map=@var{old}=@var{new} -fdebug-types-section @gol
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|
-feliminate-dwarf2-dups -fno-eliminate-unused-debug-types @gol
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-femit-struct-debug-baseonly -femit-struct-debug-reduced @gol
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-femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol
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-feliminate-unused-debug-symbols -femit-class-debug-always @gol
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|
-fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol
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-fvar-tracking -fvar-tracking-assignments}
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@item Optimization Options
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@xref{Optimize Options,,Options that Control Optimization}.
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@gccoptlist{-faggressive-loop-optimizations -falign-functions[=@var{n}] @gol
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-falign-jumps[=@var{n}] @gol
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-falign-labels[=@var{n}] -falign-loops[=@var{n}] @gol
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|
-fassociative-math -fauto-profile -fauto-profile[=@var{path}] @gol
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|
-fauto-inc-dec -fbranch-probabilities @gol
|
|
-fbranch-target-load-optimize -fbranch-target-load-optimize2 @gol
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|
-fbtr-bb-exclusive -fcaller-saves @gol
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|
-fcombine-stack-adjustments -fconserve-stack @gol
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|
-fcompare-elim -fcprop-registers -fcrossjumping @gol
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|
-fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol
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|
-fcx-limited-range @gol
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|
-fdata-sections -fdce -fdelayed-branch @gol
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|
-fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively @gol
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-fdevirtualize-at-ltrans -fdse @gol
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|
-fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol
|
|
-ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
|
|
-fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol
|
|
-fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol
|
|
-fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol
|
|
-fif-conversion2 -findirect-inlining @gol
|
|
-finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol
|
|
-finline-small-functions -fipa-cp -fipa-cp-clone @gol
|
|
-fipa-cp-alignment -fipa-bit-cp @gol
|
|
-fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-icf @gol
|
|
-fira-algorithm=@var{algorithm} @gol
|
|
-fira-region=@var{region} -fira-hoist-pressure @gol
|
|
-fira-loop-pressure -fno-ira-share-save-slots @gol
|
|
-fno-ira-share-spill-slots @gol
|
|
-fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute @gol
|
|
-fivopts -fkeep-inline-functions -fkeep-static-functions @gol
|
|
-fkeep-static-consts -flimit-function-alignment -flive-range-shrinkage @gol
|
|
-floop-block -floop-interchange -floop-strip-mine @gol
|
|
-floop-unroll-and-jam -floop-nest-optimize @gol
|
|
-floop-parallelize-all -flra-remat -flto -flto-compression-level @gol
|
|
-flto-partition=@var{alg} -fmerge-all-constants @gol
|
|
-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol
|
|
-fmove-loop-invariants -fno-branch-count-reg @gol
|
|
-fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse @gol
|
|
-fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole @gol
|
|
-fno-peephole2 -fno-printf-return-value -fno-sched-interblock @gol
|
|
-fno-sched-spec -fno-signed-zeros @gol
|
|
-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol
|
|
-fomit-frame-pointer -foptimize-sibling-calls @gol
|
|
-fpartial-inlining -fpeel-loops -fpredictive-commoning @gol
|
|
-fprefetch-loop-arrays @gol
|
|
-fprofile-correction @gol
|
|
-fprofile-use -fprofile-use=@var{path} -fprofile-values @gol
|
|
-fprofile-reorder-functions @gol
|
|
-freciprocal-math -free -frename-registers -freorder-blocks @gol
|
|
-freorder-blocks-algorithm=@var{algorithm} @gol
|
|
-freorder-blocks-and-partition -freorder-functions @gol
|
|
-frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol
|
|
-frounding-math -fsched2-use-superblocks -fsched-pressure @gol
|
|
-fsched-spec-load -fsched-spec-load-dangerous @gol
|
|
-fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol
|
|
-fsched-group-heuristic -fsched-critical-path-heuristic @gol
|
|
-fsched-spec-insn-heuristic -fsched-rank-heuristic @gol
|
|
-fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol
|
|
-fschedule-fusion @gol
|
|
-fschedule-insns -fschedule-insns2 -fsection-anchors @gol
|
|
-fselective-scheduling -fselective-scheduling2 @gol
|
|
-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol
|
|
-fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate @gol
|
|
-fsignaling-nans @gol
|
|
-fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops@gol
|
|
-fsplit-paths @gol
|
|
-fsplit-wide-types -fssa-backprop -fssa-phiopt @gol
|
|
-fstdarg-opt -fstore-merging -fstrict-aliasing @gol
|
|
-fstrict-overflow -fthread-jumps -ftracer -ftree-bit-ccp @gol
|
|
-ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol
|
|
-ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts @gol
|
|
-ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting @gol
|
|
-ftree-loop-if-convert -ftree-loop-im @gol
|
|
-ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol
|
|
-ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
|
|
-ftree-loop-vectorize @gol
|
|
-ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol
|
|
-ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra @gol
|
|
-ftree-switch-conversion -ftree-tail-merge @gol
|
|
-ftree-ter -ftree-vectorize -ftree-vrp -funconstrained-commons @gol
|
|
-funit-at-a-time -funroll-all-loops -funroll-loops @gol
|
|
-funsafe-math-optimizations -funswitch-loops @gol
|
|
-fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt @gol
|
|
-fweb -fwhole-program -fwpa -fuse-linker-plugin @gol
|
|
--param @var{name}=@var{value}
|
|
-O -O0 -O1 -O2 -O3 -Os -Ofast -Og}
|
|
|
|
@item Program Instrumentation Options
|
|
@xref{Instrumentation Options,,Program Instrumentation Options}.
|
|
@gccoptlist{-p -pg -fprofile-arcs --coverage -ftest-coverage @gol
|
|
-fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol
|
|
-fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol
|
|
-fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... @gol
|
|
-fsanitize-undefined-trap-on-error -fbounds-check @gol
|
|
-fcheck-pointer-bounds -fchkp-check-incomplete-type @gol
|
|
-fchkp-first-field-has-own-bounds -fchkp-narrow-bounds @gol
|
|
-fchkp-narrow-to-innermost-array -fchkp-optimize @gol
|
|
-fchkp-use-fast-string-functions -fchkp-use-nochk-string-functions @gol
|
|
-fchkp-use-static-bounds -fchkp-use-static-const-bounds @gol
|
|
-fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read @gol
|
|
-fchkp-check-read -fchkp-check-write -fchkp-store-bounds @gol
|
|
-fchkp-instrument-calls -fchkp-instrument-marked-only @gol
|
|
-fchkp-use-wrappers -fchkp-flexible-struct-trailing-arrays@gol
|
|
-fstack-protector -fstack-protector-all -fstack-protector-strong @gol
|
|
-fstack-protector-explicit -fstack-check @gol
|
|
-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
|
|
-fno-stack-limit -fsplit-stack @gol
|
|
-fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} @gol
|
|
-fvtv-counts -fvtv-debug @gol
|
|
-finstrument-functions @gol
|
|
-finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol
|
|
-finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}}
|
|
|
|
@item Preprocessor Options
|
|
@xref{Preprocessor Options,,Options Controlling the Preprocessor}.
|
|
@gccoptlist{-A@var{question}=@var{answer} @gol
|
|
-A-@var{question}@r{[}=@var{answer}@r{]} @gol
|
|
-C -CC -D@var{macro}@r{[}=@var{defn}@r{]} @gol
|
|
-dD -dI -dM -dN -dU @gol
|
|
-fdebug-cpp -fdirectives-only -fdollars-in-identifiers @gol
|
|
-fexec-charset=@var{charset} -fextended-identifiers @gol
|
|
-finput-charset=@var{charset} -fno-canonical-system-headers @gol
|
|
-fpch-deps -fpch-preprocess -fpreprocessed @gol
|
|
-ftabstop=@var{width} -ftrack-macro-expansion @gol
|
|
-fwide-exec-charset=@var{charset} -fworking-directory @gol
|
|
-H -imacros @var{file} -include @var{file} @gol
|
|
-M -MD -MF -MG -MM -MMD -MP -MQ -MT @gol
|
|
-no-integrated-cpp -P -pthread -remap @gol
|
|
-traditional -traditional-cpp -trigraphs @gol
|
|
-U@var{macro} -undef @gol
|
|
-Wp,@var{option} -Xpreprocessor @var{option}}
|
|
|
|
@item Assembler Options
|
|
@xref{Assembler Options,,Passing Options to the Assembler}.
|
|
@gccoptlist{-Wa,@var{option} -Xassembler @var{option}}
|
|
|
|
@item Linker Options
|
|
@xref{Link Options,,Options for Linking}.
|
|
@gccoptlist{@var{object-file-name} -fuse-ld=@var{linker} -l@var{library} @gol
|
|
-nostartfiles -nodefaultlibs -nostdlib -pie -pthread -rdynamic @gol
|
|
-s -static -static-libgcc -static-libstdc++ @gol
|
|
-static-libasan -static-libtsan -static-liblsan -static-libubsan @gol
|
|
-static-libmpx -static-libmpxwrappers @gol
|
|
-shared -shared-libgcc -symbolic @gol
|
|
-T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol
|
|
-u @var{symbol} -z @var{keyword}}
|
|
|
|
@item Directory Options
|
|
@xref{Directory Options,,Options for Directory Search}.
|
|
@gccoptlist{-B@var{prefix} -I@var{dir} -I- @gol
|
|
-idirafter @var{dir} @gol
|
|
-imacros @var{file} -imultilib @var{dir} @gol
|
|
-iplugindir=@var{dir} -iprefix @var{file} @gol
|
|
-iquote @var{dir} -isysroot @var{dir} -isystem @var{dir} @gol
|
|
-iwithprefix @var{dir} -iwithprefixbefore @var{dir} @gol
|
|
-L@var{dir} -no-canonical-prefixes --no-sysroot-suffix @gol
|
|
-nostdinc -nostdinc++ --sysroot=@var{dir}}
|
|
|
|
@item Code Generation Options
|
|
@xref{Code Gen Options,,Options for Code Generation Conventions}.
|
|
@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol
|
|
-ffixed-@var{reg} -fexceptions @gol
|
|
-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol
|
|
-fasynchronous-unwind-tables @gol
|
|
-fno-gnu-unique @gol
|
|
-finhibit-size-directive -fno-common -fno-ident @gol
|
|
-fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol
|
|
-fno-jump-tables @gol
|
|
-frecord-gcc-switches @gol
|
|
-freg-struct-return -fshort-enums -fshort-wchar @gol
|
|
-fverbose-asm -fpack-struct[=@var{n}] @gol
|
|
-fleading-underscore -ftls-model=@var{model} @gol
|
|
-fstack-reuse=@var{reuse_level} @gol
|
|
-ftrampolines -ftrapv -fwrapv @gol
|
|
-fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} @gol
|
|
-fstrict-volatile-bitfields -fsync-libcalls}
|
|
|
|
@item Developer Options
|
|
@xref{Developer Options,,GCC Developer Options}.
|
|
@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol
|
|
-dumpfullversion -fchecking -fchecking=@var{n} -fdbg-cnt-list @gol
|
|
-fdbg-cnt=@var{counter-value-list} @gol
|
|
-fdisable-ipa-@var{pass_name} @gol
|
|
-fdisable-rtl-@var{pass_name} @gol
|
|
-fdisable-rtl-@var{pass-name}=@var{range-list} @gol
|
|
-fdisable-tree-@var{pass_name} @gol
|
|
-fdisable-tree-@var{pass-name}=@var{range-list} @gol
|
|
-fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol
|
|
-fdump-translation-unit@r{[}-@var{n}@r{]} @gol
|
|
-fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol
|
|
-fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol
|
|
-fdump-passes @gol
|
|
-fdump-rtl-@var{pass} -fdump-rtl-@var{pass}=@var{filename} @gol
|
|
-fdump-statistics @gol
|
|
-fdump-tree-all @gol
|
|
-fdump-tree-original@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-optimized@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-cfg -fdump-tree-alias @gol
|
|
-fdump-tree-ch @gol
|
|
-fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-gimple@r{[}-raw@r{]} @gol
|
|
-fdump-tree-dom@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-dse@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-backprop@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-nrv -fdump-tree-vect @gol
|
|
-fdump-tree-sink @gol
|
|
-fdump-tree-sra@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-fre@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-vtable-verify @gol
|
|
-fdump-tree-vrp@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-split-paths@r{[}-@var{n}@r{]} @gol
|
|
-fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol
|
|
-fdump-final-insns=@var{file} @gol
|
|
-fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol
|
|
-fenable-@var{kind}-@var{pass} @gol
|
|
-fenable-@var{kind}-@var{pass}=@var{range-list} @gol
|
|
-fira-verbose=@var{n} @gol
|
|
-flto-report -flto-report-wpa -fmem-report-wpa @gol
|
|
-fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report @gol
|
|
-fopt-info -fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol
|
|
-fprofile-report @gol
|
|
-frandom-seed=@var{string} -fsched-verbose=@var{n} @gol
|
|
-fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol
|
|
-fstats -fstack-usage -ftime-report -ftime-report-details @gol
|
|
-fvar-tracking-assignments-toggle -gtoggle @gol
|
|
-print-file-name=@var{library} -print-libgcc-file-name @gol
|
|
-print-multi-directory -print-multi-lib -print-multi-os-directory @gol
|
|
-print-prog-name=@var{program} -print-search-dirs -Q @gol
|
|
-print-sysroot -print-sysroot-headers-suffix @gol
|
|
-save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}}
|
|
|
|
@item Machine-Dependent Options
|
|
@xref{Submodel Options,,Machine-Dependent Options}.
|
|
@c This list is ordered alphanumerically by subsection name.
|
|
@c Try and put the significant identifier (CPU or system) first,
|
|
@c so users have a clue at guessing where the ones they want will be.
|
|
|
|
@emph{AArch64 Options}
|
|
@gccoptlist{-mabi=@var{name} -mbig-endian -mlittle-endian @gol
|
|
-mgeneral-regs-only @gol
|
|
-mcmodel=tiny -mcmodel=small -mcmodel=large @gol
|
|
-mstrict-align @gol
|
|
-momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
|
|
-mtls-dialect=desc -mtls-dialect=traditional @gol
|
|
-mtls-size=@var{size} @gol
|
|
-mfix-cortex-a53-835769 -mno-fix-cortex-a53-835769 @gol
|
|
-mfix-cortex-a53-843419 -mno-fix-cortex-a53-843419 @gol
|
|
-mlow-precision-recip-sqrt -mno-low-precision-recip-sqrt@gol
|
|
-mlow-precision-sqrt -mno-low-precision-sqrt@gol
|
|
-mlow-precision-div -mno-low-precision-div @gol
|
|
-march=@var{name} -mcpu=@var{name} -mtune=@var{name}}
|
|
|
|
@emph{Adapteva Epiphany Options}
|
|
@gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol
|
|
-mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol
|
|
-msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol
|
|
-mround-nearest -mlong-calls -mshort-calls -msmall16 @gol
|
|
-mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol
|
|
-msplit-vecmove-early -m1reg-@var{reg}}
|
|
|
|
@emph{ARC Options}
|
|
@gccoptlist{-mbarrel-shifter @gol
|
|
-mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 @gol
|
|
-mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr @gol
|
|
-mea -mno-mpy -mmul32x16 -mmul64 -matomic @gol
|
|
-mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap @gol
|
|
-mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape @gol
|
|
-mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof @gol
|
|
-mlong-calls -mmedium-calls -msdata @gol
|
|
-mvolatile-cache -mtp-regno=@var{regno} @gol
|
|
-malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc @gol
|
|
-mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi @gol
|
|
-mexpand-adddi -mindexed-loads -mlra -mlra-priority-none @gol
|
|
-mlra-priority-compact mlra-priority-noncompact -mno-millicode @gol
|
|
-mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} @gol
|
|
-mtune=@var{cpu} -mmultcost=@var{num} @gol
|
|
-munalign-prob-threshold=@var{probability} -mmpy-option=@var{multo} @gol
|
|
-mdiv-rem -mcode-density -mll64 -mfpu=@var{fpu}}
|
|
|
|
@emph{ARM Options}
|
|
@gccoptlist{-mapcs-frame -mno-apcs-frame @gol
|
|
-mabi=@var{name} @gol
|
|
-mapcs-stack-check -mno-apcs-stack-check @gol
|
|
-mapcs-reentrant -mno-apcs-reentrant @gol
|
|
-msched-prolog -mno-sched-prolog @gol
|
|
-mlittle-endian -mbig-endian @gol
|
|
-mfloat-abi=@var{name} @gol
|
|
-mfp16-format=@var{name}
|
|
-mthumb-interwork -mno-thumb-interwork @gol
|
|
-mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol
|
|
-mtune=@var{name} -mprint-tune-info @gol
|
|
-mstructure-size-boundary=@var{n} @gol
|
|
-mabort-on-noreturn @gol
|
|
-mlong-calls -mno-long-calls @gol
|
|
-msingle-pic-base -mno-single-pic-base @gol
|
|
-mpic-register=@var{reg} @gol
|
|
-mnop-fun-dllimport @gol
|
|
-mpoke-function-name @gol
|
|
-mthumb -marm @gol
|
|
-mtpcs-frame -mtpcs-leaf-frame @gol
|
|
-mcaller-super-interworking -mcallee-super-interworking @gol
|
|
-mtp=@var{name} -mtls-dialect=@var{dialect} @gol
|
|
-mword-relocations @gol
|
|
-mfix-cortex-m3-ldrd @gol
|
|
-munaligned-access @gol
|
|
-mneon-for-64bits @gol
|
|
-mslow-flash-data @gol
|
|
-masm-syntax-unified @gol
|
|
-mrestrict-it @gol
|
|
-mpure-code @gol
|
|
-mcmse}
|
|
|
|
@emph{AVR Options}
|
|
@gccoptlist{-mmcu=@var{mcu} -mabsdata -maccumulate-args @gol
|
|
-mbranch-cost=@var{cost} @gol
|
|
-mcall-prologues -mint8 -mn_flash=@var{size} -mno-interrupts @gol
|
|
-mrelax -mrmw -mstrict-X -mtiny-stack -mfract-convert-truncate @gol
|
|
-nodevicelib @gol
|
|
-Waddr-space-convert -Wmisspelled-isr}
|
|
|
|
@emph{Blackfin Options}
|
|
@gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol
|
|
-msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol
|
|
-mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol
|
|
-mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol
|
|
-mno-id-shared-library -mshared-library-id=@var{n} @gol
|
|
-mleaf-id-shared-library -mno-leaf-id-shared-library @gol
|
|
-msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol
|
|
-mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol
|
|
-micplb}
|
|
|
|
@emph{C6X Options}
|
|
@gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol
|
|
-msim -msdata=@var{sdata-type}}
|
|
|
|
@emph{CRIS Options}
|
|
@gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol
|
|
-mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol
|
|
-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol
|
|
-mstack-align -mdata-align -mconst-align @gol
|
|
-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol
|
|
-melf -maout -melinux -mlinux -sim -sim2 @gol
|
|
-mmul-bug-workaround -mno-mul-bug-workaround}
|
|
|
|
@emph{CR16 Options}
|
|
@gccoptlist{-mmac @gol
|
|
-mcr16cplus -mcr16c @gol
|
|
-msim -mint32 -mbit-ops
|
|
-mdata-model=@var{model}}
|
|
|
|
@emph{Darwin Options}
|
|
@gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol
|
|
-arch_only -bind_at_load -bundle -bundle_loader @gol
|
|
-client_name -compatibility_version -current_version @gol
|
|
-dead_strip @gol
|
|
-dependency-file -dylib_file -dylinker_install_name @gol
|
|
-dynamic -dynamiclib -exported_symbols_list @gol
|
|
-filelist -flat_namespace -force_cpusubtype_ALL @gol
|
|
-force_flat_namespace -headerpad_max_install_names @gol
|
|
-iframework @gol
|
|
-image_base -init -install_name -keep_private_externs @gol
|
|
-multi_module -multiply_defined -multiply_defined_unused @gol
|
|
-noall_load -no_dead_strip_inits_and_terms @gol
|
|
-nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol
|
|
-pagezero_size -prebind -prebind_all_twolevel_modules @gol
|
|
-private_bundle -read_only_relocs -sectalign @gol
|
|
-sectobjectsymbols -whyload -seg1addr @gol
|
|
-sectcreate -sectobjectsymbols -sectorder @gol
|
|
-segaddr -segs_read_only_addr -segs_read_write_addr @gol
|
|
-seg_addr_table -seg_addr_table_filename -seglinkedit @gol
|
|
-segprot -segs_read_only_addr -segs_read_write_addr @gol
|
|
-single_module -static -sub_library -sub_umbrella @gol
|
|
-twolevel_namespace -umbrella -undefined @gol
|
|
-unexported_symbols_list -weak_reference_mismatches @gol
|
|
-whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol
|
|
-mkernel -mone-byte-bool}
|
|
|
|
@emph{DEC Alpha Options}
|
|
@gccoptlist{-mno-fp-regs -msoft-float @gol
|
|
-mieee -mieee-with-inexact -mieee-conformant @gol
|
|
-mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol
|
|
-mtrap-precision=@var{mode} -mbuild-constants @gol
|
|
-mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol
|
|
-mbwx -mmax -mfix -mcix @gol
|
|
-mfloat-vax -mfloat-ieee @gol
|
|
-mexplicit-relocs -msmall-data -mlarge-data @gol
|
|
-msmall-text -mlarge-text @gol
|
|
-mmemory-latency=@var{time}}
|
|
|
|
@emph{FR30 Options}
|
|
@gccoptlist{-msmall-model -mno-lsim}
|
|
|
|
@emph{FT32 Options}
|
|
@gccoptlist{-msim -mlra -mnodiv}
|
|
|
|
@emph{FRV Options}
|
|
@gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol
|
|
-mhard-float -msoft-float @gol
|
|
-malloc-cc -mfixed-cc -mdword -mno-dword @gol
|
|
-mdouble -mno-double @gol
|
|
-mmedia -mno-media -mmuladd -mno-muladd @gol
|
|
-mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol
|
|
-mlinked-fp -mlong-calls -malign-labels @gol
|
|
-mlibrary-pic -macc-4 -macc-8 @gol
|
|
-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol
|
|
-moptimize-membar -mno-optimize-membar @gol
|
|
-mscc -mno-scc -mcond-exec -mno-cond-exec @gol
|
|
-mvliw-branch -mno-vliw-branch @gol
|
|
-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol
|
|
-mno-nested-cond-exec -mtomcat-stats @gol
|
|
-mTLS -mtls @gol
|
|
-mcpu=@var{cpu}}
|
|
|
|
@emph{GNU/Linux Options}
|
|
@gccoptlist{-mglibc -muclibc -mmusl -mbionic -mandroid @gol
|
|
-tno-android-cc -tno-android-ld}
|
|
|
|
@emph{H8/300 Options}
|
|
@gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300}
|
|
|
|
@emph{HPPA Options}
|
|
@gccoptlist{-march=@var{architecture-type} @gol
|
|
-mcaller-copies -mdisable-fpregs -mdisable-indexing @gol
|
|
-mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol
|
|
-mfixed-range=@var{register-range} @gol
|
|
-mjump-in-delay -mlinker-opt -mlong-calls @gol
|
|
-mlong-load-store -mno-disable-fpregs @gol
|
|
-mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol
|
|
-mno-jump-in-delay -mno-long-load-store @gol
|
|
-mno-portable-runtime -mno-soft-float @gol
|
|
-mno-space-regs -msoft-float -mpa-risc-1-0 @gol
|
|
-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol
|
|
-mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol
|
|
-munix=@var{unix-std} -nolibdld -static -threads}
|
|
|
|
@emph{IA-64 Options}
|
|
@gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol
|
|
-mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol
|
|
-mconstant-gp -mauto-pic -mfused-madd @gol
|
|
-minline-float-divide-min-latency @gol
|
|
-minline-float-divide-max-throughput @gol
|
|
-mno-inline-float-divide @gol
|
|
-minline-int-divide-min-latency @gol
|
|
-minline-int-divide-max-throughput @gol
|
|
-mno-inline-int-divide @gol
|
|
-minline-sqrt-min-latency -minline-sqrt-max-throughput @gol
|
|
-mno-inline-sqrt @gol
|
|
-mdwarf2-asm -mearly-stop-bits @gol
|
|
-mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol
|
|
-mtune=@var{cpu-type} -milp32 -mlp64 @gol
|
|
-msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol
|
|
-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol
|
|
-msched-spec-ldc -msched-spec-control-ldc @gol
|
|
-msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol
|
|
-msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol
|
|
-msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol
|
|
-msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}}
|
|
|
|
@emph{LM32 Options}
|
|
@gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol
|
|
-msign-extend-enabled -muser-enabled}
|
|
|
|
@emph{M32R/D Options}
|
|
@gccoptlist{-m32r2 -m32rx -m32r @gol
|
|
-mdebug @gol
|
|
-malign-loops -mno-align-loops @gol
|
|
-missue-rate=@var{number} @gol
|
|
-mbranch-cost=@var{number} @gol
|
|
-mmodel=@var{code-size-model-type} @gol
|
|
-msdata=@var{sdata-type} @gol
|
|
-mno-flush-func -mflush-func=@var{name} @gol
|
|
-mno-flush-trap -mflush-trap=@var{number} @gol
|
|
-G @var{num}}
|
|
|
|
@emph{M32C Options}
|
|
@gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}}
|
|
|
|
@emph{M680x0 Options}
|
|
@gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} @gol
|
|
-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol
|
|
-m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol
|
|
-mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol
|
|
-mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol
|
|
-mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol
|
|
-malign-int -mstrict-align -msep-data -mno-sep-data @gol
|
|
-mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol
|
|
-mxgot -mno-xgot -mlong-jump-table-offsets}
|
|
|
|
@emph{MCore Options}
|
|
@gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol
|
|
-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol
|
|
-m4byte-functions -mno-4byte-functions -mcallgraph-data @gol
|
|
-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol
|
|
-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment}
|
|
|
|
@emph{MeP Options}
|
|
@gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol
|
|
-mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol
|
|
-mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol
|
|
-mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol
|
|
-mtiny=@var{n}}
|
|
|
|
@emph{MicroBlaze Options}
|
|
@gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol
|
|
-mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol
|
|
-mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol
|
|
-mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol
|
|
-mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model}}
|
|
|
|
@emph{MIPS Options}
|
|
@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol
|
|
-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 @gol
|
|
-mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 @gol
|
|
-mips16 -mno-mips16 -mflip-mips16 @gol
|
|
-minterlink-compressed -mno-interlink-compressed @gol
|
|
-minterlink-mips16 -mno-interlink-mips16 @gol
|
|
-mabi=@var{abi} -mabicalls -mno-abicalls @gol
|
|
-mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol
|
|
-mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol
|
|
-mno-float -msingle-float -mdouble-float @gol
|
|
-modd-spreg -mno-odd-spreg @gol
|
|
-mabs=@var{mode} -mnan=@var{encoding} @gol
|
|
-mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol
|
|
-mmcu -mmno-mcu @gol
|
|
-meva -mno-eva @gol
|
|
-mvirt -mno-virt @gol
|
|
-mxpa -mno-xpa @gol
|
|
-mmicromips -mno-micromips @gol
|
|
-mmsa -mno-msa @gol
|
|
-mfpu=@var{fpu-type} @gol
|
|
-msmartmips -mno-smartmips @gol
|
|
-mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol
|
|
-mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol
|
|
-mlong64 -mlong32 -msym32 -mno-sym32 @gol
|
|
-G@var{num} -mlocal-sdata -mno-local-sdata @gol
|
|
-mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol
|
|
-membedded-data -mno-embedded-data @gol
|
|
-muninit-const-in-rodata -mno-uninit-const-in-rodata @gol
|
|
-mcode-readable=@var{setting} @gol
|
|
-msplit-addresses -mno-split-addresses @gol
|
|
-mexplicit-relocs -mno-explicit-relocs @gol
|
|
-mcheck-zero-division -mno-check-zero-division @gol
|
|
-mdivide-traps -mdivide-breaks @gol
|
|
-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol
|
|
-mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp @gol
|
|
-mfix-24k -mno-fix-24k @gol
|
|
-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol
|
|
-mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 @gol
|
|
-mfix-vr4120 -mno-fix-vr4120 @gol
|
|
-mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol
|
|
-mflush-func=@var{func} -mno-flush-func @gol
|
|
-mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol
|
|
-mcompact-branches=@var{policy} @gol
|
|
-mfp-exceptions -mno-fp-exceptions @gol
|
|
-mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol
|
|
-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address @gol
|
|
-mframe-header-opt -mno-frame-header-opt}
|
|
|
|
@emph{MMIX Options}
|
|
@gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol
|
|
-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol
|
|
-melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol
|
|
-mno-base-addresses -msingle-exit -mno-single-exit}
|
|
|
|
@emph{MN10300 Options}
|
|
@gccoptlist{-mmult-bug -mno-mult-bug @gol
|
|
-mno-am33 -mam33 -mam33-2 -mam34 @gol
|
|
-mtune=@var{cpu-type} @gol
|
|
-mreturn-pointer-on-d0 @gol
|
|
-mno-crt0 -mrelax -mliw -msetlb}
|
|
|
|
@emph{Moxie Options}
|
|
@gccoptlist{-meb -mel -mmul.x -mno-crt0}
|
|
|
|
@emph{MSP430 Options}
|
|
@gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax @gol
|
|
-mwarn-mcu @gol
|
|
-mcode-region= -mdata-region= @gol
|
|
-msilicon-errata= -msilicon-errata-warn= @gol
|
|
-mhwmult= -minrt}
|
|
|
|
@emph{NDS32 Options}
|
|
@gccoptlist{-mbig-endian -mlittle-endian @gol
|
|
-mreduced-regs -mfull-regs @gol
|
|
-mcmov -mno-cmov @gol
|
|
-mperf-ext -mno-perf-ext @gol
|
|
-mv3push -mno-v3push @gol
|
|
-m16bit -mno-16bit @gol
|
|
-misr-vector-size=@var{num} @gol
|
|
-mcache-block-size=@var{num} @gol
|
|
-march=@var{arch} @gol
|
|
-mcmodel=@var{code-model} @gol
|
|
-mctor-dtor -mrelax}
|
|
|
|
@emph{Nios II Options}
|
|
@gccoptlist{-G @var{num} -mgpopt=@var{option} -mgpopt -mno-gpopt @gol
|
|
-mel -meb @gol
|
|
-mno-bypass-cache -mbypass-cache @gol
|
|
-mno-cache-volatile -mcache-volatile @gol
|
|
-mno-fast-sw-div -mfast-sw-div @gol
|
|
-mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div @gol
|
|
-mcustom-@var{insn}=@var{N} -mno-custom-@var{insn} @gol
|
|
-mcustom-fpu-cfg=@var{name} @gol
|
|
-mhal -msmallc -msys-crt0=@var{name} -msys-lib=@var{name} @gol
|
|
-march=@var{arch} -mbmx -mno-bmx -mcdx -mno-cdx}
|
|
|
|
@emph{Nvidia PTX Options}
|
|
@gccoptlist{-m32 -m64 -mmainkernel -moptimize}
|
|
|
|
@emph{PDP-11 Options}
|
|
@gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol
|
|
-mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol
|
|
-mint16 -mno-int32 -mfloat32 -mno-float64 @gol
|
|
-mfloat64 -mno-float32 -mabshi -mno-abshi @gol
|
|
-mbranch-expensive -mbranch-cheap @gol
|
|
-munix-asm -mdec-asm}
|
|
|
|
@emph{picoChip Options}
|
|
@gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol
|
|
-msymbol-as-address -mno-inefficient-warnings}
|
|
|
|
@emph{PowerPC Options}
|
|
See RS/6000 and PowerPC Options.
|
|
|
|
@emph{RL78 Options}
|
|
@gccoptlist{-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs @gol
|
|
-mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 @gol
|
|
-m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts}
|
|
|
|
@emph{RS/6000 and PowerPC Options}
|
|
@gccoptlist{-mcpu=@var{cpu-type} @gol
|
|
-mtune=@var{cpu-type} @gol
|
|
-mcmodel=@var{code-model} @gol
|
|
-mpowerpc64 @gol
|
|
-maltivec -mno-altivec @gol
|
|
-mpowerpc-gpopt -mno-powerpc-gpopt @gol
|
|
-mpowerpc-gfxopt -mno-powerpc-gfxopt @gol
|
|
-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol
|
|
-mfprnd -mno-fprnd @gol
|
|
-mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol
|
|
-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol
|
|
-m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol
|
|
-malign-power -malign-natural @gol
|
|
-msoft-float -mhard-float -mmultiple -mno-multiple @gol
|
|
-msingle-float -mdouble-float -msimple-fpu @gol
|
|
-mstring -mno-string -mupdate -mno-update @gol
|
|
-mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol
|
|
-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol
|
|
-mstrict-align -mno-strict-align -mrelocatable @gol
|
|
-mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol
|
|
-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol
|
|
-mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base @gol
|
|
-mprioritize-restricted-insns=@var{priority} @gol
|
|
-msched-costly-dep=@var{dependence_type} @gol
|
|
-minsert-sched-nops=@var{scheme} @gol
|
|
-mcall-sysv -mcall-netbsd @gol
|
|
-maix-struct-return -msvr4-struct-return @gol
|
|
-mabi=@var{abi-type} -msecure-plt -mbss-plt @gol
|
|
-mblock-move-inline-limit=@var{num} @gol
|
|
-misel -mno-isel @gol
|
|
-misel=yes -misel=no @gol
|
|
-mspe -mno-spe @gol
|
|
-mspe=yes -mspe=no @gol
|
|
-mpaired @gol
|
|
-mgen-cell-microcode -mwarn-cell-microcode @gol
|
|
-mvrsave -mno-vrsave @gol
|
|
-mmulhw -mno-mulhw @gol
|
|
-mdlmzb -mno-dlmzb @gol
|
|
-mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol
|
|
-mprototype -mno-prototype @gol
|
|
-msim -mmvme -mads -myellowknife -memb -msdata @gol
|
|
-msdata=@var{opt} -mvxworks -G @var{num} @gol
|
|
-mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol
|
|
-mno-recip-precision @gol
|
|
-mveclibabi=@var{type} -mfriz -mno-friz @gol
|
|
-mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol
|
|
-msave-toc-indirect -mno-save-toc-indirect @gol
|
|
-mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector @gol
|
|
-mcrypto -mno-crypto -mhtm -mno-htm -mdirect-move -mno-direct-move @gol
|
|
-mquad-memory -mno-quad-memory @gol
|
|
-mquad-memory-atomic -mno-quad-memory-atomic @gol
|
|
-mcompat-align-parm -mno-compat-align-parm @gol
|
|
-mupper-regs-df -mno-upper-regs-df -mupper-regs-sf -mno-upper-regs-sf @gol
|
|
-mupper-regs-di -mno-upper-regs-di @gol
|
|
-mupper-regs -mno-upper-regs @gol
|
|
-mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware @gol
|
|
-mgnu-attribute -mno-gnu-attribute @gol
|
|
-mlra -mno-lra}
|
|
|
|
@emph{RX Options}
|
|
@gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol
|
|
-mcpu=@gol
|
|
-mbig-endian-data -mlittle-endian-data @gol
|
|
-msmall-data @gol
|
|
-msim -mno-sim@gol
|
|
-mas100-syntax -mno-as100-syntax@gol
|
|
-mrelax@gol
|
|
-mmax-constant-size=@gol
|
|
-mint-register=@gol
|
|
-mpid@gol
|
|
-mallow-string-insns -mno-allow-string-insns@gol
|
|
-mjsr@gol
|
|
-mno-warn-multiple-fast-interrupts@gol
|
|
-msave-acc-in-interrupts}
|
|
|
|
@emph{S/390 and zSeries Options}
|
|
@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
|
|
-mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol
|
|
-mlong-double-64 -mlong-double-128 @gol
|
|
-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol
|
|
-msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol
|
|
-m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol
|
|
-mhtm -mvx -mzvector @gol
|
|
-mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol
|
|
-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard @gol
|
|
-mhotpatch=@var{halfwords},@var{halfwords}}
|
|
|
|
@emph{Score Options}
|
|
@gccoptlist{-meb -mel @gol
|
|
-mnhwloop @gol
|
|
-muls @gol
|
|
-mmac @gol
|
|
-mscore5 -mscore5u -mscore7 -mscore7d}
|
|
|
|
@emph{SH Options}
|
|
@gccoptlist{-m1 -m2 -m2e @gol
|
|
-m2a-nofpu -m2a-single-only -m2a-single -m2a @gol
|
|
-m3 -m3e @gol
|
|
-m4-nofpu -m4-single-only -m4-single -m4 @gol
|
|
-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol
|
|
-mb -ml -mdalign -mrelax @gol
|
|
-mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave @gol
|
|
-mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol
|
|
-mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol
|
|
-mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol
|
|
-maccumulate-outgoing-args @gol
|
|
-matomic-model=@var{atomic-model} @gol
|
|
-mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch @gol
|
|
-mcbranch-force-delay-slot @gol
|
|
-mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol
|
|
-mpretend-cmove -mtas}
|
|
|
|
@emph{Solaris 2 Options}
|
|
@gccoptlist{-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text @gol
|
|
-pthreads}
|
|
|
|
@emph{SPARC Options}
|
|
@gccoptlist{-mcpu=@var{cpu-type} @gol
|
|
-mtune=@var{cpu-type} @gol
|
|
-mcmodel=@var{code-model} @gol
|
|
-mmemory-model=@var{mem-model} @gol
|
|
-m32 -m64 -mapp-regs -mno-app-regs @gol
|
|
-mfaster-structs -mno-faster-structs -mflat -mno-flat @gol
|
|
-mfpu -mno-fpu -mhard-float -msoft-float @gol
|
|
-mhard-quad-float -msoft-quad-float @gol
|
|
-mstack-bias -mno-stack-bias @gol
|
|
-mstd-struct-return -mno-std-struct-return @gol
|
|
-munaligned-doubles -mno-unaligned-doubles @gol
|
|
-muser-mode -mno-user-mode @gol
|
|
-mv8plus -mno-v8plus -mvis -mno-vis @gol
|
|
-mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol
|
|
-mcbcond -mno-cbcond -mfmaf -mno-fmaf @gol
|
|
-mpopc -mno-popc -msubxc -mno-subxc@gol
|
|
-mfix-at697f -mfix-ut699 @gol
|
|
-mlra -mno-lra}
|
|
|
|
@emph{SPU Options}
|
|
@gccoptlist{-mwarn-reloc -merror-reloc @gol
|
|
-msafe-dma -munsafe-dma @gol
|
|
-mbranch-hints @gol
|
|
-msmall-mem -mlarge-mem -mstdmain @gol
|
|
-mfixed-range=@var{register-range} @gol
|
|
-mea32 -mea64 @gol
|
|
-maddress-space-conversion -mno-address-space-conversion @gol
|
|
-mcache-size=@var{cache-size} @gol
|
|
-matomic-updates -mno-atomic-updates}
|
|
|
|
@emph{System V Options}
|
|
@gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}}
|
|
|
|
@emph{TILE-Gx Options}
|
|
@gccoptlist{-mcpu=CPU -m32 -m64 -mbig-endian -mlittle-endian @gol
|
|
-mcmodel=@var{code-model}}
|
|
|
|
@emph{TILEPro Options}
|
|
@gccoptlist{-mcpu=@var{cpu} -m32}
|
|
|
|
@emph{V850 Options}
|
|
@gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol
|
|
-mprolog-function -mno-prolog-function -mspace @gol
|
|
-mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol
|
|
-mapp-regs -mno-app-regs @gol
|
|
-mdisable-callt -mno-disable-callt @gol
|
|
-mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol
|
|
-mv850e -mv850 -mv850e3v5 @gol
|
|
-mloop @gol
|
|
-mrelax @gol
|
|
-mlong-jumps @gol
|
|
-msoft-float @gol
|
|
-mhard-float @gol
|
|
-mgcc-abi @gol
|
|
-mrh850-abi @gol
|
|
-mbig-switch}
|
|
|
|
@emph{VAX Options}
|
|
@gccoptlist{-mg -mgnu -munix}
|
|
|
|
@emph{Visium Options}
|
|
@gccoptlist{-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float @gol
|
|
-mcpu=@var{cpu-type} -mtune=@var{cpu-type} -msv-mode -muser-mode}
|
|
|
|
@emph{VMS Options}
|
|
@gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol
|
|
-mpointer-size=@var{size}}
|
|
|
|
@emph{VxWorks Options}
|
|
@gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol
|
|
-Xbind-lazy -Xbind-now}
|
|
|
|
@emph{x86 Options}
|
|
@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol
|
|
-mtune-ctrl=@var{feature-list} -mdump-tune-features -mno-default @gol
|
|
-mfpmath=@var{unit} @gol
|
|
-masm=@var{dialect} -mno-fancy-math-387 @gol
|
|
-mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float @gol
|
|
-mno-wide-multiply -mrtd -malign-double @gol
|
|
-mpreferred-stack-boundary=@var{num} @gol
|
|
-mincoming-stack-boundary=@var{num} @gol
|
|
-mcld -mcx16 -msahf -mmovbe -mcrc32 @gol
|
|
-mrecip -mrecip=@var{opt} @gol
|
|
-mvzeroupper -mprefer-avx128 @gol
|
|
-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol
|
|
-mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl @gol
|
|
-mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes @gol
|
|
-mpclmul -mfsgsbase -mrdrnd -mf16c -mfma @gol
|
|
-mprefetchwt1 -mclflushopt -mxsavec -mxsaves @gol
|
|
-msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt @gol
|
|
-mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx -mmwaitx @gol
|
|
-mclzero -mpku -mthreads @gol
|
|
-mms-bitfields -mno-align-stringops -minline-all-stringops @gol
|
|
-minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol
|
|
-mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} @gol
|
|
-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol
|
|
-m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 @gol
|
|
-mregparm=@var{num} -msseregparm @gol
|
|
-mveclibabi=@var{type} -mvect8-ret-in-mem @gol
|
|
-mpc32 -mpc64 -mpc80 -mstackrealign @gol
|
|
-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol
|
|
-mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol
|
|
-m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=@var{num} @gol
|
|
-msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol
|
|
-mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol
|
|
-malign-data=@var{type} -mstack-protector-guard=@var{guard} @gol
|
|
-mmitigate-rop -mgeneral-regs-only}
|
|
|
|
@emph{x86 Windows Options}
|
|
@gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol
|
|
-mnop-fun-dllimport -mthread @gol
|
|
-municode -mwin32 -mwindows -fno-set-stack-executable}
|
|
|
|
@emph{Xstormy16 Options}
|
|
@gccoptlist{-msim}
|
|
|
|
@emph{Xtensa Options}
|
|
@gccoptlist{-mconst16 -mno-const16 @gol
|
|
-mfused-madd -mno-fused-madd @gol
|
|
-mforce-no-pic @gol
|
|
-mserialize-volatile -mno-serialize-volatile @gol
|
|
-mtext-section-literals -mno-text-section-literals @gol
|
|
-mauto-litpools -mno-auto-litpools @gol
|
|
-mtarget-align -mno-target-align @gol
|
|
-mlongcalls -mno-longcalls}
|
|
|
|
@emph{zSeries Options}
|
|
See S/390 and zSeries Options.
|
|
@end table
|
|
|
|
|
|
@node Overall Options
|
|
@section Options Controlling the Kind of Output
|
|
|
|
Compilation can involve up to four stages: preprocessing, compilation
|
|
proper, assembly and linking, always in that order. GCC is capable of
|
|
preprocessing and compiling several files either into several
|
|
assembler input files, or into one assembler input file; then each
|
|
assembler input file produces an object file, and linking combines all
|
|
the object files (those newly compiled, and those specified as input)
|
|
into an executable file.
|
|
|
|
@cindex file name suffix
|
|
For any given input file, the file name suffix determines what kind of
|
|
compilation is done:
|
|
|
|
@table @gcctabopt
|
|
@item @var{file}.c
|
|
C source code that must be preprocessed.
|
|
|
|
@item @var{file}.i
|
|
C source code that should not be preprocessed.
|
|
|
|
@item @var{file}.ii
|
|
C++ source code that should not be preprocessed.
|
|
|
|
@item @var{file}.m
|
|
Objective-C source code. Note that you must link with the @file{libobjc}
|
|
library to make an Objective-C program work.
|
|
|
|
@item @var{file}.mi
|
|
Objective-C source code that should not be preprocessed.
|
|
|
|
@item @var{file}.mm
|
|
@itemx @var{file}.M
|
|
Objective-C++ source code. Note that you must link with the @file{libobjc}
|
|
library to make an Objective-C++ program work. Note that @samp{.M} refers
|
|
to a literal capital M@.
|
|
|
|
@item @var{file}.mii
|
|
Objective-C++ source code that should not be preprocessed.
|
|
|
|
@item @var{file}.h
|
|
C, C++, Objective-C or Objective-C++ header file to be turned into a
|
|
precompiled header (default), or C, C++ header file to be turned into an
|
|
Ada spec (via the @option{-fdump-ada-spec} switch).
|
|
|
|
@item @var{file}.cc
|
|
@itemx @var{file}.cp
|
|
@itemx @var{file}.cxx
|
|
@itemx @var{file}.cpp
|
|
@itemx @var{file}.CPP
|
|
@itemx @var{file}.c++
|
|
@itemx @var{file}.C
|
|
C++ source code that must be preprocessed. Note that in @samp{.cxx},
|
|
the last two letters must both be literally @samp{x}. Likewise,
|
|
@samp{.C} refers to a literal capital C@.
|
|
|
|
@item @var{file}.mm
|
|
@itemx @var{file}.M
|
|
Objective-C++ source code that must be preprocessed.
|
|
|
|
@item @var{file}.mii
|
|
Objective-C++ source code that should not be preprocessed.
|
|
|
|
@item @var{file}.hh
|
|
@itemx @var{file}.H
|
|
@itemx @var{file}.hp
|
|
@itemx @var{file}.hxx
|
|
@itemx @var{file}.hpp
|
|
@itemx @var{file}.HPP
|
|
@itemx @var{file}.h++
|
|
@itemx @var{file}.tcc
|
|
C++ header file to be turned into a precompiled header or Ada spec.
|
|
|
|
@item @var{file}.f
|
|
@itemx @var{file}.for
|
|
@itemx @var{file}.ftn
|
|
Fixed form Fortran source code that should not be preprocessed.
|
|
|
|
@item @var{file}.F
|
|
@itemx @var{file}.FOR
|
|
@itemx @var{file}.fpp
|
|
@itemx @var{file}.FPP
|
|
@itemx @var{file}.FTN
|
|
Fixed form Fortran source code that must be preprocessed (with the traditional
|
|
preprocessor).
|
|
|
|
@item @var{file}.f90
|
|
@itemx @var{file}.f95
|
|
@itemx @var{file}.f03
|
|
@itemx @var{file}.f08
|
|
Free form Fortran source code that should not be preprocessed.
|
|
|
|
@item @var{file}.F90
|
|
@itemx @var{file}.F95
|
|
@itemx @var{file}.F03
|
|
@itemx @var{file}.F08
|
|
Free form Fortran source code that must be preprocessed (with the
|
|
traditional preprocessor).
|
|
|
|
@item @var{file}.go
|
|
Go source code.
|
|
|
|
@item @var{file}.ads
|
|
Ada source code file that contains a library unit declaration (a
|
|
declaration of a package, subprogram, or generic, or a generic
|
|
instantiation), or a library unit renaming declaration (a package,
|
|
generic, or subprogram renaming declaration). Such files are also
|
|
called @dfn{specs}.
|
|
|
|
@item @var{file}.adb
|
|
Ada source code file containing a library unit body (a subprogram or
|
|
package body). Such files are also called @dfn{bodies}.
|
|
|
|
@c GCC also knows about some suffixes for languages not yet included:
|
|
@c Pascal:
|
|
@c @var{file}.p
|
|
@c @var{file}.pas
|
|
@c Ratfor:
|
|
@c @var{file}.r
|
|
|
|
@item @var{file}.s
|
|
Assembler code.
|
|
|
|
@item @var{file}.S
|
|
@itemx @var{file}.sx
|
|
Assembler code that must be preprocessed.
|
|
|
|
@item @var{other}
|
|
An object file to be fed straight into linking.
|
|
Any file name with no recognized suffix is treated this way.
|
|
@end table
|
|
|
|
@opindex x
|
|
You can specify the input language explicitly with the @option{-x} option:
|
|
|
|
@table @gcctabopt
|
|
@item -x @var{language}
|
|
Specify explicitly the @var{language} for the following input files
|
|
(rather than letting the compiler choose a default based on the file
|
|
name suffix). This option applies to all following input files until
|
|
the next @option{-x} option. Possible values for @var{language} are:
|
|
@smallexample
|
|
c c-header cpp-output
|
|
c++ c++-header c++-cpp-output
|
|
objective-c objective-c-header objective-c-cpp-output
|
|
objective-c++ objective-c++-header objective-c++-cpp-output
|
|
assembler assembler-with-cpp
|
|
ada
|
|
f77 f77-cpp-input f95 f95-cpp-input
|
|
go
|
|
@end smallexample
|
|
|
|
@item -x none
|
|
Turn off any specification of a language, so that subsequent files are
|
|
handled according to their file name suffixes (as they are if @option{-x}
|
|
has not been used at all).
|
|
@end table
|
|
|
|
If you only want some of the stages of compilation, you can use
|
|
@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
|
|
one of the options @option{-c}, @option{-S}, or @option{-E} to say where
|
|
@command{gcc} is to stop. Note that some combinations (for example,
|
|
@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.
|
|
|
|
@table @gcctabopt
|
|
@item -c
|
|
@opindex c
|
|
Compile or assemble the source files, but do not link. The linking
|
|
stage simply is not done. The ultimate output is in the form of an
|
|
object file for each source file.
|
|
|
|
By default, the object file name for a source file is made by replacing
|
|
the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.
|
|
|
|
Unrecognized input files, not requiring compilation or assembly, are
|
|
ignored.
|
|
|
|
@item -S
|
|
@opindex S
|
|
Stop after the stage of compilation proper; do not assemble. The output
|
|
is in the form of an assembler code file for each non-assembler input
|
|
file specified.
|
|
|
|
By default, the assembler file name for a source file is made by
|
|
replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.
|
|
|
|
Input files that don't require compilation are ignored.
|
|
|
|
@item -E
|
|
@opindex E
|
|
Stop after the preprocessing stage; do not run the compiler proper. The
|
|
output is in the form of preprocessed source code, which is sent to the
|
|
standard output.
|
|
|
|
Input files that don't require preprocessing are ignored.
|
|
|
|
@cindex output file option
|
|
@item -o @var{file}
|
|
@opindex o
|
|
Place output in file @var{file}. This applies to whatever
|
|
sort of output is being produced, whether it be an executable file,
|
|
an object file, an assembler file or preprocessed C code.
|
|
|
|
If @option{-o} is not specified, the default is to put an executable
|
|
file in @file{a.out}, the object file for
|
|
@file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
|
|
assembler file in @file{@var{source}.s}, a precompiled header file in
|
|
@file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
|
|
standard output.
|
|
|
|
@item -v
|
|
@opindex v
|
|
Print (on standard error output) the commands executed to run the stages
|
|
of compilation. Also print the version number of the compiler driver
|
|
program and of the preprocessor and the compiler proper.
|
|
|
|
@item -###
|
|
@opindex ###
|
|
Like @option{-v} except the commands are not executed and arguments
|
|
are quoted unless they contain only alphanumeric characters or @code{./-_}.
|
|
This is useful for shell scripts to capture the driver-generated command lines.
|
|
|
|
@item --help
|
|
@opindex help
|
|
Print (on the standard output) a description of the command-line options
|
|
understood by @command{gcc}. If the @option{-v} option is also specified
|
|
then @option{--help} is also passed on to the various processes
|
|
invoked by @command{gcc}, so that they can display the command-line options
|
|
they accept. If the @option{-Wextra} option has also been specified
|
|
(prior to the @option{--help} option), then command-line options that
|
|
have no documentation associated with them are also displayed.
|
|
|
|
@item --target-help
|
|
@opindex target-help
|
|
Print (on the standard output) a description of target-specific command-line
|
|
options for each tool. For some targets extra target-specific
|
|
information may also be printed.
|
|
|
|
@item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]}
|
|
Print (on the standard output) a description of the command-line
|
|
options understood by the compiler that fit into all specified classes
|
|
and qualifiers. These are the supported classes:
|
|
|
|
@table @asis
|
|
@item @samp{optimizers}
|
|
Display all of the optimization options supported by the
|
|
compiler.
|
|
|
|
@item @samp{warnings}
|
|
Display all of the options controlling warning messages
|
|
produced by the compiler.
|
|
|
|
@item @samp{target}
|
|
Display target-specific options. Unlike the
|
|
@option{--target-help} option however, target-specific options of the
|
|
linker and assembler are not displayed. This is because those
|
|
tools do not currently support the extended @option{--help=} syntax.
|
|
|
|
@item @samp{params}
|
|
Display the values recognized by the @option{--param}
|
|
option.
|
|
|
|
@item @var{language}
|
|
Display the options supported for @var{language}, where
|
|
@var{language} is the name of one of the languages supported in this
|
|
version of GCC@.
|
|
|
|
@item @samp{common}
|
|
Display the options that are common to all languages.
|
|
@end table
|
|
|
|
These are the supported qualifiers:
|
|
|
|
@table @asis
|
|
@item @samp{undocumented}
|
|
Display only those options that are undocumented.
|
|
|
|
@item @samp{joined}
|
|
Display options taking an argument that appears after an equal
|
|
sign in the same continuous piece of text, such as:
|
|
@samp{--help=target}.
|
|
|
|
@item @samp{separate}
|
|
Display options taking an argument that appears as a separate word
|
|
following the original option, such as: @samp{-o output-file}.
|
|
@end table
|
|
|
|
Thus for example to display all the undocumented target-specific
|
|
switches supported by the compiler, use:
|
|
|
|
@smallexample
|
|
--help=target,undocumented
|
|
@end smallexample
|
|
|
|
The sense of a qualifier can be inverted by prefixing it with the
|
|
@samp{^} character, so for example to display all binary warning
|
|
options (i.e., ones that are either on or off and that do not take an
|
|
argument) that have a description, use:
|
|
|
|
@smallexample
|
|
--help=warnings,^joined,^undocumented
|
|
@end smallexample
|
|
|
|
The argument to @option{--help=} should not consist solely of inverted
|
|
qualifiers.
|
|
|
|
Combining several classes is possible, although this usually
|
|
restricts the output so much that there is nothing to display. One
|
|
case where it does work, however, is when one of the classes is
|
|
@var{target}. For example, to display all the target-specific
|
|
optimization options, use:
|
|
|
|
@smallexample
|
|
--help=target,optimizers
|
|
@end smallexample
|
|
|
|
The @option{--help=} option can be repeated on the command line. Each
|
|
successive use displays its requested class of options, skipping
|
|
those that have already been displayed.
|
|
|
|
If the @option{-Q} option appears on the command line before the
|
|
@option{--help=} option, then the descriptive text displayed by
|
|
@option{--help=} is changed. Instead of describing the displayed
|
|
options, an indication is given as to whether the option is enabled,
|
|
disabled or set to a specific value (assuming that the compiler
|
|
knows this at the point where the @option{--help=} option is used).
|
|
|
|
Here is a truncated example from the ARM port of @command{gcc}:
|
|
|
|
@smallexample
|
|
% gcc -Q -mabi=2 --help=target -c
|
|
The following options are target specific:
|
|
-mabi= 2
|
|
-mabort-on-noreturn [disabled]
|
|
-mapcs [disabled]
|
|
@end smallexample
|
|
|
|
The output is sensitive to the effects of previous command-line
|
|
options, so for example it is possible to find out which optimizations
|
|
are enabled at @option{-O2} by using:
|
|
|
|
@smallexample
|
|
-Q -O2 --help=optimizers
|
|
@end smallexample
|
|
|
|
Alternatively you can discover which binary optimizations are enabled
|
|
by @option{-O3} by using:
|
|
|
|
@smallexample
|
|
gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
|
|
gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
|
|
diff /tmp/O2-opts /tmp/O3-opts | grep enabled
|
|
@end smallexample
|
|
|
|
@item --version
|
|
@opindex version
|
|
Display the version number and copyrights of the invoked GCC@.
|
|
|
|
@item -pass-exit-codes
|
|
@opindex pass-exit-codes
|
|
Normally the @command{gcc} program exits with the code of 1 if any
|
|
phase of the compiler returns a non-success return code. If you specify
|
|
@option{-pass-exit-codes}, the @command{gcc} program instead returns with
|
|
the numerically highest error produced by any phase returning an error
|
|
indication. The C, C++, and Fortran front ends return 4 if an internal
|
|
compiler error is encountered.
|
|
|
|
@item -pipe
|
|
@opindex pipe
|
|
Use pipes rather than temporary files for communication between the
|
|
various stages of compilation. This fails to work on some systems where
|
|
the assembler is unable to read from a pipe; but the GNU assembler has
|
|
no trouble.
|
|
|
|
@item -specs=@var{file}
|
|
@opindex specs
|
|
Process @var{file} after the compiler reads in the standard @file{specs}
|
|
file, in order to override the defaults which the @command{gcc} driver
|
|
program uses when determining what switches to pass to @command{cc1},
|
|
@command{cc1plus}, @command{as}, @command{ld}, etc. More than one
|
|
@option{-specs=@var{file}} can be specified on the command line, and they
|
|
are processed in order, from left to right. @xref{Spec Files}, for
|
|
information about the format of the @var{file}.
|
|
|
|
@item -wrapper
|
|
@opindex wrapper
|
|
Invoke all subcommands under a wrapper program. The name of the
|
|
wrapper program and its parameters are passed as a comma separated
|
|
list.
|
|
|
|
@smallexample
|
|
gcc -c t.c -wrapper gdb,--args
|
|
@end smallexample
|
|
|
|
@noindent
|
|
This invokes all subprograms of @command{gcc} under
|
|
@samp{gdb --args}, thus the invocation of @command{cc1} is
|
|
@samp{gdb --args cc1 @dots{}}.
|
|
|
|
@item -fplugin=@var{name}.so
|
|
@opindex fplugin
|
|
Load the plugin code in file @var{name}.so, assumed to be a
|
|
shared object to be dlopen'd by the compiler. The base name of
|
|
the shared object file is used to identify the plugin for the
|
|
purposes of argument parsing (See
|
|
@option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below).
|
|
Each plugin should define the callback functions specified in the
|
|
Plugins API.
|
|
|
|
@item -fplugin-arg-@var{name}-@var{key}=@var{value}
|
|
@opindex fplugin-arg
|
|
Define an argument called @var{key} with a value of @var{value}
|
|
for the plugin called @var{name}.
|
|
|
|
@item -fdump-ada-spec@r{[}-slim@r{]}
|
|
@opindex fdump-ada-spec
|
|
For C and C++ source and include files, generate corresponding Ada specs.
|
|
@xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn,
|
|
GNAT User's Guide}, which provides detailed documentation on this feature.
|
|
|
|
@item -fada-spec-parent=@var{unit}
|
|
@opindex fada-spec-parent
|
|
In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate
|
|
Ada specs as child units of parent @var{unit}.
|
|
|
|
@item -fdump-go-spec=@var{file}
|
|
@opindex fdump-go-spec
|
|
For input files in any language, generate corresponding Go
|
|
declarations in @var{file}. This generates Go @code{const},
|
|
@code{type}, @code{var}, and @code{func} declarations which may be a
|
|
useful way to start writing a Go interface to code written in some
|
|
other language.
|
|
|
|
@include @value{srcdir}/../libiberty/at-file.texi
|
|
@end table
|
|
|
|
@node Invoking G++
|
|
@section Compiling C++ Programs
|
|
|
|
@cindex suffixes for C++ source
|
|
@cindex C++ source file suffixes
|
|
C++ source files conventionally use one of the suffixes @samp{.C},
|
|
@samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
|
|
@samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
|
|
@samp{.H}, or (for shared template code) @samp{.tcc}; and
|
|
preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes
|
|
files with these names and compiles them as C++ programs even if you
|
|
call the compiler the same way as for compiling C programs (usually
|
|
with the name @command{gcc}).
|
|
|
|
@findex g++
|
|
@findex c++
|
|
However, the use of @command{gcc} does not add the C++ library.
|
|
@command{g++} is a program that calls GCC and automatically specifies linking
|
|
against the C++ library. It treats @samp{.c},
|
|
@samp{.h} and @samp{.i} files as C++ source files instead of C source
|
|
files unless @option{-x} is used. This program is also useful when
|
|
precompiling a C header file with a @samp{.h} extension for use in C++
|
|
compilations. On many systems, @command{g++} is also installed with
|
|
the name @command{c++}.
|
|
|
|
@cindex invoking @command{g++}
|
|
When you compile C++ programs, you may specify many of the same
|
|
command-line options that you use for compiling programs in any
|
|
language; or command-line options meaningful for C and related
|
|
languages; or options that are meaningful only for C++ programs.
|
|
@xref{C Dialect Options,,Options Controlling C Dialect}, for
|
|
explanations of options for languages related to C@.
|
|
@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
|
|
explanations of options that are meaningful only for C++ programs.
|
|
|
|
@node C Dialect Options
|
|
@section Options Controlling C Dialect
|
|
@cindex dialect options
|
|
@cindex language dialect options
|
|
@cindex options, dialect
|
|
|
|
The following options control the dialect of C (or languages derived
|
|
from C, such as C++, Objective-C and Objective-C++) that the compiler
|
|
accepts:
|
|
|
|
@table @gcctabopt
|
|
@cindex ANSI support
|
|
@cindex ISO support
|
|
@item -ansi
|
|
@opindex ansi
|
|
In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is
|
|
equivalent to @option{-std=c++98}.
|
|
|
|
This turns off certain features of GCC that are incompatible with ISO
|
|
C90 (when compiling C code), or of standard C++ (when compiling C++ code),
|
|
such as the @code{asm} and @code{typeof} keywords, and
|
|
predefined macros such as @code{unix} and @code{vax} that identify the
|
|
type of system you are using. It also enables the undesirable and
|
|
rarely used ISO trigraph feature. For the C compiler,
|
|
it disables recognition of C++ style @samp{//} comments as well as
|
|
the @code{inline} keyword.
|
|
|
|
The alternate keywords @code{__asm__}, @code{__extension__},
|
|
@code{__inline__} and @code{__typeof__} continue to work despite
|
|
@option{-ansi}. You would not want to use them in an ISO C program, of
|
|
course, but it is useful to put them in header files that might be included
|
|
in compilations done with @option{-ansi}. Alternate predefined macros
|
|
such as @code{__unix__} and @code{__vax__} are also available, with or
|
|
without @option{-ansi}.
|
|
|
|
The @option{-ansi} option does not cause non-ISO programs to be
|
|
rejected gratuitously. For that, @option{-Wpedantic} is required in
|
|
addition to @option{-ansi}. @xref{Warning Options}.
|
|
|
|
The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi}
|
|
option is used. Some header files may notice this macro and refrain
|
|
from declaring certain functions or defining certain macros that the
|
|
ISO standard doesn't call for; this is to avoid interfering with any
|
|
programs that might use these names for other things.
|
|
|
|
Functions that are normally built in but do not have semantics
|
|
defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in
|
|
functions when @option{-ansi} is used. @xref{Other Builtins,,Other
|
|
built-in functions provided by GCC}, for details of the functions
|
|
affected.
|
|
|
|
@item -std=
|
|
@opindex std
|
|
Determine the language standard. @xref{Standards,,Language Standards
|
|
Supported by GCC}, for details of these standard versions. This option
|
|
is currently only supported when compiling C or C++.
|
|
|
|
The compiler can accept several base standards, such as @samp{c90} or
|
|
@samp{c++98}, and GNU dialects of those standards, such as
|
|
@samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the
|
|
compiler accepts all programs following that standard plus those
|
|
using GNU extensions that do not contradict it. For example,
|
|
@option{-std=c90} turns off certain features of GCC that are
|
|
incompatible with ISO C90, such as the @code{asm} and @code{typeof}
|
|
keywords, but not other GNU extensions that do not have a meaning in
|
|
ISO C90, such as omitting the middle term of a @code{?:}
|
|
expression. On the other hand, when a GNU dialect of a standard is
|
|
specified, all features supported by the compiler are enabled, even when
|
|
those features change the meaning of the base standard. As a result, some
|
|
strict-conforming programs may be rejected. The particular standard
|
|
is used by @option{-Wpedantic} to identify which features are GNU
|
|
extensions given that version of the standard. For example
|
|
@option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//}
|
|
comments, while @option{-std=gnu99 -Wpedantic} does not.
|
|
|
|
A value for this option must be provided; possible values are
|
|
|
|
@table @samp
|
|
@item c90
|
|
@itemx c89
|
|
@itemx iso9899:1990
|
|
Support all ISO C90 programs (certain GNU extensions that conflict
|
|
with ISO C90 are disabled). Same as @option{-ansi} for C code.
|
|
|
|
@item iso9899:199409
|
|
ISO C90 as modified in amendment 1.
|
|
|
|
@item c99
|
|
@itemx c9x
|
|
@itemx iso9899:1999
|
|
@itemx iso9899:199x
|
|
ISO C99. This standard is substantially completely supported, modulo
|
|
bugs and floating-point issues
|
|
(mainly but not entirely relating to optional C99 features from
|
|
Annexes F and G). See
|
|
@w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The
|
|
names @samp{c9x} and @samp{iso9899:199x} are deprecated.
|
|
|
|
@item c11
|
|
@itemx c1x
|
|
@itemx iso9899:2011
|
|
ISO C11, the 2011 revision of the ISO C standard. This standard is
|
|
substantially completely supported, modulo bugs, floating-point issues
|
|
(mainly but not entirely relating to optional C11 features from
|
|
Annexes F and G) and the optional Annexes K (Bounds-checking
|
|
interfaces) and L (Analyzability). The name @samp{c1x} is deprecated.
|
|
|
|
@item gnu90
|
|
@itemx gnu89
|
|
GNU dialect of ISO C90 (including some C99 features).
|
|
|
|
@item gnu99
|
|
@itemx gnu9x
|
|
GNU dialect of ISO C99. The name @samp{gnu9x} is deprecated.
|
|
|
|
@item gnu11
|
|
@itemx gnu1x
|
|
GNU dialect of ISO C11. This is the default for C code.
|
|
The name @samp{gnu1x} is deprecated.
|
|
|
|
@item c++98
|
|
@itemx c++03
|
|
The 1998 ISO C++ standard plus the 2003 technical corrigendum and some
|
|
additional defect reports. Same as @option{-ansi} for C++ code.
|
|
|
|
@item gnu++98
|
|
@itemx gnu++03
|
|
GNU dialect of @option{-std=c++98}.
|
|
|
|
@item c++11
|
|
@itemx c++0x
|
|
The 2011 ISO C++ standard plus amendments.
|
|
The name @samp{c++0x} is deprecated.
|
|
|
|
@item gnu++11
|
|
@itemx gnu++0x
|
|
GNU dialect of @option{-std=c++11}.
|
|
The name @samp{gnu++0x} is deprecated.
|
|
|
|
@item c++14
|
|
@itemx c++1y
|
|
The 2014 ISO C++ standard plus amendments.
|
|
The name @samp{c++1y} is deprecated.
|
|
|
|
@item gnu++14
|
|
@itemx gnu++1y
|
|
GNU dialect of @option{-std=c++14}.
|
|
This is the default for C++ code.
|
|
The name @samp{gnu++1y} is deprecated.
|
|
|
|
@item c++1z
|
|
The next revision of the ISO C++ standard, tentatively planned for
|
|
2017. Support is highly experimental, and will almost certainly
|
|
change in incompatible ways in future releases.
|
|
|
|
@item gnu++1z
|
|
GNU dialect of @option{-std=c++1z}. Support is highly experimental,
|
|
and will almost certainly change in incompatible ways in future
|
|
releases.
|
|
@end table
|
|
|
|
@item -fgnu89-inline
|
|
@opindex fgnu89-inline
|
|
The option @option{-fgnu89-inline} tells GCC to use the traditional
|
|
GNU semantics for @code{inline} functions when in C99 mode.
|
|
@xref{Inline,,An Inline Function is As Fast As a Macro}.
|
|
Using this option is roughly equivalent to adding the
|
|
@code{gnu_inline} function attribute to all inline functions
|
|
(@pxref{Function Attributes}).
|
|
|
|
The option @option{-fno-gnu89-inline} explicitly tells GCC to use the
|
|
C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it
|
|
specifies the default behavior).
|
|
This option is not supported in @option{-std=c90} or
|
|
@option{-std=gnu90} mode.
|
|
|
|
The preprocessor macros @code{__GNUC_GNU_INLINE__} and
|
|
@code{__GNUC_STDC_INLINE__} may be used to check which semantics are
|
|
in effect for @code{inline} functions. @xref{Common Predefined
|
|
Macros,,,cpp,The C Preprocessor}.
|
|
|
|
@item -fpermitted-flt-eval-methods=@var{style}
|
|
@opindex fpermitted-flt-eval-methods
|
|
@opindex fpermitted-flt-eval-methods=c11
|
|
@opindex fpermitted-flt-eval-methods=ts-18661-3
|
|
ISO/IEC TS 18661-3 defines new permissible values for
|
|
@code{FLT_EVAL_METHOD} that indicate that operations and constants with
|
|
a semantic type that is an interchange or extended format should be
|
|
evaluated to the precision and range of that type. These new values are
|
|
a superset of those permitted under C99/C11, which does not specify the
|
|
meaning of other positive values of @code{FLT_EVAL_METHOD}. As such, code
|
|
conforming to C11 may not have been written expecting the possibility of
|
|
the new values.
|
|
|
|
@option{-fpermitted-flt-eval-methods} specifies whether the compiler
|
|
should allow only the values of @code{FLT_EVAL_METHOD} specified in C99/C11,
|
|
or the extended set of values specified in ISO/IEC TS 18661-3.
|
|
|
|
@var{style} is either @code{c11} or @code{ts-18661-3} as appropriate.
|
|
|
|
The default when in a standards compliant mode (@option{-std=c11} or similar)
|
|
is @option{-fpermitted-flt-eval-methods=c11}. The default when in a GNU
|
|
dialect (@option{-std=gnu11} or similar) is
|
|
@option{-fpermitted-flt-eval-methods=ts-18661-3}.
|
|
|
|
@item -aux-info @var{filename}
|
|
@opindex aux-info
|
|
Output to the given filename prototyped declarations for all functions
|
|
declared and/or defined in a translation unit, including those in header
|
|
files. This option is silently ignored in any language other than C@.
|
|
|
|
Besides declarations, the file indicates, in comments, the origin of
|
|
each declaration (source file and line), whether the declaration was
|
|
implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or
|
|
@samp{O} for old, respectively, in the first character after the line
|
|
number and the colon), and whether it came from a declaration or a
|
|
definition (@samp{C} or @samp{F}, respectively, in the following
|
|
character). In the case of function definitions, a K&R-style list of
|
|
arguments followed by their declarations is also provided, inside
|
|
comments, after the declaration.
|
|
|
|
@item -fallow-parameterless-variadic-functions
|
|
@opindex fallow-parameterless-variadic-functions
|
|
Accept variadic functions without named parameters.
|
|
|
|
Although it is possible to define such a function, this is not very
|
|
useful as it is not possible to read the arguments. This is only
|
|
supported for C as this construct is allowed by C++.
|
|
|
|
@item -fno-asm
|
|
@opindex fno-asm
|
|
Do not recognize @code{asm}, @code{inline} or @code{typeof} as a
|
|
keyword, so that code can use these words as identifiers. You can use
|
|
the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__}
|
|
instead. @option{-ansi} implies @option{-fno-asm}.
|
|
|
|
In C++, this switch only affects the @code{typeof} keyword, since
|
|
@code{asm} and @code{inline} are standard keywords. You may want to
|
|
use the @option{-fno-gnu-keywords} flag instead, which has the same
|
|
effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this
|
|
switch only affects the @code{asm} and @code{typeof} keywords, since
|
|
@code{inline} is a standard keyword in ISO C99.
|
|
|
|
@item -fno-builtin
|
|
@itemx -fno-builtin-@var{function}
|
|
@opindex fno-builtin
|
|
@cindex built-in functions
|
|
Don't recognize built-in functions that do not begin with
|
|
@samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in
|
|
functions provided by GCC}, for details of the functions affected,
|
|
including those which are not built-in functions when @option{-ansi} or
|
|
@option{-std} options for strict ISO C conformance are used because they
|
|
do not have an ISO standard meaning.
|
|
|
|
GCC normally generates special code to handle certain built-in functions
|
|
more efficiently; for instance, calls to @code{alloca} may become single
|
|
instructions which adjust the stack directly, and calls to @code{memcpy}
|
|
may become inline copy loops. The resulting code is often both smaller
|
|
and faster, but since the function calls no longer appear as such, you
|
|
cannot set a breakpoint on those calls, nor can you change the behavior
|
|
of the functions by linking with a different library. In addition,
|
|
when a function is recognized as a built-in function, GCC may use
|
|
information about that function to warn about problems with calls to
|
|
that function, or to generate more efficient code, even if the
|
|
resulting code still contains calls to that function. For example,
|
|
warnings are given with @option{-Wformat} for bad calls to
|
|
@code{printf} when @code{printf} is built in and @code{strlen} is
|
|
known not to modify global memory.
|
|
|
|
With the @option{-fno-builtin-@var{function}} option
|
|
only the built-in function @var{function} is
|
|
disabled. @var{function} must not begin with @samp{__builtin_}. If a
|
|
function is named that is not built-in in this version of GCC, this
|
|
option is ignored. There is no corresponding
|
|
@option{-fbuiltin-@var{function}} option; if you wish to enable
|
|
built-in functions selectively when using @option{-fno-builtin} or
|
|
@option{-ffreestanding}, you may define macros such as:
|
|
|
|
@smallexample
|
|
#define abs(n) __builtin_abs ((n))
|
|
#define strcpy(d, s) __builtin_strcpy ((d), (s))
|
|
@end smallexample
|
|
|
|
@item -fgimple
|
|
@opindex fgimple
|
|
|
|
Enable parsing of function definitions marked with @code{__GIMPLE}.
|
|
This is an experimental feature that allows unit testing of GIMPLE
|
|
passes.
|
|
|
|
@item -fhosted
|
|
@opindex fhosted
|
|
@cindex hosted environment
|
|
|
|
Assert that compilation targets a hosted environment. This implies
|
|
@option{-fbuiltin}. A hosted environment is one in which the
|
|
entire standard library is available, and in which @code{main} has a return
|
|
type of @code{int}. Examples are nearly everything except a kernel.
|
|
This is equivalent to @option{-fno-freestanding}.
|
|
|
|
@item -ffreestanding
|
|
@opindex ffreestanding
|
|
@cindex hosted environment
|
|
|
|
Assert that compilation targets a freestanding environment. This
|
|
implies @option{-fno-builtin}. A freestanding environment
|
|
is one in which the standard library may not exist, and program startup may
|
|
not necessarily be at @code{main}. The most obvious example is an OS kernel.
|
|
This is equivalent to @option{-fno-hosted}.
|
|
|
|
@xref{Standards,,Language Standards Supported by GCC}, for details of
|
|
freestanding and hosted environments.
|
|
|
|
@item -fopenacc
|
|
@opindex fopenacc
|
|
@cindex OpenACC accelerator programming
|
|
Enable handling of OpenACC directives @code{#pragma acc} in C/C++ and
|
|
@code{!$acc} in Fortran. When @option{-fopenacc} is specified, the
|
|
compiler generates accelerated code according to the OpenACC Application
|
|
Programming Interface v2.0 @w{@uref{http://www.openacc.org/}}. This option
|
|
implies @option{-pthread}, and thus is only supported on targets that
|
|
have support for @option{-pthread}.
|
|
|
|
@item -fopenacc-dim=@var{geom}
|
|
@opindex fopenacc-dim
|
|
@cindex OpenACC accelerator programming
|
|
Specify default compute dimensions for parallel offload regions that do
|
|
not explicitly specify. The @var{geom} value is a triple of
|
|
':'-separated sizes, in order 'gang', 'worker' and, 'vector'. A size
|
|
can be omitted, to use a target-specific default value.
|
|
|
|
@item -fopenmp
|
|
@opindex fopenmp
|
|
@cindex OpenMP parallel
|
|
Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and
|
|
@code{!$omp} in Fortran. When @option{-fopenmp} is specified, the
|
|
compiler generates parallel code according to the OpenMP Application
|
|
Program Interface v4.0 @w{@uref{http://www.openmp.org/}}. This option
|
|
implies @option{-pthread}, and thus is only supported on targets that
|
|
have support for @option{-pthread}. @option{-fopenmp} implies
|
|
@option{-fopenmp-simd}.
|
|
|
|
@item -fopenmp-simd
|
|
@opindex fopenmp-simd
|
|
@cindex OpenMP SIMD
|
|
@cindex SIMD
|
|
Enable handling of OpenMP's SIMD directives with @code{#pragma omp}
|
|
in C/C++ and @code{!$omp} in Fortran. Other OpenMP directives
|
|
are ignored.
|
|
|
|
@item -fcilkplus
|
|
@opindex fcilkplus
|
|
@cindex Enable Cilk Plus
|
|
Enable the usage of Cilk Plus language extension features for C/C++.
|
|
When the option @option{-fcilkplus} is specified, enable the usage of
|
|
the Cilk Plus Language extension features for C/C++. The present
|
|
implementation follows ABI version 1.2. This is an experimental
|
|
feature that is only partially complete, and whose interface may
|
|
change in future versions of GCC as the official specification
|
|
changes. Currently, all features but @code{_Cilk_for} have been
|
|
implemented.
|
|
|
|
@item -fgnu-tm
|
|
@opindex fgnu-tm
|
|
When the option @option{-fgnu-tm} is specified, the compiler
|
|
generates code for the Linux variant of Intel's current Transactional
|
|
Memory ABI specification document (Revision 1.1, May 6 2009). This is
|
|
an experimental feature whose interface may change in future versions
|
|
of GCC, as the official specification changes. Please note that not
|
|
all architectures are supported for this feature.
|
|
|
|
For more information on GCC's support for transactional memory,
|
|
@xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU
|
|
Transactional Memory Library}.
|
|
|
|
Note that the transactional memory feature is not supported with
|
|
non-call exceptions (@option{-fnon-call-exceptions}).
|
|
|
|
@item -fms-extensions
|
|
@opindex fms-extensions
|
|
Accept some non-standard constructs used in Microsoft header files.
|
|
|
|
In C++ code, this allows member names in structures to be similar
|
|
to previous types declarations.
|
|
|
|
@smallexample
|
|
typedef int UOW;
|
|
struct ABC @{
|
|
UOW UOW;
|
|
@};
|
|
@end smallexample
|
|
|
|
Some cases of unnamed fields in structures and unions are only
|
|
accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union
|
|
fields within structs/unions}, for details.
|
|
|
|
Note that this option is off for all targets but x86
|
|
targets using ms-abi.
|
|
|
|
@item -fplan9-extensions
|
|
@opindex fplan9-extensions
|
|
Accept some non-standard constructs used in Plan 9 code.
|
|
|
|
This enables @option{-fms-extensions}, permits passing pointers to
|
|
structures with anonymous fields to functions that expect pointers to
|
|
elements of the type of the field, and permits referring to anonymous
|
|
fields declared using a typedef. @xref{Unnamed Fields,,Unnamed
|
|
struct/union fields within structs/unions}, for details. This is only
|
|
supported for C, not C++.
|
|
|
|
@item -fcond-mismatch
|
|
@opindex fcond-mismatch
|
|
Allow conditional expressions with mismatched types in the second and
|
|
third arguments. The value of such an expression is void. This option
|
|
is not supported for C++.
|
|
|
|
@item -flax-vector-conversions
|
|
@opindex flax-vector-conversions
|
|
Allow implicit conversions between vectors with differing numbers of
|
|
elements and/or incompatible element types. This option should not be
|
|
used for new code.
|
|
|
|
@item -funsigned-char
|
|
@opindex funsigned-char
|
|
Let the type @code{char} be unsigned, like @code{unsigned char}.
|
|
|
|
Each kind of machine has a default for what @code{char} should
|
|
be. It is either like @code{unsigned char} by default or like
|
|
@code{signed char} by default.
|
|
|
|
Ideally, a portable program should always use @code{signed char} or
|
|
@code{unsigned char} when it depends on the signedness of an object.
|
|
But many programs have been written to use plain @code{char} and
|
|
expect it to be signed, or expect it to be unsigned, depending on the
|
|
machines they were written for. This option, and its inverse, let you
|
|
make such a program work with the opposite default.
|
|
|
|
The type @code{char} is always a distinct type from each of
|
|
@code{signed char} or @code{unsigned char}, even though its behavior
|
|
is always just like one of those two.
|
|
|
|
@item -fsigned-char
|
|
@opindex fsigned-char
|
|
Let the type @code{char} be signed, like @code{signed char}.
|
|
|
|
Note that this is equivalent to @option{-fno-unsigned-char}, which is
|
|
the negative form of @option{-funsigned-char}. Likewise, the option
|
|
@option{-fno-signed-char} is equivalent to @option{-funsigned-char}.
|
|
|
|
@item -fsigned-bitfields
|
|
@itemx -funsigned-bitfields
|
|
@itemx -fno-signed-bitfields
|
|
@itemx -fno-unsigned-bitfields
|
|
@opindex fsigned-bitfields
|
|
@opindex funsigned-bitfields
|
|
@opindex fno-signed-bitfields
|
|
@opindex fno-unsigned-bitfields
|
|
These options control whether a bit-field is signed or unsigned, when the
|
|
declaration does not use either @code{signed} or @code{unsigned}. By
|
|
default, such a bit-field is signed, because this is consistent: the
|
|
basic integer types such as @code{int} are signed types.
|
|
|
|
@item -fsso-struct=@var{endianness}
|
|
@opindex fsso-struct
|
|
Set the default scalar storage order of structures and unions to the
|
|
specified endianness. The accepted values are @samp{big-endian},
|
|
@samp{little-endian} and @samp{native} for the native endianness of
|
|
the target (the default). This option is not supported for C++.
|
|
|
|
@strong{Warning:} the @option{-fsso-struct} switch causes GCC to generate
|
|
code that is not binary compatible with code generated without it if the
|
|
specified endianness is not the native endianness of the target.
|
|
@end table
|
|
|
|
@node C++ Dialect Options
|
|
@section Options Controlling C++ Dialect
|
|
|
|
@cindex compiler options, C++
|
|
@cindex C++ options, command-line
|
|
@cindex options, C++
|
|
This section describes the command-line options that are only meaningful
|
|
for C++ programs. You can also use most of the GNU compiler options
|
|
regardless of what language your program is in. For example, you
|
|
might compile a file @file{firstClass.C} like this:
|
|
|
|
@smallexample
|
|
g++ -g -fstrict-enums -O -c firstClass.C
|
|
@end smallexample
|
|
|
|
@noindent
|
|
In this example, only @option{-fstrict-enums} is an option meant
|
|
only for C++ programs; you can use the other options with any
|
|
language supported by GCC@.
|
|
|
|
Some options for compiling C programs, such as @option{-std}, are also
|
|
relevant for C++ programs.
|
|
@xref{C Dialect Options,,Options Controlling C Dialect}.
|
|
|
|
Here is a list of options that are @emph{only} for compiling C++ programs:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -fabi-version=@var{n}
|
|
@opindex fabi-version
|
|
Use version @var{n} of the C++ ABI@. The default is version 0.
|
|
|
|
Version 0 refers to the version conforming most closely to
|
|
the C++ ABI specification. Therefore, the ABI obtained using version 0
|
|
will change in different versions of G++ as ABI bugs are fixed.
|
|
|
|
Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.
|
|
|
|
Version 2 is the version of the C++ ABI that first appeared in G++
|
|
3.4, and was the default through G++ 4.9.
|
|
|
|
Version 3 corrects an error in mangling a constant address as a
|
|
template argument.
|
|
|
|
Version 4, which first appeared in G++ 4.5, implements a standard
|
|
mangling for vector types.
|
|
|
|
Version 5, which first appeared in G++ 4.6, corrects the mangling of
|
|
attribute const/volatile on function pointer types, decltype of a
|
|
plain decl, and use of a function parameter in the declaration of
|
|
another parameter.
|
|
|
|
Version 6, which first appeared in G++ 4.7, corrects the promotion
|
|
behavior of C++11 scoped enums and the mangling of template argument
|
|
packs, const/static_cast, prefix ++ and --, and a class scope function
|
|
used as a template argument.
|
|
|
|
Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a
|
|
builtin type and corrects the mangling of lambdas in default argument
|
|
scope.
|
|
|
|
Version 8, which first appeared in G++ 4.9, corrects the substitution
|
|
behavior of function types with function-cv-qualifiers.
|
|
|
|
Version 9, which first appeared in G++ 5.2, corrects the alignment of
|
|
@code{nullptr_t}.
|
|
|
|
Version 10, which first appeared in G++ 6.1, adds mangling of
|
|
attributes that affect type identity, such as ia32 calling convention
|
|
attributes (e.g. @samp{stdcall}).
|
|
|
|
Version 11, which first appeared in G++ 7, corrects the mangling of
|
|
sizeof... expressions. It also implies
|
|
@option{-fnew-inheriting-ctors}.
|
|
|
|
See also @option{-Wabi}.
|
|
|
|
@item -fabi-compat-version=@var{n}
|
|
@opindex fabi-compat-version
|
|
On targets that support strong aliases, G++
|
|
works around mangling changes by creating an alias with the correct
|
|
mangled name when defining a symbol with an incorrect mangled name.
|
|
This switch specifies which ABI version to use for the alias.
|
|
|
|
With @option{-fabi-version=0} (the default), this defaults to 8 (GCC 5
|
|
compatibility). If another ABI version is explicitly selected, this
|
|
defaults to 0. For compatibility with GCC versions 3.2 through 4.9,
|
|
use @option{-fabi-compat-version=2}.
|
|
|
|
If this option is not provided but @option{-Wabi=@var{n}} is, that
|
|
version is used for compatibility aliases. If this option is provided
|
|
along with @option{-Wabi} (without the version), the version from this
|
|
option is used for the warning.
|
|
|
|
@item -fno-access-control
|
|
@opindex fno-access-control
|
|
Turn off all access checking. This switch is mainly useful for working
|
|
around bugs in the access control code.
|
|
|
|
@item -faligned-new
|
|
@opindex faligned-new
|
|
Enable support for C++17 @code{new} of types that require more
|
|
alignment than @code{void* ::operator new(std::size_t)} provides. A
|
|
numeric argument such as @code{-faligned-new=32} can be used to
|
|
specify how much alignment (in bytes) is provided by that function,
|
|
but few users will need to override the default of
|
|
@code{alignof(std::max_align_t)}.
|
|
|
|
@item -fcheck-new
|
|
@opindex fcheck-new
|
|
Check that the pointer returned by @code{operator new} is non-null
|
|
before attempting to modify the storage allocated. This check is
|
|
normally unnecessary because the C++ standard specifies that
|
|
@code{operator new} only returns @code{0} if it is declared
|
|
@code{throw()}, in which case the compiler always checks the
|
|
return value even without this option. In all other cases, when
|
|
@code{operator new} has a non-empty exception specification, memory
|
|
exhaustion is signalled by throwing @code{std::bad_alloc}. See also
|
|
@samp{new (nothrow)}.
|
|
|
|
@item -fconcepts
|
|
@opindex fconcepts
|
|
Enable support for the C++ Extensions for Concepts Technical
|
|
Specification, ISO 19217 (2015), which allows code like
|
|
|
|
@smallexample
|
|
template <class T> concept bool Addable = requires (T t) @{ t + t; @};
|
|
template <Addable T> T add (T a, T b) @{ return a + b; @}
|
|
@end smallexample
|
|
|
|
@item -fconstexpr-depth=@var{n}
|
|
@opindex fconstexpr-depth
|
|
Set the maximum nested evaluation depth for C++11 constexpr functions
|
|
to @var{n}. A limit is needed to detect endless recursion during
|
|
constant expression evaluation. The minimum specified by the standard
|
|
is 512.
|
|
|
|
@item -fconstexpr-loop-limit=@var{n}
|
|
@opindex fconstexpr-loop-limit
|
|
Set the maximum number of iterations for a loop in C++14 constexpr functions
|
|
to @var{n}. A limit is needed to detect infinite loops during
|
|
constant expression evaluation. The default is 262144 (1<<18).
|
|
|
|
@item -fdeduce-init-list
|
|
@opindex fdeduce-init-list
|
|
Enable deduction of a template type parameter as
|
|
@code{std::initializer_list} from a brace-enclosed initializer list, i.e.@:
|
|
|
|
@smallexample
|
|
template <class T> auto forward(T t) -> decltype (realfn (t))
|
|
@{
|
|
return realfn (t);
|
|
@}
|
|
|
|
void f()
|
|
@{
|
|
forward(@{1,2@}); // call forward<std::initializer_list<int>>
|
|
@}
|
|
@end smallexample
|
|
|
|
This deduction was implemented as a possible extension to the
|
|
originally proposed semantics for the C++11 standard, but was not part
|
|
of the final standard, so it is disabled by default. This option is
|
|
deprecated, and may be removed in a future version of G++.
|
|
|
|
@item -ffriend-injection
|
|
@opindex ffriend-injection
|
|
Inject friend functions into the enclosing namespace, so that they are
|
|
visible outside the scope of the class in which they are declared.
|
|
Friend functions were documented to work this way in the old Annotated
|
|
C++ Reference Manual.
|
|
However, in ISO C++ a friend function that is not declared
|
|
in an enclosing scope can only be found using argument dependent
|
|
lookup. GCC defaults to the standard behavior.
|
|
|
|
This option is for compatibility, and may be removed in a future
|
|
release of G++.
|
|
|
|
@item -fno-elide-constructors
|
|
@opindex fno-elide-constructors
|
|
The C++ standard allows an implementation to omit creating a temporary
|
|
that is only used to initialize another object of the same type.
|
|
Specifying this option disables that optimization, and forces G++ to
|
|
call the copy constructor in all cases. This option also causes G++
|
|
to call trivial member functions which otherwise would be expanded inline.
|
|
|
|
In C++17, the compiler is required to omit these temporaries, but this
|
|
option still affects trivial member functions.
|
|
|
|
@item -fno-enforce-eh-specs
|
|
@opindex fno-enforce-eh-specs
|
|
Don't generate code to check for violation of exception specifications
|
|
at run time. This option violates the C++ standard, but may be useful
|
|
for reducing code size in production builds, much like defining
|
|
@code{NDEBUG}. This does not give user code permission to throw
|
|
exceptions in violation of the exception specifications; the compiler
|
|
still optimizes based on the specifications, so throwing an
|
|
unexpected exception results in undefined behavior at run time.
|
|
|
|
@item -fextern-tls-init
|
|
@itemx -fno-extern-tls-init
|
|
@opindex fextern-tls-init
|
|
@opindex fno-extern-tls-init
|
|
The C++11 and OpenMP standards allow @code{thread_local} and
|
|
@code{threadprivate} variables to have dynamic (runtime)
|
|
initialization. To support this, any use of such a variable goes
|
|
through a wrapper function that performs any necessary initialization.
|
|
When the use and definition of the variable are in the same
|
|
translation unit, this overhead can be optimized away, but when the
|
|
use is in a different translation unit there is significant overhead
|
|
even if the variable doesn't actually need dynamic initialization. If
|
|
the programmer can be sure that no use of the variable in a
|
|
non-defining TU needs to trigger dynamic initialization (either
|
|
because the variable is statically initialized, or a use of the
|
|
variable in the defining TU will be executed before any uses in
|
|
another TU), they can avoid this overhead with the
|
|
@option{-fno-extern-tls-init} option.
|
|
|
|
On targets that support symbol aliases, the default is
|
|
@option{-fextern-tls-init}. On targets that do not support symbol
|
|
aliases, the default is @option{-fno-extern-tls-init}.
|
|
|
|
@item -ffor-scope
|
|
@itemx -fno-for-scope
|
|
@opindex ffor-scope
|
|
@opindex fno-for-scope
|
|
If @option{-ffor-scope} is specified, the scope of variables declared in
|
|
a @i{for-init-statement} is limited to the @code{for} loop itself,
|
|
as specified by the C++ standard.
|
|
If @option{-fno-for-scope} is specified, the scope of variables declared in
|
|
a @i{for-init-statement} extends to the end of the enclosing scope,
|
|
as was the case in old versions of G++, and other (traditional)
|
|
implementations of C++.
|
|
|
|
If neither flag is given, the default is to follow the standard,
|
|
but to allow and give a warning for old-style code that would
|
|
otherwise be invalid, or have different behavior.
|
|
|
|
@item -fno-gnu-keywords
|
|
@opindex fno-gnu-keywords
|
|
Do not recognize @code{typeof} as a keyword, so that code can use this
|
|
word as an identifier. You can use the keyword @code{__typeof__} instead.
|
|
This option is implied by the strict ISO C++ dialects: @option{-ansi},
|
|
@option{-std=c++98}, @option{-std=c++11}, etc.
|
|
|
|
@item -fno-implicit-templates
|
|
@opindex fno-implicit-templates
|
|
Never emit code for non-inline templates that are instantiated
|
|
implicitly (i.e.@: by use); only emit code for explicit instantiations.
|
|
@xref{Template Instantiation}, for more information.
|
|
|
|
@item -fno-implicit-inline-templates
|
|
@opindex fno-implicit-inline-templates
|
|
Don't emit code for implicit instantiations of inline templates, either.
|
|
The default is to handle inlines differently so that compiles with and
|
|
without optimization need the same set of explicit instantiations.
|
|
|
|
@item -fno-implement-inlines
|
|
@opindex fno-implement-inlines
|
|
To save space, do not emit out-of-line copies of inline functions
|
|
controlled by @code{#pragma implementation}. This causes linker
|
|
errors if these functions are not inlined everywhere they are called.
|
|
|
|
@item -fms-extensions
|
|
@opindex fms-extensions
|
|
Disable Wpedantic warnings about constructs used in MFC, such as implicit
|
|
int and getting a pointer to member function via non-standard syntax.
|
|
|
|
@item -fnew-inheriting-ctors
|
|
@opindex fnew-inheriting-ctors
|
|
Enable the P0136 adjustment to the semantics of C++11 constructor
|
|
inheritance. This is part of C++17 but also considered to be a Defect
|
|
Report against C++11 and C++14. This flag is enabled by default
|
|
unless @option{-fabi-version=10} or lower is specified.
|
|
|
|
@item -fnew-ttp-matching
|
|
@opindex fnew-ttp-matching
|
|
Enable the P0522 resolution to Core issue 150, template template
|
|
parameters and default arguments: this allows a template with default
|
|
template arguments as an argument for a template template parameter
|
|
with fewer template parameters. This flag is enabled by default for
|
|
@option{-std=c++1z}.
|
|
|
|
@item -fno-nonansi-builtins
|
|
@opindex fno-nonansi-builtins
|
|
Disable built-in declarations of functions that are not mandated by
|
|
ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit},
|
|
@code{index}, @code{bzero}, @code{conjf}, and other related functions.
|
|
|
|
@item -fnothrow-opt
|
|
@opindex fnothrow-opt
|
|
Treat a @code{throw()} exception specification as if it were a
|
|
@code{noexcept} specification to reduce or eliminate the text size
|
|
overhead relative to a function with no exception specification. If
|
|
the function has local variables of types with non-trivial
|
|
destructors, the exception specification actually makes the
|
|
function smaller because the EH cleanups for those variables can be
|
|
optimized away. The semantic effect is that an exception thrown out of
|
|
a function with such an exception specification results in a call
|
|
to @code{terminate} rather than @code{unexpected}.
|
|
|
|
@item -fno-operator-names
|
|
@opindex fno-operator-names
|
|
Do not treat the operator name keywords @code{and}, @code{bitand},
|
|
@code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as
|
|
synonyms as keywords.
|
|
|
|
@item -fno-optional-diags
|
|
@opindex fno-optional-diags
|
|
Disable diagnostics that the standard says a compiler does not need to
|
|
issue. Currently, the only such diagnostic issued by G++ is the one for
|
|
a name having multiple meanings within a class.
|
|
|
|
@item -fpermissive
|
|
@opindex fpermissive
|
|
Downgrade some diagnostics about nonconformant code from errors to
|
|
warnings. Thus, using @option{-fpermissive} allows some
|
|
nonconforming code to compile.
|
|
|
|
@item -fno-pretty-templates
|
|
@opindex fno-pretty-templates
|
|
When an error message refers to a specialization of a function
|
|
template, the compiler normally prints the signature of the
|
|
template followed by the template arguments and any typedefs or
|
|
typenames in the signature (e.g. @code{void f(T) [with T = int]}
|
|
rather than @code{void f(int)}) so that it's clear which template is
|
|
involved. When an error message refers to a specialization of a class
|
|
template, the compiler omits any template arguments that match
|
|
the default template arguments for that template. If either of these
|
|
behaviors make it harder to understand the error message rather than
|
|
easier, you can use @option{-fno-pretty-templates} to disable them.
|
|
|
|
@item -frepo
|
|
@opindex frepo
|
|
Enable automatic template instantiation at link time. This option also
|
|
implies @option{-fno-implicit-templates}. @xref{Template
|
|
Instantiation}, for more information.
|
|
|
|
@item -fno-rtti
|
|
@opindex fno-rtti
|
|
Disable generation of information about every class with virtual
|
|
functions for use by the C++ run-time type identification features
|
|
(@code{dynamic_cast} and @code{typeid}). If you don't use those parts
|
|
of the language, you can save some space by using this flag. Note that
|
|
exception handling uses the same information, but G++ generates it as
|
|
needed. The @code{dynamic_cast} operator can still be used for casts that
|
|
do not require run-time type information, i.e.@: casts to @code{void *} or to
|
|
unambiguous base classes.
|
|
|
|
@item -fsized-deallocation
|
|
@opindex fsized-deallocation
|
|
Enable the built-in global declarations
|
|
@smallexample
|
|
void operator delete (void *, std::size_t) noexcept;
|
|
void operator delete[] (void *, std::size_t) noexcept;
|
|
@end smallexample
|
|
as introduced in C++14. This is useful for user-defined replacement
|
|
deallocation functions that, for example, use the size of the object
|
|
to make deallocation faster. Enabled by default under
|
|
@option{-std=c++14} and above. The flag @option{-Wsized-deallocation}
|
|
warns about places that might want to add a definition.
|
|
|
|
@item -fstrict-enums
|
|
@opindex fstrict-enums
|
|
Allow the compiler to optimize using the assumption that a value of
|
|
enumerated type can only be one of the values of the enumeration (as
|
|
defined in the C++ standard; basically, a value that can be
|
|
represented in the minimum number of bits needed to represent all the
|
|
enumerators). This assumption may not be valid if the program uses a
|
|
cast to convert an arbitrary integer value to the enumerated type.
|
|
|
|
@item -fstrong-eval-order
|
|
@opindex fstrong-eval-order
|
|
Evaluate member access, array subscripting, and shift expressions in
|
|
left-to-right order, and evaluate assignment in right-to-left order,
|
|
as adopted for C++17. Enabled by default with @option{-std=c++1z}.
|
|
@option{-fstrong-eval-order=some} enables just the ordering of member
|
|
access and shift expressions, and is the default without
|
|
@option{-std=c++1z}.
|
|
|
|
@item -ftemplate-backtrace-limit=@var{n}
|
|
@opindex ftemplate-backtrace-limit
|
|
Set the maximum number of template instantiation notes for a single
|
|
warning or error to @var{n}. The default value is 10.
|
|
|
|
@item -ftemplate-depth=@var{n}
|
|
@opindex ftemplate-depth
|
|
Set the maximum instantiation depth for template classes to @var{n}.
|
|
A limit on the template instantiation depth is needed to detect
|
|
endless recursions during template class instantiation. ANSI/ISO C++
|
|
conforming programs must not rely on a maximum depth greater than 17
|
|
(changed to 1024 in C++11). The default value is 900, as the compiler
|
|
can run out of stack space before hitting 1024 in some situations.
|
|
|
|
@item -fno-threadsafe-statics
|
|
@opindex fno-threadsafe-statics
|
|
Do not emit the extra code to use the routines specified in the C++
|
|
ABI for thread-safe initialization of local statics. You can use this
|
|
option to reduce code size slightly in code that doesn't need to be
|
|
thread-safe.
|
|
|
|
@item -fuse-cxa-atexit
|
|
@opindex fuse-cxa-atexit
|
|
Register destructors for objects with static storage duration with the
|
|
@code{__cxa_atexit} function rather than the @code{atexit} function.
|
|
This option is required for fully standards-compliant handling of static
|
|
destructors, but only works if your C library supports
|
|
@code{__cxa_atexit}.
|
|
|
|
@item -fno-use-cxa-get-exception-ptr
|
|
@opindex fno-use-cxa-get-exception-ptr
|
|
Don't use the @code{__cxa_get_exception_ptr} runtime routine. This
|
|
causes @code{std::uncaught_exception} to be incorrect, but is necessary
|
|
if the runtime routine is not available.
|
|
|
|
@item -fvisibility-inlines-hidden
|
|
@opindex fvisibility-inlines-hidden
|
|
This switch declares that the user does not attempt to compare
|
|
pointers to inline functions or methods where the addresses of the two functions
|
|
are taken in different shared objects.
|
|
|
|
The effect of this is that GCC may, effectively, mark inline methods with
|
|
@code{__attribute__ ((visibility ("hidden")))} so that they do not
|
|
appear in the export table of a DSO and do not require a PLT indirection
|
|
when used within the DSO@. Enabling this option can have a dramatic effect
|
|
on load and link times of a DSO as it massively reduces the size of the
|
|
dynamic export table when the library makes heavy use of templates.
|
|
|
|
The behavior of this switch is not quite the same as marking the
|
|
methods as hidden directly, because it does not affect static variables
|
|
local to the function or cause the compiler to deduce that
|
|
the function is defined in only one shared object.
|
|
|
|
You may mark a method as having a visibility explicitly to negate the
|
|
effect of the switch for that method. For example, if you do want to
|
|
compare pointers to a particular inline method, you might mark it as
|
|
having default visibility. Marking the enclosing class with explicit
|
|
visibility has no effect.
|
|
|
|
Explicitly instantiated inline methods are unaffected by this option
|
|
as their linkage might otherwise cross a shared library boundary.
|
|
@xref{Template Instantiation}.
|
|
|
|
@item -fvisibility-ms-compat
|
|
@opindex fvisibility-ms-compat
|
|
This flag attempts to use visibility settings to make GCC's C++
|
|
linkage model compatible with that of Microsoft Visual Studio.
|
|
|
|
The flag makes these changes to GCC's linkage model:
|
|
|
|
@enumerate
|
|
@item
|
|
It sets the default visibility to @code{hidden}, like
|
|
@option{-fvisibility=hidden}.
|
|
|
|
@item
|
|
Types, but not their members, are not hidden by default.
|
|
|
|
@item
|
|
The One Definition Rule is relaxed for types without explicit
|
|
visibility specifications that are defined in more than one
|
|
shared object: those declarations are permitted if they are
|
|
permitted when this option is not used.
|
|
@end enumerate
|
|
|
|
In new code it is better to use @option{-fvisibility=hidden} and
|
|
export those classes that are intended to be externally visible.
|
|
Unfortunately it is possible for code to rely, perhaps accidentally,
|
|
on the Visual Studio behavior.
|
|
|
|
Among the consequences of these changes are that static data members
|
|
of the same type with the same name but defined in different shared
|
|
objects are different, so changing one does not change the other;
|
|
and that pointers to function members defined in different shared
|
|
objects may not compare equal. When this flag is given, it is a
|
|
violation of the ODR to define types with the same name differently.
|
|
|
|
@item -fno-weak
|
|
@opindex fno-weak
|
|
Do not use weak symbol support, even if it is provided by the linker.
|
|
By default, G++ uses weak symbols if they are available. This
|
|
option exists only for testing, and should not be used by end-users;
|
|
it results in inferior code and has no benefits. This option may
|
|
be removed in a future release of G++.
|
|
|
|
@item -nostdinc++
|
|
@opindex nostdinc++
|
|
Do not search for header files in the standard directories specific to
|
|
C++, but do still search the other standard directories. (This option
|
|
is used when building the C++ library.)
|
|
@end table
|
|
|
|
In addition, these optimization, warning, and code generation options
|
|
have meanings only for C++ programs:
|
|
|
|
@table @gcctabopt
|
|
@item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)}
|
|
@opindex Wabi
|
|
@opindex Wno-abi
|
|
Warn when G++ it generates code that is probably not compatible with
|
|
the vendor-neutral C++ ABI@. Since G++ now defaults to updating the
|
|
ABI with each major release, normally @option{-Wabi} will warn only if
|
|
there is a check added later in a release series for an ABI issue
|
|
discovered since the initial release. @option{-Wabi} will warn about
|
|
more things if an older ABI version is selected (with
|
|
@option{-fabi-version=@var{n}}).
|
|
|
|
@option{-Wabi} can also be used with an explicit version number to
|
|
warn about compatibility with a particular @option{-fabi-version}
|
|
level, e.g. @option{-Wabi=2} to warn about changes relative to
|
|
@option{-fabi-version=2}.
|
|
|
|
If an explicit version number is provided and
|
|
@option{-fabi-compat-version} is not specified, the version number
|
|
from this option is used for compatibility aliases. If no explicit
|
|
version number is provided with this option, but
|
|
@option{-fabi-compat-version} is specified, that version number is
|
|
used for ABI warnings.
|
|
|
|
Although an effort has been made to warn about
|
|
all such cases, there are probably some cases that are not warned about,
|
|
even though G++ is generating incompatible code. There may also be
|
|
cases where warnings are emitted even though the code that is generated
|
|
is compatible.
|
|
|
|
You should rewrite your code to avoid these warnings if you are
|
|
concerned about the fact that code generated by G++ may not be binary
|
|
compatible with code generated by other compilers.
|
|
|
|
Known incompatibilities in @option{-fabi-version=2} (which was the
|
|
default from GCC 3.4 to 4.9) include:
|
|
|
|
@itemize @bullet
|
|
|
|
@item
|
|
A template with a non-type template parameter of reference type was
|
|
mangled incorrectly:
|
|
@smallexample
|
|
extern int N;
|
|
template <int &> struct S @{@};
|
|
void n (S<N>) @{2@}
|
|
@end smallexample
|
|
|
|
This was fixed in @option{-fabi-version=3}.
|
|
|
|
@item
|
|
SIMD vector types declared using @code{__attribute ((vector_size))} were
|
|
mangled in a non-standard way that does not allow for overloading of
|
|
functions taking vectors of different sizes.
|
|
|
|
The mangling was changed in @option{-fabi-version=4}.
|
|
|
|
@item
|
|
@code{__attribute ((const))} and @code{noreturn} were mangled as type
|
|
qualifiers, and @code{decltype} of a plain declaration was folded away.
|
|
|
|
These mangling issues were fixed in @option{-fabi-version=5}.
|
|
|
|
@item
|
|
Scoped enumerators passed as arguments to a variadic function are
|
|
promoted like unscoped enumerators, causing @code{va_arg} to complain.
|
|
On most targets this does not actually affect the parameter passing
|
|
ABI, as there is no way to pass an argument smaller than @code{int}.
|
|
|
|
Also, the ABI changed the mangling of template argument packs,
|
|
@code{const_cast}, @code{static_cast}, prefix increment/decrement, and
|
|
a class scope function used as a template argument.
|
|
|
|
These issues were corrected in @option{-fabi-version=6}.
|
|
|
|
@item
|
|
Lambdas in default argument scope were mangled incorrectly, and the
|
|
ABI changed the mangling of @code{nullptr_t}.
|
|
|
|
These issues were corrected in @option{-fabi-version=7}.
|
|
|
|
@item
|
|
When mangling a function type with function-cv-qualifiers, the
|
|
un-qualified function type was incorrectly treated as a substitution
|
|
candidate.
|
|
|
|
This was fixed in @option{-fabi-version=8}, the default for GCC 5.1.
|
|
|
|
@item
|
|
@code{decltype(nullptr)} incorrectly had an alignment of 1, leading to
|
|
unaligned accesses. Note that this did not affect the ABI of a
|
|
function with a @code{nullptr_t} parameter, as parameters have a
|
|
minimum alignment.
|
|
|
|
This was fixed in @option{-fabi-version=9}, the default for GCC 5.2.
|
|
|
|
@item
|
|
Target-specific attributes that affect the identity of a type, such as
|
|
ia32 calling conventions on a function type (stdcall, regparm, etc.),
|
|
did not affect the mangled name, leading to name collisions when
|
|
function pointers were used as template arguments.
|
|
|
|
This was fixed in @option{-fabi-version=10}, the default for GCC 6.1.
|
|
|
|
@end itemize
|
|
|
|
It also warns about psABI-related changes. The known psABI changes at this
|
|
point include:
|
|
|
|
@itemize @bullet
|
|
|
|
@item
|
|
For SysV/x86-64, unions with @code{long double} members are
|
|
passed in memory as specified in psABI. For example:
|
|
|
|
@smallexample
|
|
union U @{
|
|
long double ld;
|
|
int i;
|
|
@};
|
|
@end smallexample
|
|
|
|
@noindent
|
|
@code{union U} is always passed in memory.
|
|
|
|
@end itemize
|
|
|
|
@item -Wabi-tag @r{(C++ and Objective-C++ only)}
|
|
@opindex Wabi-tag
|
|
@opindex -Wabi-tag
|
|
Warn when a type with an ABI tag is used in a context that does not
|
|
have that ABI tag. See @ref{C++ Attributes} for more information
|
|
about ABI tags.
|
|
|
|
@item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)}
|
|
@opindex Wctor-dtor-privacy
|
|
@opindex Wno-ctor-dtor-privacy
|
|
Warn when a class seems unusable because all the constructors or
|
|
destructors in that class are private, and it has neither friends nor
|
|
public static member functions. Also warn if there are no non-private
|
|
methods, and there's at least one private member function that isn't
|
|
a constructor or destructor.
|
|
|
|
@item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)}
|
|
@opindex Wdelete-non-virtual-dtor
|
|
@opindex Wno-delete-non-virtual-dtor
|
|
Warn when @code{delete} is used to destroy an instance of a class that
|
|
has virtual functions and non-virtual destructor. It is unsafe to delete
|
|
an instance of a derived class through a pointer to a base class if the
|
|
base class does not have a virtual destructor. This warning is enabled
|
|
by @option{-Wall}.
|
|
|
|
@item -Wliteral-suffix @r{(C++ and Objective-C++ only)}
|
|
@opindex Wliteral-suffix
|
|
@opindex Wno-literal-suffix
|
|
Warn when a string or character literal is followed by a ud-suffix which does
|
|
not begin with an underscore. As a conforming extension, GCC treats such
|
|
suffixes as separate preprocessing tokens in order to maintain backwards
|
|
compatibility with code that uses formatting macros from @code{<inttypes.h>}.
|
|
For example:
|
|
|
|
@smallexample
|
|
#define __STDC_FORMAT_MACROS
|
|
#include <inttypes.h>
|
|
#include <stdio.h>
|
|
|
|
int main() @{
|
|
int64_t i64 = 123;
|
|
printf("My int64: %" PRId64"\n", i64);
|
|
@}
|
|
@end smallexample
|
|
|
|
In this case, @code{PRId64} is treated as a separate preprocessing token.
|
|
|
|
This warning is enabled by default.
|
|
|
|
@item -Wlto-type-mismatch
|
|
@opindex Wlto-type-mismatch
|
|
@opindex Wno-lto-type-mismatch
|
|
|
|
During the link-time optimization warn about type mismatches in
|
|
global declarations from different compilation units.
|
|
Requires @option{-flto} to be enabled. Enabled by default.
|
|
|
|
@item -Wnarrowing @r{(C++ and Objective-C++ only)}
|
|
@opindex Wnarrowing
|
|
@opindex Wno-narrowing
|
|
With @option{-std=gnu++98} or @option{-std=c++98}, warn when a narrowing
|
|
conversion prohibited by C++11 occurs within
|
|
@samp{@{ @}}, e.g.
|
|
|
|
@smallexample
|
|
int i = @{ 2.2 @}; // error: narrowing from double to int
|
|
@end smallexample
|
|
|
|
This flag is included in @option{-Wall} and @option{-Wc++11-compat}.
|
|
|
|
When a later standard is in effect, e.g. when using @option{-std=c++11},
|
|
narrowing conversions are diagnosed by default, as required by the standard.
|
|
A narrowing conversion from a constant produces an error,
|
|
and a narrowing conversion from a non-constant produces a warning,
|
|
but @option{-Wno-narrowing} suppresses the diagnostic.
|
|
Note that this does not affect the meaning of well-formed code;
|
|
narrowing conversions are still considered ill-formed in SFINAE contexts.
|
|
|
|
@item -Wnoexcept @r{(C++ and Objective-C++ only)}
|
|
@opindex Wnoexcept
|
|
@opindex Wno-noexcept
|
|
Warn when a noexcept-expression evaluates to false because of a call
|
|
to a function that does not have a non-throwing exception
|
|
specification (i.e. @code{throw()} or @code{noexcept}) but is known by
|
|
the compiler to never throw an exception.
|
|
|
|
@item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)}
|
|
@opindex Wnon-virtual-dtor
|
|
@opindex Wno-non-virtual-dtor
|
|
Warn when a class has virtual functions and an accessible non-virtual
|
|
destructor itself or in an accessible polymorphic base class, in which
|
|
case it is possible but unsafe to delete an instance of a derived
|
|
class through a pointer to the class itself or base class. This
|
|
warning is automatically enabled if @option{-Weffc++} is specified.
|
|
|
|
@item -Wregister @r{(C++ and Objective-C++ only)}
|
|
@opindex Wregister
|
|
@opindex Wno-register
|
|
Warn on uses of the @code{register} storage class specifier, except
|
|
when it is part of the GNU @ref{Explicit Register Variables} extension.
|
|
The use of the @code{register} keyword as storage class specifier has
|
|
been deprecated in C++11 and removed in C++17.
|
|
Enabled by default with @option{-std=c++1z}.
|
|
|
|
@item -Wreorder @r{(C++ and Objective-C++ only)}
|
|
@opindex Wreorder
|
|
@opindex Wno-reorder
|
|
@cindex reordering, warning
|
|
@cindex warning for reordering of member initializers
|
|
Warn when the order of member initializers given in the code does not
|
|
match the order in which they must be executed. For instance:
|
|
|
|
@smallexample
|
|
struct A @{
|
|
int i;
|
|
int j;
|
|
A(): j (0), i (1) @{ @}
|
|
@};
|
|
@end smallexample
|
|
|
|
@noindent
|
|
The compiler rearranges the member initializers for @code{i}
|
|
and @code{j} to match the declaration order of the members, emitting
|
|
a warning to that effect. This warning is enabled by @option{-Wall}.
|
|
|
|
@item -fext-numeric-literals @r{(C++ and Objective-C++ only)}
|
|
@opindex fext-numeric-literals
|
|
@opindex fno-ext-numeric-literals
|
|
Accept imaginary, fixed-point, or machine-defined
|
|
literal number suffixes as GNU extensions.
|
|
When this option is turned off these suffixes are treated
|
|
as C++11 user-defined literal numeric suffixes.
|
|
This is on by default for all pre-C++11 dialects and all GNU dialects:
|
|
@option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11},
|
|
@option{-std=gnu++14}.
|
|
This option is off by default
|
|
for ISO C++11 onwards (@option{-std=c++11}, ...).
|
|
@end table
|
|
|
|
The following @option{-W@dots{}} options are not affected by @option{-Wall}.
|
|
|
|
@table @gcctabopt
|
|
@item -Weffc++ @r{(C++ and Objective-C++ only)}
|
|
@opindex Weffc++
|
|
@opindex Wno-effc++
|
|
Warn about violations of the following style guidelines from Scott Meyers'
|
|
@cite{Effective C++} series of books:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
Define a copy constructor and an assignment operator for classes
|
|
with dynamically-allocated memory.
|
|
|
|
@item
|
|
Prefer initialization to assignment in constructors.
|
|
|
|
@item
|
|
Have @code{operator=} return a reference to @code{*this}.
|
|
|
|
@item
|
|
Don't try to return a reference when you must return an object.
|
|
|
|
@item
|
|
Distinguish between prefix and postfix forms of increment and
|
|
decrement operators.
|
|
|
|
@item
|
|
Never overload @code{&&}, @code{||}, or @code{,}.
|
|
|
|
@end itemize
|
|
|
|
This option also enables @option{-Wnon-virtual-dtor}, which is also
|
|
one of the effective C++ recommendations. However, the check is
|
|
extended to warn about the lack of virtual destructor in accessible
|
|
non-polymorphic bases classes too.
|
|
|
|
When selecting this option, be aware that the standard library
|
|
headers do not obey all of these guidelines; use @samp{grep -v}
|
|
to filter out those warnings.
|
|
|
|
@item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)}
|
|
@opindex Wstrict-null-sentinel
|
|
@opindex Wno-strict-null-sentinel
|
|
Warn about the use of an uncasted @code{NULL} as sentinel. When
|
|
compiling only with GCC this is a valid sentinel, as @code{NULL} is defined
|
|
to @code{__null}. Although it is a null pointer constant rather than a
|
|
null pointer, it is guaranteed to be of the same size as a pointer.
|
|
But this use is not portable across different compilers.
|
|
|
|
@item -Wno-non-template-friend @r{(C++ and Objective-C++ only)}
|
|
@opindex Wno-non-template-friend
|
|
@opindex Wnon-template-friend
|
|
Disable warnings when non-templatized friend functions are declared
|
|
within a template. Since the advent of explicit template specification
|
|
support in G++, if the name of the friend is an unqualified-id (i.e.,
|
|
@samp{friend foo(int)}), the C++ language specification demands that the
|
|
friend declare or define an ordinary, nontemplate function. (Section
|
|
14.5.3). Before G++ implemented explicit specification, unqualified-ids
|
|
could be interpreted as a particular specialization of a templatized
|
|
function. Because this non-conforming behavior is no longer the default
|
|
behavior for G++, @option{-Wnon-template-friend} allows the compiler to
|
|
check existing code for potential trouble spots and is on by default.
|
|
This new compiler behavior can be turned off with
|
|
@option{-Wno-non-template-friend}, which keeps the conformant compiler code
|
|
but disables the helpful warning.
|
|
|
|
@item -Wold-style-cast @r{(C++ and Objective-C++ only)}
|
|
@opindex Wold-style-cast
|
|
@opindex Wno-old-style-cast
|
|
Warn if an old-style (C-style) cast to a non-void type is used within
|
|
a C++ program. The new-style casts (@code{dynamic_cast},
|
|
@code{static_cast}, @code{reinterpret_cast}, and @code{const_cast}) are
|
|
less vulnerable to unintended effects and much easier to search for.
|
|
|
|
@item -Woverloaded-virtual @r{(C++ and Objective-C++ only)}
|
|
@opindex Woverloaded-virtual
|
|
@opindex Wno-overloaded-virtual
|
|
@cindex overloaded virtual function, warning
|
|
@cindex warning for overloaded virtual function
|
|
Warn when a function declaration hides virtual functions from a
|
|
base class. For example, in:
|
|
|
|
@smallexample
|
|
struct A @{
|
|
virtual void f();
|
|
@};
|
|
|
|
struct B: public A @{
|
|
void f(int);
|
|
@};
|
|
@end smallexample
|
|
|
|
the @code{A} class version of @code{f} is hidden in @code{B}, and code
|
|
like:
|
|
|
|
@smallexample
|
|
B* b;
|
|
b->f();
|
|
@end smallexample
|
|
|
|
@noindent
|
|
fails to compile.
|
|
|
|
@item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)}
|
|
@opindex Wno-pmf-conversions
|
|
@opindex Wpmf-conversions
|
|
Disable the diagnostic for converting a bound pointer to member function
|
|
to a plain pointer.
|
|
|
|
@item -Wsign-promo @r{(C++ and Objective-C++ only)}
|
|
@opindex Wsign-promo
|
|
@opindex Wno-sign-promo
|
|
Warn when overload resolution chooses a promotion from unsigned or
|
|
enumerated type to a signed type, over a conversion to an unsigned type of
|
|
the same size. Previous versions of G++ tried to preserve
|
|
unsignedness, but the standard mandates the current behavior.
|
|
|
|
@item -Wtemplates @r{(C++ and Objective-C++ only)}
|
|
@opindex Wtemplates
|
|
Warn when a primary template declaration is encountered. Some coding
|
|
rules disallow templates, and this may be used to enforce that rule.
|
|
The warning is inactive inside a system header file, such as the STL, so
|
|
one can still use the STL. One may also instantiate or specialize
|
|
templates.
|
|
|
|
@item -Wmultiple-inheritance @r{(C++ and Objective-C++ only)}
|
|
@opindex Wmultiple-inheritance
|
|
Warn when a class is defined with multiple direct base classes. Some
|
|
coding rules disallow multiple inheritance, and this may be used to
|
|
enforce that rule. The warning is inactive inside a system header file,
|
|
such as the STL, so one can still use the STL. One may also define
|
|
classes that indirectly use multiple inheritance.
|
|
|
|
@item -Wvirtual-inheritance
|
|
@opindex Wvirtual-inheritance
|
|
Warn when a class is defined with a virtual direct base classe. Some
|
|
coding rules disallow multiple inheritance, and this may be used to
|
|
enforce that rule. The warning is inactive inside a system header file,
|
|
such as the STL, so one can still use the STL. One may also define
|
|
classes that indirectly use virtual inheritance.
|
|
|
|
@item -Wnamespaces
|
|
@opindex Wnamespaces
|
|
Warn when a namespace definition is opened. Some coding rules disallow
|
|
namespaces, and this may be used to enforce that rule. The warning is
|
|
inactive inside a system header file, such as the STL, so one can still
|
|
use the STL. One may also use using directives and qualified names.
|
|
|
|
@item -Wno-terminate @r{(C++ and Objective-C++ only)}
|
|
@opindex Wterminate
|
|
@opindex Wno-terminate
|
|
Disable the warning about a throw-expression that will immediately
|
|
result in a call to @code{terminate}.
|
|
@end table
|
|
|
|
@node Objective-C and Objective-C++ Dialect Options
|
|
@section Options Controlling Objective-C and Objective-C++ Dialects
|
|
|
|
@cindex compiler options, Objective-C and Objective-C++
|
|
@cindex Objective-C and Objective-C++ options, command-line
|
|
@cindex options, Objective-C and Objective-C++
|
|
(NOTE: This manual does not describe the Objective-C and Objective-C++
|
|
languages themselves. @xref{Standards,,Language Standards
|
|
Supported by GCC}, for references.)
|
|
|
|
This section describes the command-line options that are only meaningful
|
|
for Objective-C and Objective-C++ programs. You can also use most of
|
|
the language-independent GNU compiler options.
|
|
For example, you might compile a file @file{some_class.m} like this:
|
|
|
|
@smallexample
|
|
gcc -g -fgnu-runtime -O -c some_class.m
|
|
@end smallexample
|
|
|
|
@noindent
|
|
In this example, @option{-fgnu-runtime} is an option meant only for
|
|
Objective-C and Objective-C++ programs; you can use the other options with
|
|
any language supported by GCC@.
|
|
|
|
Note that since Objective-C is an extension of the C language, Objective-C
|
|
compilations may also use options specific to the C front-end (e.g.,
|
|
@option{-Wtraditional}). Similarly, Objective-C++ compilations may use
|
|
C++-specific options (e.g., @option{-Wabi}).
|
|
|
|
Here is a list of options that are @emph{only} for compiling Objective-C
|
|
and Objective-C++ programs:
|
|
|
|
@table @gcctabopt
|
|
@item -fconstant-string-class=@var{class-name}
|
|
@opindex fconstant-string-class
|
|
Use @var{class-name} as the name of the class to instantiate for each
|
|
literal string specified with the syntax @code{@@"@dots{}"}. The default
|
|
class name is @code{NXConstantString} if the GNU runtime is being used, and
|
|
@code{NSConstantString} if the NeXT runtime is being used (see below). The
|
|
@option{-fconstant-cfstrings} option, if also present, overrides the
|
|
@option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals
|
|
to be laid out as constant CoreFoundation strings.
|
|
|
|
@item -fgnu-runtime
|
|
@opindex fgnu-runtime
|
|
Generate object code compatible with the standard GNU Objective-C
|
|
runtime. This is the default for most types of systems.
|
|
|
|
@item -fnext-runtime
|
|
@opindex fnext-runtime
|
|
Generate output compatible with the NeXT runtime. This is the default
|
|
for NeXT-based systems, including Darwin and Mac OS X@. The macro
|
|
@code{__NEXT_RUNTIME__} is predefined if (and only if) this option is
|
|
used.
|
|
|
|
@item -fno-nil-receivers
|
|
@opindex fno-nil-receivers
|
|
Assume that all Objective-C message dispatches (@code{[receiver
|
|
message:arg]}) in this translation unit ensure that the receiver is
|
|
not @code{nil}. This allows for more efficient entry points in the
|
|
runtime to be used. This option is only available in conjunction with
|
|
the NeXT runtime and ABI version 0 or 1.
|
|
|
|
@item -fobjc-abi-version=@var{n}
|
|
@opindex fobjc-abi-version
|
|
Use version @var{n} of the Objective-C ABI for the selected runtime.
|
|
This option is currently supported only for the NeXT runtime. In that
|
|
case, Version 0 is the traditional (32-bit) ABI without support for
|
|
properties and other Objective-C 2.0 additions. Version 1 is the
|
|
traditional (32-bit) ABI with support for properties and other
|
|
Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If
|
|
nothing is specified, the default is Version 0 on 32-bit target
|
|
machines, and Version 2 on 64-bit target machines.
|
|
|
|
@item -fobjc-call-cxx-cdtors
|
|
@opindex fobjc-call-cxx-cdtors
|
|
For each Objective-C class, check if any of its instance variables is a
|
|
C++ object with a non-trivial default constructor. If so, synthesize a
|
|
special @code{- (id) .cxx_construct} instance method which runs
|
|
non-trivial default constructors on any such instance variables, in order,
|
|
and then return @code{self}. Similarly, check if any instance variable
|
|
is a C++ object with a non-trivial destructor, and if so, synthesize a
|
|
special @code{- (void) .cxx_destruct} method which runs
|
|
all such default destructors, in reverse order.
|
|
|
|
The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct}
|
|
methods thusly generated only operate on instance variables
|
|
declared in the current Objective-C class, and not those inherited
|
|
from superclasses. It is the responsibility of the Objective-C
|
|
runtime to invoke all such methods in an object's inheritance
|
|
hierarchy. The @code{- (id) .cxx_construct} methods are invoked
|
|
by the runtime immediately after a new object instance is allocated;
|
|
the @code{- (void) .cxx_destruct} methods are invoked immediately
|
|
before the runtime deallocates an object instance.
|
|
|
|
As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has
|
|
support for invoking the @code{- (id) .cxx_construct} and
|
|
@code{- (void) .cxx_destruct} methods.
|
|
|
|
@item -fobjc-direct-dispatch
|
|
@opindex fobjc-direct-dispatch
|
|
Allow fast jumps to the message dispatcher. On Darwin this is
|
|
accomplished via the comm page.
|
|
|
|
@item -fobjc-exceptions
|
|
@opindex fobjc-exceptions
|
|
Enable syntactic support for structured exception handling in
|
|
Objective-C, similar to what is offered by C++. This option
|
|
is required to use the Objective-C keywords @code{@@try},
|
|
@code{@@throw}, @code{@@catch}, @code{@@finally} and
|
|
@code{@@synchronized}. This option is available with both the GNU
|
|
runtime and the NeXT runtime (but not available in conjunction with
|
|
the NeXT runtime on Mac OS X 10.2 and earlier).
|
|
|
|
@item -fobjc-gc
|
|
@opindex fobjc-gc
|
|
Enable garbage collection (GC) in Objective-C and Objective-C++
|
|
programs. This option is only available with the NeXT runtime; the
|
|
GNU runtime has a different garbage collection implementation that
|
|
does not require special compiler flags.
|
|
|
|
@item -fobjc-nilcheck
|
|
@opindex fobjc-nilcheck
|
|
For the NeXT runtime with version 2 of the ABI, check for a nil
|
|
receiver in method invocations before doing the actual method call.
|
|
This is the default and can be disabled using
|
|
@option{-fno-objc-nilcheck}. Class methods and super calls are never
|
|
checked for nil in this way no matter what this flag is set to.
|
|
Currently this flag does nothing when the GNU runtime, or an older
|
|
version of the NeXT runtime ABI, is used.
|
|
|
|
@item -fobjc-std=objc1
|
|
@opindex fobjc-std
|
|
Conform to the language syntax of Objective-C 1.0, the language
|
|
recognized by GCC 4.0. This only affects the Objective-C additions to
|
|
the C/C++ language; it does not affect conformance to C/C++ standards,
|
|
which is controlled by the separate C/C++ dialect option flags. When
|
|
this option is used with the Objective-C or Objective-C++ compiler,
|
|
any Objective-C syntax that is not recognized by GCC 4.0 is rejected.
|
|
This is useful if you need to make sure that your Objective-C code can
|
|
be compiled with older versions of GCC@.
|
|
|
|
@item -freplace-objc-classes
|
|
@opindex freplace-objc-classes
|
|
Emit a special marker instructing @command{ld(1)} not to statically link in
|
|
the resulting object file, and allow @command{dyld(1)} to load it in at
|
|
run time instead. This is used in conjunction with the Fix-and-Continue
|
|
debugging mode, where the object file in question may be recompiled and
|
|
dynamically reloaded in the course of program execution, without the need
|
|
to restart the program itself. Currently, Fix-and-Continue functionality
|
|
is only available in conjunction with the NeXT runtime on Mac OS X 10.3
|
|
and later.
|
|
|
|
@item -fzero-link
|
|
@opindex fzero-link
|
|
When compiling for the NeXT runtime, the compiler ordinarily replaces calls
|
|
to @code{objc_getClass("@dots{}")} (when the name of the class is known at
|
|
compile time) with static class references that get initialized at load time,
|
|
which improves run-time performance. Specifying the @option{-fzero-link} flag
|
|
suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")}
|
|
to be retained. This is useful in Zero-Link debugging mode, since it allows
|
|
for individual class implementations to be modified during program execution.
|
|
The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")}
|
|
regardless of command-line options.
|
|
|
|
@item -fno-local-ivars
|
|
@opindex fno-local-ivars
|
|
@opindex flocal-ivars
|
|
By default instance variables in Objective-C can be accessed as if
|
|
they were local variables from within the methods of the class they're
|
|
declared in. This can lead to shadowing between instance variables
|
|
and other variables declared either locally inside a class method or
|
|
globally with the same name. Specifying the @option{-fno-local-ivars}
|
|
flag disables this behavior thus avoiding variable shadowing issues.
|
|
|
|
@item -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]}
|
|
@opindex fivar-visibility
|
|
Set the default instance variable visibility to the specified option
|
|
so that instance variables declared outside the scope of any access
|
|
modifier directives default to the specified visibility.
|
|
|
|
@item -gen-decls
|
|
@opindex gen-decls
|
|
Dump interface declarations for all classes seen in the source file to a
|
|
file named @file{@var{sourcename}.decl}.
|
|
|
|
@item -Wassign-intercept @r{(Objective-C and Objective-C++ only)}
|
|
@opindex Wassign-intercept
|
|
@opindex Wno-assign-intercept
|
|
Warn whenever an Objective-C assignment is being intercepted by the
|
|
garbage collector.
|
|
|
|
@item -Wno-protocol @r{(Objective-C and Objective-C++ only)}
|
|
@opindex Wno-protocol
|
|
@opindex Wprotocol
|
|
If a class is declared to implement a protocol, a warning is issued for
|
|
every method in the protocol that is not implemented by the class. The
|
|
default behavior is to issue a warning for every method not explicitly
|
|
implemented in the class, even if a method implementation is inherited
|
|
from the superclass. If you use the @option{-Wno-protocol} option, then
|
|
methods inherited from the superclass are considered to be implemented,
|
|
and no warning is issued for them.
|
|
|
|
@item -Wselector @r{(Objective-C and Objective-C++ only)}
|
|
@opindex Wselector
|
|
@opindex Wno-selector
|
|
Warn if multiple methods of different types for the same selector are
|
|
found during compilation. The check is performed on the list of methods
|
|
in the final stage of compilation. Additionally, a check is performed
|
|
for each selector appearing in a @code{@@selector(@dots{})}
|
|
expression, and a corresponding method for that selector has been found
|
|
during compilation. Because these checks scan the method table only at
|
|
the end of compilation, these warnings are not produced if the final
|
|
stage of compilation is not reached, for example because an error is
|
|
found during compilation, or because the @option{-fsyntax-only} option is
|
|
being used.
|
|
|
|
@item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)}
|
|
@opindex Wstrict-selector-match
|
|
@opindex Wno-strict-selector-match
|
|
Warn if multiple methods with differing argument and/or return types are
|
|
found for a given selector when attempting to send a message using this
|
|
selector to a receiver of type @code{id} or @code{Class}. When this flag
|
|
is off (which is the default behavior), the compiler omits such warnings
|
|
if any differences found are confined to types that share the same size
|
|
and alignment.
|
|
|
|
@item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)}
|
|
@opindex Wundeclared-selector
|
|
@opindex Wno-undeclared-selector
|
|
Warn if a @code{@@selector(@dots{})} expression referring to an
|
|
undeclared selector is found. A selector is considered undeclared if no
|
|
method with that name has been declared before the
|
|
@code{@@selector(@dots{})} expression, either explicitly in an
|
|
@code{@@interface} or @code{@@protocol} declaration, or implicitly in
|
|
an @code{@@implementation} section. This option always performs its
|
|
checks as soon as a @code{@@selector(@dots{})} expression is found,
|
|
while @option{-Wselector} only performs its checks in the final stage of
|
|
compilation. This also enforces the coding style convention
|
|
that methods and selectors must be declared before being used.
|
|
|
|
@item -print-objc-runtime-info
|
|
@opindex print-objc-runtime-info
|
|
Generate C header describing the largest structure that is passed by
|
|
value, if any.
|
|
|
|
@end table
|
|
|
|
@node Diagnostic Message Formatting Options
|
|
@section Options to Control Diagnostic Messages Formatting
|
|
@cindex options to control diagnostics formatting
|
|
@cindex diagnostic messages
|
|
@cindex message formatting
|
|
|
|
Traditionally, diagnostic messages have been formatted irrespective of
|
|
the output device's aspect (e.g.@: its width, @dots{}). You can use the
|
|
options described below
|
|
to control the formatting algorithm for diagnostic messages,
|
|
e.g.@: how many characters per line, how often source location
|
|
information should be reported. Note that some language front ends may not
|
|
honor these options.
|
|
|
|
@table @gcctabopt
|
|
@item -fmessage-length=@var{n}
|
|
@opindex fmessage-length
|
|
Try to format error messages so that they fit on lines of about
|
|
@var{n} characters. If @var{n} is zero, then no line-wrapping is
|
|
done; each error message appears on a single line. This is the
|
|
default for all front ends.
|
|
|
|
@item -fdiagnostics-show-location=once
|
|
@opindex fdiagnostics-show-location
|
|
Only meaningful in line-wrapping mode. Instructs the diagnostic messages
|
|
reporter to emit source location information @emph{once}; that is, in
|
|
case the message is too long to fit on a single physical line and has to
|
|
be wrapped, the source location won't be emitted (as prefix) again,
|
|
over and over, in subsequent continuation lines. This is the default
|
|
behavior.
|
|
|
|
@item -fdiagnostics-show-location=every-line
|
|
Only meaningful in line-wrapping mode. Instructs the diagnostic
|
|
messages reporter to emit the same source location information (as
|
|
prefix) for physical lines that result from the process of breaking
|
|
a message which is too long to fit on a single line.
|
|
|
|
@item -fdiagnostics-color[=@var{WHEN}]
|
|
@itemx -fno-diagnostics-color
|
|
@opindex fdiagnostics-color
|
|
@cindex highlight, color
|
|
@vindex GCC_COLORS @r{environment variable}
|
|
Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always},
|
|
or @samp{auto}. The default depends on how the compiler has been configured,
|
|
it can be any of the above @var{WHEN} options or also @samp{never}
|
|
if @env{GCC_COLORS} environment variable isn't present in the environment,
|
|
and @samp{auto} otherwise.
|
|
@samp{auto} means to use color only when the standard error is a terminal.
|
|
The forms @option{-fdiagnostics-color} and @option{-fno-diagnostics-color} are
|
|
aliases for @option{-fdiagnostics-color=always} and
|
|
@option{-fdiagnostics-color=never}, respectively.
|
|
|
|
The colors are defined by the environment variable @env{GCC_COLORS}.
|
|
Its value is a colon-separated list of capabilities and Select Graphic
|
|
Rendition (SGR) substrings. SGR commands are interpreted by the
|
|
terminal or terminal emulator. (See the section in the documentation
|
|
of your text terminal for permitted values and their meanings as
|
|
character attributes.) These substring values are integers in decimal
|
|
representation and can be concatenated with semicolons.
|
|
Common values to concatenate include
|
|
@samp{1} for bold,
|
|
@samp{4} for underline,
|
|
@samp{5} for blink,
|
|
@samp{7} for inverse,
|
|
@samp{39} for default foreground color,
|
|
@samp{30} to @samp{37} for foreground colors,
|
|
@samp{90} to @samp{97} for 16-color mode foreground colors,
|
|
@samp{38;5;0} to @samp{38;5;255}
|
|
for 88-color and 256-color modes foreground colors,
|
|
@samp{49} for default background color,
|
|
@samp{40} to @samp{47} for background colors,
|
|
@samp{100} to @samp{107} for 16-color mode background colors,
|
|
and @samp{48;5;0} to @samp{48;5;255}
|
|
for 88-color and 256-color modes background colors.
|
|
|
|
The default @env{GCC_COLORS} is
|
|
@smallexample
|
|
error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
|
|
quote=01:fixit-insert=32:fixit-delete=31:\
|
|
diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32
|
|
@end smallexample
|
|
@noindent
|
|
where @samp{01;31} is bold red, @samp{01;35} is bold magenta,
|
|
@samp{01;36} is bold cyan, @samp{32} is green, @samp{34} is blue,
|
|
@samp{01} is bold, and @samp{31} is red.
|
|
Setting @env{GCC_COLORS} to the empty string disables colors.
|
|
Supported capabilities are as follows.
|
|
|
|
@table @code
|
|
@item error=
|
|
@vindex error GCC_COLORS @r{capability}
|
|
SGR substring for error: markers.
|
|
|
|
@item warning=
|
|
@vindex warning GCC_COLORS @r{capability}
|
|
SGR substring for warning: markers.
|
|
|
|
@item note=
|
|
@vindex note GCC_COLORS @r{capability}
|
|
SGR substring for note: markers.
|
|
|
|
@item range1=
|
|
@vindex range1 GCC_COLORS @r{capability}
|
|
SGR substring for first additional range.
|
|
|
|
@item range2=
|
|
@vindex range2 GCC_COLORS @r{capability}
|
|
SGR substring for second additional range.
|
|
|
|
@item locus=
|
|
@vindex locus GCC_COLORS @r{capability}
|
|
SGR substring for location information, @samp{file:line} or
|
|
@samp{file:line:column} etc.
|
|
|
|
@item quote=
|
|
@vindex quote GCC_COLORS @r{capability}
|
|
SGR substring for information printed within quotes.
|
|
|
|
@item fixit-insert=
|
|
@vindex fixit-insert GCC_COLORS @r{capability}
|
|
SGR substring for fix-it hints suggesting text to
|
|
be inserted or replaced.
|
|
|
|
@item fixit-delete=
|
|
@vindex fixit-delete GCC_COLORS @r{capability}
|
|
SGR substring for fix-it hints suggesting text to
|
|
be deleted.
|
|
|
|
@item diff-filename=
|
|
@vindex diff-filename GCC_COLORS @r{capability}
|
|
SGR substring for filename headers within generated patches.
|
|
|
|
@item diff-hunk=
|
|
@vindex diff-hunk GCC_COLORS @r{capability}
|
|
SGR substring for the starts of hunks within generated patches.
|
|
|
|
@item diff-delete=
|
|
@vindex diff-delete GCC_COLORS @r{capability}
|
|
SGR substring for deleted lines within generated patches.
|
|
|
|
@item diff-insert=
|
|
@vindex diff-insert GCC_COLORS @r{capability}
|
|
SGR substring for inserted lines within generated patches.
|
|
@end table
|
|
|
|
@item -fno-diagnostics-show-option
|
|
@opindex fno-diagnostics-show-option
|
|
@opindex fdiagnostics-show-option
|
|
By default, each diagnostic emitted includes text indicating the
|
|
command-line option that directly controls the diagnostic (if such an
|
|
option is known to the diagnostic machinery). Specifying the
|
|
@option{-fno-diagnostics-show-option} flag suppresses that behavior.
|
|
|
|
@item -fno-diagnostics-show-caret
|
|
@opindex fno-diagnostics-show-caret
|
|
@opindex fdiagnostics-show-caret
|
|
By default, each diagnostic emitted includes the original source line
|
|
and a caret @samp{^} indicating the column. This option suppresses this
|
|
information. The source line is truncated to @var{n} characters, if
|
|
the @option{-fmessage-length=n} option is given. When the output is done
|
|
to the terminal, the width is limited to the width given by the
|
|
@env{COLUMNS} environment variable or, if not set, to the terminal width.
|
|
|
|
@item -fdiagnostics-parseable-fixits
|
|
@opindex fdiagnostics-parseable-fixits
|
|
Emit fix-it hints in a machine-parseable format, suitable for consumption
|
|
by IDEs. For each fix-it, a line will be printed after the relevant
|
|
diagnostic, starting with the string ``fix-it:''. For example:
|
|
|
|
@smallexample
|
|
fix-it:"test.c":@{45:3-45:21@}:"gtk_widget_show_all"
|
|
@end smallexample
|
|
|
|
The location is expressed as a half-open range, expressed as a count of
|
|
bytes, starting at byte 1 for the initial column. In the above example,
|
|
bytes 3 through 20 of line 45 of ``test.c'' are to be replaced with the
|
|
given string:
|
|
|
|
@smallexample
|
|
00000000011111111112222222222
|
|
12345678901234567890123456789
|
|
gtk_widget_showall (dlg);
|
|
^^^^^^^^^^^^^^^^^^
|
|
gtk_widget_show_all
|
|
@end smallexample
|
|
|
|
The filename and replacement string escape backslash as ``\\", tab as ``\t'',
|
|
newline as ``\n'', double quotes as ``\"'', non-printable characters as octal
|
|
(e.g. vertical tab as ``\013'').
|
|
|
|
An empty replacement string indicates that the given range is to be removed.
|
|
An empty range (e.g. ``45:3-45:3'') indicates that the string is to
|
|
be inserted at the given position.
|
|
|
|
@item -fdiagnostics-generate-patch
|
|
@opindex fdiagnostics-generate-patch
|
|
Print fix-it hints to stderr in unified diff format, after any diagnostics
|
|
are printed. For example:
|
|
|
|
@smallexample
|
|
--- test.c
|
|
+++ test.c
|
|
@@ -42,5 +42,5 @@
|
|
|
|
void show_cb(GtkDialog *dlg)
|
|
@{
|
|
- gtk_widget_showall(dlg);
|
|
+ gtk_widget_show_all(dlg);
|
|
@}
|
|
|
|
@end smallexample
|
|
|
|
The diff may or may not be colorized, following the same rules
|
|
as for diagnostics (see @option{-fdiagnostics-color}).
|
|
|
|
@item -fno-show-column
|
|
@opindex fno-show-column
|
|
Do not print column numbers in diagnostics. This may be necessary if
|
|
diagnostics are being scanned by a program that does not understand the
|
|
column numbers, such as @command{dejagnu}.
|
|
|
|
@end table
|
|
|
|
@node Warning Options
|
|
@section Options to Request or Suppress Warnings
|
|
@cindex options to control warnings
|
|
@cindex warning messages
|
|
@cindex messages, warning
|
|
@cindex suppressing warnings
|
|
|
|
Warnings are diagnostic messages that report constructions that
|
|
are not inherently erroneous but that are risky or suggest there
|
|
may have been an error.
|
|
|
|
The following language-independent options do not enable specific
|
|
warnings but control the kinds of diagnostics produced by GCC@.
|
|
|
|
@table @gcctabopt
|
|
@cindex syntax checking
|
|
@item -fsyntax-only
|
|
@opindex fsyntax-only
|
|
Check the code for syntax errors, but don't do anything beyond that.
|
|
|
|
@item -fmax-errors=@var{n}
|
|
@opindex fmax-errors
|
|
Limits the maximum number of error messages to @var{n}, at which point
|
|
GCC bails out rather than attempting to continue processing the source
|
|
code. If @var{n} is 0 (the default), there is no limit on the number
|
|
of error messages produced. If @option{-Wfatal-errors} is also
|
|
specified, then @option{-Wfatal-errors} takes precedence over this
|
|
option.
|
|
|
|
@item -w
|
|
@opindex w
|
|
Inhibit all warning messages.
|
|
|
|
@item -Werror
|
|
@opindex Werror
|
|
@opindex Wno-error
|
|
Make all warnings into errors.
|
|
|
|
@item -Werror=
|
|
@opindex Werror=
|
|
@opindex Wno-error=
|
|
Make the specified warning into an error. The specifier for a warning
|
|
is appended; for example @option{-Werror=switch} turns the warnings
|
|
controlled by @option{-Wswitch} into errors. This switch takes a
|
|
negative form, to be used to negate @option{-Werror} for specific
|
|
warnings; for example @option{-Wno-error=switch} makes
|
|
@option{-Wswitch} warnings not be errors, even when @option{-Werror}
|
|
is in effect.
|
|
|
|
The warning message for each controllable warning includes the
|
|
option that controls the warning. That option can then be used with
|
|
@option{-Werror=} and @option{-Wno-error=} as described above.
|
|
(Printing of the option in the warning message can be disabled using the
|
|
@option{-fno-diagnostics-show-option} flag.)
|
|
|
|
Note that specifying @option{-Werror=}@var{foo} automatically implies
|
|
@option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not
|
|
imply anything.
|
|
|
|
@item -Wfatal-errors
|
|
@opindex Wfatal-errors
|
|
@opindex Wno-fatal-errors
|
|
This option causes the compiler to abort compilation on the first error
|
|
occurred rather than trying to keep going and printing further error
|
|
messages.
|
|
|
|
@end table
|
|
|
|
You can request many specific warnings with options beginning with
|
|
@samp{-W}, for example @option{-Wimplicit} to request warnings on
|
|
implicit declarations. Each of these specific warning options also
|
|
has a negative form beginning @samp{-Wno-} to turn off warnings; for
|
|
example, @option{-Wno-implicit}. This manual lists only one of the
|
|
two forms, whichever is not the default. For further
|
|
language-specific options also refer to @ref{C++ Dialect Options} and
|
|
@ref{Objective-C and Objective-C++ Dialect Options}.
|
|
|
|
Some options, such as @option{-Wall} and @option{-Wextra}, turn on other
|
|
options, such as @option{-Wunused}, which may turn on further options,
|
|
such as @option{-Wunused-value}. The combined effect of positive and
|
|
negative forms is that more specific options have priority over less
|
|
specific ones, independently of their position in the command-line. For
|
|
options of the same specificity, the last one takes effect. Options
|
|
enabled or disabled via pragmas (@pxref{Diagnostic Pragmas}) take effect
|
|
as if they appeared at the end of the command-line.
|
|
|
|
When an unrecognized warning option is requested (e.g.,
|
|
@option{-Wunknown-warning}), GCC emits a diagnostic stating
|
|
that the option is not recognized. However, if the @option{-Wno-} form
|
|
is used, the behavior is slightly different: no diagnostic is
|
|
produced for @option{-Wno-unknown-warning} unless other diagnostics
|
|
are being produced. This allows the use of new @option{-Wno-} options
|
|
with old compilers, but if something goes wrong, the compiler
|
|
warns that an unrecognized option is present.
|
|
|
|
@table @gcctabopt
|
|
@item -Wpedantic
|
|
@itemx -pedantic
|
|
@opindex pedantic
|
|
@opindex Wpedantic
|
|
Issue all the warnings demanded by strict ISO C and ISO C++;
|
|
reject all programs that use forbidden extensions, and some other
|
|
programs that do not follow ISO C and ISO C++. For ISO C, follows the
|
|
version of the ISO C standard specified by any @option{-std} option used.
|
|
|
|
Valid ISO C and ISO C++ programs should compile properly with or without
|
|
this option (though a rare few require @option{-ansi} or a
|
|
@option{-std} option specifying the required version of ISO C)@. However,
|
|
without this option, certain GNU extensions and traditional C and C++
|
|
features are supported as well. With this option, they are rejected.
|
|
|
|
@option{-Wpedantic} does not cause warning messages for use of the
|
|
alternate keywords whose names begin and end with @samp{__}. Pedantic
|
|
warnings are also disabled in the expression that follows
|
|
@code{__extension__}. However, only system header files should use
|
|
these escape routes; application programs should avoid them.
|
|
@xref{Alternate Keywords}.
|
|
|
|
Some users try to use @option{-Wpedantic} to check programs for strict ISO
|
|
C conformance. They soon find that it does not do quite what they want:
|
|
it finds some non-ISO practices, but not all---only those for which
|
|
ISO C @emph{requires} a diagnostic, and some others for which
|
|
diagnostics have been added.
|
|
|
|
A feature to report any failure to conform to ISO C might be useful in
|
|
some instances, but would require considerable additional work and would
|
|
be quite different from @option{-Wpedantic}. We don't have plans to
|
|
support such a feature in the near future.
|
|
|
|
Where the standard specified with @option{-std} represents a GNU
|
|
extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a
|
|
corresponding @dfn{base standard}, the version of ISO C on which the GNU
|
|
extended dialect is based. Warnings from @option{-Wpedantic} are given
|
|
where they are required by the base standard. (It does not make sense
|
|
for such warnings to be given only for features not in the specified GNU
|
|
C dialect, since by definition the GNU dialects of C include all
|
|
features the compiler supports with the given option, and there would be
|
|
nothing to warn about.)
|
|
|
|
@item -pedantic-errors
|
|
@opindex pedantic-errors
|
|
Give an error whenever the @dfn{base standard} (see @option{-Wpedantic})
|
|
requires a diagnostic, in some cases where there is undefined behavior
|
|
at compile-time and in some other cases that do not prevent compilation
|
|
of programs that are valid according to the standard. This is not
|
|
equivalent to @option{-Werror=pedantic}, since there are errors enabled
|
|
by this option and not enabled by the latter and vice versa.
|
|
|
|
@item -Wall
|
|
@opindex Wall
|
|
@opindex Wno-all
|
|
This enables all the warnings about constructions that some users
|
|
consider questionable, and that are easy to avoid (or modify to
|
|
prevent the warning), even in conjunction with macros. This also
|
|
enables some language-specific warnings described in @ref{C++ Dialect
|
|
Options} and @ref{Objective-C and Objective-C++ Dialect Options}.
|
|
|
|
@option{-Wall} turns on the following warning flags:
|
|
|
|
@gccoptlist{-Waddress @gol
|
|
-Warray-bounds=1 @r{(only with} @option{-O2}@r{)} @gol
|
|
-Wbool-compare @gol
|
|
-Wbool-operation @gol
|
|
-Wc++11-compat -Wc++14-compat@gol
|
|
-Wchar-subscripts @gol
|
|
-Wcomment @gol
|
|
-Wduplicate-decl-specifier @r{(C and Objective-C only)} @gol
|
|
-Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol
|
|
-Wformat @gol
|
|
-Wint-in-bool-context @gol
|
|
-Wimplicit @r{(C and Objective-C only)} @gol
|
|
-Wimplicit-int @r{(C and Objective-C only)} @gol
|
|
-Wimplicit-function-declaration @r{(C and Objective-C only)} @gol
|
|
-Winit-self @r{(only for C++)} @gol
|
|
-Wlogical-not-parentheses @gol
|
|
-Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol
|
|
-Wmaybe-uninitialized @gol
|
|
-Wmemset-elt-size @gol
|
|
-Wmemset-transposed-args @gol
|
|
-Wmisleading-indentation @r{(only for C/C++)} @gol
|
|
-Wmissing-braces @r{(only for C/ObjC)} @gol
|
|
-Wnarrowing @r{(only for C++)} @gol
|
|
-Wnonnull @gol
|
|
-Wnonnull-compare @gol
|
|
-Wopenmp-simd @gol
|
|
-Wparentheses @gol
|
|
-Wpointer-sign @gol
|
|
-Wreorder @gol
|
|
-Wreturn-type @gol
|
|
-Wsequence-point @gol
|
|
-Wsign-compare @r{(only in C++)} @gol
|
|
-Wsizeof-pointer-memaccess @gol
|
|
-Wstrict-aliasing @gol
|
|
-Wstrict-overflow=1 @gol
|
|
-Wswitch @gol
|
|
-Wtautological-compare @gol
|
|
-Wtrigraphs @gol
|
|
-Wuninitialized @gol
|
|
-Wunknown-pragmas @gol
|
|
-Wunused-function @gol
|
|
-Wunused-label @gol
|
|
-Wunused-value @gol
|
|
-Wunused-variable @gol
|
|
-Wvolatile-register-var @gol
|
|
}
|
|
|
|
Note that some warning flags are not implied by @option{-Wall}. Some of
|
|
them warn about constructions that users generally do not consider
|
|
questionable, but which occasionally you might wish to check for;
|
|
others warn about constructions that are necessary or hard to avoid in
|
|
some cases, and there is no simple way to modify the code to suppress
|
|
the warning. Some of them are enabled by @option{-Wextra} but many of
|
|
them must be enabled individually.
|
|
|
|
@item -Wextra
|
|
@opindex W
|
|
@opindex Wextra
|
|
@opindex Wno-extra
|
|
This enables some extra warning flags that are not enabled by
|
|
@option{-Wall}. (This option used to be called @option{-W}. The older
|
|
name is still supported, but the newer name is more descriptive.)
|
|
|
|
@gccoptlist{-Wclobbered @gol
|
|
-Wempty-body @gol
|
|
-Wignored-qualifiers @gol
|
|
-Wimplicit-fallthrough=3 @gol
|
|
-Wmissing-field-initializers @gol
|
|
-Wmissing-parameter-type @r{(C only)} @gol
|
|
-Wold-style-declaration @r{(C only)} @gol
|
|
-Woverride-init @gol
|
|
-Wsign-compare @r{(C only)} @gol
|
|
-Wtype-limits @gol
|
|
-Wuninitialized @gol
|
|
-Wshift-negative-value @r{(in C++03 and in C99 and newer)} @gol
|
|
-Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
|
|
-Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol
|
|
}
|
|
|
|
The option @option{-Wextra} also prints warning messages for the
|
|
following cases:
|
|
|
|
@itemize @bullet
|
|
|
|
@item
|
|
A pointer is compared against integer zero with @code{<}, @code{<=},
|
|
@code{>}, or @code{>=}.
|
|
|
|
@item
|
|
(C++ only) An enumerator and a non-enumerator both appear in a
|
|
conditional expression.
|
|
|
|
@item
|
|
(C++ only) Ambiguous virtual bases.
|
|
|
|
@item
|
|
(C++ only) Subscripting an array that has been declared @code{register}.
|
|
|
|
@item
|
|
(C++ only) Taking the address of a variable that has been declared
|
|
@code{register}.
|
|
|
|
@item
|
|
(C++ only) A base class is not initialized in the copy constructor
|
|
of a derived class.
|
|
|
|
@end itemize
|
|
|
|
@item -Wchar-subscripts
|
|
@opindex Wchar-subscripts
|
|
@opindex Wno-char-subscripts
|
|
Warn if an array subscript has type @code{char}. This is a common cause
|
|
of error, as programmers often forget that this type is signed on some
|
|
machines.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wno-coverage-mismatch
|
|
@opindex Wno-coverage-mismatch
|
|
Warn if feedback profiles do not match when using the
|
|
@option{-fprofile-use} option.
|
|
If a source file is changed between compiling with @option{-fprofile-gen} and
|
|
with @option{-fprofile-use}, the files with the profile feedback can fail
|
|
to match the source file and GCC cannot use the profile feedback
|
|
information. By default, this warning is enabled and is treated as an
|
|
error. @option{-Wno-coverage-mismatch} can be used to disable the
|
|
warning or @option{-Wno-error=coverage-mismatch} can be used to
|
|
disable the error. Disabling the error for this warning can result in
|
|
poorly optimized code and is useful only in the
|
|
case of very minor changes such as bug fixes to an existing code-base.
|
|
Completely disabling the warning is not recommended.
|
|
|
|
@item -Wno-cpp
|
|
@r{(C, Objective-C, C++, Objective-C++ and Fortran only)}
|
|
|
|
Suppress warning messages emitted by @code{#warning} directives.
|
|
|
|
@item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)}
|
|
@opindex Wdouble-promotion
|
|
@opindex Wno-double-promotion
|
|
Give a warning when a value of type @code{float} is implicitly
|
|
promoted to @code{double}. CPUs with a 32-bit ``single-precision''
|
|
floating-point unit implement @code{float} in hardware, but emulate
|
|
@code{double} in software. On such a machine, doing computations
|
|
using @code{double} values is much more expensive because of the
|
|
overhead required for software emulation.
|
|
|
|
It is easy to accidentally do computations with @code{double} because
|
|
floating-point literals are implicitly of type @code{double}. For
|
|
example, in:
|
|
@smallexample
|
|
@group
|
|
float area(float radius)
|
|
@{
|
|
return 3.14159 * radius * radius;
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
the compiler performs the entire computation with @code{double}
|
|
because the floating-point literal is a @code{double}.
|
|
|
|
@item -Wduplicate-decl-specifier @r{(C and Objective-C only)}
|
|
@opindex Wduplicate-decl-specifier
|
|
@opindex Wno-duplicate-decl-specifier
|
|
Warn if a declaration has duplicate @code{const}, @code{volatile},
|
|
@code{restrict} or @code{_Atomic} specifier. This warning is enabled by
|
|
@option{-Wall}.
|
|
|
|
@item -Wformat
|
|
@itemx -Wformat=@var{n}
|
|
@opindex Wformat
|
|
@opindex Wno-format
|
|
@opindex ffreestanding
|
|
@opindex fno-builtin
|
|
@opindex Wformat=
|
|
Check calls to @code{printf} and @code{scanf}, etc., to make sure that
|
|
the arguments supplied have types appropriate to the format string
|
|
specified, and that the conversions specified in the format string make
|
|
sense. This includes standard functions, and others specified by format
|
|
attributes (@pxref{Function Attributes}), in the @code{printf},
|
|
@code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension,
|
|
not in the C standard) families (or other target-specific families).
|
|
Which functions are checked without format attributes having been
|
|
specified depends on the standard version selected, and such checks of
|
|
functions without the attribute specified are disabled by
|
|
@option{-ffreestanding} or @option{-fno-builtin}.
|
|
|
|
The formats are checked against the format features supported by GNU
|
|
libc version 2.2. These include all ISO C90 and C99 features, as well
|
|
as features from the Single Unix Specification and some BSD and GNU
|
|
extensions. Other library implementations may not support all these
|
|
features; GCC does not support warning about features that go beyond a
|
|
particular library's limitations. However, if @option{-Wpedantic} is used
|
|
with @option{-Wformat}, warnings are given about format features not
|
|
in the selected standard version (but not for @code{strfmon} formats,
|
|
since those are not in any version of the C standard). @xref{C Dialect
|
|
Options,,Options Controlling C Dialect}.
|
|
|
|
@table @gcctabopt
|
|
@item -Wformat=1
|
|
@itemx -Wformat
|
|
@opindex Wformat
|
|
@opindex Wformat=1
|
|
Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and
|
|
@option{-Wno-format} is equivalent to @option{-Wformat=0}. Since
|
|
@option{-Wformat} also checks for null format arguments for several
|
|
functions, @option{-Wformat} also implies @option{-Wnonnull}. Some
|
|
aspects of this level of format checking can be disabled by the
|
|
options: @option{-Wno-format-contains-nul},
|
|
@option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}.
|
|
@option{-Wformat} is enabled by @option{-Wall}.
|
|
|
|
@item -Wno-format-contains-nul
|
|
@opindex Wno-format-contains-nul
|
|
@opindex Wformat-contains-nul
|
|
If @option{-Wformat} is specified, do not warn about format strings that
|
|
contain NUL bytes.
|
|
|
|
@item -Wno-format-extra-args
|
|
@opindex Wno-format-extra-args
|
|
@opindex Wformat-extra-args
|
|
If @option{-Wformat} is specified, do not warn about excess arguments to a
|
|
@code{printf} or @code{scanf} format function. The C standard specifies
|
|
that such arguments are ignored.
|
|
|
|
Where the unused arguments lie between used arguments that are
|
|
specified with @samp{$} operand number specifications, normally
|
|
warnings are still given, since the implementation could not know what
|
|
type to pass to @code{va_arg} to skip the unused arguments. However,
|
|
in the case of @code{scanf} formats, this option suppresses the
|
|
warning if the unused arguments are all pointers, since the Single
|
|
Unix Specification says that such unused arguments are allowed.
|
|
|
|
@item -Wformat-overflow
|
|
@itemx -Wformat-overflow=@var{level}
|
|
@opindex Wformat-overflow
|
|
@opindex Wno-format-overflow
|
|
Warn about calls to formatted input/output functions such as @code{sprintf}
|
|
and @code{vsprintf} that might overflow the destination buffer. When the
|
|
exact number of bytes written by a format directive cannot be determined
|
|
at compile-time it is estimated based on heuristics that depend on the
|
|
@var{level} argument and on optimization. While enabling optimization
|
|
will in most cases improve the accuracy of the warning, it may also
|
|
result in false positives.
|
|
|
|
@table @gcctabopt
|
|
@item -Wformat-overflow
|
|
@item -Wformat-overflow=1
|
|
@opindex Wformat-overflow
|
|
@opindex Wno-format-overflow
|
|
Level @var{1} of @option{-Wformat-overflow} enabled by @option{-Wformat}
|
|
employs a conservative approach that warns only about calls that most
|
|
likely overflow the buffer. At this level, numeric arguments to format
|
|
directives with unknown values are assumed to have the value of one, and
|
|
strings of unknown length to be empty. Numeric arguments that are known
|
|
to be bounded to a subrange of their type, or string arguments whose output
|
|
is bounded either by their directive's precision or by a finite set of
|
|
string literals, are assumed to take on the value within the range that
|
|
results in the most bytes on output. For example, the call to @code{sprintf}
|
|
below is diagnosed because even with both @var{a} and @var{b} equal to zero,
|
|
the terminating NUL character (@code{'\0'}) appended by the function
|
|
to the destination buffer will be written past its end. Increasing
|
|
the size of the buffer by a single byte is sufficient to avoid the
|
|
warning, though it may not be sufficient to avoid the overflow.
|
|
|
|
@smallexample
|
|
void f (int a, int b)
|
|
@{
|
|
char buf [12];
|
|
sprintf (buf, "a = %i, b = %i\n", a, b);
|
|
@}
|
|
@end smallexample
|
|
|
|
@item -Wformat-overflow=2
|
|
Level @var{2} warns also about calls that might overflow the destination
|
|
buffer given an argument of sufficient length or magnitude. At level
|
|
@var{2}, unknown numeric arguments are assumed to have the minimum
|
|
representable value for signed types with a precision greater than 1, and
|
|
the maximum representable value otherwise. Unknown string arguments whose
|
|
length cannot be assumed to be bounded either by the directive's precision,
|
|
or by a finite set of string literals they may evaluate to, or the character
|
|
array they may point to, are assumed to be 1 character long.
|
|
|
|
At level @var{2}, the call in the example above is again diagnosed, but
|
|
this time because with @var{a} equal to a 32-bit @code{INT_MIN} the first
|
|
@code{%i} directive will write some of its digits beyond the end of
|
|
the destination buffer. To make the call safe regardless of the values
|
|
of the two variables, the size of the destination buffer must be increased
|
|
to at least 34 bytes. GCC includes the minimum size of the buffer in
|
|
an informational note following the warning.
|
|
|
|
An alternative to increasing the size of the destination buffer is to
|
|
constrain the range of formatted values. The maximum length of string
|
|
arguments can be bounded by specifying the precision in the format
|
|
directive. When numeric arguments of format directives can be assumed
|
|
to be bounded by less than the precision of their type, choosing
|
|
an appropriate length modifier to the format specifier will reduce
|
|
the required buffer size. For example, if @var{a} and @var{b} in the
|
|
example above can be assumed to be within the precision of
|
|
the @code{short int} type then using either the @code{%hi} format
|
|
directive or casting the argument to @code{short} reduces the maximum
|
|
required size of the buffer to 24 bytes.
|
|
|
|
@smallexample
|
|
void f (int a, int b)
|
|
@{
|
|
char buf [23];
|
|
sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
|
|
@}
|
|
@end smallexample
|
|
@end table
|
|
|
|
@item -Wno-format-zero-length
|
|
@opindex Wno-format-zero-length
|
|
@opindex Wformat-zero-length
|
|
If @option{-Wformat} is specified, do not warn about zero-length formats.
|
|
The C standard specifies that zero-length formats are allowed.
|
|
|
|
|
|
@item -Wformat=2
|
|
@opindex Wformat=2
|
|
Enable @option{-Wformat} plus additional format checks. Currently
|
|
equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security
|
|
-Wformat-y2k}.
|
|
|
|
@item -Wformat-nonliteral
|
|
@opindex Wformat-nonliteral
|
|
@opindex Wno-format-nonliteral
|
|
If @option{-Wformat} is specified, also warn if the format string is not a
|
|
string literal and so cannot be checked, unless the format function
|
|
takes its format arguments as a @code{va_list}.
|
|
|
|
@item -Wformat-security
|
|
@opindex Wformat-security
|
|
@opindex Wno-format-security
|
|
If @option{-Wformat} is specified, also warn about uses of format
|
|
functions that represent possible security problems. At present, this
|
|
warns about calls to @code{printf} and @code{scanf} functions where the
|
|
format string is not a string literal and there are no format arguments,
|
|
as in @code{printf (foo);}. This may be a security hole if the format
|
|
string came from untrusted input and contains @samp{%n}. (This is
|
|
currently a subset of what @option{-Wformat-nonliteral} warns about, but
|
|
in future warnings may be added to @option{-Wformat-security} that are not
|
|
included in @option{-Wformat-nonliteral}.)
|
|
|
|
@item -Wformat-signedness
|
|
@opindex Wformat-signedness
|
|
@opindex Wno-format-signedness
|
|
If @option{-Wformat} is specified, also warn if the format string
|
|
requires an unsigned argument and the argument is signed and vice versa.
|
|
|
|
@item -Wformat-truncation
|
|
@itemx -Wformat-truncation=@var{level}
|
|
@opindex Wformat-truncation
|
|
@opindex Wno-format-truncation
|
|
Warn about calls to formatted input/output functions such as @code{snprintf}
|
|
and @code{vsnprintf} that might result in output truncation. When the exact
|
|
number of bytes written by a format directive cannot be determined at
|
|
compile-time it is estimated based on heuristics that depend on
|
|
the @var{level} argument and on optimization. While enabling optimization
|
|
will in most cases improve the accuracy of the warning, it may also result
|
|
in false positives. Except as noted otherwise, the option uses the same
|
|
logic @option{-Wformat-overflow}.
|
|
|
|
@table @gcctabopt
|
|
@item -Wformat-truncation
|
|
@item -Wformat-truncation=1
|
|
@opindex Wformat-truncation
|
|
@opindex Wno-format-overflow
|
|
Level @var{1} of @option{-Wformat-truncation} enabled by @option{-Wformat}
|
|
employs a conservative approach that warns only about calls to bounded
|
|
functions whose return value is unused and that will most likely result
|
|
in output truncatation.
|
|
|
|
@item -Wformat-truncation=2
|
|
Level @var{2} warns also about calls to bounded functions whose return
|
|
value is used and that might result in truncation given an argument of
|
|
sufficient length or magnitude.
|
|
@end table
|
|
|
|
@item -Wformat-y2k
|
|
@opindex Wformat-y2k
|
|
@opindex Wno-format-y2k
|
|
If @option{-Wformat} is specified, also warn about @code{strftime}
|
|
formats that may yield only a two-digit year.
|
|
@end table
|
|
|
|
@item -Wnonnull
|
|
@opindex Wnonnull
|
|
@opindex Wno-nonnull
|
|
Warn about passing a null pointer for arguments marked as
|
|
requiring a non-null value by the @code{nonnull} function attribute.
|
|
|
|
@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It
|
|
can be disabled with the @option{-Wno-nonnull} option.
|
|
|
|
@item -Wnonnull-compare
|
|
@opindex Wnonnull-compare
|
|
@opindex Wno-nonnull-compare
|
|
Warn when comparing an argument marked with the @code{nonnull}
|
|
function attribute against null inside the function.
|
|
|
|
@option{-Wnonnull-compare} is included in @option{-Wall}. It
|
|
can be disabled with the @option{-Wno-nonnull-compare} option.
|
|
|
|
@item -Wnull-dereference
|
|
@opindex Wnull-dereference
|
|
@opindex Wno-null-dereference
|
|
Warn if the compiler detects paths that trigger erroneous or
|
|
undefined behavior due to dereferencing a null pointer. This option
|
|
is only active when @option{-fdelete-null-pointer-checks} is active,
|
|
which is enabled by optimizations in most targets. The precision of
|
|
the warnings depends on the optimization options used.
|
|
|
|
@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)}
|
|
@opindex Winit-self
|
|
@opindex Wno-init-self
|
|
Warn about uninitialized variables that are initialized with themselves.
|
|
Note this option can only be used with the @option{-Wuninitialized} option.
|
|
|
|
For example, GCC warns about @code{i} being uninitialized in the
|
|
following snippet only when @option{-Winit-self} has been specified:
|
|
@smallexample
|
|
@group
|
|
int f()
|
|
@{
|
|
int i = i;
|
|
return i;
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
This warning is enabled by @option{-Wall} in C++.
|
|
|
|
@item -Wimplicit-int @r{(C and Objective-C only)}
|
|
@opindex Wimplicit-int
|
|
@opindex Wno-implicit-int
|
|
Warn when a declaration does not specify a type.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wimplicit-function-declaration @r{(C and Objective-C only)}
|
|
@opindex Wimplicit-function-declaration
|
|
@opindex Wno-implicit-function-declaration
|
|
Give a warning whenever a function is used before being declared. In
|
|
C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is
|
|
enabled by default and it is made into an error by
|
|
@option{-pedantic-errors}. This warning is also enabled by
|
|
@option{-Wall}.
|
|
|
|
@item -Wimplicit @r{(C and Objective-C only)}
|
|
@opindex Wimplicit
|
|
@opindex Wno-implicit
|
|
Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wimplicit-fallthrough
|
|
@opindex Wimplicit-fallthrough
|
|
@opindex Wno-implicit-fallthrough
|
|
@option{-Wimplicit-fallthrough} is the same as @option{-Wimplicit-fallthrough=3}
|
|
and @option{-Wno-implicit-fallthrough} is the same as
|
|
@option{-Wimplicit-fallthrough=0}.
|
|
|
|
@item -Wimplicit-fallthrough=@var{n}
|
|
@opindex Wimplicit-fallthrough=
|
|
Warn when a switch case falls through. For example:
|
|
|
|
@smallexample
|
|
@group
|
|
switch (cond)
|
|
@{
|
|
case 1:
|
|
a = 1;
|
|
break;
|
|
case 2:
|
|
a = 2;
|
|
case 3:
|
|
a = 3;
|
|
break;
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
This warning does not warn when the last statement of a case cannot
|
|
fall through, e.g. when there is a return statement or a call to function
|
|
declared with the noreturn attribute. @option{-Wimplicit-fallthrough=}
|
|
also takes into account control flow statements, such as ifs, and only
|
|
warns when appropriate. E.g.@:
|
|
|
|
@smallexample
|
|
@group
|
|
switch (cond)
|
|
@{
|
|
case 1:
|
|
if (i > 3) @{
|
|
bar (5);
|
|
break;
|
|
@} else if (i < 1) @{
|
|
bar (0);
|
|
@} else
|
|
return;
|
|
default:
|
|
@dots{}
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
Since there are occasions where a switch case fall through is desirable,
|
|
GCC provides an attribute, @code{__attribute__ ((fallthrough))}, that is
|
|
to be used along with a null statement to suppress this warning that
|
|
would normally occur:
|
|
|
|
@smallexample
|
|
@group
|
|
switch (cond)
|
|
@{
|
|
case 1:
|
|
bar (0);
|
|
__attribute__ ((fallthrough));
|
|
default:
|
|
@dots{}
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
C++17 provides a standard way to suppress the @option{-Wimplicit-fallthrough}
|
|
warning using @code{[[fallthrough]];} instead of the GNU attribute. In C++11
|
|
or C++14 users can use @code{[[gnu::fallthrough]];}, which is a GNU extension.
|
|
Instead of the these attributes, it is also possible to add a fallthrough
|
|
comment to silence the warning. The whole body of the C or C++ style comment
|
|
should match the given regular expressions listed below. The option argument
|
|
@var{n} specifies what kind of comments are accepted:
|
|
|
|
@itemize @bullet
|
|
|
|
@item @option{-Wimplicit-fallthrough=0} disables the warning altogether.
|
|
|
|
@item @option{-Wimplicit-fallthrough=1} matches @code{.*} regular
|
|
expression, any comment is used as fallthrough comment.
|
|
|
|
@item @option{-Wimplicit-fallthrough=2} case insensitively matches
|
|
@code{.*falls?[ \t-]*thr(ough|u).*} regular expression.
|
|
|
|
@item @option{-Wimplicit-fallthrough=3} case sensitively matches one of the
|
|
following regular expressions:
|
|
|
|
@itemize @bullet
|
|
|
|
@item @code{-fallthrough}
|
|
|
|
@item @code{@@fallthrough@@}
|
|
|
|
@item @code{lint -fallthrough[ \t]*}
|
|
|
|
@item @code{[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?@*FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?}
|
|
|
|
@item @code{[ \t.!]*(Else,? |Intentional(ly)? )?@*Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?}
|
|
|
|
@item @code{[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?@*fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?}
|
|
|
|
@end itemize
|
|
|
|
@item @option{-Wimplicit-fallthrough=4} case sensitively matches one of the
|
|
following regular expressions:
|
|
|
|
@itemize @bullet
|
|
|
|
@item @code{-fallthrough}
|
|
|
|
@item @code{@@fallthrough@@}
|
|
|
|
@item @code{lint -fallthrough[ \t]*}
|
|
|
|
@item @code{[ \t]*FALLTHR(OUGH|U)[ \t]*}
|
|
|
|
@end itemize
|
|
|
|
@item @option{-Wimplicit-fallthrough=5} doesn't recognize any comments as
|
|
fallthrough comments, only attributes disable the warning.
|
|
|
|
@end itemize
|
|
|
|
The comment needs to be followed after optional whitespace and other comments
|
|
by @code{case} or @code{default} keywords or by a user label that preceeds some
|
|
@code{case} or @code{default} label.
|
|
|
|
@smallexample
|
|
@group
|
|
switch (cond)
|
|
@{
|
|
case 1:
|
|
bar (0);
|
|
/* FALLTHRU */
|
|
default:
|
|
@dots{}
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
The @option{-Wimplicit-fallthrough=3} warning is enabled by @option{-Wextra}.
|
|
|
|
@item -Wignored-qualifiers @r{(C and C++ only)}
|
|
@opindex Wignored-qualifiers
|
|
@opindex Wno-ignored-qualifiers
|
|
Warn if the return type of a function has a type qualifier
|
|
such as @code{const}. For ISO C such a type qualifier has no effect,
|
|
since the value returned by a function is not an lvalue.
|
|
For C++, the warning is only emitted for scalar types or @code{void}.
|
|
ISO C prohibits qualified @code{void} return types on function
|
|
definitions, so such return types always receive a warning
|
|
even without this option.
|
|
|
|
This warning is also enabled by @option{-Wextra}.
|
|
|
|
@item -Wignored-attributes @r{(C and C++ only)}
|
|
@opindex Wignored-attributes
|
|
@opindex Wno-ignored-attributes
|
|
Warn when an attribute is ignored. This is different from the
|
|
@option{-Wattributes} option in that it warns whenever the compiler decides
|
|
to drop an attribute, not that the attribute is either unknown, used in a
|
|
wrong place, etc. This warning is enabled by default.
|
|
|
|
@item -Wmain
|
|
@opindex Wmain
|
|
@opindex Wno-main
|
|
Warn if the type of @code{main} is suspicious. @code{main} should be
|
|
a function with external linkage, returning int, taking either zero
|
|
arguments, two, or three arguments of appropriate types. This warning
|
|
is enabled by default in C++ and is enabled by either @option{-Wall}
|
|
or @option{-Wpedantic}.
|
|
|
|
@item -Wmisleading-indentation @r{(C and C++ only)}
|
|
@opindex Wmisleading-indentation
|
|
@opindex Wno-misleading-indentation
|
|
Warn when the indentation of the code does not reflect the block structure.
|
|
Specifically, a warning is issued for @code{if}, @code{else}, @code{while}, and
|
|
@code{for} clauses with a guarded statement that does not use braces,
|
|
followed by an unguarded statement with the same indentation.
|
|
|
|
In the following example, the call to ``bar'' is misleadingly indented as
|
|
if it were guarded by the ``if'' conditional.
|
|
|
|
@smallexample
|
|
if (some_condition ())
|
|
foo ();
|
|
bar (); /* Gotcha: this is not guarded by the "if". */
|
|
@end smallexample
|
|
|
|
In the case of mixed tabs and spaces, the warning uses the
|
|
@option{-ftabstop=} option to determine if the statements line up
|
|
(defaulting to 8).
|
|
|
|
The warning is not issued for code involving multiline preprocessor logic
|
|
such as the following example.
|
|
|
|
@smallexample
|
|
if (flagA)
|
|
foo (0);
|
|
#if SOME_CONDITION_THAT_DOES_NOT_HOLD
|
|
if (flagB)
|
|
#endif
|
|
foo (1);
|
|
@end smallexample
|
|
|
|
The warning is not issued after a @code{#line} directive, since this
|
|
typically indicates autogenerated code, and no assumptions can be made
|
|
about the layout of the file that the directive references.
|
|
|
|
This warning is enabled by @option{-Wall} in C and C++.
|
|
|
|
@item -Wmissing-braces
|
|
@opindex Wmissing-braces
|
|
@opindex Wno-missing-braces
|
|
Warn if an aggregate or union initializer is not fully bracketed. In
|
|
the following example, the initializer for @code{a} is not fully
|
|
bracketed, but that for @code{b} is fully bracketed. This warning is
|
|
enabled by @option{-Wall} in C.
|
|
|
|
@smallexample
|
|
int a[2][2] = @{ 0, 1, 2, 3 @};
|
|
int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @};
|
|
@end smallexample
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)}
|
|
@opindex Wmissing-include-dirs
|
|
@opindex Wno-missing-include-dirs
|
|
Warn if a user-supplied include directory does not exist.
|
|
|
|
@item -Wparentheses
|
|
@opindex Wparentheses
|
|
@opindex Wno-parentheses
|
|
Warn if parentheses are omitted in certain contexts, such
|
|
as when there is an assignment in a context where a truth value
|
|
is expected, or when operators are nested whose precedence people
|
|
often get confused about.
|
|
|
|
Also warn if a comparison like @code{x<=y<=z} appears; this is
|
|
equivalent to @code{(x<=y ? 1 : 0) <= z}, which is a different
|
|
interpretation from that of ordinary mathematical notation.
|
|
|
|
Also warn for dangerous uses of the GNU extension to
|
|
@code{?:} with omitted middle operand. When the condition
|
|
in the @code{?}: operator is a boolean expression, the omitted value is
|
|
always 1. Often programmers expect it to be a value computed
|
|
inside the conditional expression instead.
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wsequence-point
|
|
@opindex Wsequence-point
|
|
@opindex Wno-sequence-point
|
|
Warn about code that may have undefined semantics because of violations
|
|
of sequence point rules in the C and C++ standards.
|
|
|
|
The C and C++ standards define the order in which expressions in a C/C++
|
|
program are evaluated in terms of @dfn{sequence points}, which represent
|
|
a partial ordering between the execution of parts of the program: those
|
|
executed before the sequence point, and those executed after it. These
|
|
occur after the evaluation of a full expression (one which is not part
|
|
of a larger expression), after the evaluation of the first operand of a
|
|
@code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a
|
|
function is called (but after the evaluation of its arguments and the
|
|
expression denoting the called function), and in certain other places.
|
|
Other than as expressed by the sequence point rules, the order of
|
|
evaluation of subexpressions of an expression is not specified. All
|
|
these rules describe only a partial order rather than a total order,
|
|
since, for example, if two functions are called within one expression
|
|
with no sequence point between them, the order in which the functions
|
|
are called is not specified. However, the standards committee have
|
|
ruled that function calls do not overlap.
|
|
|
|
It is not specified when between sequence points modifications to the
|
|
values of objects take effect. Programs whose behavior depends on this
|
|
have undefined behavior; the C and C++ standards specify that ``Between
|
|
the previous and next sequence point an object shall have its stored
|
|
value modified at most once by the evaluation of an expression.
|
|
Furthermore, the prior value shall be read only to determine the value
|
|
to be stored.''. If a program breaks these rules, the results on any
|
|
particular implementation are entirely unpredictable.
|
|
|
|
Examples of code with undefined behavior are @code{a = a++;}, @code{a[n]
|
|
= b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not
|
|
diagnosed by this option, and it may give an occasional false positive
|
|
result, but in general it has been found fairly effective at detecting
|
|
this sort of problem in programs.
|
|
|
|
The C++17 standard will define the order of evaluation of operands in
|
|
more cases: in particular it requires that the right-hand side of an
|
|
assignment be evaluated before the left-hand side, so the above
|
|
examples are no longer undefined. But this warning will still warn
|
|
about them, to help people avoid writing code that is undefined in C
|
|
and earlier revisions of C++.
|
|
|
|
The standard is worded confusingly, therefore there is some debate
|
|
over the precise meaning of the sequence point rules in subtle cases.
|
|
Links to discussions of the problem, including proposed formal
|
|
definitions, may be found on the GCC readings page, at
|
|
@uref{http://gcc.gnu.org/@/readings.html}.
|
|
|
|
This warning is enabled by @option{-Wall} for C and C++.
|
|
|
|
@item -Wno-return-local-addr
|
|
@opindex Wno-return-local-addr
|
|
@opindex Wreturn-local-addr
|
|
Do not warn about returning a pointer (or in C++, a reference) to a
|
|
variable that goes out of scope after the function returns.
|
|
|
|
@item -Wreturn-type
|
|
@opindex Wreturn-type
|
|
@opindex Wno-return-type
|
|
Warn whenever a function is defined with a return type that defaults
|
|
to @code{int}. Also warn about any @code{return} statement with no
|
|
return value in a function whose return type is not @code{void}
|
|
(falling off the end of the function body is considered returning
|
|
without a value).
|
|
|
|
For C only, warn about a @code{return} statement with an expression in a
|
|
function whose return type is @code{void}, unless the expression type is
|
|
also @code{void}. As a GNU extension, the latter case is accepted
|
|
without a warning unless @option{-Wpedantic} is used.
|
|
|
|
For C++, a function without return type always produces a diagnostic
|
|
message, even when @option{-Wno-return-type} is specified. The only
|
|
exceptions are @code{main} and functions defined in system headers.
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wshift-count-negative
|
|
@opindex Wshift-count-negative
|
|
@opindex Wno-shift-count-negative
|
|
Warn if shift count is negative. This warning is enabled by default.
|
|
|
|
@item -Wshift-count-overflow
|
|
@opindex Wshift-count-overflow
|
|
@opindex Wno-shift-count-overflow
|
|
Warn if shift count >= width of type. This warning is enabled by default.
|
|
|
|
@item -Wshift-negative-value
|
|
@opindex Wshift-negative-value
|
|
@opindex Wno-shift-negative-value
|
|
Warn if left shifting a negative value. This warning is enabled by
|
|
@option{-Wextra} in C99 and C++11 modes (and newer).
|
|
|
|
@item -Wshift-overflow
|
|
@itemx -Wshift-overflow=@var{n}
|
|
@opindex Wshift-overflow
|
|
@opindex Wno-shift-overflow
|
|
Warn about left shift overflows. This warning is enabled by
|
|
default in C99 and C++11 modes (and newer).
|
|
|
|
@table @gcctabopt
|
|
@item -Wshift-overflow=1
|
|
This is the warning level of @option{-Wshift-overflow} and is enabled
|
|
by default in C99 and C++11 modes (and newer). This warning level does
|
|
not warn about left-shifting 1 into the sign bit. (However, in C, such
|
|
an overflow is still rejected in contexts where an integer constant expression
|
|
is required.)
|
|
|
|
@item -Wshift-overflow=2
|
|
This warning level also warns about left-shifting 1 into the sign bit,
|
|
unless C++14 mode is active.
|
|
@end table
|
|
|
|
@item -Wswitch
|
|
@opindex Wswitch
|
|
@opindex Wno-switch
|
|
Warn whenever a @code{switch} statement has an index of enumerated type
|
|
and lacks a @code{case} for one or more of the named codes of that
|
|
enumeration. (The presence of a @code{default} label prevents this
|
|
warning.) @code{case} labels outside the enumeration range also
|
|
provoke warnings when this option is used (even if there is a
|
|
@code{default} label).
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wswitch-default
|
|
@opindex Wswitch-default
|
|
@opindex Wno-switch-default
|
|
Warn whenever a @code{switch} statement does not have a @code{default}
|
|
case.
|
|
|
|
@item -Wswitch-enum
|
|
@opindex Wswitch-enum
|
|
@opindex Wno-switch-enum
|
|
Warn whenever a @code{switch} statement has an index of enumerated type
|
|
and lacks a @code{case} for one or more of the named codes of that
|
|
enumeration. @code{case} labels outside the enumeration range also
|
|
provoke warnings when this option is used. The only difference
|
|
between @option{-Wswitch} and this option is that this option gives a
|
|
warning about an omitted enumeration code even if there is a
|
|
@code{default} label.
|
|
|
|
@item -Wswitch-bool
|
|
@opindex Wswitch-bool
|
|
@opindex Wno-switch-bool
|
|
Warn whenever a @code{switch} statement has an index of boolean type
|
|
and the case values are outside the range of a boolean type.
|
|
It is possible to suppress this warning by casting the controlling
|
|
expression to a type other than @code{bool}. For example:
|
|
@smallexample
|
|
@group
|
|
switch ((int) (a == 4))
|
|
@{
|
|
@dots{}
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
This warning is enabled by default for C and C++ programs.
|
|
|
|
@item -Wswitch-unreachable
|
|
@opindex Wswitch-unreachable
|
|
@opindex Wno-switch-unreachable
|
|
Warn whenever a @code{switch} statement contains statements between the
|
|
controlling expression and the first case label, which will never be
|
|
executed. For example:
|
|
@smallexample
|
|
@group
|
|
switch (cond)
|
|
@{
|
|
i = 15;
|
|
@dots{}
|
|
case 5:
|
|
@dots{}
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
@option{-Wswitch-unreachable} does not warn if the statement between the
|
|
controlling expression and the first case label is just a declaration:
|
|
@smallexample
|
|
@group
|
|
switch (cond)
|
|
@{
|
|
int i;
|
|
@dots{}
|
|
case 5:
|
|
i = 5;
|
|
@dots{}
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
This warning is enabled by default for C and C++ programs.
|
|
|
|
@item -Wsync-nand @r{(C and C++ only)}
|
|
@opindex Wsync-nand
|
|
@opindex Wno-sync-nand
|
|
Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch}
|
|
built-in functions are used. These functions changed semantics in GCC 4.4.
|
|
|
|
@item -Wunused-but-set-parameter
|
|
@opindex Wunused-but-set-parameter
|
|
@opindex Wno-unused-but-set-parameter
|
|
Warn whenever a function parameter is assigned to, but otherwise unused
|
|
(aside from its declaration).
|
|
|
|
To suppress this warning use the @code{unused} attribute
|
|
(@pxref{Variable Attributes}).
|
|
|
|
This warning is also enabled by @option{-Wunused} together with
|
|
@option{-Wextra}.
|
|
|
|
@item -Wunused-but-set-variable
|
|
@opindex Wunused-but-set-variable
|
|
@opindex Wno-unused-but-set-variable
|
|
Warn whenever a local variable is assigned to, but otherwise unused
|
|
(aside from its declaration).
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
To suppress this warning use the @code{unused} attribute
|
|
(@pxref{Variable Attributes}).
|
|
|
|
This warning is also enabled by @option{-Wunused}, which is enabled
|
|
by @option{-Wall}.
|
|
|
|
@item -Wunused-function
|
|
@opindex Wunused-function
|
|
@opindex Wno-unused-function
|
|
Warn whenever a static function is declared but not defined or a
|
|
non-inline static function is unused.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wunused-label
|
|
@opindex Wunused-label
|
|
@opindex Wno-unused-label
|
|
Warn whenever a label is declared but not used.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
To suppress this warning use the @code{unused} attribute
|
|
(@pxref{Variable Attributes}).
|
|
|
|
@item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)}
|
|
@opindex Wunused-local-typedefs
|
|
Warn when a typedef locally defined in a function is not used.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wunused-parameter
|
|
@opindex Wunused-parameter
|
|
@opindex Wno-unused-parameter
|
|
Warn whenever a function parameter is unused aside from its declaration.
|
|
|
|
To suppress this warning use the @code{unused} attribute
|
|
(@pxref{Variable Attributes}).
|
|
|
|
@item -Wno-unused-result
|
|
@opindex Wunused-result
|
|
@opindex Wno-unused-result
|
|
Do not warn if a caller of a function marked with attribute
|
|
@code{warn_unused_result} (@pxref{Function Attributes}) does not use
|
|
its return value. The default is @option{-Wunused-result}.
|
|
|
|
@item -Wunused-variable
|
|
@opindex Wunused-variable
|
|
@opindex Wno-unused-variable
|
|
Warn whenever a local or static variable is unused aside from its
|
|
declaration. This option implies @option{-Wunused-const-variable=1} for C,
|
|
but not for C++. This warning is enabled by @option{-Wall}.
|
|
|
|
To suppress this warning use the @code{unused} attribute
|
|
(@pxref{Variable Attributes}).
|
|
|
|
@item -Wunused-const-variable
|
|
@itemx -Wunused-const-variable=@var{n}
|
|
@opindex Wunused-const-variable
|
|
@opindex Wno-unused-const-variable
|
|
Warn whenever a constant static variable is unused aside from its declaration.
|
|
@option{-Wunused-const-variable=1} is enabled by @option{-Wunused-variable}
|
|
for C, but not for C++. In C this declares variable storage, but in C++ this
|
|
is not an error since const variables take the place of @code{#define}s.
|
|
|
|
To suppress this warning use the @code{unused} attribute
|
|
(@pxref{Variable Attributes}).
|
|
|
|
@table @gcctabopt
|
|
@item -Wunused-const-variable=1
|
|
This is the warning level that is enabled by @option{-Wunused-variable} for
|
|
C. It warns only about unused static const variables defined in the main
|
|
compilation unit, but not about static const variables declared in any
|
|
header included.
|
|
|
|
@item -Wunused-const-variable=2
|
|
This warning level also warns for unused constant static variables in
|
|
headers (excluding system headers). This is the warning level of
|
|
@option{-Wunused-const-variable} and must be explicitly requested since
|
|
in C++ this isn't an error and in C it might be harder to clean up all
|
|
headers included.
|
|
@end table
|
|
|
|
@item -Wunused-value
|
|
@opindex Wunused-value
|
|
@opindex Wno-unused-value
|
|
Warn whenever a statement computes a result that is explicitly not
|
|
used. To suppress this warning cast the unused expression to
|
|
@code{void}. This includes an expression-statement or the left-hand
|
|
side of a comma expression that contains no side effects. For example,
|
|
an expression such as @code{x[i,j]} causes a warning, while
|
|
@code{x[(void)i,j]} does not.
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wunused
|
|
@opindex Wunused
|
|
@opindex Wno-unused
|
|
All the above @option{-Wunused} options combined.
|
|
|
|
In order to get a warning about an unused function parameter, you must
|
|
either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies
|
|
@option{-Wunused}), or separately specify @option{-Wunused-parameter}.
|
|
|
|
@item -Wuninitialized
|
|
@opindex Wuninitialized
|
|
@opindex Wno-uninitialized
|
|
Warn if an automatic variable is used without first being initialized
|
|
or if a variable may be clobbered by a @code{setjmp} call. In C++,
|
|
warn if a non-static reference or non-static @code{const} member
|
|
appears in a class without constructors.
|
|
|
|
If you want to warn about code that uses the uninitialized value of the
|
|
variable in its own initializer, use the @option{-Winit-self} option.
|
|
|
|
These warnings occur for individual uninitialized or clobbered
|
|
elements of structure, union or array variables as well as for
|
|
variables that are uninitialized or clobbered as a whole. They do
|
|
not occur for variables or elements declared @code{volatile}. Because
|
|
these warnings depend on optimization, the exact variables or elements
|
|
for which there are warnings depends on the precise optimization
|
|
options and version of GCC used.
|
|
|
|
Note that there may be no warning about a variable that is used only
|
|
to compute a value that itself is never used, because such
|
|
computations may be deleted by data flow analysis before the warnings
|
|
are printed.
|
|
|
|
@item -Winvalid-memory-model
|
|
@opindex Winvalid-memory-model
|
|
@opindex Wno-invalid-memory-model
|
|
Warn for invocations of @ref{__atomic Builtins}, @ref{__sync Builtins},
|
|
and the C11 atomic generic functions with a memory consistency argument
|
|
that is either invalid for the operation or outside the range of values
|
|
of the @code{memory_order} enumeration. For example, since the
|
|
@code{__atomic_store} and @code{__atomic_store_n} built-ins are only
|
|
defined for the relaxed, release, and sequentially consistent memory
|
|
orders the following code is diagnosed:
|
|
|
|
@smallexample
|
|
void store (int *i)
|
|
@{
|
|
__atomic_store_n (i, 0, memory_order_consume);
|
|
@}
|
|
@end smallexample
|
|
|
|
@option{-Winvalid-memory-model} is enabled by default.
|
|
|
|
@item -Wmaybe-uninitialized
|
|
@opindex Wmaybe-uninitialized
|
|
@opindex Wno-maybe-uninitialized
|
|
For an automatic variable, if there exists a path from the function
|
|
entry to a use of the variable that is initialized, but there exist
|
|
some other paths for which the variable is not initialized, the compiler
|
|
emits a warning if it cannot prove the uninitialized paths are not
|
|
executed at run time. These warnings are made optional because GCC is
|
|
not smart enough to see all the reasons why the code might be correct
|
|
in spite of appearing to have an error. Here is one example of how
|
|
this can happen:
|
|
|
|
@smallexample
|
|
@group
|
|
@{
|
|
int x;
|
|
switch (y)
|
|
@{
|
|
case 1: x = 1;
|
|
break;
|
|
case 2: x = 4;
|
|
break;
|
|
case 3: x = 5;
|
|
@}
|
|
foo (x);
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
@noindent
|
|
If the value of @code{y} is always 1, 2 or 3, then @code{x} is
|
|
always initialized, but GCC doesn't know this. To suppress the
|
|
warning, you need to provide a default case with assert(0) or
|
|
similar code.
|
|
|
|
@cindex @code{longjmp} warnings
|
|
This option also warns when a non-volatile automatic variable might be
|
|
changed by a call to @code{longjmp}. These warnings as well are possible
|
|
only in optimizing compilation.
|
|
|
|
The compiler sees only the calls to @code{setjmp}. It cannot know
|
|
where @code{longjmp} will be called; in fact, a signal handler could
|
|
call it at any point in the code. As a result, you may get a warning
|
|
even when there is in fact no problem because @code{longjmp} cannot
|
|
in fact be called at the place that would cause a problem.
|
|
|
|
Some spurious warnings can be avoided if you declare all the functions
|
|
you use that never return as @code{noreturn}. @xref{Function
|
|
Attributes}.
|
|
|
|
This warning is enabled by @option{-Wall} or @option{-Wextra}.
|
|
|
|
@item -Wunknown-pragmas
|
|
@opindex Wunknown-pragmas
|
|
@opindex Wno-unknown-pragmas
|
|
@cindex warning for unknown pragmas
|
|
@cindex unknown pragmas, warning
|
|
@cindex pragmas, warning of unknown
|
|
Warn when a @code{#pragma} directive is encountered that is not understood by
|
|
GCC@. If this command-line option is used, warnings are even issued
|
|
for unknown pragmas in system header files. This is not the case if
|
|
the warnings are only enabled by the @option{-Wall} command-line option.
|
|
|
|
@item -Wno-pragmas
|
|
@opindex Wno-pragmas
|
|
@opindex Wpragmas
|
|
Do not warn about misuses of pragmas, such as incorrect parameters,
|
|
invalid syntax, or conflicts between pragmas. See also
|
|
@option{-Wunknown-pragmas}.
|
|
|
|
@item -Wstrict-aliasing
|
|
@opindex Wstrict-aliasing
|
|
@opindex Wno-strict-aliasing
|
|
This option is only active when @option{-fstrict-aliasing} is active.
|
|
It warns about code that might break the strict aliasing rules that the
|
|
compiler is using for optimization. The warning does not catch all
|
|
cases, but does attempt to catch the more common pitfalls. It is
|
|
included in @option{-Wall}.
|
|
It is equivalent to @option{-Wstrict-aliasing=3}
|
|
|
|
@item -Wstrict-aliasing=n
|
|
@opindex Wstrict-aliasing=n
|
|
This option is only active when @option{-fstrict-aliasing} is active.
|
|
It warns about code that might break the strict aliasing rules that the
|
|
compiler is using for optimization.
|
|
Higher levels correspond to higher accuracy (fewer false positives).
|
|
Higher levels also correspond to more effort, similar to the way @option{-O}
|
|
works.
|
|
@option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}.
|
|
|
|
Level 1: Most aggressive, quick, least accurate.
|
|
Possibly useful when higher levels
|
|
do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few
|
|
false negatives. However, it has many false positives.
|
|
Warns for all pointer conversions between possibly incompatible types,
|
|
even if never dereferenced. Runs in the front end only.
|
|
|
|
Level 2: Aggressive, quick, not too precise.
|
|
May still have many false positives (not as many as level 1 though),
|
|
and few false negatives (but possibly more than level 1).
|
|
Unlike level 1, it only warns when an address is taken. Warns about
|
|
incomplete types. Runs in the front end only.
|
|
|
|
Level 3 (default for @option{-Wstrict-aliasing}):
|
|
Should have very few false positives and few false
|
|
negatives. Slightly slower than levels 1 or 2 when optimization is enabled.
|
|
Takes care of the common pun+dereference pattern in the front end:
|
|
@code{*(int*)&some_float}.
|
|
If optimization is enabled, it also runs in the back end, where it deals
|
|
with multiple statement cases using flow-sensitive points-to information.
|
|
Only warns when the converted pointer is dereferenced.
|
|
Does not warn about incomplete types.
|
|
|
|
@item -Wstrict-overflow
|
|
@itemx -Wstrict-overflow=@var{n}
|
|
@opindex Wstrict-overflow
|
|
@opindex Wno-strict-overflow
|
|
This option is only active when @option{-fstrict-overflow} is active.
|
|
It warns about cases where the compiler optimizes based on the
|
|
assumption that signed overflow does not occur. Note that it does not
|
|
warn about all cases where the code might overflow: it only warns
|
|
about cases where the compiler implements some optimization. Thus
|
|
this warning depends on the optimization level.
|
|
|
|
An optimization that assumes that signed overflow does not occur is
|
|
perfectly safe if the values of the variables involved are such that
|
|
overflow never does, in fact, occur. Therefore this warning can
|
|
easily give a false positive: a warning about code that is not
|
|
actually a problem. To help focus on important issues, several
|
|
warning levels are defined. No warnings are issued for the use of
|
|
undefined signed overflow when estimating how many iterations a loop
|
|
requires, in particular when determining whether a loop will be
|
|
executed at all.
|
|
|
|
@table @gcctabopt
|
|
@item -Wstrict-overflow=1
|
|
Warn about cases that are both questionable and easy to avoid. For
|
|
example, with @option{-fstrict-overflow}, the compiler simplifies
|
|
@code{x + 1 > x} to @code{1}. This level of
|
|
@option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels
|
|
are not, and must be explicitly requested.
|
|
|
|
@item -Wstrict-overflow=2
|
|
Also warn about other cases where a comparison is simplified to a
|
|
constant. For example: @code{abs (x) >= 0}. This can only be
|
|
simplified when @option{-fstrict-overflow} is in effect, because
|
|
@code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than
|
|
zero. @option{-Wstrict-overflow} (with no level) is the same as
|
|
@option{-Wstrict-overflow=2}.
|
|
|
|
@item -Wstrict-overflow=3
|
|
Also warn about other cases where a comparison is simplified. For
|
|
example: @code{x + 1 > 1} is simplified to @code{x > 0}.
|
|
|
|
@item -Wstrict-overflow=4
|
|
Also warn about other simplifications not covered by the above cases.
|
|
For example: @code{(x * 10) / 5} is simplified to @code{x * 2}.
|
|
|
|
@item -Wstrict-overflow=5
|
|
Also warn about cases where the compiler reduces the magnitude of a
|
|
constant involved in a comparison. For example: @code{x + 2 > y} is
|
|
simplified to @code{x + 1 >= y}. This is reported only at the
|
|
highest warning level because this simplification applies to many
|
|
comparisons, so this warning level gives a very large number of
|
|
false positives.
|
|
@end table
|
|
|
|
@item -Wstringop-overflow
|
|
@itemx -Wstringop-overflow=@var{type}
|
|
@opindex Wstringop-overflow
|
|
@opindex Wno-stringop-overflow
|
|
Warn for calls to string manipulation functions such as @code{memcpy} and
|
|
@code{strcpy} that are determined to overflow the destination buffer. The
|
|
optional argument is one greater than the type of Object Size Checking to
|
|
perform to determine the size of the destination. @xref{Object Size Checking}.
|
|
The argument is meaningful only for functions that operate on character arrays
|
|
but not for raw memory functions like @code{memcpy} which always make use
|
|
of Object Size type-0. The option also warns for calls that specify a size
|
|
in excess of the largest possible object or at most @code{SIZE_MAX / 2} bytes.
|
|
The option produces the best results with optimization enabled but can detect
|
|
a small subset of simple buffer overflows even without optimization in
|
|
calls to the GCC built-in functions like @code{__builtin_memcpy} that
|
|
correspond to the standard functions. In any case, the option warns about
|
|
just a subset of buffer overflows detected by the corresponding overflow
|
|
checking built-ins. For example, the option will issue a warning for
|
|
the @code{strcpy} call below because it copies at least 5 characters
|
|
(the string @code{"blue"} including the terminating NUL) into the buffer
|
|
of size 4.
|
|
|
|
@smallexample
|
|
enum Color @{ blue, purple, yellow @};
|
|
const char* f (enum Color clr)
|
|
@{
|
|
static char buf [4];
|
|
const char *str;
|
|
switch (clr)
|
|
@{
|
|
case blue: str = "blue"; break;
|
|
case purple: str = "purple"; break;
|
|
case yellow: str = "yellow"; break;
|
|
@}
|
|
|
|
return strcpy (buf, str); // warning here
|
|
@}
|
|
@end smallexample
|
|
|
|
Option @option{-Wstringop-overflow=2} is enabled by default.
|
|
|
|
@table @gcctabopt
|
|
@item -Wstringop-overflow
|
|
@item -Wstringop-overflow=1
|
|
@opindex Wstringop-overflow
|
|
@opindex Wno-stringop-overflow
|
|
The @option{-Wstringop-overflow=1} option uses type-zero Object Size Checking
|
|
to determine the sizes of destination objects. This is the default setting
|
|
of the option. At this setting the option will not warn for writes past
|
|
the end of subobjects of larger objects accessed by pointers unless the
|
|
size of the largest surrounding object is known. When the destination may
|
|
be one of several objects it is assumed to be the largest one of them. On
|
|
Linux systems, when optimization is enabled at this setting the option warns
|
|
for the same code as when the @code{_FORTIFY_SOURCE} macro is defined to
|
|
a non-zero value.
|
|
|
|
@item -Wstringop-overflow=2
|
|
The @option{-Wstringop-overflow=2} option uses type-one Object Size Checking
|
|
to determine the sizes of destination objects. At this setting the option
|
|
will warn about overflows when writing to members of the largest complete
|
|
objects whose exact size is known. It will, however, not warn for excessive
|
|
writes to the same members of unknown objects referenced by pointers since
|
|
they may point to arrays containing unknown numbers of elements.
|
|
|
|
@item -Wstringop-overflow=3
|
|
The @option{-Wstringop-overflow=3} option uses type-two Object Size Checking
|
|
to determine the sizes of destination objects. At this setting the option
|
|
warns about overflowing the smallest object or data member. This is the
|
|
most restrictive setting of the option that may result in warnings for safe
|
|
code.
|
|
|
|
@item -Wstringop-overflow=4
|
|
The @option{-Wstringop-overflow=4} option uses type-three Object Size Checking
|
|
to determine the sizes of destination objects. At this setting the option
|
|
will warn about overflowing any data members, and when the destination is
|
|
one of several objects it uses the size of the largest of them to decide
|
|
whether to issue a warning. Similarly to @option{-Wstringop-overflow=3} this
|
|
setting of the option may result in warnings for benign code.
|
|
@end table
|
|
|
|
@item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]}
|
|
@opindex Wsuggest-attribute=
|
|
@opindex Wno-suggest-attribute=
|
|
Warn for cases where adding an attribute may be beneficial. The
|
|
attributes currently supported are listed below.
|
|
|
|
@table @gcctabopt
|
|
@item -Wsuggest-attribute=pure
|
|
@itemx -Wsuggest-attribute=const
|
|
@itemx -Wsuggest-attribute=noreturn
|
|
@opindex Wsuggest-attribute=pure
|
|
@opindex Wno-suggest-attribute=pure
|
|
@opindex Wsuggest-attribute=const
|
|
@opindex Wno-suggest-attribute=const
|
|
@opindex Wsuggest-attribute=noreturn
|
|
@opindex Wno-suggest-attribute=noreturn
|
|
|
|
Warn about functions that might be candidates for attributes
|
|
@code{pure}, @code{const} or @code{noreturn}. The compiler only warns for
|
|
functions visible in other compilation units or (in the case of @code{pure} and
|
|
@code{const}) if it cannot prove that the function returns normally. A function
|
|
returns normally if it doesn't contain an infinite loop or return abnormally
|
|
by throwing, calling @code{abort} or trapping. This analysis requires option
|
|
@option{-fipa-pure-const}, which is enabled by default at @option{-O} and
|
|
higher. Higher optimization levels improve the accuracy of the analysis.
|
|
|
|
@item -Wsuggest-attribute=format
|
|
@itemx -Wmissing-format-attribute
|
|
@opindex Wsuggest-attribute=format
|
|
@opindex Wmissing-format-attribute
|
|
@opindex Wno-suggest-attribute=format
|
|
@opindex Wno-missing-format-attribute
|
|
@opindex Wformat
|
|
@opindex Wno-format
|
|
|
|
Warn about function pointers that might be candidates for @code{format}
|
|
attributes. Note these are only possible candidates, not absolute ones.
|
|
GCC guesses that function pointers with @code{format} attributes that
|
|
are used in assignment, initialization, parameter passing or return
|
|
statements should have a corresponding @code{format} attribute in the
|
|
resulting type. I.e.@: the left-hand side of the assignment or
|
|
initialization, the type of the parameter variable, or the return type
|
|
of the containing function respectively should also have a @code{format}
|
|
attribute to avoid the warning.
|
|
|
|
GCC also warns about function definitions that might be
|
|
candidates for @code{format} attributes. Again, these are only
|
|
possible candidates. GCC guesses that @code{format} attributes
|
|
might be appropriate for any function that calls a function like
|
|
@code{vprintf} or @code{vscanf}, but this might not always be the
|
|
case, and some functions for which @code{format} attributes are
|
|
appropriate may not be detected.
|
|
@end table
|
|
|
|
@item -Wsuggest-final-types
|
|
@opindex Wno-suggest-final-types
|
|
@opindex Wsuggest-final-types
|
|
Warn about types with virtual methods where code quality would be improved
|
|
if the type were declared with the C++11 @code{final} specifier,
|
|
or, if possible,
|
|
declared in an anonymous namespace. This allows GCC to more aggressively
|
|
devirtualize the polymorphic calls. This warning is more effective with link
|
|
time optimization, where the information about the class hierarchy graph is
|
|
more complete.
|
|
|
|
@item -Wsuggest-final-methods
|
|
@opindex Wno-suggest-final-methods
|
|
@opindex Wsuggest-final-methods
|
|
Warn about virtual methods where code quality would be improved if the method
|
|
were declared with the C++11 @code{final} specifier,
|
|
or, if possible, its type were
|
|
declared in an anonymous namespace or with the @code{final} specifier.
|
|
This warning is
|
|
more effective with link time optimization, where the information about the
|
|
class hierarchy graph is more complete. It is recommended to first consider
|
|
suggestions of @option{-Wsuggest-final-types} and then rebuild with new
|
|
annotations.
|
|
|
|
@item -Wsuggest-override
|
|
Warn about overriding virtual functions that are not marked with the override
|
|
keyword.
|
|
|
|
@item -Walloc-zero
|
|
@opindex Wno-alloc-zero
|
|
@opindex Walloc-zero
|
|
Warn about calls to allocation functions decorated with attribute
|
|
@code{alloc_size} that specify zero bytes, including those to the built-in
|
|
forms of the functions @code{aligned_alloc}, @code{alloca}, @code{calloc},
|
|
@code{malloc}, and @code{realloc}. Because the behavior of these functions
|
|
when called with a zero size differs among implementations (and in the case
|
|
of @code{realloc} has been deprecated) relying on it may result in subtle
|
|
portability bugs and should be avoided.
|
|
|
|
@item -Walloc-size-larger-than=@var{n}
|
|
Warn about calls to functions decorated with attribute @code{alloc_size}
|
|
that attempt to allocate objects larger than the specified number of bytes,
|
|
or where the result of the size computation in an integer type with infinite
|
|
precision would exceed @code{SIZE_MAX / 2}. The option argument @var{n}
|
|
may end in one of the standard suffixes designating a multiple of bytes
|
|
such as @code{kB} and @code{KiB} for kilobyte and kibibyte, respectively,
|
|
@code{MB} and @code{MiB} for magabyte and mebibyte, and so on.
|
|
@xref{Function Attributes}.
|
|
|
|
@item -Walloca
|
|
@opindex Wno-alloca
|
|
@opindex Walloca
|
|
This option warns on all uses of @code{alloca} in the source.
|
|
|
|
@item -Walloca-larger-than=@var{n}
|
|
This option warns on calls to @code{alloca} that are not bounded by a
|
|
controlling predicate limiting its argument of integer type to at most
|
|
@var{n} bytes, or calls to @code{alloca} where the bound is unknown.
|
|
Arguments of non-integer types are considered unbounded even if they
|
|
appear to be constrained to the expected range.
|
|
|
|
For example, a bounded case of @code{alloca} could be:
|
|
|
|
@smallexample
|
|
void func (size_t n)
|
|
@{
|
|
void *p;
|
|
if (n <= 1000)
|
|
p = alloca (n);
|
|
else
|
|
p = malloc (n);
|
|
f (p);
|
|
@}
|
|
@end smallexample
|
|
|
|
In the above example, passing @code{-Walloca-larger-than=1000} would not
|
|
issue a warning because the call to @code{alloca} is known to be at most
|
|
1000 bytes. However, if @code{-Walloca-larger-than=500} were passed,
|
|
the compiler would emit a warning.
|
|
|
|
Unbounded uses, on the other hand, are uses of @code{alloca} with no
|
|
controlling predicate constraining its integer argument. For example:
|
|
|
|
@smallexample
|
|
void func ()
|
|
@{
|
|
void *p = alloca (n);
|
|
f (p);
|
|
@}
|
|
@end smallexample
|
|
|
|
If @code{-Walloca-larger-than=500} were passed, the above would trigger
|
|
a warning, but this time because of the lack of bounds checking.
|
|
|
|
Note, that even seemingly correct code involving signed integers could
|
|
cause a warning:
|
|
|
|
@smallexample
|
|
void func (signed int n)
|
|
@{
|
|
if (n < 500)
|
|
@{
|
|
p = alloca (n);
|
|
f (p);
|
|
@}
|
|
@}
|
|
@end smallexample
|
|
|
|
In the above example, @var{n} could be negative, causing a larger than
|
|
expected argument to be implicitly cast into the @code{alloca} call.
|
|
|
|
This option also warns when @code{alloca} is used in a loop.
|
|
|
|
This warning is not enabled by @option{-Wall}, and is only active when
|
|
@option{-ftree-vrp} is active (default for @option{-O2} and above).
|
|
|
|
See also @option{-Wvla-larger-than=@var{n}}.
|
|
|
|
@item -Warray-bounds
|
|
@itemx -Warray-bounds=@var{n}
|
|
@opindex Wno-array-bounds
|
|
@opindex Warray-bounds
|
|
This option is only active when @option{-ftree-vrp} is active
|
|
(default for @option{-O2} and above). It warns about subscripts to arrays
|
|
that are always out of bounds. This warning is enabled by @option{-Wall}.
|
|
|
|
@table @gcctabopt
|
|
@item -Warray-bounds=1
|
|
This is the warning level of @option{-Warray-bounds} and is enabled
|
|
by @option{-Wall}; higher levels are not, and must be explicitly requested.
|
|
|
|
@item -Warray-bounds=2
|
|
This warning level also warns about out of bounds access for
|
|
arrays at the end of a struct and for arrays accessed through
|
|
pointers. This warning level may give a larger number of
|
|
false positives and is deactivated by default.
|
|
@end table
|
|
|
|
@item -Wbool-compare
|
|
@opindex Wno-bool-compare
|
|
@opindex Wbool-compare
|
|
Warn about boolean expression compared with an integer value different from
|
|
@code{true}/@code{false}. For instance, the following comparison is
|
|
always false:
|
|
@smallexample
|
|
int n = 5;
|
|
@dots{}
|
|
if ((n > 1) == 2) @{ @dots{} @}
|
|
@end smallexample
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wbool-operation
|
|
@opindex Wno-bool-operation
|
|
@opindex Wbool-operation
|
|
Warn about suspicious operations on expressions of a boolean type. For
|
|
instance, bitwise negation of a boolean is very likely a bug in the program.
|
|
For C, this warning also warns about incrementing or decrementing a boolean,
|
|
which rarely makes sense. (In C++, decrementing a boolean is always invalid.
|
|
Incrementing a boolean is invalid in C++1z, and deprecated otherwise.)
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wduplicated-cond
|
|
@opindex Wno-duplicated-cond
|
|
@opindex Wduplicated-cond
|
|
Warn about duplicated conditions in an if-else-if chain. For instance,
|
|
warn for the following code:
|
|
@smallexample
|
|
if (p->q != NULL) @{ @dots{} @}
|
|
else if (p->q != NULL) @{ @dots{} @}
|
|
@end smallexample
|
|
|
|
@item -Wframe-address
|
|
@opindex Wno-frame-address
|
|
@opindex Wframe-address
|
|
Warn when the @samp{__builtin_frame_address} or @samp{__builtin_return_address}
|
|
is called with an argument greater than 0. Such calls may return indeterminate
|
|
values or crash the program. The warning is included in @option{-Wall}.
|
|
|
|
@item -Wno-discarded-qualifiers @r{(C and Objective-C only)}
|
|
@opindex Wno-discarded-qualifiers
|
|
@opindex Wdiscarded-qualifiers
|
|
Do not warn if type qualifiers on pointers are being discarded.
|
|
Typically, the compiler warns if a @code{const char *} variable is
|
|
passed to a function that takes a @code{char *} parameter. This option
|
|
can be used to suppress such a warning.
|
|
|
|
@item -Wno-discarded-array-qualifiers @r{(C and Objective-C only)}
|
|
@opindex Wno-discarded-array-qualifiers
|
|
@opindex Wdiscarded-array-qualifiers
|
|
Do not warn if type qualifiers on arrays which are pointer targets
|
|
are being discarded. Typically, the compiler warns if a
|
|
@code{const int (*)[]} variable is passed to a function that
|
|
takes a @code{int (*)[]} parameter. This option can be used to
|
|
suppress such a warning.
|
|
|
|
@item -Wno-incompatible-pointer-types @r{(C and Objective-C only)}
|
|
@opindex Wno-incompatible-pointer-types
|
|
@opindex Wincompatible-pointer-types
|
|
Do not warn when there is a conversion between pointers that have incompatible
|
|
types. This warning is for cases not covered by @option{-Wno-pointer-sign},
|
|
which warns for pointer argument passing or assignment with different
|
|
signedness.
|
|
|
|
@item -Wno-int-conversion @r{(C and Objective-C only)}
|
|
@opindex Wno-int-conversion
|
|
@opindex Wint-conversion
|
|
Do not warn about incompatible integer to pointer and pointer to integer
|
|
conversions. This warning is about implicit conversions; for explicit
|
|
conversions the warnings @option{-Wno-int-to-pointer-cast} and
|
|
@option{-Wno-pointer-to-int-cast} may be used.
|
|
|
|
@item -Wno-div-by-zero
|
|
@opindex Wno-div-by-zero
|
|
@opindex Wdiv-by-zero
|
|
Do not warn about compile-time integer division by zero. Floating-point
|
|
division by zero is not warned about, as it can be a legitimate way of
|
|
obtaining infinities and NaNs.
|
|
|
|
@item -Wsystem-headers
|
|
@opindex Wsystem-headers
|
|
@opindex Wno-system-headers
|
|
@cindex warnings from system headers
|
|
@cindex system headers, warnings from
|
|
Print warning messages for constructs found in system header files.
|
|
Warnings from system headers are normally suppressed, on the assumption
|
|
that they usually do not indicate real problems and would only make the
|
|
compiler output harder to read. Using this command-line option tells
|
|
GCC to emit warnings from system headers as if they occurred in user
|
|
code. However, note that using @option{-Wall} in conjunction with this
|
|
option does @emph{not} warn about unknown pragmas in system
|
|
headers---for that, @option{-Wunknown-pragmas} must also be used.
|
|
|
|
@item -Wtautological-compare
|
|
@opindex Wtautological-compare
|
|
@opindex Wno-tautological-compare
|
|
Warn if a self-comparison always evaluates to true or false. This
|
|
warning detects various mistakes such as:
|
|
@smallexample
|
|
int i = 1;
|
|
@dots{}
|
|
if (i > i) @{ @dots{} @}
|
|
@end smallexample
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wtrampolines
|
|
@opindex Wtrampolines
|
|
@opindex Wno-trampolines
|
|
Warn about trampolines generated for pointers to nested functions.
|
|
A trampoline is a small piece of data or code that is created at run
|
|
time on the stack when the address of a nested function is taken, and is
|
|
used to call the nested function indirectly. For some targets, it is
|
|
made up of data only and thus requires no special treatment. But, for
|
|
most targets, it is made up of code and thus requires the stack to be
|
|
made executable in order for the program to work properly.
|
|
|
|
@item -Wfloat-equal
|
|
@opindex Wfloat-equal
|
|
@opindex Wno-float-equal
|
|
Warn if floating-point values are used in equality comparisons.
|
|
|
|
The idea behind this is that sometimes it is convenient (for the
|
|
programmer) to consider floating-point values as approximations to
|
|
infinitely precise real numbers. If you are doing this, then you need
|
|
to compute (by analyzing the code, or in some other way) the maximum or
|
|
likely maximum error that the computation introduces, and allow for it
|
|
when performing comparisons (and when producing output, but that's a
|
|
different problem). In particular, instead of testing for equality, you
|
|
should check to see whether the two values have ranges that overlap; and
|
|
this is done with the relational operators, so equality comparisons are
|
|
probably mistaken.
|
|
|
|
@item -Wtraditional @r{(C and Objective-C only)}
|
|
@opindex Wtraditional
|
|
@opindex Wno-traditional
|
|
Warn about certain constructs that behave differently in traditional and
|
|
ISO C@. Also warn about ISO C constructs that have no traditional C
|
|
equivalent, and/or problematic constructs that should be avoided.
|
|
|
|
@itemize @bullet
|
|
@item
|
|
Macro parameters that appear within string literals in the macro body.
|
|
In traditional C macro replacement takes place within string literals,
|
|
but in ISO C it does not.
|
|
|
|
@item
|
|
In traditional C, some preprocessor directives did not exist.
|
|
Traditional preprocessors only considered a line to be a directive
|
|
if the @samp{#} appeared in column 1 on the line. Therefore
|
|
@option{-Wtraditional} warns about directives that traditional C
|
|
understands but ignores because the @samp{#} does not appear as the
|
|
first character on the line. It also suggests you hide directives like
|
|
@code{#pragma} not understood by traditional C by indenting them. Some
|
|
traditional implementations do not recognize @code{#elif}, so this option
|
|
suggests avoiding it altogether.
|
|
|
|
@item
|
|
A function-like macro that appears without arguments.
|
|
|
|
@item
|
|
The unary plus operator.
|
|
|
|
@item
|
|
The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point
|
|
constant suffixes. (Traditional C does support the @samp{L} suffix on integer
|
|
constants.) Note, these suffixes appear in macros defined in the system
|
|
headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}.
|
|
Use of these macros in user code might normally lead to spurious
|
|
warnings, however GCC's integrated preprocessor has enough context to
|
|
avoid warning in these cases.
|
|
|
|
@item
|
|
A function declared external in one block and then used after the end of
|
|
the block.
|
|
|
|
@item
|
|
A @code{switch} statement has an operand of type @code{long}.
|
|
|
|
@item
|
|
A non-@code{static} function declaration follows a @code{static} one.
|
|
This construct is not accepted by some traditional C compilers.
|
|
|
|
@item
|
|
The ISO type of an integer constant has a different width or
|
|
signedness from its traditional type. This warning is only issued if
|
|
the base of the constant is ten. I.e.@: hexadecimal or octal values, which
|
|
typically represent bit patterns, are not warned about.
|
|
|
|
@item
|
|
Usage of ISO string concatenation is detected.
|
|
|
|
@item
|
|
Initialization of automatic aggregates.
|
|
|
|
@item
|
|
Identifier conflicts with labels. Traditional C lacks a separate
|
|
namespace for labels.
|
|
|
|
@item
|
|
Initialization of unions. If the initializer is zero, the warning is
|
|
omitted. This is done under the assumption that the zero initializer in
|
|
user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing
|
|
initializer warnings and relies on default initialization to zero in the
|
|
traditional C case.
|
|
|
|
@item
|
|
Conversions by prototypes between fixed/floating-point values and vice
|
|
versa. The absence of these prototypes when compiling with traditional
|
|
C causes serious problems. This is a subset of the possible
|
|
conversion warnings; for the full set use @option{-Wtraditional-conversion}.
|
|
|
|
@item
|
|
Use of ISO C style function definitions. This warning intentionally is
|
|
@emph{not} issued for prototype declarations or variadic functions
|
|
because these ISO C features appear in your code when using
|
|
libiberty's traditional C compatibility macros, @code{PARAMS} and
|
|
@code{VPARAMS}. This warning is also bypassed for nested functions
|
|
because that feature is already a GCC extension and thus not relevant to
|
|
traditional C compatibility.
|
|
@end itemize
|
|
|
|
@item -Wtraditional-conversion @r{(C and Objective-C only)}
|
|
@opindex Wtraditional-conversion
|
|
@opindex Wno-traditional-conversion
|
|
Warn if a prototype causes a type conversion that is different from what
|
|
would happen to the same argument in the absence of a prototype. This
|
|
includes conversions of fixed point to floating and vice versa, and
|
|
conversions changing the width or signedness of a fixed-point argument
|
|
except when the same as the default promotion.
|
|
|
|
@item -Wdeclaration-after-statement @r{(C and Objective-C only)}
|
|
@opindex Wdeclaration-after-statement
|
|
@opindex Wno-declaration-after-statement
|
|
Warn when a declaration is found after a statement in a block. This
|
|
construct, known from C++, was introduced with ISO C99 and is by default
|
|
allowed in GCC@. It is not supported by ISO C90. @xref{Mixed Declarations}.
|
|
|
|
@item -Wshadow
|
|
@opindex Wshadow
|
|
@opindex Wno-shadow
|
|
Warn whenever a local variable or type declaration shadows another
|
|
variable, parameter, type, class member (in C++), or instance variable
|
|
(in Objective-C) or whenever a built-in function is shadowed. Note
|
|
that in C++, the compiler warns if a local variable shadows an
|
|
explicit typedef, but not if it shadows a struct/class/enum.
|
|
Same as @option{-Wshadow=global}.
|
|
|
|
@item -Wno-shadow-ivar @r{(Objective-C only)}
|
|
@opindex Wno-shadow-ivar
|
|
@opindex Wshadow-ivar
|
|
Do not warn whenever a local variable shadows an instance variable in an
|
|
Objective-C method.
|
|
|
|
@item -Wshadow=global
|
|
@opindex Wshadow=local
|
|
The default for @option{-Wshadow}. Warns for any (global) shadowing.
|
|
|
|
@item -Wshadow=local
|
|
@opindex Wshadow=local
|
|
Warn when a local variable shadows another local variable or parameter.
|
|
This warning is enabled by @option{-Wshadow=global}.
|
|
|
|
@item -Wshadow=compatible-local
|
|
@opindex Wshadow=compatible-local
|
|
Warn when a local variable shadows another local variable or parameter
|
|
whose type is compatible with that of the shadowing variable. In C++,
|
|
type compatibility here means the type of the shadowing variable can be
|
|
converted to that of the shadowed variable. The creation of this flag
|
|
(in addition to @option{-Wshadow=local}) is based on the idea that when
|
|
a local variable shadows another one of incompatible type, it is most
|
|
likely intentional, not a bug or typo, as shown in the following example:
|
|
|
|
@smallexample
|
|
@group
|
|
for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
|
|
@{
|
|
for (int i = 0; i < N; ++i)
|
|
@{
|
|
...
|
|
@}
|
|
...
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
Since the two variable @code{i} in the example above have incompatible types,
|
|
enabling only @option{-Wshadow=compatible-local} will not emit a warning.
|
|
Because their types are incompatible, if a programmer accidentally uses one
|
|
in place of the other, type checking will catch that and emit an error or
|
|
warning. So not warning (about shadowing) in this case will not lead to
|
|
undetected bugs. Use of this flag instead of @option{-Wshadow=local} can
|
|
possibly reduce the number of warnings triggered by intentional shadowing.
|
|
|
|
This warning is enabled by @option{-Wshadow=local}.
|
|
|
|
@item -Wlarger-than=@var{len}
|
|
@opindex Wlarger-than=@var{len}
|
|
@opindex Wlarger-than-@var{len}
|
|
Warn whenever an object of larger than @var{len} bytes is defined.
|
|
|
|
@item -Wframe-larger-than=@var{len}
|
|
@opindex Wframe-larger-than
|
|
Warn if the size of a function frame is larger than @var{len} bytes.
|
|
The computation done to determine the stack frame size is approximate
|
|
and not conservative.
|
|
The actual requirements may be somewhat greater than @var{len}
|
|
even if you do not get a warning. In addition, any space allocated
|
|
via @code{alloca}, variable-length arrays, or related constructs
|
|
is not included by the compiler when determining
|
|
whether or not to issue a warning.
|
|
|
|
@item -Wno-free-nonheap-object
|
|
@opindex Wno-free-nonheap-object
|
|
@opindex Wfree-nonheap-object
|
|
Do not warn when attempting to free an object that was not allocated
|
|
on the heap.
|
|
|
|
@item -Wstack-usage=@var{len}
|
|
@opindex Wstack-usage
|
|
Warn if the stack usage of a function might be larger than @var{len} bytes.
|
|
The computation done to determine the stack usage is conservative.
|
|
Any space allocated via @code{alloca}, variable-length arrays, or related
|
|
constructs is included by the compiler when determining whether or not to
|
|
issue a warning.
|
|
|
|
The message is in keeping with the output of @option{-fstack-usage}.
|
|
|
|
@itemize
|
|
@item
|
|
If the stack usage is fully static but exceeds the specified amount, it's:
|
|
|
|
@smallexample
|
|
warning: stack usage is 1120 bytes
|
|
@end smallexample
|
|
@item
|
|
If the stack usage is (partly) dynamic but bounded, it's:
|
|
|
|
@smallexample
|
|
warning: stack usage might be 1648 bytes
|
|
@end smallexample
|
|
@item
|
|
If the stack usage is (partly) dynamic and not bounded, it's:
|
|
|
|
@smallexample
|
|
warning: stack usage might be unbounded
|
|
@end smallexample
|
|
@end itemize
|
|
|
|
@item -Wunsafe-loop-optimizations
|
|
@opindex Wunsafe-loop-optimizations
|
|
@opindex Wno-unsafe-loop-optimizations
|
|
Warn if the loop cannot be optimized because the compiler cannot
|
|
assume anything on the bounds of the loop indices. With
|
|
@option{-funsafe-loop-optimizations} warn if the compiler makes
|
|
such assumptions.
|
|
|
|
@item -Wno-pedantic-ms-format @r{(MinGW targets only)}
|
|
@opindex Wno-pedantic-ms-format
|
|
@opindex Wpedantic-ms-format
|
|
When used in combination with @option{-Wformat}
|
|
and @option{-pedantic} without GNU extensions, this option
|
|
disables the warnings about non-ISO @code{printf} / @code{scanf} format
|
|
width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets,
|
|
which depend on the MS runtime.
|
|
|
|
@item -Waligned-new
|
|
@opindex Waligned-new
|
|
@opindex Wno-aligned-new
|
|
Warn about a new-expression of a type that requires greater alignment
|
|
than the @code{alignof(std::max_align_t)} but uses an allocation
|
|
function without an explicit alignment parameter. This option is
|
|
enabled by @option{-Wall}.
|
|
|
|
Normally this only warns about global allocation functions, but
|
|
@option{-Waligned-new=all} also warns about class member allocation
|
|
functions.
|
|
|
|
@item -Wplacement-new
|
|
@itemx -Wplacement-new=@var{n}
|
|
@opindex Wplacement-new
|
|
@opindex Wno-placement-new
|
|
Warn about placement new expressions with undefined behavior, such as
|
|
constructing an object in a buffer that is smaller than the type of
|
|
the object. For example, the placement new expression below is diagnosed
|
|
because it attempts to construct an array of 64 integers in a buffer only
|
|
64 bytes large.
|
|
@smallexample
|
|
char buf [64];
|
|
new (buf) int[64];
|
|
@end smallexample
|
|
This warning is enabled by default.
|
|
|
|
@table @gcctabopt
|
|
@item -Wplacement-new=1
|
|
This is the default warning level of @option{-Wplacement-new}. At this
|
|
level the warning is not issued for some strictly undefined constructs that
|
|
GCC allows as extensions for compatibility with legacy code. For example,
|
|
the following @code{new} expression is not diagnosed at this level even
|
|
though it has undefined behavior according to the C++ standard because
|
|
it writes past the end of the one-element array.
|
|
@smallexample
|
|
struct S @{ int n, a[1]; @};
|
|
S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
|
|
new (s->a)int [32]();
|
|
@end smallexample
|
|
|
|
@item -Wplacement-new=2
|
|
At this level, in addition to diagnosing all the same constructs as at level
|
|
1, a diagnostic is also issued for placement new expressions that construct
|
|
an object in the last member of structure whose type is an array of a single
|
|
element and whose size is less than the size of the object being constructed.
|
|
While the previous example would be diagnosed, the following construct makes
|
|
use of the flexible member array extension to avoid the warning at level 2.
|
|
@smallexample
|
|
struct S @{ int n, a[]; @};
|
|
S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
|
|
new (s->a)int [32]();
|
|
@end smallexample
|
|
|
|
@end table
|
|
|
|
@item -Wpointer-arith
|
|
@opindex Wpointer-arith
|
|
@opindex Wno-pointer-arith
|
|
Warn about anything that depends on the ``size of'' a function type or
|
|
of @code{void}. GNU C assigns these types a size of 1, for
|
|
convenience in calculations with @code{void *} pointers and pointers
|
|
to functions. In C++, warn also when an arithmetic operation involves
|
|
@code{NULL}. This warning is also enabled by @option{-Wpedantic}.
|
|
|
|
@item -Wpointer-compare
|
|
@opindex Wpointer-compare
|
|
@opindex Wno-pointer-compare
|
|
Warn if a pointer is compared with a zero character constant. This usually
|
|
means that the pointer was meant to be dereferenced. For example:
|
|
|
|
@smallexample
|
|
const char *p = foo ();
|
|
if (p == '\0')
|
|
return 42;
|
|
@end smallexample
|
|
|
|
Note that the code above is invalid in C++11.
|
|
|
|
This warning is enabled by default.
|
|
|
|
@item -Wtype-limits
|
|
@opindex Wtype-limits
|
|
@opindex Wno-type-limits
|
|
Warn if a comparison is always true or always false due to the limited
|
|
range of the data type, but do not warn for constant expressions. For
|
|
example, warn if an unsigned variable is compared against zero with
|
|
@code{<} or @code{>=}. This warning is also enabled by
|
|
@option{-Wextra}.
|
|
|
|
@include cppwarnopts.texi
|
|
|
|
@item -Wbad-function-cast @r{(C and Objective-C only)}
|
|
@opindex Wbad-function-cast
|
|
@opindex Wno-bad-function-cast
|
|
Warn when a function call is cast to a non-matching type.
|
|
For example, warn if a call to a function returning an integer type
|
|
is cast to a pointer type.
|
|
|
|
@item -Wc90-c99-compat @r{(C and Objective-C only)}
|
|
@opindex Wc90-c99-compat
|
|
@opindex Wno-c90-c99-compat
|
|
Warn about features not present in ISO C90, but present in ISO C99.
|
|
For instance, warn about use of variable length arrays, @code{long long}
|
|
type, @code{bool} type, compound literals, designated initializers, and so
|
|
on. This option is independent of the standards mode. Warnings are disabled
|
|
in the expression that follows @code{__extension__}.
|
|
|
|
@item -Wc99-c11-compat @r{(C and Objective-C only)}
|
|
@opindex Wc99-c11-compat
|
|
@opindex Wno-c99-c11-compat
|
|
Warn about features not present in ISO C99, but present in ISO C11.
|
|
For instance, warn about use of anonymous structures and unions,
|
|
@code{_Atomic} type qualifier, @code{_Thread_local} storage-class specifier,
|
|
@code{_Alignas} specifier, @code{Alignof} operator, @code{_Generic} keyword,
|
|
and so on. This option is independent of the standards mode. Warnings are
|
|
disabled in the expression that follows @code{__extension__}.
|
|
|
|
@item -Wc++-compat @r{(C and Objective-C only)}
|
|
@opindex Wc++-compat
|
|
Warn about ISO C constructs that are outside of the common subset of
|
|
ISO C and ISO C++, e.g.@: request for implicit conversion from
|
|
@code{void *} to a pointer to non-@code{void} type.
|
|
|
|
@item -Wc++11-compat @r{(C++ and Objective-C++ only)}
|
|
@opindex Wc++11-compat
|
|
Warn about C++ constructs whose meaning differs between ISO C++ 1998
|
|
and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords
|
|
in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is
|
|
enabled by @option{-Wall}.
|
|
|
|
@item -Wc++14-compat @r{(C++ and Objective-C++ only)}
|
|
@opindex Wc++14-compat
|
|
Warn about C++ constructs whose meaning differs between ISO C++ 2011
|
|
and ISO C++ 2014. This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wc++1z-compat @r{(C++ and Objective-C++ only)}
|
|
@opindex Wc++1z-compat
|
|
Warn about C++ constructs whose meaning differs between ISO C++ 2014
|
|
and the forthoming ISO C++ 2017(?). This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wcast-qual
|
|
@opindex Wcast-qual
|
|
@opindex Wno-cast-qual
|
|
Warn whenever a pointer is cast so as to remove a type qualifier from
|
|
the target type. For example, warn if a @code{const char *} is cast
|
|
to an ordinary @code{char *}.
|
|
|
|
Also warn when making a cast that introduces a type qualifier in an
|
|
unsafe way. For example, casting @code{char **} to @code{const char **}
|
|
is unsafe, as in this example:
|
|
|
|
@smallexample
|
|
/* p is char ** value. */
|
|
const char **q = (const char **) p;
|
|
/* Assignment of readonly string to const char * is OK. */
|
|
*q = "string";
|
|
/* Now char** pointer points to read-only memory. */
|
|
**p = 'b';
|
|
@end smallexample
|
|
|
|
@item -Wcast-align
|
|
@opindex Wcast-align
|
|
@opindex Wno-cast-align
|
|
Warn whenever a pointer is cast such that the required alignment of the
|
|
target is increased. For example, warn if a @code{char *} is cast to
|
|
an @code{int *} on machines where integers can only be accessed at
|
|
two- or four-byte boundaries.
|
|
|
|
@item -Wwrite-strings
|
|
@opindex Wwrite-strings
|
|
@opindex Wno-write-strings
|
|
When compiling C, give string constants the type @code{const
|
|
char[@var{length}]} so that copying the address of one into a
|
|
non-@code{const} @code{char *} pointer produces a warning. These
|
|
warnings help you find at compile time code that can try to write
|
|
into a string constant, but only if you have been very careful about
|
|
using @code{const} in declarations and prototypes. Otherwise, it is
|
|
just a nuisance. This is why we did not make @option{-Wall} request
|
|
these warnings.
|
|
|
|
When compiling C++, warn about the deprecated conversion from string
|
|
literals to @code{char *}. This warning is enabled by default for C++
|
|
programs.
|
|
|
|
@item -Wclobbered
|
|
@opindex Wclobbered
|
|
@opindex Wno-clobbered
|
|
Warn for variables that might be changed by @code{longjmp} or
|
|
@code{vfork}. This warning is also enabled by @option{-Wextra}.
|
|
|
|
@item -Wconditionally-supported @r{(C++ and Objective-C++ only)}
|
|
@opindex Wconditionally-supported
|
|
@opindex Wno-conditionally-supported
|
|
Warn for conditionally-supported (C++11 [intro.defs]) constructs.
|
|
|
|
@item -Wconversion
|
|
@opindex Wconversion
|
|
@opindex Wno-conversion
|
|
Warn for implicit conversions that may alter a value. This includes
|
|
conversions between real and integer, like @code{abs (x)} when
|
|
@code{x} is @code{double}; conversions between signed and unsigned,
|
|
like @code{unsigned ui = -1}; and conversions to smaller types, like
|
|
@code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs
|
|
((int) x)} and @code{ui = (unsigned) -1}, or if the value is not
|
|
changed by the conversion like in @code{abs (2.0)}. Warnings about
|
|
conversions between signed and unsigned integers can be disabled by
|
|
using @option{-Wno-sign-conversion}.
|
|
|
|
For C++, also warn for confusing overload resolution for user-defined
|
|
conversions; and conversions that never use a type conversion
|
|
operator: conversions to @code{void}, the same type, a base class or a
|
|
reference to them. Warnings about conversions between signed and
|
|
unsigned integers are disabled by default in C++ unless
|
|
@option{-Wsign-conversion} is explicitly enabled.
|
|
|
|
@item -Wno-conversion-null @r{(C++ and Objective-C++ only)}
|
|
@opindex Wconversion-null
|
|
@opindex Wno-conversion-null
|
|
Do not warn for conversions between @code{NULL} and non-pointer
|
|
types. @option{-Wconversion-null} is enabled by default.
|
|
|
|
@item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)}
|
|
@opindex Wzero-as-null-pointer-constant
|
|
@opindex Wno-zero-as-null-pointer-constant
|
|
Warn when a literal @samp{0} is used as null pointer constant. This can
|
|
be useful to facilitate the conversion to @code{nullptr} in C++11.
|
|
|
|
@item -Wsubobject-linkage @r{(C++ and Objective-C++ only)}
|
|
@opindex Wsubobject-linkage
|
|
@opindex Wno-subobject-linkage
|
|
Warn if a class type has a base or a field whose type uses the anonymous
|
|
namespace or depends on a type with no linkage. If a type A depends on
|
|
a type B with no or internal linkage, defining it in multiple
|
|
translation units would be an ODR violation because the meaning of B
|
|
is different in each translation unit. If A only appears in a single
|
|
translation unit, the best way to silence the warning is to give it
|
|
internal linkage by putting it in an anonymous namespace as well. The
|
|
compiler doesn't give this warning for types defined in the main .C
|
|
file, as those are unlikely to have multiple definitions.
|
|
@option{-Wsubobject-linkage} is enabled by default.
|
|
|
|
@item -Wdangling-else
|
|
@opindex Wdangling-else
|
|
@opindex Wno-dangling-else
|
|
Warn about constructions where there may be confusion to which
|
|
@code{if} statement an @code{else} branch belongs. Here is an example of
|
|
such a case:
|
|
|
|
@smallexample
|
|
@group
|
|
@{
|
|
if (a)
|
|
if (b)
|
|
foo ();
|
|
else
|
|
bar ();
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
In C/C++, every @code{else} branch belongs to the innermost possible
|
|
@code{if} statement, which in this example is @code{if (b)}. This is
|
|
often not what the programmer expected, as illustrated in the above
|
|
example by indentation the programmer chose. When there is the
|
|
potential for this confusion, GCC issues a warning when this flag
|
|
is specified. To eliminate the warning, add explicit braces around
|
|
the innermost @code{if} statement so there is no way the @code{else}
|
|
can belong to the enclosing @code{if}. The resulting code
|
|
looks like this:
|
|
|
|
@smallexample
|
|
@group
|
|
@{
|
|
if (a)
|
|
@{
|
|
if (b)
|
|
foo ();
|
|
else
|
|
bar ();
|
|
@}
|
|
@}
|
|
@end group
|
|
@end smallexample
|
|
|
|
This warning is enabled by @option{-Wparentheses}.
|
|
|
|
@item -Wdate-time
|
|
@opindex Wdate-time
|
|
@opindex Wno-date-time
|
|
Warn when macros @code{__TIME__}, @code{__DATE__} or @code{__TIMESTAMP__}
|
|
are encountered as they might prevent bit-wise-identical reproducible
|
|
compilations.
|
|
|
|
@item -Wdelete-incomplete @r{(C++ and Objective-C++ only)}
|
|
@opindex Wdelete-incomplete
|
|
@opindex Wno-delete-incomplete
|
|
Warn when deleting a pointer to incomplete type, which may cause
|
|
undefined behavior at runtime. This warning is enabled by default.
|
|
|
|
@item -Wuseless-cast @r{(C++ and Objective-C++ only)}
|
|
@opindex Wuseless-cast
|
|
@opindex Wno-useless-cast
|
|
Warn when an expression is casted to its own type.
|
|
|
|
@item -Wempty-body
|
|
@opindex Wempty-body
|
|
@opindex Wno-empty-body
|
|
Warn if an empty body occurs in an @code{if}, @code{else} or @code{do
|
|
while} statement. This warning is also enabled by @option{-Wextra}.
|
|
|
|
@item -Wenum-compare
|
|
@opindex Wenum-compare
|
|
@opindex Wno-enum-compare
|
|
Warn about a comparison between values of different enumerated types.
|
|
In C++ enumeral mismatches in conditional expressions are also
|
|
diagnosed and the warning is enabled by default. In C this warning is
|
|
enabled by @option{-Wall}.
|
|
|
|
@item -Wjump-misses-init @r{(C, Objective-C only)}
|
|
@opindex Wjump-misses-init
|
|
@opindex Wno-jump-misses-init
|
|
Warn if a @code{goto} statement or a @code{switch} statement jumps
|
|
forward across the initialization of a variable, or jumps backward to a
|
|
label after the variable has been initialized. This only warns about
|
|
variables that are initialized when they are declared. This warning is
|
|
only supported for C and Objective-C; in C++ this sort of branch is an
|
|
error in any case.
|
|
|
|
@option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It
|
|
can be disabled with the @option{-Wno-jump-misses-init} option.
|
|
|
|
@item -Wsign-compare
|
|
@opindex Wsign-compare
|
|
@opindex Wno-sign-compare
|
|
@cindex warning for comparison of signed and unsigned values
|
|
@cindex comparison of signed and unsigned values, warning
|
|
@cindex signed and unsigned values, comparison warning
|
|
Warn when a comparison between signed and unsigned values could produce
|
|
an incorrect result when the signed value is converted to unsigned.
|
|
In C++, this warning is also enabled by @option{-Wall}. In C, it is
|
|
also enabled by @option{-Wextra}.
|
|
|
|
@item -Wsign-conversion
|
|
@opindex Wsign-conversion
|
|
@opindex Wno-sign-conversion
|
|
Warn for implicit conversions that may change the sign of an integer
|
|
value, like assigning a signed integer expression to an unsigned
|
|
integer variable. An explicit cast silences the warning. In C, this
|
|
option is enabled also by @option{-Wconversion}.
|
|
|
|
@item -Wfloat-conversion
|
|
@opindex Wfloat-conversion
|
|
@opindex Wno-float-conversion
|
|
Warn for implicit conversions that reduce the precision of a real value.
|
|
This includes conversions from real to integer, and from higher precision
|
|
real to lower precision real values. This option is also enabled by
|
|
@option{-Wconversion}.
|
|
|
|
@item -Wno-scalar-storage-order
|
|
@opindex -Wno-scalar-storage-order
|
|
@opindex -Wscalar-storage-order
|
|
Do not warn on suspicious constructs involving reverse scalar storage order.
|
|
|
|
@item -Wsized-deallocation @r{(C++ and Objective-C++ only)}
|
|
@opindex Wsized-deallocation
|
|
@opindex Wno-sized-deallocation
|
|
Warn about a definition of an unsized deallocation function
|
|
@smallexample
|
|
void operator delete (void *) noexcept;
|
|
void operator delete[] (void *) noexcept;
|
|
@end smallexample
|
|
without a definition of the corresponding sized deallocation function
|
|
@smallexample
|
|
void operator delete (void *, std::size_t) noexcept;
|
|
void operator delete[] (void *, std::size_t) noexcept;
|
|
@end smallexample
|
|
or vice versa. Enabled by @option{-Wextra} along with
|
|
@option{-fsized-deallocation}.
|
|
|
|
@item -Wsizeof-pointer-memaccess
|
|
@opindex Wsizeof-pointer-memaccess
|
|
@opindex Wno-sizeof-pointer-memaccess
|
|
Warn for suspicious length parameters to certain string and memory built-in
|
|
functions if the argument uses @code{sizeof}. This warning warns e.g.@:
|
|
about @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not an array,
|
|
but a pointer, and suggests a possible fix, or about
|
|
@code{memcpy (&foo, ptr, sizeof (&foo));}. This warning is enabled by
|
|
@option{-Wall}.
|
|
|
|
@item -Wsizeof-array-argument
|
|
@opindex Wsizeof-array-argument
|
|
@opindex Wno-sizeof-array-argument
|
|
Warn when the @code{sizeof} operator is applied to a parameter that is
|
|
declared as an array in a function definition. This warning is enabled by
|
|
default for C and C++ programs.
|
|
|
|
@item -Wmemset-elt-size
|
|
@opindex Wmemset-elt-size
|
|
@opindex Wno-memset-elt-size
|
|
Warn for suspicious calls to the @code{memset} built-in function, if the
|
|
first argument references an array, and the third argument is a number
|
|
equal to the number of elements, but not equal to the size of the array
|
|
in memory. This indicates that the user has omitted a multiplication by
|
|
the element size. This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wmemset-transposed-args
|
|
@opindex Wmemset-transposed-args
|
|
@opindex Wno-memset-transposed-args
|
|
Warn for suspicious calls to the @code{memset} built-in function, if the
|
|
second argument is not zero and the third argument is zero. This warns e.g.@
|
|
about @code{memset (buf, sizeof buf, 0)} where most probably
|
|
@code{memset (buf, 0, sizeof buf)} was meant instead. The diagnostics
|
|
is only emitted if the third argument is literal zero. If it is some
|
|
expression that is folded to zero, a cast of zero to some type, etc.,
|
|
it is far less likely that the user has mistakenly exchanged the arguments
|
|
and no warning is emitted. This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Waddress
|
|
@opindex Waddress
|
|
@opindex Wno-address
|
|
Warn about suspicious uses of memory addresses. These include using
|
|
the address of a function in a conditional expression, such as
|
|
@code{void func(void); if (func)}, and comparisons against the memory
|
|
address of a string literal, such as @code{if (x == "abc")}. Such
|
|
uses typically indicate a programmer error: the address of a function
|
|
always evaluates to true, so their use in a conditional usually
|
|
indicate that the programmer forgot the parentheses in a function
|
|
call; and comparisons against string literals result in unspecified
|
|
behavior and are not portable in C, so they usually indicate that the
|
|
programmer intended to use @code{strcmp}. This warning is enabled by
|
|
@option{-Wall}.
|
|
|
|
@item -Wlogical-op
|
|
@opindex Wlogical-op
|
|
@opindex Wno-logical-op
|
|
Warn about suspicious uses of logical operators in expressions.
|
|
This includes using logical operators in contexts where a
|
|
bit-wise operator is likely to be expected. Also warns when
|
|
the operands of a logical operator are the same:
|
|
@smallexample
|
|
extern int a;
|
|
if (a < 0 && a < 0) @{ @dots{} @}
|
|
@end smallexample
|
|
|
|
@item -Wlogical-not-parentheses
|
|
@opindex Wlogical-not-parentheses
|
|
@opindex Wno-logical-not-parentheses
|
|
Warn about logical not used on the left hand side operand of a comparison.
|
|
This option does not warn if the right operand is considered to be a boolean
|
|
expression. Its purpose is to detect suspicious code like the following:
|
|
@smallexample
|
|
int a;
|
|
@dots{}
|
|
if (!a > 1) @{ @dots{} @}
|
|
@end smallexample
|
|
|
|
It is possible to suppress the warning by wrapping the LHS into
|
|
parentheses:
|
|
@smallexample
|
|
if ((!a) > 1) @{ @dots{} @}
|
|
@end smallexample
|
|
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Waggregate-return
|
|
@opindex Waggregate-return
|
|
@opindex Wno-aggregate-return
|
|
Warn if any functions that return structures or unions are defined or
|
|
called. (In languages where you can return an array, this also elicits
|
|
a warning.)
|
|
|
|
@item -Wno-aggressive-loop-optimizations
|
|
@opindex Wno-aggressive-loop-optimizations
|
|
@opindex Waggressive-loop-optimizations
|
|
Warn if in a loop with constant number of iterations the compiler detects
|
|
undefined behavior in some statement during one or more of the iterations.
|
|
|
|
@item -Wno-attributes
|
|
@opindex Wno-attributes
|
|
@opindex Wattributes
|
|
Do not warn if an unexpected @code{__attribute__} is used, such as
|
|
unrecognized attributes, function attributes applied to variables,
|
|
etc. This does not stop errors for incorrect use of supported
|
|
attributes.
|
|
|
|
@item -Wno-builtin-declaration-mismatch
|
|
@opindex Wno-builtin-declaration-mismatch
|
|
@opindex Wbuiltin-declaration-mismatch
|
|
Warn if a built-in function is declared with the wrong signature.
|
|
This warning is enabled by default.
|
|
|
|
@item -Wno-builtin-macro-redefined
|
|
@opindex Wno-builtin-macro-redefined
|
|
@opindex Wbuiltin-macro-redefined
|
|
Do not warn if certain built-in macros are redefined. This suppresses
|
|
warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__},
|
|
@code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}.
|
|
|
|
@item -Wstrict-prototypes @r{(C and Objective-C only)}
|
|
@opindex Wstrict-prototypes
|
|
@opindex Wno-strict-prototypes
|
|
Warn if a function is declared or defined without specifying the
|
|
argument types. (An old-style function definition is permitted without
|
|
a warning if preceded by a declaration that specifies the argument
|
|
types.)
|
|
|
|
@item -Wold-style-declaration @r{(C and Objective-C only)}
|
|
@opindex Wold-style-declaration
|
|
@opindex Wno-old-style-declaration
|
|
Warn for obsolescent usages, according to the C Standard, in a
|
|
declaration. For example, warn if storage-class specifiers like
|
|
@code{static} are not the first things in a declaration. This warning
|
|
is also enabled by @option{-Wextra}.
|
|
|
|
@item -Wold-style-definition @r{(C and Objective-C only)}
|
|
@opindex Wold-style-definition
|
|
@opindex Wno-old-style-definition
|
|
Warn if an old-style function definition is used. A warning is given
|
|
even if there is a previous prototype.
|
|
|
|
@item -Wmissing-parameter-type @r{(C and Objective-C only)}
|
|
@opindex Wmissing-parameter-type
|
|
@opindex Wno-missing-parameter-type
|
|
A function parameter is declared without a type specifier in K&R-style
|
|
functions:
|
|
|
|
@smallexample
|
|
void foo(bar) @{ @}
|
|
@end smallexample
|
|
|
|
This warning is also enabled by @option{-Wextra}.
|
|
|
|
@item -Wmissing-prototypes @r{(C and Objective-C only)}
|
|
@opindex Wmissing-prototypes
|
|
@opindex Wno-missing-prototypes
|
|
Warn if a global function is defined without a previous prototype
|
|
declaration. This warning is issued even if the definition itself
|
|
provides a prototype. Use this option to detect global functions
|
|
that do not have a matching prototype declaration in a header file.
|
|
This option is not valid for C++ because all function declarations
|
|
provide prototypes and a non-matching declaration declares an
|
|
overload rather than conflict with an earlier declaration.
|
|
Use @option{-Wmissing-declarations} to detect missing declarations in C++.
|
|
|
|
@item -Wmissing-declarations
|
|
@opindex Wmissing-declarations
|
|
@opindex Wno-missing-declarations
|
|
Warn if a global function is defined without a previous declaration.
|
|
Do so even if the definition itself provides a prototype.
|
|
Use this option to detect global functions that are not declared in
|
|
header files. In C, no warnings are issued for functions with previous
|
|
non-prototype declarations; use @option{-Wmissing-prototypes} to detect
|
|
missing prototypes. In C++, no warnings are issued for function templates,
|
|
or for inline functions, or for functions in anonymous namespaces.
|
|
|
|
@item -Wmissing-field-initializers
|
|
@opindex Wmissing-field-initializers
|
|
@opindex Wno-missing-field-initializers
|
|
@opindex W
|
|
@opindex Wextra
|
|
@opindex Wno-extra
|
|
Warn if a structure's initializer has some fields missing. For
|
|
example, the following code causes such a warning, because
|
|
@code{x.h} is implicitly zero:
|
|
|
|
@smallexample
|
|
struct s @{ int f, g, h; @};
|
|
struct s x = @{ 3, 4 @};
|
|
@end smallexample
|
|
|
|
This option does not warn about designated initializers, so the following
|
|
modification does not trigger a warning:
|
|
|
|
@smallexample
|
|
struct s @{ int f, g, h; @};
|
|
struct s x = @{ .f = 3, .g = 4 @};
|
|
@end smallexample
|
|
|
|
In C++ this option does not warn either about the empty @{ @}
|
|
initializer, for example:
|
|
|
|
@smallexample
|
|
struct s @{ int f, g, h; @};
|
|
s x = @{ @};
|
|
@end smallexample
|
|
|
|
This warning is included in @option{-Wextra}. To get other @option{-Wextra}
|
|
warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}.
|
|
|
|
@item -Wno-multichar
|
|
@opindex Wno-multichar
|
|
@opindex Wmultichar
|
|
Do not warn if a multicharacter constant (@samp{'FOOF'}) is used.
|
|
Usually they indicate a typo in the user's code, as they have
|
|
implementation-defined values, and should not be used in portable code.
|
|
|
|
@item -Wnormalized@r{[}=@r{<}none@r{|}id@r{|}nfc@r{|}nfkc@r{>]}
|
|
@opindex Wnormalized=
|
|
@opindex Wnormalized
|
|
@opindex Wno-normalized
|
|
@cindex NFC
|
|
@cindex NFKC
|
|
@cindex character set, input normalization
|
|
In ISO C and ISO C++, two identifiers are different if they are
|
|
different sequences of characters. However, sometimes when characters
|
|
outside the basic ASCII character set are used, you can have two
|
|
different character sequences that look the same. To avoid confusion,
|
|
the ISO 10646 standard sets out some @dfn{normalization rules} which
|
|
when applied ensure that two sequences that look the same are turned into
|
|
the same sequence. GCC can warn you if you are using identifiers that
|
|
have not been normalized; this option controls that warning.
|
|
|
|
There are four levels of warning supported by GCC@. The default is
|
|
@option{-Wnormalized=nfc}, which warns about any identifier that is
|
|
not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the
|
|
recommended form for most uses. It is equivalent to
|
|
@option{-Wnormalized}.
|
|
|
|
Unfortunately, there are some characters allowed in identifiers by
|
|
ISO C and ISO C++ that, when turned into NFC, are not allowed in
|
|
identifiers. That is, there's no way to use these symbols in portable
|
|
ISO C or C++ and have all your identifiers in NFC@.
|
|
@option{-Wnormalized=id} suppresses the warning for these characters.
|
|
It is hoped that future versions of the standards involved will correct
|
|
this, which is why this option is not the default.
|
|
|
|
You can switch the warning off for all characters by writing
|
|
@option{-Wnormalized=none} or @option{-Wno-normalized}. You should
|
|
only do this if you are using some other normalization scheme (like
|
|
``D''), because otherwise you can easily create bugs that are
|
|
literally impossible to see.
|
|
|
|
Some characters in ISO 10646 have distinct meanings but look identical
|
|
in some fonts or display methodologies, especially once formatting has
|
|
been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL
|
|
LETTER N'', displays just like a regular @code{n} that has been
|
|
placed in a superscript. ISO 10646 defines the @dfn{NFKC}
|
|
normalization scheme to convert all these into a standard form as
|
|
well, and GCC warns if your code is not in NFKC if you use
|
|
@option{-Wnormalized=nfkc}. This warning is comparable to warning
|
|
about every identifier that contains the letter O because it might be
|
|
confused with the digit 0, and so is not the default, but may be
|
|
useful as a local coding convention if the programming environment
|
|
cannot be fixed to display these characters distinctly.
|
|
|
|
@item -Wno-deprecated
|
|
@opindex Wno-deprecated
|
|
@opindex Wdeprecated
|
|
Do not warn about usage of deprecated features. @xref{Deprecated Features}.
|
|
|
|
@item -Wno-deprecated-declarations
|
|
@opindex Wno-deprecated-declarations
|
|
@opindex Wdeprecated-declarations
|
|
Do not warn about uses of functions (@pxref{Function Attributes}),
|
|
variables (@pxref{Variable Attributes}), and types (@pxref{Type
|
|
Attributes}) marked as deprecated by using the @code{deprecated}
|
|
attribute.
|
|
|
|
@item -Wno-overflow
|
|
@opindex Wno-overflow
|
|
@opindex Woverflow
|
|
Do not warn about compile-time overflow in constant expressions.
|
|
|
|
@item -Wno-odr
|
|
@opindex Wno-odr
|
|
@opindex Wodr
|
|
Warn about One Definition Rule violations during link-time optimization.
|
|
Requires @option{-flto-odr-type-merging} to be enabled. Enabled by default.
|
|
|
|
@item -Wopenmp-simd
|
|
@opindex Wopenm-simd
|
|
Warn if the vectorizer cost model overrides the OpenMP or the Cilk Plus
|
|
simd directive set by user. The @option{-fsimd-cost-model=unlimited}
|
|
option can be used to relax the cost model.
|
|
|
|
@item -Woverride-init @r{(C and Objective-C only)}
|
|
@opindex Woverride-init
|
|
@opindex Wno-override-init
|
|
@opindex W
|
|
@opindex Wextra
|
|
@opindex Wno-extra
|
|
Warn if an initialized field without side effects is overridden when
|
|
using designated initializers (@pxref{Designated Inits, , Designated
|
|
Initializers}).
|
|
|
|
This warning is included in @option{-Wextra}. To get other
|
|
@option{-Wextra} warnings without this one, use @option{-Wextra
|
|
-Wno-override-init}.
|
|
|
|
@item -Woverride-init-side-effects @r{(C and Objective-C only)}
|
|
@opindex Woverride-init-side-effects
|
|
@opindex Wno-override-init-side-effects
|
|
Warn if an initialized field with side effects is overridden when
|
|
using designated initializers (@pxref{Designated Inits, , Designated
|
|
Initializers}). This warning is enabled by default.
|
|
|
|
@item -Wpacked
|
|
@opindex Wpacked
|
|
@opindex Wno-packed
|
|
Warn if a structure is given the packed attribute, but the packed
|
|
attribute has no effect on the layout or size of the structure.
|
|
Such structures may be mis-aligned for little benefit. For
|
|
instance, in this code, the variable @code{f.x} in @code{struct bar}
|
|
is misaligned even though @code{struct bar} does not itself
|
|
have the packed attribute:
|
|
|
|
@smallexample
|
|
@group
|
|
struct foo @{
|
|
int x;
|
|
char a, b, c, d;
|
|
@} __attribute__((packed));
|
|
struct bar @{
|
|
char z;
|
|
struct foo f;
|
|
@};
|
|
@end group
|
|
@end smallexample
|
|
|
|
@item -Wpacked-bitfield-compat
|
|
@opindex Wpacked-bitfield-compat
|
|
@opindex Wno-packed-bitfield-compat
|
|
The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute
|
|
on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but
|
|
the change can lead to differences in the structure layout. GCC
|
|
informs you when the offset of such a field has changed in GCC 4.4.
|
|
For example there is no longer a 4-bit padding between field @code{a}
|
|
and @code{b} in this structure:
|
|
|
|
@smallexample
|
|
struct foo
|
|
@{
|
|
char a:4;
|
|
char b:8;
|
|
@} __attribute__ ((packed));
|
|
@end smallexample
|
|
|
|
This warning is enabled by default. Use
|
|
@option{-Wno-packed-bitfield-compat} to disable this warning.
|
|
|
|
@item -Wpadded
|
|
@opindex Wpadded
|
|
@opindex Wno-padded
|
|
Warn if padding is included in a structure, either to align an element
|
|
of the structure or to align the whole structure. Sometimes when this
|
|
happens it is possible to rearrange the fields of the structure to
|
|
reduce the padding and so make the structure smaller.
|
|
|
|
@item -Wredundant-decls
|
|
@opindex Wredundant-decls
|
|
@opindex Wno-redundant-decls
|
|
Warn if anything is declared more than once in the same scope, even in
|
|
cases where multiple declaration is valid and changes nothing.
|
|
|
|
@item -Wrestrict
|
|
@opindex Wrestrict
|
|
@opindex Wno-restrict
|
|
Warn when an argument passed to a restrict-qualified parameter
|
|
aliases with another argument.
|
|
|
|
@item -Wnested-externs @r{(C and Objective-C only)}
|
|
@opindex Wnested-externs
|
|
@opindex Wno-nested-externs
|
|
Warn if an @code{extern} declaration is encountered within a function.
|
|
|
|
@item -Wno-inherited-variadic-ctor
|
|
@opindex Winherited-variadic-ctor
|
|
@opindex Wno-inherited-variadic-ctor
|
|
Suppress warnings about use of C++11 inheriting constructors when the
|
|
base class inherited from has a C variadic constructor; the warning is
|
|
on by default because the ellipsis is not inherited.
|
|
|
|
@item -Winline
|
|
@opindex Winline
|
|
@opindex Wno-inline
|
|
Warn if a function that is declared as inline cannot be inlined.
|
|
Even with this option, the compiler does not warn about failures to
|
|
inline functions declared in system headers.
|
|
|
|
The compiler uses a variety of heuristics to determine whether or not
|
|
to inline a function. For example, the compiler takes into account
|
|
the size of the function being inlined and the amount of inlining
|
|
that has already been done in the current function. Therefore,
|
|
seemingly insignificant changes in the source program can cause the
|
|
warnings produced by @option{-Winline} to appear or disappear.
|
|
|
|
@item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)}
|
|
@opindex Wno-invalid-offsetof
|
|
@opindex Winvalid-offsetof
|
|
Suppress warnings from applying the @code{offsetof} macro to a non-POD
|
|
type. According to the 2014 ISO C++ standard, applying @code{offsetof}
|
|
to a non-standard-layout type is undefined. In existing C++ implementations,
|
|
however, @code{offsetof} typically gives meaningful results.
|
|
This flag is for users who are aware that they are
|
|
writing nonportable code and who have deliberately chosen to ignore the
|
|
warning about it.
|
|
|
|
The restrictions on @code{offsetof} may be relaxed in a future version
|
|
of the C++ standard.
|
|
|
|
@item -Wint-in-bool-context
|
|
@opindex Wint-in-bool-context
|
|
@opindex Wno-int-in-bool-context
|
|
Warn for suspicious use of integer values where boolean values are expected,
|
|
such as conditional expressions (?:) using non-boolean integer constants in
|
|
boolean context, like @code{if (a <= b ? 2 : 3)}. Or left shifting of signed
|
|
integers in boolean context, like @code{for (a = 0; 1 << a; a++);}. Likewise
|
|
for all kinds of multiplications regardless of the data type.
|
|
This warning is enabled by @option{-Wall}.
|
|
|
|
@item -Wno-int-to-pointer-cast
|
|
@opindex Wno-int-to-pointer-cast
|
|
@opindex Wint-to-pointer-cast
|
|
Suppress warnings from casts to pointer type of an integer of a
|
|
different size. In C++, casting to a pointer type of smaller size is
|
|
an error. @option{Wint-to-pointer-cast} is enabled by default.
|
|
|
|
|
|
@item -Wno-pointer-to-int-cast @r{(C and Objective-C only)}
|
|
@opindex Wno-pointer-to-int-cast
|
|
@opindex Wpointer-to-int-cast
|
|
Suppress warnings from casts from a pointer to an integer type of a
|
|
different size.
|
|
|
|
@item -Winvalid-pch
|
|
@opindex Winvalid-pch
|
|
@opindex Wno-invalid-pch
|
|
Warn if a precompiled header (@pxref{Precompiled Headers}) is found in
|
|
the search path but can't be used.
|
|
|
|
@item -Wlong-long
|
|
@opindex Wlong-long
|
|
@opindex Wno-long-long
|
|
Warn if @code{long long} type is used. This is enabled by either
|
|
@option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98
|
|
modes. To inhibit the warning messages, use @option{-Wno-long-long}.
|
|
|
|
@item -Wvariadic-macros
|
|
@opindex Wvariadic-macros
|
|
@opindex Wno-variadic-macros
|
|
Warn if variadic macros are used in ISO C90 mode, or if the GNU
|
|
alternate syntax is used in ISO C99 mode. This is enabled by either
|
|
@option{-Wpedantic} or @option{-Wtraditional}. To inhibit the warning
|
|
messages, use @option{-Wno-variadic-macros}.
|
|
|
|
@item -Wvarargs
|
|
@opindex Wvarargs
|
|
@opindex Wno-varargs
|
|
Warn upon questionable usage of the macros used to handle variable
|
|
arguments like @code{va_start}. This is default. To inhibit the
|
|
warning messages, use @option{-Wno-varargs}.
|
|
|
|
@item -Wvector-operation-performance
|
|
@opindex Wvector-operation-performance
|
|
@opindex Wno-vector-operation-performance
|
|
Warn if vector operation is not implemented via SIMD capabilities of the
|
|
architecture. Mainly useful for the performance tuning.
|
|
Vector operation can be implemented @code{piecewise}, which means that the
|
|
scalar operation is performed on every vector element;
|
|
@code{in parallel}, which means that the vector operation is implemented
|
|
using scalars of wider type, which normally is more performance efficient;
|
|
and @code{as a single scalar}, which means that vector fits into a
|
|
scalar type.
|
|
|
|
@item -Wno-virtual-move-assign
|
|
@opindex Wvirtual-move-assign
|
|
@opindex Wno-virtual-move-assign
|
|
Suppress warnings about inheriting from a virtual base with a
|
|
non-trivial C++11 move assignment operator. This is dangerous because
|
|
if the virtual base is reachable along more than one path, it is
|
|
moved multiple times, which can mean both objects end up in the
|
|
moved-from state. If the move assignment operator is written to avoid
|
|
moving from a moved-from object, this warning can be disabled.
|
|
|
|
@item -Wvla
|
|
@opindex Wvla
|
|
@opindex Wno-vla
|
|
Warn if a variable-length array is used in the code.
|
|
@option{-Wno-vla} prevents the @option{-Wpedantic} warning of
|
|
the variable-length array.
|
|
|
|
@item -Wvla-larger-than=@var{n}
|
|
If this option is used, the compiler will warn on uses of
|
|
variable-length arrays where the size is either unbounded, or bounded
|
|
by an argument that can be larger than @var{n} bytes. This is similar
|
|
to how @option{-Walloca-larger-than=@var{n}} works, but with
|
|
variable-length arrays.
|
|
|
|
Note that GCC may optimize small variable-length arrays of a known
|
|
value into plain arrays, so this warning may not get triggered for
|
|
such arrays.
|
|
|
|
This warning is not enabled by @option{-Wall}, and is only active when
|
|
@option{-ftree-vrp} is active (default for @option{-O2} and above).
|
|
|
|
See also @option{-Walloca-larger-than=@var{n}}.
|
|
|
|
@item -Wvolatile-register-var
|
|
@opindex Wvolatile-register-var
|
|
@opindex Wno-volatile-register-var
|
|
Warn if a register variable is declared volatile. The volatile
|
|
modifier does not inhibit all optimizations that may eliminate reads
|
|
and/or writes to register variables. This warning is enabled by
|
|
@option{-Wall}.
|
|
|
|
@item -Wdisabled-optimization
|
|
@opindex Wdisabled-optimization
|
|
@opindex Wno-disabled-optimization
|
|
Warn if a requested optimization pass is disabled. This warning does
|
|
not generally indicate that there is anything wrong with your code; it
|
|
merely indicates that GCC's optimizers are unable to handle the code
|
|
effectively. Often, the problem is that your code is too big or too
|
|
complex; GCC refuses to optimize programs when the optimization
|
|
itself is likely to take inordinate amounts of time.
|
|
|
|
@item -Wpointer-sign @r{(C and Objective-C only)}
|
|
@opindex Wpointer-sign
|
|
@opindex Wno-pointer-sign
|
|
Warn for pointer argument passing or assignment with different signedness.
|
|
This option is only supported for C and Objective-C@. It is implied by
|
|
@option{-Wall} and by @option{-Wpedantic}, which can be disabled with
|
|
@option{-Wno-pointer-sign}.
|
|
|
|
@item -Wstack-protector
|
|
@opindex Wstack-protector
|
|
@opindex Wno-stack-protector
|
|
This option is only active when @option{-fstack-protector} is active. It
|
|
warns about functions that are not protected against stack smashing.
|
|
|
|
@item -Woverlength-strings
|
|
@opindex Woverlength-strings
|
|
@opindex Wno-overlength-strings
|
|
Warn about string constants that are longer than the ``minimum
|
|
maximum'' length specified in the C standard. Modern compilers
|
|
generally allow string constants that are much longer than the
|
|
standard's minimum limit, but very portable programs should avoid
|
|
using longer strings.
|
|
|
|
The limit applies @emph{after} string constant concatenation, and does
|
|
not count the trailing NUL@. In C90, the limit was 509 characters; in
|
|
C99, it was raised to 4095. C++98 does not specify a normative
|
|
minimum maximum, so we do not diagnose overlength strings in C++@.
|
|
|
|
This option is implied by @option{-Wpedantic}, and can be disabled with
|
|
@option{-Wno-overlength-strings}.
|
|
|
|
@item -Wunsuffixed-float-constants @r{(C and Objective-C only)}
|
|
@opindex Wunsuffixed-float-constants
|
|
|
|
Issue a warning for any floating constant that does not have
|
|
a suffix. When used together with @option{-Wsystem-headers} it
|
|
warns about such constants in system header files. This can be useful
|
|
when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma
|
|
from the decimal floating-point extension to C99.
|
|
|
|
@item -Wno-designated-init @r{(C and Objective-C only)}
|
|
Suppress warnings when a positional initializer is used to initialize
|
|
a structure that has been marked with the @code{designated_init}
|
|
attribute.
|
|
|
|
@item -Whsa
|
|
Issue a warning when HSAIL cannot be emitted for the compiled function or
|
|
OpenMP construct.
|
|
|
|
@end table
|
|
|
|
@node Debugging Options
|
|
@section Options for Debugging Your Program
|
|
@cindex options, debugging
|
|
@cindex debugging information options
|
|
|
|
To tell GCC to emit extra information for use by a debugger, in almost
|
|
all cases you need only to add @option{-g} to your other options.
|
|
|
|
GCC allows you to use @option{-g} with
|
|
@option{-O}. The shortcuts taken by optimized code may occasionally
|
|
be surprising: some variables you declared may not exist
|
|
at all; flow of control may briefly move where you did not expect it;
|
|
some statements may not be executed because they compute constant
|
|
results or their values are already at hand; some statements may
|
|
execute in different places because they have been moved out of loops.
|
|
Nevertheless it is possible to debug optimized output. This makes
|
|
it reasonable to use the optimizer for programs that might have bugs.
|
|
|
|
If you are not using some other optimization option, consider
|
|
using @option{-Og} (@pxref{Optimize Options}) with @option{-g}.
|
|
With no @option{-O} option at all, some compiler passes that collect
|
|
information useful for debugging do not run at all, so that
|
|
@option{-Og} may result in a better debugging experience.
|
|
|
|
@table @gcctabopt
|
|
@item -g
|
|
@opindex g
|
|
Produce debugging information in the operating system's native format
|
|
(stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging
|
|
information.
|
|
|
|
On most systems that use stabs format, @option{-g} enables use of extra
|
|
debugging information that only GDB can use; this extra information
|
|
makes debugging work better in GDB but probably makes other debuggers
|
|
crash or
|
|
refuse to read the program. If you want to control for certain whether
|
|
to generate the extra information, use @option{-gstabs+}, @option{-gstabs},
|
|
@option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below).
|
|
|
|
@item -ggdb
|
|
@opindex ggdb
|
|
Produce debugging information for use by GDB@. This means to use the
|
|
most expressive format available (DWARF, stabs, or the native format
|
|
if neither of those are supported), including GDB extensions if at all
|
|
possible.
|
|
|
|
@item -gdwarf
|
|
@itemx -gdwarf-@var{version}
|
|
@opindex gdwarf
|
|
Produce debugging information in DWARF format (if that is supported).
|
|
The value of @var{version} may be either 2, 3, 4 or 5; the default version
|
|
for most targets is 4. DWARF Version 5 is only experimental.
|
|
|
|
Note that with DWARF Version 2, some ports require and always
|
|
use some non-conflicting DWARF 3 extensions in the unwind tables.
|
|
|
|
Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments}
|
|
for maximum benefit.
|
|
|
|
GCC no longer supports DWARF Version 1, which is substantially
|
|
different than Version 2 and later. For historical reasons, some
|
|
other DWARF-related options (including @option{-feliminate-dwarf2-dups}
|
|
and @option{-fno-dwarf2-cfi-asm}) retain a reference to DWARF Version 2
|
|
in their names, but apply to all currently-supported versions of DWARF.
|
|
|
|
@item -gstabs
|
|
@opindex gstabs
|
|
Produce debugging information in stabs format (if that is supported),
|
|
without GDB extensions. This is the format used by DBX on most BSD
|
|
systems. On MIPS, Alpha and System V Release 4 systems this option
|
|
produces stabs debugging output that is not understood by DBX or SDB@.
|
|
On System V Release 4 systems this option requires the GNU assembler.
|
|
|
|
@item -gstabs+
|
|
@opindex gstabs+
|
|
Produce debugging information in stabs format (if that is supported),
|
|
using GNU extensions understood only by the GNU debugger (GDB)@. The
|
|
use of these extensions is likely to make other debuggers crash or
|
|
refuse to read the program.
|
|
|
|
@item -gcoff
|
|
@opindex gcoff
|
|
Produce debugging information in COFF format (if that is supported).
|
|
This is the format used by SDB on most System V systems prior to
|
|
System V Release 4.
|
|
|
|
@item -gxcoff
|
|
@opindex gxcoff
|
|
Produce debugging information in XCOFF format (if that is supported).
|
|
This is the format used by the DBX debugger on IBM RS/6000 systems.
|
|
|
|
@item -gxcoff+
|
|
@opindex gxcoff+
|
|
Produce debugging information in XCOFF format (if that is supported),
|
|
using GNU extensions understood only by the GNU debugger (GDB)@. The
|
|
use of these extensions is likely to make other debuggers crash or
|
|
refuse to read the program, and may cause assemblers other than the GNU
|
|
assembler (GAS) to fail with an error.
|
|
|
|
@item -gvms
|
|
@opindex gvms
|
|
Produce debugging information in Alpha/VMS debug format (if that is
|
|
supported). This is the format used by DEBUG on Alpha/VMS systems.
|
|
|
|
@item -g@var{level}
|
|
@itemx -ggdb@var{level}
|
|
@itemx -gstabs@var{level}
|
|
@itemx -gcoff@var{level}
|
|
@itemx -gxcoff@var{level}
|
|
@itemx -gvms@var{level}
|
|
Request debugging information and also use @var{level} to specify how
|
|
much information. The default level is 2.
|
|
|
|
Level 0 produces no debug information at all. Thus, @option{-g0} negates
|
|
@option{-g}.
|
|
|
|
Level 1 produces minimal information, enough for making backtraces in
|
|
parts of the program that you don't plan to debug. This includes
|
|
descriptions of functions and external variables, and line number
|
|
tables, but no information about local variables.
|
|
|
|
Level 3 includes extra information, such as all the macro definitions
|
|
present in the program. Some debuggers support macro expansion when
|
|
you use @option{-g3}.
|
|
|
|
@option{-gdwarf} does not accept a concatenated debug level, to avoid
|
|
confusion with @option{-gdwarf-@var{level}}.
|
|
Instead use an additional @option{-g@var{level}} option to change the
|
|
debug level for DWARF.
|
|
|
|
@item -feliminate-unused-debug-symbols
|
|
@opindex feliminate-unused-debug-symbols
|
|
Produce debugging information in stabs format (if that is supported),
|
|
for only symbols that are actually used.
|
|
|
|
@item -femit-class-debug-always
|
|
@opindex femit-class-debug-always
|
|
Instead of emitting debugging information for a C++ class in only one
|
|
object file, emit it in all object files using the class. This option
|
|
should be used only with debuggers that are unable to handle the way GCC
|
|
normally emits debugging information for classes because using this
|
|
option increases the size of debugging information by as much as a
|
|
factor of two.
|
|
|
|
@item -fno-merge-debug-strings
|
|
@opindex fmerge-debug-strings
|
|
@opindex fno-merge-debug-strings
|
|
Direct the linker to not merge together strings in the debugging
|
|
information that are identical in different object files. Merging is
|
|
not supported by all assemblers or linkers. Merging decreases the size
|
|
of the debug information in the output file at the cost of increasing
|
|
link processing time. Merging is enabled by default.
|
|
|
|
@item -fdebug-prefix-map=@var{old}=@var{new}
|
|
@opindex fdebug-prefix-map
|
|
When compiling files in directory @file{@var{old}}, record debugging
|
|
information describing them as in @file{@var{new}} instead.
|
|
|
|
@item -fvar-tracking
|
|
@opindex fvar-tracking
|
|
Run variable tracking pass. It computes where variables are stored at each
|
|
position in code. Better debugging information is then generated
|
|
(if the debugging information format supports this information).
|
|
|
|
It is enabled by default when compiling with optimization (@option{-Os},
|
|
@option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and
|
|
the debug info format supports it.
|
|
|
|
@item -fvar-tracking-assignments
|
|
@opindex fvar-tracking-assignments
|
|
@opindex fno-var-tracking-assignments
|
|
Annotate assignments to user variables early in the compilation and
|
|
attempt to carry the annotations over throughout the compilation all the
|
|
way to the end, in an attempt to improve debug information while
|
|
optimizing. Use of @option{-gdwarf-4} is recommended along with it.
|
|
|
|
It can be enabled even if var-tracking is disabled, in which case
|
|
annotations are created and maintained, but discarded at the end.
|
|
By default, this flag is enabled together with @option{-fvar-tracking},
|
|
except when selective scheduling is enabled.
|
|
|
|
@item -gsplit-dwarf
|
|
@opindex gsplit-dwarf
|
|
Separate as much DWARF debugging information as possible into a
|
|
separate output file with the extension @file{.dwo}. This option allows
|
|
the build system to avoid linking files with debug information. To
|
|
be useful, this option requires a debugger capable of reading @file{.dwo}
|
|
files.
|
|
|
|
@item -gpubnames
|
|
@opindex gpubnames
|
|
Generate DWARF @code{.debug_pubnames} and @code{.debug_pubtypes} sections.
|
|
|
|
@item -ggnu-pubnames
|
|
@opindex ggnu-pubnames
|
|
Generate @code{.debug_pubnames} and @code{.debug_pubtypes} sections in a format
|
|
suitable for conversion into a GDB@ index. This option is only useful
|
|
with a linker that can produce GDB@ index version 7.
|
|
|
|
@item -fdebug-types-section
|
|
@opindex fdebug-types-section
|
|
@opindex fno-debug-types-section
|
|
When using DWARF Version 4 or higher, type DIEs can be put into
|
|
their own @code{.debug_types} section instead of making them part of the
|
|
@code{.debug_info} section. It is more efficient to put them in a separate
|
|
comdat sections since the linker can then remove duplicates.
|
|
But not all DWARF consumers support @code{.debug_types} sections yet
|
|
and on some objects @code{.debug_types} produces larger instead of smaller
|
|
debugging information.
|
|
|
|
@item -grecord-gcc-switches
|
|
@item -gno-record-gcc-switches
|
|
@opindex grecord-gcc-switches
|
|
@opindex gno-record-gcc-switches
|
|
This switch causes the command-line options used to invoke the
|
|
compiler that may affect code generation to be appended to the
|
|
DW_AT_producer attribute in DWARF debugging information. The options
|
|
are concatenated with spaces separating them from each other and from
|
|
the compiler version.
|
|
It is enabled by default.
|
|
See also @option{-frecord-gcc-switches} for another
|
|
way of storing compiler options into the object file.
|
|
|
|
@item -gstrict-dwarf
|
|
@opindex gstrict-dwarf
|
|
Disallow using extensions of later DWARF standard version than selected
|
|
with @option{-gdwarf-@var{version}}. On most targets using non-conflicting
|
|
DWARF extensions from later standard versions is allowed.
|
|
|
|
@item -gno-strict-dwarf
|
|
@opindex gno-strict-dwarf
|
|
Allow using extensions of later DWARF standard version than selected with
|
|
@option{-gdwarf-@var{version}}.
|
|
|
|
@item -gz@r{[}=@var{type}@r{]}
|
|
@opindex gz
|
|
Produce compressed debug sections in DWARF format, if that is supported.
|
|
If @var{type} is not given, the default type depends on the capabilities
|
|
of the assembler and linker used. @var{type} may be one of
|
|
@samp{none} (don't compress debug sections), @samp{zlib} (use zlib
|
|
compression in ELF gABI format), or @samp{zlib-gnu} (use zlib
|
|
compression in traditional GNU format). If the linker doesn't support
|
|
writing compressed debug sections, the option is rejected. Otherwise,
|
|
if the assembler does not support them, @option{-gz} is silently ignored
|
|
when producing object files.
|
|
|
|
@item -feliminate-dwarf2-dups
|
|
@opindex feliminate-dwarf2-dups
|
|
Compress DWARF debugging information by eliminating duplicated
|
|
information about each symbol. This option only makes sense when
|
|
generating DWARF debugging information.
|
|
|
|
@item -femit-struct-debug-baseonly
|
|
@opindex femit-struct-debug-baseonly
|
|
Emit debug information for struct-like types
|
|
only when the base name of the compilation source file
|
|
matches the base name of file in which the struct is defined.
|
|
|
|
This option substantially reduces the size of debugging information,
|
|
but at significant potential loss in type information to the debugger.
|
|
See @option{-femit-struct-debug-reduced} for a less aggressive option.
|
|
See @option{-femit-struct-debug-detailed} for more detailed control.
|
|
|
|
This option works only with DWARF debug output.
|
|
|
|
@item -femit-struct-debug-reduced
|
|
@opindex femit-struct-debug-reduced
|
|
Emit debug information for struct-like types
|
|
only when the base name of the compilation source file
|
|
matches the base name of file in which the type is defined,
|
|
unless the struct is a template or defined in a system header.
|
|
|
|
This option significantly reduces the size of debugging information,
|
|
with some potential loss in type information to the debugger.
|
|
See @option{-femit-struct-debug-baseonly} for a more aggressive option.
|
|
See @option{-femit-struct-debug-detailed} for more detailed control.
|
|
|
|
This option works only with DWARF debug output.
|
|
|
|
@item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]}
|
|
@opindex femit-struct-debug-detailed
|
|
Specify the struct-like types
|
|
for which the compiler generates debug information.
|
|
The intent is to reduce duplicate struct debug information
|
|
between different object files within the same program.
|
|
|
|
This option is a detailed version of
|
|
@option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly},
|
|
which serves for most needs.
|
|
|
|
A specification has the syntax@*
|
|
[@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none})
|
|
|
|
The optional first word limits the specification to
|
|
structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}).
|
|
A struct type is used directly when it is the type of a variable, member.
|
|
Indirect uses arise through pointers to structs.
|
|
That is, when use of an incomplete struct is valid, the use is indirect.
|
|
An example is
|
|
@samp{struct one direct; struct two * indirect;}.
|
|
|
|
The optional second word limits the specification to
|
|
ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}).
|
|
Generic structs are a bit complicated to explain.
|
|
For C++, these are non-explicit specializations of template classes,
|
|
or non-template classes within the above.
|
|
Other programming languages have generics,
|
|
but @option{-femit-struct-debug-detailed} does not yet implement them.
|
|
|
|
The third word specifies the source files for those
|
|
structs for which the compiler should emit debug information.
|
|
The values @samp{none} and @samp{any} have the normal meaning.
|
|
The value @samp{base} means that
|
|
the base of name of the file in which the type declaration appears
|
|
must match the base of the name of the main compilation file.
|
|
In practice, this means that when compiling @file{foo.c}, debug information
|
|
is generated for types declared in that file and @file{foo.h},
|
|
but not other header files.
|
|
The value @samp{sys} means those types satisfying @samp{base}
|
|
or declared in system or compiler headers.
|
|
|
|
You may need to experiment to determine the best settings for your application.
|
|
|
|
The default is @option{-femit-struct-debug-detailed=all}.
|
|
|
|
This option works only with DWARF debug output.
|
|
|
|
@item -fno-dwarf2-cfi-asm
|
|
@opindex fdwarf2-cfi-asm
|
|
@opindex fno-dwarf2-cfi-asm
|
|
Emit DWARF unwind info as compiler generated @code{.eh_frame} section
|
|
instead of using GAS @code{.cfi_*} directives.
|
|
|
|
@item -fno-eliminate-unused-debug-types
|
|
@opindex feliminate-unused-debug-types
|
|
@opindex fno-eliminate-unused-debug-types
|
|
Normally, when producing DWARF output, GCC avoids producing debug symbol
|
|
output for types that are nowhere used in the source file being compiled.
|
|
Sometimes it is useful to have GCC emit debugging
|
|
information for all types declared in a compilation
|
|
unit, regardless of whether or not they are actually used
|
|
in that compilation unit, for example
|
|
if, in the debugger, you want to cast a value to a type that is
|
|
not actually used in your program (but is declared). More often,
|
|
however, this results in a significant amount of wasted space.
|
|
@end table
|
|
|
|
@node Optimize Options
|
|
@section Options That Control Optimization
|
|
@cindex optimize options
|
|
@cindex options, optimization
|
|
|
|
These options control various sorts of optimizations.
|
|
|
|
Without any optimization option, the compiler's goal is to reduce the
|
|
cost of compilation and to make debugging produce the expected
|
|
results. Statements are independent: if you stop the program with a
|
|
breakpoint between statements, you can then assign a new value to any
|
|
variable or change the program counter to any other statement in the
|
|
function and get exactly the results you expect from the source
|
|
code.
|
|
|
|
Turning on optimization flags makes the compiler attempt to improve
|
|
the performance and/or code size at the expense of compilation time
|
|
and possibly the ability to debug the program.
|
|
|
|
The compiler performs optimization based on the knowledge it has of the
|
|
program. Compiling multiple files at once to a single output file mode allows
|
|
the compiler to use information gained from all of the files when compiling
|
|
each of them.
|
|
|
|
Not all optimizations are controlled directly by a flag. Only
|
|
optimizations that have a flag are listed in this section.
|
|
|
|
Most optimizations are only enabled if an @option{-O} level is set on
|
|
the command line. Otherwise they are disabled, even if individual
|
|
optimization flags are specified.
|
|
|
|
Depending on the target and how GCC was configured, a slightly different
|
|
set of optimizations may be enabled at each @option{-O} level than
|
|
those listed here. You can invoke GCC with @option{-Q --help=optimizers}
|
|
to find out the exact set of optimizations that are enabled at each level.
|
|
@xref{Overall Options}, for examples.
|
|
|
|
@table @gcctabopt
|
|
@item -O
|
|
@itemx -O1
|
|
@opindex O
|
|
@opindex O1
|
|
Optimize. Optimizing compilation takes somewhat more time, and a lot
|
|
more memory for a large function.
|
|
|
|
With @option{-O}, the compiler tries to reduce code size and execution
|
|
time, without performing any optimizations that take a great deal of
|
|
compilation time.
|
|
|
|
@option{-O} turns on the following optimization flags:
|
|
@gccoptlist{
|
|
-fauto-inc-dec @gol
|
|
-fbranch-count-reg @gol
|
|
-fcombine-stack-adjustments @gol
|
|
-fcompare-elim @gol
|
|
-fcprop-registers @gol
|
|
-fdce @gol
|
|
-fdefer-pop @gol
|
|
-fdelayed-branch @gol
|
|
-fdse @gol
|
|
-fforward-propagate @gol
|
|
-fguess-branch-probability @gol
|
|
-fif-conversion2 @gol
|
|
-fif-conversion @gol
|
|
-finline-functions-called-once @gol
|
|
-fipa-pure-const @gol
|
|
-fipa-profile @gol
|
|
-fipa-reference @gol
|
|
-fmerge-constants @gol
|
|
-fmove-loop-invariants @gol
|
|
-freorder-blocks @gol
|
|
-fshrink-wrap @gol
|
|
-fshrink-wrap-separate @gol
|
|
-fsplit-wide-types @gol
|
|
-fssa-backprop @gol
|
|
-fssa-phiopt @gol
|
|
-fstore-merging @gol
|
|
-ftree-bit-ccp @gol
|
|
-ftree-ccp @gol
|
|
-ftree-ch @gol
|
|
-ftree-coalesce-vars @gol
|
|
-ftree-copy-prop @gol
|
|
-ftree-dce @gol
|
|
-ftree-dominator-opts @gol
|
|
-ftree-dse @gol
|
|
-ftree-forwprop @gol
|
|
-ftree-fre @gol
|
|
-ftree-phiprop @gol
|
|
-ftree-sink @gol
|
|
-ftree-slsr @gol
|
|
-ftree-sra @gol
|
|
-ftree-pta @gol
|
|
-ftree-ter @gol
|
|
-funit-at-a-time}
|
|
|
|
@option{-O} also turns on @option{-fomit-frame-pointer} on machines
|
|
where doing so does not interfere with debugging.
|
|
|
|
@item -O2
|
|
@opindex O2
|
|
Optimize even more. GCC performs nearly all supported optimizations
|
|
that do not involve a space-speed tradeoff.
|
|
As compared to @option{-O}, this option increases both compilation time
|
|
and the performance of the generated code.
|
|
|
|
@option{-O2} turns on all optimization flags specified by @option{-O}. It
|
|
also turns on the following optimization flags:
|
|
@gccoptlist{-fthread-jumps @gol
|
|
-falign-functions -falign-jumps @gol
|
|
-falign-loops -falign-labels @gol
|
|
-fcaller-saves @gol
|
|
-fcrossjumping @gol
|
|
-fcse-follow-jumps -fcse-skip-blocks @gol
|
|
-fdelete-null-pointer-checks @gol
|
|
-fdevirtualize -fdevirtualize-speculatively @gol
|
|
-fexpensive-optimizations @gol
|
|
-fgcse -fgcse-lm @gol
|
|
-fhoist-adjacent-loads @gol
|
|
-finline-small-functions @gol
|
|
-findirect-inlining @gol
|
|
-fipa-cp @gol
|
|
-fipa-cp-alignment @gol
|
|
-fipa-bit-cp @gol
|
|
-fipa-sra @gol
|
|
-fipa-icf @gol
|
|
-fisolate-erroneous-paths-dereference @gol
|
|
-flra-remat @gol
|
|
-foptimize-sibling-calls @gol
|
|
-foptimize-strlen @gol
|
|
-fpartial-inlining @gol
|
|
-fpeephole2 @gol
|
|
-freorder-blocks-algorithm=stc @gol
|
|
-freorder-blocks-and-partition -freorder-functions @gol
|
|
-frerun-cse-after-loop @gol
|
|
-fsched-interblock -fsched-spec @gol
|
|
-fschedule-insns -fschedule-insns2 @gol
|
|
-fstrict-aliasing -fstrict-overflow @gol
|
|
-ftree-builtin-call-dce @gol
|
|
-ftree-switch-conversion -ftree-tail-merge @gol
|
|
-fcode-hoisting @gol
|
|
-ftree-pre @gol
|
|
-ftree-vrp @gol
|
|
-fipa-ra}
|
|
|
|
Please note the warning under @option{-fgcse} about
|
|
invoking @option{-O2} on programs that use computed gotos.
|
|
|
|
@item -O3
|
|
@opindex O3
|
|
Optimize yet more. @option{-O3} turns on all optimizations specified
|
|
by @option{-O2} and also turns on the @option{-finline-functions},
|
|
@option{-funswitch-loops}, @option{-fpredictive-commoning},
|
|
@option{-fgcse-after-reload}, @option{-ftree-loop-vectorize},
|
|
@option{-ftree-loop-distribute-patterns}, @option{-fsplit-paths}
|
|
@option{-ftree-slp-vectorize}, @option{-fvect-cost-model},
|
|
@option{-ftree-partial-pre}, @option{-fpeel-loops}
|
|
and @option{-fipa-cp-clone} options.
|
|
|
|
@item -O0
|
|
@opindex O0
|
|
Reduce compilation time and make debugging produce the expected
|
|
results. This is the default.
|
|
|
|
@item -Os
|
|
@opindex Os
|
|
Optimize for size. @option{-Os} enables all @option{-O2} optimizations that
|
|
do not typically increase code size. It also performs further
|
|
optimizations designed to reduce code size.
|
|
|
|
@option{-Os} disables the following optimization flags:
|
|
@gccoptlist{-falign-functions -falign-jumps -falign-loops @gol
|
|
-falign-labels -freorder-blocks -freorder-blocks-algorithm=stc @gol
|
|
-freorder-blocks-and-partition -fprefetch-loop-arrays}
|
|
|
|
@item -Ofast
|
|
@opindex Ofast
|
|
Disregard strict standards compliance. @option{-Ofast} enables all
|
|
@option{-O3} optimizations. It also enables optimizations that are not
|
|
valid for all standard-compliant programs.
|
|
It turns on @option{-ffast-math} and the Fortran-specific
|
|
@option{-fno-protect-parens} and @option{-fstack-arrays}.
|
|
|
|
@item -Og
|
|
@opindex Og
|
|
Optimize debugging experience. @option{-Og} enables optimizations
|
|
that do not interfere with debugging. It should be the optimization
|
|
level of choice for the standard edit-compile-debug cycle, offering
|
|
a reasonable level of optimization while maintaining fast compilation
|
|
and a good debugging experience.
|
|
@end table
|
|
|
|
If you use multiple @option{-O} options, with or without level numbers,
|
|
the last such option is the one that is effective.
|
|
|
|
Options of the form @option{-f@var{flag}} specify machine-independent
|
|
flags. Most flags have both positive and negative forms; the negative
|
|
form of @option{-ffoo} is @option{-fno-foo}. In the table
|
|
below, only one of the forms is listed---the one you typically
|
|
use. You can figure out the other form by either removing @samp{no-}
|
|
or adding it.
|
|
|
|
The following options control specific optimizations. They are either
|
|
activated by @option{-O} options or are related to ones that are. You
|
|
can use the following flags in the rare cases when ``fine-tuning'' of
|
|
optimizations to be performed is desired.
|
|
|
|
@table @gcctabopt
|
|
@item -fno-defer-pop
|
|
@opindex fno-defer-pop
|
|
Always pop the arguments to each function call as soon as that function
|
|
returns. For machines that must pop arguments after a function call,
|
|
the compiler normally lets arguments accumulate on the stack for several
|
|
function calls and pops them all at once.
|
|
|
|
Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fforward-propagate
|
|
@opindex fforward-propagate
|
|
Perform a forward propagation pass on RTL@. The pass tries to combine two
|
|
instructions and checks if the result can be simplified. If loop unrolling
|
|
is active, two passes are performed and the second is scheduled after
|
|
loop unrolling.
|
|
|
|
This option is enabled by default at optimization levels @option{-O},
|
|
@option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -ffp-contract=@var{style}
|
|
@opindex ffp-contract
|
|
@option{-ffp-contract=off} disables floating-point expression contraction.
|
|
@option{-ffp-contract=fast} enables floating-point expression contraction
|
|
such as forming of fused multiply-add operations if the target has
|
|
native support for them.
|
|
@option{-ffp-contract=on} enables floating-point expression contraction
|
|
if allowed by the language standard. This is currently not implemented
|
|
and treated equal to @option{-ffp-contract=off}.
|
|
|
|
The default is @option{-ffp-contract=fast}.
|
|
|
|
@item -fomit-frame-pointer
|
|
@opindex fomit-frame-pointer
|
|
Don't keep the frame pointer in a register for functions that
|
|
don't need one. This avoids the instructions to save, set up and
|
|
restore frame pointers; it also makes an extra register available
|
|
in many functions. @strong{It also makes debugging impossible on
|
|
some machines.}
|
|
|
|
On some machines, such as the VAX, this flag has no effect, because
|
|
the standard calling sequence automatically handles the frame pointer
|
|
and nothing is saved by pretending it doesn't exist. The
|
|
machine-description macro @code{FRAME_POINTER_REQUIRED} controls
|
|
whether a target machine supports this flag. @xref{Registers,,Register
|
|
Usage, gccint, GNU Compiler Collection (GCC) Internals}.
|
|
|
|
The default setting (when not optimizing for
|
|
size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets is
|
|
@option{-fomit-frame-pointer}. You can configure GCC with the
|
|
@option{--enable-frame-pointer} configure option to change the default.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -foptimize-sibling-calls
|
|
@opindex foptimize-sibling-calls
|
|
Optimize sibling and tail recursive calls.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -foptimize-strlen
|
|
@opindex foptimize-strlen
|
|
Optimize various standard C string functions (e.g. @code{strlen},
|
|
@code{strchr} or @code{strcpy}) and
|
|
their @code{_FORTIFY_SOURCE} counterparts into faster alternatives.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -fno-inline
|
|
@opindex fno-inline
|
|
Do not expand any functions inline apart from those marked with
|
|
the @code{always_inline} attribute. This is the default when not
|
|
optimizing.
|
|
|
|
Single functions can be exempted from inlining by marking them
|
|
with the @code{noinline} attribute.
|
|
|
|
@item -finline-small-functions
|
|
@opindex finline-small-functions
|
|
Integrate functions into their callers when their body is smaller than expected
|
|
function call code (so overall size of program gets smaller). The compiler
|
|
heuristically decides which functions are simple enough to be worth integrating
|
|
in this way. This inlining applies to all functions, even those not declared
|
|
inline.
|
|
|
|
Enabled at level @option{-O2}.
|
|
|
|
@item -findirect-inlining
|
|
@opindex findirect-inlining
|
|
Inline also indirect calls that are discovered to be known at compile
|
|
time thanks to previous inlining. This option has any effect only
|
|
when inlining itself is turned on by the @option{-finline-functions}
|
|
or @option{-finline-small-functions} options.
|
|
|
|
Enabled at level @option{-O2}.
|
|
|
|
@item -finline-functions
|
|
@opindex finline-functions
|
|
Consider all functions for inlining, even if they are not declared inline.
|
|
The compiler heuristically decides which functions are worth integrating
|
|
in this way.
|
|
|
|
If all calls to a given function are integrated, and the function is
|
|
declared @code{static}, then the function is normally not output as
|
|
assembler code in its own right.
|
|
|
|
Enabled at level @option{-O3}.
|
|
|
|
@item -finline-functions-called-once
|
|
@opindex finline-functions-called-once
|
|
Consider all @code{static} functions called once for inlining into their
|
|
caller even if they are not marked @code{inline}. If a call to a given
|
|
function is integrated, then the function is not output as assembler code
|
|
in its own right.
|
|
|
|
Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}.
|
|
|
|
@item -fearly-inlining
|
|
@opindex fearly-inlining
|
|
Inline functions marked by @code{always_inline} and functions whose body seems
|
|
smaller than the function call overhead early before doing
|
|
@option{-fprofile-generate} instrumentation and real inlining pass. Doing so
|
|
makes profiling significantly cheaper and usually inlining faster on programs
|
|
having large chains of nested wrapper functions.
|
|
|
|
Enabled by default.
|
|
|
|
@item -fipa-sra
|
|
@opindex fipa-sra
|
|
Perform interprocedural scalar replacement of aggregates, removal of
|
|
unused parameters and replacement of parameters passed by reference
|
|
by parameters passed by value.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}.
|
|
|
|
@item -finline-limit=@var{n}
|
|
@opindex finline-limit
|
|
By default, GCC limits the size of functions that can be inlined. This flag
|
|
allows coarse control of this limit. @var{n} is the size of functions that
|
|
can be inlined in number of pseudo instructions.
|
|
|
|
Inlining is actually controlled by a number of parameters, which may be
|
|
specified individually by using @option{--param @var{name}=@var{value}}.
|
|
The @option{-finline-limit=@var{n}} option sets some of these parameters
|
|
as follows:
|
|
|
|
@table @gcctabopt
|
|
@item max-inline-insns-single
|
|
is set to @var{n}/2.
|
|
@item max-inline-insns-auto
|
|
is set to @var{n}/2.
|
|
@end table
|
|
|
|
See below for a documentation of the individual
|
|
parameters controlling inlining and for the defaults of these parameters.
|
|
|
|
@emph{Note:} there may be no value to @option{-finline-limit} that results
|
|
in default behavior.
|
|
|
|
@emph{Note:} pseudo instruction represents, in this particular context, an
|
|
abstract measurement of function's size. In no way does it represent a count
|
|
of assembly instructions and as such its exact meaning might change from one
|
|
release to an another.
|
|
|
|
@item -fno-keep-inline-dllexport
|
|
@opindex fno-keep-inline-dllexport
|
|
This is a more fine-grained version of @option{-fkeep-inline-functions},
|
|
which applies only to functions that are declared using the @code{dllexport}
|
|
attribute or declspec. @xref{Function Attributes,,Declaring Attributes of
|
|
Functions}.
|
|
|
|
@item -fkeep-inline-functions
|
|
@opindex fkeep-inline-functions
|
|
In C, emit @code{static} functions that are declared @code{inline}
|
|
into the object file, even if the function has been inlined into all
|
|
of its callers. This switch does not affect functions using the
|
|
@code{extern inline} extension in GNU C90@. In C++, emit any and all
|
|
inline functions into the object file.
|
|
|
|
@item -fkeep-static-functions
|
|
@opindex fkeep-static-functions
|
|
Emit @code{static} functions into the object file, even if the function
|
|
is never used.
|
|
|
|
@item -fkeep-static-consts
|
|
@opindex fkeep-static-consts
|
|
Emit variables declared @code{static const} when optimization isn't turned
|
|
on, even if the variables aren't referenced.
|
|
|
|
GCC enables this option by default. If you want to force the compiler to
|
|
check if a variable is referenced, regardless of whether or not
|
|
optimization is turned on, use the @option{-fno-keep-static-consts} option.
|
|
|
|
@item -fmerge-constants
|
|
@opindex fmerge-constants
|
|
Attempt to merge identical constants (string constants and floating-point
|
|
constants) across compilation units.
|
|
|
|
This option is the default for optimized compilation if the assembler and
|
|
linker support it. Use @option{-fno-merge-constants} to inhibit this
|
|
behavior.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fmerge-all-constants
|
|
@opindex fmerge-all-constants
|
|
Attempt to merge identical constants and identical variables.
|
|
|
|
This option implies @option{-fmerge-constants}. In addition to
|
|
@option{-fmerge-constants} this considers e.g.@: even constant initialized
|
|
arrays or initialized constant variables with integral or floating-point
|
|
types. Languages like C or C++ require each variable, including multiple
|
|
instances of the same variable in recursive calls, to have distinct locations,
|
|
so using this option results in non-conforming
|
|
behavior.
|
|
|
|
@item -fmodulo-sched
|
|
@opindex fmodulo-sched
|
|
Perform swing modulo scheduling immediately before the first scheduling
|
|
pass. This pass looks at innermost loops and reorders their
|
|
instructions by overlapping different iterations.
|
|
|
|
@item -fmodulo-sched-allow-regmoves
|
|
@opindex fmodulo-sched-allow-regmoves
|
|
Perform more aggressive SMS-based modulo scheduling with register moves
|
|
allowed. By setting this flag certain anti-dependences edges are
|
|
deleted, which triggers the generation of reg-moves based on the
|
|
life-range analysis. This option is effective only with
|
|
@option{-fmodulo-sched} enabled.
|
|
|
|
@item -fno-branch-count-reg
|
|
@opindex fno-branch-count-reg
|
|
Avoid running a pass scanning for opportunities to use ``decrement and
|
|
branch'' instructions on a count register instead of generating sequences
|
|
of instructions that decrement a register, compare it against zero, and
|
|
then branch based upon the result. This option is only meaningful on
|
|
architectures that support such instructions, which include x86, PowerPC,
|
|
IA-64 and S/390. Note that the @option{-fno-branch-count-reg} option
|
|
doesn't remove the decrement and branch instructions from the generated
|
|
instruction stream introduced by other optimization passes.
|
|
|
|
Enabled by default at @option{-O1} and higher.
|
|
|
|
The default is @option{-fbranch-count-reg}.
|
|
|
|
@item -fno-function-cse
|
|
@opindex fno-function-cse
|
|
Do not put function addresses in registers; make each instruction that
|
|
calls a constant function contain the function's address explicitly.
|
|
|
|
This option results in less efficient code, but some strange hacks
|
|
that alter the assembler output may be confused by the optimizations
|
|
performed when this option is not used.
|
|
|
|
The default is @option{-ffunction-cse}
|
|
|
|
@item -fno-zero-initialized-in-bss
|
|
@opindex fno-zero-initialized-in-bss
|
|
If the target supports a BSS section, GCC by default puts variables that
|
|
are initialized to zero into BSS@. This can save space in the resulting
|
|
code.
|
|
|
|
This option turns off this behavior because some programs explicitly
|
|
rely on variables going to the data section---e.g., so that the
|
|
resulting executable can find the beginning of that section and/or make
|
|
assumptions based on that.
|
|
|
|
The default is @option{-fzero-initialized-in-bss}.
|
|
|
|
@item -fthread-jumps
|
|
@opindex fthread-jumps
|
|
Perform optimizations that check to see if a jump branches to a
|
|
location where another comparison subsumed by the first is found. If
|
|
so, the first branch is redirected to either the destination of the
|
|
second branch or a point immediately following it, depending on whether
|
|
the condition is known to be true or false.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fsplit-wide-types
|
|
@opindex fsplit-wide-types
|
|
When using a type that occupies multiple registers, such as @code{long
|
|
long} on a 32-bit system, split the registers apart and allocate them
|
|
independently. This normally generates better code for those types,
|
|
but may make debugging more difficult.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3},
|
|
@option{-Os}.
|
|
|
|
@item -fcse-follow-jumps
|
|
@opindex fcse-follow-jumps
|
|
In common subexpression elimination (CSE), scan through jump instructions
|
|
when the target of the jump is not reached by any other path. For
|
|
example, when CSE encounters an @code{if} statement with an
|
|
@code{else} clause, CSE follows the jump when the condition
|
|
tested is false.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fcse-skip-blocks
|
|
@opindex fcse-skip-blocks
|
|
This is similar to @option{-fcse-follow-jumps}, but causes CSE to
|
|
follow jumps that conditionally skip over blocks. When CSE
|
|
encounters a simple @code{if} statement with no else clause,
|
|
@option{-fcse-skip-blocks} causes CSE to follow the jump around the
|
|
body of the @code{if}.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -frerun-cse-after-loop
|
|
@opindex frerun-cse-after-loop
|
|
Re-run common subexpression elimination after loop optimizations are
|
|
performed.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fgcse
|
|
@opindex fgcse
|
|
Perform a global common subexpression elimination pass.
|
|
This pass also performs global constant and copy propagation.
|
|
|
|
@emph{Note:} When compiling a program using computed gotos, a GCC
|
|
extension, you may get better run-time performance if you disable
|
|
the global common subexpression elimination pass by adding
|
|
@option{-fno-gcse} to the command line.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fgcse-lm
|
|
@opindex fgcse-lm
|
|
When @option{-fgcse-lm} is enabled, global common subexpression elimination
|
|
attempts to move loads that are only killed by stores into themselves. This
|
|
allows a loop containing a load/store sequence to be changed to a load outside
|
|
the loop, and a copy/store within the loop.
|
|
|
|
Enabled by default when @option{-fgcse} is enabled.
|
|
|
|
@item -fgcse-sm
|
|
@opindex fgcse-sm
|
|
When @option{-fgcse-sm} is enabled, a store motion pass is run after
|
|
global common subexpression elimination. This pass attempts to move
|
|
stores out of loops. When used in conjunction with @option{-fgcse-lm},
|
|
loops containing a load/store sequence can be changed to a load before
|
|
the loop and a store after the loop.
|
|
|
|
Not enabled at any optimization level.
|
|
|
|
@item -fgcse-las
|
|
@opindex fgcse-las
|
|
When @option{-fgcse-las} is enabled, the global common subexpression
|
|
elimination pass eliminates redundant loads that come after stores to the
|
|
same memory location (both partial and full redundancies).
|
|
|
|
Not enabled at any optimization level.
|
|
|
|
@item -fgcse-after-reload
|
|
@opindex fgcse-after-reload
|
|
When @option{-fgcse-after-reload} is enabled, a redundant load elimination
|
|
pass is performed after reload. The purpose of this pass is to clean up
|
|
redundant spilling.
|
|
|
|
@item -faggressive-loop-optimizations
|
|
@opindex faggressive-loop-optimizations
|
|
This option tells the loop optimizer to use language constraints to
|
|
derive bounds for the number of iterations of a loop. This assumes that
|
|
loop code does not invoke undefined behavior by for example causing signed
|
|
integer overflows or out-of-bound array accesses. The bounds for the
|
|
number of iterations of a loop are used to guide loop unrolling and peeling
|
|
and loop exit test optimizations.
|
|
This option is enabled by default.
|
|
|
|
@item -funconstrained-commons
|
|
@opindex funconstrained-commons
|
|
This option tells the compiler that variables declared in common blocks
|
|
(e.g. Fortran) may later be overridden with longer trailing arrays. This
|
|
prevents certain optimizations that depend on knowing the array bounds.
|
|
|
|
@item -fcrossjumping
|
|
@opindex fcrossjumping
|
|
Perform cross-jumping transformation.
|
|
This transformation unifies equivalent code and saves code size. The
|
|
resulting code may or may not perform better than without cross-jumping.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fauto-inc-dec
|
|
@opindex fauto-inc-dec
|
|
Combine increments or decrements of addresses with memory accesses.
|
|
This pass is always skipped on architectures that do not have
|
|
instructions to support this. Enabled by default at @option{-O} and
|
|
higher on architectures that support this.
|
|
|
|
@item -fdce
|
|
@opindex fdce
|
|
Perform dead code elimination (DCE) on RTL@.
|
|
Enabled by default at @option{-O} and higher.
|
|
|
|
@item -fdse
|
|
@opindex fdse
|
|
Perform dead store elimination (DSE) on RTL@.
|
|
Enabled by default at @option{-O} and higher.
|
|
|
|
@item -fif-conversion
|
|
@opindex fif-conversion
|
|
Attempt to transform conditional jumps into branch-less equivalents. This
|
|
includes use of conditional moves, min, max, set flags and abs instructions, and
|
|
some tricks doable by standard arithmetics. The use of conditional execution
|
|
on chips where it is available is controlled by @option{-fif-conversion2}.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fif-conversion2
|
|
@opindex fif-conversion2
|
|
Use conditional execution (where available) to transform conditional jumps into
|
|
branch-less equivalents.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fdeclone-ctor-dtor
|
|
@opindex fdeclone-ctor-dtor
|
|
The C++ ABI requires multiple entry points for constructors and
|
|
destructors: one for a base subobject, one for a complete object, and
|
|
one for a virtual destructor that calls operator delete afterwards.
|
|
For a hierarchy with virtual bases, the base and complete variants are
|
|
clones, which means two copies of the function. With this option, the
|
|
base and complete variants are changed to be thunks that call a common
|
|
implementation.
|
|
|
|
Enabled by @option{-Os}.
|
|
|
|
@item -fdelete-null-pointer-checks
|
|
@opindex fdelete-null-pointer-checks
|
|
Assume that programs cannot safely dereference null pointers, and that
|
|
no code or data element resides at address zero.
|
|
This option enables simple constant
|
|
folding optimizations at all optimization levels. In addition, other
|
|
optimization passes in GCC use this flag to control global dataflow
|
|
analyses that eliminate useless checks for null pointers; these assume
|
|
that a memory access to address zero always results in a trap, so
|
|
that if a pointer is checked after it has already been dereferenced,
|
|
it cannot be null.
|
|
|
|
Note however that in some environments this assumption is not true.
|
|
Use @option{-fno-delete-null-pointer-checks} to disable this optimization
|
|
for programs that depend on that behavior.
|
|
|
|
This option is enabled by default on most targets. On Nios II ELF, it
|
|
defaults to off. On AVR and CR16, this option is completely disabled.
|
|
|
|
Passes that use the dataflow information
|
|
are enabled independently at different optimization levels.
|
|
|
|
@item -fdevirtualize
|
|
@opindex fdevirtualize
|
|
Attempt to convert calls to virtual functions to direct calls. This
|
|
is done both within a procedure and interprocedurally as part of
|
|
indirect inlining (@option{-findirect-inlining}) and interprocedural constant
|
|
propagation (@option{-fipa-cp}).
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fdevirtualize-speculatively
|
|
@opindex fdevirtualize-speculatively
|
|
Attempt to convert calls to virtual functions to speculative direct calls.
|
|
Based on the analysis of the type inheritance graph, determine for a given call
|
|
the set of likely targets. If the set is small, preferably of size 1, change
|
|
the call into a conditional deciding between direct and indirect calls. The
|
|
speculative calls enable more optimizations, such as inlining. When they seem
|
|
useless after further optimization, they are converted back into original form.
|
|
|
|
@item -fdevirtualize-at-ltrans
|
|
@opindex fdevirtualize-at-ltrans
|
|
Stream extra information needed for aggressive devirtualization when running
|
|
the link-time optimizer in local transformation mode.
|
|
This option enables more devirtualization but
|
|
significantly increases the size of streamed data. For this reason it is
|
|
disabled by default.
|
|
|
|
@item -fexpensive-optimizations
|
|
@opindex fexpensive-optimizations
|
|
Perform a number of minor optimizations that are relatively expensive.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -free
|
|
@opindex free
|
|
Attempt to remove redundant extension instructions. This is especially
|
|
helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit
|
|
registers after writing to their lower 32-bit half.
|
|
|
|
Enabled for Alpha, AArch64 and x86 at levels @option{-O2},
|
|
@option{-O3}, @option{-Os}.
|
|
|
|
@item -fno-lifetime-dse
|
|
@opindex fno-lifetime-dse
|
|
In C++ the value of an object is only affected by changes within its
|
|
lifetime: when the constructor begins, the object has an indeterminate
|
|
value, and any changes during the lifetime of the object are dead when
|
|
the object is destroyed. Normally dead store elimination will take
|
|
advantage of this; if your code relies on the value of the object
|
|
storage persisting beyond the lifetime of the object, you can use this
|
|
flag to disable this optimization. To preserve stores before the
|
|
constructor starts (e.g. because your operator new clears the object
|
|
storage) but still treat the object as dead after the destructor you,
|
|
can use @option{-flifetime-dse=1}. The default behavior can be
|
|
explicitly selected with @option{-flifetime-dse=2}.
|
|
@option{-flifetime-dse=0} is equivalent to @option{-fno-lifetime-dse}.
|
|
|
|
@item -flive-range-shrinkage
|
|
@opindex flive-range-shrinkage
|
|
Attempt to decrease register pressure through register live range
|
|
shrinkage. This is helpful for fast processors with small or moderate
|
|
size register sets.
|
|
|
|
@item -fira-algorithm=@var{algorithm}
|
|
@opindex fira-algorithm
|
|
Use the specified coloring algorithm for the integrated register
|
|
allocator. The @var{algorithm} argument can be @samp{priority}, which
|
|
specifies Chow's priority coloring, or @samp{CB}, which specifies
|
|
Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented
|
|
for all architectures, but for those targets that do support it, it is
|
|
the default because it generates better code.
|
|
|
|
@item -fira-region=@var{region}
|
|
@opindex fira-region
|
|
Use specified regions for the integrated register allocator. The
|
|
@var{region} argument should be one of the following:
|
|
|
|
@table @samp
|
|
|
|
@item all
|
|
Use all loops as register allocation regions.
|
|
This can give the best results for machines with a small and/or
|
|
irregular register set.
|
|
|
|
@item mixed
|
|
Use all loops except for loops with small register pressure
|
|
as the regions. This value usually gives
|
|
the best results in most cases and for most architectures,
|
|
and is enabled by default when compiling with optimization for speed
|
|
(@option{-O}, @option{-O2}, @dots{}).
|
|
|
|
@item one
|
|
Use all functions as a single region.
|
|
This typically results in the smallest code size, and is enabled by default for
|
|
@option{-Os} or @option{-O0}.
|
|
|
|
@end table
|
|
|
|
@item -fira-hoist-pressure
|
|
@opindex fira-hoist-pressure
|
|
Use IRA to evaluate register pressure in the code hoisting pass for
|
|
decisions to hoist expressions. This option usually results in smaller
|
|
code, but it can slow the compiler down.
|
|
|
|
This option is enabled at level @option{-Os} for all targets.
|
|
|
|
@item -fira-loop-pressure
|
|
@opindex fira-loop-pressure
|
|
Use IRA to evaluate register pressure in loops for decisions to move
|
|
loop invariants. This option usually results in generation
|
|
of faster and smaller code on machines with large register files (>= 32
|
|
registers), but it can slow the compiler down.
|
|
|
|
This option is enabled at level @option{-O3} for some targets.
|
|
|
|
@item -fno-ira-share-save-slots
|
|
@opindex fno-ira-share-save-slots
|
|
Disable sharing of stack slots used for saving call-used hard
|
|
registers living through a call. Each hard register gets a
|
|
separate stack slot, and as a result function stack frames are
|
|
larger.
|
|
|
|
@item -fno-ira-share-spill-slots
|
|
@opindex fno-ira-share-spill-slots
|
|
Disable sharing of stack slots allocated for pseudo-registers. Each
|
|
pseudo-register that does not get a hard register gets a separate
|
|
stack slot, and as a result function stack frames are larger.
|
|
|
|
@item -flra-remat
|
|
@opindex flra-remat
|
|
Enable CFG-sensitive rematerialization in LRA. Instead of loading
|
|
values of spilled pseudos, LRA tries to rematerialize (recalculate)
|
|
values if it is profitable.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fdelayed-branch
|
|
@opindex fdelayed-branch
|
|
If supported for the target machine, attempt to reorder instructions
|
|
to exploit instruction slots available after delayed branch
|
|
instructions.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fschedule-insns
|
|
@opindex fschedule-insns
|
|
If supported for the target machine, attempt to reorder instructions to
|
|
eliminate execution stalls due to required data being unavailable. This
|
|
helps machines that have slow floating point or memory load instructions
|
|
by allowing other instructions to be issued until the result of the load
|
|
or floating-point instruction is required.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -fschedule-insns2
|
|
@opindex fschedule-insns2
|
|
Similar to @option{-fschedule-insns}, but requests an additional pass of
|
|
instruction scheduling after register allocation has been done. This is
|
|
especially useful on machines with a relatively small number of
|
|
registers and where memory load instructions take more than one cycle.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fno-sched-interblock
|
|
@opindex fno-sched-interblock
|
|
Don't schedule instructions across basic blocks. This is normally
|
|
enabled by default when scheduling before register allocation, i.e.@:
|
|
with @option{-fschedule-insns} or at @option{-O2} or higher.
|
|
|
|
@item -fno-sched-spec
|
|
@opindex fno-sched-spec
|
|
Don't allow speculative motion of non-load instructions. This is normally
|
|
enabled by default when scheduling before register allocation, i.e.@:
|
|
with @option{-fschedule-insns} or at @option{-O2} or higher.
|
|
|
|
@item -fsched-pressure
|
|
@opindex fsched-pressure
|
|
Enable register pressure sensitive insn scheduling before register
|
|
allocation. This only makes sense when scheduling before register
|
|
allocation is enabled, i.e.@: with @option{-fschedule-insns} or at
|
|
@option{-O2} or higher. Usage of this option can improve the
|
|
generated code and decrease its size by preventing register pressure
|
|
increase above the number of available hard registers and subsequent
|
|
spills in register allocation.
|
|
|
|
@item -fsched-spec-load
|
|
@opindex fsched-spec-load
|
|
Allow speculative motion of some load instructions. This only makes
|
|
sense when scheduling before register allocation, i.e.@: with
|
|
@option{-fschedule-insns} or at @option{-O2} or higher.
|
|
|
|
@item -fsched-spec-load-dangerous
|
|
@opindex fsched-spec-load-dangerous
|
|
Allow speculative motion of more load instructions. This only makes
|
|
sense when scheduling before register allocation, i.e.@: with
|
|
@option{-fschedule-insns} or at @option{-O2} or higher.
|
|
|
|
@item -fsched-stalled-insns
|
|
@itemx -fsched-stalled-insns=@var{n}
|
|
@opindex fsched-stalled-insns
|
|
Define how many insns (if any) can be moved prematurely from the queue
|
|
of stalled insns into the ready list during the second scheduling pass.
|
|
@option{-fno-sched-stalled-insns} means that no insns are moved
|
|
prematurely, @option{-fsched-stalled-insns=0} means there is no limit
|
|
on how many queued insns can be moved prematurely.
|
|
@option{-fsched-stalled-insns} without a value is equivalent to
|
|
@option{-fsched-stalled-insns=1}.
|
|
|
|
@item -fsched-stalled-insns-dep
|
|
@itemx -fsched-stalled-insns-dep=@var{n}
|
|
@opindex fsched-stalled-insns-dep
|
|
Define how many insn groups (cycles) are examined for a dependency
|
|
on a stalled insn that is a candidate for premature removal from the queue
|
|
of stalled insns. This has an effect only during the second scheduling pass,
|
|
and only if @option{-fsched-stalled-insns} is used.
|
|
@option{-fno-sched-stalled-insns-dep} is equivalent to
|
|
@option{-fsched-stalled-insns-dep=0}.
|
|
@option{-fsched-stalled-insns-dep} without a value is equivalent to
|
|
@option{-fsched-stalled-insns-dep=1}.
|
|
|
|
@item -fsched2-use-superblocks
|
|
@opindex fsched2-use-superblocks
|
|
When scheduling after register allocation, use superblock scheduling.
|
|
This allows motion across basic block boundaries,
|
|
resulting in faster schedules. This option is experimental, as not all machine
|
|
descriptions used by GCC model the CPU closely enough to avoid unreliable
|
|
results from the algorithm.
|
|
|
|
This only makes sense when scheduling after register allocation, i.e.@: with
|
|
@option{-fschedule-insns2} or at @option{-O2} or higher.
|
|
|
|
@item -fsched-group-heuristic
|
|
@opindex fsched-group-heuristic
|
|
Enable the group heuristic in the scheduler. This heuristic favors
|
|
the instruction that belongs to a schedule group. This is enabled
|
|
by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns}
|
|
or @option{-fschedule-insns2} or at @option{-O2} or higher.
|
|
|
|
@item -fsched-critical-path-heuristic
|
|
@opindex fsched-critical-path-heuristic
|
|
Enable the critical-path heuristic in the scheduler. This heuristic favors
|
|
instructions on the critical path. This is enabled by default when
|
|
scheduling is enabled, i.e.@: with @option{-fschedule-insns}
|
|
or @option{-fschedule-insns2} or at @option{-O2} or higher.
|
|
|
|
@item -fsched-spec-insn-heuristic
|
|
@opindex fsched-spec-insn-heuristic
|
|
Enable the speculative instruction heuristic in the scheduler. This
|
|
heuristic favors speculative instructions with greater dependency weakness.
|
|
This is enabled by default when scheduling is enabled, i.e.@:
|
|
with @option{-fschedule-insns} or @option{-fschedule-insns2}
|
|
or at @option{-O2} or higher.
|
|
|
|
@item -fsched-rank-heuristic
|
|
@opindex fsched-rank-heuristic
|
|
Enable the rank heuristic in the scheduler. This heuristic favors
|
|
the instruction belonging to a basic block with greater size or frequency.
|
|
This is enabled by default when scheduling is enabled, i.e.@:
|
|
with @option{-fschedule-insns} or @option{-fschedule-insns2} or
|
|
at @option{-O2} or higher.
|
|
|
|
@item -fsched-last-insn-heuristic
|
|
@opindex fsched-last-insn-heuristic
|
|
Enable the last-instruction heuristic in the scheduler. This heuristic
|
|
favors the instruction that is less dependent on the last instruction
|
|
scheduled. This is enabled by default when scheduling is enabled,
|
|
i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or
|
|
at @option{-O2} or higher.
|
|
|
|
@item -fsched-dep-count-heuristic
|
|
@opindex fsched-dep-count-heuristic
|
|
Enable the dependent-count heuristic in the scheduler. This heuristic
|
|
favors the instruction that has more instructions depending on it.
|
|
This is enabled by default when scheduling is enabled, i.e.@:
|
|
with @option{-fschedule-insns} or @option{-fschedule-insns2} or
|
|
at @option{-O2} or higher.
|
|
|
|
@item -freschedule-modulo-scheduled-loops
|
|
@opindex freschedule-modulo-scheduled-loops
|
|
Modulo scheduling is performed before traditional scheduling. If a loop
|
|
is modulo scheduled, later scheduling passes may change its schedule.
|
|
Use this option to control that behavior.
|
|
|
|
@item -fselective-scheduling
|
|
@opindex fselective-scheduling
|
|
Schedule instructions using selective scheduling algorithm. Selective
|
|
scheduling runs instead of the first scheduler pass.
|
|
|
|
@item -fselective-scheduling2
|
|
@opindex fselective-scheduling2
|
|
Schedule instructions using selective scheduling algorithm. Selective
|
|
scheduling runs instead of the second scheduler pass.
|
|
|
|
@item -fsel-sched-pipelining
|
|
@opindex fsel-sched-pipelining
|
|
Enable software pipelining of innermost loops during selective scheduling.
|
|
This option has no effect unless one of @option{-fselective-scheduling} or
|
|
@option{-fselective-scheduling2} is turned on.
|
|
|
|
@item -fsel-sched-pipelining-outer-loops
|
|
@opindex fsel-sched-pipelining-outer-loops
|
|
When pipelining loops during selective scheduling, also pipeline outer loops.
|
|
This option has no effect unless @option{-fsel-sched-pipelining} is turned on.
|
|
|
|
@item -fsemantic-interposition
|
|
@opindex fsemantic-interposition
|
|
Some object formats, like ELF, allow interposing of symbols by the
|
|
dynamic linker.
|
|
This means that for symbols exported from the DSO, the compiler cannot perform
|
|
interprocedural propagation, inlining and other optimizations in anticipation
|
|
that the function or variable in question may change. While this feature is
|
|
useful, for example, to rewrite memory allocation functions by a debugging
|
|
implementation, it is expensive in the terms of code quality.
|
|
With @option{-fno-semantic-interposition} the compiler assumes that
|
|
if interposition happens for functions the overwriting function will have
|
|
precisely the same semantics (and side effects).
|
|
Similarly if interposition happens
|
|
for variables, the constructor of the variable will be the same. The flag
|
|
has no effect for functions explicitly declared inline
|
|
(where it is never allowed for interposition to change semantics)
|
|
and for symbols explicitly declared weak.
|
|
|
|
@item -fshrink-wrap
|
|
@opindex fshrink-wrap
|
|
Emit function prologues only before parts of the function that need it,
|
|
rather than at the top of the function. This flag is enabled by default at
|
|
@option{-O} and higher.
|
|
|
|
@item -fshrink-wrap-separate
|
|
@opindex fshrink-wrap-separate
|
|
Shrink-wrap separate parts of the prologue and epilogue separately, so that
|
|
those parts are only executed when needed.
|
|
This option is on by default, but has no effect unless @option{-fshrink-wrap}
|
|
is also turned on and the target supports this.
|
|
|
|
@item -fcaller-saves
|
|
@opindex fcaller-saves
|
|
Enable allocation of values to registers that are clobbered by
|
|
function calls, by emitting extra instructions to save and restore the
|
|
registers around such calls. Such allocation is done only when it
|
|
seems to result in better code.
|
|
|
|
This option is always enabled by default on certain machines, usually
|
|
those which have no call-preserved registers to use instead.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fcombine-stack-adjustments
|
|
@opindex fcombine-stack-adjustments
|
|
Tracks stack adjustments (pushes and pops) and stack memory references
|
|
and then tries to find ways to combine them.
|
|
|
|
Enabled by default at @option{-O1} and higher.
|
|
|
|
@item -fipa-ra
|
|
@opindex fipa-ra
|
|
Use caller save registers for allocation if those registers are not used by
|
|
any called function. In that case it is not necessary to save and restore
|
|
them around calls. This is only possible if called functions are part of
|
|
same compilation unit as current function and they are compiled before it.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, however the option
|
|
is disabled if generated code will be instrumented for profiling
|
|
(@option{-p}, or @option{-pg}) or if callee's register usage cannot be known
|
|
exactly (this happens on targets that do not expose prologues
|
|
and epilogues in RTL).
|
|
|
|
@item -fconserve-stack
|
|
@opindex fconserve-stack
|
|
Attempt to minimize stack usage. The compiler attempts to use less
|
|
stack space, even if that makes the program slower. This option
|
|
implies setting the @option{large-stack-frame} parameter to 100
|
|
and the @option{large-stack-frame-growth} parameter to 400.
|
|
|
|
@item -ftree-reassoc
|
|
@opindex ftree-reassoc
|
|
Perform reassociation on trees. This flag is enabled by default
|
|
at @option{-O} and higher.
|
|
|
|
@item -fcode-hoisting
|
|
@opindex fcode-hoisting
|
|
Perform code hoisting. Code hoisting tries to move the
|
|
evaluation of expressions executed on all paths to the function exit
|
|
as early as possible. This is especially useful as a code size
|
|
optimization, but it often helps for code speed as well.
|
|
This flag is enabled by default at @option{-O2} and higher.
|
|
|
|
@item -ftree-pre
|
|
@opindex ftree-pre
|
|
Perform partial redundancy elimination (PRE) on trees. This flag is
|
|
enabled by default at @option{-O2} and @option{-O3}.
|
|
|
|
@item -ftree-partial-pre
|
|
@opindex ftree-partial-pre
|
|
Make partial redundancy elimination (PRE) more aggressive. This flag is
|
|
enabled by default at @option{-O3}.
|
|
|
|
@item -ftree-forwprop
|
|
@opindex ftree-forwprop
|
|
Perform forward propagation on trees. This flag is enabled by default
|
|
at @option{-O} and higher.
|
|
|
|
@item -ftree-fre
|
|
@opindex ftree-fre
|
|
Perform full redundancy elimination (FRE) on trees. The difference
|
|
between FRE and PRE is that FRE only considers expressions
|
|
that are computed on all paths leading to the redundant computation.
|
|
This analysis is faster than PRE, though it exposes fewer redundancies.
|
|
This flag is enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-phiprop
|
|
@opindex ftree-phiprop
|
|
Perform hoisting of loads from conditional pointers on trees. This
|
|
pass is enabled by default at @option{-O} and higher.
|
|
|
|
@item -fhoist-adjacent-loads
|
|
@opindex fhoist-adjacent-loads
|
|
Speculatively hoist loads from both branches of an if-then-else if the
|
|
loads are from adjacent locations in the same structure and the target
|
|
architecture has a conditional move instruction. This flag is enabled
|
|
by default at @option{-O2} and higher.
|
|
|
|
@item -ftree-copy-prop
|
|
@opindex ftree-copy-prop
|
|
Perform copy propagation on trees. This pass eliminates unnecessary
|
|
copy operations. This flag is enabled by default at @option{-O} and
|
|
higher.
|
|
|
|
@item -fipa-pure-const
|
|
@opindex fipa-pure-const
|
|
Discover which functions are pure or constant.
|
|
Enabled by default at @option{-O} and higher.
|
|
|
|
@item -fipa-reference
|
|
@opindex fipa-reference
|
|
Discover which static variables do not escape the
|
|
compilation unit.
|
|
Enabled by default at @option{-O} and higher.
|
|
|
|
@item -fipa-pta
|
|
@opindex fipa-pta
|
|
Perform interprocedural pointer analysis and interprocedural modification
|
|
and reference analysis. This option can cause excessive memory and
|
|
compile-time usage on large compilation units. It is not enabled by
|
|
default at any optimization level.
|
|
|
|
@item -fipa-profile
|
|
@opindex fipa-profile
|
|
Perform interprocedural profile propagation. The functions called only from
|
|
cold functions are marked as cold. Also functions executed once (such as
|
|
@code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold
|
|
functions and loop less parts of functions executed once are then optimized for
|
|
size.
|
|
Enabled by default at @option{-O} and higher.
|
|
|
|
@item -fipa-cp
|
|
@opindex fipa-cp
|
|
Perform interprocedural constant propagation.
|
|
This optimization analyzes the program to determine when values passed
|
|
to functions are constants and then optimizes accordingly.
|
|
This optimization can substantially increase performance
|
|
if the application has constants passed to functions.
|
|
This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}.
|
|
|
|
@item -fipa-cp-clone
|
|
@opindex fipa-cp-clone
|
|
Perform function cloning to make interprocedural constant propagation stronger.
|
|
When enabled, interprocedural constant propagation performs function cloning
|
|
when externally visible function can be called with constant arguments.
|
|
Because this optimization can create multiple copies of functions,
|
|
it may significantly increase code size
|
|
(see @option{--param ipcp-unit-growth=@var{value}}).
|
|
This flag is enabled by default at @option{-O3}.
|
|
|
|
@item -fipa-cp-alignment
|
|
@opindex -fipa-cp-alignment
|
|
When enabled, this optimization propagates alignment of function
|
|
parameters to support better vectorization and string operations.
|
|
|
|
This flag is enabled by default at @option{-O2} and @option{-Os}. It
|
|
requires that @option{-fipa-cp} is enabled.
|
|
@option{-fipa-cp-alignment} is obsolete, use @option{-fipa-bit-cp} instead.
|
|
|
|
@item -fipa-bit-cp
|
|
@opindex -fipa-bit-cp
|
|
When enabled, perform ipa bitwise constant propagation. This flag is
|
|
enabled by default at @option{-O2}. It requires that @option{-fipa-cp}
|
|
is enabled.
|
|
|
|
@item -fipa-icf
|
|
@opindex fipa-icf
|
|
Perform Identical Code Folding for functions and read-only variables.
|
|
The optimization reduces code size and may disturb unwind stacks by replacing
|
|
a function by equivalent one with a different name. The optimization works
|
|
more effectively with link time optimization enabled.
|
|
|
|
Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF
|
|
works on different levels and thus the optimizations are not same - there are
|
|
equivalences that are found only by GCC and equivalences found only by Gold.
|
|
|
|
This flag is enabled by default at @option{-O2} and @option{-Os}.
|
|
|
|
@item -fisolate-erroneous-paths-dereference
|
|
@opindex fisolate-erroneous-paths-dereference
|
|
Detect paths that trigger erroneous or undefined behavior due to
|
|
dereferencing a null pointer. Isolate those paths from the main control
|
|
flow and turn the statement with erroneous or undefined behavior into a trap.
|
|
This flag is enabled by default at @option{-O2} and higher and depends on
|
|
@option{-fdelete-null-pointer-checks} also being enabled.
|
|
|
|
@item -fisolate-erroneous-paths-attribute
|
|
@opindex fisolate-erroneous-paths-attribute
|
|
Detect paths that trigger erroneous or undefined behavior due a null value
|
|
being used in a way forbidden by a @code{returns_nonnull} or @code{nonnull}
|
|
attribute. Isolate those paths from the main control flow and turn the
|
|
statement with erroneous or undefined behavior into a trap. This is not
|
|
currently enabled, but may be enabled by @option{-O2} in the future.
|
|
|
|
@item -ftree-sink
|
|
@opindex ftree-sink
|
|
Perform forward store motion on trees. This flag is
|
|
enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-bit-ccp
|
|
@opindex ftree-bit-ccp
|
|
Perform sparse conditional bit constant propagation on trees and propagate
|
|
pointer alignment information.
|
|
This pass only operates on local scalar variables and is enabled by default
|
|
at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled.
|
|
|
|
@item -ftree-ccp
|
|
@opindex ftree-ccp
|
|
Perform sparse conditional constant propagation (CCP) on trees. This
|
|
pass only operates on local scalar variables and is enabled by default
|
|
at @option{-O} and higher.
|
|
|
|
@item -fssa-backprop
|
|
@opindex fssa-backprop
|
|
Propagate information about uses of a value up the definition chain
|
|
in order to simplify the definitions. For example, this pass strips
|
|
sign operations if the sign of a value never matters. The flag is
|
|
enabled by default at @option{-O} and higher.
|
|
|
|
@item -fssa-phiopt
|
|
@opindex fssa-phiopt
|
|
Perform pattern matching on SSA PHI nodes to optimize conditional
|
|
code. This pass is enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-switch-conversion
|
|
@opindex ftree-switch-conversion
|
|
Perform conversion of simple initializations in a switch to
|
|
initializations from a scalar array. This flag is enabled by default
|
|
at @option{-O2} and higher.
|
|
|
|
@item -ftree-tail-merge
|
|
@opindex ftree-tail-merge
|
|
Look for identical code sequences. When found, replace one with a jump to the
|
|
other. This optimization is known as tail merging or cross jumping. This flag
|
|
is enabled by default at @option{-O2} and higher. The compilation time
|
|
in this pass can
|
|
be limited using @option{max-tail-merge-comparisons} parameter and
|
|
@option{max-tail-merge-iterations} parameter.
|
|
|
|
@item -ftree-dce
|
|
@opindex ftree-dce
|
|
Perform dead code elimination (DCE) on trees. This flag is enabled by
|
|
default at @option{-O} and higher.
|
|
|
|
@item -ftree-builtin-call-dce
|
|
@opindex ftree-builtin-call-dce
|
|
Perform conditional dead code elimination (DCE) for calls to built-in functions
|
|
that may set @code{errno} but are otherwise side-effect free. This flag is
|
|
enabled by default at @option{-O2} and higher if @option{-Os} is not also
|
|
specified.
|
|
|
|
@item -ftree-dominator-opts
|
|
@opindex ftree-dominator-opts
|
|
Perform a variety of simple scalar cleanups (constant/copy
|
|
propagation, redundancy elimination, range propagation and expression
|
|
simplification) based on a dominator tree traversal. This also
|
|
performs jump threading (to reduce jumps to jumps). This flag is
|
|
enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-dse
|
|
@opindex ftree-dse
|
|
Perform dead store elimination (DSE) on trees. A dead store is a store into
|
|
a memory location that is later overwritten by another store without
|
|
any intervening loads. In this case the earlier store can be deleted. This
|
|
flag is enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-ch
|
|
@opindex ftree-ch
|
|
Perform loop header copying on trees. This is beneficial since it increases
|
|
effectiveness of code motion optimizations. It also saves one jump. This flag
|
|
is enabled by default at @option{-O} and higher. It is not enabled
|
|
for @option{-Os}, since it usually increases code size.
|
|
|
|
@item -ftree-loop-optimize
|
|
@opindex ftree-loop-optimize
|
|
Perform loop optimizations on trees. This flag is enabled by default
|
|
at @option{-O} and higher.
|
|
|
|
@item -ftree-loop-linear
|
|
@itemx -floop-interchange
|
|
@itemx -floop-strip-mine
|
|
@itemx -floop-block
|
|
@itemx -floop-unroll-and-jam
|
|
@opindex ftree-loop-linear
|
|
@opindex floop-interchange
|
|
@opindex floop-strip-mine
|
|
@opindex floop-block
|
|
@opindex floop-unroll-and-jam
|
|
Perform loop nest optimizations. Same as
|
|
@option{-floop-nest-optimize}. To use this code transformation, GCC has
|
|
to be configured with @option{--with-isl} to enable the Graphite loop
|
|
transformation infrastructure.
|
|
|
|
@item -fgraphite-identity
|
|
@opindex fgraphite-identity
|
|
Enable the identity transformation for graphite. For every SCoP we generate
|
|
the polyhedral representation and transform it back to gimple. Using
|
|
@option{-fgraphite-identity} we can check the costs or benefits of the
|
|
GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations
|
|
are also performed by the code generator isl, like index splitting and
|
|
dead code elimination in loops.
|
|
|
|
@item -floop-nest-optimize
|
|
@opindex floop-nest-optimize
|
|
Enable the isl based loop nest optimizer. This is a generic loop nest
|
|
optimizer based on the Pluto optimization algorithms. It calculates a loop
|
|
structure optimized for data-locality and parallelism. This option
|
|
is experimental.
|
|
|
|
@item -floop-parallelize-all
|
|
@opindex floop-parallelize-all
|
|
Use the Graphite data dependence analysis to identify loops that can
|
|
be parallelized. Parallelize all the loops that can be analyzed to
|
|
not contain loop carried dependences without checking that it is
|
|
profitable to parallelize the loops.
|
|
|
|
@item -ftree-coalesce-vars
|
|
@opindex ftree-coalesce-vars
|
|
While transforming the program out of the SSA representation, attempt to
|
|
reduce copying by coalescing versions of different user-defined
|
|
variables, instead of just compiler temporaries. This may severely
|
|
limit the ability to debug an optimized program compiled with
|
|
@option{-fno-var-tracking-assignments}. In the negated form, this flag
|
|
prevents SSA coalescing of user variables. This option is enabled by
|
|
default if optimization is enabled, and it does very little otherwise.
|
|
|
|
@item -ftree-loop-if-convert
|
|
@opindex ftree-loop-if-convert
|
|
Attempt to transform conditional jumps in the innermost loops to
|
|
branch-less equivalents. The intent is to remove control-flow from
|
|
the innermost loops in order to improve the ability of the
|
|
vectorization pass to handle these loops. This is enabled by default
|
|
if vectorization is enabled.
|
|
|
|
@item -ftree-loop-distribution
|
|
@opindex ftree-loop-distribution
|
|
Perform loop distribution. This flag can improve cache performance on
|
|
big loop bodies and allow further loop optimizations, like
|
|
parallelization or vectorization, to take place. For example, the loop
|
|
@smallexample
|
|
DO I = 1, N
|
|
A(I) = B(I) + C
|
|
D(I) = E(I) * F
|
|
ENDDO
|
|
@end smallexample
|
|
is transformed to
|
|
@smallexample
|
|
DO I = 1, N
|
|
A(I) = B(I) + C
|
|
ENDDO
|
|
DO I = 1, N
|
|
D(I) = E(I) * F
|
|
ENDDO
|
|
@end smallexample
|
|
|
|
@item -ftree-loop-distribute-patterns
|
|
@opindex ftree-loop-distribute-patterns
|
|
Perform loop distribution of patterns that can be code generated with
|
|
calls to a library. This flag is enabled by default at @option{-O3}.
|
|
|
|
This pass distributes the initialization loops and generates a call to
|
|
memset zero. For example, the loop
|
|
@smallexample
|
|
DO I = 1, N
|
|
A(I) = 0
|
|
B(I) = A(I) + I
|
|
ENDDO
|
|
@end smallexample
|
|
is transformed to
|
|
@smallexample
|
|
DO I = 1, N
|
|
A(I) = 0
|
|
ENDDO
|
|
DO I = 1, N
|
|
B(I) = A(I) + I
|
|
ENDDO
|
|
@end smallexample
|
|
and the initialization loop is transformed into a call to memset zero.
|
|
|
|
@item -ftree-loop-im
|
|
@opindex ftree-loop-im
|
|
Perform loop invariant motion on trees. This pass moves only invariants that
|
|
are hard to handle at RTL level (function calls, operations that expand to
|
|
nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
|
|
operands of conditions that are invariant out of the loop, so that we can use
|
|
just trivial invariantness analysis in loop unswitching. The pass also includes
|
|
store motion.
|
|
|
|
@item -ftree-loop-ivcanon
|
|
@opindex ftree-loop-ivcanon
|
|
Create a canonical counter for number of iterations in loops for which
|
|
determining number of iterations requires complicated analysis. Later
|
|
optimizations then may determine the number easily. Useful especially
|
|
in connection with unrolling.
|
|
|
|
@item -fivopts
|
|
@opindex fivopts
|
|
Perform induction variable optimizations (strength reduction, induction
|
|
variable merging and induction variable elimination) on trees.
|
|
|
|
@item -ftree-parallelize-loops=n
|
|
@opindex ftree-parallelize-loops
|
|
Parallelize loops, i.e., split their iteration space to run in n threads.
|
|
This is only possible for loops whose iterations are independent
|
|
and can be arbitrarily reordered. The optimization is only
|
|
profitable on multiprocessor machines, for loops that are CPU-intensive,
|
|
rather than constrained e.g.@: by memory bandwidth. This option
|
|
implies @option{-pthread}, and thus is only supported on targets
|
|
that have support for @option{-pthread}.
|
|
|
|
@item -ftree-pta
|
|
@opindex ftree-pta
|
|
Perform function-local points-to analysis on trees. This flag is
|
|
enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-sra
|
|
@opindex ftree-sra
|
|
Perform scalar replacement of aggregates. This pass replaces structure
|
|
references with scalars to prevent committing structures to memory too
|
|
early. This flag is enabled by default at @option{-O} and higher.
|
|
|
|
@item -fstore-merging
|
|
@opindex fstore-merging
|
|
Perform merging of narrow stores to consecutive memory addresses. This pass
|
|
merges contiguous stores of immediate values narrower than a word into fewer
|
|
wider stores to reduce the number of instructions. This is enabled by default
|
|
at @option{-O} and higher.
|
|
|
|
@item -ftree-ter
|
|
@opindex ftree-ter
|
|
Perform temporary expression replacement during the SSA->normal phase. Single
|
|
use/single def temporaries are replaced at their use location with their
|
|
defining expression. This results in non-GIMPLE code, but gives the expanders
|
|
much more complex trees to work on resulting in better RTL generation. This is
|
|
enabled by default at @option{-O} and higher.
|
|
|
|
@item -ftree-slsr
|
|
@opindex ftree-slsr
|
|
Perform straight-line strength reduction on trees. This recognizes related
|
|
expressions involving multiplications and replaces them by less expensive
|
|
calculations when possible. This is enabled by default at @option{-O} and
|
|
higher.
|
|
|
|
@item -ftree-vectorize
|
|
@opindex ftree-vectorize
|
|
Perform vectorization on trees. This flag enables @option{-ftree-loop-vectorize}
|
|
and @option{-ftree-slp-vectorize} if not explicitly specified.
|
|
|
|
@item -ftree-loop-vectorize
|
|
@opindex ftree-loop-vectorize
|
|
Perform loop vectorization on trees. This flag is enabled by default at
|
|
@option{-O3} and when @option{-ftree-vectorize} is enabled.
|
|
|
|
@item -ftree-slp-vectorize
|
|
@opindex ftree-slp-vectorize
|
|
Perform basic block vectorization on trees. This flag is enabled by default at
|
|
@option{-O3} and when @option{-ftree-vectorize} is enabled.
|
|
|
|
@item -fvect-cost-model=@var{model}
|
|
@opindex fvect-cost-model
|
|
Alter the cost model used for vectorization. The @var{model} argument
|
|
should be one of @samp{unlimited}, @samp{dynamic} or @samp{cheap}.
|
|
With the @samp{unlimited} model the vectorized code-path is assumed
|
|
to be profitable while with the @samp{dynamic} model a runtime check
|
|
guards the vectorized code-path to enable it only for iteration
|
|
counts that will likely execute faster than when executing the original
|
|
scalar loop. The @samp{cheap} model disables vectorization of
|
|
loops where doing so would be cost prohibitive for example due to
|
|
required runtime checks for data dependence or alignment but otherwise
|
|
is equal to the @samp{dynamic} model.
|
|
The default cost model depends on other optimization flags and is
|
|
either @samp{dynamic} or @samp{cheap}.
|
|
|
|
@item -fsimd-cost-model=@var{model}
|
|
@opindex fsimd-cost-model
|
|
Alter the cost model used for vectorization of loops marked with the OpenMP
|
|
or Cilk Plus simd directive. The @var{model} argument should be one of
|
|
@samp{unlimited}, @samp{dynamic}, @samp{cheap}. All values of @var{model}
|
|
have the same meaning as described in @option{-fvect-cost-model} and by
|
|
default a cost model defined with @option{-fvect-cost-model} is used.
|
|
|
|
@item -ftree-vrp
|
|
@opindex ftree-vrp
|
|
Perform Value Range Propagation on trees. This is similar to the
|
|
constant propagation pass, but instead of values, ranges of values are
|
|
propagated. This allows the optimizers to remove unnecessary range
|
|
checks like array bound checks and null pointer checks. This is
|
|
enabled by default at @option{-O2} and higher. Null pointer check
|
|
elimination is only done if @option{-fdelete-null-pointer-checks} is
|
|
enabled.
|
|
|
|
@item -fsplit-paths
|
|
@opindex fsplit-paths
|
|
Split paths leading to loop backedges. This can improve dead code
|
|
elimination and common subexpression elimination. This is enabled by
|
|
default at @option{-O2} and above.
|
|
|
|
@item -fsplit-ivs-in-unroller
|
|
@opindex fsplit-ivs-in-unroller
|
|
Enables expression of values of induction variables in later iterations
|
|
of the unrolled loop using the value in the first iteration. This breaks
|
|
long dependency chains, thus improving efficiency of the scheduling passes.
|
|
|
|
A combination of @option{-fweb} and CSE is often sufficient to obtain the
|
|
same effect. However, that is not reliable in cases where the loop body
|
|
is more complicated than a single basic block. It also does not work at all
|
|
on some architectures due to restrictions in the CSE pass.
|
|
|
|
This optimization is enabled by default.
|
|
|
|
@item -fvariable-expansion-in-unroller
|
|
@opindex fvariable-expansion-in-unroller
|
|
With this option, the compiler creates multiple copies of some
|
|
local variables when unrolling a loop, which can result in superior code.
|
|
|
|
@item -fpartial-inlining
|
|
@opindex fpartial-inlining
|
|
Inline parts of functions. This option has any effect only
|
|
when inlining itself is turned on by the @option{-finline-functions}
|
|
or @option{-finline-small-functions} options.
|
|
|
|
Enabled at level @option{-O2}.
|
|
|
|
@item -fpredictive-commoning
|
|
@opindex fpredictive-commoning
|
|
Perform predictive commoning optimization, i.e., reusing computations
|
|
(especially memory loads and stores) performed in previous
|
|
iterations of loops.
|
|
|
|
This option is enabled at level @option{-O3}.
|
|
|
|
@item -fprefetch-loop-arrays
|
|
@opindex fprefetch-loop-arrays
|
|
If supported by the target machine, generate instructions to prefetch
|
|
memory to improve the performance of loops that access large arrays.
|
|
|
|
This option may generate better or worse code; results are highly
|
|
dependent on the structure of loops within the source code.
|
|
|
|
Disabled at level @option{-Os}.
|
|
|
|
@item -fno-printf-return-value
|
|
@opindex fno-printf-return-value
|
|
Do not substitute constants for known return value of formatted output
|
|
functions such as @code{sprintf}, @code{snprintf}, @code{vsprintf}, and
|
|
@code{vsnprintf} (but not @code{printf} of @code{fprintf}). This
|
|
transformation allows GCC to optimize or even eliminate branches based
|
|
on the known return value of these functions called with arguments that
|
|
are either constant, or whose values are known to be in a range that
|
|
makes determining the exact return value possible. For example, when
|
|
@option{-fprintf-return-value} is in effect, both the branch and the
|
|
body of the @code{if} statement (but not the call to @code{snprint})
|
|
can be optimized away when @code{i} is a 32-bit or smaller integer
|
|
because the return value is guaranteed to be at most 8.
|
|
|
|
@smallexample
|
|
char buf[9];
|
|
if (snprintf (buf, "%08x", i) >= sizeof buf)
|
|
@dots{}
|
|
@end smallexample
|
|
|
|
The @option{-fprintf-return-value} option relies on other optimizations
|
|
and yields best results with @option{-O2}. It works in tandem with the
|
|
@option{-Wformat-overflow} and @option{-Wformat-truncation} options.
|
|
The @option{-fprintf-return-value} option is enabled by default.
|
|
|
|
@item -fno-peephole
|
|
@itemx -fno-peephole2
|
|
@opindex fno-peephole
|
|
@opindex fno-peephole2
|
|
Disable any machine-specific peephole optimizations. The difference
|
|
between @option{-fno-peephole} and @option{-fno-peephole2} is in how they
|
|
are implemented in the compiler; some targets use one, some use the
|
|
other, a few use both.
|
|
|
|
@option{-fpeephole} is enabled by default.
|
|
@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fno-guess-branch-probability
|
|
@opindex fno-guess-branch-probability
|
|
Do not guess branch probabilities using heuristics.
|
|
|
|
GCC uses heuristics to guess branch probabilities if they are
|
|
not provided by profiling feedback (@option{-fprofile-arcs}). These
|
|
heuristics are based on the control flow graph. If some branch probabilities
|
|
are specified by @code{__builtin_expect}, then the heuristics are
|
|
used to guess branch probabilities for the rest of the control flow graph,
|
|
taking the @code{__builtin_expect} info into account. The interactions
|
|
between the heuristics and @code{__builtin_expect} can be complex, and in
|
|
some cases, it may be useful to disable the heuristics so that the effects
|
|
of @code{__builtin_expect} are easier to understand.
|
|
|
|
The default is @option{-fguess-branch-probability} at levels
|
|
@option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -freorder-blocks
|
|
@opindex freorder-blocks
|
|
Reorder basic blocks in the compiled function in order to reduce number of
|
|
taken branches and improve code locality.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -freorder-blocks-algorithm=@var{algorithm}
|
|
@opindex freorder-blocks-algorithm
|
|
Use the specified algorithm for basic block reordering. The
|
|
@var{algorithm} argument can be @samp{simple}, which does not increase
|
|
code size (except sometimes due to secondary effects like alignment),
|
|
or @samp{stc}, the ``software trace cache'' algorithm, which tries to
|
|
put all often executed code together, minimizing the number of branches
|
|
executed by making extra copies of code.
|
|
|
|
The default is @samp{simple} at levels @option{-O}, @option{-Os}, and
|
|
@samp{stc} at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -freorder-blocks-and-partition
|
|
@opindex freorder-blocks-and-partition
|
|
In addition to reordering basic blocks in the compiled function, in order
|
|
to reduce number of taken branches, partitions hot and cold basic blocks
|
|
into separate sections of the assembly and @file{.o} files, to improve
|
|
paging and cache locality performance.
|
|
|
|
This optimization is automatically turned off in the presence of
|
|
exception handling, for linkonce sections, for functions with a user-defined
|
|
section attribute and on any architecture that does not support named
|
|
sections.
|
|
|
|
Enabled for x86 at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -freorder-functions
|
|
@opindex freorder-functions
|
|
Reorder functions in the object file in order to
|
|
improve code locality. This is implemented by using special
|
|
subsections @code{.text.hot} for most frequently executed functions and
|
|
@code{.text.unlikely} for unlikely executed functions. Reordering is done by
|
|
the linker so object file format must support named sections and linker must
|
|
place them in a reasonable way.
|
|
|
|
Also profile feedback must be available to make this option effective. See
|
|
@option{-fprofile-arcs} for details.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fstrict-aliasing
|
|
@opindex fstrict-aliasing
|
|
Allow the compiler to assume the strictest aliasing rules applicable to
|
|
the language being compiled. For C (and C++), this activates
|
|
optimizations based on the type of expressions. In particular, an
|
|
object of one type is assumed never to reside at the same address as an
|
|
object of a different type, unless the types are almost the same. For
|
|
example, an @code{unsigned int} can alias an @code{int}, but not a
|
|
@code{void*} or a @code{double}. A character type may alias any other
|
|
type.
|
|
|
|
@anchor{Type-punning}Pay special attention to code like this:
|
|
@smallexample
|
|
union a_union @{
|
|
int i;
|
|
double d;
|
|
@};
|
|
|
|
int f() @{
|
|
union a_union t;
|
|
t.d = 3.0;
|
|
return t.i;
|
|
@}
|
|
@end smallexample
|
|
The practice of reading from a different union member than the one most
|
|
recently written to (called ``type-punning'') is common. Even with
|
|
@option{-fstrict-aliasing}, type-punning is allowed, provided the memory
|
|
is accessed through the union type. So, the code above works as
|
|
expected. @xref{Structures unions enumerations and bit-fields
|
|
implementation}. However, this code might not:
|
|
@smallexample
|
|
int f() @{
|
|
union a_union t;
|
|
int* ip;
|
|
t.d = 3.0;
|
|
ip = &t.i;
|
|
return *ip;
|
|
@}
|
|
@end smallexample
|
|
|
|
Similarly, access by taking the address, casting the resulting pointer
|
|
and dereferencing the result has undefined behavior, even if the cast
|
|
uses a union type, e.g.:
|
|
@smallexample
|
|
int f() @{
|
|
double d = 3.0;
|
|
return ((union a_union *) &d)->i;
|
|
@}
|
|
@end smallexample
|
|
|
|
The @option{-fstrict-aliasing} option is enabled at levels
|
|
@option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fstrict-overflow
|
|
@opindex fstrict-overflow
|
|
Allow the compiler to assume strict signed overflow rules, depending
|
|
on the language being compiled. For C (and C++) this means that
|
|
overflow when doing arithmetic with signed numbers is undefined, which
|
|
means that the compiler may assume that it does not happen. This
|
|
permits various optimizations. For example, the compiler assumes
|
|
that an expression like @code{i + 10 > i} is always true for
|
|
signed @code{i}. This assumption is only valid if signed overflow is
|
|
undefined, as the expression is false if @code{i + 10} overflows when
|
|
using twos complement arithmetic. When this option is in effect any
|
|
attempt to determine whether an operation on signed numbers
|
|
overflows must be written carefully to not actually involve overflow.
|
|
|
|
This option also allows the compiler to assume strict pointer
|
|
semantics: given a pointer to an object, if adding an offset to that
|
|
pointer does not produce a pointer to the same object, the addition is
|
|
undefined. This permits the compiler to conclude that @code{p + u >
|
|
p} is always true for a pointer @code{p} and unsigned integer
|
|
@code{u}. This assumption is only valid because pointer wraparound is
|
|
undefined, as the expression is false if @code{p + u} overflows using
|
|
twos complement arithmetic.
|
|
|
|
See also the @option{-fwrapv} option. Using @option{-fwrapv} means
|
|
that integer signed overflow is fully defined: it wraps. When
|
|
@option{-fwrapv} is used, there is no difference between
|
|
@option{-fstrict-overflow} and @option{-fno-strict-overflow} for
|
|
integers. With @option{-fwrapv} certain types of overflow are
|
|
permitted. For example, if the compiler gets an overflow when doing
|
|
arithmetic on constants, the overflowed value can still be used with
|
|
@option{-fwrapv}, but not otherwise.
|
|
|
|
The @option{-fstrict-overflow} option is enabled at levels
|
|
@option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -falign-functions
|
|
@itemx -falign-functions=@var{n}
|
|
@opindex falign-functions
|
|
Align the start of functions to the next power-of-two greater than
|
|
@var{n}, skipping up to @var{n} bytes. For instance,
|
|
@option{-falign-functions=32} aligns functions to the next 32-byte
|
|
boundary, but @option{-falign-functions=24} aligns to the next
|
|
32-byte boundary only if this can be done by skipping 23 bytes or less.
|
|
|
|
@option{-fno-align-functions} and @option{-falign-functions=1} are
|
|
equivalent and mean that functions are not aligned.
|
|
|
|
Some assemblers only support this flag when @var{n} is a power of two;
|
|
in that case, it is rounded up.
|
|
|
|
If @var{n} is not specified or is zero, use a machine-dependent default.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -flimit-function-alignment
|
|
If this option is enabled, the compiler tries to avoid unnecessarily
|
|
overaligning functions. It attempts to instruct the assembler to align
|
|
by the amount specified by @option{-falign-functions}, but not to
|
|
skip more bytes than the size of the function.
|
|
|
|
@item -falign-labels
|
|
@itemx -falign-labels=@var{n}
|
|
@opindex falign-labels
|
|
Align all branch targets to a power-of-two boundary, skipping up to
|
|
@var{n} bytes like @option{-falign-functions}. This option can easily
|
|
make code slower, because it must insert dummy operations for when the
|
|
branch target is reached in the usual flow of the code.
|
|
|
|
@option{-fno-align-labels} and @option{-falign-labels=1} are
|
|
equivalent and mean that labels are not aligned.
|
|
|
|
If @option{-falign-loops} or @option{-falign-jumps} are applicable and
|
|
are greater than this value, then their values are used instead.
|
|
|
|
If @var{n} is not specified or is zero, use a machine-dependent default
|
|
which is very likely to be @samp{1}, meaning no alignment.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -falign-loops
|
|
@itemx -falign-loops=@var{n}
|
|
@opindex falign-loops
|
|
Align loops to a power-of-two boundary, skipping up to @var{n} bytes
|
|
like @option{-falign-functions}. If the loops are
|
|
executed many times, this makes up for any execution of the dummy
|
|
operations.
|
|
|
|
@option{-fno-align-loops} and @option{-falign-loops=1} are
|
|
equivalent and mean that loops are not aligned.
|
|
|
|
If @var{n} is not specified or is zero, use a machine-dependent default.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -falign-jumps
|
|
@itemx -falign-jumps=@var{n}
|
|
@opindex falign-jumps
|
|
Align branch targets to a power-of-two boundary, for branch targets
|
|
where the targets can only be reached by jumping, skipping up to @var{n}
|
|
bytes like @option{-falign-functions}. In this case, no dummy operations
|
|
need be executed.
|
|
|
|
@option{-fno-align-jumps} and @option{-falign-jumps=1} are
|
|
equivalent and mean that loops are not aligned.
|
|
|
|
If @var{n} is not specified or is zero, use a machine-dependent default.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}.
|
|
|
|
@item -funit-at-a-time
|
|
@opindex funit-at-a-time
|
|
This option is left for compatibility reasons. @option{-funit-at-a-time}
|
|
has no effect, while @option{-fno-unit-at-a-time} implies
|
|
@option{-fno-toplevel-reorder} and @option{-fno-section-anchors}.
|
|
|
|
Enabled by default.
|
|
|
|
@item -fno-toplevel-reorder
|
|
@opindex fno-toplevel-reorder
|
|
Do not reorder top-level functions, variables, and @code{asm}
|
|
statements. Output them in the same order that they appear in the
|
|
input file. When this option is used, unreferenced static variables
|
|
are not removed. This option is intended to support existing code
|
|
that relies on a particular ordering. For new code, it is better to
|
|
use attributes when possible.
|
|
|
|
Enabled at level @option{-O0}. When disabled explicitly, it also implies
|
|
@option{-fno-section-anchors}, which is otherwise enabled at @option{-O0} on some
|
|
targets.
|
|
|
|
@item -fweb
|
|
@opindex fweb
|
|
Constructs webs as commonly used for register allocation purposes and assign
|
|
each web individual pseudo register. This allows the register allocation pass
|
|
to operate on pseudos directly, but also strengthens several other optimization
|
|
passes, such as CSE, loop optimizer and trivial dead code remover. It can,
|
|
however, make debugging impossible, since variables no longer stay in a
|
|
``home register''.
|
|
|
|
Enabled by default with @option{-funroll-loops}.
|
|
|
|
@item -fwhole-program
|
|
@opindex fwhole-program
|
|
Assume that the current compilation unit represents the whole program being
|
|
compiled. All public functions and variables with the exception of @code{main}
|
|
and those merged by attribute @code{externally_visible} become static functions
|
|
and in effect are optimized more aggressively by interprocedural optimizers.
|
|
|
|
This option should not be used in combination with @option{-flto}.
|
|
Instead relying on a linker plugin should provide safer and more precise
|
|
information.
|
|
|
|
@item -flto[=@var{n}]
|
|
@opindex flto
|
|
This option runs the standard link-time optimizer. When invoked
|
|
with source code, it generates GIMPLE (one of GCC's internal
|
|
representations) and writes it to special ELF sections in the object
|
|
file. When the object files are linked together, all the function
|
|
bodies are read from these ELF sections and instantiated as if they
|
|
had been part of the same translation unit.
|
|
|
|
To use the link-time optimizer, @option{-flto} and optimization
|
|
options should be specified at compile time and during the final link.
|
|
It is recommended that you compile all the files participating in the
|
|
same link with the same options and also specify those options at
|
|
link time.
|
|
For example:
|
|
|
|
@smallexample
|
|
gcc -c -O2 -flto foo.c
|
|
gcc -c -O2 -flto bar.c
|
|
gcc -o myprog -flto -O2 foo.o bar.o
|
|
@end smallexample
|
|
|
|
The first two invocations to GCC save a bytecode representation
|
|
of GIMPLE into special ELF sections inside @file{foo.o} and
|
|
@file{bar.o}. The final invocation reads the GIMPLE bytecode from
|
|
@file{foo.o} and @file{bar.o}, merges the two files into a single
|
|
internal image, and compiles the result as usual. Since both
|
|
@file{foo.o} and @file{bar.o} are merged into a single image, this
|
|
causes all the interprocedural analyses and optimizations in GCC to
|
|
work across the two files as if they were a single one. This means,
|
|
for example, that the inliner is able to inline functions in
|
|
@file{bar.o} into functions in @file{foo.o} and vice-versa.
|
|
|
|
Another (simpler) way to enable link-time optimization is:
|
|
|
|
@smallexample
|
|
gcc -o myprog -flto -O2 foo.c bar.c
|
|
@end smallexample
|
|
|
|
The above generates bytecode for @file{foo.c} and @file{bar.c},
|
|
merges them together into a single GIMPLE representation and optimizes
|
|
them as usual to produce @file{myprog}.
|
|
|
|
The only important thing to keep in mind is that to enable link-time
|
|
optimizations you need to use the GCC driver to perform the link step.
|
|
GCC then automatically performs link-time optimization if any of the
|
|
objects involved were compiled with the @option{-flto} command-line option.
|
|
You generally
|
|
should specify the optimization options to be used for link-time
|
|
optimization though GCC tries to be clever at guessing an
|
|
optimization level to use from the options used at compile time
|
|
if you fail to specify one at link time. You can always override
|
|
the automatic decision to do link-time optimization at link time
|
|
by passing @option{-fno-lto} to the link command.
|
|
|
|
To make whole program optimization effective, it is necessary to make
|
|
certain whole program assumptions. The compiler needs to know
|
|
what functions and variables can be accessed by libraries and runtime
|
|
outside of the link-time optimized unit. When supported by the linker,
|
|
the linker plugin (see @option{-fuse-linker-plugin}) passes information
|
|
to the compiler about used and externally visible symbols. When
|
|
the linker plugin is not available, @option{-fwhole-program} should be
|
|
used to allow the compiler to make these assumptions, which leads
|
|
to more aggressive optimization decisions.
|
|
|
|
When @option{-fuse-linker-plugin} is not enabled, when a file is
|
|
compiled with @option{-flto}, the generated object file is larger than
|
|
a regular object file because it contains GIMPLE bytecodes and the usual
|
|
final code (see @option{-ffat-lto-objects}. This means that
|
|
object files with LTO information can be linked as normal object
|
|
files; if @option{-fno-lto} is passed to the linker, no
|
|
interprocedural optimizations are applied. Note that when
|
|
@option{-fno-fat-lto-objects} is enabled the compile stage is faster
|
|
but you cannot perform a regular, non-LTO link on them.
|
|
|
|
Additionally, the optimization flags used to compile individual files
|
|
are not necessarily related to those used at link time. For instance,
|
|
|
|
@smallexample
|
|
gcc -c -O0 -ffat-lto-objects -flto foo.c
|
|
gcc -c -O0 -ffat-lto-objects -flto bar.c
|
|
gcc -o myprog -O3 foo.o bar.o
|
|
@end smallexample
|
|
|
|
This produces individual object files with unoptimized assembler
|
|
code, but the resulting binary @file{myprog} is optimized at
|
|
@option{-O3}. If, instead, the final binary is generated with
|
|
@option{-fno-lto}, then @file{myprog} is not optimized.
|
|
|
|
When producing the final binary, GCC only
|
|
applies link-time optimizations to those files that contain bytecode.
|
|
Therefore, you can mix and match object files and libraries with
|
|
GIMPLE bytecodes and final object code. GCC automatically selects
|
|
which files to optimize in LTO mode and which files to link without
|
|
further processing.
|
|
|
|
There are some code generation flags preserved by GCC when
|
|
generating bytecodes, as they need to be used during the final link
|
|
stage. Generally options specified at link time override those
|
|
specified at compile time.
|
|
|
|
If you do not specify an optimization level option @option{-O} at
|
|
link time, then GCC uses the highest optimization level
|
|
used when compiling the object files.
|
|
|
|
Currently, the following options and their settings are taken from
|
|
the first object file that explicitly specifies them:
|
|
@option{-fPIC}, @option{-fpic}, @option{-fpie}, @option{-fcommon},
|
|
@option{-fexceptions}, @option{-fnon-call-exceptions}, @option{-fgnu-tm}
|
|
and all the @option{-m} target flags.
|
|
|
|
Certain ABI-changing flags are required to match in all compilation units,
|
|
and trying to override this at link time with a conflicting value
|
|
is ignored. This includes options such as @option{-freg-struct-return}
|
|
and @option{-fpcc-struct-return}.
|
|
|
|
Other options such as @option{-ffp-contract}, @option{-fno-strict-overflow},
|
|
@option{-fwrapv}, @option{-fno-trapv} or @option{-fno-strict-aliasing}
|
|
are passed through to the link stage and merged conservatively for
|
|
conflicting translation units. Specifically
|
|
@option{-fno-strict-overflow}, @option{-fwrapv} and @option{-fno-trapv} take
|
|
precedence; and for example @option{-ffp-contract=off} takes precedence
|
|
over @option{-ffp-contract=fast}. You can override them at link time.
|
|
|
|
If LTO encounters objects with C linkage declared with incompatible
|
|
types in separate translation units to be linked together (undefined
|
|
behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be
|
|
issued. The behavior is still undefined at run time. Similar
|
|
diagnostics may be raised for other languages.
|
|
|
|
Another feature of LTO is that it is possible to apply interprocedural
|
|
optimizations on files written in different languages:
|
|
|
|
@smallexample
|
|
gcc -c -flto foo.c
|
|
g++ -c -flto bar.cc
|
|
gfortran -c -flto baz.f90
|
|
g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
|
|
@end smallexample
|
|
|
|
Notice that the final link is done with @command{g++} to get the C++
|
|
runtime libraries and @option{-lgfortran} is added to get the Fortran
|
|
runtime libraries. In general, when mixing languages in LTO mode, you
|
|
should use the same link command options as when mixing languages in a
|
|
regular (non-LTO) compilation.
|
|
|
|
If object files containing GIMPLE bytecode are stored in a library archive, say
|
|
@file{libfoo.a}, it is possible to extract and use them in an LTO link if you
|
|
are using a linker with plugin support. To create static libraries suitable
|
|
for LTO, use @command{gcc-ar} and @command{gcc-ranlib} instead of @command{ar}
|
|
and @command{ranlib};
|
|
to show the symbols of object files with GIMPLE bytecode, use
|
|
@command{gcc-nm}. Those commands require that @command{ar}, @command{ranlib}
|
|
and @command{nm} have been compiled with plugin support. At link time, use the the
|
|
flag @option{-fuse-linker-plugin} to ensure that the library participates in
|
|
the LTO optimization process:
|
|
|
|
@smallexample
|
|
gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
|
|
@end smallexample
|
|
|
|
With the linker plugin enabled, the linker extracts the needed
|
|
GIMPLE files from @file{libfoo.a} and passes them on to the running GCC
|
|
to make them part of the aggregated GIMPLE image to be optimized.
|
|
|
|
If you are not using a linker with plugin support and/or do not
|
|
enable the linker plugin, then the objects inside @file{libfoo.a}
|
|
are extracted and linked as usual, but they do not participate
|
|
in the LTO optimization process. In order to make a static library suitable
|
|
for both LTO optimization and usual linkage, compile its object files with
|
|
@option{-flto} @option{-ffat-lto-objects}.
|
|
|
|
Link-time optimizations do not require the presence of the whole program to
|
|
operate. If the program does not require any symbols to be exported, it is
|
|
possible to combine @option{-flto} and @option{-fwhole-program} to allow
|
|
the interprocedural optimizers to use more aggressive assumptions which may
|
|
lead to improved optimization opportunities.
|
|
Use of @option{-fwhole-program} is not needed when linker plugin is
|
|
active (see @option{-fuse-linker-plugin}).
|
|
|
|
The current implementation of LTO makes no
|
|
attempt to generate bytecode that is portable between different
|
|
types of hosts. The bytecode files are versioned and there is a
|
|
strict version check, so bytecode files generated in one version of
|
|
GCC do not work with an older or newer version of GCC.
|
|
|
|
Link-time optimization does not work well with generation of debugging
|
|
information. Combining @option{-flto} with
|
|
@option{-g} is currently experimental and expected to produce unexpected
|
|
results.
|
|
|
|
If you specify the optional @var{n}, the optimization and code
|
|
generation done at link time is executed in parallel using @var{n}
|
|
parallel jobs by utilizing an installed @command{make} program. The
|
|
environment variable @env{MAKE} may be used to override the program
|
|
used. The default value for @var{n} is 1.
|
|
|
|
You can also specify @option{-flto=jobserver} to use GNU make's
|
|
job server mode to determine the number of parallel jobs. This
|
|
is useful when the Makefile calling GCC is already executing in parallel.
|
|
You must prepend a @samp{+} to the command recipe in the parent Makefile
|
|
for this to work. This option likely only works if @env{MAKE} is
|
|
GNU make.
|
|
|
|
@item -flto-partition=@var{alg}
|
|
@opindex flto-partition
|
|
Specify the partitioning algorithm used by the link-time optimizer.
|
|
The value is either @samp{1to1} to specify a partitioning mirroring
|
|
the original source files or @samp{balanced} to specify partitioning
|
|
into equally sized chunks (whenever possible) or @samp{max} to create
|
|
new partition for every symbol where possible. Specifying @samp{none}
|
|
as an algorithm disables partitioning and streaming completely.
|
|
The default value is @samp{balanced}. While @samp{1to1} can be used
|
|
as an workaround for various code ordering issues, the @samp{max}
|
|
partitioning is intended for internal testing only.
|
|
The value @samp{one} specifies that exactly one partition should be
|
|
used while the value @samp{none} bypasses partitioning and executes
|
|
the link-time optimization step directly from the WPA phase.
|
|
|
|
@item -flto-odr-type-merging
|
|
@opindex flto-odr-type-merging
|
|
Enable streaming of mangled types names of C++ types and their unification
|
|
at link time. This increases size of LTO object files, but enables
|
|
diagnostics about One Definition Rule violations.
|
|
|
|
@item -flto-compression-level=@var{n}
|
|
@opindex flto-compression-level
|
|
This option specifies the level of compression used for intermediate
|
|
language written to LTO object files, and is only meaningful in
|
|
conjunction with LTO mode (@option{-flto}). Valid
|
|
values are 0 (no compression) to 9 (maximum compression). Values
|
|
outside this range are clamped to either 0 or 9. If the option is not
|
|
given, a default balanced compression setting is used.
|
|
|
|
@item -fuse-linker-plugin
|
|
@opindex fuse-linker-plugin
|
|
Enables the use of a linker plugin during link-time optimization. This
|
|
option relies on plugin support in the linker, which is available in gold
|
|
or in GNU ld 2.21 or newer.
|
|
|
|
This option enables the extraction of object files with GIMPLE bytecode out
|
|
of library archives. This improves the quality of optimization by exposing
|
|
more code to the link-time optimizer. This information specifies what
|
|
symbols can be accessed externally (by non-LTO object or during dynamic
|
|
linking). Resulting code quality improvements on binaries (and shared
|
|
libraries that use hidden visibility) are similar to @option{-fwhole-program}.
|
|
See @option{-flto} for a description of the effect of this flag and how to
|
|
use it.
|
|
|
|
This option is enabled by default when LTO support in GCC is enabled
|
|
and GCC was configured for use with
|
|
a linker supporting plugins (GNU ld 2.21 or newer or gold).
|
|
|
|
@item -ffat-lto-objects
|
|
@opindex ffat-lto-objects
|
|
Fat LTO objects are object files that contain both the intermediate language
|
|
and the object code. This makes them usable for both LTO linking and normal
|
|
linking. This option is effective only when compiling with @option{-flto}
|
|
and is ignored at link time.
|
|
|
|
@option{-fno-fat-lto-objects} improves compilation time over plain LTO, but
|
|
requires the complete toolchain to be aware of LTO. It requires a linker with
|
|
linker plugin support for basic functionality. Additionally,
|
|
@command{nm}, @command{ar} and @command{ranlib}
|
|
need to support linker plugins to allow a full-featured build environment
|
|
(capable of building static libraries etc). GCC provides the @command{gcc-ar},
|
|
@command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options
|
|
to these tools. With non fat LTO makefiles need to be modified to use them.
|
|
|
|
The default is @option{-fno-fat-lto-objects} on targets with linker plugin
|
|
support.
|
|
|
|
@item -fcompare-elim
|
|
@opindex fcompare-elim
|
|
After register allocation and post-register allocation instruction splitting,
|
|
identify arithmetic instructions that compute processor flags similar to a
|
|
comparison operation based on that arithmetic. If possible, eliminate the
|
|
explicit comparison operation.
|
|
|
|
This pass only applies to certain targets that cannot explicitly represent
|
|
the comparison operation before register allocation is complete.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fcprop-registers
|
|
@opindex fcprop-registers
|
|
After register allocation and post-register allocation instruction splitting,
|
|
perform a copy-propagation pass to try to reduce scheduling dependencies
|
|
and occasionally eliminate the copy.
|
|
|
|
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -fprofile-correction
|
|
@opindex fprofile-correction
|
|
Profiles collected using an instrumented binary for multi-threaded programs may
|
|
be inconsistent due to missed counter updates. When this option is specified,
|
|
GCC uses heuristics to correct or smooth out such inconsistencies. By
|
|
default, GCC emits an error message when an inconsistent profile is detected.
|
|
|
|
@item -fprofile-use
|
|
@itemx -fprofile-use=@var{path}
|
|
@opindex fprofile-use
|
|
Enable profile feedback-directed optimizations,
|
|
and the following optimizations
|
|
which are generally profitable only with profile feedback available:
|
|
@option{-fbranch-probabilities}, @option{-fvpt},
|
|
@option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
|
|
@option{-ftree-vectorize}, and @option{ftree-loop-distribute-patterns}.
|
|
|
|
Before you can use this option, you must first generate profiling information.
|
|
@xref{Instrumentation Options}, for information about the
|
|
@option{-fprofile-generate} option.
|
|
|
|
By default, GCC emits an error message if the feedback profiles do not
|
|
match the source code. This error can be turned into a warning by using
|
|
@option{-Wcoverage-mismatch}. Note this may result in poorly optimized
|
|
code.
|
|
|
|
If @var{path} is specified, GCC looks at the @var{path} to find
|
|
the profile feedback data files. See @option{-fprofile-dir}.
|
|
|
|
@item -fauto-profile
|
|
@itemx -fauto-profile=@var{path}
|
|
@opindex fauto-profile
|
|
Enable sampling-based feedback-directed optimizations,
|
|
and the following optimizations
|
|
which are generally profitable only with profile feedback available:
|
|
@option{-fbranch-probabilities}, @option{-fvpt},
|
|
@option{-funroll-loops}, @option{-fpeel-loops}, @option{-ftracer},
|
|
@option{-ftree-vectorize},
|
|
@option{-finline-functions}, @option{-fipa-cp}, @option{-fipa-cp-clone},
|
|
@option{-fpredictive-commoning}, @option{-funswitch-loops},
|
|
@option{-fgcse-after-reload}, and @option{-ftree-loop-distribute-patterns}.
|
|
|
|
@var{path} is the name of a file containing AutoFDO profile information.
|
|
If omitted, it defaults to @file{fbdata.afdo} in the current directory.
|
|
|
|
Producing an AutoFDO profile data file requires running your program
|
|
with the @command{perf} utility on a supported GNU/Linux target system.
|
|
For more information, see @uref{https://perf.wiki.kernel.org/}.
|
|
|
|
E.g.
|
|
@smallexample
|
|
perf record -e br_inst_retired:near_taken -b -o perf.data \
|
|
-- your_program
|
|
@end smallexample
|
|
|
|
Then use the @command{create_gcov} tool to convert the raw profile data
|
|
to a format that can be used by GCC.@ You must also supply the
|
|
unstripped binary for your program to this tool.
|
|
See @uref{https://github.com/google/autofdo}.
|
|
|
|
E.g.
|
|
@smallexample
|
|
create_gcov --binary=your_program.unstripped --profile=perf.data \
|
|
--gcov=profile.afdo
|
|
@end smallexample
|
|
@end table
|
|
|
|
The following options control compiler behavior regarding floating-point
|
|
arithmetic. These options trade off between speed and
|
|
correctness. All must be specifically enabled.
|
|
|
|
@table @gcctabopt
|
|
@item -ffloat-store
|
|
@opindex ffloat-store
|
|
Do not store floating-point variables in registers, and inhibit other
|
|
options that might change whether a floating-point value is taken from a
|
|
register or memory.
|
|
|
|
@cindex floating-point precision
|
|
This option prevents undesirable excess precision on machines such as
|
|
the 68000 where the floating registers (of the 68881) keep more
|
|
precision than a @code{double} is supposed to have. Similarly for the
|
|
x86 architecture. For most programs, the excess precision does only
|
|
good, but a few programs rely on the precise definition of IEEE floating
|
|
point. Use @option{-ffloat-store} for such programs, after modifying
|
|
them to store all pertinent intermediate computations into variables.
|
|
|
|
@item -fexcess-precision=@var{style}
|
|
@opindex fexcess-precision
|
|
This option allows further control over excess precision on machines
|
|
where floating-point operations occur in a format with more precision or
|
|
range than the IEEE standard and interchange floating-point types. By
|
|
default, @option{-fexcess-precision=fast} is in effect; this means that
|
|
operations may be carried out in a wider precision than the types specified
|
|
in the source if that would result in faster code, and it is unpredictable
|
|
when rounding to the types specified in the source code takes place.
|
|
When compiling C, if @option{-fexcess-precision=standard} is specified then
|
|
excess precision follows the rules specified in ISO C99; in particular,
|
|
both casts and assignments cause values to be rounded to their
|
|
semantic types (whereas @option{-ffloat-store} only affects
|
|
assignments). This option is enabled by default for C if a strict
|
|
conformance option such as @option{-std=c99} is used.
|
|
@option{-ffast-math} enables @option{-fexcess-precision=fast} by default
|
|
regardless of whether a strict conformance option is used.
|
|
|
|
@opindex mfpmath
|
|
@option{-fexcess-precision=standard} is not implemented for languages
|
|
other than C. On the x86, it has no effect if @option{-mfpmath=sse}
|
|
or @option{-mfpmath=sse+387} is specified; in the former case, IEEE
|
|
semantics apply without excess precision, and in the latter, rounding
|
|
is unpredictable.
|
|
|
|
@item -ffast-math
|
|
@opindex ffast-math
|
|
Sets the options @option{-fno-math-errno}, @option{-funsafe-math-optimizations},
|
|
@option{-ffinite-math-only}, @option{-fno-rounding-math},
|
|
@option{-fno-signaling-nans}, @option{-fcx-limited-range} and
|
|
@option{-fexcess-precision=fast}.
|
|
|
|
This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
|
|
|
|
This option is not turned on by any @option{-O} option besides
|
|
@option{-Ofast} since it can result in incorrect output for programs
|
|
that depend on an exact implementation of IEEE or ISO rules/specifications
|
|
for math functions. It may, however, yield faster code for programs
|
|
that do not require the guarantees of these specifications.
|
|
|
|
@item -fno-math-errno
|
|
@opindex fno-math-errno
|
|
Do not set @code{errno} after calling math functions that are executed
|
|
with a single instruction, e.g., @code{sqrt}. A program that relies on
|
|
IEEE exceptions for math error handling may want to use this flag
|
|
for speed while maintaining IEEE arithmetic compatibility.
|
|
|
|
This option is not turned on by any @option{-O} option since
|
|
it can result in incorrect output for programs that depend on
|
|
an exact implementation of IEEE or ISO rules/specifications for
|
|
math functions. It may, however, yield faster code for programs
|
|
that do not require the guarantees of these specifications.
|
|
|
|
The default is @option{-fmath-errno}.
|
|
|
|
On Darwin systems, the math library never sets @code{errno}. There is
|
|
therefore no reason for the compiler to consider the possibility that
|
|
it might, and @option{-fno-math-errno} is the default.
|
|
|
|
@item -funsafe-math-optimizations
|
|
@opindex funsafe-math-optimizations
|
|
|
|
Allow optimizations for floating-point arithmetic that (a) assume
|
|
that arguments and results are valid and (b) may violate IEEE or
|
|
ANSI standards. When used at link time, it may include libraries
|
|
or startup files that change the default FPU control word or other
|
|
similar optimizations.
|
|
|
|
This option is not turned on by any @option{-O} option since
|
|
it can result in incorrect output for programs that depend on
|
|
an exact implementation of IEEE or ISO rules/specifications for
|
|
math functions. It may, however, yield faster code for programs
|
|
that do not require the guarantees of these specifications.
|
|
Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math},
|
|
@option{-fassociative-math} and @option{-freciprocal-math}.
|
|
|
|
The default is @option{-fno-unsafe-math-optimizations}.
|
|
|
|
@item -fassociative-math
|
|
@opindex fassociative-math
|
|
|
|
Allow re-association of operands in series of floating-point operations.
|
|
This violates the ISO C and C++ language standard by possibly changing
|
|
computation result. NOTE: re-ordering may change the sign of zero as
|
|
well as ignore NaNs and inhibit or create underflow or overflow (and
|
|
thus cannot be used on code that relies on rounding behavior like
|
|
@code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons
|
|
and thus may not be used when ordered comparisons are required.
|
|
This option requires that both @option{-fno-signed-zeros} and
|
|
@option{-fno-trapping-math} be in effect. Moreover, it doesn't make
|
|
much sense with @option{-frounding-math}. For Fortran the option
|
|
is automatically enabled when both @option{-fno-signed-zeros} and
|
|
@option{-fno-trapping-math} are in effect.
|
|
|
|
The default is @option{-fno-associative-math}.
|
|
|
|
@item -freciprocal-math
|
|
@opindex freciprocal-math
|
|
|
|
Allow the reciprocal of a value to be used instead of dividing by
|
|
the value if this enables optimizations. For example @code{x / y}
|
|
can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)}
|
|
is subject to common subexpression elimination. Note that this loses
|
|
precision and increases the number of flops operating on the value.
|
|
|
|
The default is @option{-fno-reciprocal-math}.
|
|
|
|
@item -ffinite-math-only
|
|
@opindex ffinite-math-only
|
|
Allow optimizations for floating-point arithmetic that assume
|
|
that arguments and results are not NaNs or +-Infs.
|
|
|
|
This option is not turned on by any @option{-O} option since
|
|
it can result in incorrect output for programs that depend on
|
|
an exact implementation of IEEE or ISO rules/specifications for
|
|
math functions. It may, however, yield faster code for programs
|
|
that do not require the guarantees of these specifications.
|
|
|
|
The default is @option{-fno-finite-math-only}.
|
|
|
|
@item -fno-signed-zeros
|
|
@opindex fno-signed-zeros
|
|
Allow optimizations for floating-point arithmetic that ignore the
|
|
signedness of zero. IEEE arithmetic specifies the behavior of
|
|
distinct +0.0 and @minus{}0.0 values, which then prohibits simplification
|
|
of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}).
|
|
This option implies that the sign of a zero result isn't significant.
|
|
|
|
The default is @option{-fsigned-zeros}.
|
|
|
|
@item -fno-trapping-math
|
|
@opindex fno-trapping-math
|
|
Compile code assuming that floating-point operations cannot generate
|
|
user-visible traps. These traps include division by zero, overflow,
|
|
underflow, inexact result and invalid operation. This option requires
|
|
that @option{-fno-signaling-nans} be in effect. Setting this option may
|
|
allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example.
|
|
|
|
This option should never be turned on by any @option{-O} option since
|
|
it can result in incorrect output for programs that depend on
|
|
an exact implementation of IEEE or ISO rules/specifications for
|
|
math functions.
|
|
|
|
The default is @option{-ftrapping-math}.
|
|
|
|
@item -frounding-math
|
|
@opindex frounding-math
|
|
Disable transformations and optimizations that assume default floating-point
|
|
rounding behavior. This is round-to-zero for all floating point
|
|
to integer conversions, and round-to-nearest for all other arithmetic
|
|
truncations. This option should be specified for programs that change
|
|
the FP rounding mode dynamically, or that may be executed with a
|
|
non-default rounding mode. This option disables constant folding of
|
|
floating-point expressions at compile time (which may be affected by
|
|
rounding mode) and arithmetic transformations that are unsafe in the
|
|
presence of sign-dependent rounding modes.
|
|
|
|
The default is @option{-fno-rounding-math}.
|
|
|
|
This option is experimental and does not currently guarantee to
|
|
disable all GCC optimizations that are affected by rounding mode.
|
|
Future versions of GCC may provide finer control of this setting
|
|
using C99's @code{FENV_ACCESS} pragma. This command-line option
|
|
will be used to specify the default state for @code{FENV_ACCESS}.
|
|
|
|
@item -fsignaling-nans
|
|
@opindex fsignaling-nans
|
|
Compile code assuming that IEEE signaling NaNs may generate user-visible
|
|
traps during floating-point operations. Setting this option disables
|
|
optimizations that may change the number of exceptions visible with
|
|
signaling NaNs. This option implies @option{-ftrapping-math}.
|
|
|
|
This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
|
|
be defined.
|
|
|
|
The default is @option{-fno-signaling-nans}.
|
|
|
|
This option is experimental and does not currently guarantee to
|
|
disable all GCC optimizations that affect signaling NaN behavior.
|
|
|
|
@item -fno-fp-int-builtin-inexact
|
|
@opindex fno-fp-int-builtin-inexact
|
|
Do not allow the built-in functions @code{ceil}, @code{floor},
|
|
@code{round} and @code{trunc}, and their @code{float} and @code{long
|
|
double} variants, to generate code that raises the ``inexact''
|
|
floating-point exception for noninteger arguments. ISO C99 and C11
|
|
allow these functions to raise the ``inexact'' exception, but ISO/IEC
|
|
TS 18661-1:2014, the C bindings to IEEE 754-2008, does not allow these
|
|
functions to do so.
|
|
|
|
The default is @option{-ffp-int-builtin-inexact}, allowing the
|
|
exception to be raised. This option does nothing unless
|
|
@option{-ftrapping-math} is in effect.
|
|
|
|
Even if @option{-fno-fp-int-builtin-inexact} is used, if the functions
|
|
generate a call to a library function then the ``inexact'' exception
|
|
may be raised if the library implementation does not follow TS 18661.
|
|
|
|
@item -fsingle-precision-constant
|
|
@opindex fsingle-precision-constant
|
|
Treat floating-point constants as single precision instead of
|
|
implicitly converting them to double-precision constants.
|
|
|
|
@item -fcx-limited-range
|
|
@opindex fcx-limited-range
|
|
When enabled, this option states that a range reduction step is not
|
|
needed when performing complex division. Also, there is no checking
|
|
whether the result of a complex multiplication or division is @code{NaN
|
|
+ I*NaN}, with an attempt to rescue the situation in that case. The
|
|
default is @option{-fno-cx-limited-range}, but is enabled by
|
|
@option{-ffast-math}.
|
|
|
|
This option controls the default setting of the ISO C99
|
|
@code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to
|
|
all languages.
|
|
|
|
@item -fcx-fortran-rules
|
|
@opindex fcx-fortran-rules
|
|
Complex multiplication and division follow Fortran rules. Range
|
|
reduction is done as part of complex division, but there is no checking
|
|
whether the result of a complex multiplication or division is @code{NaN
|
|
+ I*NaN}, with an attempt to rescue the situation in that case.
|
|
|
|
The default is @option{-fno-cx-fortran-rules}.
|
|
|
|
@end table
|
|
|
|
The following options control optimizations that may improve
|
|
performance, but are not enabled by any @option{-O} options. This
|
|
section includes experimental options that may produce broken code.
|
|
|
|
@table @gcctabopt
|
|
@item -fbranch-probabilities
|
|
@opindex fbranch-probabilities
|
|
After running a program compiled with @option{-fprofile-arcs}
|
|
(@pxref{Instrumentation Options}),
|
|
you can compile it a second time using
|
|
@option{-fbranch-probabilities}, to improve optimizations based on
|
|
the number of times each branch was taken. When a program
|
|
compiled with @option{-fprofile-arcs} exits, it saves arc execution
|
|
counts to a file called @file{@var{sourcename}.gcda} for each source
|
|
file. The information in this data file is very dependent on the
|
|
structure of the generated code, so you must use the same source code
|
|
and the same optimization options for both compilations.
|
|
|
|
With @option{-fbranch-probabilities}, GCC puts a
|
|
@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
|
|
These can be used to improve optimization. Currently, they are only
|
|
used in one place: in @file{reorg.c}, instead of guessing which path a
|
|
branch is most likely to take, the @samp{REG_BR_PROB} values are used to
|
|
exactly determine which path is taken more often.
|
|
|
|
@item -fprofile-values
|
|
@opindex fprofile-values
|
|
If combined with @option{-fprofile-arcs}, it adds code so that some
|
|
data about values of expressions in the program is gathered.
|
|
|
|
With @option{-fbranch-probabilities}, it reads back the data gathered
|
|
from profiling values of expressions for usage in optimizations.
|
|
|
|
Enabled with @option{-fprofile-generate} and @option{-fprofile-use}.
|
|
|
|
@item -fprofile-reorder-functions
|
|
@opindex fprofile-reorder-functions
|
|
Function reordering based on profile instrumentation collects
|
|
first time of execution of a function and orders these functions
|
|
in ascending order.
|
|
|
|
Enabled with @option{-fprofile-use}.
|
|
|
|
@item -fvpt
|
|
@opindex fvpt
|
|
If combined with @option{-fprofile-arcs}, this option instructs the compiler
|
|
to add code to gather information about values of expressions.
|
|
|
|
With @option{-fbranch-probabilities}, it reads back the data gathered
|
|
and actually performs the optimizations based on them.
|
|
Currently the optimizations include specialization of division operations
|
|
using the knowledge about the value of the denominator.
|
|
|
|
@item -frename-registers
|
|
@opindex frename-registers
|
|
Attempt to avoid false dependencies in scheduled code by making use
|
|
of registers left over after register allocation. This optimization
|
|
most benefits processors with lots of registers. Depending on the
|
|
debug information format adopted by the target, however, it can
|
|
make debugging impossible, since variables no longer stay in
|
|
a ``home register''.
|
|
|
|
Enabled by default with @option{-funroll-loops}.
|
|
|
|
@item -fschedule-fusion
|
|
@opindex fschedule-fusion
|
|
Performs a target dependent pass over the instruction stream to schedule
|
|
instructions of same type together because target machine can execute them
|
|
more efficiently if they are adjacent to each other in the instruction flow.
|
|
|
|
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
|
|
|
|
@item -ftracer
|
|
@opindex ftracer
|
|
Perform tail duplication to enlarge superblock size. This transformation
|
|
simplifies the control flow of the function allowing other optimizations to do
|
|
a better job.
|
|
|
|
Enabled with @option{-fprofile-use}.
|
|
|
|
@item -funroll-loops
|
|
@opindex funroll-loops
|
|
Unroll loops whose number of iterations can be determined at compile time or
|
|
upon entry to the loop. @option{-funroll-loops} implies
|
|
@option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}.
|
|
It also turns on complete loop peeling (i.e.@: complete removal of loops with
|
|
a small constant number of iterations). This option makes code larger, and may
|
|
or may not make it run faster.
|
|
|
|
Enabled with @option{-fprofile-use}.
|
|
|
|
@item -funroll-all-loops
|
|
@opindex funroll-all-loops
|
|
Unroll all loops, even if their number of iterations is uncertain when
|
|
the loop is entered. This usually makes programs run more slowly.
|
|
@option{-funroll-all-loops} implies the same options as
|
|
@option{-funroll-loops}.
|
|
|
|
@item -fpeel-loops
|
|
@opindex fpeel-loops
|
|
Peels loops for which there is enough information that they do not
|
|
roll much (from profile feedback or static analysis). It also turns on
|
|
complete loop peeling (i.e.@: complete removal of loops with small constant
|
|
number of iterations).
|
|
|
|
Enabled with @option{-O3} and/or @option{-fprofile-use}.
|
|
|
|
@item -fmove-loop-invariants
|
|
@opindex fmove-loop-invariants
|
|
Enables the loop invariant motion pass in the RTL loop optimizer. Enabled
|
|
at level @option{-O1}
|
|
|
|
@item -fsplit-loops
|
|
@opindex fsplit-loops
|
|
Split a loop into two if it contains a condition that's always true
|
|
for one side of the iteration space and false for the other.
|
|
|
|
@item -funswitch-loops
|
|
@opindex funswitch-loops
|
|
Move branches with loop invariant conditions out of the loop, with duplicates
|
|
of the loop on both branches (modified according to result of the condition).
|
|
|
|
@item -ffunction-sections
|
|
@itemx -fdata-sections
|
|
@opindex ffunction-sections
|
|
@opindex fdata-sections
|
|
Place each function or data item into its own section in the output
|
|
file if the target supports arbitrary sections. The name of the
|
|
function or the name of the data item determines the section's name
|
|
in the output file.
|
|
|
|
Use these options on systems where the linker can perform optimizations
|
|
to improve locality of reference in the instruction space. Most systems
|
|
using the ELF object format and SPARC processors running Solaris 2 have
|
|
linkers with such optimizations. AIX may have these optimizations in
|
|
the future.
|
|
|
|
Only use these options when there are significant benefits from doing
|
|
so. When you specify these options, the assembler and linker
|
|
create larger object and executable files and are also slower.
|
|
You cannot use @command{gprof} on all systems if you
|
|
specify this option, and you may have problems with debugging if
|
|
you specify both this option and @option{-g}.
|
|
|
|
@item -fbranch-target-load-optimize
|
|
@opindex fbranch-target-load-optimize
|
|
Perform branch target register load optimization before prologue / epilogue
|
|
threading.
|
|
The use of target registers can typically be exposed only during reload,
|
|
thus hoisting loads out of loops and doing inter-block scheduling needs
|
|
a separate optimization pass.
|
|
|
|
@item -fbranch-target-load-optimize2
|
|
@opindex fbranch-target-load-optimize2
|
|
Perform branch target register load optimization after prologue / epilogue
|
|
threading.
|
|
|
|
@item -fbtr-bb-exclusive
|
|
@opindex fbtr-bb-exclusive
|
|
When performing branch target register load optimization, don't reuse
|
|
branch target registers within any basic block.
|
|
|
|
@item -fstdarg-opt
|
|
@opindex fstdarg-opt
|
|
Optimize the prologue of variadic argument functions with respect to usage of
|
|
those arguments.
|
|
|
|
@item -fsection-anchors
|
|
@opindex fsection-anchors
|
|
Try to reduce the number of symbolic address calculations by using
|
|
shared ``anchor'' symbols to address nearby objects. This transformation
|
|
can help to reduce the number of GOT entries and GOT accesses on some
|
|
targets.
|
|
|
|
For example, the implementation of the following function @code{foo}:
|
|
|
|
@smallexample
|
|
static int a, b, c;
|
|
int foo (void) @{ return a + b + c; @}
|
|
@end smallexample
|
|
|
|
@noindent
|
|
usually calculates the addresses of all three variables, but if you
|
|
compile it with @option{-fsection-anchors}, it accesses the variables
|
|
from a common anchor point instead. The effect is similar to the
|
|
following pseudocode (which isn't valid C):
|
|
|
|
@smallexample
|
|
int foo (void)
|
|
@{
|
|
register int *xr = &x;
|
|
return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
|
|
@}
|
|
@end smallexample
|
|
|
|
Not all targets support this option.
|
|
|
|
@item --param @var{name}=@var{value}
|
|
@opindex param
|
|
In some places, GCC uses various constants to control the amount of
|
|
optimization that is done. For example, GCC does not inline functions
|
|
that contain more than a certain number of instructions. You can
|
|
control some of these constants on the command line using the
|
|
@option{--param} option.
|
|
|
|
The names of specific parameters, and the meaning of the values, are
|
|
tied to the internals of the compiler, and are subject to change
|
|
without notice in future releases.
|
|
|
|
In each case, the @var{value} is an integer. The allowable choices for
|
|
@var{name} are:
|
|
|
|
@table @gcctabopt
|
|
@item predictable-branch-outcome
|
|
When branch is predicted to be taken with probability lower than this threshold
|
|
(in percent), then it is considered well predictable. The default is 10.
|
|
|
|
@item max-rtl-if-conversion-insns
|
|
RTL if-conversion tries to remove conditional branches around a block and
|
|
replace them with conditionally executed instructions. This parameter
|
|
gives the maximum number of instructions in a block which should be
|
|
considered for if-conversion. The default is 10, though the compiler will
|
|
also use other heuristics to decide whether if-conversion is likely to be
|
|
profitable.
|
|
|
|
@item max-rtl-if-conversion-predictable-cost
|
|
@item max-rtl-if-conversion-unpredictable-cost
|
|
RTL if-conversion will try to remove conditional branches around a block
|
|
and replace them with conditionally executed instructions. These parameters
|
|
give the maximum permissible cost for the sequence that would be generated
|
|
by if-conversion depending on whether the branch is statically determined
|
|
to be predictable or not. The units for this parameter are the same as
|
|
those for the GCC internal seq_cost metric. The compiler will try to
|
|
provide a reasonable default for this parameter using the BRANCH_COST
|
|
target macro.
|
|
|
|
@item max-crossjump-edges
|
|
The maximum number of incoming edges to consider for cross-jumping.
|
|
The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in
|
|
the number of edges incoming to each block. Increasing values mean
|
|
more aggressive optimization, making the compilation time increase with
|
|
probably small improvement in executable size.
|
|
|
|
@item min-crossjump-insns
|
|
The minimum number of instructions that must be matched at the end
|
|
of two blocks before cross-jumping is performed on them. This
|
|
value is ignored in the case where all instructions in the block being
|
|
cross-jumped from are matched. The default value is 5.
|
|
|
|
@item max-grow-copy-bb-insns
|
|
The maximum code size expansion factor when copying basic blocks
|
|
instead of jumping. The expansion is relative to a jump instruction.
|
|
The default value is 8.
|
|
|
|
@item max-goto-duplication-insns
|
|
The maximum number of instructions to duplicate to a block that jumps
|
|
to a computed goto. To avoid @math{O(N^2)} behavior in a number of
|
|
passes, GCC factors computed gotos early in the compilation process,
|
|
and unfactors them as late as possible. Only computed jumps at the
|
|
end of a basic blocks with no more than max-goto-duplication-insns are
|
|
unfactored. The default value is 8.
|
|
|
|
@item max-delay-slot-insn-search
|
|
The maximum number of instructions to consider when looking for an
|
|
instruction to fill a delay slot. If more than this arbitrary number of
|
|
instructions are searched, the time savings from filling the delay slot
|
|
are minimal, so stop searching. Increasing values mean more
|
|
aggressive optimization, making the compilation time increase with probably
|
|
small improvement in execution time.
|
|
|
|
@item max-delay-slot-live-search
|
|
When trying to fill delay slots, the maximum number of instructions to
|
|
consider when searching for a block with valid live register
|
|
information. Increasing this arbitrarily chosen value means more
|
|
aggressive optimization, increasing the compilation time. This parameter
|
|
should be removed when the delay slot code is rewritten to maintain the
|
|
control-flow graph.
|
|
|
|
@item max-gcse-memory
|
|
The approximate maximum amount of memory that can be allocated in
|
|
order to perform the global common subexpression elimination
|
|
optimization. If more memory than specified is required, the
|
|
optimization is not done.
|
|
|
|
@item max-gcse-insertion-ratio
|
|
If the ratio of expression insertions to deletions is larger than this value
|
|
for any expression, then RTL PRE inserts or removes the expression and thus
|
|
leaves partially redundant computations in the instruction stream. The default value is 20.
|
|
|
|
@item max-pending-list-length
|
|
The maximum number of pending dependencies scheduling allows
|
|
before flushing the current state and starting over. Large functions
|
|
with few branches or calls can create excessively large lists which
|
|
needlessly consume memory and resources.
|
|
|
|
@item max-modulo-backtrack-attempts
|
|
The maximum number of backtrack attempts the scheduler should make
|
|
when modulo scheduling a loop. Larger values can exponentially increase
|
|
compilation time.
|
|
|
|
@item max-inline-insns-single
|
|
Several parameters control the tree inliner used in GCC@.
|
|
This number sets the maximum number of instructions (counted in GCC's
|
|
internal representation) in a single function that the tree inliner
|
|
considers for inlining. This only affects functions declared
|
|
inline and methods implemented in a class declaration (C++).
|
|
The default value is 400.
|
|
|
|
@item max-inline-insns-auto
|
|
When you use @option{-finline-functions} (included in @option{-O3}),
|
|
a lot of functions that would otherwise not be considered for inlining
|
|
by the compiler are investigated. To those functions, a different
|
|
(more restrictive) limit compared to functions declared inline can
|
|
be applied.
|
|
The default value is 40.
|
|
|
|
@item inline-min-speedup
|
|
When estimated performance improvement of caller + callee runtime exceeds this
|
|
threshold (in precent), the function can be inlined regardless the limit on
|
|
@option{--param max-inline-insns-single} and @option{--param
|
|
max-inline-insns-auto}.
|
|
|
|
@item large-function-insns
|
|
The limit specifying really large functions. For functions larger than this
|
|
limit after inlining, inlining is constrained by
|
|
@option{--param large-function-growth}. This parameter is useful primarily
|
|
to avoid extreme compilation time caused by non-linear algorithms used by the
|
|
back end.
|
|
The default value is 2700.
|
|
|
|
@item large-function-growth
|
|
Specifies maximal growth of large function caused by inlining in percents.
|
|
The default value is 100 which limits large function growth to 2.0 times
|
|
the original size.
|
|
|
|
@item large-unit-insns
|
|
The limit specifying large translation unit. Growth caused by inlining of
|
|
units larger than this limit is limited by @option{--param inline-unit-growth}.
|
|
For small units this might be too tight.
|
|
For example, consider a unit consisting of function A
|
|
that is inline and B that just calls A three times. If B is small relative to
|
|
A, the growth of unit is 300\% and yet such inlining is very sane. For very
|
|
large units consisting of small inlineable functions, however, the overall unit
|
|
growth limit is needed to avoid exponential explosion of code size. Thus for
|
|
smaller units, the size is increased to @option{--param large-unit-insns}
|
|
before applying @option{--param inline-unit-growth}. The default is 10000.
|
|
|
|
@item inline-unit-growth
|
|
Specifies maximal overall growth of the compilation unit caused by inlining.
|
|
The default value is 20 which limits unit growth to 1.2 times the original
|
|
size. Cold functions (either marked cold via an attribute or by profile
|
|
feedback) are not accounted into the unit size.
|
|
|
|
@item ipcp-unit-growth
|
|
Specifies maximal overall growth of the compilation unit caused by
|
|
interprocedural constant propagation. The default value is 10 which limits
|
|
unit growth to 1.1 times the original size.
|
|
|
|
@item large-stack-frame
|
|
The limit specifying large stack frames. While inlining the algorithm is trying
|
|
to not grow past this limit too much. The default value is 256 bytes.
|
|
|
|
@item large-stack-frame-growth
|
|
Specifies maximal growth of large stack frames caused by inlining in percents.
|
|
The default value is 1000 which limits large stack frame growth to 11 times
|
|
the original size.
|
|
|
|
@item max-inline-insns-recursive
|
|
@itemx max-inline-insns-recursive-auto
|
|
Specifies the maximum number of instructions an out-of-line copy of a
|
|
self-recursive inline
|
|
function can grow into by performing recursive inlining.
|
|
|
|
@option{--param max-inline-insns-recursive} applies to functions
|
|
declared inline.
|
|
For functions not declared inline, recursive inlining
|
|
happens only when @option{-finline-functions} (included in @option{-O3}) is
|
|
enabled; @option{--param max-inline-insns-recursive-auto} applies instead. The
|
|
default value is 450.
|
|
|
|
@item max-inline-recursive-depth
|
|
@itemx max-inline-recursive-depth-auto
|
|
Specifies the maximum recursion depth used for recursive inlining.
|
|
|
|
@option{--param max-inline-recursive-depth} applies to functions
|
|
declared inline. For functions not declared inline, recursive inlining
|
|
happens only when @option{-finline-functions} (included in @option{-O3}) is
|
|
enabled; @option{--param max-inline-recursive-depth-auto} applies instead. The
|
|
default value is 8.
|
|
|
|
@item min-inline-recursive-probability
|
|
Recursive inlining is profitable only for function having deep recursion
|
|
in average and can hurt for function having little recursion depth by
|
|
increasing the prologue size or complexity of function body to other
|
|
optimizers.
|
|
|
|
When profile feedback is available (see @option{-fprofile-generate}) the actual
|
|
recursion depth can be guessed from the probability that function recurses
|
|
via a given call expression. This parameter limits inlining only to call
|
|
expressions whose probability exceeds the given threshold (in percents).
|
|
The default value is 10.
|
|
|
|
@item early-inlining-insns
|
|
Specify growth that the early inliner can make. In effect it increases
|
|
the amount of inlining for code having a large abstraction penalty.
|
|
The default value is 14.
|
|
|
|
@item max-early-inliner-iterations
|
|
Limit of iterations of the early inliner. This basically bounds
|
|
the number of nested indirect calls the early inliner can resolve.
|
|
Deeper chains are still handled by late inlining.
|
|
|
|
@item comdat-sharing-probability
|
|
Probability (in percent) that C++ inline function with comdat visibility
|
|
are shared across multiple compilation units. The default value is 20.
|
|
|
|
@item profile-func-internal-id
|
|
A parameter to control whether to use function internal id in profile
|
|
database lookup. If the value is 0, the compiler uses an id that
|
|
is based on function assembler name and filename, which makes old profile
|
|
data more tolerant to source changes such as function reordering etc.
|
|
The default value is 0.
|
|
|
|
@item min-vect-loop-bound
|
|
The minimum number of iterations under which loops are not vectorized
|
|
when @option{-ftree-vectorize} is used. The number of iterations after
|
|
vectorization needs to be greater than the value specified by this option
|
|
to allow vectorization. The default value is 0.
|
|
|
|
@item gcse-cost-distance-ratio
|
|
Scaling factor in calculation of maximum distance an expression
|
|
can be moved by GCSE optimizations. This is currently supported only in the
|
|
code hoisting pass. The bigger the ratio, the more aggressive code hoisting
|
|
is with simple expressions, i.e., the expressions that have cost
|
|
less than @option{gcse-unrestricted-cost}. Specifying 0 disables
|
|
hoisting of simple expressions. The default value is 10.
|
|
|
|
@item gcse-unrestricted-cost
|
|
Cost, roughly measured as the cost of a single typical machine
|
|
instruction, at which GCSE optimizations do not constrain
|
|
the distance an expression can travel. This is currently
|
|
supported only in the code hoisting pass. The lesser the cost,
|
|
the more aggressive code hoisting is. Specifying 0
|
|
allows all expressions to travel unrestricted distances.
|
|
The default value is 3.
|
|
|
|
@item max-hoist-depth
|
|
The depth of search in the dominator tree for expressions to hoist.
|
|
This is used to avoid quadratic behavior in hoisting algorithm.
|
|
The value of 0 does not limit on the search, but may slow down compilation
|
|
of huge functions. The default value is 30.
|
|
|
|
@item max-tail-merge-comparisons
|
|
The maximum amount of similar bbs to compare a bb with. This is used to
|
|
avoid quadratic behavior in tree tail merging. The default value is 10.
|
|
|
|
@item max-tail-merge-iterations
|
|
The maximum amount of iterations of the pass over the function. This is used to
|
|
limit compilation time in tree tail merging. The default value is 2.
|
|
|
|
@item store-merging-allow-unaligned
|
|
Allow the store merging pass to introduce unaligned stores if it is legal to
|
|
do so. The default value is 1.
|
|
|
|
@item max-stores-to-merge
|
|
The maximum number of stores to attempt to merge into wider stores in the store
|
|
merging pass. The minimum value is 2 and the default is 64.
|
|
|
|
@item max-unrolled-insns
|
|
The maximum number of instructions that a loop may have to be unrolled.
|
|
If a loop is unrolled, this parameter also determines how many times
|
|
the loop code is unrolled.
|
|
|
|
@item max-average-unrolled-insns
|
|
The maximum number of instructions biased by probabilities of their execution
|
|
that a loop may have to be unrolled. If a loop is unrolled,
|
|
this parameter also determines how many times the loop code is unrolled.
|
|
|
|
@item max-unroll-times
|
|
The maximum number of unrollings of a single loop.
|
|
|
|
@item max-peeled-insns
|
|
The maximum number of instructions that a loop may have to be peeled.
|
|
If a loop is peeled, this parameter also determines how many times
|
|
the loop code is peeled.
|
|
|
|
@item max-peel-times
|
|
The maximum number of peelings of a single loop.
|
|
|
|
@item max-peel-branches
|
|
The maximum number of branches on the hot path through the peeled sequence.
|
|
|
|
@item max-completely-peeled-insns
|
|
The maximum number of insns of a completely peeled loop.
|
|
|
|
@item max-completely-peel-times
|
|
The maximum number of iterations of a loop to be suitable for complete peeling.
|
|
|
|
@item max-completely-peel-loop-nest-depth
|
|
The maximum depth of a loop nest suitable for complete peeling.
|
|
|
|
@item max-unswitch-insns
|
|
The maximum number of insns of an unswitched loop.
|
|
|
|
@item max-unswitch-level
|
|
The maximum number of branches unswitched in a single loop.
|
|
|
|
@item max-loop-headers-insns
|
|
The maximum number of insns in loop header duplicated by he copy loop headers
|
|
pass.
|
|
|
|
@item lim-expensive
|
|
The minimum cost of an expensive expression in the loop invariant motion.
|
|
|
|
@item iv-consider-all-candidates-bound
|
|
Bound on number of candidates for induction variables, below which
|
|
all candidates are considered for each use in induction variable
|
|
optimizations. If there are more candidates than this,
|
|
only the most relevant ones are considered to avoid quadratic time complexity.
|
|
|
|
@item iv-max-considered-uses
|
|
The induction variable optimizations give up on loops that contain more
|
|
induction variable uses.
|
|
|
|
@item iv-always-prune-cand-set-bound
|
|
If the number of candidates in the set is smaller than this value,
|
|
always try to remove unnecessary ivs from the set
|
|
when adding a new one.
|
|
|
|
@item avg-loop-niter
|
|
Average number of iterations of a loop.
|
|
|
|
@item dse-max-object-size
|
|
Maximum size (in bytes) of objects tracked bytewise by dead store elimination.
|
|
Larger values may result in larger compilation times.
|
|
|
|
@item scev-max-expr-size
|
|
Bound on size of expressions used in the scalar evolutions analyzer.
|
|
Large expressions slow the analyzer.
|
|
|
|
@item scev-max-expr-complexity
|
|
Bound on the complexity of the expressions in the scalar evolutions analyzer.
|
|
Complex expressions slow the analyzer.
|
|
|
|
@item max-tree-if-conversion-phi-args
|
|
Maximum number of arguments in a PHI supported by TREE if conversion
|
|
unless the loop is marked with simd pragma.
|
|
|
|
@item vect-max-version-for-alignment-checks
|
|
The maximum number of run-time checks that can be performed when
|
|
doing loop versioning for alignment in the vectorizer.
|
|
|
|
@item vect-max-version-for-alias-checks
|
|
The maximum number of run-time checks that can be performed when
|
|
doing loop versioning for alias in the vectorizer.
|
|
|
|
@item vect-max-peeling-for-alignment
|
|
The maximum number of loop peels to enhance access alignment
|
|
for vectorizer. Value -1 means no limit.
|
|
|
|
@item max-iterations-to-track
|
|
The maximum number of iterations of a loop the brute-force algorithm
|
|
for analysis of the number of iterations of the loop tries to evaluate.
|
|
|
|
@item hot-bb-count-ws-permille
|
|
A basic block profile count is considered hot if it contributes to
|
|
the given permillage (i.e. 0...1000) of the entire profiled execution.
|
|
|
|
@item hot-bb-frequency-fraction
|
|
Select fraction of the entry block frequency of executions of basic block in
|
|
function given basic block needs to have to be considered hot.
|
|
|
|
@item max-predicted-iterations
|
|
The maximum number of loop iterations we predict statically. This is useful
|
|
in cases where a function contains a single loop with known bound and
|
|
another loop with unknown bound.
|
|
The known number of iterations is predicted correctly, while
|
|
the unknown number of iterations average to roughly 10. This means that the
|
|
loop without bounds appears artificially cold relative to the other one.
|
|
|
|
@item builtin-expect-probability
|
|
Control the probability of the expression having the specified value. This
|
|
parameter takes a percentage (i.e. 0 ... 100) as input.
|
|
The default probability of 90 is obtained empirically.
|
|
|
|
@item align-threshold
|
|
|
|
Select fraction of the maximal frequency of executions of a basic block in
|
|
a function to align the basic block.
|
|
|
|
@item align-loop-iterations
|
|
|
|
A loop expected to iterate at least the selected number of iterations is
|
|
aligned.
|
|
|
|
@item tracer-dynamic-coverage
|
|
@itemx tracer-dynamic-coverage-feedback
|
|
|
|
This value is used to limit superblock formation once the given percentage of
|
|
executed instructions is covered. This limits unnecessary code size
|
|
expansion.
|
|
|
|
The @option{tracer-dynamic-coverage-feedback} parameter
|
|
is used only when profile
|
|
feedback is available. The real profiles (as opposed to statically estimated
|
|
ones) are much less balanced allowing the threshold to be larger value.
|
|
|
|
@item tracer-max-code-growth
|
|
Stop tail duplication once code growth has reached given percentage. This is
|
|
a rather artificial limit, as most of the duplicates are eliminated later in
|
|
cross jumping, so it may be set to much higher values than is the desired code
|
|
growth.
|
|
|
|
@item tracer-min-branch-ratio
|
|
|
|
Stop reverse growth when the reverse probability of best edge is less than this
|
|
threshold (in percent).
|
|
|
|
@item tracer-min-branch-probability
|
|
@itemx tracer-min-branch-probability-feedback
|
|
|
|
Stop forward growth if the best edge has probability lower than this
|
|
threshold.
|
|
|
|
Similarly to @option{tracer-dynamic-coverage} two parameters are
|
|
provided. @option{tracer-min-branch-probability-feedback} is used for
|
|
compilation with profile feedback and @option{tracer-min-branch-probability}
|
|
compilation without. The value for compilation with profile feedback
|
|
needs to be more conservative (higher) in order to make tracer
|
|
effective.
|
|
|
|
@item max-cse-path-length
|
|
|
|
The maximum number of basic blocks on path that CSE considers.
|
|
The default is 10.
|
|
|
|
@item max-cse-insns
|
|
The maximum number of instructions CSE processes before flushing.
|
|
The default is 1000.
|
|
|
|
@item ggc-min-expand
|
|
|
|
GCC uses a garbage collector to manage its own memory allocation. This
|
|
parameter specifies the minimum percentage by which the garbage
|
|
collector's heap should be allowed to expand between collections.
|
|
Tuning this may improve compilation speed; it has no effect on code
|
|
generation.
|
|
|
|
The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
|
|
RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is
|
|
the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If
|
|
GCC is not able to calculate RAM on a particular platform, the lower
|
|
bound of 30% is used. Setting this parameter and
|
|
@option{ggc-min-heapsize} to zero causes a full collection to occur at
|
|
every opportunity. This is extremely slow, but can be useful for
|
|
debugging.
|
|
|
|
@item ggc-min-heapsize
|
|
|
|
Minimum size of the garbage collector's heap before it begins bothering
|
|
to collect garbage. The first collection occurs after the heap expands
|
|
by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again,
|
|
tuning this may improve compilation speed, and has no effect on code
|
|
generation.
|
|
|
|
The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that
|
|
tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
|
|
with a lower bound of 4096 (four megabytes) and an upper bound of
|
|
131072 (128 megabytes). If GCC is not able to calculate RAM on a
|
|
particular platform, the lower bound is used. Setting this parameter
|
|
very large effectively disables garbage collection. Setting this
|
|
parameter and @option{ggc-min-expand} to zero causes a full collection
|
|
to occur at every opportunity.
|
|
|
|
@item max-reload-search-insns
|
|
The maximum number of instruction reload should look backward for equivalent
|
|
register. Increasing values mean more aggressive optimization, making the
|
|
compilation time increase with probably slightly better performance.
|
|
The default value is 100.
|
|
|
|
@item max-cselib-memory-locations
|
|
The maximum number of memory locations cselib should take into account.
|
|
Increasing values mean more aggressive optimization, making the compilation time
|
|
increase with probably slightly better performance. The default value is 500.
|
|
|
|
@item max-sched-ready-insns
|
|
The maximum number of instructions ready to be issued the scheduler should
|
|
consider at any given time during the first scheduling pass. Increasing
|
|
values mean more thorough searches, making the compilation time increase
|
|
with probably little benefit. The default value is 100.
|
|
|
|
@item max-sched-region-blocks
|
|
The maximum number of blocks in a region to be considered for
|
|
interblock scheduling. The default value is 10.
|
|
|
|
@item max-pipeline-region-blocks
|
|
The maximum number of blocks in a region to be considered for
|
|
pipelining in the selective scheduler. The default value is 15.
|
|
|
|
@item max-sched-region-insns
|
|
The maximum number of insns in a region to be considered for
|
|
interblock scheduling. The default value is 100.
|
|
|
|
@item max-pipeline-region-insns
|
|
The maximum number of insns in a region to be considered for
|
|
pipelining in the selective scheduler. The default value is 200.
|
|
|
|
@item min-spec-prob
|
|
The minimum probability (in percents) of reaching a source block
|
|
for interblock speculative scheduling. The default value is 40.
|
|
|
|
@item max-sched-extend-regions-iters
|
|
The maximum number of iterations through CFG to extend regions.
|
|
A value of 0 (the default) disables region extensions.
|
|
|
|
@item max-sched-insn-conflict-delay
|
|
The maximum conflict delay for an insn to be considered for speculative motion.
|
|
The default value is 3.
|
|
|
|
@item sched-spec-prob-cutoff
|
|
The minimal probability of speculation success (in percents), so that
|
|
speculative insns are scheduled.
|
|
The default value is 40.
|
|
|
|
@item sched-state-edge-prob-cutoff
|
|
The minimum probability an edge must have for the scheduler to save its
|
|
state across it.
|
|
The default value is 10.
|
|
|
|
@item sched-mem-true-dep-cost
|
|
Minimal distance (in CPU cycles) between store and load targeting same
|
|
memory locations. The default value is 1.
|
|
|
|
@item selsched-max-lookahead
|
|
The maximum size of the lookahead window of selective scheduling. It is a
|
|
depth of search for available instructions.
|
|
The default value is 50.
|
|
|
|
@item selsched-max-sched-times
|
|
The maximum number of times that an instruction is scheduled during
|
|
selective scheduling. This is the limit on the number of iterations
|
|
through which the instruction may be pipelined. The default value is 2.
|
|
|
|
@item selsched-insns-to-rename
|
|
The maximum number of best instructions in the ready list that are considered
|
|
for renaming in the selective scheduler. The default value is 2.
|
|
|
|
@item sms-min-sc
|
|
The minimum value of stage count that swing modulo scheduler
|
|
generates. The default value is 2.
|
|
|
|
@item max-last-value-rtl
|
|
The maximum size measured as number of RTLs that can be recorded in an expression
|
|
in combiner for a pseudo register as last known value of that register. The default
|
|
is 10000.
|
|
|
|
@item max-combine-insns
|
|
The maximum number of instructions the RTL combiner tries to combine.
|
|
The default value is 2 at @option{-Og} and 4 otherwise.
|
|
|
|
@item integer-share-limit
|
|
Small integer constants can use a shared data structure, reducing the
|
|
compiler's memory usage and increasing its speed. This sets the maximum
|
|
value of a shared integer constant. The default value is 256.
|
|
|
|
@item ssp-buffer-size
|
|
The minimum size of buffers (i.e.@: arrays) that receive stack smashing
|
|
protection when @option{-fstack-protection} is used.
|
|
|
|
@item min-size-for-stack-sharing
|
|
The minimum size of variables taking part in stack slot sharing when not
|
|
optimizing. The default value is 32.
|
|
|
|
@item max-jump-thread-duplication-stmts
|
|
Maximum number of statements allowed in a block that needs to be
|
|
duplicated when threading jumps.
|
|
|
|
@item max-fields-for-field-sensitive
|
|
Maximum number of fields in a structure treated in
|
|
a field sensitive manner during pointer analysis. The default is zero
|
|
for @option{-O0} and @option{-O1},
|
|
and 100 for @option{-Os}, @option{-O2}, and @option{-O3}.
|
|
|
|
@item prefetch-latency
|
|
Estimate on average number of instructions that are executed before
|
|
prefetch finishes. The distance prefetched ahead is proportional
|
|
to this constant. Increasing this number may also lead to less
|
|
streams being prefetched (see @option{simultaneous-prefetches}).
|
|
|
|
@item simultaneous-prefetches
|
|
Maximum number of prefetches that can run at the same time.
|
|
|
|
@item l1-cache-line-size
|
|
The size of cache line in L1 cache, in bytes.
|
|
|
|
@item l1-cache-size
|
|
The size of L1 cache, in kilobytes.
|
|
|
|
@item l2-cache-size
|
|
The size of L2 cache, in kilobytes.
|
|
|
|
@item min-insn-to-prefetch-ratio
|
|
The minimum ratio between the number of instructions and the
|
|
number of prefetches to enable prefetching in a loop.
|
|
|
|
@item prefetch-min-insn-to-mem-ratio
|
|
The minimum ratio between the number of instructions and the
|
|
number of memory references to enable prefetching in a loop.
|
|
|
|
@item use-canonical-types
|
|
Whether the compiler should use the ``canonical'' type system. By
|
|
default, this should always be 1, which uses a more efficient internal
|
|
mechanism for comparing types in C++ and Objective-C++. However, if
|
|
bugs in the canonical type system are causing compilation failures,
|
|
set this value to 0 to disable canonical types.
|
|
|
|
@item switch-conversion-max-branch-ratio
|
|
Switch initialization conversion refuses to create arrays that are
|
|
bigger than @option{switch-conversion-max-branch-ratio} times the number of
|
|
branches in the switch.
|
|
|
|
@item max-partial-antic-length
|
|
Maximum length of the partial antic set computed during the tree
|
|
partial redundancy elimination optimization (@option{-ftree-pre}) when
|
|
optimizing at @option{-O3} and above. For some sorts of source code
|
|
the enhanced partial redundancy elimination optimization can run away,
|
|
consuming all of the memory available on the host machine. This
|
|
parameter sets a limit on the length of the sets that are computed,
|
|
which prevents the runaway behavior. Setting a value of 0 for
|
|
this parameter allows an unlimited set length.
|
|
|
|
@item sccvn-max-scc-size
|
|
Maximum size of a strongly connected component (SCC) during SCCVN
|
|
processing. If this limit is hit, SCCVN processing for the whole
|
|
function is not done and optimizations depending on it are
|
|
disabled. The default maximum SCC size is 10000.
|
|
|
|
@item sccvn-max-alias-queries-per-access
|
|
Maximum number of alias-oracle queries we perform when looking for
|
|
redundancies for loads and stores. If this limit is hit the search
|
|
is aborted and the load or store is not considered redundant. The
|
|
number of queries is algorithmically limited to the number of
|
|
stores on all paths from the load to the function entry.
|
|
The default maximum number of queries is 1000.
|
|
|
|
@item ira-max-loops-num
|
|
IRA uses regional register allocation by default. If a function
|
|
contains more loops than the number given by this parameter, only at most
|
|
the given number of the most frequently-executed loops form regions
|
|
for regional register allocation. The default value of the
|
|
parameter is 100.
|
|
|
|
@item ira-max-conflict-table-size
|
|
Although IRA uses a sophisticated algorithm to compress the conflict
|
|
table, the table can still require excessive amounts of memory for
|
|
huge functions. If the conflict table for a function could be more
|
|
than the size in MB given by this parameter, the register allocator
|
|
instead uses a faster, simpler, and lower-quality
|
|
algorithm that does not require building a pseudo-register conflict table.
|
|
The default value of the parameter is 2000.
|
|
|
|
@item ira-loop-reserved-regs
|
|
IRA can be used to evaluate more accurate register pressure in loops
|
|
for decisions to move loop invariants (see @option{-O3}). The number
|
|
of available registers reserved for some other purposes is given
|
|
by this parameter. The default value of the parameter is 2, which is
|
|
the minimal number of registers needed by typical instructions.
|
|
This value is the best found from numerous experiments.
|
|
|
|
@item lra-inheritance-ebb-probability-cutoff
|
|
LRA tries to reuse values reloaded in registers in subsequent insns.
|
|
This optimization is called inheritance. EBB is used as a region to
|
|
do this optimization. The parameter defines a minimal fall-through
|
|
edge probability in percentage used to add BB to inheritance EBB in
|
|
LRA. The default value of the parameter is 40. The value was chosen
|
|
from numerous runs of SPEC2000 on x86-64.
|
|
|
|
@item loop-invariant-max-bbs-in-loop
|
|
Loop invariant motion can be very expensive, both in compilation time and
|
|
in amount of needed compile-time memory, with very large loops. Loops
|
|
with more basic blocks than this parameter won't have loop invariant
|
|
motion optimization performed on them. The default value of the
|
|
parameter is 1000 for @option{-O1} and 10000 for @option{-O2} and above.
|
|
|
|
@item loop-max-datarefs-for-datadeps
|
|
Building data dependencies is expensive for very large loops. This
|
|
parameter limits the number of data references in loops that are
|
|
considered for data dependence analysis. These large loops are no
|
|
handled by the optimizations using loop data dependencies.
|
|
The default value is 1000.
|
|
|
|
@item max-vartrack-size
|
|
Sets a maximum number of hash table slots to use during variable
|
|
tracking dataflow analysis of any function. If this limit is exceeded
|
|
with variable tracking at assignments enabled, analysis for that
|
|
function is retried without it, after removing all debug insns from
|
|
the function. If the limit is exceeded even without debug insns, var
|
|
tracking analysis is completely disabled for the function. Setting
|
|
the parameter to zero makes it unlimited.
|
|
|
|
@item max-vartrack-expr-depth
|
|
Sets a maximum number of recursion levels when attempting to map
|
|
variable names or debug temporaries to value expressions. This trades
|
|
compilation time for more complete debug information. If this is set too
|
|
low, value expressions that are available and could be represented in
|
|
debug information may end up not being used; setting this higher may
|
|
enable the compiler to find more complex debug expressions, but compile
|
|
time and memory use may grow. The default is 12.
|
|
|
|
@item min-nondebug-insn-uid
|
|
Use uids starting at this parameter for nondebug insns. The range below
|
|
the parameter is reserved exclusively for debug insns created by
|
|
@option{-fvar-tracking-assignments}, but debug insns may get
|
|
(non-overlapping) uids above it if the reserved range is exhausted.
|
|
|
|
@item ipa-sra-ptr-growth-factor
|
|
IPA-SRA replaces a pointer to an aggregate with one or more new
|
|
parameters only when their cumulative size is less or equal to
|
|
@option{ipa-sra-ptr-growth-factor} times the size of the original
|
|
pointer parameter.
|
|
|
|
@item sra-max-scalarization-size-Ospeed
|
|
@item sra-max-scalarization-size-Osize
|
|
The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to
|
|
replace scalar parts of aggregates with uses of independent scalar
|
|
variables. These parameters control the maximum size, in storage units,
|
|
of aggregate which is considered for replacement when compiling for
|
|
speed
|
|
(@option{sra-max-scalarization-size-Ospeed}) or size
|
|
(@option{sra-max-scalarization-size-Osize}) respectively.
|
|
|
|
@item tm-max-aggregate-size
|
|
When making copies of thread-local variables in a transaction, this
|
|
parameter specifies the size in bytes after which variables are
|
|
saved with the logging functions as opposed to save/restore code
|
|
sequence pairs. This option only applies when using
|
|
@option{-fgnu-tm}.
|
|
|
|
@item graphite-max-nb-scop-params
|
|
To avoid exponential effects in the Graphite loop transforms, the
|
|
number of parameters in a Static Control Part (SCoP) is bounded. The
|
|
default value is 10 parameters. A variable whose value is unknown at
|
|
compilation time and defined outside a SCoP is a parameter of the SCoP.
|
|
|
|
@item graphite-max-bbs-per-function
|
|
To avoid exponential effects in the detection of SCoPs, the size of
|
|
the functions analyzed by Graphite is bounded. The default value is
|
|
100 basic blocks.
|
|
|
|
@item loop-block-tile-size
|
|
Loop blocking or strip mining transforms, enabled with
|
|
@option{-floop-block} or @option{-floop-strip-mine}, strip mine each
|
|
loop in the loop nest by a given number of iterations. The strip
|
|
length can be changed using the @option{loop-block-tile-size}
|
|
parameter. The default value is 51 iterations.
|
|
|
|
@item loop-unroll-jam-size
|
|
Specify the unroll factor for the @option{-floop-unroll-and-jam} option. The
|
|
default value is 4.
|
|
|
|
@item loop-unroll-jam-depth
|
|
Specify the dimension to be unrolled (counting from the most inner loop)
|
|
for the @option{-floop-unroll-and-jam}. The default value is 2.
|
|
|
|
@item ipa-cp-value-list-size
|
|
IPA-CP attempts to track all possible values and types passed to a function's
|
|
parameter in order to propagate them and perform devirtualization.
|
|
@option{ipa-cp-value-list-size} is the maximum number of values and types it
|
|
stores per one formal parameter of a function.
|
|
|
|
@item ipa-cp-eval-threshold
|
|
IPA-CP calculates its own score of cloning profitability heuristics
|
|
and performs those cloning opportunities with scores that exceed
|
|
@option{ipa-cp-eval-threshold}.
|
|
|
|
@item ipa-cp-recursion-penalty
|
|
Percentage penalty the recursive functions will receive when they
|
|
are evaluated for cloning.
|
|
|
|
@item ipa-cp-single-call-penalty
|
|
Percentage penalty functions containing a single call to another
|
|
function will receive when they are evaluated for cloning.
|
|
|
|
|
|
@item ipa-max-agg-items
|
|
IPA-CP is also capable to propagate a number of scalar values passed
|
|
in an aggregate. @option{ipa-max-agg-items} controls the maximum
|
|
number of such values per one parameter.
|
|
|
|
@item ipa-cp-loop-hint-bonus
|
|
When IPA-CP determines that a cloning candidate would make the number
|
|
of iterations of a loop known, it adds a bonus of
|
|
@option{ipa-cp-loop-hint-bonus} to the profitability score of
|
|
the candidate.
|
|
|
|
@item ipa-cp-array-index-hint-bonus
|
|
When IPA-CP determines that a cloning candidate would make the index of
|
|
an array access known, it adds a bonus of
|
|
@option{ipa-cp-array-index-hint-bonus} to the profitability
|
|
score of the candidate.
|
|
|
|
@item ipa-max-aa-steps
|
|
During its analysis of function bodies, IPA-CP employs alias analysis
|
|
in order to track values pointed to by function parameters. In order
|
|
not spend too much time analyzing huge functions, it gives up and
|
|
consider all memory clobbered after examining
|
|
@option{ipa-max-aa-steps} statements modifying memory.
|
|
|
|
@item lto-partitions
|
|
Specify desired number of partitions produced during WHOPR compilation.
|
|
The number of partitions should exceed the number of CPUs used for compilation.
|
|
The default value is 32.
|
|
|
|
@item lto-min-partition
|
|
Size of minimal partition for WHOPR (in estimated instructions).
|
|
This prevents expenses of splitting very small programs into too many
|
|
partitions.
|
|
|
|
@item lto-max-partition
|
|
Size of max partition for WHOPR (in estimated instructions).
|
|
to provide an upper bound for individual size of partition.
|
|
Meant to be used only with balanced partitioning.
|
|
|
|
@item cxx-max-namespaces-for-diagnostic-help
|
|
The maximum number of namespaces to consult for suggestions when C++
|
|
name lookup fails for an identifier. The default is 1000.
|
|
|
|
@item sink-frequency-threshold
|
|
The maximum relative execution frequency (in percents) of the target block
|
|
relative to a statement's original block to allow statement sinking of a
|
|
statement. Larger numbers result in more aggressive statement sinking.
|
|
The default value is 75. A small positive adjustment is applied for
|
|
statements with memory operands as those are even more profitable so sink.
|
|
|
|
@item max-stores-to-sink
|
|
The maximum number of conditional store pairs that can be sunk. Set to 0
|
|
if either vectorization (@option{-ftree-vectorize}) or if-conversion
|
|
(@option{-ftree-loop-if-convert}) is disabled. The default is 2.
|
|
|
|
@item allow-store-data-races
|
|
Allow optimizers to introduce new data races on stores.
|
|
Set to 1 to allow, otherwise to 0. This option is enabled by default
|
|
at optimization level @option{-Ofast}.
|
|
|
|
@item case-values-threshold
|
|
The smallest number of different values for which it is best to use a
|
|
jump-table instead of a tree of conditional branches. If the value is
|
|
0, use the default for the machine. The default is 0.
|
|
|
|
@item tree-reassoc-width
|
|
Set the maximum number of instructions executed in parallel in
|
|
reassociated tree. This parameter overrides target dependent
|
|
heuristics used by default if has non zero value.
|
|
|
|
@item sched-pressure-algorithm
|
|
Choose between the two available implementations of
|
|
@option{-fsched-pressure}. Algorithm 1 is the original implementation
|
|
and is the more likely to prevent instructions from being reordered.
|
|
Algorithm 2 was designed to be a compromise between the relatively
|
|
conservative approach taken by algorithm 1 and the rather aggressive
|
|
approach taken by the default scheduler. It relies more heavily on
|
|
having a regular register file and accurate register pressure classes.
|
|
See @file{haifa-sched.c} in the GCC sources for more details.
|
|
|
|
The default choice depends on the target.
|
|
|
|
@item max-slsr-cand-scan
|
|
Set the maximum number of existing candidates that are considered when
|
|
seeking a basis for a new straight-line strength reduction candidate.
|
|
|
|
@item asan-globals
|
|
Enable buffer overflow detection for global objects. This kind
|
|
of protection is enabled by default if you are using
|
|
@option{-fsanitize=address} option.
|
|
To disable global objects protection use @option{--param asan-globals=0}.
|
|
|
|
@item asan-stack
|
|
Enable buffer overflow detection for stack objects. This kind of
|
|
protection is enabled by default when using @option{-fsanitize=address}.
|
|
To disable stack protection use @option{--param asan-stack=0} option.
|
|
|
|
@item asan-instrument-reads
|
|
Enable buffer overflow detection for memory reads. This kind of
|
|
protection is enabled by default when using @option{-fsanitize=address}.
|
|
To disable memory reads protection use
|
|
@option{--param asan-instrument-reads=0}.
|
|
|
|
@item asan-instrument-writes
|
|
Enable buffer overflow detection for memory writes. This kind of
|
|
protection is enabled by default when using @option{-fsanitize=address}.
|
|
To disable memory writes protection use
|
|
@option{--param asan-instrument-writes=0} option.
|
|
|
|
@item asan-memintrin
|
|
Enable detection for built-in functions. This kind of protection
|
|
is enabled by default when using @option{-fsanitize=address}.
|
|
To disable built-in functions protection use
|
|
@option{--param asan-memintrin=0}.
|
|
|
|
@item asan-use-after-return
|
|
Enable detection of use-after-return. This kind of protection
|
|
is enabled by default when using @option{-fsanitize=address} option.
|
|
To disable use-after-return detection use
|
|
@option{--param asan-use-after-return=0}.
|
|
|
|
Note: The check is disabled by default at runtime. To enable the check,
|
|
you should set environment variable @env{ASAN_OPTIONS} to
|
|
@code{detect_stack_use_after_return=1}.
|
|
|
|
@item asan-instrumentation-with-call-threshold
|
|
If number of memory accesses in function being instrumented
|
|
is greater or equal to this number, use callbacks instead of inline checks.
|
|
E.g. to disable inline code use
|
|
@option{--param asan-instrumentation-with-call-threshold=0}.
|
|
|
|
@item use-after-scope-direct-emission-threshold
|
|
If size of a local variables in bytes is smaller of equal to this number,
|
|
direct instruction emission is utilized to poison and unpoison local variables.
|
|
|
|
@item chkp-max-ctor-size
|
|
Static constructors generated by Pointer Bounds Checker may become very
|
|
large and significantly increase compile time at optimization level
|
|
@option{-O1} and higher. This parameter is a maximum nubmer of statements
|
|
in a single generated constructor. Default value is 5000.
|
|
|
|
@item max-fsm-thread-path-insns
|
|
Maximum number of instructions to copy when duplicating blocks on a
|
|
finite state automaton jump thread path. The default is 100.
|
|
|
|
@item max-fsm-thread-length
|
|
Maximum number of basic blocks on a finite state automaton jump thread
|
|
path. The default is 10.
|
|
|
|
@item max-fsm-thread-paths
|
|
Maximum number of new jump thread paths to create for a finite state
|
|
automaton. The default is 50.
|
|
|
|
@item parloops-chunk-size
|
|
Chunk size of omp schedule for loops parallelized by parloops. The default
|
|
is 0.
|
|
|
|
@item parloops-schedule
|
|
Schedule type of omp schedule for loops parallelized by parloops (static,
|
|
dynamic, guided, auto, runtime). The default is static.
|
|
|
|
@item max-ssa-name-query-depth
|
|
Maximum depth of recursion when querying properties of SSA names in things
|
|
like fold routines. One level of recursion corresponds to following a
|
|
use-def chain.
|
|
|
|
@item hsa-gen-debug-stores
|
|
Enable emission of special debug stores within HSA kernels which are
|
|
then read and reported by libgomp plugin. Generation of these stores
|
|
is disabled by default, use @option{--param hsa-gen-debug-stores=1} to
|
|
enable it.
|
|
|
|
@item max-speculative-devirt-maydefs
|
|
The maximum number of may-defs we analyze when looking for a must-def
|
|
specifying the dynamic type of an object that invokes a virtual call
|
|
we may be able to devirtualize speculatively.
|
|
|
|
@item max-vrp-switch-assertions
|
|
The maximum number of assertions to add along the default edge of a switch
|
|
statement during VRP. The default is 10.
|
|
@end table
|
|
@end table
|
|
|
|
@node Instrumentation Options
|
|
@section Program Instrumentation Options
|
|
@cindex instrumentation options
|
|
@cindex program instrumentation options
|
|
@cindex run-time error checking options
|
|
@cindex profiling options
|
|
@cindex options, program instrumentation
|
|
@cindex options, run-time error checking
|
|
@cindex options, profiling
|
|
|
|
GCC supports a number of command-line options that control adding
|
|
run-time instrumentation to the code it normally generates.
|
|
For example, one purpose of instrumentation is collect profiling
|
|
statistics for use in finding program hot spots, code coverage
|
|
analysis, or profile-guided optimizations.
|
|
Another class of program instrumentation is adding run-time checking
|
|
to detect programming errors like invalid pointer
|
|
dereferences or out-of-bounds array accesses, as well as deliberately
|
|
hostile attacks such as stack smashing or C++ vtable hijacking.
|
|
There is also a general hook which can be used to implement other
|
|
forms of tracing or function-level instrumentation for debug or
|
|
program analysis purposes.
|
|
|
|
@table @gcctabopt
|
|
@cindex @command{prof}
|
|
@item -p
|
|
@opindex p
|
|
Generate extra code to write profile information suitable for the
|
|
analysis program @command{prof}. You must use this option when compiling
|
|
the source files you want data about, and you must also use it when
|
|
linking.
|
|
|
|
@cindex @command{gprof}
|
|
@item -pg
|
|
@opindex pg
|
|
Generate extra code to write profile information suitable for the
|
|
analysis program @command{gprof}. You must use this option when compiling
|
|
the source files you want data about, and you must also use it when
|
|
linking.
|
|
|
|
@item -fprofile-arcs
|
|
@opindex fprofile-arcs
|
|
Add code so that program flow @dfn{arcs} are instrumented. During
|
|
execution the program records how many times each branch and call is
|
|
executed and how many times it is taken or returns. When the compiled
|
|
program exits it saves this data to a file called
|
|
@file{@var{auxname}.gcda} for each source file. The data may be used for
|
|
profile-directed optimizations (@option{-fbranch-probabilities}), or for
|
|
test coverage analysis (@option{-ftest-coverage}). Each object file's
|
|
@var{auxname} is generated from the name of the output file, if
|
|
explicitly specified and it is not the final executable, otherwise it is
|
|
the basename of the source file. In both cases any suffix is removed
|
|
(e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or
|
|
@file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}).
|
|
@xref{Cross-profiling}.
|
|
|
|
@cindex @command{gcov}
|
|
@item --coverage
|
|
@opindex coverage
|
|
|
|
This option is used to compile and link code instrumented for coverage
|
|
analysis. The option is a synonym for @option{-fprofile-arcs}
|
|
@option{-ftest-coverage} (when compiling) and @option{-lgcov} (when
|
|
linking). See the documentation for those options for more details.
|
|
|
|
@itemize
|
|
|
|
@item
|
|
Compile the source files with @option{-fprofile-arcs} plus optimization
|
|
and code generation options. For test coverage analysis, use the
|
|
additional @option{-ftest-coverage} option. You do not need to profile
|
|
every source file in a program.
|
|
|
|
@item
|
|
Link your object files with @option{-lgcov} or @option{-fprofile-arcs}
|
|
(the latter implies the former).
|
|
|
|
@item
|
|
Run the program on a representative workload to generate the arc profile
|
|
information. This may be repeated any number of times. You can run
|
|
concurrent instances of your program, and provided that the file system
|
|
supports locking, the data files will be correctly updated. Also
|
|
@code{fork} calls are detected and correctly handled (double counting
|
|
will not happen).
|
|
|
|
@item
|
|
For profile-directed optimizations, compile the source files again with
|
|
the same optimization and code generation options plus
|
|
@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that
|
|
Control Optimization}).
|
|
|
|
@item
|
|
For test coverage analysis, use @command{gcov} to produce human readable
|
|
information from the @file{.gcno} and @file{.gcda} files. Refer to the
|
|
@command{gcov} documentation for further information.
|
|
|
|
@end itemize
|
|
|
|
With @option{-fprofile-arcs}, for each function of your program GCC
|
|
creates a program flow graph, then finds a spanning tree for the graph.
|
|
Only arcs that are not on the spanning tree have to be instrumented: the
|
|
compiler adds code to count the number of times that these arcs are
|
|
executed. When an arc is the only exit or only entrance to a block, the
|
|
instrumentation code can be added to the block; otherwise, a new basic
|
|
block must be created to hold the instrumentation code.
|
|
|
|
@need 2000
|
|
@item -ftest-coverage
|
|
@opindex ftest-coverage
|
|
Produce a notes file that the @command{gcov} code-coverage utility
|
|
(@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to
|
|
show program coverage. Each source file's note file is called
|
|
@file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option
|
|
above for a description of @var{auxname} and instructions on how to
|
|
generate test coverage data. Coverage data matches the source files
|
|
more closely if you do not optimize.
|
|
|
|
@item -fprofile-dir=@var{path}
|
|
@opindex fprofile-dir
|
|
|
|
Set the directory to search for the profile data files in to @var{path}.
|
|
This option affects only the profile data generated by
|
|
@option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs}
|
|
and used by @option{-fprofile-use} and @option{-fbranch-probabilities}
|
|
and its related options. Both absolute and relative paths can be used.
|
|
By default, GCC uses the current directory as @var{path}, thus the
|
|
profile data file appears in the same directory as the object file.
|
|
|
|
@item -fprofile-generate
|
|
@itemx -fprofile-generate=@var{path}
|
|
@opindex fprofile-generate
|
|
|
|
Enable options usually used for instrumenting application to produce
|
|
profile useful for later recompilation with profile feedback based
|
|
optimization. You must use @option{-fprofile-generate} both when
|
|
compiling and when linking your program.
|
|
|
|
The following options are enabled: @option{-fprofile-arcs}, @option{-fprofile-values}, @option{-fvpt}.
|
|
|
|
If @var{path} is specified, GCC looks at the @var{path} to find
|
|
the profile feedback data files. See @option{-fprofile-dir}.
|
|
|
|
To optimize the program based on the collected profile information, use
|
|
@option{-fprofile-use}. @xref{Optimize Options}, for more information.
|
|
|
|
@item -fprofile-update=@var{method}
|
|
@opindex fprofile-update
|
|
|
|
Alter the update method for an application instrumented for profile
|
|
feedback based optimization. The @var{method} argument should be one of
|
|
@samp{single}, @samp{atomic} or @samp{prefer-atomic}.
|
|
The first one is useful for single-threaded applications,
|
|
while the second one prevents profile corruption by emitting thread-safe code.
|
|
|
|
@strong{Warning:} When an application does not properly join all threads
|
|
(or creates an detached thread), a profile file can be still corrupted.
|
|
|
|
Using @samp{prefer-atomic} would be transformed either to @samp{atomic},
|
|
when supported by a target, or to @samp{single} otherwise. The GCC driver
|
|
automatically selects @samp{prefer-atomic} when @option{-pthread}
|
|
is present in the command line.
|
|
|
|
@item -fsanitize=address
|
|
@opindex fsanitize=address
|
|
Enable AddressSanitizer, a fast memory error detector.
|
|
Memory access instructions are instrumented to detect
|
|
out-of-bounds and use-after-free bugs.
|
|
The option enables @option{-fsanitize-address-use-after-scope}.
|
|
See @uref{https://github.com/google/sanitizers/wiki/AddressSanitizer} for
|
|
more details. The run-time behavior can be influenced using the
|
|
@env{ASAN_OPTIONS} environment variable. When set to @code{help=1},
|
|
the available options are shown at startup of the instrumented program. See
|
|
@url{https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags}
|
|
for a list of supported options.
|
|
The option can't be combined with @option{-fsanitize=thread}.
|
|
|
|
@item -fsanitize=kernel-address
|
|
@opindex fsanitize=kernel-address
|
|
Enable AddressSanitizer for Linux kernel.
|
|
See @uref{https://github.com/google/kasan/wiki} for more details.
|
|
|
|
@item -fsanitize=thread
|
|
@opindex fsanitize=thread
|
|
Enable ThreadSanitizer, a fast data race detector.
|
|
Memory access instructions are instrumented to detect
|
|
data race bugs. See @uref{https://github.com/google/sanitizers/wiki#threadsanitizer} for more
|
|
details. The run-time behavior can be influenced using the @env{TSAN_OPTIONS}
|
|
environment variable; see
|
|
@url{https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags} for a list of
|
|
supported options.
|
|
The option can't be combined with @option{-fsanitize=address}
|
|
and/or @option{-fsanitize=leak}.
|
|
|
|
@item -fsanitize=leak
|
|
@opindex fsanitize=leak
|
|
Enable LeakSanitizer, a memory leak detector.
|
|
This option only matters for linking of executables and
|
|
the executable is linked against a library that overrides @code{malloc}
|
|
and other allocator functions. See
|
|
@uref{https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer} for more
|
|
details. The run-time behavior can be influenced using the
|
|
@env{LSAN_OPTIONS} environment variable.
|
|
The option can't be combined with @option{-fsanitize=thread}.
|
|
|
|
@item -fsanitize=undefined
|
|
@opindex fsanitize=undefined
|
|
Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector.
|
|
Various computations are instrumented to detect undefined behavior
|
|
at runtime. Current suboptions are:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -fsanitize=shift
|
|
@opindex fsanitize=shift
|
|
This option enables checking that the result of a shift operation is
|
|
not undefined. Note that what exactly is considered undefined differs
|
|
slightly between C and C++, as well as between ISO C90 and C99, etc.
|
|
This option has two suboptions, @option{-fsanitize=shift-base} and
|
|
@option{-fsanitize=shift-exponent}.
|
|
|
|
@item -fsanitize=shift-exponent
|
|
@opindex fsanitize=shift-exponent
|
|
This option enables checking that the second argument of a shift operation
|
|
is not negative and is smaller than the precision of the promoted first
|
|
argument.
|
|
|
|
@item -fsanitize=shift-base
|
|
@opindex fsanitize=shift-base
|
|
If the second argument of a shift operation is within range, check that the
|
|
result of a shift operation is not undefined. Note that what exactly is
|
|
considered undefined differs slightly between C and C++, as well as between
|
|
ISO C90 and C99, etc.
|
|
|
|
@item -fsanitize=integer-divide-by-zero
|
|
@opindex fsanitize=integer-divide-by-zero
|
|
Detect integer division by zero as well as @code{INT_MIN / -1} division.
|
|
|
|
@item -fsanitize=unreachable
|
|
@opindex fsanitize=unreachable
|
|
With this option, the compiler turns the @code{__builtin_unreachable}
|
|
call into a diagnostics message call instead. When reaching the
|
|
@code{__builtin_unreachable} call, the behavior is undefined.
|
|
|
|
@item -fsanitize=vla-bound
|
|
@opindex fsanitize=vla-bound
|
|
This option instructs the compiler to check that the size of a variable
|
|
length array is positive.
|
|
|
|
@item -fsanitize=null
|
|
@opindex fsanitize=null
|
|
This option enables pointer checking. Particularly, the application
|
|
built with this option turned on will issue an error message when it
|
|
tries to dereference a NULL pointer, or if a reference (possibly an
|
|
rvalue reference) is bound to a NULL pointer, or if a method is invoked
|
|
on an object pointed by a NULL pointer.
|
|
|
|
@item -fsanitize=return
|
|
@opindex fsanitize=return
|
|
This option enables return statement checking. Programs
|
|
built with this option turned on will issue an error message
|
|
when the end of a non-void function is reached without actually
|
|
returning a value. This option works in C++ only.
|
|
|
|
@item -fsanitize=signed-integer-overflow
|
|
@opindex fsanitize=signed-integer-overflow
|
|
This option enables signed integer overflow checking. We check that
|
|
the result of @code{+}, @code{*}, and both unary and binary @code{-}
|
|
does not overflow in the signed arithmetics. Note, integer promotion
|
|
rules must be taken into account. That is, the following is not an
|
|
overflow:
|
|
@smallexample
|
|
signed char a = SCHAR_MAX;
|
|
a++;
|
|
@end smallexample
|
|
|
|
@item -fsanitize=bounds
|
|
@opindex fsanitize=bounds
|
|
This option enables instrumentation of array bounds. Various out of bounds
|
|
accesses are detected. Flexible array members, flexible array member-like
|
|
arrays, and initializers of variables with static storage are not instrumented.
|
|
|
|
@item -fsanitize=bounds-strict
|
|
@opindex fsanitize=bounds-strict
|
|
This option enables strict instrumentation of array bounds. Most out of bounds
|
|
accesses are detected, including flexible array members and flexible array
|
|
member-like arrays. Initializers of variables with static storage are not
|
|
instrumented.
|
|
|
|
@item -fsanitize=alignment
|
|
@opindex fsanitize=alignment
|
|
|
|
This option enables checking of alignment of pointers when they are
|
|
dereferenced, or when a reference is bound to insufficiently aligned target,
|
|
or when a method or constructor is invoked on insufficiently aligned object.
|
|
|
|
@item -fsanitize=object-size
|
|
@opindex fsanitize=object-size
|
|
This option enables instrumentation of memory references using the
|
|
@code{__builtin_object_size} function. Various out of bounds pointer
|
|
accesses are detected.
|
|
|
|
@item -fsanitize=float-divide-by-zero
|
|
@opindex fsanitize=float-divide-by-zero
|
|
Detect floating-point division by zero. Unlike other similar options,
|
|
@option{-fsanitize=float-divide-by-zero} is not enabled by
|
|
@option{-fsanitize=undefined}, since floating-point division by zero can
|
|
be a legitimate way of obtaining infinities and NaNs.
|
|
|
|
@item -fsanitize=float-cast-overflow
|
|
@opindex fsanitize=float-cast-overflow
|
|
This option enables floating-point type to integer conversion checking.
|
|
We check that the result of the conversion does not overflow.
|
|
Unlike other similar options, @option{-fsanitize=float-cast-overflow} is
|
|
not enabled by @option{-fsanitize=undefined}.
|
|
This option does not work well with @code{FE_INVALID} exceptions enabled.
|
|
|
|
@item -fsanitize=nonnull-attribute
|
|
@opindex fsanitize=nonnull-attribute
|
|
|
|
This option enables instrumentation of calls, checking whether null values
|
|
are not passed to arguments marked as requiring a non-null value by the
|
|
@code{nonnull} function attribute.
|
|
|
|
@item -fsanitize=returns-nonnull-attribute
|
|
@opindex fsanitize=returns-nonnull-attribute
|
|
|
|
This option enables instrumentation of return statements in functions
|
|
marked with @code{returns_nonnull} function attribute, to detect returning
|
|
of null values from such functions.
|
|
|
|
@item -fsanitize=bool
|
|
@opindex fsanitize=bool
|
|
|
|
This option enables instrumentation of loads from bool. If a value other
|
|
than 0/1 is loaded, a run-time error is issued.
|
|
|
|
@item -fsanitize=enum
|
|
@opindex fsanitize=enum
|
|
|
|
This option enables instrumentation of loads from an enum type. If
|
|
a value outside the range of values for the enum type is loaded,
|
|
a run-time error is issued.
|
|
|
|
@item -fsanitize=vptr
|
|
@opindex fsanitize=vptr
|
|
|
|
This option enables instrumentation of C++ member function calls, member
|
|
accesses and some conversions between pointers to base and derived classes,
|
|
to verify the referenced object has the correct dynamic type.
|
|
|
|
@end table
|
|
|
|
While @option{-ftrapv} causes traps for signed overflows to be emitted,
|
|
@option{-fsanitize=undefined} gives a diagnostic message.
|
|
This currently works only for the C family of languages.
|
|
|
|
@item -fno-sanitize=all
|
|
@opindex fno-sanitize=all
|
|
|
|
This option disables all previously enabled sanitizers.
|
|
@option{-fsanitize=all} is not allowed, as some sanitizers cannot be used
|
|
together.
|
|
|
|
@item -fasan-shadow-offset=@var{number}
|
|
@opindex fasan-shadow-offset
|
|
This option forces GCC to use custom shadow offset in AddressSanitizer checks.
|
|
It is useful for experimenting with different shadow memory layouts in
|
|
Kernel AddressSanitizer.
|
|
|
|
@item -fsanitize-sections=@var{s1},@var{s2},...
|
|
@opindex fsanitize-sections
|
|
Sanitize global variables in selected user-defined sections. @var{si} may
|
|
contain wildcards.
|
|
|
|
@item -fsanitize-recover@r{[}=@var{opts}@r{]}
|
|
@opindex fsanitize-recover
|
|
@opindex fno-sanitize-recover
|
|
@option{-fsanitize-recover=} controls error recovery mode for sanitizers
|
|
mentioned in comma-separated list of @var{opts}. Enabling this option
|
|
for a sanitizer component causes it to attempt to continue
|
|
running the program as if no error happened. This means multiple
|
|
runtime errors can be reported in a single program run, and the exit
|
|
code of the program may indicate success even when errors
|
|
have been reported. The @option{-fno-sanitize-recover=} option
|
|
can be used to alter
|
|
this behavior: only the first detected error is reported
|
|
and program then exits with a non-zero exit code.
|
|
|
|
Currently this feature only works for @option{-fsanitize=undefined} (and its suboptions
|
|
except for @option{-fsanitize=unreachable} and @option{-fsanitize=return}),
|
|
@option{-fsanitize=float-cast-overflow}, @option{-fsanitize=float-divide-by-zero},
|
|
@option{-fsanitize=bounds-strict},
|
|
@option{-fsanitize=kernel-address} and @option{-fsanitize=address}.
|
|
For these sanitizers error recovery is turned on by default,
|
|
except @option{-fsanitize=address}, for which this feature is experimental.
|
|
@option{-fsanitize-recover=all} and @option{-fno-sanitize-recover=all} is also
|
|
accepted, the former enables recovery for all sanitizers that support it,
|
|
the latter disables recovery for all sanitizers that support it.
|
|
|
|
Even if a recovery mode is turned on the compiler side, it needs to be also
|
|
enabled on the runtime library side, otherwise the failures are still fatal.
|
|
The runtime library defaults to @code{halt_on_error=0} for
|
|
ThreadSanitizer and UndefinedBehaviorSanitizer, while default value for
|
|
AddressSanitizer is @code{halt_on_error=1}. This can be overridden through
|
|
setting the @code{halt_on_error} flag in the corresponding environment variable.
|
|
|
|
Syntax without an explicit @var{opts} parameter is deprecated. It is
|
|
equivalent to specifying an @var{opts} list of:
|
|
|
|
@smallexample
|
|
undefined,float-cast-overflow,float-divide-by-zero,bounds-strict
|
|
@end smallexample
|
|
|
|
@item -fsanitize-address-use-after-scope
|
|
@opindex fsanitize-address-use-after-scope
|
|
Enable sanitization of local variables to detect use-after-scope bugs.
|
|
The option sets @option{-fstack-reuse} to @samp{none}.
|
|
|
|
@item -fsanitize-undefined-trap-on-error
|
|
@opindex fsanitize-undefined-trap-on-error
|
|
The @option{-fsanitize-undefined-trap-on-error} option instructs the compiler to
|
|
report undefined behavior using @code{__builtin_trap} rather than
|
|
a @code{libubsan} library routine. The advantage of this is that the
|
|
@code{libubsan} library is not needed and is not linked in, so this
|
|
is usable even in freestanding environments.
|
|
|
|
@item -fsanitize-coverage=trace-pc
|
|
@opindex fsanitize-coverage=trace-pc
|
|
Enable coverage-guided fuzzing code instrumentation.
|
|
Inserts a call to @code{__sanitizer_cov_trace_pc} into every basic block.
|
|
|
|
@item -fbounds-check
|
|
@opindex fbounds-check
|
|
For front ends that support it, generate additional code to check that
|
|
indices used to access arrays are within the declared range. This is
|
|
currently only supported by the Fortran front end, where this option
|
|
defaults to false.
|
|
|
|
@item -fcheck-pointer-bounds
|
|
@opindex fcheck-pointer-bounds
|
|
@opindex fno-check-pointer-bounds
|
|
@cindex Pointer Bounds Checker options
|
|
Enable Pointer Bounds Checker instrumentation. Each memory reference
|
|
is instrumented with checks of the pointer used for memory access against
|
|
bounds associated with that pointer.
|
|
|
|
Currently there
|
|
is only an implementation for Intel MPX available, thus x86 GNU/Linux target
|
|
and @option{-mmpx} are required to enable this feature.
|
|
MPX-based instrumentation requires
|
|
a runtime library to enable MPX in hardware and handle bounds
|
|
violation signals. By default when @option{-fcheck-pointer-bounds}
|
|
and @option{-mmpx} options are used to link a program, the GCC driver
|
|
links against the @file{libmpx} and @file{libmpxwrappers} libraries.
|
|
Bounds checking on calls to dynamic libraries requires a linker
|
|
with @option{-z bndplt} support; if GCC was configured with a linker
|
|
without support for this option (including the Gold linker and older
|
|
versions of ld), a warning is given if you link with @option{-mmpx}
|
|
without also specifying @option{-static}, since the overall effectiveness
|
|
of the bounds checking protection is reduced.
|
|
See also @option{-static-libmpxwrappers}.
|
|
|
|
MPX-based instrumentation
|
|
may be used for debugging and also may be included in production code
|
|
to increase program security. Depending on usage, you may
|
|
have different requirements for the runtime library. The current version
|
|
of the MPX runtime library is more oriented for use as a debugging
|
|
tool. MPX runtime library usage implies @option{-lpthread}. See
|
|
also @option{-static-libmpx}. The runtime library behavior can be
|
|
influenced using various @env{CHKP_RT_*} environment variables. See
|
|
@uref{https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler}
|
|
for more details.
|
|
|
|
Generated instrumentation may be controlled by various
|
|
@option{-fchkp-*} options and by the @code{bnd_variable_size}
|
|
structure field attribute (@pxref{Type Attributes}) and
|
|
@code{bnd_legacy}, and @code{bnd_instrument} function attributes
|
|
(@pxref{Function Attributes}). GCC also provides a number of built-in
|
|
functions for controlling the Pointer Bounds Checker. @xref{Pointer
|
|
Bounds Checker builtins}, for more information.
|
|
|
|
@item -fchkp-check-incomplete-type
|
|
@opindex fchkp-check-incomplete-type
|
|
@opindex fno-chkp-check-incomplete-type
|
|
Generate pointer bounds checks for variables with incomplete type.
|
|
Enabled by default.
|
|
|
|
@item -fchkp-narrow-bounds
|
|
@opindex fchkp-narrow-bounds
|
|
@opindex fno-chkp-narrow-bounds
|
|
Controls bounds used by Pointer Bounds Checker for pointers to object
|
|
fields. If narrowing is enabled then field bounds are used. Otherwise
|
|
object bounds are used. See also @option{-fchkp-narrow-to-innermost-array}
|
|
and @option{-fchkp-first-field-has-own-bounds}. Enabled by default.
|
|
|
|
@item -fchkp-first-field-has-own-bounds
|
|
@opindex fchkp-first-field-has-own-bounds
|
|
@opindex fno-chkp-first-field-has-own-bounds
|
|
Forces Pointer Bounds Checker to use narrowed bounds for the address of the
|
|
first field in the structure. By default a pointer to the first field has
|
|
the same bounds as a pointer to the whole structure.
|
|
|
|
@item -fchkp-flexible-struct-trailing-arrays
|
|
@opindex fchkp-flexible-struct-trailing-arrays
|
|
@opindex fno-chkp-flexible-struct-trailing-arrays
|
|
Forces Pointer Bounds Checker to treat all trailing arrays in structures as
|
|
possibly flexible. By default only array fields with zero length or that are
|
|
marked with attribute bnd_variable_size are treated as flexible.
|
|
|
|
@item -fchkp-narrow-to-innermost-array
|
|
@opindex fchkp-narrow-to-innermost-array
|
|
@opindex fno-chkp-narrow-to-innermost-array
|
|
Forces Pointer Bounds Checker to use bounds of the innermost arrays in
|
|
case of nested static array access. By default this option is disabled and
|
|
bounds of the outermost array are used.
|
|
|
|
@item -fchkp-optimize
|
|
@opindex fchkp-optimize
|
|
@opindex fno-chkp-optimize
|
|
Enables Pointer Bounds Checker optimizations. Enabled by default at
|
|
optimization levels @option{-O}, @option{-O2}, @option{-O3}.
|
|
|
|
@item -fchkp-use-fast-string-functions
|
|
@opindex fchkp-use-fast-string-functions
|
|
@opindex fno-chkp-use-fast-string-functions
|
|
Enables use of @code{*_nobnd} versions of string functions (not copying bounds)
|
|
by Pointer Bounds Checker. Disabled by default.
|
|
|
|
@item -fchkp-use-nochk-string-functions
|
|
@opindex fchkp-use-nochk-string-functions
|
|
@opindex fno-chkp-use-nochk-string-functions
|
|
Enables use of @code{*_nochk} versions of string functions (not checking bounds)
|
|
by Pointer Bounds Checker. Disabled by default.
|
|
|
|
@item -fchkp-use-static-bounds
|
|
@opindex fchkp-use-static-bounds
|
|
@opindex fno-chkp-use-static-bounds
|
|
Allow Pointer Bounds Checker to generate static bounds holding
|
|
bounds of static variables. Enabled by default.
|
|
|
|
@item -fchkp-use-static-const-bounds
|
|
@opindex fchkp-use-static-const-bounds
|
|
@opindex fno-chkp-use-static-const-bounds
|
|
Use statically-initialized bounds for constant bounds instead of
|
|
generating them each time they are required. By default enabled when
|
|
@option{-fchkp-use-static-bounds} is enabled.
|
|
|
|
@item -fchkp-treat-zero-dynamic-size-as-infinite
|
|
@opindex fchkp-treat-zero-dynamic-size-as-infinite
|
|
@opindex fno-chkp-treat-zero-dynamic-size-as-infinite
|
|
With this option, objects with incomplete type whose
|
|
dynamically-obtained size is zero are treated as having infinite size
|
|
instead by Pointer Bounds
|
|
Checker. This option may be helpful if a program is linked with a library
|
|
missing size information for some symbols. Disabled by default.
|
|
|
|
@item -fchkp-check-read
|
|
@opindex fchkp-check-read
|
|
@opindex fno-chkp-check-read
|
|
Instructs Pointer Bounds Checker to generate checks for all read
|
|
accesses to memory. Enabled by default.
|
|
|
|
@item -fchkp-check-write
|
|
@opindex fchkp-check-write
|
|
@opindex fno-chkp-check-write
|
|
Instructs Pointer Bounds Checker to generate checks for all write
|
|
accesses to memory. Enabled by default.
|
|
|
|
@item -fchkp-store-bounds
|
|
@opindex fchkp-store-bounds
|
|
@opindex fno-chkp-store-bounds
|
|
Instructs Pointer Bounds Checker to generate bounds stores for
|
|
pointer writes. Enabled by default.
|
|
|
|
@item -fchkp-instrument-calls
|
|
@opindex fchkp-instrument-calls
|
|
@opindex fno-chkp-instrument-calls
|
|
Instructs Pointer Bounds Checker to pass pointer bounds to calls.
|
|
Enabled by default.
|
|
|
|
@item -fchkp-instrument-marked-only
|
|
@opindex fchkp-instrument-marked-only
|
|
@opindex fno-chkp-instrument-marked-only
|
|
Instructs Pointer Bounds Checker to instrument only functions
|
|
marked with the @code{bnd_instrument} attribute
|
|
(@pxref{Function Attributes}). Disabled by default.
|
|
|
|
@item -fchkp-use-wrappers
|
|
@opindex fchkp-use-wrappers
|
|
@opindex fno-chkp-use-wrappers
|
|
Allows Pointer Bounds Checker to replace calls to built-in functions
|
|
with calls to wrapper functions. When @option{-fchkp-use-wrappers}
|
|
is used to link a program, the GCC driver automatically links
|
|
against @file{libmpxwrappers}. See also @option{-static-libmpxwrappers}.
|
|
Enabled by default.
|
|
|
|
@item -fstack-protector
|
|
@opindex fstack-protector
|
|
Emit extra code to check for buffer overflows, such as stack smashing
|
|
attacks. This is done by adding a guard variable to functions with
|
|
vulnerable objects. This includes functions that call @code{alloca}, and
|
|
functions with buffers larger than 8 bytes. The guards are initialized
|
|
when a function is entered and then checked when the function exits.
|
|
If a guard check fails, an error message is printed and the program exits.
|
|
|
|
@item -fstack-protector-all
|
|
@opindex fstack-protector-all
|
|
Like @option{-fstack-protector} except that all functions are protected.
|
|
|
|
@item -fstack-protector-strong
|
|
@opindex fstack-protector-strong
|
|
Like @option{-fstack-protector} but includes additional functions to
|
|
be protected --- those that have local array definitions, or have
|
|
references to local frame addresses.
|
|
|
|
@item -fstack-protector-explicit
|
|
@opindex fstack-protector-explicit
|
|
Like @option{-fstack-protector} but only protects those functions which
|
|
have the @code{stack_protect} attribute.
|
|
|
|
@item -fstack-check
|
|
@opindex fstack-check
|
|
Generate code to verify that you do not go beyond the boundary of the
|
|
stack. You should specify this flag if you are running in an
|
|
environment with multiple threads, but you only rarely need to specify it in
|
|
a single-threaded environment since stack overflow is automatically
|
|
detected on nearly all systems if there is only one stack.
|
|
|
|
Note that this switch does not actually cause checking to be done; the
|
|
operating system or the language runtime must do that. The switch causes
|
|
generation of code to ensure that they see the stack being extended.
|
|
|
|
You can additionally specify a string parameter: @samp{no} means no
|
|
checking, @samp{generic} means force the use of old-style checking,
|
|
@samp{specific} means use the best checking method and is equivalent
|
|
to bare @option{-fstack-check}.
|
|
|
|
Old-style checking is a generic mechanism that requires no specific
|
|
target support in the compiler but comes with the following drawbacks:
|
|
|
|
@enumerate
|
|
@item
|
|
Modified allocation strategy for large objects: they are always
|
|
allocated dynamically if their size exceeds a fixed threshold.
|
|
|
|
@item
|
|
Fixed limit on the size of the static frame of functions: when it is
|
|
topped by a particular function, stack checking is not reliable and
|
|
a warning is issued by the compiler.
|
|
|
|
@item
|
|
Inefficiency: because of both the modified allocation strategy and the
|
|
generic implementation, code performance is hampered.
|
|
@end enumerate
|
|
|
|
Note that old-style stack checking is also the fallback method for
|
|
@samp{specific} if no target support has been added in the compiler.
|
|
|
|
@item -fstack-limit-register=@var{reg}
|
|
@itemx -fstack-limit-symbol=@var{sym}
|
|
@itemx -fno-stack-limit
|
|
@opindex fstack-limit-register
|
|
@opindex fstack-limit-symbol
|
|
@opindex fno-stack-limit
|
|
Generate code to ensure that the stack does not grow beyond a certain value,
|
|
either the value of a register or the address of a symbol. If a larger
|
|
stack is required, a signal is raised at run time. For most targets,
|
|
the signal is raised before the stack overruns the boundary, so
|
|
it is possible to catch the signal without taking special precautions.
|
|
|
|
For instance, if the stack starts at absolute address @samp{0x80000000}
|
|
and grows downwards, you can use the flags
|
|
@option{-fstack-limit-symbol=__stack_limit} and
|
|
@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit
|
|
of 128KB@. Note that this may only work with the GNU linker.
|
|
|
|
You can locally override stack limit checking by using the
|
|
@code{no_stack_limit} function attribute (@pxref{Function Attributes}).
|
|
|
|
@item -fsplit-stack
|
|
@opindex fsplit-stack
|
|
Generate code to automatically split the stack before it overflows.
|
|
The resulting program has a discontiguous stack which can only
|
|
overflow if the program is unable to allocate any more memory. This
|
|
is most useful when running threaded programs, as it is no longer
|
|
necessary to calculate a good stack size to use for each thread. This
|
|
is currently only implemented for the x86 targets running
|
|
GNU/Linux.
|
|
|
|
When code compiled with @option{-fsplit-stack} calls code compiled
|
|
without @option{-fsplit-stack}, there may not be much stack space
|
|
available for the latter code to run. If compiling all code,
|
|
including library code, with @option{-fsplit-stack} is not an option,
|
|
then the linker can fix up these calls so that the code compiled
|
|
without @option{-fsplit-stack} always has a large stack. Support for
|
|
this is implemented in the gold linker in GNU binutils release 2.21
|
|
and later.
|
|
|
|
@item -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]}
|
|
@opindex fvtable-verify
|
|
This option is only available when compiling C++ code.
|
|
It turns on (or off, if using @option{-fvtable-verify=none}) the security
|
|
feature that verifies at run time, for every virtual call, that
|
|
the vtable pointer through which the call is made is valid for the type of
|
|
the object, and has not been corrupted or overwritten. If an invalid vtable
|
|
pointer is detected at run time, an error is reported and execution of the
|
|
program is immediately halted.
|
|
|
|
This option causes run-time data structures to be built at program startup,
|
|
which are used for verifying the vtable pointers.
|
|
The options @samp{std} and @samp{preinit}
|
|
control the timing of when these data structures are built. In both cases the
|
|
data structures are built before execution reaches @code{main}. Using
|
|
@option{-fvtable-verify=std} causes the data structures to be built after
|
|
shared libraries have been loaded and initialized.
|
|
@option{-fvtable-verify=preinit} causes them to be built before shared
|
|
libraries have been loaded and initialized.
|
|
|
|
If this option appears multiple times in the command line with different
|
|
values specified, @samp{none} takes highest priority over both @samp{std} and
|
|
@samp{preinit}; @samp{preinit} takes priority over @samp{std}.
|
|
|
|
@item -fvtv-debug
|
|
@opindex fvtv-debug
|
|
When used in conjunction with @option{-fvtable-verify=std} or
|
|
@option{-fvtable-verify=preinit}, causes debug versions of the
|
|
runtime functions for the vtable verification feature to be called.
|
|
This flag also causes the compiler to log information about which
|
|
vtable pointers it finds for each class.
|
|
This information is written to a file named @file{vtv_set_ptr_data.log}
|
|
in the directory named by the environment variable @env{VTV_LOGS_DIR}
|
|
if that is defined or the current working directory otherwise.
|
|
|
|
Note: This feature @emph{appends} data to the log file. If you want a fresh log
|
|
file, be sure to delete any existing one.
|
|
|
|
@item -fvtv-counts
|
|
@opindex fvtv-counts
|
|
This is a debugging flag. When used in conjunction with
|
|
@option{-fvtable-verify=std} or @option{-fvtable-verify=preinit}, this
|
|
causes the compiler to keep track of the total number of virtual calls
|
|
it encounters and the number of verifications it inserts. It also
|
|
counts the number of calls to certain run-time library functions
|
|
that it inserts and logs this information for each compilation unit.
|
|
The compiler writes this information to a file named
|
|
@file{vtv_count_data.log} in the directory named by the environment
|
|
variable @env{VTV_LOGS_DIR} if that is defined or the current working
|
|
directory otherwise. It also counts the size of the vtable pointer sets
|
|
for each class, and writes this information to @file{vtv_class_set_sizes.log}
|
|
in the same directory.
|
|
|
|
Note: This feature @emph{appends} data to the log files. To get fresh log
|
|
files, be sure to delete any existing ones.
|
|
|
|
@item -finstrument-functions
|
|
@opindex finstrument-functions
|
|
Generate instrumentation calls for entry and exit to functions. Just
|
|
after function entry and just before function exit, the following
|
|
profiling functions are called with the address of the current
|
|
function and its call site. (On some platforms,
|
|
@code{__builtin_return_address} does not work beyond the current
|
|
function, so the call site information may not be available to the
|
|
profiling functions otherwise.)
|
|
|
|
@smallexample
|
|
void __cyg_profile_func_enter (void *this_fn,
|
|
void *call_site);
|
|
void __cyg_profile_func_exit (void *this_fn,
|
|
void *call_site);
|
|
@end smallexample
|
|
|
|
The first argument is the address of the start of the current function,
|
|
which may be looked up exactly in the symbol table.
|
|
|
|
This instrumentation is also done for functions expanded inline in other
|
|
functions. The profiling calls indicate where, conceptually, the
|
|
inline function is entered and exited. This means that addressable
|
|
versions of such functions must be available. If all your uses of a
|
|
function are expanded inline, this may mean an additional expansion of
|
|
code size. If you use @code{extern inline} in your C code, an
|
|
addressable version of such functions must be provided. (This is
|
|
normally the case anyway, but if you get lucky and the optimizer always
|
|
expands the functions inline, you might have gotten away without
|
|
providing static copies.)
|
|
|
|
A function may be given the attribute @code{no_instrument_function}, in
|
|
which case this instrumentation is not done. This can be used, for
|
|
example, for the profiling functions listed above, high-priority
|
|
interrupt routines, and any functions from which the profiling functions
|
|
cannot safely be called (perhaps signal handlers, if the profiling
|
|
routines generate output or allocate memory).
|
|
|
|
@item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}
|
|
@opindex finstrument-functions-exclude-file-list
|
|
|
|
Set the list of functions that are excluded from instrumentation (see
|
|
the description of @option{-finstrument-functions}). If the file that
|
|
contains a function definition matches with one of @var{file}, then
|
|
that function is not instrumented. The match is done on substrings:
|
|
if the @var{file} parameter is a substring of the file name, it is
|
|
considered to be a match.
|
|
|
|
For example:
|
|
|
|
@smallexample
|
|
-finstrument-functions-exclude-file-list=/bits/stl,include/sys
|
|
@end smallexample
|
|
|
|
@noindent
|
|
excludes any inline function defined in files whose pathnames
|
|
contain @file{/bits/stl} or @file{include/sys}.
|
|
|
|
If, for some reason, you want to include letter @samp{,} in one of
|
|
@var{sym}, write @samp{\,}. For example,
|
|
@option{-finstrument-functions-exclude-file-list='\,\,tmp'}
|
|
(note the single quote surrounding the option).
|
|
|
|
@item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{}
|
|
@opindex finstrument-functions-exclude-function-list
|
|
|
|
This is similar to @option{-finstrument-functions-exclude-file-list},
|
|
but this option sets the list of function names to be excluded from
|
|
instrumentation. The function name to be matched is its user-visible
|
|
name, such as @code{vector<int> blah(const vector<int> &)}, not the
|
|
internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The
|
|
match is done on substrings: if the @var{sym} parameter is a substring
|
|
of the function name, it is considered to be a match. For C99 and C++
|
|
extended identifiers, the function name must be given in UTF-8, not
|
|
using universal character names.
|
|
|
|
@end table
|
|
|
|
|
|
@node Preprocessor Options
|
|
@section Options Controlling the Preprocessor
|
|
@cindex preprocessor options
|
|
@cindex options, preprocessor
|
|
|
|
These options control the C preprocessor, which is run on each C source
|
|
file before actual compilation.
|
|
|
|
If you use the @option{-E} option, nothing is done except preprocessing.
|
|
Some of these options make sense only together with @option{-E} because
|
|
they cause the preprocessor output to be unsuitable for actual
|
|
compilation.
|
|
|
|
In addition to the options listed here, there are a number of options
|
|
to control search paths for include files documented in
|
|
@ref{Directory Options}.
|
|
Options to control preprocessor diagnostics are listed in
|
|
@ref{Warning Options}.
|
|
|
|
@table @gcctabopt
|
|
@include cppopts.texi
|
|
|
|
@item -Wp,@var{option}
|
|
@opindex Wp
|
|
You can use @option{-Wp,@var{option}} to bypass the compiler driver
|
|
and pass @var{option} directly through to the preprocessor. If
|
|
@var{option} contains commas, it is split into multiple options at the
|
|
commas. However, many options are modified, translated or interpreted
|
|
by the compiler driver before being passed to the preprocessor, and
|
|
@option{-Wp} forcibly bypasses this phase. The preprocessor's direct
|
|
interface is undocumented and subject to change, so whenever possible
|
|
you should avoid using @option{-Wp} and let the driver handle the
|
|
options instead.
|
|
|
|
@item -Xpreprocessor @var{option}
|
|
@opindex Xpreprocessor
|
|
Pass @var{option} as an option to the preprocessor. You can use this to
|
|
supply system-specific preprocessor options that GCC does not
|
|
recognize.
|
|
|
|
If you want to pass an option that takes an argument, you must use
|
|
@option{-Xpreprocessor} twice, once for the option and once for the argument.
|
|
|
|
@item -no-integrated-cpp
|
|
@opindex no-integrated-cpp
|
|
Perform preprocessing as a separate pass before compilation.
|
|
By default, GCC performs preprocessing as an integrated part of
|
|
input tokenization and parsing.
|
|
If this option is provided, the appropriate language front end
|
|
(@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++,
|
|
and Objective-C, respectively) is instead invoked twice,
|
|
once for preprocessing only and once for actual compilation
|
|
of the preprocessed input.
|
|
This option may be useful in conjunction with the @option{-B} or
|
|
@option{-wrapper} options to specify an alternate preprocessor or
|
|
perform additional processing of the program source between
|
|
normal preprocessing and compilation.
|
|
|
|
@end table
|
|
|
|
@node Assembler Options
|
|
@section Passing Options to the Assembler
|
|
|
|
@c prevent bad page break with this line
|
|
You can pass options to the assembler.
|
|
|
|
@table @gcctabopt
|
|
@item -Wa,@var{option}
|
|
@opindex Wa
|
|
Pass @var{option} as an option to the assembler. If @var{option}
|
|
contains commas, it is split into multiple options at the commas.
|
|
|
|
@item -Xassembler @var{option}
|
|
@opindex Xassembler
|
|
Pass @var{option} as an option to the assembler. You can use this to
|
|
supply system-specific assembler options that GCC does not
|
|
recognize.
|
|
|
|
If you want to pass an option that takes an argument, you must use
|
|
@option{-Xassembler} twice, once for the option and once for the argument.
|
|
|
|
@end table
|
|
|
|
@node Link Options
|
|
@section Options for Linking
|
|
@cindex link options
|
|
@cindex options, linking
|
|
|
|
These options come into play when the compiler links object files into
|
|
an executable output file. They are meaningless if the compiler is
|
|
not doing a link step.
|
|
|
|
@table @gcctabopt
|
|
@cindex file names
|
|
@item @var{object-file-name}
|
|
A file name that does not end in a special recognized suffix is
|
|
considered to name an object file or library. (Object files are
|
|
distinguished from libraries by the linker according to the file
|
|
contents.) If linking is done, these object files are used as input
|
|
to the linker.
|
|
|
|
@item -c
|
|
@itemx -S
|
|
@itemx -E
|
|
@opindex c
|
|
@opindex S
|
|
@opindex E
|
|
If any of these options is used, then the linker is not run, and
|
|
object file names should not be used as arguments. @xref{Overall
|
|
Options}.
|
|
|
|
@item -fuse-ld=bfd
|
|
@opindex fuse-ld=bfd
|
|
Use the @command{bfd} linker instead of the default linker.
|
|
|
|
@item -fuse-ld=gold
|
|
@opindex fuse-ld=gold
|
|
Use the @command{gold} linker instead of the default linker.
|
|
|
|
@cindex Libraries
|
|
@item -l@var{library}
|
|
@itemx -l @var{library}
|
|
@opindex l
|
|
Search the library named @var{library} when linking. (The second
|
|
alternative with the library as a separate argument is only for
|
|
POSIX compliance and is not recommended.)
|
|
|
|
It makes a difference where in the command you write this option; the
|
|
linker searches and processes libraries and object files in the order they
|
|
are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z}
|
|
after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers
|
|
to functions in @samp{z}, those functions may not be loaded.
|
|
|
|
The linker searches a standard list of directories for the library,
|
|
which is actually a file named @file{lib@var{library}.a}. The linker
|
|
then uses this file as if it had been specified precisely by name.
|
|
|
|
The directories searched include several standard system directories
|
|
plus any that you specify with @option{-L}.
|
|
|
|
Normally the files found this way are library files---archive files
|
|
whose members are object files. The linker handles an archive file by
|
|
scanning through it for members which define symbols that have so far
|
|
been referenced but not defined. But if the file that is found is an
|
|
ordinary object file, it is linked in the usual fashion. The only
|
|
difference between using an @option{-l} option and specifying a file name
|
|
is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a}
|
|
and searches several directories.
|
|
|
|
@item -lobjc
|
|
@opindex lobjc
|
|
You need this special case of the @option{-l} option in order to
|
|
link an Objective-C or Objective-C++ program.
|
|
|
|
@item -nostartfiles
|
|
@opindex nostartfiles
|
|
Do not use the standard system startup files when linking.
|
|
The standard system libraries are used normally, unless @option{-nostdlib}
|
|
or @option{-nodefaultlibs} is used.
|
|
|
|
@item -nodefaultlibs
|
|
@opindex nodefaultlibs
|
|
Do not use the standard system libraries when linking.
|
|
Only the libraries you specify are passed to the linker, and options
|
|
specifying linkage of the system libraries, such as @option{-static-libgcc}
|
|
or @option{-shared-libgcc}, are ignored.
|
|
The standard startup files are used normally, unless @option{-nostartfiles}
|
|
is used.
|
|
|
|
The compiler may generate calls to @code{memcmp},
|
|
@code{memset}, @code{memcpy} and @code{memmove}.
|
|
These entries are usually resolved by entries in
|
|
libc. These entry points should be supplied through some other
|
|
mechanism when this option is specified.
|
|
|
|
@item -nostdlib
|
|
@opindex nostdlib
|
|
Do not use the standard system startup files or libraries when linking.
|
|
No startup files and only the libraries you specify are passed to
|
|
the linker, and options specifying linkage of the system libraries, such as
|
|
@option{-static-libgcc} or @option{-shared-libgcc}, are ignored.
|
|
|
|
The compiler may generate calls to @code{memcmp}, @code{memset},
|
|
@code{memcpy} and @code{memmove}.
|
|
These entries are usually resolved by entries in
|
|
libc. These entry points should be supplied through some other
|
|
mechanism when this option is specified.
|
|
|
|
@cindex @option{-lgcc}, use with @option{-nostdlib}
|
|
@cindex @option{-nostdlib} and unresolved references
|
|
@cindex unresolved references and @option{-nostdlib}
|
|
@cindex @option{-lgcc}, use with @option{-nodefaultlibs}
|
|
@cindex @option{-nodefaultlibs} and unresolved references
|
|
@cindex unresolved references and @option{-nodefaultlibs}
|
|
One of the standard libraries bypassed by @option{-nostdlib} and
|
|
@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines
|
|
which GCC uses to overcome shortcomings of particular machines, or special
|
|
needs for some languages.
|
|
(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler
|
|
Collection (GCC) Internals},
|
|
for more discussion of @file{libgcc.a}.)
|
|
In most cases, you need @file{libgcc.a} even when you want to avoid
|
|
other standard libraries. In other words, when you specify @option{-nostdlib}
|
|
or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well.
|
|
This ensures that you have no unresolved references to internal GCC
|
|
library subroutines.
|
|
(An example of such an internal subroutine is @code{__main}, used to ensure C++
|
|
constructors are called; @pxref{Collect2,,@code{collect2}, gccint,
|
|
GNU Compiler Collection (GCC) Internals}.)
|
|
|
|
@item -pie
|
|
@opindex pie
|
|
Produce a position independent executable on targets that support it.
|
|
For predictable results, you must also specify the same set of options
|
|
used for compilation (@option{-fpie}, @option{-fPIE},
|
|
or model suboptions) when you specify this linker option.
|
|
|
|
@item -no-pie
|
|
@opindex no-pie
|
|
Don't produce a position independent executable.
|
|
|
|
@item -pthread
|
|
@opindex pthread
|
|
Link with the POSIX threads library. This option is supported on
|
|
GNU/Linux targets, most other Unix derivatives, and also on
|
|
x86 Cygwin and MinGW targets. On some targets this option also sets
|
|
flags for the preprocessor, so it should be used consistently for both
|
|
compilation and linking.
|
|
|
|
@item -rdynamic
|
|
@opindex rdynamic
|
|
Pass the flag @option{-export-dynamic} to the ELF linker, on targets
|
|
that support it. This instructs the linker to add all symbols, not
|
|
only used ones, to the dynamic symbol table. This option is needed
|
|
for some uses of @code{dlopen} or to allow obtaining backtraces
|
|
from within a program.
|
|
|
|
@item -s
|
|
@opindex s
|
|
Remove all symbol table and relocation information from the executable.
|
|
|
|
@item -static
|
|
@opindex static
|
|
On systems that support dynamic linking, this prevents linking with the shared
|
|
libraries. On other systems, this option has no effect.
|
|
|
|
@item -shared
|
|
@opindex shared
|
|
Produce a shared object which can then be linked with other objects to
|
|
form an executable. Not all systems support this option. For predictable
|
|
results, you must also specify the same set of options used for compilation
|
|
(@option{-fpic}, @option{-fPIC}, or model suboptions) when
|
|
you specify this linker option.@footnote{On some systems, @samp{gcc -shared}
|
|
needs to build supplementary stub code for constructors to work. On
|
|
multi-libbed systems, @samp{gcc -shared} must select the correct support
|
|
libraries to link against. Failing to supply the correct flags may lead
|
|
to subtle defects. Supplying them in cases where they are not necessary
|
|
is innocuous.}
|
|
|
|
@item -shared-libgcc
|
|
@itemx -static-libgcc
|
|
@opindex shared-libgcc
|
|
@opindex static-libgcc
|
|
On systems that provide @file{libgcc} as a shared library, these options
|
|
force the use of either the shared or static version, respectively.
|
|
If no shared version of @file{libgcc} was built when the compiler was
|
|
configured, these options have no effect.
|
|
|
|
There are several situations in which an application should use the
|
|
shared @file{libgcc} instead of the static version. The most common
|
|
of these is when the application wishes to throw and catch exceptions
|
|
across different shared libraries. In that case, each of the libraries
|
|
as well as the application itself should use the shared @file{libgcc}.
|
|
|
|
Therefore, the G++ and driver automatically adds @option{-shared-libgcc}
|
|
whenever you build a shared library or a main executable, because C++
|
|
programs typically use exceptions, so this is the right thing to do.
|
|
|
|
If, instead, you use the GCC driver to create shared libraries, you may
|
|
find that they are not always linked with the shared @file{libgcc}.
|
|
If GCC finds, at its configuration time, that you have a non-GNU linker
|
|
or a GNU linker that does not support option @option{--eh-frame-hdr},
|
|
it links the shared version of @file{libgcc} into shared libraries
|
|
by default. Otherwise, it takes advantage of the linker and optimizes
|
|
away the linking with the shared version of @file{libgcc}, linking with
|
|
the static version of libgcc by default. This allows exceptions to
|
|
propagate through such shared libraries, without incurring relocation
|
|
costs at library load time.
|
|
|
|
However, if a library or main executable is supposed to throw or catch
|
|
exceptions, you must link it using the G++ driver, as appropriate
|
|
for the languages used in the program, or using the option
|
|
@option{-shared-libgcc}, such that it is linked with the shared
|
|
@file{libgcc}.
|
|
|
|
@item -static-libasan
|
|
@opindex static-libasan
|
|
When the @option{-fsanitize=address} option is used to link a program,
|
|
the GCC driver automatically links against @option{libasan}. If
|
|
@file{libasan} is available as a shared library, and the @option{-static}
|
|
option is not used, then this links against the shared version of
|
|
@file{libasan}. The @option{-static-libasan} option directs the GCC
|
|
driver to link @file{libasan} statically, without necessarily linking
|
|
other libraries statically.
|
|
|
|
@item -static-libtsan
|
|
@opindex static-libtsan
|
|
When the @option{-fsanitize=thread} option is used to link a program,
|
|
the GCC driver automatically links against @option{libtsan}. If
|
|
@file{libtsan} is available as a shared library, and the @option{-static}
|
|
option is not used, then this links against the shared version of
|
|
@file{libtsan}. The @option{-static-libtsan} option directs the GCC
|
|
driver to link @file{libtsan} statically, without necessarily linking
|
|
other libraries statically.
|
|
|
|
@item -static-liblsan
|
|
@opindex static-liblsan
|
|
When the @option{-fsanitize=leak} option is used to link a program,
|
|
the GCC driver automatically links against @option{liblsan}. If
|
|
@file{liblsan} is available as a shared library, and the @option{-static}
|
|
option is not used, then this links against the shared version of
|
|
@file{liblsan}. The @option{-static-liblsan} option directs the GCC
|
|
driver to link @file{liblsan} statically, without necessarily linking
|
|
other libraries statically.
|
|
|
|
@item -static-libubsan
|
|
@opindex static-libubsan
|
|
When the @option{-fsanitize=undefined} option is used to link a program,
|
|
the GCC driver automatically links against @option{libubsan}. If
|
|
@file{libubsan} is available as a shared library, and the @option{-static}
|
|
option is not used, then this links against the shared version of
|
|
@file{libubsan}. The @option{-static-libubsan} option directs the GCC
|
|
driver to link @file{libubsan} statically, without necessarily linking
|
|
other libraries statically.
|
|
|
|
@item -static-libmpx
|
|
@opindex static-libmpx
|
|
When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are
|
|
used to link a program, the GCC driver automatically links against
|
|
@file{libmpx}. If @file{libmpx} is available as a shared library,
|
|
and the @option{-static} option is not used, then this links against
|
|
the shared version of @file{libmpx}. The @option{-static-libmpx}
|
|
option directs the GCC driver to link @file{libmpx} statically,
|
|
without necessarily linking other libraries statically.
|
|
|
|
@item -static-libmpxwrappers
|
|
@opindex static-libmpxwrappers
|
|
When the @option{-fcheck-pointer bounds} and @option{-mmpx} options are used
|
|
to link a program without also using @option{-fno-chkp-use-wrappers}, the
|
|
GCC driver automatically links against @file{libmpxwrappers}. If
|
|
@file{libmpxwrappers} is available as a shared library, and the
|
|
@option{-static} option is not used, then this links against the shared
|
|
version of @file{libmpxwrappers}. The @option{-static-libmpxwrappers}
|
|
option directs the GCC driver to link @file{libmpxwrappers} statically,
|
|
without necessarily linking other libraries statically.
|
|
|
|
@item -static-libstdc++
|
|
@opindex static-libstdc++
|
|
When the @command{g++} program is used to link a C++ program, it
|
|
normally automatically links against @option{libstdc++}. If
|
|
@file{libstdc++} is available as a shared library, and the
|
|
@option{-static} option is not used, then this links against the
|
|
shared version of @file{libstdc++}. That is normally fine. However, it
|
|
is sometimes useful to freeze the version of @file{libstdc++} used by
|
|
the program without going all the way to a fully static link. The
|
|
@option{-static-libstdc++} option directs the @command{g++} driver to
|
|
link @file{libstdc++} statically, without necessarily linking other
|
|
libraries statically.
|
|
|
|
@item -symbolic
|
|
@opindex symbolic
|
|
Bind references to global symbols when building a shared object. Warn
|
|
about any unresolved references (unless overridden by the link editor
|
|
option @option{-Xlinker -z -Xlinker defs}). Only a few systems support
|
|
this option.
|
|
|
|
@item -T @var{script}
|
|
@opindex T
|
|
@cindex linker script
|
|
Use @var{script} as the linker script. This option is supported by most
|
|
systems using the GNU linker. On some targets, such as bare-board
|
|
targets without an operating system, the @option{-T} option may be required
|
|
when linking to avoid references to undefined symbols.
|
|
|
|
@item -Xlinker @var{option}
|
|
@opindex Xlinker
|
|
Pass @var{option} as an option to the linker. You can use this to
|
|
supply system-specific linker options that GCC does not recognize.
|
|
|
|
If you want to pass an option that takes a separate argument, you must use
|
|
@option{-Xlinker} twice, once for the option and once for the argument.
|
|
For example, to pass @option{-assert definitions}, you must write
|
|
@option{-Xlinker -assert -Xlinker definitions}. It does not work to write
|
|
@option{-Xlinker "-assert definitions"}, because this passes the entire
|
|
string as a single argument, which is not what the linker expects.
|
|
|
|
When using the GNU linker, it is usually more convenient to pass
|
|
arguments to linker options using the @option{@var{option}=@var{value}}
|
|
syntax than as separate arguments. For example, you can specify
|
|
@option{-Xlinker -Map=output.map} rather than
|
|
@option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support
|
|
this syntax for command-line options.
|
|
|
|
@item -Wl,@var{option}
|
|
@opindex Wl
|
|
Pass @var{option} as an option to the linker. If @var{option} contains
|
|
commas, it is split into multiple options at the commas. You can use this
|
|
syntax to pass an argument to the option.
|
|
For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the
|
|
linker. When using the GNU linker, you can also get the same effect with
|
|
@option{-Wl,-Map=output.map}.
|
|
|
|
@item -u @var{symbol}
|
|
@opindex u
|
|
Pretend the symbol @var{symbol} is undefined, to force linking of
|
|
library modules to define it. You can use @option{-u} multiple times with
|
|
different symbols to force loading of additional library modules.
|
|
|
|
@item -z @var{keyword}
|
|
@opindex z
|
|
@option{-z} is passed directly on to the linker along with the keyword
|
|
@var{keyword}. See the section in the documentation of your linker for
|
|
permitted values and their meanings.
|
|
@end table
|
|
|
|
@node Directory Options
|
|
@section Options for Directory Search
|
|
@cindex directory options
|
|
@cindex options, directory search
|
|
@cindex search path
|
|
|
|
These options specify directories to search for header files, for
|
|
libraries and for parts of the compiler:
|
|
|
|
@table @gcctabopt
|
|
@include cppdiropts.texi
|
|
|
|
@item -iplugindir=@var{dir}
|
|
@opindex iplugindir=
|
|
Set the directory to search for plugins that are passed
|
|
by @option{-fplugin=@var{name}} instead of
|
|
@option{-fplugin=@var{path}/@var{name}.so}. This option is not meant
|
|
to be used by the user, but only passed by the driver.
|
|
|
|
@item -L@var{dir}
|
|
@opindex L
|
|
Add directory @var{dir} to the list of directories to be searched
|
|
for @option{-l}.
|
|
|
|
@item -B@var{prefix}
|
|
@opindex B
|
|
This option specifies where to find the executables, libraries,
|
|
include files, and data files of the compiler itself.
|
|
|
|
The compiler driver program runs one or more of the subprograms
|
|
@command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries
|
|
@var{prefix} as a prefix for each program it tries to run, both with and
|
|
without @samp{@var{machine}/@var{version}/} for the corresponding target
|
|
machine and compiler version.
|
|
|
|
For each subprogram to be run, the compiler driver first tries the
|
|
@option{-B} prefix, if any. If that name is not found, or if @option{-B}
|
|
is not specified, the driver tries two standard prefixes,
|
|
@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of
|
|
those results in a file name that is found, the unmodified program
|
|
name is searched for using the directories specified in your
|
|
@env{PATH} environment variable.
|
|
|
|
The compiler checks to see if the path provided by @option{-B}
|
|
refers to a directory, and if necessary it adds a directory
|
|
separator character at the end of the path.
|
|
|
|
@option{-B} prefixes that effectively specify directory names also apply
|
|
to libraries in the linker, because the compiler translates these
|
|
options into @option{-L} options for the linker. They also apply to
|
|
include files in the preprocessor, because the compiler translates these
|
|
options into @option{-isystem} options for the preprocessor. In this case,
|
|
the compiler appends @samp{include} to the prefix.
|
|
|
|
The runtime support file @file{libgcc.a} can also be searched for using
|
|
the @option{-B} prefix, if needed. If it is not found there, the two
|
|
standard prefixes above are tried, and that is all. The file is left
|
|
out of the link if it is not found by those means.
|
|
|
|
Another way to specify a prefix much like the @option{-B} prefix is to use
|
|
the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment
|
|
Variables}.
|
|
|
|
As a special kludge, if the path provided by @option{-B} is
|
|
@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to
|
|
9, then it is replaced by @file{[dir/]include}. This is to help
|
|
with boot-strapping the compiler.
|
|
|
|
@item -no-canonical-prefixes
|
|
@opindex no-canonical-prefixes
|
|
Do not expand any symbolic links, resolve references to @samp{/../}
|
|
or @samp{/./}, or make the path absolute when generating a relative
|
|
prefix.
|
|
|
|
@item --sysroot=@var{dir}
|
|
@opindex sysroot
|
|
Use @var{dir} as the logical root directory for headers and libraries.
|
|
For example, if the compiler normally searches for headers in
|
|
@file{/usr/include} and libraries in @file{/usr/lib}, it instead
|
|
searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}.
|
|
|
|
If you use both this option and the @option{-isysroot} option, then
|
|
the @option{--sysroot} option applies to libraries, but the
|
|
@option{-isysroot} option applies to header files.
|
|
|
|
The GNU linker (beginning with version 2.16) has the necessary support
|
|
for this option. If your linker does not support this option, the
|
|
header file aspect of @option{--sysroot} still works, but the
|
|
library aspect does not.
|
|
|
|
@item --no-sysroot-suffix
|
|
@opindex no-sysroot-suffix
|
|
For some targets, a suffix is added to the root directory specified
|
|
with @option{--sysroot}, depending on the other options used, so that
|
|
headers may for example be found in
|
|
@file{@var{dir}/@var{suffix}/usr/include} instead of
|
|
@file{@var{dir}/usr/include}. This option disables the addition of
|
|
such a suffix.
|
|
|
|
@end table
|
|
|
|
@node Code Gen Options
|
|
@section Options for Code Generation Conventions
|
|
@cindex code generation conventions
|
|
@cindex options, code generation
|
|
@cindex run-time options
|
|
|
|
These machine-independent options control the interface conventions
|
|
used in code generation.
|
|
|
|
Most of them have both positive and negative forms; the negative form
|
|
of @option{-ffoo} is @option{-fno-foo}. In the table below, only
|
|
one of the forms is listed---the one that is not the default. You
|
|
can figure out the other form by either removing @samp{no-} or adding
|
|
it.
|
|
|
|
@table @gcctabopt
|
|
@item -fstack-reuse=@var{reuse-level}
|
|
@opindex fstack_reuse
|
|
This option controls stack space reuse for user declared local/auto variables
|
|
and compiler generated temporaries. @var{reuse_level} can be @samp{all},
|
|
@samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all
|
|
local variables and temporaries, @samp{named_vars} enables the reuse only for
|
|
user defined local variables with names, and @samp{none} disables stack reuse
|
|
completely. The default value is @samp{all}. The option is needed when the
|
|
program extends the lifetime of a scoped local variable or a compiler generated
|
|
temporary beyond the end point defined by the language. When a lifetime of
|
|
a variable ends, and if the variable lives in memory, the optimizing compiler
|
|
has the freedom to reuse its stack space with other temporaries or scoped
|
|
local variables whose live range does not overlap with it. Legacy code extending
|
|
local lifetime is likely to break with the stack reuse optimization.
|
|
|
|
For example,
|
|
|
|
@smallexample
|
|
int *p;
|
|
@{
|
|
int local1;
|
|
|
|
p = &local1;
|
|
local1 = 10;
|
|
....
|
|
@}
|
|
@{
|
|
int local2;
|
|
local2 = 20;
|
|
...
|
|
@}
|
|
|
|
if (*p == 10) // out of scope use of local1
|
|
@{
|
|
|
|
@}
|
|
@end smallexample
|
|
|
|
Another example:
|
|
@smallexample
|
|
|
|
struct A
|
|
@{
|
|
A(int k) : i(k), j(k) @{ @}
|
|
int i;
|
|
int j;
|
|
@};
|
|
|
|
A *ap;
|
|
|
|
void foo(const A& ar)
|
|
@{
|
|
ap = &ar;
|
|
@}
|
|
|
|
void bar()
|
|
@{
|
|
foo(A(10)); // temp object's lifetime ends when foo returns
|
|
|
|
@{
|
|
A a(20);
|
|
....
|
|
@}
|
|
ap->i+= 10; // ap references out of scope temp whose space
|
|
// is reused with a. What is the value of ap->i?
|
|
@}
|
|
|
|
@end smallexample
|
|
|
|
The lifetime of a compiler generated temporary is well defined by the C++
|
|
standard. When a lifetime of a temporary ends, and if the temporary lives
|
|
in memory, the optimizing compiler has the freedom to reuse its stack
|
|
space with other temporaries or scoped local variables whose live range
|
|
does not overlap with it. However some of the legacy code relies on
|
|
the behavior of older compilers in which temporaries' stack space is
|
|
not reused, the aggressive stack reuse can lead to runtime errors. This
|
|
option is used to control the temporary stack reuse optimization.
|
|
|
|
@item -ftrapv
|
|
@opindex ftrapv
|
|
This option generates traps for signed overflow on addition, subtraction,
|
|
multiplication operations.
|
|
The options @option{-ftrapv} and @option{-fwrapv} override each other, so using
|
|
@option{-ftrapv} @option{-fwrapv} on the command-line results in
|
|
@option{-fwrapv} being effective. Note that only active options override, so
|
|
using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line
|
|
results in @option{-ftrapv} being effective.
|
|
|
|
@item -fwrapv
|
|
@opindex fwrapv
|
|
This option instructs the compiler to assume that signed arithmetic
|
|
overflow of addition, subtraction and multiplication wraps around
|
|
using twos-complement representation. This flag enables some optimizations
|
|
and disables others.
|
|
The options @option{-ftrapv} and @option{-fwrapv} override each other, so using
|
|
@option{-ftrapv} @option{-fwrapv} on the command-line results in
|
|
@option{-fwrapv} being effective. Note that only active options override, so
|
|
using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line
|
|
results in @option{-ftrapv} being effective.
|
|
|
|
@item -fexceptions
|
|
@opindex fexceptions
|
|
Enable exception handling. Generates extra code needed to propagate
|
|
exceptions. For some targets, this implies GCC generates frame
|
|
unwind information for all functions, which can produce significant data
|
|
size overhead, although it does not affect execution. If you do not
|
|
specify this option, GCC enables it by default for languages like
|
|
C++ that normally require exception handling, and disables it for
|
|
languages like C that do not normally require it. However, you may need
|
|
to enable this option when compiling C code that needs to interoperate
|
|
properly with exception handlers written in C++. You may also wish to
|
|
disable this option if you are compiling older C++ programs that don't
|
|
use exception handling.
|
|
|
|
@item -fnon-call-exceptions
|
|
@opindex fnon-call-exceptions
|
|
Generate code that allows trapping instructions to throw exceptions.
|
|
Note that this requires platform-specific runtime support that does
|
|
not exist everywhere. Moreover, it only allows @emph{trapping}
|
|
instructions to throw exceptions, i.e.@: memory references or floating-point
|
|
instructions. It does not allow exceptions to be thrown from
|
|
arbitrary signal handlers such as @code{SIGALRM}.
|
|
|
|
@item -fdelete-dead-exceptions
|
|
@opindex fdelete-dead-exceptions
|
|
Consider that instructions that may throw exceptions but don't otherwise
|
|
contribute to the execution of the program can be optimized away.
|
|
This option is enabled by default for the Ada front end, as permitted by
|
|
the Ada language specification.
|
|
Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels.
|
|
|
|
@item -funwind-tables
|
|
@opindex funwind-tables
|
|
Similar to @option{-fexceptions}, except that it just generates any needed
|
|
static data, but does not affect the generated code in any other way.
|
|
You normally do not need to enable this option; instead, a language processor
|
|
that needs this handling enables it on your behalf.
|
|
|
|
@item -fasynchronous-unwind-tables
|
|
@opindex fasynchronous-unwind-tables
|
|
Generate unwind table in DWARF format, if supported by target machine. The
|
|
table is exact at each instruction boundary, so it can be used for stack
|
|
unwinding from asynchronous events (such as debugger or garbage collector).
|
|
|
|
@item -fno-gnu-unique
|
|
@opindex fno-gnu-unique
|
|
On systems with recent GNU assembler and C library, the C++ compiler
|
|
uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions
|
|
of template static data members and static local variables in inline
|
|
functions are unique even in the presence of @code{RTLD_LOCAL}; this
|
|
is necessary to avoid problems with a library used by two different
|
|
@code{RTLD_LOCAL} plugins depending on a definition in one of them and
|
|
therefore disagreeing with the other one about the binding of the
|
|
symbol. But this causes @code{dlclose} to be ignored for affected
|
|
DSOs; if your program relies on reinitialization of a DSO via
|
|
@code{dlclose} and @code{dlopen}, you can use
|
|
@option{-fno-gnu-unique}.
|
|
|
|
@item -fpcc-struct-return
|
|
@opindex fpcc-struct-return
|
|
Return ``short'' @code{struct} and @code{union} values in memory like
|
|
longer ones, rather than in registers. This convention is less
|
|
efficient, but it has the advantage of allowing intercallability between
|
|
GCC-compiled files and files compiled with other compilers, particularly
|
|
the Portable C Compiler (pcc).
|
|
|
|
The precise convention for returning structures in memory depends
|
|
on the target configuration macros.
|
|
|
|
Short structures and unions are those whose size and alignment match
|
|
that of some integer type.
|
|
|
|
@strong{Warning:} code compiled with the @option{-fpcc-struct-return}
|
|
switch is not binary compatible with code compiled with the
|
|
@option{-freg-struct-return} switch.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -freg-struct-return
|
|
@opindex freg-struct-return
|
|
Return @code{struct} and @code{union} values in registers when possible.
|
|
This is more efficient for small structures than
|
|
@option{-fpcc-struct-return}.
|
|
|
|
If you specify neither @option{-fpcc-struct-return} nor
|
|
@option{-freg-struct-return}, GCC defaults to whichever convention is
|
|
standard for the target. If there is no standard convention, GCC
|
|
defaults to @option{-fpcc-struct-return}, except on targets where GCC is
|
|
the principal compiler. In those cases, we can choose the standard, and
|
|
we chose the more efficient register return alternative.
|
|
|
|
@strong{Warning:} code compiled with the @option{-freg-struct-return}
|
|
switch is not binary compatible with code compiled with the
|
|
@option{-fpcc-struct-return} switch.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -fshort-enums
|
|
@opindex fshort-enums
|
|
Allocate to an @code{enum} type only as many bytes as it needs for the
|
|
declared range of possible values. Specifically, the @code{enum} type
|
|
is equivalent to the smallest integer type that has enough room.
|
|
|
|
@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate
|
|
code that is not binary compatible with code generated without that switch.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -fshort-wchar
|
|
@opindex fshort-wchar
|
|
Override the underlying type for @code{wchar_t} to be @code{short
|
|
unsigned int} instead of the default for the target. This option is
|
|
useful for building programs to run under WINE@.
|
|
|
|
@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate
|
|
code that is not binary compatible with code generated without that switch.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -fno-common
|
|
@opindex fno-common
|
|
@cindex tentative definitions
|
|
In C code, this option controls the placement of global variables
|
|
defined without an initializer, known as @dfn{tentative definitions}
|
|
in the C standard. Tentative definitions are distinct from declarations
|
|
of a variable with the @code{extern} keyword, which do not allocate storage.
|
|
|
|
Unix C compilers have traditionally allocated storage for
|
|
uninitialized global variables in a common block. This allows the
|
|
linker to resolve all tentative definitions of the same variable
|
|
in different compilation units to the same object, or to a non-tentative
|
|
definition.
|
|
This is the behavior specified by @option{-fcommon}, and is the default for
|
|
GCC on most targets.
|
|
On the other hand, this behavior is not required by ISO
|
|
C, and on some targets may carry a speed or code size penalty on
|
|
variable references.
|
|
|
|
The @option{-fno-common} option specifies that the compiler should instead
|
|
place uninitialized global variables in the data section of the object file.
|
|
This inhibits the merging of tentative definitions by the linker so
|
|
you get a multiple-definition error if the same
|
|
variable is defined in more than one compilation unit.
|
|
Compiling with @option{-fno-common} is useful on targets for which
|
|
it provides better performance, or if you wish to verify that the
|
|
program will work on other systems that always treat uninitialized
|
|
variable definitions this way.
|
|
|
|
@item -fno-ident
|
|
@opindex fno-ident
|
|
Ignore the @code{#ident} directive.
|
|
|
|
@item -finhibit-size-directive
|
|
@opindex finhibit-size-directive
|
|
Don't output a @code{.size} assembler directive, or anything else that
|
|
would cause trouble if the function is split in the middle, and the
|
|
two halves are placed at locations far apart in memory. This option is
|
|
used when compiling @file{crtstuff.c}; you should not need to use it
|
|
for anything else.
|
|
|
|
@item -fverbose-asm
|
|
@opindex fverbose-asm
|
|
Put extra commentary information in the generated assembly code to
|
|
make it more readable. This option is generally only of use to those
|
|
who actually need to read the generated assembly code (perhaps while
|
|
debugging the compiler itself).
|
|
|
|
@option{-fno-verbose-asm}, the default, causes the
|
|
extra information to be omitted and is useful when comparing two assembler
|
|
files.
|
|
|
|
The added comments include:
|
|
|
|
@itemize @bullet
|
|
|
|
@item
|
|
information on the compiler version and command-line options,
|
|
|
|
@item
|
|
the source code lines associated with the assembly instructions,
|
|
in the form FILENAME:LINENUMBER:CONTENT OF LINE,
|
|
|
|
@item
|
|
hints on which high-level expressions correspond to
|
|
the various assembly instruction operands.
|
|
|
|
@end itemize
|
|
|
|
For example, given this C source file:
|
|
|
|
@smallexample
|
|
int test (int n)
|
|
@{
|
|
int i;
|
|
int total = 0;
|
|
|
|
for (i = 0; i < n; i++)
|
|
total += i * i;
|
|
|
|
return total;
|
|
@}
|
|
@end smallexample
|
|
|
|
compiling to (x86_64) assembly via @option{-S} and emitting the result
|
|
direct to stdout via @option{-o} @option{-}
|
|
|
|
@smallexample
|
|
gcc -S test.c -fverbose-asm -Os -o -
|
|
@end smallexample
|
|
|
|
gives output similar to this:
|
|
|
|
@smallexample
|
|
.file "test.c"
|
|
# GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
|
|
[...snip...]
|
|
# options passed:
|
|
[...snip...]
|
|
|
|
.text
|
|
.globl test
|
|
.type test, @@function
|
|
test:
|
|
.LFB0:
|
|
.cfi_startproc
|
|
# test.c:4: int total = 0;
|
|
xorl %eax, %eax # <retval>
|
|
# test.c:6: for (i = 0; i < n; i++)
|
|
xorl %edx, %edx # i
|
|
.L2:
|
|
# test.c:6: for (i = 0; i < n; i++)
|
|
cmpl %edi, %edx # n, i
|
|
jge .L5 #,
|
|
# test.c:7: total += i * i;
|
|
movl %edx, %ecx # i, tmp92
|
|
imull %edx, %ecx # i, tmp92
|
|
# test.c:6: for (i = 0; i < n; i++)
|
|
incl %edx # i
|
|
# test.c:7: total += i * i;
|
|
addl %ecx, %eax # tmp92, <retval>
|
|
jmp .L2 #
|
|
.L5:
|
|
# test.c:10: @}
|
|
ret
|
|
.cfi_endproc
|
|
.LFE0:
|
|
.size test, .-test
|
|
.ident "GCC: (GNU) 7.0.0 20160809 (experimental)"
|
|
.section .note.GNU-stack,"",@@progbits
|
|
@end smallexample
|
|
|
|
The comments are intended for humans rather than machines and hence the
|
|
precise format of the comments is subject to change.
|
|
|
|
@item -frecord-gcc-switches
|
|
@opindex frecord-gcc-switches
|
|
This switch causes the command line used to invoke the
|
|
compiler to be recorded into the object file that is being created.
|
|
This switch is only implemented on some targets and the exact format
|
|
of the recording is target and binary file format dependent, but it
|
|
usually takes the form of a section containing ASCII text. This
|
|
switch is related to the @option{-fverbose-asm} switch, but that
|
|
switch only records information in the assembler output file as
|
|
comments, so it never reaches the object file.
|
|
See also @option{-grecord-gcc-switches} for another
|
|
way of storing compiler options into the object file.
|
|
|
|
@item -fpic
|
|
@opindex fpic
|
|
@cindex global offset table
|
|
@cindex PIC
|
|
Generate position-independent code (PIC) suitable for use in a shared
|
|
library, if supported for the target machine. Such code accesses all
|
|
constant addresses through a global offset table (GOT)@. The dynamic
|
|
loader resolves the GOT entries when the program starts (the dynamic
|
|
loader is not part of GCC; it is part of the operating system). If
|
|
the GOT size for the linked executable exceeds a machine-specific
|
|
maximum size, you get an error message from the linker indicating that
|
|
@option{-fpic} does not work; in that case, recompile with @option{-fPIC}
|
|
instead. (These maximums are 8k on the SPARC, 28k on AArch64 and 32k
|
|
on the m68k and RS/6000. The x86 has no such limit.)
|
|
|
|
Position-independent code requires special support, and therefore works
|
|
only on certain machines. For the x86, GCC supports PIC for System V
|
|
but not for the Sun 386i. Code generated for the IBM RS/6000 is always
|
|
position-independent.
|
|
|
|
When this flag is set, the macros @code{__pic__} and @code{__PIC__}
|
|
are defined to 1.
|
|
|
|
@item -fPIC
|
|
@opindex fPIC
|
|
If supported for the target machine, emit position-independent code,
|
|
suitable for dynamic linking and avoiding any limit on the size of the
|
|
global offset table. This option makes a difference on AArch64, m68k,
|
|
PowerPC and SPARC@.
|
|
|
|
Position-independent code requires special support, and therefore works
|
|
only on certain machines.
|
|
|
|
When this flag is set, the macros @code{__pic__} and @code{__PIC__}
|
|
are defined to 2.
|
|
|
|
@item -fpie
|
|
@itemx -fPIE
|
|
@opindex fpie
|
|
@opindex fPIE
|
|
These options are similar to @option{-fpic} and @option{-fPIC}, but
|
|
generated position independent code can be only linked into executables.
|
|
Usually these options are used when @option{-pie} GCC option is
|
|
used during linking.
|
|
|
|
@option{-fpie} and @option{-fPIE} both define the macros
|
|
@code{__pie__} and @code{__PIE__}. The macros have the value 1
|
|
for @option{-fpie} and 2 for @option{-fPIE}.
|
|
|
|
@item -fno-plt
|
|
@opindex fno-plt
|
|
Do not use the PLT for external function calls in position-independent code.
|
|
Instead, load the callee address at call sites from the GOT and branch to it.
|
|
This leads to more efficient code by eliminating PLT stubs and exposing
|
|
GOT loads to optimizations. On architectures such as 32-bit x86 where
|
|
PLT stubs expect the GOT pointer in a specific register, this gives more
|
|
register allocation freedom to the compiler.
|
|
Lazy binding requires use of the PLT;
|
|
with @option{-fno-plt} all external symbols are resolved at load time.
|
|
|
|
Alternatively, the function attribute @code{noplt} can be used to avoid calls
|
|
through the PLT for specific external functions.
|
|
|
|
In position-dependent code, a few targets also convert calls to
|
|
functions that are marked to not use the PLT to use the GOT instead.
|
|
|
|
@item -fno-jump-tables
|
|
@opindex fno-jump-tables
|
|
Do not use jump tables for switch statements even where it would be
|
|
more efficient than other code generation strategies. This option is
|
|
of use in conjunction with @option{-fpic} or @option{-fPIC} for
|
|
building code that forms part of a dynamic linker and cannot
|
|
reference the address of a jump table. On some targets, jump tables
|
|
do not require a GOT and this option is not needed.
|
|
|
|
@item -ffixed-@var{reg}
|
|
@opindex ffixed
|
|
Treat the register named @var{reg} as a fixed register; generated code
|
|
should never refer to it (except perhaps as a stack pointer, frame
|
|
pointer or in some other fixed role).
|
|
|
|
@var{reg} must be the name of a register. The register names accepted
|
|
are machine-specific and are defined in the @code{REGISTER_NAMES}
|
|
macro in the machine description macro file.
|
|
|
|
This flag does not have a negative form, because it specifies a
|
|
three-way choice.
|
|
|
|
@item -fcall-used-@var{reg}
|
|
@opindex fcall-used
|
|
Treat the register named @var{reg} as an allocable register that is
|
|
clobbered by function calls. It may be allocated for temporaries or
|
|
variables that do not live across a call. Functions compiled this way
|
|
do not save and restore the register @var{reg}.
|
|
|
|
It is an error to use this flag with the frame pointer or stack pointer.
|
|
Use of this flag for other registers that have fixed pervasive roles in
|
|
the machine's execution model produces disastrous results.
|
|
|
|
This flag does not have a negative form, because it specifies a
|
|
three-way choice.
|
|
|
|
@item -fcall-saved-@var{reg}
|
|
@opindex fcall-saved
|
|
Treat the register named @var{reg} as an allocable register saved by
|
|
functions. It may be allocated even for temporaries or variables that
|
|
live across a call. Functions compiled this way save and restore
|
|
the register @var{reg} if they use it.
|
|
|
|
It is an error to use this flag with the frame pointer or stack pointer.
|
|
Use of this flag for other registers that have fixed pervasive roles in
|
|
the machine's execution model produces disastrous results.
|
|
|
|
A different sort of disaster results from the use of this flag for
|
|
a register in which function values may be returned.
|
|
|
|
This flag does not have a negative form, because it specifies a
|
|
three-way choice.
|
|
|
|
@item -fpack-struct[=@var{n}]
|
|
@opindex fpack-struct
|
|
Without a value specified, pack all structure members together without
|
|
holes. When a value is specified (which must be a small power of two), pack
|
|
structure members according to this value, representing the maximum
|
|
alignment (that is, objects with default alignment requirements larger than
|
|
this are output potentially unaligned at the next fitting location.
|
|
|
|
@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate
|
|
code that is not binary compatible with code generated without that switch.
|
|
Additionally, it makes the code suboptimal.
|
|
Use it to conform to a non-default application binary interface.
|
|
|
|
@item -fleading-underscore
|
|
@opindex fleading-underscore
|
|
This option and its counterpart, @option{-fno-leading-underscore}, forcibly
|
|
change the way C symbols are represented in the object file. One use
|
|
is to help link with legacy assembly code.
|
|
|
|
@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to
|
|
generate code that is not binary compatible with code generated without that
|
|
switch. Use it to conform to a non-default application binary interface.
|
|
Not all targets provide complete support for this switch.
|
|
|
|
@item -ftls-model=@var{model}
|
|
@opindex ftls-model
|
|
Alter the thread-local storage model to be used (@pxref{Thread-Local}).
|
|
The @var{model} argument should be one of @samp{global-dynamic},
|
|
@samp{local-dynamic}, @samp{initial-exec} or @samp{local-exec}.
|
|
Note that the choice is subject to optimization: the compiler may use
|
|
a more efficient model for symbols not visible outside of the translation
|
|
unit, or if @option{-fpic} is not given on the command line.
|
|
|
|
The default without @option{-fpic} is @samp{initial-exec}; with
|
|
@option{-fpic} the default is @samp{global-dynamic}.
|
|
|
|
@item -ftrampolines
|
|
@opindex ftrampolines
|
|
For targets that normally need trampolines for nested functions, always
|
|
generate them instead of using descriptors. Otherwise, for targets that
|
|
do not need them, like for example HP-PA or IA-64, do nothing.
|
|
|
|
A trampoline is a small piece of code that is created at run time on the
|
|
stack when the address of a nested function is taken, and is used to call
|
|
the nested function indirectly. Therefore, it requires the stack to be
|
|
made executable in order for the program to work properly.
|
|
|
|
@option{-fno-trampolines} is enabled by default on a language by language
|
|
basis to let the compiler avoid generating them, if it computes that this
|
|
is safe, and replace them with descriptors. Descriptors are made up of data
|
|
only, but the generated code must be prepared to deal with them. As of this
|
|
writing, @option{-fno-trampolines} is enabled by default only for Ada.
|
|
|
|
Moreover, code compiled with @option{-ftrampolines} and code compiled with
|
|
@option{-fno-trampolines} are not binary compatible if nested functions are
|
|
present. This option must therefore be used on a program-wide basis and be
|
|
manipulated with extreme care.
|
|
|
|
@item -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]}
|
|
@opindex fvisibility
|
|
Set the default ELF image symbol visibility to the specified option---all
|
|
symbols are marked with this unless overridden within the code.
|
|
Using this feature can very substantially improve linking and
|
|
load times of shared object libraries, produce more optimized
|
|
code, provide near-perfect API export and prevent symbol clashes.
|
|
It is @strong{strongly} recommended that you use this in any shared objects
|
|
you distribute.
|
|
|
|
Despite the nomenclature, @samp{default} always means public; i.e.,
|
|
available to be linked against from outside the shared object.
|
|
@samp{protected} and @samp{internal} are pretty useless in real-world
|
|
usage so the only other commonly used option is @samp{hidden}.
|
|
The default if @option{-fvisibility} isn't specified is
|
|
@samp{default}, i.e., make every symbol public.
|
|
|
|
A good explanation of the benefits offered by ensuring ELF
|
|
symbols have the correct visibility is given by ``How To Write
|
|
Shared Libraries'' by Ulrich Drepper (which can be found at
|
|
@w{@uref{http://www.akkadia.org/drepper/}})---however a superior
|
|
solution made possible by this option to marking things hidden when
|
|
the default is public is to make the default hidden and mark things
|
|
public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden}
|
|
and @code{__attribute__ ((visibility("default")))} instead of
|
|
@code{__declspec(dllexport)} you get almost identical semantics with
|
|
identical syntax. This is a great boon to those working with
|
|
cross-platform projects.
|
|
|
|
For those adding visibility support to existing code, you may find
|
|
@code{#pragma GCC visibility} of use. This works by you enclosing
|
|
the declarations you wish to set visibility for with (for example)
|
|
@code{#pragma GCC visibility push(hidden)} and
|
|
@code{#pragma GCC visibility pop}.
|
|
Bear in mind that symbol visibility should be viewed @strong{as
|
|
part of the API interface contract} and thus all new code should
|
|
always specify visibility when it is not the default; i.e., declarations
|
|
only for use within the local DSO should @strong{always} be marked explicitly
|
|
as hidden as so to avoid PLT indirection overheads---making this
|
|
abundantly clear also aids readability and self-documentation of the code.
|
|
Note that due to ISO C++ specification requirements, @code{operator new} and
|
|
@code{operator delete} must always be of default visibility.
|
|
|
|
Be aware that headers from outside your project, in particular system
|
|
headers and headers from any other library you use, may not be
|
|
expecting to be compiled with visibility other than the default. You
|
|
may need to explicitly say @code{#pragma GCC visibility push(default)}
|
|
before including any such headers.
|
|
|
|
@code{extern} declarations are not affected by @option{-fvisibility}, so
|
|
a lot of code can be recompiled with @option{-fvisibility=hidden} with
|
|
no modifications. However, this means that calls to @code{extern}
|
|
functions with no explicit visibility use the PLT, so it is more
|
|
effective to use @code{__attribute ((visibility))} and/or
|
|
@code{#pragma GCC visibility} to tell the compiler which @code{extern}
|
|
declarations should be treated as hidden.
|
|
|
|
Note that @option{-fvisibility} does affect C++ vague linkage
|
|
entities. This means that, for instance, an exception class that is
|
|
be thrown between DSOs must be explicitly marked with default
|
|
visibility so that the @samp{type_info} nodes are unified between
|
|
the DSOs.
|
|
|
|
An overview of these techniques, their benefits and how to use them
|
|
is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}.
|
|
|
|
@item -fstrict-volatile-bitfields
|
|
@opindex fstrict-volatile-bitfields
|
|
This option should be used if accesses to volatile bit-fields (or other
|
|
structure fields, although the compiler usually honors those types
|
|
anyway) should use a single access of the width of the
|
|
field's type, aligned to a natural alignment if possible. For
|
|
example, targets with memory-mapped peripheral registers might require
|
|
all such accesses to be 16 bits wide; with this flag you can
|
|
declare all peripheral bit-fields as @code{unsigned short} (assuming short
|
|
is 16 bits on these targets) to force GCC to use 16-bit accesses
|
|
instead of, perhaps, a more efficient 32-bit access.
|
|
|
|
If this option is disabled, the compiler uses the most efficient
|
|
instruction. In the previous example, that might be a 32-bit load
|
|
instruction, even though that accesses bytes that do not contain
|
|
any portion of the bit-field, or memory-mapped registers unrelated to
|
|
the one being updated.
|
|
|
|
In some cases, such as when the @code{packed} attribute is applied to a
|
|
structure field, it may not be possible to access the field with a single
|
|
read or write that is correctly aligned for the target machine. In this
|
|
case GCC falls back to generating multiple accesses rather than code that
|
|
will fault or truncate the result at run time.
|
|
|
|
Note: Due to restrictions of the C/C++11 memory model, write accesses are
|
|
not allowed to touch non bit-field members. It is therefore recommended
|
|
to define all bits of the field's type as bit-field members.
|
|
|
|
The default value of this option is determined by the application binary
|
|
interface for the target processor.
|
|
|
|
@item -fsync-libcalls
|
|
@opindex fsync-libcalls
|
|
This option controls whether any out-of-line instance of the @code{__sync}
|
|
family of functions may be used to implement the C++11 @code{__atomic}
|
|
family of functions.
|
|
|
|
The default value of this option is enabled, thus the only useful form
|
|
of the option is @option{-fno-sync-libcalls}. This option is used in
|
|
the implementation of the @file{libatomic} runtime library.
|
|
|
|
@end table
|
|
|
|
@node Developer Options
|
|
@section GCC Developer Options
|
|
@cindex developer options
|
|
@cindex debugging GCC
|
|
@cindex debug dump options
|
|
@cindex dump options
|
|
@cindex compilation statistics
|
|
|
|
This section describes command-line options that are primarily of
|
|
interest to GCC developers, including options to support compiler
|
|
testing and investigation of compiler bugs and compile-time
|
|
performance problems. This includes options that produce debug dumps
|
|
at various points in the compilation; that print statistics such as
|
|
memory use and execution time; and that print information about GCC's
|
|
configuration, such as where it searches for libraries. You should
|
|
rarely need to use any of these options for ordinary compilation and
|
|
linking tasks.
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -d@var{letters}
|
|
@itemx -fdump-rtl-@var{pass}
|
|
@itemx -fdump-rtl-@var{pass}=@var{filename}
|
|
@opindex d
|
|
@opindex fdump-rtl-@var{pass}
|
|
Says to make debugging dumps during compilation at times specified by
|
|
@var{letters}. This is used for debugging the RTL-based passes of the
|
|
compiler. The file names for most of the dumps are made by appending
|
|
a pass number and a word to the @var{dumpname}, and the files are
|
|
created in the directory of the output file. In case of
|
|
@option{=@var{filename}} option, the dump is output on the given file
|
|
instead of the pass numbered dump files. Note that the pass number is
|
|
assigned as passes are registered into the pass manager. Most passes
|
|
are registered in the order that they will execute and for these passes
|
|
the number corresponds to the pass execution order. However, passes
|
|
registered by plugins, passes specific to compilation targets, or
|
|
passes that are otherwise registered after all the other passes are
|
|
numbered higher than a pass named "final", even if they are executed
|
|
earlier. @var{dumpname} is generated from the name of the output
|
|
file if explicitly specified and not an executable, otherwise it is
|
|
the basename of the source file.
|
|
|
|
Some @option{-d@var{letters}} switches have different meaning when
|
|
@option{-E} is used for preprocessing. @xref{Preprocessor Options},
|
|
for information about preprocessor-specific dump options.
|
|
|
|
Debug dumps can be enabled with a @option{-fdump-rtl} switch or some
|
|
@option{-d} option @var{letters}. Here are the possible
|
|
letters for use in @var{pass} and @var{letters}, and their meanings:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -fdump-rtl-alignments
|
|
@opindex fdump-rtl-alignments
|
|
Dump after branch alignments have been computed.
|
|
|
|
@item -fdump-rtl-asmcons
|
|
@opindex fdump-rtl-asmcons
|
|
Dump after fixing rtl statements that have unsatisfied in/out constraints.
|
|
|
|
@item -fdump-rtl-auto_inc_dec
|
|
@opindex fdump-rtl-auto_inc_dec
|
|
Dump after auto-inc-dec discovery. This pass is only run on
|
|
architectures that have auto inc or auto dec instructions.
|
|
|
|
@item -fdump-rtl-barriers
|
|
@opindex fdump-rtl-barriers
|
|
Dump after cleaning up the barrier instructions.
|
|
|
|
@item -fdump-rtl-bbpart
|
|
@opindex fdump-rtl-bbpart
|
|
Dump after partitioning hot and cold basic blocks.
|
|
|
|
@item -fdump-rtl-bbro
|
|
@opindex fdump-rtl-bbro
|
|
Dump after block reordering.
|
|
|
|
@item -fdump-rtl-btl1
|
|
@itemx -fdump-rtl-btl2
|
|
@opindex fdump-rtl-btl2
|
|
@opindex fdump-rtl-btl2
|
|
@option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping
|
|
after the two branch
|
|
target load optimization passes.
|
|
|
|
@item -fdump-rtl-bypass
|
|
@opindex fdump-rtl-bypass
|
|
Dump after jump bypassing and control flow optimizations.
|
|
|
|
@item -fdump-rtl-combine
|
|
@opindex fdump-rtl-combine
|
|
Dump after the RTL instruction combination pass.
|
|
|
|
@item -fdump-rtl-compgotos
|
|
@opindex fdump-rtl-compgotos
|
|
Dump after duplicating the computed gotos.
|
|
|
|
@item -fdump-rtl-ce1
|
|
@itemx -fdump-rtl-ce2
|
|
@itemx -fdump-rtl-ce3
|
|
@opindex fdump-rtl-ce1
|
|
@opindex fdump-rtl-ce2
|
|
@opindex fdump-rtl-ce3
|
|
@option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and
|
|
@option{-fdump-rtl-ce3} enable dumping after the three
|
|
if conversion passes.
|
|
|
|
@item -fdump-rtl-cprop_hardreg
|
|
@opindex fdump-rtl-cprop_hardreg
|
|
Dump after hard register copy propagation.
|
|
|
|
@item -fdump-rtl-csa
|
|
@opindex fdump-rtl-csa
|
|
Dump after combining stack adjustments.
|
|
|
|
@item -fdump-rtl-cse1
|
|
@itemx -fdump-rtl-cse2
|
|
@opindex fdump-rtl-cse1
|
|
@opindex fdump-rtl-cse2
|
|
@option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after
|
|
the two common subexpression elimination passes.
|
|
|
|
@item -fdump-rtl-dce
|
|
@opindex fdump-rtl-dce
|
|
Dump after the standalone dead code elimination passes.
|
|
|
|
@item -fdump-rtl-dbr
|
|
@opindex fdump-rtl-dbr
|
|
Dump after delayed branch scheduling.
|
|
|
|
@item -fdump-rtl-dce1
|
|
@itemx -fdump-rtl-dce2
|
|
@opindex fdump-rtl-dce1
|
|
@opindex fdump-rtl-dce2
|
|
@option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after
|
|
the two dead store elimination passes.
|
|
|
|
@item -fdump-rtl-eh
|
|
@opindex fdump-rtl-eh
|
|
Dump after finalization of EH handling code.
|
|
|
|
@item -fdump-rtl-eh_ranges
|
|
@opindex fdump-rtl-eh_ranges
|
|
Dump after conversion of EH handling range regions.
|
|
|
|
@item -fdump-rtl-expand
|
|
@opindex fdump-rtl-expand
|
|
Dump after RTL generation.
|
|
|
|
@item -fdump-rtl-fwprop1
|
|
@itemx -fdump-rtl-fwprop2
|
|
@opindex fdump-rtl-fwprop1
|
|
@opindex fdump-rtl-fwprop2
|
|
@option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable
|
|
dumping after the two forward propagation passes.
|
|
|
|
@item -fdump-rtl-gcse1
|
|
@itemx -fdump-rtl-gcse2
|
|
@opindex fdump-rtl-gcse1
|
|
@opindex fdump-rtl-gcse2
|
|
@option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping
|
|
after global common subexpression elimination.
|
|
|
|
@item -fdump-rtl-init-regs
|
|
@opindex fdump-rtl-init-regs
|
|
Dump after the initialization of the registers.
|
|
|
|
@item -fdump-rtl-initvals
|
|
@opindex fdump-rtl-initvals
|
|
Dump after the computation of the initial value sets.
|
|
|
|
@item -fdump-rtl-into_cfglayout
|
|
@opindex fdump-rtl-into_cfglayout
|
|
Dump after converting to cfglayout mode.
|
|
|
|
@item -fdump-rtl-ira
|
|
@opindex fdump-rtl-ira
|
|
Dump after iterated register allocation.
|
|
|
|
@item -fdump-rtl-jump
|
|
@opindex fdump-rtl-jump
|
|
Dump after the second jump optimization.
|
|
|
|
@item -fdump-rtl-loop2
|
|
@opindex fdump-rtl-loop2
|
|
@option{-fdump-rtl-loop2} enables dumping after the rtl
|
|
loop optimization passes.
|
|
|
|
@item -fdump-rtl-mach
|
|
@opindex fdump-rtl-mach
|
|
Dump after performing the machine dependent reorganization pass, if that
|
|
pass exists.
|
|
|
|
@item -fdump-rtl-mode_sw
|
|
@opindex fdump-rtl-mode_sw
|
|
Dump after removing redundant mode switches.
|
|
|
|
@item -fdump-rtl-rnreg
|
|
@opindex fdump-rtl-rnreg
|
|
Dump after register renumbering.
|
|
|
|
@item -fdump-rtl-outof_cfglayout
|
|
@opindex fdump-rtl-outof_cfglayout
|
|
Dump after converting from cfglayout mode.
|
|
|
|
@item -fdump-rtl-peephole2
|
|
@opindex fdump-rtl-peephole2
|
|
Dump after the peephole pass.
|
|
|
|
@item -fdump-rtl-postreload
|
|
@opindex fdump-rtl-postreload
|
|
Dump after post-reload optimizations.
|
|
|
|
@item -fdump-rtl-pro_and_epilogue
|
|
@opindex fdump-rtl-pro_and_epilogue
|
|
Dump after generating the function prologues and epilogues.
|
|
|
|
@item -fdump-rtl-sched1
|
|
@itemx -fdump-rtl-sched2
|
|
@opindex fdump-rtl-sched1
|
|
@opindex fdump-rtl-sched2
|
|
@option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping
|
|
after the basic block scheduling passes.
|
|
|
|
@item -fdump-rtl-ree
|
|
@opindex fdump-rtl-ree
|
|
Dump after sign/zero extension elimination.
|
|
|
|
@item -fdump-rtl-seqabstr
|
|
@opindex fdump-rtl-seqabstr
|
|
Dump after common sequence discovery.
|
|
|
|
@item -fdump-rtl-shorten
|
|
@opindex fdump-rtl-shorten
|
|
Dump after shortening branches.
|
|
|
|
@item -fdump-rtl-sibling
|
|
@opindex fdump-rtl-sibling
|
|
Dump after sibling call optimizations.
|
|
|
|
@item -fdump-rtl-split1
|
|
@itemx -fdump-rtl-split2
|
|
@itemx -fdump-rtl-split3
|
|
@itemx -fdump-rtl-split4
|
|
@itemx -fdump-rtl-split5
|
|
@opindex fdump-rtl-split1
|
|
@opindex fdump-rtl-split2
|
|
@opindex fdump-rtl-split3
|
|
@opindex fdump-rtl-split4
|
|
@opindex fdump-rtl-split5
|
|
These options enable dumping after five rounds of
|
|
instruction splitting.
|
|
|
|
@item -fdump-rtl-sms
|
|
@opindex fdump-rtl-sms
|
|
Dump after modulo scheduling. This pass is only run on some
|
|
architectures.
|
|
|
|
@item -fdump-rtl-stack
|
|
@opindex fdump-rtl-stack
|
|
Dump after conversion from GCC's ``flat register file'' registers to the
|
|
x87's stack-like registers. This pass is only run on x86 variants.
|
|
|
|
@item -fdump-rtl-subreg1
|
|
@itemx -fdump-rtl-subreg2
|
|
@opindex fdump-rtl-subreg1
|
|
@opindex fdump-rtl-subreg2
|
|
@option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after
|
|
the two subreg expansion passes.
|
|
|
|
@item -fdump-rtl-unshare
|
|
@opindex fdump-rtl-unshare
|
|
Dump after all rtl has been unshared.
|
|
|
|
@item -fdump-rtl-vartrack
|
|
@opindex fdump-rtl-vartrack
|
|
Dump after variable tracking.
|
|
|
|
@item -fdump-rtl-vregs
|
|
@opindex fdump-rtl-vregs
|
|
Dump after converting virtual registers to hard registers.
|
|
|
|
@item -fdump-rtl-web
|
|
@opindex fdump-rtl-web
|
|
Dump after live range splitting.
|
|
|
|
@item -fdump-rtl-regclass
|
|
@itemx -fdump-rtl-subregs_of_mode_init
|
|
@itemx -fdump-rtl-subregs_of_mode_finish
|
|
@itemx -fdump-rtl-dfinit
|
|
@itemx -fdump-rtl-dfinish
|
|
@opindex fdump-rtl-regclass
|
|
@opindex fdump-rtl-subregs_of_mode_init
|
|
@opindex fdump-rtl-subregs_of_mode_finish
|
|
@opindex fdump-rtl-dfinit
|
|
@opindex fdump-rtl-dfinish
|
|
These dumps are defined but always produce empty files.
|
|
|
|
@item -da
|
|
@itemx -fdump-rtl-all
|
|
@opindex da
|
|
@opindex fdump-rtl-all
|
|
Produce all the dumps listed above.
|
|
|
|
@item -dA
|
|
@opindex dA
|
|
Annotate the assembler output with miscellaneous debugging information.
|
|
|
|
@item -dD
|
|
@opindex dD
|
|
Dump all macro definitions, at the end of preprocessing, in addition to
|
|
normal output.
|
|
|
|
@item -dH
|
|
@opindex dH
|
|
Produce a core dump whenever an error occurs.
|
|
|
|
@item -dp
|
|
@opindex dp
|
|
Annotate the assembler output with a comment indicating which
|
|
pattern and alternative is used. The length of each instruction is
|
|
also printed.
|
|
|
|
@item -dP
|
|
@opindex dP
|
|
Dump the RTL in the assembler output as a comment before each instruction.
|
|
Also turns on @option{-dp} annotation.
|
|
|
|
@item -dx
|
|
@opindex dx
|
|
Just generate RTL for a function instead of compiling it. Usually used
|
|
with @option{-fdump-rtl-expand}.
|
|
@end table
|
|
|
|
@item -fdump-noaddr
|
|
@opindex fdump-noaddr
|
|
When doing debugging dumps, suppress address output. This makes it more
|
|
feasible to use diff on debugging dumps for compiler invocations with
|
|
different compiler binaries and/or different
|
|
text / bss / data / heap / stack / dso start locations.
|
|
|
|
@item -freport-bug
|
|
@opindex freport-bug
|
|
Collect and dump debug information into a temporary file if an
|
|
internal compiler error (ICE) occurs.
|
|
|
|
@item -fdump-unnumbered
|
|
@opindex fdump-unnumbered
|
|
When doing debugging dumps, suppress instruction numbers and address output.
|
|
This makes it more feasible to use diff on debugging dumps for compiler
|
|
invocations with different options, in particular with and without
|
|
@option{-g}.
|
|
|
|
@item -fdump-unnumbered-links
|
|
@opindex fdump-unnumbered-links
|
|
When doing debugging dumps (see @option{-d} option above), suppress
|
|
instruction numbers for the links to the previous and next instructions
|
|
in a sequence.
|
|
|
|
@item -fdump-translation-unit @r{(C++ only)}
|
|
@itemx -fdump-translation-unit-@var{options} @r{(C++ only)}
|
|
@opindex fdump-translation-unit
|
|
Dump a representation of the tree structure for the entire translation
|
|
unit to a file. The file name is made by appending @file{.tu} to the
|
|
source file name, and the file is created in the same directory as the
|
|
output file. If the @samp{-@var{options}} form is used, @var{options}
|
|
controls the details of the dump as described for the
|
|
@option{-fdump-tree} options.
|
|
|
|
@item -fdump-class-hierarchy @r{(C++ only)}
|
|
@itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)}
|
|
@opindex fdump-class-hierarchy
|
|
Dump a representation of each class's hierarchy and virtual function
|
|
table layout to a file. The file name is made by appending
|
|
@file{.class} to the source file name, and the file is created in the
|
|
same directory as the output file. If the @samp{-@var{options}} form
|
|
is used, @var{options} controls the details of the dump as described
|
|
for the @option{-fdump-tree} options.
|
|
|
|
@item -fdump-ipa-@var{switch}
|
|
@opindex fdump-ipa
|
|
Control the dumping at various stages of inter-procedural analysis
|
|
language tree to a file. The file name is generated by appending a
|
|
switch specific suffix to the source file name, and the file is created
|
|
in the same directory as the output file. The following dumps are
|
|
possible:
|
|
|
|
@table @samp
|
|
@item all
|
|
Enables all inter-procedural analysis dumps.
|
|
|
|
@item cgraph
|
|
Dumps information about call-graph optimization, unused function removal,
|
|
and inlining decisions.
|
|
|
|
@item inline
|
|
Dump after function inlining.
|
|
|
|
@end table
|
|
|
|
@item -fdump-passes
|
|
@opindex fdump-passes
|
|
Dump the list of optimization passes that are turned on and off by
|
|
the current command-line options.
|
|
|
|
@item -fdump-statistics-@var{option}
|
|
@opindex fdump-statistics
|
|
Enable and control dumping of pass statistics in a separate file. The
|
|
file name is generated by appending a suffix ending in
|
|
@samp{.statistics} to the source file name, and the file is created in
|
|
the same directory as the output file. If the @samp{-@var{option}}
|
|
form is used, @samp{-stats} causes counters to be summed over the
|
|
whole compilation unit while @samp{-details} dumps every event as
|
|
the passes generate them. The default with no option is to sum
|
|
counters for each function compiled.
|
|
|
|
@item -fdump-tree-@var{switch}
|
|
@itemx -fdump-tree-@var{switch}-@var{options}
|
|
@itemx -fdump-tree-@var{switch}-@var{options}=@var{filename}
|
|
@opindex fdump-tree
|
|
Control the dumping at various stages of processing the intermediate
|
|
language tree to a file. The file name is generated by appending a
|
|
switch-specific suffix to the source file name, and the file is
|
|
created in the same directory as the output file. In case of
|
|
@option{=@var{filename}} option, the dump is output on the given file
|
|
instead of the auto named dump files. If the @samp{-@var{options}}
|
|
form is used, @var{options} is a list of @samp{-} separated options
|
|
which control the details of the dump. Not all options are applicable
|
|
to all dumps; those that are not meaningful are ignored. The
|
|
following options are available
|
|
|
|
@table @samp
|
|
@item address
|
|
Print the address of each node. Usually this is not meaningful as it
|
|
changes according to the environment and source file. Its primary use
|
|
is for tying up a dump file with a debug environment.
|
|
@item asmname
|
|
If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that
|
|
in the dump instead of @code{DECL_NAME}. Its primary use is ease of
|
|
use working backward from mangled names in the assembly file.
|
|
@item slim
|
|
When dumping front-end intermediate representations, inhibit dumping
|
|
of members of a scope or body of a function merely because that scope
|
|
has been reached. Only dump such items when they are directly reachable
|
|
by some other path.
|
|
|
|
When dumping pretty-printed trees, this option inhibits dumping the
|
|
bodies of control structures.
|
|
|
|
When dumping RTL, print the RTL in slim (condensed) form instead of
|
|
the default LISP-like representation.
|
|
@item raw
|
|
Print a raw representation of the tree. By default, trees are
|
|
pretty-printed into a C-like representation.
|
|
@item details
|
|
Enable more detailed dumps (not honored by every dump option). Also
|
|
include information from the optimization passes.
|
|
@item stats
|
|
Enable dumping various statistics about the pass (not honored by every dump
|
|
option).
|
|
@item blocks
|
|
Enable showing basic block boundaries (disabled in raw dumps).
|
|
@item graph
|
|
For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}),
|
|
dump a representation of the control flow graph suitable for viewing with
|
|
GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in
|
|
the file is pretty-printed as a subgraph, so that GraphViz can render them
|
|
all in a single plot.
|
|
|
|
This option currently only works for RTL dumps, and the RTL is always
|
|
dumped in slim form.
|
|
@item vops
|
|
Enable showing virtual operands for every statement.
|
|
@item lineno
|
|
Enable showing line numbers for statements.
|
|
@item uid
|
|
Enable showing the unique ID (@code{DECL_UID}) for each variable.
|
|
@item verbose
|
|
Enable showing the tree dump for each statement.
|
|
@item eh
|
|
Enable showing the EH region number holding each statement.
|
|
@item scev
|
|
Enable showing scalar evolution analysis details.
|
|
@item optimized
|
|
Enable showing optimization information (only available in certain
|
|
passes).
|
|
@item missed
|
|
Enable showing missed optimization information (only available in certain
|
|
passes).
|
|
@item note
|
|
Enable other detailed optimization information (only available in
|
|
certain passes).
|
|
@item =@var{filename}
|
|
Instead of an auto named dump file, output into the given file
|
|
name. The file names @file{stdout} and @file{stderr} are treated
|
|
specially and are considered already open standard streams. For
|
|
example,
|
|
|
|
@smallexample
|
|
gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
|
|
-fdump-tree-pre=stderr file.c
|
|
@end smallexample
|
|
|
|
outputs vectorizer dump into @file{foo.dump}, while the PRE dump is
|
|
output on to @file{stderr}. If two conflicting dump filenames are
|
|
given for the same pass, then the latter option overrides the earlier
|
|
one.
|
|
|
|
@item split-paths
|
|
@opindex fdump-tree-split-paths
|
|
Dump each function after splitting paths to loop backedges. The file
|
|
name is made by appending @file{.split-paths} to the source file name.
|
|
|
|
@item all
|
|
Turn on all options, except @option{raw}, @option{slim}, @option{verbose}
|
|
and @option{lineno}.
|
|
|
|
@item optall
|
|
Turn on all optimization options, i.e., @option{optimized},
|
|
@option{missed}, and @option{note}.
|
|
@end table
|
|
|
|
The following tree dumps are possible:
|
|
@table @samp
|
|
|
|
@item original
|
|
@opindex fdump-tree-original
|
|
Dump before any tree based optimization, to @file{@var{file}.original}.
|
|
|
|
@item optimized
|
|
@opindex fdump-tree-optimized
|
|
Dump after all tree based optimization, to @file{@var{file}.optimized}.
|
|
|
|
@item gimple
|
|
@opindex fdump-tree-gimple
|
|
Dump each function before and after the gimplification pass to a file. The
|
|
file name is made by appending @file{.gimple} to the source file name.
|
|
|
|
@item cfg
|
|
@opindex fdump-tree-cfg
|
|
Dump the control flow graph of each function to a file. The file name is
|
|
made by appending @file{.cfg} to the source file name.
|
|
|
|
@item ch
|
|
@opindex fdump-tree-ch
|
|
Dump each function after copying loop headers. The file name is made by
|
|
appending @file{.ch} to the source file name.
|
|
|
|
@item ssa
|
|
@opindex fdump-tree-ssa
|
|
Dump SSA related information to a file. The file name is made by appending
|
|
@file{.ssa} to the source file name.
|
|
|
|
@item alias
|
|
@opindex fdump-tree-alias
|
|
Dump aliasing information for each function. The file name is made by
|
|
appending @file{.alias} to the source file name.
|
|
|
|
@item ccp
|
|
@opindex fdump-tree-ccp
|
|
Dump each function after CCP@. The file name is made by appending
|
|
@file{.ccp} to the source file name.
|
|
|
|
@item storeccp
|
|
@opindex fdump-tree-storeccp
|
|
Dump each function after STORE-CCP@. The file name is made by appending
|
|
@file{.storeccp} to the source file name.
|
|
|
|
@item pre
|
|
@opindex fdump-tree-pre
|
|
Dump trees after partial redundancy elimination and/or code hoisting.
|
|
The file name is made by appending @file{.pre} to the source file name.
|
|
|
|
@item fre
|
|
@opindex fdump-tree-fre
|
|
Dump trees after full redundancy elimination. The file name is made
|
|
by appending @file{.fre} to the source file name.
|
|
|
|
@item copyprop
|
|
@opindex fdump-tree-copyprop
|
|
Dump trees after copy propagation. The file name is made
|
|
by appending @file{.copyprop} to the source file name.
|
|
|
|
@item store_copyprop
|
|
@opindex fdump-tree-store_copyprop
|
|
Dump trees after store copy-propagation. The file name is made
|
|
by appending @file{.store_copyprop} to the source file name.
|
|
|
|
@item dce
|
|
@opindex fdump-tree-dce
|
|
Dump each function after dead code elimination. The file name is made by
|
|
appending @file{.dce} to the source file name.
|
|
|
|
@item sra
|
|
@opindex fdump-tree-sra
|
|
Dump each function after performing scalar replacement of aggregates. The
|
|
file name is made by appending @file{.sra} to the source file name.
|
|
|
|
@item sink
|
|
@opindex fdump-tree-sink
|
|
Dump each function after performing code sinking. The file name is made
|
|
by appending @file{.sink} to the source file name.
|
|
|
|
@item dom
|
|
@opindex fdump-tree-dom
|
|
Dump each function after applying dominator tree optimizations. The file
|
|
name is made by appending @file{.dom} to the source file name.
|
|
|
|
@item dse
|
|
@opindex fdump-tree-dse
|
|
Dump each function after applying dead store elimination. The file
|
|
name is made by appending @file{.dse} to the source file name.
|
|
|
|
@item phiopt
|
|
@opindex fdump-tree-phiopt
|
|
Dump each function after optimizing PHI nodes into straightline code. The file
|
|
name is made by appending @file{.phiopt} to the source file name.
|
|
|
|
@item backprop
|
|
@opindex fdump-tree-backprop
|
|
Dump each function after back-propagating use information up the definition
|
|
chain. The file name is made by appending @file{.backprop} to the
|
|
source file name.
|
|
|
|
@item forwprop
|
|
@opindex fdump-tree-forwprop
|
|
Dump each function after forward propagating single use variables. The file
|
|
name is made by appending @file{.forwprop} to the source file name.
|
|
|
|
@item nrv
|
|
@opindex fdump-tree-nrv
|
|
Dump each function after applying the named return value optimization on
|
|
generic trees. The file name is made by appending @file{.nrv} to the source
|
|
file name.
|
|
|
|
@item vect
|
|
@opindex fdump-tree-vect
|
|
Dump each function after applying vectorization of loops. The file name is
|
|
made by appending @file{.vect} to the source file name.
|
|
|
|
@item slp
|
|
@opindex fdump-tree-slp
|
|
Dump each function after applying vectorization of basic blocks. The file name
|
|
is made by appending @file{.slp} to the source file name.
|
|
|
|
@item vrp
|
|
@opindex fdump-tree-vrp
|
|
Dump each function after Value Range Propagation (VRP). The file name
|
|
is made by appending @file{.vrp} to the source file name.
|
|
|
|
@item early vrp
|
|
@opindex fdump-tree-evrp
|
|
Dump each function after Early Value Range Propagation (EVRP). The file name
|
|
is made by appending @file{.evrp} to the source file name.
|
|
|
|
@item oaccdevlow
|
|
@opindex fdump-tree-oaccdevlow
|
|
Dump each function after applying device-specific OpenACC transformations.
|
|
The file name is made by appending @file{.oaccdevlow} to the source file name.
|
|
|
|
@item all
|
|
@opindex fdump-tree-all
|
|
Enable all the available tree dumps with the flags provided in this option.
|
|
@end table
|
|
|
|
@item -fopt-info
|
|
@itemx -fopt-info-@var{options}
|
|
@itemx -fopt-info-@var{options}=@var{filename}
|
|
@opindex fopt-info
|
|
Controls optimization dumps from various optimization passes. If the
|
|
@samp{-@var{options}} form is used, @var{options} is a list of
|
|
@samp{-} separated option keywords to select the dump details and
|
|
optimizations.
|
|
|
|
The @var{options} can be divided into two groups: options describing the
|
|
verbosity of the dump, and options describing which optimizations
|
|
should be included. The options from both the groups can be freely
|
|
mixed as they are non-overlapping. However, in case of any conflicts,
|
|
the later options override the earlier options on the command
|
|
line.
|
|
|
|
The following options control the dump verbosity:
|
|
|
|
@table @samp
|
|
@item optimized
|
|
Print information when an optimization is successfully applied. It is
|
|
up to a pass to decide which information is relevant. For example, the
|
|
vectorizer passes print the source location of loops which are
|
|
successfully vectorized.
|
|
@item missed
|
|
Print information about missed optimizations. Individual passes
|
|
control which information to include in the output.
|
|
@item note
|
|
Print verbose information about optimizations, such as certain
|
|
transformations, more detailed messages about decisions etc.
|
|
@item all
|
|
Print detailed optimization information. This includes
|
|
@samp{optimized}, @samp{missed}, and @samp{note}.
|
|
@end table
|
|
|
|
One or more of the following option keywords can be used to describe a
|
|
group of optimizations:
|
|
|
|
@table @samp
|
|
@item ipa
|
|
Enable dumps from all interprocedural optimizations.
|
|
@item loop
|
|
Enable dumps from all loop optimizations.
|
|
@item inline
|
|
Enable dumps from all inlining optimizations.
|
|
@item vec
|
|
Enable dumps from all vectorization optimizations.
|
|
@item optall
|
|
Enable dumps from all optimizations. This is a superset of
|
|
the optimization groups listed above.
|
|
@end table
|
|
|
|
If @var{options} is
|
|
omitted, it defaults to @samp{optimized-optall}, which means to dump all
|
|
info about successful optimizations from all the passes.
|
|
|
|
If the @var{filename} is provided, then the dumps from all the
|
|
applicable optimizations are concatenated into the @var{filename}.
|
|
Otherwise the dump is output onto @file{stderr}. Though multiple
|
|
@option{-fopt-info} options are accepted, only one of them can include
|
|
a @var{filename}. If other filenames are provided then all but the
|
|
first such option are ignored.
|
|
|
|
Note that the output @var{filename} is overwritten
|
|
in case of multiple translation units. If a combined output from
|
|
multiple translation units is desired, @file{stderr} should be used
|
|
instead.
|
|
|
|
In the following example, the optimization info is output to
|
|
@file{stderr}:
|
|
|
|
@smallexample
|
|
gcc -O3 -fopt-info
|
|
@end smallexample
|
|
|
|
This example:
|
|
@smallexample
|
|
gcc -O3 -fopt-info-missed=missed.all
|
|
@end smallexample
|
|
|
|
@noindent
|
|
outputs missed optimization report from all the passes into
|
|
@file{missed.all}, and this one:
|
|
|
|
@smallexample
|
|
gcc -O2 -ftree-vectorize -fopt-info-vec-missed
|
|
@end smallexample
|
|
|
|
@noindent
|
|
prints information about missed optimization opportunities from
|
|
vectorization passes on @file{stderr}.
|
|
Note that @option{-fopt-info-vec-missed} is equivalent to
|
|
@option{-fopt-info-missed-vec}.
|
|
|
|
As another example,
|
|
@smallexample
|
|
gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
|
|
@end smallexample
|
|
|
|
@noindent
|
|
outputs information about missed optimizations as well as
|
|
optimized locations from all the inlining passes into
|
|
@file{inline.txt}.
|
|
|
|
Finally, consider:
|
|
|
|
@smallexample
|
|
gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Here the two output filenames @file{vec.miss} and @file{loop.opt} are
|
|
in conflict since only one output file is allowed. In this case, only
|
|
the first option takes effect and the subsequent options are
|
|
ignored. Thus only @file{vec.miss} is produced which contains
|
|
dumps from the vectorizer about missed opportunities.
|
|
|
|
@item -fsched-verbose=@var{n}
|
|
@opindex fsched-verbose
|
|
On targets that use instruction scheduling, this option controls the
|
|
amount of debugging output the scheduler prints to the dump files.
|
|
|
|
For @var{n} greater than zero, @option{-fsched-verbose} outputs the
|
|
same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}.
|
|
For @var{n} greater than one, it also output basic block probabilities,
|
|
detailed ready list information and unit/insn info. For @var{n} greater
|
|
than two, it includes RTL at abort point, control-flow and regions info.
|
|
And for @var{n} over four, @option{-fsched-verbose} also includes
|
|
dependence info.
|
|
|
|
|
|
|
|
@item -fenable-@var{kind}-@var{pass}
|
|
@itemx -fdisable-@var{kind}-@var{pass}=@var{range-list}
|
|
@opindex fdisable-
|
|
@opindex fenable-
|
|
|
|
This is a set of options that are used to explicitly disable/enable
|
|
optimization passes. These options are intended for use for debugging GCC.
|
|
Compiler users should use regular options for enabling/disabling
|
|
passes instead.
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -fdisable-ipa-@var{pass}
|
|
Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
|
|
statically invoked in the compiler multiple times, the pass name should be
|
|
appended with a sequential number starting from 1.
|
|
|
|
@item -fdisable-rtl-@var{pass}
|
|
@itemx -fdisable-rtl-@var{pass}=@var{range-list}
|
|
Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is
|
|
statically invoked in the compiler multiple times, the pass name should be
|
|
appended with a sequential number starting from 1. @var{range-list} is a
|
|
comma-separated list of function ranges or assembler names. Each range is a number
|
|
pair separated by a colon. The range is inclusive in both ends. If the range
|
|
is trivial, the number pair can be simplified as a single number. If the
|
|
function's call graph node's @var{uid} falls within one of the specified ranges,
|
|
the @var{pass} is disabled for that function. The @var{uid} is shown in the
|
|
function header of a dump file, and the pass names can be dumped by using
|
|
option @option{-fdump-passes}.
|
|
|
|
@item -fdisable-tree-@var{pass}
|
|
@itemx -fdisable-tree-@var{pass}=@var{range-list}
|
|
Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of
|
|
option arguments.
|
|
|
|
@item -fenable-ipa-@var{pass}
|
|
Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is
|
|
statically invoked in the compiler multiple times, the pass name should be
|
|
appended with a sequential number starting from 1.
|
|
|
|
@item -fenable-rtl-@var{pass}
|
|
@itemx -fenable-rtl-@var{pass}=@var{range-list}
|
|
Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument
|
|
description and examples.
|
|
|
|
@item -fenable-tree-@var{pass}
|
|
@itemx -fenable-tree-@var{pass}=@var{range-list}
|
|
Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description
|
|
of option arguments.
|
|
|
|
@end table
|
|
|
|
Here are some examples showing uses of these options.
|
|
|
|
@smallexample
|
|
|
|
# disable ccp1 for all functions
|
|
-fdisable-tree-ccp1
|
|
# disable complete unroll for function whose cgraph node uid is 1
|
|
-fenable-tree-cunroll=1
|
|
# disable gcse2 for functions at the following ranges [1,1],
|
|
# [300,400], and [400,1000]
|
|
# disable gcse2 for functions foo and foo2
|
|
-fdisable-rtl-gcse2=foo,foo2
|
|
# disable early inlining
|
|
-fdisable-tree-einline
|
|
# disable ipa inlining
|
|
-fdisable-ipa-inline
|
|
# enable tree full unroll
|
|
-fenable-tree-unroll
|
|
|
|
@end smallexample
|
|
|
|
@item -fchecking
|
|
@itemx -fchecking=@var{n}
|
|
@opindex fchecking
|
|
@opindex fno-checking
|
|
Enable internal consistency checking. The default depends on
|
|
the compiler configuration. @option{-fchecking=2} enables further
|
|
internal consistency checking that might affect code generation.
|
|
|
|
@item -frandom-seed=@var{string}
|
|
@opindex frandom-seed
|
|
This option provides a seed that GCC uses in place of
|
|
random numbers in generating certain symbol names
|
|
that have to be different in every compiled file. It is also used to
|
|
place unique stamps in coverage data files and the object files that
|
|
produce them. You can use the @option{-frandom-seed} option to produce
|
|
reproducibly identical object files.
|
|
|
|
The @var{string} can either be a number (decimal, octal or hex) or an
|
|
arbitrary string (in which case it's converted to a number by
|
|
computing CRC32).
|
|
|
|
The @var{string} should be different for every file you compile.
|
|
|
|
@item -save-temps
|
|
@itemx -save-temps=cwd
|
|
@opindex save-temps
|
|
Store the usual ``temporary'' intermediate files permanently; place them
|
|
in the current directory and name them based on the source file. Thus,
|
|
compiling @file{foo.c} with @option{-c -save-temps} produces files
|
|
@file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a
|
|
preprocessed @file{foo.i} output file even though the compiler now
|
|
normally uses an integrated preprocessor.
|
|
|
|
When used in combination with the @option{-x} command-line option,
|
|
@option{-save-temps} is sensible enough to avoid over writing an
|
|
input source file with the same extension as an intermediate file.
|
|
The corresponding intermediate file may be obtained by renaming the
|
|
source file before using @option{-save-temps}.
|
|
|
|
If you invoke GCC in parallel, compiling several different source
|
|
files that share a common base name in different subdirectories or the
|
|
same source file compiled for multiple output destinations, it is
|
|
likely that the different parallel compilers will interfere with each
|
|
other, and overwrite the temporary files. For instance:
|
|
|
|
@smallexample
|
|
gcc -save-temps -o outdir1/foo.o indir1/foo.c&
|
|
gcc -save-temps -o outdir2/foo.o indir2/foo.c&
|
|
@end smallexample
|
|
|
|
may result in @file{foo.i} and @file{foo.o} being written to
|
|
simultaneously by both compilers.
|
|
|
|
@item -save-temps=obj
|
|
@opindex save-temps=obj
|
|
Store the usual ``temporary'' intermediate files permanently. If the
|
|
@option{-o} option is used, the temporary files are based on the
|
|
object file. If the @option{-o} option is not used, the
|
|
@option{-save-temps=obj} switch behaves like @option{-save-temps}.
|
|
|
|
For example:
|
|
|
|
@smallexample
|
|
gcc -save-temps=obj -c foo.c
|
|
gcc -save-temps=obj -c bar.c -o dir/xbar.o
|
|
gcc -save-temps=obj foobar.c -o dir2/yfoobar
|
|
@end smallexample
|
|
|
|
@noindent
|
|
creates @file{foo.i}, @file{foo.s}, @file{dir/xbar.i},
|
|
@file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and
|
|
@file{dir2/yfoobar.o}.
|
|
|
|
@item -time@r{[}=@var{file}@r{]}
|
|
@opindex time
|
|
Report the CPU time taken by each subprocess in the compilation
|
|
sequence. For C source files, this is the compiler proper and assembler
|
|
(plus the linker if linking is done).
|
|
|
|
Without the specification of an output file, the output looks like this:
|
|
|
|
@smallexample
|
|
# cc1 0.12 0.01
|
|
# as 0.00 0.01
|
|
@end smallexample
|
|
|
|
The first number on each line is the ``user time'', that is time spent
|
|
executing the program itself. The second number is ``system time'',
|
|
time spent executing operating system routines on behalf of the program.
|
|
Both numbers are in seconds.
|
|
|
|
With the specification of an output file, the output is appended to the
|
|
named file, and it looks like this:
|
|
|
|
@smallexample
|
|
0.12 0.01 cc1 @var{options}
|
|
0.00 0.01 as @var{options}
|
|
@end smallexample
|
|
|
|
The ``user time'' and the ``system time'' are moved before the program
|
|
name, and the options passed to the program are displayed, so that one
|
|
can later tell what file was being compiled, and with which options.
|
|
|
|
@item -fdump-final-insns@r{[}=@var{file}@r{]}
|
|
@opindex fdump-final-insns
|
|
Dump the final internal representation (RTL) to @var{file}. If the
|
|
optional argument is omitted (or if @var{file} is @code{.}), the name
|
|
of the dump file is determined by appending @code{.gkd} to the
|
|
compilation output file name.
|
|
|
|
@item -fcompare-debug@r{[}=@var{opts}@r{]}
|
|
@opindex fcompare-debug
|
|
@opindex fno-compare-debug
|
|
If no error occurs during compilation, run the compiler a second time,
|
|
adding @var{opts} and @option{-fcompare-debug-second} to the arguments
|
|
passed to the second compilation. Dump the final internal
|
|
representation in both compilations, and print an error if they differ.
|
|
|
|
If the equal sign is omitted, the default @option{-gtoggle} is used.
|
|
|
|
The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty
|
|
and nonzero, implicitly enables @option{-fcompare-debug}. If
|
|
@env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash,
|
|
then it is used for @var{opts}, otherwise the default @option{-gtoggle}
|
|
is used.
|
|
|
|
@option{-fcompare-debug=}, with the equal sign but without @var{opts},
|
|
is equivalent to @option{-fno-compare-debug}, which disables the dumping
|
|
of the final representation and the second compilation, preventing even
|
|
@env{GCC_COMPARE_DEBUG} from taking effect.
|
|
|
|
To verify full coverage during @option{-fcompare-debug} testing, set
|
|
@env{GCC_COMPARE_DEBUG} to say @option{-fcompare-debug-not-overridden},
|
|
which GCC rejects as an invalid option in any actual compilation
|
|
(rather than preprocessing, assembly or linking). To get just a
|
|
warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug
|
|
not overridden} will do.
|
|
|
|
@item -fcompare-debug-second
|
|
@opindex fcompare-debug-second
|
|
This option is implicitly passed to the compiler for the second
|
|
compilation requested by @option{-fcompare-debug}, along with options to
|
|
silence warnings, and omitting other options that would cause
|
|
side-effect compiler outputs to files or to the standard output. Dump
|
|
files and preserved temporary files are renamed so as to contain the
|
|
@code{.gk} additional extension during the second compilation, to avoid
|
|
overwriting those generated by the first.
|
|
|
|
When this option is passed to the compiler driver, it causes the
|
|
@emph{first} compilation to be skipped, which makes it useful for little
|
|
other than debugging the compiler proper.
|
|
|
|
@item -gtoggle
|
|
@opindex gtoggle
|
|
Turn off generation of debug info, if leaving out this option
|
|
generates it, or turn it on at level 2 otherwise. The position of this
|
|
argument in the command line does not matter; it takes effect after all
|
|
other options are processed, and it does so only once, no matter how
|
|
many times it is given. This is mainly intended to be used with
|
|
@option{-fcompare-debug}.
|
|
|
|
@item -fvar-tracking-assignments-toggle
|
|
@opindex fvar-tracking-assignments-toggle
|
|
@opindex fno-var-tracking-assignments-toggle
|
|
Toggle @option{-fvar-tracking-assignments}, in the same way that
|
|
@option{-gtoggle} toggles @option{-g}.
|
|
|
|
@item -Q
|
|
@opindex Q
|
|
Makes the compiler print out each function name as it is compiled, and
|
|
print some statistics about each pass when it finishes.
|
|
|
|
@item -ftime-report
|
|
@opindex ftime-report
|
|
Makes the compiler print some statistics about the time consumed by each
|
|
pass when it finishes.
|
|
|
|
@item -ftime-report-details
|
|
@opindex ftime-report-details
|
|
Record the time consumed by infrastructure parts separately for each pass.
|
|
|
|
@item -fira-verbose=@var{n}
|
|
@opindex fira-verbose
|
|
Control the verbosity of the dump file for the integrated register allocator.
|
|
The default value is 5. If the value @var{n} is greater or equal to 10,
|
|
the dump output is sent to stderr using the same format as @var{n} minus 10.
|
|
|
|
@item -flto-report
|
|
@opindex flto-report
|
|
Prints a report with internal details on the workings of the link-time
|
|
optimizer. The contents of this report vary from version to version.
|
|
It is meant to be useful to GCC developers when processing object
|
|
files in LTO mode (via @option{-flto}).
|
|
|
|
Disabled by default.
|
|
|
|
@item -flto-report-wpa
|
|
@opindex flto-report-wpa
|
|
Like @option{-flto-report}, but only print for the WPA phase of Link
|
|
Time Optimization.
|
|
|
|
@item -fmem-report
|
|
@opindex fmem-report
|
|
Makes the compiler print some statistics about permanent memory
|
|
allocation when it finishes.
|
|
|
|
@item -fmem-report-wpa
|
|
@opindex fmem-report-wpa
|
|
Makes the compiler print some statistics about permanent memory
|
|
allocation for the WPA phase only.
|
|
|
|
@item -fpre-ipa-mem-report
|
|
@opindex fpre-ipa-mem-report
|
|
@item -fpost-ipa-mem-report
|
|
@opindex fpost-ipa-mem-report
|
|
Makes the compiler print some statistics about permanent memory
|
|
allocation before or after interprocedural optimization.
|
|
|
|
@item -fprofile-report
|
|
@opindex fprofile-report
|
|
Makes the compiler print some statistics about consistency of the
|
|
(estimated) profile and effect of individual passes.
|
|
|
|
@item -fstack-usage
|
|
@opindex fstack-usage
|
|
Makes the compiler output stack usage information for the program, on a
|
|
per-function basis. The filename for the dump is made by appending
|
|
@file{.su} to the @var{auxname}. @var{auxname} is generated from the name of
|
|
the output file, if explicitly specified and it is not an executable,
|
|
otherwise it is the basename of the source file. An entry is made up
|
|
of three fields:
|
|
|
|
@itemize
|
|
@item
|
|
The name of the function.
|
|
@item
|
|
A number of bytes.
|
|
@item
|
|
One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}.
|
|
@end itemize
|
|
|
|
The qualifier @code{static} means that the function manipulates the stack
|
|
statically: a fixed number of bytes are allocated for the frame on function
|
|
entry and released on function exit; no stack adjustments are otherwise made
|
|
in the function. The second field is this fixed number of bytes.
|
|
|
|
The qualifier @code{dynamic} means that the function manipulates the stack
|
|
dynamically: in addition to the static allocation described above, stack
|
|
adjustments are made in the body of the function, for example to push/pop
|
|
arguments around function calls. If the qualifier @code{bounded} is also
|
|
present, the amount of these adjustments is bounded at compile time and
|
|
the second field is an upper bound of the total amount of stack used by
|
|
the function. If it is not present, the amount of these adjustments is
|
|
not bounded at compile time and the second field only represents the
|
|
bounded part.
|
|
|
|
@item -fstats
|
|
@opindex fstats
|
|
Emit statistics about front-end processing at the end of the compilation.
|
|
This option is supported only by the C++ front end, and
|
|
the information is generally only useful to the G++ development team.
|
|
|
|
@item -fdbg-cnt-list
|
|
@opindex fdbg-cnt-list
|
|
Print the name and the counter upper bound for all debug counters.
|
|
|
|
|
|
@item -fdbg-cnt=@var{counter-value-list}
|
|
@opindex fdbg-cnt
|
|
Set the internal debug counter upper bound. @var{counter-value-list}
|
|
is a comma-separated list of @var{name}:@var{value} pairs
|
|
which sets the upper bound of each debug counter @var{name} to @var{value}.
|
|
All debug counters have the initial upper bound of @code{UINT_MAX};
|
|
thus @code{dbg_cnt} returns true always unless the upper bound
|
|
is set by this option.
|
|
For example, with @option{-fdbg-cnt=dce:10,tail_call:0},
|
|
@code{dbg_cnt(dce)} returns true only for first 10 invocations.
|
|
|
|
@item -print-file-name=@var{library}
|
|
@opindex print-file-name
|
|
Print the full absolute name of the library file @var{library} that
|
|
would be used when linking---and don't do anything else. With this
|
|
option, GCC does not compile or link anything; it just prints the
|
|
file name.
|
|
|
|
@item -print-multi-directory
|
|
@opindex print-multi-directory
|
|
Print the directory name corresponding to the multilib selected by any
|
|
other switches present in the command line. This directory is supposed
|
|
to exist in @env{GCC_EXEC_PREFIX}.
|
|
|
|
@item -print-multi-lib
|
|
@opindex print-multi-lib
|
|
Print the mapping from multilib directory names to compiler switches
|
|
that enable them. The directory name is separated from the switches by
|
|
@samp{;}, and each switch starts with an @samp{@@} instead of the
|
|
@samp{-}, without spaces between multiple switches. This is supposed to
|
|
ease shell processing.
|
|
|
|
@item -print-multi-os-directory
|
|
@opindex print-multi-os-directory
|
|
Print the path to OS libraries for the selected
|
|
multilib, relative to some @file{lib} subdirectory. If OS libraries are
|
|
present in the @file{lib} subdirectory and no multilibs are used, this is
|
|
usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}}
|
|
sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or
|
|
@file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}}
|
|
subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}.
|
|
|
|
@item -print-multiarch
|
|
@opindex print-multiarch
|
|
Print the path to OS libraries for the selected multiarch,
|
|
relative to some @file{lib} subdirectory.
|
|
|
|
@item -print-prog-name=@var{program}
|
|
@opindex print-prog-name
|
|
Like @option{-print-file-name}, but searches for a program such as @command{cpp}.
|
|
|
|
@item -print-libgcc-file-name
|
|
@opindex print-libgcc-file-name
|
|
Same as @option{-print-file-name=libgcc.a}.
|
|
|
|
This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs}
|
|
but you do want to link with @file{libgcc.a}. You can do:
|
|
|
|
@smallexample
|
|
gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name`
|
|
@end smallexample
|
|
|
|
@item -print-search-dirs
|
|
@opindex print-search-dirs
|
|
Print the name of the configured installation directory and a list of
|
|
program and library directories @command{gcc} searches---and don't do anything else.
|
|
|
|
This is useful when @command{gcc} prints the error message
|
|
@samp{installation problem, cannot exec cpp0: No such file or directory}.
|
|
To resolve this you either need to put @file{cpp0} and the other compiler
|
|
components where @command{gcc} expects to find them, or you can set the environment
|
|
variable @env{GCC_EXEC_PREFIX} to the directory where you installed them.
|
|
Don't forget the trailing @samp{/}.
|
|
@xref{Environment Variables}.
|
|
|
|
@item -print-sysroot
|
|
@opindex print-sysroot
|
|
Print the target sysroot directory that is used during
|
|
compilation. This is the target sysroot specified either at configure
|
|
time or using the @option{--sysroot} option, possibly with an extra
|
|
suffix that depends on compilation options. If no target sysroot is
|
|
specified, the option prints nothing.
|
|
|
|
@item -print-sysroot-headers-suffix
|
|
@opindex print-sysroot-headers-suffix
|
|
Print the suffix added to the target sysroot when searching for
|
|
headers, or give an error if the compiler is not configured with such
|
|
a suffix---and don't do anything else.
|
|
|
|
@item -dumpmachine
|
|
@opindex dumpmachine
|
|
Print the compiler's target machine (for example,
|
|
@samp{i686-pc-linux-gnu})---and don't do anything else.
|
|
|
|
@item -dumpversion
|
|
@opindex dumpversion
|
|
Print the compiler version (for example, @code{3.0}, @code{6.3.0} or @code{7})---and don't do
|
|
anything else. This is the compiler version used in filesystem paths,
|
|
specs, can be depending on how the compiler has been configured just
|
|
a single number (major version), two numbers separated by dot (major and
|
|
minor version) or three numbers separated by dots (major, minor and patchlevel
|
|
version).
|
|
|
|
@item -dumpfullversion
|
|
@opindex dumpfullversion
|
|
Print the full compiler version, always 3 numbers separated by dots,
|
|
major, minor and patchlevel version.
|
|
|
|
@item -dumpspecs
|
|
@opindex dumpspecs
|
|
Print the compiler's built-in specs---and don't do anything else. (This
|
|
is used when GCC itself is being built.) @xref{Spec Files}.
|
|
@end table
|
|
|
|
@node Submodel Options
|
|
@section Machine-Dependent Options
|
|
@cindex submodel options
|
|
@cindex specifying hardware config
|
|
@cindex hardware models and configurations, specifying
|
|
@cindex target-dependent options
|
|
@cindex machine-dependent options
|
|
|
|
Each target machine supported by GCC can have its own options---for
|
|
example, to allow you to compile for a particular processor variant or
|
|
ABI, or to control optimizations specific to that machine. By
|
|
convention, the names of machine-specific options start with
|
|
@samp{-m}.
|
|
|
|
Some configurations of the compiler also support additional target-specific
|
|
options, usually for compatibility with other compilers on the same
|
|
platform.
|
|
|
|
@c This list is ordered alphanumerically by subsection name.
|
|
@c It should be the same order and spelling as these options are listed
|
|
@c in Machine Dependent Options
|
|
|
|
@menu
|
|
* AArch64 Options::
|
|
* Adapteva Epiphany Options::
|
|
* ARC Options::
|
|
* ARM Options::
|
|
* AVR Options::
|
|
* Blackfin Options::
|
|
* C6X Options::
|
|
* CRIS Options::
|
|
* CR16 Options::
|
|
* Darwin Options::
|
|
* DEC Alpha Options::
|
|
* FR30 Options::
|
|
* FT32 Options::
|
|
* FRV Options::
|
|
* GNU/Linux Options::
|
|
* H8/300 Options::
|
|
* HPPA Options::
|
|
* IA-64 Options::
|
|
* LM32 Options::
|
|
* M32C Options::
|
|
* M32R/D Options::
|
|
* M680x0 Options::
|
|
* MCore Options::
|
|
* MeP Options::
|
|
* MicroBlaze Options::
|
|
* MIPS Options::
|
|
* MMIX Options::
|
|
* MN10300 Options::
|
|
* Moxie Options::
|
|
* MSP430 Options::
|
|
* NDS32 Options::
|
|
* Nios II Options::
|
|
* Nvidia PTX Options::
|
|
* PDP-11 Options::
|
|
* picoChip Options::
|
|
* PowerPC Options::
|
|
* RL78 Options::
|
|
* RS/6000 and PowerPC Options::
|
|
* RX Options::
|
|
* S/390 and zSeries Options::
|
|
* Score Options::
|
|
* SH Options::
|
|
* Solaris 2 Options::
|
|
* SPARC Options::
|
|
* SPU Options::
|
|
* System V Options::
|
|
* TILE-Gx Options::
|
|
* TILEPro Options::
|
|
* V850 Options::
|
|
* VAX Options::
|
|
* Visium Options::
|
|
* VMS Options::
|
|
* VxWorks Options::
|
|
* x86 Options::
|
|
* x86 Windows Options::
|
|
* Xstormy16 Options::
|
|
* Xtensa Options::
|
|
* zSeries Options::
|
|
@end menu
|
|
|
|
@node AArch64 Options
|
|
@subsection AArch64 Options
|
|
@cindex AArch64 Options
|
|
|
|
These options are defined for AArch64 implementations:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mabi=@var{name}
|
|
@opindex mabi
|
|
Generate code for the specified data model. Permissible values
|
|
are @samp{ilp32} for SysV-like data model where int, long int and pointers
|
|
are 32 bits, and @samp{lp64} for SysV-like data model where int is 32 bits,
|
|
but long int and pointers are 64 bits.
|
|
|
|
The default depends on the specific target configuration. Note that
|
|
the LP64 and ILP32 ABIs are not link-compatible; you must compile your
|
|
entire program with the same ABI, and link with a compatible set of libraries.
|
|
|
|
@item -mbig-endian
|
|
@opindex mbig-endian
|
|
Generate big-endian code. This is the default when GCC is configured for an
|
|
@samp{aarch64_be-*-*} target.
|
|
|
|
@item -mgeneral-regs-only
|
|
@opindex mgeneral-regs-only
|
|
Generate code which uses only the general-purpose registers. This will prevent
|
|
the compiler from using floating-point and Advanced SIMD registers but will not
|
|
impose any restrictions on the assembler.
|
|
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
Generate little-endian code. This is the default when GCC is configured for an
|
|
@samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target.
|
|
|
|
@item -mcmodel=tiny
|
|
@opindex mcmodel=tiny
|
|
Generate code for the tiny code model. The program and its statically defined
|
|
symbols must be within 1MB of each other. Programs can be statically or
|
|
dynamically linked.
|
|
|
|
@item -mcmodel=small
|
|
@opindex mcmodel=small
|
|
Generate code for the small code model. The program and its statically defined
|
|
symbols must be within 4GB of each other. Programs can be statically or
|
|
dynamically linked. This is the default code model.
|
|
|
|
@item -mcmodel=large
|
|
@opindex mcmodel=large
|
|
Generate code for the large code model. This makes no assumptions about
|
|
addresses and sizes of sections. Programs can be statically linked only.
|
|
|
|
@item -mstrict-align
|
|
@opindex mstrict-align
|
|
Avoid generating memory accesses that may not be aligned on a natural object
|
|
boundary as described in the architecture specification.
|
|
|
|
@item -momit-leaf-frame-pointer
|
|
@itemx -mno-omit-leaf-frame-pointer
|
|
@opindex momit-leaf-frame-pointer
|
|
@opindex mno-omit-leaf-frame-pointer
|
|
Omit or keep the frame pointer in leaf functions. The former behavior is the
|
|
default.
|
|
|
|
@item -mtls-dialect=desc
|
|
@opindex mtls-dialect=desc
|
|
Use TLS descriptors as the thread-local storage mechanism for dynamic accesses
|
|
of TLS variables. This is the default.
|
|
|
|
@item -mtls-dialect=traditional
|
|
@opindex mtls-dialect=traditional
|
|
Use traditional TLS as the thread-local storage mechanism for dynamic accesses
|
|
of TLS variables.
|
|
|
|
@item -mtls-size=@var{size}
|
|
@opindex mtls-size
|
|
Specify bit size of immediate TLS offsets. Valid values are 12, 24, 32, 48.
|
|
This option requires binutils 2.26 or newer.
|
|
|
|
@item -mfix-cortex-a53-835769
|
|
@itemx -mno-fix-cortex-a53-835769
|
|
@opindex mfix-cortex-a53-835769
|
|
@opindex mno-fix-cortex-a53-835769
|
|
Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769.
|
|
This involves inserting a NOP instruction between memory instructions and
|
|
64-bit integer multiply-accumulate instructions.
|
|
|
|
@item -mfix-cortex-a53-843419
|
|
@itemx -mno-fix-cortex-a53-843419
|
|
@opindex mfix-cortex-a53-843419
|
|
@opindex mno-fix-cortex-a53-843419
|
|
Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419.
|
|
This erratum workaround is made at link time and this will only pass the
|
|
corresponding flag to the linker.
|
|
|
|
@item -mlow-precision-recip-sqrt
|
|
@item -mno-low-precision-recip-sqrt
|
|
@opindex mlow-precision-recip-sqrt
|
|
@opindex mno-low-precision-recip-sqrt
|
|
Enable or disable the reciprocal square root approximation.
|
|
This option only has an effect if @option{-ffast-math} or
|
|
@option{-funsafe-math-optimizations} is used as well. Enabling this reduces
|
|
precision of reciprocal square root results to about 16 bits for
|
|
single precision and to 32 bits for double precision.
|
|
|
|
@item -mlow-precision-sqrt
|
|
@item -mno-low-precision-sqrt
|
|
@opindex -mlow-precision-sqrt
|
|
@opindex -mno-low-precision-sqrt
|
|
Enable or disable the square root approximation.
|
|
This option only has an effect if @option{-ffast-math} or
|
|
@option{-funsafe-math-optimizations} is used as well. Enabling this reduces
|
|
precision of square root results to about 16 bits for
|
|
single precision and to 32 bits for double precision.
|
|
If enabled, it implies @option{-mlow-precision-recip-sqrt}.
|
|
|
|
@item -mlow-precision-div
|
|
@item -mno-low-precision-div
|
|
@opindex -mlow-precision-div
|
|
@opindex -mno-low-precision-div
|
|
Enable or disable the division approximation.
|
|
This option only has an effect if @option{-ffast-math} or
|
|
@option{-funsafe-math-optimizations} is used as well. Enabling this reduces
|
|
precision of division results to about 16 bits for
|
|
single precision and to 32 bits for double precision.
|
|
|
|
@item -march=@var{name}
|
|
@opindex march
|
|
Specify the name of the target architecture and, optionally, one or
|
|
more feature modifiers. This option has the form
|
|
@option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}.
|
|
|
|
The permissible values for @var{arch} are @samp{armv8-a},
|
|
@samp{armv8.1-a}, @samp{armv8.2-a} or @var{native}.
|
|
|
|
The value @samp{armv8.2-a} implies @samp{armv8.1-a} and enables compiler
|
|
support for the ARMv8.2-A architecture extensions.
|
|
|
|
The value @samp{armv8.1-a} implies @samp{armv8-a} and enables compiler
|
|
support for the ARMv8.1-A architecture extension. In particular, it
|
|
enables the @samp{+crc} and @samp{+lse} features.
|
|
|
|
The value @samp{native} is available on native AArch64 GNU/Linux and
|
|
causes the compiler to pick the architecture of the host system. This
|
|
option has no effect if the compiler is unable to recognize the
|
|
architecture of the host system,
|
|
|
|
The permissible values for @var{feature} are listed in the sub-section
|
|
on @ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu}
|
|
Feature Modifiers}. Where conflicting feature modifiers are
|
|
specified, the right-most feature is used.
|
|
|
|
GCC uses @var{name} to determine what kind of instructions it can emit
|
|
when generating assembly code. If @option{-march} is specified
|
|
without either of @option{-mtune} or @option{-mcpu} also being
|
|
specified, the code is tuned to perform well across a range of target
|
|
processors implementing the target architecture.
|
|
|
|
@item -mtune=@var{name}
|
|
@opindex mtune
|
|
Specify the name of the target processor for which GCC should tune the
|
|
performance of the code. Permissible values for this option are:
|
|
@samp{generic}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a57},
|
|
@samp{cortex-a72}, @samp{cortex-a73}, @samp{exynos-m1}, @samp{falkor},
|
|
@samp{qdf24xx}, @samp{xgene1}, @samp{vulcan}, @samp{thunderx},
|
|
@samp{thunderxt88}, @samp{thunderxt88p1}, @samp{thunderxt81},
|
|
@samp{thunderxt83}, @samp{thunderx2t99}, @samp{cortex-a57.cortex-a53},
|
|
@samp{cortex-a72.cortex-a53}, @samp{cortex-a73.cortex-a35},
|
|
@samp{cortex-a73.cortex-a53}, @samp{native}.
|
|
|
|
The values @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53},
|
|
@samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53}
|
|
specify that GCC should tune for a big.LITTLE system.
|
|
|
|
Additionally on native AArch64 GNU/Linux systems the value
|
|
@samp{native} tunes performance to the host system. This option has no effect
|
|
if the compiler is unable to recognize the processor of the host system.
|
|
|
|
Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=}
|
|
are specified, the code is tuned to perform well across a range
|
|
of target processors.
|
|
|
|
This option cannot be suffixed by feature modifiers.
|
|
|
|
@item -mcpu=@var{name}
|
|
@opindex mcpu
|
|
Specify the name of the target processor, optionally suffixed by one
|
|
or more feature modifiers. This option has the form
|
|
@option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where
|
|
the permissible values for @var{cpu} are the same as those available
|
|
for @option{-mtune}. The permissible values for @var{feature} are
|
|
documented in the sub-section on
|
|
@ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu}
|
|
Feature Modifiers}. Where conflicting feature modifiers are
|
|
specified, the right-most feature is used.
|
|
|
|
GCC uses @var{name} to determine what kind of instructions it can emit when
|
|
generating assembly code (as if by @option{-march}) and to determine
|
|
the target processor for which to tune for performance (as if
|
|
by @option{-mtune}). Where this option is used in conjunction
|
|
with @option{-march} or @option{-mtune}, those options take precedence
|
|
over the appropriate part of this option.
|
|
|
|
@item -moverride=@var{string}
|
|
@opindex moverride
|
|
Override tuning decisions made by the back-end in response to a
|
|
@option{-mtune=} switch. The syntax, semantics, and accepted values
|
|
for @var{string} in this option are not guaranteed to be consistent
|
|
across releases.
|
|
|
|
This option is only intended to be useful when developing GCC.
|
|
|
|
@item -mpc-relative-literal-loads
|
|
@opindex mpc-relative-literal-loads
|
|
Enable PC-relative literal loads. With this option literal pools are
|
|
accessed using a single instruction and emitted after each function. This
|
|
limits the maximum size of functions to 1MB. This is enabled by default for
|
|
@option{-mcmodel=tiny}.
|
|
|
|
@end table
|
|
|
|
@subsubsection @option{-march} and @option{-mcpu} Feature Modifiers
|
|
@anchor{aarch64-feature-modifiers}
|
|
@cindex @option{-march} feature modifiers
|
|
@cindex @option{-mcpu} feature modifiers
|
|
Feature modifiers used with @option{-march} and @option{-mcpu} can be any of
|
|
the following and their inverses @option{no@var{feature}}:
|
|
|
|
@table @samp
|
|
@item crc
|
|
Enable CRC extension. This is on by default for
|
|
@option{-march=armv8.1-a}.
|
|
@item crypto
|
|
Enable Crypto extension. This also enables Advanced SIMD and floating-point
|
|
instructions.
|
|
@item fp
|
|
Enable floating-point instructions. This is on by default for all possible
|
|
values for options @option{-march} and @option{-mcpu}.
|
|
@item simd
|
|
Enable Advanced SIMD instructions. This also enables floating-point
|
|
instructions. This is on by default for all possible values for options
|
|
@option{-march} and @option{-mcpu}.
|
|
@item lse
|
|
Enable Large System Extension instructions. This is on by default for
|
|
@option{-march=armv8.1-a}.
|
|
@item fp16
|
|
Enable FP16 extension. This also enables floating-point instructions.
|
|
|
|
@end table
|
|
|
|
Feature @option{crypto} implies @option{simd}, which implies @option{fp}.
|
|
Conversely, @option{nofp} implies @option{nosimd}, which implies
|
|
@option{nocrypto}.
|
|
|
|
@node Adapteva Epiphany Options
|
|
@subsection Adapteva Epiphany Options
|
|
|
|
These @samp{-m} options are defined for Adapteva Epiphany:
|
|
|
|
@table @gcctabopt
|
|
@item -mhalf-reg-file
|
|
@opindex mhalf-reg-file
|
|
Don't allocate any register in the range @code{r32}@dots{}@code{r63}.
|
|
That allows code to run on hardware variants that lack these registers.
|
|
|
|
@item -mprefer-short-insn-regs
|
|
@opindex mprefer-short-insn-regs
|
|
Preferentially allocate registers that allow short instruction generation.
|
|
This can result in increased instruction count, so this may either reduce or
|
|
increase overall code size.
|
|
|
|
@item -mbranch-cost=@var{num}
|
|
@opindex mbranch-cost
|
|
Set the cost of branches to roughly @var{num} ``simple'' instructions.
|
|
This cost is only a heuristic and is not guaranteed to produce
|
|
consistent results across releases.
|
|
|
|
@item -mcmove
|
|
@opindex mcmove
|
|
Enable the generation of conditional moves.
|
|
|
|
@item -mnops=@var{num}
|
|
@opindex mnops
|
|
Emit @var{num} NOPs before every other generated instruction.
|
|
|
|
@item -mno-soft-cmpsf
|
|
@opindex mno-soft-cmpsf
|
|
For single-precision floating-point comparisons, emit an @code{fsub} instruction
|
|
and test the flags. This is faster than a software comparison, but can
|
|
get incorrect results in the presence of NaNs, or when two different small
|
|
numbers are compared such that their difference is calculated as zero.
|
|
The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant,
|
|
software comparisons.
|
|
|
|
@item -mstack-offset=@var{num}
|
|
@opindex mstack-offset
|
|
Set the offset between the top of the stack and the stack pointer.
|
|
E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7}
|
|
can be used by leaf functions without stack allocation.
|
|
Values other than @samp{8} or @samp{16} are untested and unlikely to work.
|
|
Note also that this option changes the ABI; compiling a program with a
|
|
different stack offset than the libraries have been compiled with
|
|
generally does not work.
|
|
This option can be useful if you want to evaluate if a different stack
|
|
offset would give you better code, but to actually use a different stack
|
|
offset to build working programs, it is recommended to configure the
|
|
toolchain with the appropriate @option{--with-stack-offset=@var{num}} option.
|
|
|
|
@item -mno-round-nearest
|
|
@opindex mno-round-nearest
|
|
Make the scheduler assume that the rounding mode has been set to
|
|
truncating. The default is @option{-mround-nearest}.
|
|
|
|
@item -mlong-calls
|
|
@opindex mlong-calls
|
|
If not otherwise specified by an attribute, assume all calls might be beyond
|
|
the offset range of the @code{b} / @code{bl} instructions, and therefore load the
|
|
function address into a register before performing a (otherwise direct) call.
|
|
This is the default.
|
|
|
|
@item -mshort-calls
|
|
@opindex short-calls
|
|
If not otherwise specified by an attribute, assume all direct calls are
|
|
in the range of the @code{b} / @code{bl} instructions, so use these instructions
|
|
for direct calls. The default is @option{-mlong-calls}.
|
|
|
|
@item -msmall16
|
|
@opindex msmall16
|
|
Assume addresses can be loaded as 16-bit unsigned values. This does not
|
|
apply to function addresses for which @option{-mlong-calls} semantics
|
|
are in effect.
|
|
|
|
@item -mfp-mode=@var{mode}
|
|
@opindex mfp-mode
|
|
Set the prevailing mode of the floating-point unit.
|
|
This determines the floating-point mode that is provided and expected
|
|
at function call and return time. Making this mode match the mode you
|
|
predominantly need at function start can make your programs smaller and
|
|
faster by avoiding unnecessary mode switches.
|
|
|
|
@var{mode} can be set to one the following values:
|
|
|
|
@table @samp
|
|
@item caller
|
|
Any mode at function entry is valid, and retained or restored when
|
|
the function returns, and when it calls other functions.
|
|
This mode is useful for compiling libraries or other compilation units
|
|
you might want to incorporate into different programs with different
|
|
prevailing FPU modes, and the convenience of being able to use a single
|
|
object file outweighs the size and speed overhead for any extra
|
|
mode switching that might be needed, compared with what would be needed
|
|
with a more specific choice of prevailing FPU mode.
|
|
|
|
@item truncate
|
|
This is the mode used for floating-point calculations with
|
|
truncating (i.e.@: round towards zero) rounding mode. That includes
|
|
conversion from floating point to integer.
|
|
|
|
@item round-nearest
|
|
This is the mode used for floating-point calculations with
|
|
round-to-nearest-or-even rounding mode.
|
|
|
|
@item int
|
|
This is the mode used to perform integer calculations in the FPU, e.g.@:
|
|
integer multiply, or integer multiply-and-accumulate.
|
|
@end table
|
|
|
|
The default is @option{-mfp-mode=caller}
|
|
|
|
@item -mnosplit-lohi
|
|
@itemx -mno-postinc
|
|
@itemx -mno-postmodify
|
|
@opindex mnosplit-lohi
|
|
@opindex mno-postinc
|
|
@opindex mno-postmodify
|
|
Code generation tweaks that disable, respectively, splitting of 32-bit
|
|
loads, generation of post-increment addresses, and generation of
|
|
post-modify addresses. The defaults are @option{msplit-lohi},
|
|
@option{-mpost-inc}, and @option{-mpost-modify}.
|
|
|
|
@item -mnovect-double
|
|
@opindex mno-vect-double
|
|
Change the preferred SIMD mode to SImode. The default is
|
|
@option{-mvect-double}, which uses DImode as preferred SIMD mode.
|
|
|
|
@item -max-vect-align=@var{num}
|
|
@opindex max-vect-align
|
|
The maximum alignment for SIMD vector mode types.
|
|
@var{num} may be 4 or 8. The default is 8.
|
|
Note that this is an ABI change, even though many library function
|
|
interfaces are unaffected if they don't use SIMD vector modes
|
|
in places that affect size and/or alignment of relevant types.
|
|
|
|
@item -msplit-vecmove-early
|
|
@opindex msplit-vecmove-early
|
|
Split vector moves into single word moves before reload. In theory this
|
|
can give better register allocation, but so far the reverse seems to be
|
|
generally the case.
|
|
|
|
@item -m1reg-@var{reg}
|
|
@opindex m1reg-
|
|
Specify a register to hold the constant @minus{}1, which makes loading small negative
|
|
constants and certain bitmasks faster.
|
|
Allowable values for @var{reg} are @samp{r43} and @samp{r63},
|
|
which specify use of that register as a fixed register,
|
|
and @samp{none}, which means that no register is used for this
|
|
purpose. The default is @option{-m1reg-none}.
|
|
|
|
@end table
|
|
|
|
@node ARC Options
|
|
@subsection ARC Options
|
|
@cindex ARC options
|
|
|
|
The following options control the architecture variant for which code
|
|
is being compiled:
|
|
|
|
@c architecture variants
|
|
@table @gcctabopt
|
|
|
|
@item -mbarrel-shifter
|
|
@opindex mbarrel-shifter
|
|
Generate instructions supported by barrel shifter. This is the default
|
|
unless @option{-mcpu=ARC601} or @samp{-mcpu=ARCEM} is in effect.
|
|
|
|
@item -mcpu=@var{cpu}
|
|
@opindex mcpu
|
|
Set architecture type, register usage, and instruction scheduling
|
|
parameters for @var{cpu}. There are also shortcut alias options
|
|
available for backward compatibility and convenience. Supported
|
|
values for @var{cpu} are
|
|
|
|
@table @samp
|
|
@opindex mA6
|
|
@opindex mARC600
|
|
@item arc600
|
|
Compile for ARC600. Aliases: @option{-mA6}, @option{-mARC600}.
|
|
|
|
@item arc601
|
|
@opindex mARC601
|
|
Compile for ARC601. Alias: @option{-mARC601}.
|
|
|
|
@item arc700
|
|
@opindex mA7
|
|
@opindex mARC700
|
|
Compile for ARC700. Aliases: @option{-mA7}, @option{-mARC700}.
|
|
This is the default when configured with @option{--with-cpu=arc700}@.
|
|
|
|
@item arcem
|
|
Compile for ARC EM.
|
|
|
|
@item archs
|
|
Compile for ARC HS.
|
|
|
|
@item em
|
|
@opindex em
|
|
Compile for ARC EM cpu with no hardware extension.
|
|
|
|
@item em4
|
|
@opindex em4
|
|
Compile for ARC EM4 cpu.
|
|
|
|
@item em4_dmips
|
|
@opindex em4_dmips
|
|
Compile for ARC EM4 DMIPS cpu.
|
|
|
|
@item em4_fpus
|
|
@opindex em4_fpus
|
|
Compile for ARC EM4 DMIPS cpu with single precision floating point
|
|
extension.
|
|
|
|
@item em4_fpuda
|
|
@opindex em4_fpuda
|
|
Compile for ARC EM4 DMIPS cpu with single precision floating point and
|
|
double assists instructions.
|
|
|
|
@item hs
|
|
@opindex hs
|
|
Compile for ARC HS cpu with no hardware extension, except the atomic
|
|
instructions.
|
|
|
|
@item hs34
|
|
@opindex hs34
|
|
Compile for ARC HS34 cpu.
|
|
|
|
@item hs38
|
|
@opindex hs38
|
|
Compile for ARC HS38 cpu.
|
|
|
|
@item hs38_linux
|
|
@opindex hs38_linux
|
|
Compile for ARC HS38 cpu with all hardware extensions on.
|
|
|
|
@item arc600_norm
|
|
@opindex arc600_norm
|
|
Compile for ARC 600 cpu with norm instruction enabled.
|
|
|
|
@item arc600_mul32x16
|
|
@opindex arc600_mul32x16
|
|
Compile for ARC 600 cpu with norm and mul32x16 instructions enabled.
|
|
|
|
@item arc600_mul64
|
|
@opindex arc600_mul64
|
|
Compile for ARC 600 cpu with norm and mul64 instructions enabled.
|
|
|
|
@item arc601_norm
|
|
@opindex arc601_norm
|
|
Compile for ARC 601 cpu with norm instruction enabled.
|
|
|
|
@item arc601_mul32x16
|
|
@opindex arc601_mul32x16
|
|
Compile for ARC 601 cpu with norm and mul32x16 instructions enabled.
|
|
|
|
@item arc601_mul64
|
|
@opindex arc601_mul64
|
|
Compile for ARC 601 cpu with norm and mul64 instructions enabled.
|
|
|
|
@item nps400
|
|
@opindex nps400
|
|
Compile for ARC 700 on NPS400 chip.
|
|
|
|
@end table
|
|
|
|
@item -mdpfp
|
|
@opindex mdpfp
|
|
@itemx -mdpfp-compact
|
|
@opindex mdpfp-compact
|
|
FPX: Generate Double Precision FPX instructions, tuned for the compact
|
|
implementation.
|
|
|
|
@item -mdpfp-fast
|
|
@opindex mdpfp-fast
|
|
FPX: Generate Double Precision FPX instructions, tuned for the fast
|
|
implementation.
|
|
|
|
@item -mno-dpfp-lrsr
|
|
@opindex mno-dpfp-lrsr
|
|
Disable LR and SR instructions from using FPX extension aux registers.
|
|
|
|
@item -mea
|
|
@opindex mea
|
|
Generate Extended arithmetic instructions. Currently only
|
|
@code{divaw}, @code{adds}, @code{subs}, and @code{sat16} are
|
|
supported. This is always enabled for @option{-mcpu=ARC700}.
|
|
|
|
@item -mno-mpy
|
|
@opindex mno-mpy
|
|
Do not generate mpy instructions for ARC700. This instruction is
|
|
deprecated.
|
|
|
|
@item -mmul32x16
|
|
@opindex mmul32x16
|
|
Generate 32x16 bit multiply and mac instructions.
|
|
|
|
@item -mmul64
|
|
@opindex mmul64
|
|
Generate mul64 and mulu64 instructions. Only valid for @option{-mcpu=ARC600}.
|
|
|
|
@item -mnorm
|
|
@opindex mnorm
|
|
Generate norm instruction. This is the default if @option{-mcpu=ARC700}
|
|
is in effect.
|
|
|
|
@item -mspfp
|
|
@opindex mspfp
|
|
@itemx -mspfp-compact
|
|
@opindex mspfp-compact
|
|
FPX: Generate Single Precision FPX instructions, tuned for the compact
|
|
implementation.
|
|
|
|
@item -mspfp-fast
|
|
@opindex mspfp-fast
|
|
FPX: Generate Single Precision FPX instructions, tuned for the fast
|
|
implementation.
|
|
|
|
@item -msimd
|
|
@opindex msimd
|
|
Enable generation of ARC SIMD instructions via target-specific
|
|
builtins. Only valid for @option{-mcpu=ARC700}.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
This option ignored; it is provided for compatibility purposes only.
|
|
Software floating point code is emitted by default, and this default
|
|
can overridden by FPX options; @samp{mspfp}, @samp{mspfp-compact}, or
|
|
@samp{mspfp-fast} for single precision, and @samp{mdpfp},
|
|
@samp{mdpfp-compact}, or @samp{mdpfp-fast} for double precision.
|
|
|
|
@item -mswap
|
|
@opindex mswap
|
|
Generate swap instructions.
|
|
|
|
@item -matomic
|
|
@opindex matomic
|
|
This enables Locked Load/Store Conditional extension to implement
|
|
atomic memopry built-in functions. Not available for ARC 6xx or ARC
|
|
EM cores.
|
|
|
|
@item -mdiv-rem
|
|
@opindex mdiv-rem
|
|
Enable DIV/REM instructions for ARCv2 cores.
|
|
|
|
@item -mcode-density
|
|
@opindex mcode-density
|
|
Enable code density instructions for ARC EM, default on for ARC HS.
|
|
|
|
@item -mll64
|
|
@opindex mll64
|
|
Enable double load/store operations for ARC HS cores.
|
|
|
|
@item -mtp-regno=@var{regno}
|
|
@opindex mtp-regno
|
|
Specify thread pointer register number.
|
|
|
|
@item -mmpy-option=@var{multo}
|
|
@opindex mmpy-option
|
|
Compile ARCv2 code with a multiplier design option. @samp{wlh1} is
|
|
the default value. The recognized values for @var{multo} are:
|
|
|
|
@table @samp
|
|
@item 0
|
|
No multiplier available.
|
|
|
|
@item 1
|
|
@opindex w
|
|
The multiply option is set to w: 16x16 multiplier, fully pipelined.
|
|
The following instructions are enabled: MPYW, and MPYUW.
|
|
|
|
@item 2
|
|
@opindex wlh1
|
|
The multiply option is set to wlh1: 32x32 multiplier, fully
|
|
pipelined (1 stage). The following instructions are additionally
|
|
enabled: MPY, MPYU, MPYM, MPYMU, and MPY_S.
|
|
|
|
@item 3
|
|
@opindex wlh2
|
|
The multiply option is set to wlh2: 32x32 multiplier, fully pipelined
|
|
(2 stages). The following instructions are additionally enabled: MPY,
|
|
MPYU, MPYM, MPYMU, and MPY_S.
|
|
|
|
@item 4
|
|
@opindex wlh3
|
|
The multiply option is set to wlh3: Two 16x16 multiplier, blocking,
|
|
sequential. The following instructions are additionally enabled: MPY,
|
|
MPYU, MPYM, MPYMU, and MPY_S.
|
|
|
|
@item 5
|
|
@opindex wlh4
|
|
The multiply option is set to wlh4: One 16x16 multiplier, blocking,
|
|
sequential. The following instructions are additionally enabled: MPY,
|
|
MPYU, MPYM, MPYMU, and MPY_S.
|
|
|
|
@item 6
|
|
@opindex wlh5
|
|
The multiply option is set to wlh5: One 32x4 multiplier, blocking,
|
|
sequential. The following instructions are additionally enabled: MPY,
|
|
MPYU, MPYM, MPYMU, and MPY_S.
|
|
|
|
@end table
|
|
|
|
This option is only available for ARCv2 cores@.
|
|
|
|
@item -mfpu=@var{fpu}
|
|
@opindex mfpu
|
|
Enables specific floating-point hardware extension for ARCv2
|
|
core. Supported values for @var{fpu} are:
|
|
|
|
@table @samp
|
|
|
|
@item fpus
|
|
@opindex fpus
|
|
Enables support for single precision floating point hardware
|
|
extensions@.
|
|
|
|
@item fpud
|
|
@opindex fpud
|
|
Enables support for double precision floating point hardware
|
|
extensions. The single precision floating point extension is also
|
|
enabled. Not available for ARC EM@.
|
|
|
|
@item fpuda
|
|
@opindex fpuda
|
|
Enables support for double precision floating point hardware
|
|
extensions using double precision assist instructions. The single
|
|
precision floating point extension is also enabled. This option is
|
|
only available for ARC EM@.
|
|
|
|
@item fpuda_div
|
|
@opindex fpuda_div
|
|
Enables support for double precision floating point hardware
|
|
extensions using double precision assist instructions, and simple
|
|
precision square-root and divide hardware extensions. The single
|
|
precision floating point extension is also enabled. This option is
|
|
only available for ARC EM@.
|
|
|
|
@item fpuda_fma
|
|
@opindex fpuda_fma
|
|
Enables support for double precision floating point hardware
|
|
extensions using double precision assist instructions, and simple
|
|
precision fused multiple and add hardware extension. The single
|
|
precision floating point extension is also enabled. This option is
|
|
only available for ARC EM@.
|
|
|
|
@item fpuda_all
|
|
@opindex fpuda_all
|
|
Enables support for double precision floating point hardware
|
|
extensions using double precision assist instructions, and all simple
|
|
precision hardware extensions. The single precision floating point
|
|
extension is also enabled. This option is only available for ARC EM@.
|
|
|
|
@item fpus_div
|
|
@opindex fpus_div
|
|
Enables support for single precision floating point, and single
|
|
precision square-root and divide hardware extensions@.
|
|
|
|
@item fpud_div
|
|
@opindex fpud_div
|
|
Enables support for double precision floating point, and double
|
|
precision square-root and divide hardware extensions. This option
|
|
includes option @samp{fpus_div}. Not available for ARC EM@.
|
|
|
|
@item fpus_fma
|
|
@opindex fpus_fma
|
|
Enables support for single precision floating point, and single
|
|
precision fused multiple and add hardware extensions@.
|
|
|
|
@item fpud_fma
|
|
@opindex fpud_fma
|
|
Enables support for double precision floating point, and double
|
|
precision fused multiple and add hardware extensions. This option
|
|
includes option @samp{fpus_fma}. Not available for ARC EM@.
|
|
|
|
@item fpus_all
|
|
@opindex fpus_all
|
|
Enables support for all single precision floating point hardware
|
|
extensions@.
|
|
|
|
@item fpud_all
|
|
@opindex fpud_all
|
|
Enables support for all single and double precision floating point
|
|
hardware extensions. Not available for ARC EM@.
|
|
|
|
@end table
|
|
|
|
@end table
|
|
|
|
The following options are passed through to the assembler, and also
|
|
define preprocessor macro symbols.
|
|
|
|
@c Flags used by the assembler, but for which we define preprocessor
|
|
@c macro symbols as well.
|
|
@table @gcctabopt
|
|
@item -mdsp-packa
|
|
@opindex mdsp-packa
|
|
Passed down to the assembler to enable the DSP Pack A extensions.
|
|
Also sets the preprocessor symbol @code{__Xdsp_packa}. This option is
|
|
deprecated.
|
|
|
|
@item -mdvbf
|
|
@opindex mdvbf
|
|
Passed down to the assembler to enable the dual viterbi butterfly
|
|
extension. Also sets the preprocessor symbol @code{__Xdvbf}. This
|
|
option is deprecated.
|
|
|
|
@c ARC700 4.10 extension instruction
|
|
@item -mlock
|
|
@opindex mlock
|
|
Passed down to the assembler to enable the Locked Load/Store
|
|
Conditional extension. Also sets the preprocessor symbol
|
|
@code{__Xlock}.
|
|
|
|
@item -mmac-d16
|
|
@opindex mmac-d16
|
|
Passed down to the assembler. Also sets the preprocessor symbol
|
|
@code{__Xxmac_d16}. This option is deprecated.
|
|
|
|
@item -mmac-24
|
|
@opindex mmac-24
|
|
Passed down to the assembler. Also sets the preprocessor symbol
|
|
@code{__Xxmac_24}. This option is deprecated.
|
|
|
|
@c ARC700 4.10 extension instruction
|
|
@item -mrtsc
|
|
@opindex mrtsc
|
|
Passed down to the assembler to enable the 64-bit Time-Stamp Counter
|
|
extension instruction. Also sets the preprocessor symbol
|
|
@code{__Xrtsc}. This option is deprecated.
|
|
|
|
@c ARC700 4.10 extension instruction
|
|
@item -mswape
|
|
@opindex mswape
|
|
Passed down to the assembler to enable the swap byte ordering
|
|
extension instruction. Also sets the preprocessor symbol
|
|
@code{__Xswape}.
|
|
|
|
@item -mtelephony
|
|
@opindex mtelephony
|
|
Passed down to the assembler to enable dual and single operand
|
|
instructions for telephony. Also sets the preprocessor symbol
|
|
@code{__Xtelephony}. This option is deprecated.
|
|
|
|
@item -mxy
|
|
@opindex mxy
|
|
Passed down to the assembler to enable the XY Memory extension. Also
|
|
sets the preprocessor symbol @code{__Xxy}.
|
|
|
|
@end table
|
|
|
|
The following options control how the assembly code is annotated:
|
|
|
|
@c Assembly annotation options
|
|
@table @gcctabopt
|
|
@item -misize
|
|
@opindex misize
|
|
Annotate assembler instructions with estimated addresses.
|
|
|
|
@item -mannotate-align
|
|
@opindex mannotate-align
|
|
Explain what alignment considerations lead to the decision to make an
|
|
instruction short or long.
|
|
|
|
@end table
|
|
|
|
The following options are passed through to the linker:
|
|
|
|
@c options passed through to the linker
|
|
@table @gcctabopt
|
|
@item -marclinux
|
|
@opindex marclinux
|
|
Passed through to the linker, to specify use of the @code{arclinux} emulation.
|
|
This option is enabled by default in tool chains built for
|
|
@w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets
|
|
when profiling is not requested.
|
|
|
|
@item -marclinux_prof
|
|
@opindex marclinux_prof
|
|
Passed through to the linker, to specify use of the
|
|
@code{arclinux_prof} emulation. This option is enabled by default in
|
|
tool chains built for @w{@code{arc-linux-uclibc}} and
|
|
@w{@code{arceb-linux-uclibc}} targets when profiling is requested.
|
|
|
|
@end table
|
|
|
|
The following options control the semantics of generated code:
|
|
|
|
@c semantically relevant code generation options
|
|
@table @gcctabopt
|
|
@item -mlong-calls
|
|
@opindex mlong-calls
|
|
Generate call insns as register indirect calls, thus providing access
|
|
to the full 32-bit address range.
|
|
|
|
@item -mmedium-calls
|
|
@opindex mmedium-calls
|
|
Don't use less than 25 bit addressing range for calls, which is the
|
|
offset available for an unconditional branch-and-link
|
|
instruction. Conditional execution of function calls is suppressed, to
|
|
allow use of the 25-bit range, rather than the 21-bit range with
|
|
conditional branch-and-link. This is the default for tool chains built
|
|
for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets.
|
|
|
|
@item -mno-sdata
|
|
@opindex mno-sdata
|
|
Do not generate sdata references. This is the default for tool chains
|
|
built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}}
|
|
targets.
|
|
|
|
@item -mvolatile-cache
|
|
@opindex mvolatile-cache
|
|
Use ordinarily cached memory accesses for volatile references. This is the
|
|
default.
|
|
|
|
@item -mno-volatile-cache
|
|
@opindex mno-volatile-cache
|
|
Enable cache bypass for volatile references.
|
|
|
|
@end table
|
|
|
|
The following options fine tune code generation:
|
|
@c code generation tuning options
|
|
@table @gcctabopt
|
|
@item -malign-call
|
|
@opindex malign-call
|
|
Do alignment optimizations for call instructions.
|
|
|
|
@item -mauto-modify-reg
|
|
@opindex mauto-modify-reg
|
|
Enable the use of pre/post modify with register displacement.
|
|
|
|
@item -mbbit-peephole
|
|
@opindex mbbit-peephole
|
|
Enable bbit peephole2.
|
|
|
|
@item -mno-brcc
|
|
@opindex mno-brcc
|
|
This option disables a target-specific pass in @file{arc_reorg} to
|
|
generate @code{BRcc} instructions. It has no effect on @code{BRcc}
|
|
generation driven by the combiner pass.
|
|
|
|
@item -mcase-vector-pcrel
|
|
@opindex mcase-vector-pcrel
|
|
Use pc-relative switch case tables - this enables case table shortening.
|
|
This is the default for @option{-Os}.
|
|
|
|
@item -mcompact-casesi
|
|
@opindex mcompact-casesi
|
|
Enable compact casesi pattern. This is the default for @option{-Os},
|
|
and only available for ARCv1 cores.
|
|
|
|
@item -mno-cond-exec
|
|
@opindex mno-cond-exec
|
|
Disable ARCompact specific pass to generate conditional execution instructions.
|
|
Due to delay slot scheduling and interactions between operand numbers,
|
|
literal sizes, instruction lengths, and the support for conditional execution,
|
|
the target-independent pass to generate conditional execution is often lacking,
|
|
so the ARC port has kept a special pass around that tries to find more
|
|
conditional execution generating opportunities after register allocation,
|
|
branch shortening, and delay slot scheduling have been done. This pass
|
|
generally, but not always, improves performance and code size, at the cost of
|
|
extra compilation time, which is why there is an option to switch it off.
|
|
If you have a problem with call instructions exceeding their allowable
|
|
offset range because they are conditionalized, you should consider using
|
|
@option{-mmedium-calls} instead.
|
|
|
|
@item -mearly-cbranchsi
|
|
@opindex mearly-cbranchsi
|
|
Enable pre-reload use of the cbranchsi pattern.
|
|
|
|
@item -mexpand-adddi
|
|
@opindex mexpand-adddi
|
|
Expand @code{adddi3} and @code{subdi3} at rtl generation time into
|
|
@code{add.f}, @code{adc} etc.
|
|
|
|
@item -mindexed-loads
|
|
@opindex mindexed-loads
|
|
Enable the use of indexed loads. This can be problematic because some
|
|
optimizers then assume that indexed stores exist, which is not
|
|
the case.
|
|
|
|
@opindex mlra
|
|
Enable Local Register Allocation. This is still experimental for ARC,
|
|
so by default the compiler uses standard reload
|
|
(i.e. @option{-mno-lra}).
|
|
|
|
@item -mlra-priority-none
|
|
@opindex mlra-priority-none
|
|
Don't indicate any priority for target registers.
|
|
|
|
@item -mlra-priority-compact
|
|
@opindex mlra-priority-compact
|
|
Indicate target register priority for r0..r3 / r12..r15.
|
|
|
|
@item -mlra-priority-noncompact
|
|
@opindex mlra-priority-noncompact
|
|
Reduce target register priority for r0..r3 / r12..r15.
|
|
|
|
@item -mno-millicode
|
|
@opindex mno-millicode
|
|
When optimizing for size (using @option{-Os}), prologues and epilogues
|
|
that have to save or restore a large number of registers are often
|
|
shortened by using call to a special function in libgcc; this is
|
|
referred to as a @emph{millicode} call. As these calls can pose
|
|
performance issues, and/or cause linking issues when linking in a
|
|
nonstandard way, this option is provided to turn off millicode call
|
|
generation.
|
|
|
|
@item -mmixed-code
|
|
@opindex mmixed-code
|
|
Tweak register allocation to help 16-bit instruction generation.
|
|
This generally has the effect of decreasing the average instruction size
|
|
while increasing the instruction count.
|
|
|
|
@item -mq-class
|
|
@opindex mq-class
|
|
Enable 'q' instruction alternatives.
|
|
This is the default for @option{-Os}.
|
|
|
|
@item -mRcq
|
|
@opindex mRcq
|
|
Enable Rcq constraint handling - most short code generation depends on this.
|
|
This is the default.
|
|
|
|
@item -mRcw
|
|
@opindex mRcw
|
|
Enable Rcw constraint handling - ccfsm condexec mostly depends on this.
|
|
This is the default.
|
|
|
|
@item -msize-level=@var{level}
|
|
@opindex msize-level
|
|
Fine-tune size optimization with regards to instruction lengths and alignment.
|
|
The recognized values for @var{level} are:
|
|
@table @samp
|
|
@item 0
|
|
No size optimization. This level is deprecated and treated like @samp{1}.
|
|
|
|
@item 1
|
|
Short instructions are used opportunistically.
|
|
|
|
@item 2
|
|
In addition, alignment of loops and of code after barriers are dropped.
|
|
|
|
@item 3
|
|
In addition, optional data alignment is dropped, and the option @option{Os} is enabled.
|
|
|
|
@end table
|
|
|
|
This defaults to @samp{3} when @option{-Os} is in effect. Otherwise,
|
|
the behavior when this is not set is equivalent to level @samp{1}.
|
|
|
|
@item -mtune=@var{cpu}
|
|
@opindex mtune
|
|
Set instruction scheduling parameters for @var{cpu}, overriding any implied
|
|
by @option{-mcpu=}.
|
|
|
|
Supported values for @var{cpu} are
|
|
|
|
@table @samp
|
|
@item ARC600
|
|
Tune for ARC600 cpu.
|
|
|
|
@item ARC601
|
|
Tune for ARC601 cpu.
|
|
|
|
@item ARC700
|
|
Tune for ARC700 cpu with standard multiplier block.
|
|
|
|
@item ARC700-xmac
|
|
Tune for ARC700 cpu with XMAC block.
|
|
|
|
@item ARC725D
|
|
Tune for ARC725D cpu.
|
|
|
|
@item ARC750D
|
|
Tune for ARC750D cpu.
|
|
|
|
@end table
|
|
|
|
@item -mmultcost=@var{num}
|
|
@opindex mmultcost
|
|
Cost to assume for a multiply instruction, with @samp{4} being equal to a
|
|
normal instruction.
|
|
|
|
@item -munalign-prob-threshold=@var{probability}
|
|
@opindex munalign-prob-threshold
|
|
Set probability threshold for unaligning branches.
|
|
When tuning for @samp{ARC700} and optimizing for speed, branches without
|
|
filled delay slot are preferably emitted unaligned and long, unless
|
|
profiling indicates that the probability for the branch to be taken
|
|
is below @var{probability}. @xref{Cross-profiling}.
|
|
The default is (REG_BR_PROB_BASE/2), i.e.@: 5000.
|
|
|
|
@end table
|
|
|
|
The following options are maintained for backward compatibility, but
|
|
are now deprecated and will be removed in a future release:
|
|
|
|
@c Deprecated options
|
|
@table @gcctabopt
|
|
|
|
@item -margonaut
|
|
@opindex margonaut
|
|
Obsolete FPX.
|
|
|
|
@item -mbig-endian
|
|
@opindex mbig-endian
|
|
@itemx -EB
|
|
@opindex EB
|
|
Compile code for big endian targets. Use of these options is now
|
|
deprecated. Users wanting big-endian code, should use the
|
|
@w{@code{arceb-elf32}} and @w{@code{arceb-linux-uclibc}} targets when
|
|
building the tool chain, for which big-endian is the default.
|
|
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
@itemx -EL
|
|
@opindex EL
|
|
Compile code for little endian targets. Use of these options is now
|
|
deprecated. Users wanting little-endian code should use the
|
|
@w{@code{arc-elf32}} and @w{@code{arc-linux-uclibc}} targets when
|
|
building the tool chain, for which little-endian is the default.
|
|
|
|
@item -mbarrel_shifter
|
|
@opindex mbarrel_shifter
|
|
Replaced by @option{-mbarrel-shifter}.
|
|
|
|
@item -mdpfp_compact
|
|
@opindex mdpfp_compact
|
|
Replaced by @option{-mdpfp-compact}.
|
|
|
|
@item -mdpfp_fast
|
|
@opindex mdpfp_fast
|
|
Replaced by @option{-mdpfp-fast}.
|
|
|
|
@item -mdsp_packa
|
|
@opindex mdsp_packa
|
|
Replaced by @option{-mdsp-packa}.
|
|
|
|
@item -mEA
|
|
@opindex mEA
|
|
Replaced by @option{-mea}.
|
|
|
|
@item -mmac_24
|
|
@opindex mmac_24
|
|
Replaced by @option{-mmac-24}.
|
|
|
|
@item -mmac_d16
|
|
@opindex mmac_d16
|
|
Replaced by @option{-mmac-d16}.
|
|
|
|
@item -mspfp_compact
|
|
@opindex mspfp_compact
|
|
Replaced by @option{-mspfp-compact}.
|
|
|
|
@item -mspfp_fast
|
|
@opindex mspfp_fast
|
|
Replaced by @option{-mspfp-fast}.
|
|
|
|
@item -mtune=@var{cpu}
|
|
@opindex mtune
|
|
Values @samp{arc600}, @samp{arc601}, @samp{arc700} and
|
|
@samp{arc700-xmac} for @var{cpu} are replaced by @samp{ARC600},
|
|
@samp{ARC601}, @samp{ARC700} and @samp{ARC700-xmac} respectively
|
|
|
|
@item -multcost=@var{num}
|
|
@opindex multcost
|
|
Replaced by @option{-mmultcost}.
|
|
|
|
@end table
|
|
|
|
@node ARM Options
|
|
@subsection ARM Options
|
|
@cindex ARM options
|
|
|
|
These @samp{-m} options are defined for the ARM port:
|
|
|
|
@table @gcctabopt
|
|
@item -mabi=@var{name}
|
|
@opindex mabi
|
|
Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu},
|
|
@samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}.
|
|
|
|
@item -mapcs-frame
|
|
@opindex mapcs-frame
|
|
Generate a stack frame that is compliant with the ARM Procedure Call
|
|
Standard for all functions, even if this is not strictly necessary for
|
|
correct execution of the code. Specifying @option{-fomit-frame-pointer}
|
|
with this option causes the stack frames not to be generated for
|
|
leaf functions. The default is @option{-mno-apcs-frame}.
|
|
This option is deprecated.
|
|
|
|
@item -mapcs
|
|
@opindex mapcs
|
|
This is a synonym for @option{-mapcs-frame} and is deprecated.
|
|
|
|
@ignore
|
|
@c not currently implemented
|
|
@item -mapcs-stack-check
|
|
@opindex mapcs-stack-check
|
|
Generate code to check the amount of stack space available upon entry to
|
|
every function (that actually uses some stack space). If there is
|
|
insufficient space available then either the function
|
|
@code{__rt_stkovf_split_small} or @code{__rt_stkovf_split_big} is
|
|
called, depending upon the amount of stack space required. The runtime
|
|
system is required to provide these functions. The default is
|
|
@option{-mno-apcs-stack-check}, since this produces smaller code.
|
|
|
|
@c not currently implemented
|
|
@item -mapcs-reentrant
|
|
@opindex mapcs-reentrant
|
|
Generate reentrant, position-independent code. The default is
|
|
@option{-mno-apcs-reentrant}.
|
|
@end ignore
|
|
|
|
@item -mthumb-interwork
|
|
@opindex mthumb-interwork
|
|
Generate code that supports calling between the ARM and Thumb
|
|
instruction sets. Without this option, on pre-v5 architectures, the
|
|
two instruction sets cannot be reliably used inside one program. The
|
|
default is @option{-mno-thumb-interwork}, since slightly larger code
|
|
is generated when @option{-mthumb-interwork} is specified. In AAPCS
|
|
configurations this option is meaningless.
|
|
|
|
@item -mno-sched-prolog
|
|
@opindex mno-sched-prolog
|
|
Prevent the reordering of instructions in the function prologue, or the
|
|
merging of those instruction with the instructions in the function's
|
|
body. This means that all functions start with a recognizable set
|
|
of instructions (or in fact one of a choice from a small set of
|
|
different function prologues), and this information can be used to
|
|
locate the start of functions inside an executable piece of code. The
|
|
default is @option{-msched-prolog}.
|
|
|
|
@item -mfloat-abi=@var{name}
|
|
@opindex mfloat-abi
|
|
Specifies which floating-point ABI to use. Permissible values
|
|
are: @samp{soft}, @samp{softfp} and @samp{hard}.
|
|
|
|
Specifying @samp{soft} causes GCC to generate output containing
|
|
library calls for floating-point operations.
|
|
@samp{softfp} allows the generation of code using hardware floating-point
|
|
instructions, but still uses the soft-float calling conventions.
|
|
@samp{hard} allows generation of floating-point instructions
|
|
and uses FPU-specific calling conventions.
|
|
|
|
The default depends on the specific target configuration. Note that
|
|
the hard-float and soft-float ABIs are not link-compatible; you must
|
|
compile your entire program with the same ABI, and link with a
|
|
compatible set of libraries.
|
|
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
Generate code for a processor running in little-endian mode. This is
|
|
the default for all standard configurations.
|
|
|
|
@item -mbig-endian
|
|
@opindex mbig-endian
|
|
Generate code for a processor running in big-endian mode; the default is
|
|
to compile code for a little-endian processor.
|
|
|
|
@item -march=@var{name}
|
|
@opindex march
|
|
This specifies the name of the target ARM architecture. GCC uses this
|
|
name to determine what kind of instructions it can emit when generating
|
|
assembly code. This option can be used in conjunction with or instead
|
|
of the @option{-mcpu=} option. Permissible names are: @samp{armv2},
|
|
@samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t},
|
|
@samp{armv5}, @samp{armv5e}, @samp{armv5t}, @samp{armv5te},
|
|
@samp{armv6}, @samp{armv6-m}, @samp{armv6j}, @samp{armv6k},
|
|
@samp{armv6kz}, @samp{armv6s-m},
|
|
@samp{armv6t2}, @samp{armv6z}, @samp{armv6zk},
|
|
@samp{armv7}, @samp{armv7-a}, @samp{armv7-m}, @samp{armv7-r}, @samp{armv7e-m},
|
|
@samp{armv7ve}, @samp{armv8-a}, @samp{armv8-a+crc}, @samp{armv8.1-a},
|
|
@samp{armv8.1-a+crc}, @samp{armv8-m.base}, @samp{armv8-m.main},
|
|
@samp{armv8-m.main+dsp}, @samp{iwmmxt}, @samp{iwmmxt2}.
|
|
|
|
Architecture revisions older than @samp{armv4t} are deprecated.
|
|
|
|
@option{-march=armv6s-m} is the @samp{armv6-m} architecture with support for
|
|
the (now mandatory) SVC instruction.
|
|
|
|
@option{-march=armv6zk} is an alias for @samp{armv6kz}, existing for backwards
|
|
compatibility.
|
|
|
|
@option{-march=armv7ve} is the @samp{armv7-a} architecture with virtualization
|
|
extensions.
|
|
|
|
@option{-march=armv8-a+crc} enables code generation for the ARMv8-A
|
|
architecture together with the optional CRC32 extensions.
|
|
|
|
@option{-march=armv8.1-a} enables compiler support for the ARMv8.1-A
|
|
architecture. This also enables the features provided by
|
|
@option{-march=armv8-a+crc}.
|
|
|
|
@option{-march=armv8.2-a} enables compiler support for the ARMv8.2-A
|
|
architecture. This also enables the features provided by
|
|
@option{-march=armv8.1-a}.
|
|
|
|
@option{-march=armv8.2-a+fp16} enables compiler support for the
|
|
ARMv8.2-A architecture with the optional FP16 instructions extension.
|
|
This also enables the features provided by @option{-march=armv8.1-a}
|
|
and implies @option{-mfp16-format=ieee}.
|
|
|
|
@option{-march=native} causes the compiler to auto-detect the architecture
|
|
of the build computer. At present, this feature is only supported on
|
|
GNU/Linux, and not all architectures are recognized. If the auto-detect
|
|
is unsuccessful the option has no effect.
|
|
|
|
@item -mtune=@var{name}
|
|
@opindex mtune
|
|
This option specifies the name of the target ARM processor for
|
|
which GCC should tune the performance of the code.
|
|
For some ARM implementations better performance can be obtained by using
|
|
this option.
|
|
Permissible names are: @samp{arm2}, @samp{arm250},
|
|
@samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610},
|
|
@samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm},
|
|
@samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700},
|
|
@samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100},
|
|
@samp{arm720},
|
|
@samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s},
|
|
@samp{arm710t}, @samp{arm720t}, @samp{arm740t},
|
|
@samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100},
|
|
@samp{strongarm1110},
|
|
@samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920},
|
|
@samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s},
|
|
@samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi},
|
|
@samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s},
|
|
@samp{arm10e}, @samp{arm1020e}, @samp{arm1022e},
|
|
@samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp},
|
|
@samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s},
|
|
@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8},
|
|
@samp{cortex-a9}, @samp{cortex-a12}, @samp{cortex-a15}, @samp{cortex-a17},
|
|
@samp{cortex-a32}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a57},
|
|
@samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-r4},
|
|
@samp{cortex-r4f}, @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-r8},
|
|
@samp{cortex-m33},
|
|
@samp{cortex-m23},
|
|
@samp{cortex-m7},
|
|
@samp{cortex-m4},
|
|
@samp{cortex-m3},
|
|
@samp{cortex-m1},
|
|
@samp{cortex-m0},
|
|
@samp{cortex-m0plus},
|
|
@samp{cortex-m1.small-multiply},
|
|
@samp{cortex-m0.small-multiply},
|
|
@samp{cortex-m0plus.small-multiply},
|
|
@samp{exynos-m1},
|
|
@samp{falkor},
|
|
@samp{qdf24xx},
|
|
@samp{marvell-pj4},
|
|
@samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312},
|
|
@samp{fa526}, @samp{fa626},
|
|
@samp{fa606te}, @samp{fa626te}, @samp{fmp626}, @samp{fa726te},
|
|
@samp{xgene1}.
|
|
|
|
Additionally, this option can specify that GCC should tune the performance
|
|
of the code for a big.LITTLE system. Permissible names are:
|
|
@samp{cortex-a15.cortex-a7}, @samp{cortex-a17.cortex-a7},
|
|
@samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53},
|
|
@samp{cortex-a72.cortex-a35}, @samp{cortex-a73.cortex-a53}.
|
|
|
|
@option{-mtune=generic-@var{arch}} specifies that GCC should tune the
|
|
performance for a blend of processors within architecture @var{arch}.
|
|
The aim is to generate code that run well on the current most popular
|
|
processors, balancing between optimizations that benefit some CPUs in the
|
|
range, and avoiding performance pitfalls of other CPUs. The effects of
|
|
this option may change in future GCC versions as CPU models come and go.
|
|
|
|
@option{-mtune=native} causes the compiler to auto-detect the CPU
|
|
of the build computer. At present, this feature is only supported on
|
|
GNU/Linux, and not all architectures are recognized. If the auto-detect is
|
|
unsuccessful the option has no effect.
|
|
|
|
@item -mcpu=@var{name}
|
|
@opindex mcpu
|
|
This specifies the name of the target ARM processor. GCC uses this name
|
|
to derive the name of the target ARM architecture (as if specified
|
|
by @option{-march}) and the ARM processor type for which to tune for
|
|
performance (as if specified by @option{-mtune}). Where this option
|
|
is used in conjunction with @option{-march} or @option{-mtune},
|
|
those options take precedence over the appropriate part of this option.
|
|
|
|
Permissible names for this option are the same as those for
|
|
@option{-mtune}.
|
|
|
|
@option{-mcpu=generic-@var{arch}} is also permissible, and is
|
|
equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}.
|
|
See @option{-mtune} for more information.
|
|
|
|
@option{-mcpu=native} causes the compiler to auto-detect the CPU
|
|
of the build computer. At present, this feature is only supported on
|
|
GNU/Linux, and not all architectures are recognized. If the auto-detect
|
|
is unsuccessful the option has no effect.
|
|
|
|
@item -mfpu=@var{name}
|
|
@opindex mfpu
|
|
This specifies what floating-point hardware (or hardware emulation) is
|
|
available on the target. Permissible names are: @samp{vfpv2}, @samp{vfpv3},
|
|
@samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd},
|
|
@samp{vfpv3xd-fp16}, @samp{neon-vfpv3}, @samp{neon-fp16}, @samp{vfpv4},
|
|
@samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4},
|
|
@samp{fpv5-d16}, @samp{fpv5-sp-d16},
|
|
@samp{fp-armv8}, @samp{neon-fp-armv8} and @samp{crypto-neon-fp-armv8}.
|
|
Note that @samp{neon} is an alias for @samp{neon-vfpv3} and @samp{vfp}
|
|
is an alias for @samp{vfpv2}.
|
|
|
|
If @option{-msoft-float} is specified this specifies the format of
|
|
floating-point values.
|
|
|
|
If the selected floating-point hardware includes the NEON extension
|
|
(e.g. @option{-mfpu}=@samp{neon}), note that floating-point
|
|
operations are not generated by GCC's auto-vectorization pass unless
|
|
@option{-funsafe-math-optimizations} is also specified. This is
|
|
because NEON hardware does not fully implement the IEEE 754 standard for
|
|
floating-point arithmetic (in particular denormal values are treated as
|
|
zero), so the use of NEON instructions may lead to a loss of precision.
|
|
|
|
You can also set the fpu name at function level by using the @code{target("fpu=")} function attributes (@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}).
|
|
|
|
@item -mfp16-format=@var{name}
|
|
@opindex mfp16-format
|
|
Specify the format of the @code{__fp16} half-precision floating-point type.
|
|
Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative};
|
|
the default is @samp{none}, in which case the @code{__fp16} type is not
|
|
defined. @xref{Half-Precision}, for more information.
|
|
|
|
@item -mstructure-size-boundary=@var{n}
|
|
@opindex mstructure-size-boundary
|
|
The sizes of all structures and unions are rounded up to a multiple
|
|
of the number of bits set by this option. Permissible values are 8, 32
|
|
and 64. The default value varies for different toolchains. For the COFF
|
|
targeted toolchain the default value is 8. A value of 64 is only allowed
|
|
if the underlying ABI supports it.
|
|
|
|
Specifying a larger number can produce faster, more efficient code, but
|
|
can also increase the size of the program. Different values are potentially
|
|
incompatible. Code compiled with one value cannot necessarily expect to
|
|
work with code or libraries compiled with another value, if they exchange
|
|
information using structures or unions.
|
|
|
|
@item -mabort-on-noreturn
|
|
@opindex mabort-on-noreturn
|
|
Generate a call to the function @code{abort} at the end of a
|
|
@code{noreturn} function. It is executed if the function tries to
|
|
return.
|
|
|
|
@item -mlong-calls
|
|
@itemx -mno-long-calls
|
|
@opindex mlong-calls
|
|
@opindex mno-long-calls
|
|
Tells the compiler to perform function calls by first loading the
|
|
address of the function into a register and then performing a subroutine
|
|
call on this register. This switch is needed if the target function
|
|
lies outside of the 64-megabyte addressing range of the offset-based
|
|
version of subroutine call instruction.
|
|
|
|
Even if this switch is enabled, not all function calls are turned
|
|
into long calls. The heuristic is that static functions, functions
|
|
that have the @code{short_call} attribute, functions that are inside
|
|
the scope of a @code{#pragma no_long_calls} directive, and functions whose
|
|
definitions have already been compiled within the current compilation
|
|
unit are not turned into long calls. The exceptions to this rule are
|
|
that weak function definitions, functions with the @code{long_call}
|
|
attribute or the @code{section} attribute, and functions that are within
|
|
the scope of a @code{#pragma long_calls} directive are always
|
|
turned into long calls.
|
|
|
|
This feature is not enabled by default. Specifying
|
|
@option{-mno-long-calls} restores the default behavior, as does
|
|
placing the function calls within the scope of a @code{#pragma
|
|
long_calls_off} directive. Note these switches have no effect on how
|
|
the compiler generates code to handle function calls via function
|
|
pointers.
|
|
|
|
@item -msingle-pic-base
|
|
@opindex msingle-pic-base
|
|
Treat the register used for PIC addressing as read-only, rather than
|
|
loading it in the prologue for each function. The runtime system is
|
|
responsible for initializing this register with an appropriate value
|
|
before execution begins.
|
|
|
|
@item -mpic-register=@var{reg}
|
|
@opindex mpic-register
|
|
Specify the register to be used for PIC addressing.
|
|
For standard PIC base case, the default is any suitable register
|
|
determined by compiler. For single PIC base case, the default is
|
|
@samp{R9} if target is EABI based or stack-checking is enabled,
|
|
otherwise the default is @samp{R10}.
|
|
|
|
@item -mpic-data-is-text-relative
|
|
@opindex mpic-data-is-text-relative
|
|
Assume that the displacement between the text and data segments is fixed
|
|
at static link time. This permits using PC-relative addressing
|
|
operations to access data known to be in the data segment. For
|
|
non-VxWorks RTP targets, this option is enabled by default. When
|
|
disabled on such targets, it will enable @option{-msingle-pic-base} by
|
|
default.
|
|
|
|
@item -mpoke-function-name
|
|
@opindex mpoke-function-name
|
|
Write the name of each function into the text section, directly
|
|
preceding the function prologue. The generated code is similar to this:
|
|
|
|
@smallexample
|
|
t0
|
|
.ascii "arm_poke_function_name", 0
|
|
.align
|
|
t1
|
|
.word 0xff000000 + (t1 - t0)
|
|
arm_poke_function_name
|
|
mov ip, sp
|
|
stmfd sp!, @{fp, ip, lr, pc@}
|
|
sub fp, ip, #4
|
|
@end smallexample
|
|
|
|
When performing a stack backtrace, code can inspect the value of
|
|
@code{pc} stored at @code{fp + 0}. If the trace function then looks at
|
|
location @code{pc - 12} and the top 8 bits are set, then we know that
|
|
there is a function name embedded immediately preceding this location
|
|
and has length @code{((pc[-3]) & 0xff000000)}.
|
|
|
|
@item -mthumb
|
|
@itemx -marm
|
|
@opindex marm
|
|
@opindex mthumb
|
|
|
|
Select between generating code that executes in ARM and Thumb
|
|
states. The default for most configurations is to generate code
|
|
that executes in ARM state, but the default can be changed by
|
|
configuring GCC with the @option{--with-mode=}@var{state}
|
|
configure option.
|
|
|
|
You can also override the ARM and Thumb mode for each function
|
|
by using the @code{target("thumb")} and @code{target("arm")} function attributes
|
|
(@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}).
|
|
|
|
@item -mtpcs-frame
|
|
@opindex mtpcs-frame
|
|
Generate a stack frame that is compliant with the Thumb Procedure Call
|
|
Standard for all non-leaf functions. (A leaf function is one that does
|
|
not call any other functions.) The default is @option{-mno-tpcs-frame}.
|
|
|
|
@item -mtpcs-leaf-frame
|
|
@opindex mtpcs-leaf-frame
|
|
Generate a stack frame that is compliant with the Thumb Procedure Call
|
|
Standard for all leaf functions. (A leaf function is one that does
|
|
not call any other functions.) The default is @option{-mno-apcs-leaf-frame}.
|
|
|
|
@item -mcallee-super-interworking
|
|
@opindex mcallee-super-interworking
|
|
Gives all externally visible functions in the file being compiled an ARM
|
|
instruction set header which switches to Thumb mode before executing the
|
|
rest of the function. This allows these functions to be called from
|
|
non-interworking code. This option is not valid in AAPCS configurations
|
|
because interworking is enabled by default.
|
|
|
|
@item -mcaller-super-interworking
|
|
@opindex mcaller-super-interworking
|
|
Allows calls via function pointers (including virtual functions) to
|
|
execute correctly regardless of whether the target code has been
|
|
compiled for interworking or not. There is a small overhead in the cost
|
|
of executing a function pointer if this option is enabled. This option
|
|
is not valid in AAPCS configurations because interworking is enabled
|
|
by default.
|
|
|
|
@item -mtp=@var{name}
|
|
@opindex mtp
|
|
Specify the access model for the thread local storage pointer. The valid
|
|
models are @samp{soft}, which generates calls to @code{__aeabi_read_tp},
|
|
@samp{cp15}, which fetches the thread pointer from @code{cp15} directly
|
|
(supported in the arm6k architecture), and @samp{auto}, which uses the
|
|
best available method for the selected processor. The default setting is
|
|
@samp{auto}.
|
|
|
|
@item -mtls-dialect=@var{dialect}
|
|
@opindex mtls-dialect
|
|
Specify the dialect to use for accessing thread local storage. Two
|
|
@var{dialect}s are supported---@samp{gnu} and @samp{gnu2}. The
|
|
@samp{gnu} dialect selects the original GNU scheme for supporting
|
|
local and global dynamic TLS models. The @samp{gnu2} dialect
|
|
selects the GNU descriptor scheme, which provides better performance
|
|
for shared libraries. The GNU descriptor scheme is compatible with
|
|
the original scheme, but does require new assembler, linker and
|
|
library support. Initial and local exec TLS models are unaffected by
|
|
this option and always use the original scheme.
|
|
|
|
@item -mword-relocations
|
|
@opindex mword-relocations
|
|
Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32).
|
|
This is enabled by default on targets (uClinux, SymbianOS) where the runtime
|
|
loader imposes this restriction, and when @option{-fpic} or @option{-fPIC}
|
|
is specified.
|
|
|
|
@item -mfix-cortex-m3-ldrd
|
|
@opindex mfix-cortex-m3-ldrd
|
|
Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions
|
|
with overlapping destination and base registers are used. This option avoids
|
|
generating these instructions. This option is enabled by default when
|
|
@option{-mcpu=cortex-m3} is specified.
|
|
|
|
@item -munaligned-access
|
|
@itemx -mno-unaligned-access
|
|
@opindex munaligned-access
|
|
@opindex mno-unaligned-access
|
|
Enables (or disables) reading and writing of 16- and 32- bit values
|
|
from addresses that are not 16- or 32- bit aligned. By default
|
|
unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for
|
|
ARMv8-M Baseline architectures, and enabled for all other
|
|
architectures. If unaligned access is not enabled then words in packed
|
|
data structures are accessed a byte at a time.
|
|
|
|
The ARM attribute @code{Tag_CPU_unaligned_access} is set in the
|
|
generated object file to either true or false, depending upon the
|
|
setting of this option. If unaligned access is enabled then the
|
|
preprocessor symbol @code{__ARM_FEATURE_UNALIGNED} is also
|
|
defined.
|
|
|
|
@item -mneon-for-64bits
|
|
@opindex mneon-for-64bits
|
|
Enables using Neon to handle scalar 64-bits operations. This is
|
|
disabled by default since the cost of moving data from core registers
|
|
to Neon is high.
|
|
|
|
@item -mslow-flash-data
|
|
@opindex mslow-flash-data
|
|
Assume loading data from flash is slower than fetching instruction.
|
|
Therefore literal load is minimized for better performance.
|
|
This option is only supported when compiling for ARMv7 M-profile and
|
|
off by default.
|
|
|
|
@item -masm-syntax-unified
|
|
@opindex masm-syntax-unified
|
|
Assume inline assembler is using unified asm syntax. The default is
|
|
currently off which implies divided syntax. This option has no impact
|
|
on Thumb2. However, this may change in future releases of GCC.
|
|
Divided syntax should be considered deprecated.
|
|
|
|
@item -mrestrict-it
|
|
@opindex mrestrict-it
|
|
Restricts generation of IT blocks to conform to the rules of ARMv8.
|
|
IT blocks can only contain a single 16-bit instruction from a select
|
|
set of instructions. This option is on by default for ARMv8 Thumb mode.
|
|
|
|
@item -mprint-tune-info
|
|
@opindex mprint-tune-info
|
|
Print CPU tuning information as comment in assembler file. This is
|
|
an option used only for regression testing of the compiler and not
|
|
intended for ordinary use in compiling code. This option is disabled
|
|
by default.
|
|
|
|
@item -mpure-code
|
|
@opindex mpure-code
|
|
Do not allow constant data to be placed in code sections.
|
|
Additionally, when compiling for ELF object format give all text sections the
|
|
ELF processor-specific section attribute @code{SHF_ARM_PURECODE}. This option
|
|
is only available when generating non-pic code for ARMv7-M targets.
|
|
|
|
@item -mcmse
|
|
@opindex mcmse
|
|
Generate secure code as per the "ARMv8-M Security Extensions: Requirements on
|
|
Development Tools Engineering Specification", which can be found on
|
|
@url{http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/ECM0359818_armv8m_security_extensions_reqs_on_dev_tools_1_0.pdf}.
|
|
@end table
|
|
|
|
@node AVR Options
|
|
@subsection AVR Options
|
|
@cindex AVR Options
|
|
|
|
These options are defined for AVR implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -mmcu=@var{mcu}
|
|
@opindex mmcu
|
|
Specify Atmel AVR instruction set architectures (ISA) or MCU type.
|
|
|
|
The default for this option is@tie{}@samp{avr2}.
|
|
|
|
GCC supports the following AVR devices and ISAs:
|
|
|
|
@include avr-mmcu.texi
|
|
|
|
@item -mabsdata
|
|
@opindex mabsdata
|
|
|
|
Assume that all data in static storage can be accessed by LDS / STS
|
|
instructions. This option has only an effect on reduced Tiny devices like
|
|
ATtiny40. See also the @code{absdata}
|
|
@ref{AVR Variable Attributes,variable attribute}.
|
|
|
|
@item -maccumulate-args
|
|
@opindex maccumulate-args
|
|
Accumulate outgoing function arguments and acquire/release the needed
|
|
stack space for outgoing function arguments once in function
|
|
prologue/epilogue. Without this option, outgoing arguments are pushed
|
|
before calling a function and popped afterwards.
|
|
|
|
Popping the arguments after the function call can be expensive on
|
|
AVR so that accumulating the stack space might lead to smaller
|
|
executables because arguments need not to be removed from the
|
|
stack after such a function call.
|
|
|
|
This option can lead to reduced code size for functions that perform
|
|
several calls to functions that get their arguments on the stack like
|
|
calls to printf-like functions.
|
|
|
|
@item -mbranch-cost=@var{cost}
|
|
@opindex mbranch-cost
|
|
Set the branch costs for conditional branch instructions to
|
|
@var{cost}. Reasonable values for @var{cost} are small, non-negative
|
|
integers. The default branch cost is 0.
|
|
|
|
@item -mcall-prologues
|
|
@opindex mcall-prologues
|
|
Functions prologues/epilogues are expanded as calls to appropriate
|
|
subroutines. Code size is smaller.
|
|
|
|
@item -mint8
|
|
@opindex mint8
|
|
Assume @code{int} to be 8-bit integer. This affects the sizes of all types: a
|
|
@code{char} is 1 byte, an @code{int} is 1 byte, a @code{long} is 2 bytes,
|
|
and @code{long long} is 4 bytes. Please note that this option does not
|
|
conform to the C standards, but it results in smaller code
|
|
size.
|
|
|
|
@item -mn-flash=@var{num}
|
|
@opindex mn-flash
|
|
Assume that the flash memory has a size of
|
|
@var{num} times 64@tie{}KiB.
|
|
|
|
@item -mno-interrupts
|
|
@opindex mno-interrupts
|
|
Generated code is not compatible with hardware interrupts.
|
|
Code size is smaller.
|
|
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
Try to replace @code{CALL} resp.@: @code{JMP} instruction by the shorter
|
|
@code{RCALL} resp.@: @code{RJMP} instruction if applicable.
|
|
Setting @option{-mrelax} just adds the @option{--mlink-relax} option to
|
|
the assembler's command line and the @option{--relax} option to the
|
|
linker's command line.
|
|
|
|
Jump relaxing is performed by the linker because jump offsets are not
|
|
known before code is located. Therefore, the assembler code generated by the
|
|
compiler is the same, but the instructions in the executable may
|
|
differ from instructions in the assembler code.
|
|
|
|
Relaxing must be turned on if linker stubs are needed, see the
|
|
section on @code{EIND} and linker stubs below.
|
|
|
|
@item -mrmw
|
|
@opindex mrmw
|
|
Assume that the device supports the Read-Modify-Write
|
|
instructions @code{XCH}, @code{LAC}, @code{LAS} and @code{LAT}.
|
|
|
|
@item -msp8
|
|
@opindex msp8
|
|
Treat the stack pointer register as an 8-bit register,
|
|
i.e.@: assume the high byte of the stack pointer is zero.
|
|
In general, you don't need to set this option by hand.
|
|
|
|
This option is used internally by the compiler to select and
|
|
build multilibs for architectures @code{avr2} and @code{avr25}.
|
|
These architectures mix devices with and without @code{SPH}.
|
|
For any setting other than @option{-mmcu=avr2} or @option{-mmcu=avr25}
|
|
the compiler driver adds or removes this option from the compiler
|
|
proper's command line, because the compiler then knows if the device
|
|
or architecture has an 8-bit stack pointer and thus no @code{SPH}
|
|
register or not.
|
|
|
|
@item -mstrict-X
|
|
@opindex mstrict-X
|
|
Use address register @code{X} in a way proposed by the hardware. This means
|
|
that @code{X} is only used in indirect, post-increment or
|
|
pre-decrement addressing.
|
|
|
|
Without this option, the @code{X} register may be used in the same way
|
|
as @code{Y} or @code{Z} which then is emulated by additional
|
|
instructions.
|
|
For example, loading a value with @code{X+const} addressing with a
|
|
small non-negative @code{const < 64} to a register @var{Rn} is
|
|
performed as
|
|
|
|
@example
|
|
adiw r26, const ; X += const
|
|
ld @var{Rn}, X ; @var{Rn} = *X
|
|
sbiw r26, const ; X -= const
|
|
@end example
|
|
|
|
@item -mtiny-stack
|
|
@opindex mtiny-stack
|
|
Only change the lower 8@tie{}bits of the stack pointer.
|
|
|
|
@item -mfract-convert-truncate
|
|
@opindex mfract-convert-truncate
|
|
Allow to use truncation instead of rounding towards zero for fractional fixed-point types.
|
|
|
|
@item -nodevicelib
|
|
@opindex nodevicelib
|
|
Don't link against AVR-LibC's device specific library @code{lib<mcu>.a}.
|
|
|
|
@item -Waddr-space-convert
|
|
@opindex Waddr-space-convert
|
|
Warn about conversions between address spaces in the case where the
|
|
resulting address space is not contained in the incoming address space.
|
|
|
|
@item -Wmisspelled-isr
|
|
@opindex Wmisspelled-isr
|
|
Warn if the ISR is misspelled, i.e. without __vector prefix.
|
|
Enabled by default.
|
|
@end table
|
|
|
|
@subsubsection @code{EIND} and Devices with More Than 128 Ki Bytes of Flash
|
|
@cindex @code{EIND}
|
|
Pointers in the implementation are 16@tie{}bits wide.
|
|
The address of a function or label is represented as word address so
|
|
that indirect jumps and calls can target any code address in the
|
|
range of 64@tie{}Ki words.
|
|
|
|
In order to facilitate indirect jump on devices with more than 128@tie{}Ki
|
|
bytes of program memory space, there is a special function register called
|
|
@code{EIND} that serves as most significant part of the target address
|
|
when @code{EICALL} or @code{EIJMP} instructions are used.
|
|
|
|
Indirect jumps and calls on these devices are handled as follows by
|
|
the compiler and are subject to some limitations:
|
|
|
|
@itemize @bullet
|
|
|
|
@item
|
|
The compiler never sets @code{EIND}.
|
|
|
|
@item
|
|
The compiler uses @code{EIND} implicitly in @code{EICALL}/@code{EIJMP}
|
|
instructions or might read @code{EIND} directly in order to emulate an
|
|
indirect call/jump by means of a @code{RET} instruction.
|
|
|
|
@item
|
|
The compiler assumes that @code{EIND} never changes during the startup
|
|
code or during the application. In particular, @code{EIND} is not
|
|
saved/restored in function or interrupt service routine
|
|
prologue/epilogue.
|
|
|
|
@item
|
|
For indirect calls to functions and computed goto, the linker
|
|
generates @emph{stubs}. Stubs are jump pads sometimes also called
|
|
@emph{trampolines}. Thus, the indirect call/jump jumps to such a stub.
|
|
The stub contains a direct jump to the desired address.
|
|
|
|
@item
|
|
Linker relaxation must be turned on so that the linker generates
|
|
the stubs correctly in all situations. See the compiler option
|
|
@option{-mrelax} and the linker option @option{--relax}.
|
|
There are corner cases where the linker is supposed to generate stubs
|
|
but aborts without relaxation and without a helpful error message.
|
|
|
|
@item
|
|
The default linker script is arranged for code with @code{EIND = 0}.
|
|
If code is supposed to work for a setup with @code{EIND != 0}, a custom
|
|
linker script has to be used in order to place the sections whose
|
|
name start with @code{.trampolines} into the segment where @code{EIND}
|
|
points to.
|
|
|
|
@item
|
|
The startup code from libgcc never sets @code{EIND}.
|
|
Notice that startup code is a blend of code from libgcc and AVR-LibC.
|
|
For the impact of AVR-LibC on @code{EIND}, see the
|
|
@w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC user manual}}.
|
|
|
|
@item
|
|
It is legitimate for user-specific startup code to set up @code{EIND}
|
|
early, for example by means of initialization code located in
|
|
section @code{.init3}. Such code runs prior to general startup code
|
|
that initializes RAM and calls constructors, but after the bit
|
|
of startup code from AVR-LibC that sets @code{EIND} to the segment
|
|
where the vector table is located.
|
|
@example
|
|
#include <avr/io.h>
|
|
|
|
static void
|
|
__attribute__((section(".init3"),naked,used,no_instrument_function))
|
|
init3_set_eind (void)
|
|
@{
|
|
__asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
|
|
"out %i0,r24" :: "n" (&EIND) : "r24","memory");
|
|
@}
|
|
@end example
|
|
|
|
@noindent
|
|
The @code{__trampolines_start} symbol is defined in the linker script.
|
|
|
|
@item
|
|
Stubs are generated automatically by the linker if
|
|
the following two conditions are met:
|
|
@itemize @minus
|
|
|
|
@item The address of a label is taken by means of the @code{gs} modifier
|
|
(short for @emph{generate stubs}) like so:
|
|
@example
|
|
LDI r24, lo8(gs(@var{func}))
|
|
LDI r25, hi8(gs(@var{func}))
|
|
@end example
|
|
@item The final location of that label is in a code segment
|
|
@emph{outside} the segment where the stubs are located.
|
|
@end itemize
|
|
|
|
@item
|
|
The compiler emits such @code{gs} modifiers for code labels in the
|
|
following situations:
|
|
@itemize @minus
|
|
@item Taking address of a function or code label.
|
|
@item Computed goto.
|
|
@item If prologue-save function is used, see @option{-mcall-prologues}
|
|
command-line option.
|
|
@item Switch/case dispatch tables. If you do not want such dispatch
|
|
tables you can specify the @option{-fno-jump-tables} command-line option.
|
|
@item C and C++ constructors/destructors called during startup/shutdown.
|
|
@item If the tools hit a @code{gs()} modifier explained above.
|
|
@end itemize
|
|
|
|
@item
|
|
Jumping to non-symbolic addresses like so is @emph{not} supported:
|
|
|
|
@example
|
|
int main (void)
|
|
@{
|
|
/* Call function at word address 0x2 */
|
|
return ((int(*)(void)) 0x2)();
|
|
@}
|
|
@end example
|
|
|
|
Instead, a stub has to be set up, i.e.@: the function has to be called
|
|
through a symbol (@code{func_4} in the example):
|
|
|
|
@example
|
|
int main (void)
|
|
@{
|
|
extern int func_4 (void);
|
|
|
|
/* Call function at byte address 0x4 */
|
|
return func_4();
|
|
@}
|
|
@end example
|
|
|
|
and the application be linked with @option{-Wl,--defsym,func_4=0x4}.
|
|
Alternatively, @code{func_4} can be defined in the linker script.
|
|
@end itemize
|
|
|
|
@subsubsection Handling of the @code{RAMPD}, @code{RAMPX}, @code{RAMPY} and @code{RAMPZ} Special Function Registers
|
|
@cindex @code{RAMPD}
|
|
@cindex @code{RAMPX}
|
|
@cindex @code{RAMPY}
|
|
@cindex @code{RAMPZ}
|
|
Some AVR devices support memories larger than the 64@tie{}KiB range
|
|
that can be accessed with 16-bit pointers. To access memory locations
|
|
outside this 64@tie{}KiB range, the contentent of a @code{RAMP}
|
|
register is used as high part of the address:
|
|
The @code{X}, @code{Y}, @code{Z} address register is concatenated
|
|
with the @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function
|
|
register, respectively, to get a wide address. Similarly,
|
|
@code{RAMPD} is used together with direct addressing.
|
|
|
|
@itemize
|
|
@item
|
|
The startup code initializes the @code{RAMP} special function
|
|
registers with zero.
|
|
|
|
@item
|
|
If a @ref{AVR Named Address Spaces,named address space} other than
|
|
generic or @code{__flash} is used, then @code{RAMPZ} is set
|
|
as needed before the operation.
|
|
|
|
@item
|
|
If the device supports RAM larger than 64@tie{}KiB and the compiler
|
|
needs to change @code{RAMPZ} to accomplish an operation, @code{RAMPZ}
|
|
is reset to zero after the operation.
|
|
|
|
@item
|
|
If the device comes with a specific @code{RAMP} register, the ISR
|
|
prologue/epilogue saves/restores that SFR and initializes it with
|
|
zero in case the ISR code might (implicitly) use it.
|
|
|
|
@item
|
|
RAM larger than 64@tie{}KiB is not supported by GCC for AVR targets.
|
|
If you use inline assembler to read from locations outside the
|
|
16-bit address range and change one of the @code{RAMP} registers,
|
|
you must reset it to zero after the access.
|
|
|
|
@end itemize
|
|
|
|
@subsubsection AVR Built-in Macros
|
|
|
|
GCC defines several built-in macros so that the user code can test
|
|
for the presence or absence of features. Almost any of the following
|
|
built-in macros are deduced from device capabilities and thus
|
|
triggered by the @option{-mmcu=} command-line option.
|
|
|
|
For even more AVR-specific built-in macros see
|
|
@ref{AVR Named Address Spaces} and @ref{AVR Built-in Functions}.
|
|
|
|
@table @code
|
|
|
|
@item __AVR_ARCH__
|
|
Build-in macro that resolves to a decimal number that identifies the
|
|
architecture and depends on the @option{-mmcu=@var{mcu}} option.
|
|
Possible values are:
|
|
|
|
@code{2}, @code{25}, @code{3}, @code{31}, @code{35},
|
|
@code{4}, @code{5}, @code{51}, @code{6}
|
|
|
|
for @var{mcu}=@code{avr2}, @code{avr25}, @code{avr3}, @code{avr31},
|
|
@code{avr35}, @code{avr4}, @code{avr5}, @code{avr51}, @code{avr6},
|
|
|
|
respectively and
|
|
|
|
@code{100}, @code{102}, @code{104},
|
|
@code{105}, @code{106}, @code{107}
|
|
|
|
for @var{mcu}=@code{avrtiny}, @code{avrxmega2}, @code{avrxmega4},
|
|
@code{avrxmega5}, @code{avrxmega6}, @code{avrxmega7}, respectively.
|
|
If @var{mcu} specifies a device, this built-in macro is set
|
|
accordingly. For example, with @option{-mmcu=atmega8} the macro is
|
|
defined to @code{4}.
|
|
|
|
@item __AVR_@var{Device}__
|
|
Setting @option{-mmcu=@var{device}} defines this built-in macro which reflects
|
|
the device's name. For example, @option{-mmcu=atmega8} defines the
|
|
built-in macro @code{__AVR_ATmega8__}, @option{-mmcu=attiny261a} defines
|
|
@code{__AVR_ATtiny261A__}, etc.
|
|
|
|
The built-in macros' names follow
|
|
the scheme @code{__AVR_@var{Device}__} where @var{Device} is
|
|
the device name as from the AVR user manual. The difference between
|
|
@var{Device} in the built-in macro and @var{device} in
|
|
@option{-mmcu=@var{device}} is that the latter is always lowercase.
|
|
|
|
If @var{device} is not a device but only a core architecture like
|
|
@samp{avr51}, this macro is not defined.
|
|
|
|
@item __AVR_DEVICE_NAME__
|
|
Setting @option{-mmcu=@var{device}} defines this built-in macro to
|
|
the device's name. For example, with @option{-mmcu=atmega8} the macro
|
|
is defined to @code{atmega8}.
|
|
|
|
If @var{device} is not a device but only a core architecture like
|
|
@samp{avr51}, this macro is not defined.
|
|
|
|
@item __AVR_XMEGA__
|
|
The device / architecture belongs to the XMEGA family of devices.
|
|
|
|
@item __AVR_HAVE_ELPM__
|
|
The device has the @code{ELPM} instruction.
|
|
|
|
@item __AVR_HAVE_ELPMX__
|
|
The device has the @code{ELPM R@var{n},Z} and @code{ELPM
|
|
R@var{n},Z+} instructions.
|
|
|
|
@item __AVR_HAVE_MOVW__
|
|
The device has the @code{MOVW} instruction to perform 16-bit
|
|
register-register moves.
|
|
|
|
@item __AVR_HAVE_LPMX__
|
|
The device has the @code{LPM R@var{n},Z} and
|
|
@code{LPM R@var{n},Z+} instructions.
|
|
|
|
@item __AVR_HAVE_MUL__
|
|
The device has a hardware multiplier.
|
|
|
|
@item __AVR_HAVE_JMP_CALL__
|
|
The device has the @code{JMP} and @code{CALL} instructions.
|
|
This is the case for devices with at least 16@tie{}KiB of program
|
|
memory.
|
|
|
|
@item __AVR_HAVE_EIJMP_EICALL__
|
|
@itemx __AVR_3_BYTE_PC__
|
|
The device has the @code{EIJMP} and @code{EICALL} instructions.
|
|
This is the case for devices with more than 128@tie{}KiB of program memory.
|
|
This also means that the program counter
|
|
(PC) is 3@tie{}bytes wide.
|
|
|
|
@item __AVR_2_BYTE_PC__
|
|
The program counter (PC) is 2@tie{}bytes wide. This is the case for devices
|
|
with up to 128@tie{}KiB of program memory.
|
|
|
|
@item __AVR_HAVE_8BIT_SP__
|
|
@itemx __AVR_HAVE_16BIT_SP__
|
|
The stack pointer (SP) register is treated as 8-bit respectively
|
|
16-bit register by the compiler.
|
|
The definition of these macros is affected by @option{-mtiny-stack}.
|
|
|
|
@item __AVR_HAVE_SPH__
|
|
@itemx __AVR_SP8__
|
|
The device has the SPH (high part of stack pointer) special function
|
|
register or has an 8-bit stack pointer, respectively.
|
|
The definition of these macros is affected by @option{-mmcu=} and
|
|
in the cases of @option{-mmcu=avr2} and @option{-mmcu=avr25} also
|
|
by @option{-msp8}.
|
|
|
|
@item __AVR_HAVE_RAMPD__
|
|
@itemx __AVR_HAVE_RAMPX__
|
|
@itemx __AVR_HAVE_RAMPY__
|
|
@itemx __AVR_HAVE_RAMPZ__
|
|
The device has the @code{RAMPD}, @code{RAMPX}, @code{RAMPY},
|
|
@code{RAMPZ} special function register, respectively.
|
|
|
|
@item __NO_INTERRUPTS__
|
|
This macro reflects the @option{-mno-interrupts} command-line option.
|
|
|
|
@item __AVR_ERRATA_SKIP__
|
|
@itemx __AVR_ERRATA_SKIP_JMP_CALL__
|
|
Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
|
|
instructions because of a hardware erratum. Skip instructions are
|
|
@code{SBRS}, @code{SBRC}, @code{SBIS}, @code{SBIC} and @code{CPSE}.
|
|
The second macro is only defined if @code{__AVR_HAVE_JMP_CALL__} is also
|
|
set.
|
|
|
|
@item __AVR_ISA_RMW__
|
|
The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT).
|
|
|
|
@item __AVR_SFR_OFFSET__=@var{offset}
|
|
Instructions that can address I/O special function registers directly
|
|
like @code{IN}, @code{OUT}, @code{SBI}, etc.@: may use a different
|
|
address as if addressed by an instruction to access RAM like @code{LD}
|
|
or @code{STS}. This offset depends on the device architecture and has
|
|
to be subtracted from the RAM address in order to get the
|
|
respective I/O@tie{}address.
|
|
|
|
@item __WITH_AVRLIBC__
|
|
The compiler is configured to be used together with AVR-Libc.
|
|
See the @option{--with-avrlibc} configure option.
|
|
|
|
@end table
|
|
|
|
@node Blackfin Options
|
|
@subsection Blackfin Options
|
|
@cindex Blackfin Options
|
|
|
|
@table @gcctabopt
|
|
@item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]}
|
|
@opindex mcpu=
|
|
Specifies the name of the target Blackfin processor. Currently, @var{cpu}
|
|
can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518},
|
|
@samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526},
|
|
@samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533},
|
|
@samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539},
|
|
@samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549},
|
|
@samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m},
|
|
@samp{bf561}, @samp{bf592}.
|
|
|
|
The optional @var{sirevision} specifies the silicon revision of the target
|
|
Blackfin processor. Any workarounds available for the targeted silicon revision
|
|
are enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled.
|
|
If @var{sirevision} is @samp{any}, all workarounds for the targeted processor
|
|
are enabled. The @code{__SILICON_REVISION__} macro is defined to two
|
|
hexadecimal digits representing the major and minor numbers in the silicon
|
|
revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__}
|
|
is not defined. If @var{sirevision} is @samp{any}, the
|
|
@code{__SILICON_REVISION__} is defined to be @code{0xffff}.
|
|
If this optional @var{sirevision} is not used, GCC assumes the latest known
|
|
silicon revision of the targeted Blackfin processor.
|
|
|
|
GCC defines a preprocessor macro for the specified @var{cpu}.
|
|
For the @samp{bfin-elf} toolchain, this option causes the hardware BSP
|
|
provided by libgloss to be linked in if @option{-msim} is not given.
|
|
|
|
Without this option, @samp{bf532} is used as the processor by default.
|
|
|
|
Note that support for @samp{bf561} is incomplete. For @samp{bf561},
|
|
only the preprocessor macro is defined.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Specifies that the program will be run on the simulator. This causes
|
|
the simulator BSP provided by libgloss to be linked in. This option
|
|
has effect only for @samp{bfin-elf} toolchain.
|
|
Certain other options, such as @option{-mid-shared-library} and
|
|
@option{-mfdpic}, imply @option{-msim}.
|
|
|
|
@item -momit-leaf-frame-pointer
|
|
@opindex momit-leaf-frame-pointer
|
|
Don't keep the frame pointer in a register for leaf functions. This
|
|
avoids the instructions to save, set up and restore frame pointers and
|
|
makes an extra register available in leaf functions. The option
|
|
@option{-fomit-frame-pointer} removes the frame pointer for all functions,
|
|
which might make debugging harder.
|
|
|
|
@item -mspecld-anomaly
|
|
@opindex mspecld-anomaly
|
|
When enabled, the compiler ensures that the generated code does not
|
|
contain speculative loads after jump instructions. If this option is used,
|
|
@code{__WORKAROUND_SPECULATIVE_LOADS} is defined.
|
|
|
|
@item -mno-specld-anomaly
|
|
@opindex mno-specld-anomaly
|
|
Don't generate extra code to prevent speculative loads from occurring.
|
|
|
|
@item -mcsync-anomaly
|
|
@opindex mcsync-anomaly
|
|
When enabled, the compiler ensures that the generated code does not
|
|
contain CSYNC or SSYNC instructions too soon after conditional branches.
|
|
If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined.
|
|
|
|
@item -mno-csync-anomaly
|
|
@opindex mno-csync-anomaly
|
|
Don't generate extra code to prevent CSYNC or SSYNC instructions from
|
|
occurring too soon after a conditional branch.
|
|
|
|
@item -mlow-64k
|
|
@opindex mlow-64k
|
|
When enabled, the compiler is free to take advantage of the knowledge that
|
|
the entire program fits into the low 64k of memory.
|
|
|
|
@item -mno-low-64k
|
|
@opindex mno-low-64k
|
|
Assume that the program is arbitrarily large. This is the default.
|
|
|
|
@item -mstack-check-l1
|
|
@opindex mstack-check-l1
|
|
Do stack checking using information placed into L1 scratchpad memory by the
|
|
uClinux kernel.
|
|
|
|
@item -mid-shared-library
|
|
@opindex mid-shared-library
|
|
Generate code that supports shared libraries via the library ID method.
|
|
This allows for execute in place and shared libraries in an environment
|
|
without virtual memory management. This option implies @option{-fPIC}.
|
|
With a @samp{bfin-elf} target, this option implies @option{-msim}.
|
|
|
|
@item -mno-id-shared-library
|
|
@opindex mno-id-shared-library
|
|
Generate code that doesn't assume ID-based shared libraries are being used.
|
|
This is the default.
|
|
|
|
@item -mleaf-id-shared-library
|
|
@opindex mleaf-id-shared-library
|
|
Generate code that supports shared libraries via the library ID method,
|
|
but assumes that this library or executable won't link against any other
|
|
ID shared libraries. That allows the compiler to use faster code for jumps
|
|
and calls.
|
|
|
|
@item -mno-leaf-id-shared-library
|
|
@opindex mno-leaf-id-shared-library
|
|
Do not assume that the code being compiled won't link against any ID shared
|
|
libraries. Slower code is generated for jump and call insns.
|
|
|
|
@item -mshared-library-id=n
|
|
@opindex mshared-library-id
|
|
Specifies the identification number of the ID-based shared library being
|
|
compiled. Specifying a value of 0 generates more compact code; specifying
|
|
other values forces the allocation of that number to the current
|
|
library but is no more space- or time-efficient than omitting this option.
|
|
|
|
@item -msep-data
|
|
@opindex msep-data
|
|
Generate code that allows the data segment to be located in a different
|
|
area of memory from the text segment. This allows for execute in place in
|
|
an environment without virtual memory management by eliminating relocations
|
|
against the text section.
|
|
|
|
@item -mno-sep-data
|
|
@opindex mno-sep-data
|
|
Generate code that assumes that the data segment follows the text segment.
|
|
This is the default.
|
|
|
|
@item -mlong-calls
|
|
@itemx -mno-long-calls
|
|
@opindex mlong-calls
|
|
@opindex mno-long-calls
|
|
Tells the compiler to perform function calls by first loading the
|
|
address of the function into a register and then performing a subroutine
|
|
call on this register. This switch is needed if the target function
|
|
lies outside of the 24-bit addressing range of the offset-based
|
|
version of subroutine call instruction.
|
|
|
|
This feature is not enabled by default. Specifying
|
|
@option{-mno-long-calls} restores the default behavior. Note these
|
|
switches have no effect on how the compiler generates code to handle
|
|
function calls via function pointers.
|
|
|
|
@item -mfast-fp
|
|
@opindex mfast-fp
|
|
Link with the fast floating-point library. This library relaxes some of
|
|
the IEEE floating-point standard's rules for checking inputs against
|
|
Not-a-Number (NAN), in the interest of performance.
|
|
|
|
@item -minline-plt
|
|
@opindex minline-plt
|
|
Enable inlining of PLT entries in function calls to functions that are
|
|
not known to bind locally. It has no effect without @option{-mfdpic}.
|
|
|
|
@item -mmulticore
|
|
@opindex mmulticore
|
|
Build a standalone application for multicore Blackfin processors.
|
|
This option causes proper start files and link scripts supporting
|
|
multicore to be used, and defines the macro @code{__BFIN_MULTICORE}.
|
|
It can only be used with @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}.
|
|
|
|
This option can be used with @option{-mcorea} or @option{-mcoreb}, which
|
|
selects the one-application-per-core programming model. Without
|
|
@option{-mcorea} or @option{-mcoreb}, the single-application/dual-core
|
|
programming model is used. In this model, the main function of Core B
|
|
should be named as @code{coreb_main}.
|
|
|
|
If this option is not used, the single-core application programming
|
|
model is used.
|
|
|
|
@item -mcorea
|
|
@opindex mcorea
|
|
Build a standalone application for Core A of BF561 when using
|
|
the one-application-per-core programming model. Proper start files
|
|
and link scripts are used to support Core A, and the macro
|
|
@code{__BFIN_COREA} is defined.
|
|
This option can only be used in conjunction with @option{-mmulticore}.
|
|
|
|
@item -mcoreb
|
|
@opindex mcoreb
|
|
Build a standalone application for Core B of BF561 when using
|
|
the one-application-per-core programming model. Proper start files
|
|
and link scripts are used to support Core B, and the macro
|
|
@code{__BFIN_COREB} is defined. When this option is used, @code{coreb_main}
|
|
should be used instead of @code{main}.
|
|
This option can only be used in conjunction with @option{-mmulticore}.
|
|
|
|
@item -msdram
|
|
@opindex msdram
|
|
Build a standalone application for SDRAM. Proper start files and
|
|
link scripts are used to put the application into SDRAM, and the macro
|
|
@code{__BFIN_SDRAM} is defined.
|
|
The loader should initialize SDRAM before loading the application.
|
|
|
|
@item -micplb
|
|
@opindex micplb
|
|
Assume that ICPLBs are enabled at run time. This has an effect on certain
|
|
anomaly workarounds. For Linux targets, the default is to assume ICPLBs
|
|
are enabled; for standalone applications the default is off.
|
|
@end table
|
|
|
|
@node C6X Options
|
|
@subsection C6X Options
|
|
@cindex C6X Options
|
|
|
|
@table @gcctabopt
|
|
@item -march=@var{name}
|
|
@opindex march
|
|
This specifies the name of the target architecture. GCC uses this
|
|
name to determine what kind of instructions it can emit when generating
|
|
assembly code. Permissible names are: @samp{c62x},
|
|
@samp{c64x}, @samp{c64x+}, @samp{c67x}, @samp{c67x+}, @samp{c674x}.
|
|
|
|
@item -mbig-endian
|
|
@opindex mbig-endian
|
|
Generate code for a big-endian target.
|
|
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
Generate code for a little-endian target. This is the default.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Choose startup files and linker script suitable for the simulator.
|
|
|
|
@item -msdata=default
|
|
@opindex msdata=default
|
|
Put small global and static data in the @code{.neardata} section,
|
|
which is pointed to by register @code{B14}. Put small uninitialized
|
|
global and static data in the @code{.bss} section, which is adjacent
|
|
to the @code{.neardata} section. Put small read-only data into the
|
|
@code{.rodata} section. The corresponding sections used for large
|
|
pieces of data are @code{.fardata}, @code{.far} and @code{.const}.
|
|
|
|
@item -msdata=all
|
|
@opindex msdata=all
|
|
Put all data, not just small objects, into the sections reserved for
|
|
small data, and use addressing relative to the @code{B14} register to
|
|
access them.
|
|
|
|
@item -msdata=none
|
|
@opindex msdata=none
|
|
Make no use of the sections reserved for small data, and use absolute
|
|
addresses to access all data. Put all initialized global and static
|
|
data in the @code{.fardata} section, and all uninitialized data in the
|
|
@code{.far} section. Put all constant data into the @code{.const}
|
|
section.
|
|
@end table
|
|
|
|
@node CRIS Options
|
|
@subsection CRIS Options
|
|
@cindex CRIS Options
|
|
|
|
These options are defined specifically for the CRIS ports.
|
|
|
|
@table @gcctabopt
|
|
@item -march=@var{architecture-type}
|
|
@itemx -mcpu=@var{architecture-type}
|
|
@opindex march
|
|
@opindex mcpu
|
|
Generate code for the specified architecture. The choices for
|
|
@var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for
|
|
respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@.
|
|
Default is @samp{v0} except for cris-axis-linux-gnu, where the default is
|
|
@samp{v10}.
|
|
|
|
@item -mtune=@var{architecture-type}
|
|
@opindex mtune
|
|
Tune to @var{architecture-type} everything applicable about the generated
|
|
code, except for the ABI and the set of available instructions. The
|
|
choices for @var{architecture-type} are the same as for
|
|
@option{-march=@var{architecture-type}}.
|
|
|
|
@item -mmax-stack-frame=@var{n}
|
|
@opindex mmax-stack-frame
|
|
Warn when the stack frame of a function exceeds @var{n} bytes.
|
|
|
|
@item -metrax4
|
|
@itemx -metrax100
|
|
@opindex metrax4
|
|
@opindex metrax100
|
|
The options @option{-metrax4} and @option{-metrax100} are synonyms for
|
|
@option{-march=v3} and @option{-march=v8} respectively.
|
|
|
|
@item -mmul-bug-workaround
|
|
@itemx -mno-mul-bug-workaround
|
|
@opindex mmul-bug-workaround
|
|
@opindex mno-mul-bug-workaround
|
|
Work around a bug in the @code{muls} and @code{mulu} instructions for CPU
|
|
models where it applies. This option is active by default.
|
|
|
|
@item -mpdebug
|
|
@opindex mpdebug
|
|
Enable CRIS-specific verbose debug-related information in the assembly
|
|
code. This option also has the effect of turning off the @samp{#NO_APP}
|
|
formatted-code indicator to the assembler at the beginning of the
|
|
assembly file.
|
|
|
|
@item -mcc-init
|
|
@opindex mcc-init
|
|
Do not use condition-code results from previous instruction; always emit
|
|
compare and test instructions before use of condition codes.
|
|
|
|
@item -mno-side-effects
|
|
@opindex mno-side-effects
|
|
Do not emit instructions with side effects in addressing modes other than
|
|
post-increment.
|
|
|
|
@item -mstack-align
|
|
@itemx -mno-stack-align
|
|
@itemx -mdata-align
|
|
@itemx -mno-data-align
|
|
@itemx -mconst-align
|
|
@itemx -mno-const-align
|
|
@opindex mstack-align
|
|
@opindex mno-stack-align
|
|
@opindex mdata-align
|
|
@opindex mno-data-align
|
|
@opindex mconst-align
|
|
@opindex mno-const-align
|
|
These options (@samp{no-} options) arrange (eliminate arrangements) for the
|
|
stack frame, individual data and constants to be aligned for the maximum
|
|
single data access size for the chosen CPU model. The default is to
|
|
arrange for 32-bit alignment. ABI details such as structure layout are
|
|
not affected by these options.
|
|
|
|
@item -m32-bit
|
|
@itemx -m16-bit
|
|
@itemx -m8-bit
|
|
@opindex m32-bit
|
|
@opindex m16-bit
|
|
@opindex m8-bit
|
|
Similar to the stack- data- and const-align options above, these options
|
|
arrange for stack frame, writable data and constants to all be 32-bit,
|
|
16-bit or 8-bit aligned. The default is 32-bit alignment.
|
|
|
|
@item -mno-prologue-epilogue
|
|
@itemx -mprologue-epilogue
|
|
@opindex mno-prologue-epilogue
|
|
@opindex mprologue-epilogue
|
|
With @option{-mno-prologue-epilogue}, the normal function prologue and
|
|
epilogue which set up the stack frame are omitted and no return
|
|
instructions or return sequences are generated in the code. Use this
|
|
option only together with visual inspection of the compiled code: no
|
|
warnings or errors are generated when call-saved registers must be saved,
|
|
or storage for local variables needs to be allocated.
|
|
|
|
@item -mno-gotplt
|
|
@itemx -mgotplt
|
|
@opindex mno-gotplt
|
|
@opindex mgotplt
|
|
With @option{-fpic} and @option{-fPIC}, don't generate (do generate)
|
|
instruction sequences that load addresses for functions from the PLT part
|
|
of the GOT rather than (traditional on other architectures) calls to the
|
|
PLT@. The default is @option{-mgotplt}.
|
|
|
|
@item -melf
|
|
@opindex melf
|
|
Legacy no-op option only recognized with the cris-axis-elf and
|
|
cris-axis-linux-gnu targets.
|
|
|
|
@item -mlinux
|
|
@opindex mlinux
|
|
Legacy no-op option only recognized with the cris-axis-linux-gnu target.
|
|
|
|
@item -sim
|
|
@opindex sim
|
|
This option, recognized for the cris-axis-elf, arranges
|
|
to link with input-output functions from a simulator library. Code,
|
|
initialized data and zero-initialized data are allocated consecutively.
|
|
|
|
@item -sim2
|
|
@opindex sim2
|
|
Like @option{-sim}, but pass linker options to locate initialized data at
|
|
0x40000000 and zero-initialized data at 0x80000000.
|
|
@end table
|
|
|
|
@node CR16 Options
|
|
@subsection CR16 Options
|
|
@cindex CR16 Options
|
|
|
|
These options are defined specifically for the CR16 ports.
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mmac
|
|
@opindex mmac
|
|
Enable the use of multiply-accumulate instructions. Disabled by default.
|
|
|
|
@item -mcr16cplus
|
|
@itemx -mcr16c
|
|
@opindex mcr16cplus
|
|
@opindex mcr16c
|
|
Generate code for CR16C or CR16C+ architecture. CR16C+ architecture
|
|
is default.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Links the library libsim.a which is in compatible with simulator. Applicable
|
|
to ELF compiler only.
|
|
|
|
@item -mint32
|
|
@opindex mint32
|
|
Choose integer type as 32-bit wide.
|
|
|
|
@item -mbit-ops
|
|
@opindex mbit-ops
|
|
Generates @code{sbit}/@code{cbit} instructions for bit manipulations.
|
|
|
|
@item -mdata-model=@var{model}
|
|
@opindex mdata-model
|
|
Choose a data model. The choices for @var{model} are @samp{near},
|
|
@samp{far} or @samp{medium}. @samp{medium} is default.
|
|
However, @samp{far} is not valid with @option{-mcr16c}, as the
|
|
CR16C architecture does not support the far data model.
|
|
@end table
|
|
|
|
@node Darwin Options
|
|
@subsection Darwin Options
|
|
@cindex Darwin options
|
|
|
|
These options are defined for all architectures running the Darwin operating
|
|
system.
|
|
|
|
FSF GCC on Darwin does not create ``fat'' object files; it creates
|
|
an object file for the single architecture that GCC was built to
|
|
target. Apple's GCC on Darwin does create ``fat'' files if multiple
|
|
@option{-arch} options are used; it does so by running the compiler or
|
|
linker multiple times and joining the results together with
|
|
@file{lipo}.
|
|
|
|
The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or
|
|
@samp{i686}) is determined by the flags that specify the ISA
|
|
that GCC is targeting, like @option{-mcpu} or @option{-march}. The
|
|
@option{-force_cpusubtype_ALL} option can be used to override this.
|
|
|
|
The Darwin tools vary in their behavior when presented with an ISA
|
|
mismatch. The assembler, @file{as}, only permits instructions to
|
|
be used that are valid for the subtype of the file it is generating,
|
|
so you cannot put 64-bit instructions in a @samp{ppc750} object file.
|
|
The linker for shared libraries, @file{/usr/bin/libtool}, fails
|
|
and prints an error if asked to create a shared library with a less
|
|
restrictive subtype than its input files (for instance, trying to put
|
|
a @samp{ppc970} object file in a @samp{ppc7400} library). The linker
|
|
for executables, @command{ld}, quietly gives the executable the most
|
|
restrictive subtype of any of its input files.
|
|
|
|
@table @gcctabopt
|
|
@item -F@var{dir}
|
|
@opindex F
|
|
Add the framework directory @var{dir} to the head of the list of
|
|
directories to be searched for header files. These directories are
|
|
interleaved with those specified by @option{-I} options and are
|
|
scanned in a left-to-right order.
|
|
|
|
A framework directory is a directory with frameworks in it. A
|
|
framework is a directory with a @file{Headers} and/or
|
|
@file{PrivateHeaders} directory contained directly in it that ends
|
|
in @file{.framework}. The name of a framework is the name of this
|
|
directory excluding the @file{.framework}. Headers associated with
|
|
the framework are found in one of those two directories, with
|
|
@file{Headers} being searched first. A subframework is a framework
|
|
directory that is in a framework's @file{Frameworks} directory.
|
|
Includes of subframework headers can only appear in a header of a
|
|
framework that contains the subframework, or in a sibling subframework
|
|
header. Two subframeworks are siblings if they occur in the same
|
|
framework. A subframework should not have the same name as a
|
|
framework; a warning is issued if this is violated. Currently a
|
|
subframework cannot have subframeworks; in the future, the mechanism
|
|
may be extended to support this. The standard frameworks can be found
|
|
in @file{/System/Library/Frameworks} and
|
|
@file{/Library/Frameworks}. An example include looks like
|
|
@code{#include <Framework/header.h>}, where @file{Framework} denotes
|
|
the name of the framework and @file{header.h} is found in the
|
|
@file{PrivateHeaders} or @file{Headers} directory.
|
|
|
|
@item -iframework@var{dir}
|
|
@opindex iframework
|
|
Like @option{-F} except the directory is a treated as a system
|
|
directory. The main difference between this @option{-iframework} and
|
|
@option{-F} is that with @option{-iframework} the compiler does not
|
|
warn about constructs contained within header files found via
|
|
@var{dir}. This option is valid only for the C family of languages.
|
|
|
|
@item -gused
|
|
@opindex gused
|
|
Emit debugging information for symbols that are used. For stabs
|
|
debugging format, this enables @option{-feliminate-unused-debug-symbols}.
|
|
This is by default ON@.
|
|
|
|
@item -gfull
|
|
@opindex gfull
|
|
Emit debugging information for all symbols and types.
|
|
|
|
@item -mmacosx-version-min=@var{version}
|
|
The earliest version of MacOS X that this executable will run on
|
|
is @var{version}. Typical values of @var{version} include @code{10.1},
|
|
@code{10.2}, and @code{10.3.9}.
|
|
|
|
If the compiler was built to use the system's headers by default,
|
|
then the default for this option is the system version on which the
|
|
compiler is running, otherwise the default is to make choices that
|
|
are compatible with as many systems and code bases as possible.
|
|
|
|
@item -mkernel
|
|
@opindex mkernel
|
|
Enable kernel development mode. The @option{-mkernel} option sets
|
|
@option{-static}, @option{-fno-common}, @option{-fno-use-cxa-atexit},
|
|
@option{-fno-exceptions}, @option{-fno-non-call-exceptions},
|
|
@option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where
|
|
applicable. This mode also sets @option{-mno-altivec},
|
|
@option{-msoft-float}, @option{-fno-builtin} and
|
|
@option{-mlong-branch} for PowerPC targets.
|
|
|
|
@item -mone-byte-bool
|
|
@opindex mone-byte-bool
|
|
Override the defaults for @code{bool} so that @code{sizeof(bool)==1}.
|
|
By default @code{sizeof(bool)} is @code{4} when compiling for
|
|
Darwin/PowerPC and @code{1} when compiling for Darwin/x86, so this
|
|
option has no effect on x86.
|
|
|
|
@strong{Warning:} The @option{-mone-byte-bool} switch causes GCC
|
|
to generate code that is not binary compatible with code generated
|
|
without that switch. Using this switch may require recompiling all
|
|
other modules in a program, including system libraries. Use this
|
|
switch to conform to a non-default data model.
|
|
|
|
@item -mfix-and-continue
|
|
@itemx -ffix-and-continue
|
|
@itemx -findirect-data
|
|
@opindex mfix-and-continue
|
|
@opindex ffix-and-continue
|
|
@opindex findirect-data
|
|
Generate code suitable for fast turnaround development, such as to
|
|
allow GDB to dynamically load @file{.o} files into already-running
|
|
programs. @option{-findirect-data} and @option{-ffix-and-continue}
|
|
are provided for backwards compatibility.
|
|
|
|
@item -all_load
|
|
@opindex all_load
|
|
Loads all members of static archive libraries.
|
|
See man ld(1) for more information.
|
|
|
|
@item -arch_errors_fatal
|
|
@opindex arch_errors_fatal
|
|
Cause the errors having to do with files that have the wrong architecture
|
|
to be fatal.
|
|
|
|
@item -bind_at_load
|
|
@opindex bind_at_load
|
|
Causes the output file to be marked such that the dynamic linker will
|
|
bind all undefined references when the file is loaded or launched.
|
|
|
|
@item -bundle
|
|
@opindex bundle
|
|
Produce a Mach-o bundle format file.
|
|
See man ld(1) for more information.
|
|
|
|
@item -bundle_loader @var{executable}
|
|
@opindex bundle_loader
|
|
This option specifies the @var{executable} that will load the build
|
|
output file being linked. See man ld(1) for more information.
|
|
|
|
@item -dynamiclib
|
|
@opindex dynamiclib
|
|
When passed this option, GCC produces a dynamic library instead of
|
|
an executable when linking, using the Darwin @file{libtool} command.
|
|
|
|
@item -force_cpusubtype_ALL
|
|
@opindex force_cpusubtype_ALL
|
|
This causes GCC's output file to have the @samp{ALL} subtype, instead of
|
|
one controlled by the @option{-mcpu} or @option{-march} option.
|
|
|
|
@item -allowable_client @var{client_name}
|
|
@itemx -client_name
|
|
@itemx -compatibility_version
|
|
@itemx -current_version
|
|
@itemx -dead_strip
|
|
@itemx -dependency-file
|
|
@itemx -dylib_file
|
|
@itemx -dylinker_install_name
|
|
@itemx -dynamic
|
|
@itemx -exported_symbols_list
|
|
@itemx -filelist
|
|
@need 800
|
|
@itemx -flat_namespace
|
|
@itemx -force_flat_namespace
|
|
@itemx -headerpad_max_install_names
|
|
@itemx -image_base
|
|
@itemx -init
|
|
@itemx -install_name
|
|
@itemx -keep_private_externs
|
|
@itemx -multi_module
|
|
@itemx -multiply_defined
|
|
@itemx -multiply_defined_unused
|
|
@need 800
|
|
@itemx -noall_load
|
|
@itemx -no_dead_strip_inits_and_terms
|
|
@itemx -nofixprebinding
|
|
@itemx -nomultidefs
|
|
@itemx -noprebind
|
|
@itemx -noseglinkedit
|
|
@itemx -pagezero_size
|
|
@itemx -prebind
|
|
@itemx -prebind_all_twolevel_modules
|
|
@itemx -private_bundle
|
|
@need 800
|
|
@itemx -read_only_relocs
|
|
@itemx -sectalign
|
|
@itemx -sectobjectsymbols
|
|
@itemx -whyload
|
|
@itemx -seg1addr
|
|
@itemx -sectcreate
|
|
@itemx -sectobjectsymbols
|
|
@itemx -sectorder
|
|
@itemx -segaddr
|
|
@itemx -segs_read_only_addr
|
|
@need 800
|
|
@itemx -segs_read_write_addr
|
|
@itemx -seg_addr_table
|
|
@itemx -seg_addr_table_filename
|
|
@itemx -seglinkedit
|
|
@itemx -segprot
|
|
@itemx -segs_read_only_addr
|
|
@itemx -segs_read_write_addr
|
|
@itemx -single_module
|
|
@itemx -static
|
|
@itemx -sub_library
|
|
@need 800
|
|
@itemx -sub_umbrella
|
|
@itemx -twolevel_namespace
|
|
@itemx -umbrella
|
|
@itemx -undefined
|
|
@itemx -unexported_symbols_list
|
|
@itemx -weak_reference_mismatches
|
|
@itemx -whatsloaded
|
|
@opindex allowable_client
|
|
@opindex client_name
|
|
@opindex compatibility_version
|
|
@opindex current_version
|
|
@opindex dead_strip
|
|
@opindex dependency-file
|
|
@opindex dylib_file
|
|
@opindex dylinker_install_name
|
|
@opindex dynamic
|
|
@opindex exported_symbols_list
|
|
@opindex filelist
|
|
@opindex flat_namespace
|
|
@opindex force_flat_namespace
|
|
@opindex headerpad_max_install_names
|
|
@opindex image_base
|
|
@opindex init
|
|
@opindex install_name
|
|
@opindex keep_private_externs
|
|
@opindex multi_module
|
|
@opindex multiply_defined
|
|
@opindex multiply_defined_unused
|
|
@opindex noall_load
|
|
@opindex no_dead_strip_inits_and_terms
|
|
@opindex nofixprebinding
|
|
@opindex nomultidefs
|
|
@opindex noprebind
|
|
@opindex noseglinkedit
|
|
@opindex pagezero_size
|
|
@opindex prebind
|
|
@opindex prebind_all_twolevel_modules
|
|
@opindex private_bundle
|
|
@opindex read_only_relocs
|
|
@opindex sectalign
|
|
@opindex sectobjectsymbols
|
|
@opindex whyload
|
|
@opindex seg1addr
|
|
@opindex sectcreate
|
|
@opindex sectobjectsymbols
|
|
@opindex sectorder
|
|
@opindex segaddr
|
|
@opindex segs_read_only_addr
|
|
@opindex segs_read_write_addr
|
|
@opindex seg_addr_table
|
|
@opindex seg_addr_table_filename
|
|
@opindex seglinkedit
|
|
@opindex segprot
|
|
@opindex segs_read_only_addr
|
|
@opindex segs_read_write_addr
|
|
@opindex single_module
|
|
@opindex static
|
|
@opindex sub_library
|
|
@opindex sub_umbrella
|
|
@opindex twolevel_namespace
|
|
@opindex umbrella
|
|
@opindex undefined
|
|
@opindex unexported_symbols_list
|
|
@opindex weak_reference_mismatches
|
|
@opindex whatsloaded
|
|
These options are passed to the Darwin linker. The Darwin linker man page
|
|
describes them in detail.
|
|
@end table
|
|
|
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@node DEC Alpha Options
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@subsection DEC Alpha Options
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These @samp{-m} options are defined for the DEC Alpha implementations:
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@table @gcctabopt
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@item -mno-soft-float
|
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@itemx -msoft-float
|
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@opindex mno-soft-float
|
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@opindex msoft-float
|
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Use (do not use) the hardware floating-point instructions for
|
|
floating-point operations. When @option{-msoft-float} is specified,
|
|
functions in @file{libgcc.a} are used to perform floating-point
|
|
operations. Unless they are replaced by routines that emulate the
|
|
floating-point operations, or compiled in such a way as to call such
|
|
emulations routines, these routines issue floating-point
|
|
operations. If you are compiling for an Alpha without floating-point
|
|
operations, you must ensure that the library is built so as not to call
|
|
them.
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|
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Note that Alpha implementations without floating-point operations are
|
|
required to have floating-point registers.
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|
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@item -mfp-reg
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@itemx -mno-fp-regs
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@opindex mfp-reg
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@opindex mno-fp-regs
|
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Generate code that uses (does not use) the floating-point register set.
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@option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point
|
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register set is not used, floating-point operands are passed in integer
|
|
registers as if they were integers and floating-point results are passed
|
|
in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence,
|
|
so any function with a floating-point argument or return value called by code
|
|
compiled with @option{-mno-fp-regs} must also be compiled with that
|
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option.
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A typical use of this option is building a kernel that does not use,
|
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and hence need not save and restore, any floating-point registers.
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@item -mieee
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@opindex mieee
|
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The Alpha architecture implements floating-point hardware optimized for
|
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maximum performance. It is mostly compliant with the IEEE floating-point
|
|
standard. However, for full compliance, software assistance is
|
|
required. This option generates code fully IEEE-compliant code
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@emph{except} that the @var{inexact-flag} is not maintained (see below).
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If this option is turned on, the preprocessor macro @code{_IEEE_FP} is
|
|
defined during compilation. The resulting code is less efficient but is
|
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able to correctly support denormalized numbers and exceptional IEEE
|
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values such as not-a-number and plus/minus infinity. Other Alpha
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compilers call this option @option{-ieee_with_no_inexact}.
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@item -mieee-with-inexact
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@opindex mieee-with-inexact
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This is like @option{-mieee} except the generated code also maintains
|
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the IEEE @var{inexact-flag}. Turning on this option causes the
|
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generated code to implement fully-compliant IEEE math. In addition to
|
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@code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor
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|
macro. On some Alpha implementations the resulting code may execute
|
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significantly slower than the code generated by default. Since there is
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very little code that depends on the @var{inexact-flag}, you should
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normally not specify this option. Other Alpha compilers call this
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option @option{-ieee_with_inexact}.
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@item -mfp-trap-mode=@var{trap-mode}
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@opindex mfp-trap-mode
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This option controls what floating-point related traps are enabled.
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Other Alpha compilers call this option @option{-fptm @var{trap-mode}}.
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The trap mode can be set to one of four values:
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@table @samp
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@item n
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This is the default (normal) setting. The only traps that are enabled
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are the ones that cannot be disabled in software (e.g., division by zero
|
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trap).
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@item u
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In addition to the traps enabled by @samp{n}, underflow traps are enabled
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as well.
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@item su
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Like @samp{u}, but the instructions are marked to be safe for software
|
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completion (see Alpha architecture manual for details).
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|
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@item sui
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Like @samp{su}, but inexact traps are enabled as well.
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@end table
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|
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@item -mfp-rounding-mode=@var{rounding-mode}
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@opindex mfp-rounding-mode
|
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Selects the IEEE rounding mode. Other Alpha compilers call this option
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@option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one
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of:
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@table @samp
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@item n
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Normal IEEE rounding mode. Floating-point numbers are rounded towards
|
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the nearest machine number or towards the even machine number in case
|
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of a tie.
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@item m
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Round towards minus infinity.
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@item c
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Chopped rounding mode. Floating-point numbers are rounded towards zero.
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|
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@item d
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Dynamic rounding mode. A field in the floating-point control register
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(@var{fpcr}, see Alpha architecture reference manual) controls the
|
|
rounding mode in effect. The C library initializes this register for
|
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rounding towards plus infinity. Thus, unless your program modifies the
|
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@var{fpcr}, @samp{d} corresponds to round towards plus infinity.
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@end table
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|
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@item -mtrap-precision=@var{trap-precision}
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@opindex mtrap-precision
|
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In the Alpha architecture, floating-point traps are imprecise. This
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means without software assistance it is impossible to recover from a
|
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floating trap and program execution normally needs to be terminated.
|
|
GCC can generate code that can assist operating system trap handlers
|
|
in determining the exact location that caused a floating-point trap.
|
|
Depending on the requirements of an application, different levels of
|
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precisions can be selected:
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|
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@table @samp
|
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@item p
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Program precision. This option is the default and means a trap handler
|
|
can only identify which program caused a floating-point exception.
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@item f
|
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Function precision. The trap handler can determine the function that
|
|
caused a floating-point exception.
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|
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@item i
|
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Instruction precision. The trap handler can determine the exact
|
|
instruction that caused a floating-point exception.
|
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@end table
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|
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Other Alpha compilers provide the equivalent options called
|
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@option{-scope_safe} and @option{-resumption_safe}.
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|
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@item -mieee-conformant
|
|
@opindex mieee-conformant
|
|
This option marks the generated code as IEEE conformant. You must not
|
|
use this option unless you also specify @option{-mtrap-precision=i} and either
|
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@option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect
|
|
is to emit the line @samp{.eflag 48} in the function prologue of the
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generated assembly file.
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|
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@item -mbuild-constants
|
|
@opindex mbuild-constants
|
|
Normally GCC examines a 32- or 64-bit integer constant to
|
|
see if it can construct it from smaller constants in two or three
|
|
instructions. If it cannot, it outputs the constant as a literal and
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|
generates code to load it from the data segment at run time.
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|
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Use this option to require GCC to construct @emph{all} integer constants
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|
using code, even if it takes more instructions (the maximum is six).
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You typically use this option to build a shared library dynamic
|
|
loader. Itself a shared library, it must relocate itself in memory
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|
before it can find the variables and constants in its own data segment.
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@item -mbwx
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@itemx -mno-bwx
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@itemx -mcix
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@itemx -mno-cix
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@itemx -mfix
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@itemx -mno-fix
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|
@itemx -mmax
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|
@itemx -mno-max
|
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@opindex mbwx
|
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@opindex mno-bwx
|
|
@opindex mcix
|
|
@opindex mno-cix
|
|
@opindex mfix
|
|
@opindex mno-fix
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|
@opindex mmax
|
|
@opindex mno-max
|
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Indicate whether GCC should generate code to use the optional BWX,
|
|
CIX, FIX and MAX instruction sets. The default is to use the instruction
|
|
sets supported by the CPU type specified via @option{-mcpu=} option or that
|
|
of the CPU on which GCC was built if none is specified.
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|
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@item -mfloat-vax
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|
@itemx -mfloat-ieee
|
|
@opindex mfloat-vax
|
|
@opindex mfloat-ieee
|
|
Generate code that uses (does not use) VAX F and G floating-point
|
|
arithmetic instead of IEEE single and double precision.
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|
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@item -mexplicit-relocs
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|
@itemx -mno-explicit-relocs
|
|
@opindex mexplicit-relocs
|
|
@opindex mno-explicit-relocs
|
|
Older Alpha assemblers provided no way to generate symbol relocations
|
|
except via assembler macros. Use of these macros does not allow
|
|
optimal instruction scheduling. GNU binutils as of version 2.12
|
|
supports a new syntax that allows the compiler to explicitly mark
|
|
which relocations should apply to which instructions. This option
|
|
is mostly useful for debugging, as GCC detects the capabilities of
|
|
the assembler when it is built and sets the default accordingly.
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|
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@item -msmall-data
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|
@itemx -mlarge-data
|
|
@opindex msmall-data
|
|
@opindex mlarge-data
|
|
When @option{-mexplicit-relocs} is in effect, static data is
|
|
accessed via @dfn{gp-relative} relocations. When @option{-msmall-data}
|
|
is used, objects 8 bytes long or smaller are placed in a @dfn{small data area}
|
|
(the @code{.sdata} and @code{.sbss} sections) and are accessed via
|
|
16-bit relocations off of the @code{$gp} register. This limits the
|
|
size of the small data area to 64KB, but allows the variables to be
|
|
directly accessed via a single instruction.
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|
|
The default is @option{-mlarge-data}. With this option the data area
|
|
is limited to just below 2GB@. Programs that require more than 2GB of
|
|
data must use @code{malloc} or @code{mmap} to allocate the data in the
|
|
heap instead of in the program's data segment.
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|
|
When generating code for shared libraries, @option{-fpic} implies
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@option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}.
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|
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@item -msmall-text
|
|
@itemx -mlarge-text
|
|
@opindex msmall-text
|
|
@opindex mlarge-text
|
|
When @option{-msmall-text} is used, the compiler assumes that the
|
|
code of the entire program (or shared library) fits in 4MB, and is
|
|
thus reachable with a branch instruction. When @option{-msmall-data}
|
|
is used, the compiler can assume that all local symbols share the
|
|
same @code{$gp} value, and thus reduce the number of instructions
|
|
required for a function call from 4 to 1.
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|
|
The default is @option{-mlarge-text}.
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|
|
@item -mcpu=@var{cpu_type}
|
|
@opindex mcpu
|
|
Set the instruction set and instruction scheduling parameters for
|
|
machine type @var{cpu_type}. You can specify either the @samp{EV}
|
|
style name or the corresponding chip number. GCC supports scheduling
|
|
parameters for the EV4, EV5 and EV6 family of processors and
|
|
chooses the default values for the instruction set from the processor
|
|
you specify. If you do not specify a processor type, GCC defaults
|
|
to the processor on which the compiler was built.
|
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|
|
Supported values for @var{cpu_type} are
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|
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@table @samp
|
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@item ev4
|
|
@itemx ev45
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|
@itemx 21064
|
|
Schedules as an EV4 and has no instruction set extensions.
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|
|
@item ev5
|
|
@itemx 21164
|
|
Schedules as an EV5 and has no instruction set extensions.
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|
|
@item ev56
|
|
@itemx 21164a
|
|
Schedules as an EV5 and supports the BWX extension.
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|
|
@item pca56
|
|
@itemx 21164pc
|
|
@itemx 21164PC
|
|
Schedules as an EV5 and supports the BWX and MAX extensions.
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|
|
@item ev6
|
|
@itemx 21264
|
|
Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
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|
|
@item ev67
|
|
@itemx 21264a
|
|
Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
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|
@end table
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|
|
Native toolchains also support the value @samp{native},
|
|
which selects the best architecture option for the host processor.
|
|
@option{-mcpu=native} has no effect if GCC does not recognize
|
|
the processor.
|
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|
|
@item -mtune=@var{cpu_type}
|
|
@opindex mtune
|
|
Set only the instruction scheduling parameters for machine type
|
|
@var{cpu_type}. The instruction set is not changed.
|
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|
|
Native toolchains also support the value @samp{native},
|
|
which selects the best architecture option for the host processor.
|
|
@option{-mtune=native} has no effect if GCC does not recognize
|
|
the processor.
|
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|
|
@item -mmemory-latency=@var{time}
|
|
@opindex mmemory-latency
|
|
Sets the latency the scheduler should assume for typical memory
|
|
references as seen by the application. This number is highly
|
|
dependent on the memory access patterns used by the application
|
|
and the size of the external cache on the machine.
|
|
|
|
Valid options for @var{time} are
|
|
|
|
@table @samp
|
|
@item @var{number}
|
|
A decimal number representing clock cycles.
|
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|
|
@item L1
|
|
@itemx L2
|
|
@itemx L3
|
|
@itemx main
|
|
The compiler contains estimates of the number of clock cycles for
|
|
``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches
|
|
(also called Dcache, Scache, and Bcache), as well as to main memory.
|
|
Note that L3 is only valid for EV5.
|
|
|
|
@end table
|
|
@end table
|
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|
|
@node FR30 Options
|
|
@subsection FR30 Options
|
|
@cindex FR30 Options
|
|
|
|
These options are defined specifically for the FR30 port.
|
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|
|
@table @gcctabopt
|
|
|
|
@item -msmall-model
|
|
@opindex msmall-model
|
|
Use the small address space model. This can produce smaller code, but
|
|
it does assume that all symbolic values and addresses fit into a
|
|
20-bit range.
|
|
|
|
@item -mno-lsim
|
|
@opindex mno-lsim
|
|
Assume that runtime support has been provided and so there is no need
|
|
to include the simulator library (@file{libsim.a}) on the linker
|
|
command line.
|
|
|
|
@end table
|
|
|
|
@node FT32 Options
|
|
@subsection FT32 Options
|
|
@cindex FT32 Options
|
|
|
|
These options are defined specifically for the FT32 port.
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Specifies that the program will be run on the simulator. This causes
|
|
an alternate runtime startup and library to be linked.
|
|
You must not use this option when generating programs that will run on
|
|
real hardware; you must provide your own runtime library for whatever
|
|
I/O functions are needed.
|
|
|
|
@item -mlra
|
|
@opindex mlra
|
|
Enable Local Register Allocation. This is still experimental for FT32,
|
|
so by default the compiler uses standard reload.
|
|
|
|
@item -mnodiv
|
|
@opindex mnodiv
|
|
Do not use div and mod instructions.
|
|
|
|
@end table
|
|
|
|
@node FRV Options
|
|
@subsection FRV Options
|
|
@cindex FRV Options
|
|
|
|
@table @gcctabopt
|
|
@item -mgpr-32
|
|
@opindex mgpr-32
|
|
|
|
Only use the first 32 general-purpose registers.
|
|
|
|
@item -mgpr-64
|
|
@opindex mgpr-64
|
|
|
|
Use all 64 general-purpose registers.
|
|
|
|
@item -mfpr-32
|
|
@opindex mfpr-32
|
|
|
|
Use only the first 32 floating-point registers.
|
|
|
|
@item -mfpr-64
|
|
@opindex mfpr-64
|
|
|
|
Use all 64 floating-point registers.
|
|
|
|
@item -mhard-float
|
|
@opindex mhard-float
|
|
|
|
Use hardware instructions for floating-point operations.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
|
|
Use library routines for floating-point operations.
|
|
|
|
@item -malloc-cc
|
|
@opindex malloc-cc
|
|
|
|
Dynamically allocate condition code registers.
|
|
|
|
@item -mfixed-cc
|
|
@opindex mfixed-cc
|
|
|
|
Do not try to dynamically allocate condition code registers, only
|
|
use @code{icc0} and @code{fcc0}.
|
|
|
|
@item -mdword
|
|
@opindex mdword
|
|
|
|
Change ABI to use double word insns.
|
|
|
|
@item -mno-dword
|
|
@opindex mno-dword
|
|
|
|
Do not use double word instructions.
|
|
|
|
@item -mdouble
|
|
@opindex mdouble
|
|
|
|
Use floating-point double instructions.
|
|
|
|
@item -mno-double
|
|
@opindex mno-double
|
|
|
|
Do not use floating-point double instructions.
|
|
|
|
@item -mmedia
|
|
@opindex mmedia
|
|
|
|
Use media instructions.
|
|
|
|
@item -mno-media
|
|
@opindex mno-media
|
|
|
|
Do not use media instructions.
|
|
|
|
@item -mmuladd
|
|
@opindex mmuladd
|
|
|
|
Use multiply and add/subtract instructions.
|
|
|
|
@item -mno-muladd
|
|
@opindex mno-muladd
|
|
|
|
Do not use multiply and add/subtract instructions.
|
|
|
|
@item -mfdpic
|
|
@opindex mfdpic
|
|
|
|
Select the FDPIC ABI, which uses function descriptors to represent
|
|
pointers to functions. Without any PIC/PIE-related options, it
|
|
implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it
|
|
assumes GOT entries and small data are within a 12-bit range from the
|
|
GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets
|
|
are computed with 32 bits.
|
|
With a @samp{bfin-elf} target, this option implies @option{-msim}.
|
|
|
|
@item -minline-plt
|
|
@opindex minline-plt
|
|
|
|
Enable inlining of PLT entries in function calls to functions that are
|
|
not known to bind locally. It has no effect without @option{-mfdpic}.
|
|
It's enabled by default if optimizing for speed and compiling for
|
|
shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an
|
|
optimization option such as @option{-O3} or above is present in the
|
|
command line.
|
|
|
|
@item -mTLS
|
|
@opindex mTLS
|
|
|
|
Assume a large TLS segment when generating thread-local code.
|
|
|
|
@item -mtls
|
|
@opindex mtls
|
|
|
|
Do not assume a large TLS segment when generating thread-local code.
|
|
|
|
@item -mgprel-ro
|
|
@opindex mgprel-ro
|
|
|
|
Enable the use of @code{GPREL} relocations in the FDPIC ABI for data
|
|
that is known to be in read-only sections. It's enabled by default,
|
|
except for @option{-fpic} or @option{-fpie}: even though it may help
|
|
make the global offset table smaller, it trades 1 instruction for 4.
|
|
With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4,
|
|
one of which may be shared by multiple symbols, and it avoids the need
|
|
for a GOT entry for the referenced symbol, so it's more likely to be a
|
|
win. If it is not, @option{-mno-gprel-ro} can be used to disable it.
|
|
|
|
@item -multilib-library-pic
|
|
@opindex multilib-library-pic
|
|
|
|
Link with the (library, not FD) pic libraries. It's implied by
|
|
@option{-mlibrary-pic}, as well as by @option{-fPIC} and
|
|
@option{-fpic} without @option{-mfdpic}. You should never have to use
|
|
it explicitly.
|
|
|
|
@item -mlinked-fp
|
|
@opindex mlinked-fp
|
|
|
|
Follow the EABI requirement of always creating a frame pointer whenever
|
|
a stack frame is allocated. This option is enabled by default and can
|
|
be disabled with @option{-mno-linked-fp}.
|
|
|
|
@item -mlong-calls
|
|
@opindex mlong-calls
|
|
|
|
Use indirect addressing to call functions outside the current
|
|
compilation unit. This allows the functions to be placed anywhere
|
|
within the 32-bit address space.
|
|
|
|
@item -malign-labels
|
|
@opindex malign-labels
|
|
|
|
Try to align labels to an 8-byte boundary by inserting NOPs into the
|
|
previous packet. This option only has an effect when VLIW packing
|
|
is enabled. It doesn't create new packets; it merely adds NOPs to
|
|
existing ones.
|
|
|
|
@item -mlibrary-pic
|
|
@opindex mlibrary-pic
|
|
|
|
Generate position-independent EABI code.
|
|
|
|
@item -macc-4
|
|
@opindex macc-4
|
|
|
|
Use only the first four media accumulator registers.
|
|
|
|
@item -macc-8
|
|
@opindex macc-8
|
|
|
|
Use all eight media accumulator registers.
|
|
|
|
@item -mpack
|
|
@opindex mpack
|
|
|
|
Pack VLIW instructions.
|
|
|
|
@item -mno-pack
|
|
@opindex mno-pack
|
|
|
|
Do not pack VLIW instructions.
|
|
|
|
@item -mno-eflags
|
|
@opindex mno-eflags
|
|
|
|
Do not mark ABI switches in e_flags.
|
|
|
|
@item -mcond-move
|
|
@opindex mcond-move
|
|
|
|
Enable the use of conditional-move instructions (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-cond-move
|
|
@opindex mno-cond-move
|
|
|
|
Disable the use of conditional-move instructions.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mscc
|
|
@opindex mscc
|
|
|
|
Enable the use of conditional set instructions (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-scc
|
|
@opindex mno-scc
|
|
|
|
Disable the use of conditional set instructions.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mcond-exec
|
|
@opindex mcond-exec
|
|
|
|
Enable the use of conditional execution (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-cond-exec
|
|
@opindex mno-cond-exec
|
|
|
|
Disable the use of conditional execution.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mvliw-branch
|
|
@opindex mvliw-branch
|
|
|
|
Run a pass to pack branches into VLIW instructions (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-vliw-branch
|
|
@opindex mno-vliw-branch
|
|
|
|
Do not run a pass to pack branches into VLIW instructions.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mmulti-cond-exec
|
|
@opindex mmulti-cond-exec
|
|
|
|
Enable optimization of @code{&&} and @code{||} in conditional execution
|
|
(default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-multi-cond-exec
|
|
@opindex mno-multi-cond-exec
|
|
|
|
Disable optimization of @code{&&} and @code{||} in conditional execution.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mnested-cond-exec
|
|
@opindex mnested-cond-exec
|
|
|
|
Enable nested conditional execution optimizations (default).
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -mno-nested-cond-exec
|
|
@opindex mno-nested-cond-exec
|
|
|
|
Disable nested conditional execution optimizations.
|
|
|
|
This switch is mainly for debugging the compiler and will likely be removed
|
|
in a future version.
|
|
|
|
@item -moptimize-membar
|
|
@opindex moptimize-membar
|
|
|
|
This switch removes redundant @code{membar} instructions from the
|
|
compiler-generated code. It is enabled by default.
|
|
|
|
@item -mno-optimize-membar
|
|
@opindex mno-optimize-membar
|
|
|
|
This switch disables the automatic removal of redundant @code{membar}
|
|
instructions from the generated code.
|
|
|
|
@item -mtomcat-stats
|
|
@opindex mtomcat-stats
|
|
|
|
Cause gas to print out tomcat statistics.
|
|
|
|
@item -mcpu=@var{cpu}
|
|
@opindex mcpu
|
|
|
|
Select the processor type for which to generate code. Possible values are
|
|
@samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450},
|
|
@samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}.
|
|
|
|
@end table
|
|
|
|
@node GNU/Linux Options
|
|
@subsection GNU/Linux Options
|
|
|
|
These @samp{-m} options are defined for GNU/Linux targets:
|
|
|
|
@table @gcctabopt
|
|
@item -mglibc
|
|
@opindex mglibc
|
|
Use the GNU C library. This is the default except
|
|
on @samp{*-*-linux-*uclibc*}, @samp{*-*-linux-*musl*} and
|
|
@samp{*-*-linux-*android*} targets.
|
|
|
|
@item -muclibc
|
|
@opindex muclibc
|
|
Use uClibc C library. This is the default on
|
|
@samp{*-*-linux-*uclibc*} targets.
|
|
|
|
@item -mmusl
|
|
@opindex mmusl
|
|
Use the musl C library. This is the default on
|
|
@samp{*-*-linux-*musl*} targets.
|
|
|
|
@item -mbionic
|
|
@opindex mbionic
|
|
Use Bionic C library. This is the default on
|
|
@samp{*-*-linux-*android*} targets.
|
|
|
|
@item -mandroid
|
|
@opindex mandroid
|
|
Compile code compatible with Android platform. This is the default on
|
|
@samp{*-*-linux-*android*} targets.
|
|
|
|
When compiling, this option enables @option{-mbionic}, @option{-fPIC},
|
|
@option{-fno-exceptions} and @option{-fno-rtti} by default. When linking,
|
|
this option makes the GCC driver pass Android-specific options to the linker.
|
|
Finally, this option causes the preprocessor macro @code{__ANDROID__}
|
|
to be defined.
|
|
|
|
@item -tno-android-cc
|
|
@opindex tno-android-cc
|
|
Disable compilation effects of @option{-mandroid}, i.e., do not enable
|
|
@option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and
|
|
@option{-fno-rtti} by default.
|
|
|
|
@item -tno-android-ld
|
|
@opindex tno-android-ld
|
|
Disable linking effects of @option{-mandroid}, i.e., pass standard Linux
|
|
linking options to the linker.
|
|
|
|
@end table
|
|
|
|
@node H8/300 Options
|
|
@subsection H8/300 Options
|
|
|
|
These @samp{-m} options are defined for the H8/300 implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
Shorten some address references at link time, when possible; uses the
|
|
linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300,
|
|
ld, Using ld}, for a fuller description.
|
|
|
|
@item -mh
|
|
@opindex mh
|
|
Generate code for the H8/300H@.
|
|
|
|
@item -ms
|
|
@opindex ms
|
|
Generate code for the H8S@.
|
|
|
|
@item -mn
|
|
@opindex mn
|
|
Generate code for the H8S and H8/300H in the normal mode. This switch
|
|
must be used either with @option{-mh} or @option{-ms}.
|
|
|
|
@item -ms2600
|
|
@opindex ms2600
|
|
Generate code for the H8S/2600. This switch must be used with @option{-ms}.
|
|
|
|
@item -mexr
|
|
@opindex mexr
|
|
Extended registers are stored on stack before execution of function
|
|
with monitor attribute. Default option is @option{-mexr}.
|
|
This option is valid only for H8S targets.
|
|
|
|
@item -mno-exr
|
|
@opindex mno-exr
|
|
Extended registers are not stored on stack before execution of function
|
|
with monitor attribute. Default option is @option{-mno-exr}.
|
|
This option is valid only for H8S targets.
|
|
|
|
@item -mint32
|
|
@opindex mint32
|
|
Make @code{int} data 32 bits by default.
|
|
|
|
@item -malign-300
|
|
@opindex malign-300
|
|
On the H8/300H and H8S, use the same alignment rules as for the H8/300.
|
|
The default for the H8/300H and H8S is to align longs and floats on
|
|
4-byte boundaries.
|
|
@option{-malign-300} causes them to be aligned on 2-byte boundaries.
|
|
This option has no effect on the H8/300.
|
|
@end table
|
|
|
|
@node HPPA Options
|
|
@subsection HPPA Options
|
|
@cindex HPPA Options
|
|
|
|
These @samp{-m} options are defined for the HPPA family of computers:
|
|
|
|
@table @gcctabopt
|
|
@item -march=@var{architecture-type}
|
|
@opindex march
|
|
Generate code for the specified architecture. The choices for
|
|
@var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA
|
|
1.1, and @samp{2.0} for PA 2.0 processors. Refer to
|
|
@file{/usr/lib/sched.models} on an HP-UX system to determine the proper
|
|
architecture option for your machine. Code compiled for lower numbered
|
|
architectures runs on higher numbered architectures, but not the
|
|
other way around.
|
|
|
|
@item -mpa-risc-1-0
|
|
@itemx -mpa-risc-1-1
|
|
@itemx -mpa-risc-2-0
|
|
@opindex mpa-risc-1-0
|
|
@opindex mpa-risc-1-1
|
|
@opindex mpa-risc-2-0
|
|
Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively.
|
|
|
|
@item -mcaller-copies
|
|
@opindex mcaller-copies
|
|
The caller copies function arguments passed by hidden reference. This
|
|
option should be used with care as it is not compatible with the default
|
|
32-bit runtime. However, only aggregates larger than eight bytes are
|
|
passed by hidden reference and the option provides better compatibility
|
|
with OpenMP.
|
|
|
|
@item -mjump-in-delay
|
|
@opindex mjump-in-delay
|
|
This option is ignored and provided for compatibility purposes only.
|
|
|
|
@item -mdisable-fpregs
|
|
@opindex mdisable-fpregs
|
|
Prevent floating-point registers from being used in any manner. This is
|
|
necessary for compiling kernels that perform lazy context switching of
|
|
floating-point registers. If you use this option and attempt to perform
|
|
floating-point operations, the compiler aborts.
|
|
|
|
@item -mdisable-indexing
|
|
@opindex mdisable-indexing
|
|
Prevent the compiler from using indexing address modes. This avoids some
|
|
rather obscure problems when compiling MIG generated code under MACH@.
|
|
|
|
@item -mno-space-regs
|
|
@opindex mno-space-regs
|
|
Generate code that assumes the target has no space registers. This allows
|
|
GCC to generate faster indirect calls and use unscaled index address modes.
|
|
|
|
Such code is suitable for level 0 PA systems and kernels.
|
|
|
|
@item -mfast-indirect-calls
|
|
@opindex mfast-indirect-calls
|
|
Generate code that assumes calls never cross space boundaries. This
|
|
allows GCC to emit code that performs faster indirect calls.
|
|
|
|
This option does not work in the presence of shared libraries or nested
|
|
functions.
|
|
|
|
@item -mfixed-range=@var{register-range}
|
|
@opindex mfixed-range
|
|
Generate code treating the given register range as fixed registers.
|
|
A fixed register is one that the register allocator cannot use. This is
|
|
useful when compiling kernel code. A register range is specified as
|
|
two registers separated by a dash. Multiple register ranges can be
|
|
specified separated by a comma.
|
|
|
|
@item -mlong-load-store
|
|
@opindex mlong-load-store
|
|
Generate 3-instruction load and store sequences as sometimes required by
|
|
the HP-UX 10 linker. This is equivalent to the @samp{+k} option to
|
|
the HP compilers.
|
|
|
|
@item -mportable-runtime
|
|
@opindex mportable-runtime
|
|
Use the portable calling conventions proposed by HP for ELF systems.
|
|
|
|
@item -mgas
|
|
@opindex mgas
|
|
Enable the use of assembler directives only GAS understands.
|
|
|
|
@item -mschedule=@var{cpu-type}
|
|
@opindex mschedule
|
|
Schedule code according to the constraints for the machine type
|
|
@var{cpu-type}. The choices for @var{cpu-type} are @samp{700}
|
|
@samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer
|
|
to @file{/usr/lib/sched.models} on an HP-UX system to determine the
|
|
proper scheduling option for your machine. The default scheduling is
|
|
@samp{8000}.
|
|
|
|
@item -mlinker-opt
|
|
@opindex mlinker-opt
|
|
Enable the optimization pass in the HP-UX linker. Note this makes symbolic
|
|
debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9
|
|
linkers in which they give bogus error messages when linking some programs.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Generate output containing library calls for floating point.
|
|
@strong{Warning:} the requisite libraries are not available for all HPPA
|
|
targets. Normally the facilities of the machine's usual C compiler are
|
|
used, but this cannot be done directly in cross-compilation. You must make
|
|
your own arrangements to provide suitable library functions for
|
|
cross-compilation.
|
|
|
|
@option{-msoft-float} changes the calling convention in the output file;
|
|
therefore, it is only useful if you compile @emph{all} of a program with
|
|
this option. In particular, you need to compile @file{libgcc.a}, the
|
|
library that comes with GCC, with @option{-msoft-float} in order for
|
|
this to work.
|
|
|
|
@item -msio
|
|
@opindex msio
|
|
Generate the predefine, @code{_SIO}, for server IO@. The default is
|
|
@option{-mwsio}. This generates the predefines, @code{__hp9000s700},
|
|
@code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These
|
|
options are available under HP-UX and HI-UX@.
|
|
|
|
@item -mgnu-ld
|
|
@opindex mgnu-ld
|
|
Use options specific to GNU @command{ld}.
|
|
This passes @option{-shared} to @command{ld} when
|
|
building a shared library. It is the default when GCC is configured,
|
|
explicitly or implicitly, with the GNU linker. This option does not
|
|
affect which @command{ld} is called; it only changes what parameters
|
|
are passed to that @command{ld}.
|
|
The @command{ld} that is called is determined by the
|
|
@option{--with-ld} configure option, GCC's program search path, and
|
|
finally by the user's @env{PATH}. The linker used by GCC can be printed
|
|
using @samp{which `gcc -print-prog-name=ld`}. This option is only available
|
|
on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
|
|
|
|
@item -mhp-ld
|
|
@opindex mhp-ld
|
|
Use options specific to HP @command{ld}.
|
|
This passes @option{-b} to @command{ld} when building
|
|
a shared library and passes @option{+Accept TypeMismatch} to @command{ld} on all
|
|
links. It is the default when GCC is configured, explicitly or
|
|
implicitly, with the HP linker. This option does not affect
|
|
which @command{ld} is called; it only changes what parameters are passed to that
|
|
@command{ld}.
|
|
The @command{ld} that is called is determined by the @option{--with-ld}
|
|
configure option, GCC's program search path, and finally by the user's
|
|
@env{PATH}. The linker used by GCC can be printed using @samp{which
|
|
`gcc -print-prog-name=ld`}. This option is only available on the 64-bit
|
|
HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}.
|
|
|
|
@item -mlong-calls
|
|
@opindex mno-long-calls
|
|
Generate code that uses long call sequences. This ensures that a call
|
|
is always able to reach linker generated stubs. The default is to generate
|
|
long calls only when the distance from the call site to the beginning
|
|
of the function or translation unit, as the case may be, exceeds a
|
|
predefined limit set by the branch type being used. The limits for
|
|
normal calls are 7,600,000 and 240,000 bytes, respectively for the
|
|
PA 2.0 and PA 1.X architectures. Sibcalls are always limited at
|
|
240,000 bytes.
|
|
|
|
Distances are measured from the beginning of functions when using the
|
|
@option{-ffunction-sections} option, or when using the @option{-mgas}
|
|
and @option{-mno-portable-runtime} options together under HP-UX with
|
|
the SOM linker.
|
|
|
|
It is normally not desirable to use this option as it degrades
|
|
performance. However, it may be useful in large applications,
|
|
particularly when partial linking is used to build the application.
|
|
|
|
The types of long calls used depends on the capabilities of the
|
|
assembler and linker, and the type of code being generated. The
|
|
impact on systems that support long absolute calls, and long pic
|
|
symbol-difference or pc-relative calls should be relatively small.
|
|
However, an indirect call is used on 32-bit ELF systems in pic code
|
|
and it is quite long.
|
|
|
|
@item -munix=@var{unix-std}
|
|
@opindex march
|
|
Generate compiler predefines and select a startfile for the specified
|
|
UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95}
|
|
and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95}
|
|
is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX
|
|
11.11 and later. The default values are @samp{93} for HP-UX 10.00,
|
|
@samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11
|
|
and later.
|
|
|
|
@option{-munix=93} provides the same predefines as GCC 3.3 and 3.4.
|
|
@option{-munix=95} provides additional predefines for @code{XOPEN_UNIX}
|
|
and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}.
|
|
@option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX},
|
|
@code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and
|
|
@code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}.
|
|
|
|
It is @emph{important} to note that this option changes the interfaces
|
|
for various library routines. It also affects the operational behavior
|
|
of the C library. Thus, @emph{extreme} care is needed in using this
|
|
option.
|
|
|
|
Library code that is intended to operate with more than one UNIX
|
|
standard must test, set and restore the variable @code{__xpg4_extended_mask}
|
|
as appropriate. Most GNU software doesn't provide this capability.
|
|
|
|
@item -nolibdld
|
|
@opindex nolibdld
|
|
Suppress the generation of link options to search libdld.sl when the
|
|
@option{-static} option is specified on HP-UX 10 and later.
|
|
|
|
@item -static
|
|
@opindex static
|
|
The HP-UX implementation of setlocale in libc has a dependency on
|
|
libdld.sl. There isn't an archive version of libdld.sl. Thus,
|
|
when the @option{-static} option is specified, special link options
|
|
are needed to resolve this dependency.
|
|
|
|
On HP-UX 10 and later, the GCC driver adds the necessary options to
|
|
link with libdld.sl when the @option{-static} option is specified.
|
|
This causes the resulting binary to be dynamic. On the 64-bit port,
|
|
the linkers generate dynamic binaries by default in any case. The
|
|
@option{-nolibdld} option can be used to prevent the GCC driver from
|
|
adding these link options.
|
|
|
|
@item -threads
|
|
@opindex threads
|
|
Add support for multithreading with the @dfn{dce thread} library
|
|
under HP-UX@. This option sets flags for both the preprocessor and
|
|
linker.
|
|
@end table
|
|
|
|
@node IA-64 Options
|
|
@subsection IA-64 Options
|
|
@cindex IA-64 Options
|
|
|
|
These are the @samp{-m} options defined for the Intel IA-64 architecture.
|
|
|
|
@table @gcctabopt
|
|
@item -mbig-endian
|
|
@opindex mbig-endian
|
|
Generate code for a big-endian target. This is the default for HP-UX@.
|
|
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
Generate code for a little-endian target. This is the default for AIX5
|
|
and GNU/Linux.
|
|
|
|
@item -mgnu-as
|
|
@itemx -mno-gnu-as
|
|
@opindex mgnu-as
|
|
@opindex mno-gnu-as
|
|
Generate (or don't) code for the GNU assembler. This is the default.
|
|
@c Also, this is the default if the configure option @option{--with-gnu-as}
|
|
@c is used.
|
|
|
|
@item -mgnu-ld
|
|
@itemx -mno-gnu-ld
|
|
@opindex mgnu-ld
|
|
@opindex mno-gnu-ld
|
|
Generate (or don't) code for the GNU linker. This is the default.
|
|
@c Also, this is the default if the configure option @option{--with-gnu-ld}
|
|
@c is used.
|
|
|
|
@item -mno-pic
|
|
@opindex mno-pic
|
|
Generate code that does not use a global pointer register. The result
|
|
is not position independent code, and violates the IA-64 ABI@.
|
|
|
|
@item -mvolatile-asm-stop
|
|
@itemx -mno-volatile-asm-stop
|
|
@opindex mvolatile-asm-stop
|
|
@opindex mno-volatile-asm-stop
|
|
Generate (or don't) a stop bit immediately before and after volatile asm
|
|
statements.
|
|
|
|
@item -mregister-names
|
|
@itemx -mno-register-names
|
|
@opindex mregister-names
|
|
@opindex mno-register-names
|
|
Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for
|
|
the stacked registers. This may make assembler output more readable.
|
|
|
|
@item -mno-sdata
|
|
@itemx -msdata
|
|
@opindex mno-sdata
|
|
@opindex msdata
|
|
Disable (or enable) optimizations that use the small data section. This may
|
|
be useful for working around optimizer bugs.
|
|
|
|
@item -mconstant-gp
|
|
@opindex mconstant-gp
|
|
Generate code that uses a single constant global pointer value. This is
|
|
useful when compiling kernel code.
|
|
|
|
@item -mauto-pic
|
|
@opindex mauto-pic
|
|
Generate code that is self-relocatable. This implies @option{-mconstant-gp}.
|
|
This is useful when compiling firmware code.
|
|
|
|
@item -minline-float-divide-min-latency
|
|
@opindex minline-float-divide-min-latency
|
|
Generate code for inline divides of floating-point values
|
|
using the minimum latency algorithm.
|
|
|
|
@item -minline-float-divide-max-throughput
|
|
@opindex minline-float-divide-max-throughput
|
|
Generate code for inline divides of floating-point values
|
|
using the maximum throughput algorithm.
|
|
|
|
@item -mno-inline-float-divide
|
|
@opindex mno-inline-float-divide
|
|
Do not generate inline code for divides of floating-point values.
|
|
|
|
@item -minline-int-divide-min-latency
|
|
@opindex minline-int-divide-min-latency
|
|
Generate code for inline divides of integer values
|
|
using the minimum latency algorithm.
|
|
|
|
@item -minline-int-divide-max-throughput
|
|
@opindex minline-int-divide-max-throughput
|
|
Generate code for inline divides of integer values
|
|
using the maximum throughput algorithm.
|
|
|
|
@item -mno-inline-int-divide
|
|
@opindex mno-inline-int-divide
|
|
Do not generate inline code for divides of integer values.
|
|
|
|
@item -minline-sqrt-min-latency
|
|
@opindex minline-sqrt-min-latency
|
|
Generate code for inline square roots
|
|
using the minimum latency algorithm.
|
|
|
|
@item -minline-sqrt-max-throughput
|
|
@opindex minline-sqrt-max-throughput
|
|
Generate code for inline square roots
|
|
using the maximum throughput algorithm.
|
|
|
|
@item -mno-inline-sqrt
|
|
@opindex mno-inline-sqrt
|
|
Do not generate inline code for @code{sqrt}.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Do (don't) generate code that uses the fused multiply/add or multiply/subtract
|
|
instructions. The default is to use these instructions.
|
|
|
|
@item -mno-dwarf2-asm
|
|
@itemx -mdwarf2-asm
|
|
@opindex mno-dwarf2-asm
|
|
@opindex mdwarf2-asm
|
|
Don't (or do) generate assembler code for the DWARF line number debugging
|
|
info. This may be useful when not using the GNU assembler.
|
|
|
|
@item -mearly-stop-bits
|
|
@itemx -mno-early-stop-bits
|
|
@opindex mearly-stop-bits
|
|
@opindex mno-early-stop-bits
|
|
Allow stop bits to be placed earlier than immediately preceding the
|
|
instruction that triggered the stop bit. This can improve instruction
|
|
scheduling, but does not always do so.
|
|
|
|
@item -mfixed-range=@var{register-range}
|
|
@opindex mfixed-range
|
|
Generate code treating the given register range as fixed registers.
|
|
A fixed register is one that the register allocator cannot use. This is
|
|
useful when compiling kernel code. A register range is specified as
|
|
two registers separated by a dash. Multiple register ranges can be
|
|
specified separated by a comma.
|
|
|
|
@item -mtls-size=@var{tls-size}
|
|
@opindex mtls-size
|
|
Specify bit size of immediate TLS offsets. Valid values are 14, 22, and
|
|
64.
|
|
|
|
@item -mtune=@var{cpu-type}
|
|
@opindex mtune
|
|
Tune the instruction scheduling for a particular CPU, Valid values are
|
|
@samp{itanium}, @samp{itanium1}, @samp{merced}, @samp{itanium2},
|
|
and @samp{mckinley}.
|
|
|
|
@item -milp32
|
|
@itemx -mlp64
|
|
@opindex milp32
|
|
@opindex mlp64
|
|
Generate code for a 32-bit or 64-bit environment.
|
|
The 32-bit environment sets int, long and pointer to 32 bits.
|
|
The 64-bit environment sets int to 32 bits and long and pointer
|
|
to 64 bits. These are HP-UX specific flags.
|
|
|
|
@item -mno-sched-br-data-spec
|
|
@itemx -msched-br-data-spec
|
|
@opindex mno-sched-br-data-spec
|
|
@opindex msched-br-data-spec
|
|
(Dis/En)able data speculative scheduling before reload.
|
|
This results in generation of @code{ld.a} instructions and
|
|
the corresponding check instructions (@code{ld.c} / @code{chk.a}).
|
|
The default setting is disabled.
|
|
|
|
@item -msched-ar-data-spec
|
|
@itemx -mno-sched-ar-data-spec
|
|
@opindex msched-ar-data-spec
|
|
@opindex mno-sched-ar-data-spec
|
|
(En/Dis)able data speculative scheduling after reload.
|
|
This results in generation of @code{ld.a} instructions and
|
|
the corresponding check instructions (@code{ld.c} / @code{chk.a}).
|
|
The default setting is enabled.
|
|
|
|
@item -mno-sched-control-spec
|
|
@itemx -msched-control-spec
|
|
@opindex mno-sched-control-spec
|
|
@opindex msched-control-spec
|
|
(Dis/En)able control speculative scheduling. This feature is
|
|
available only during region scheduling (i.e.@: before reload).
|
|
This results in generation of the @code{ld.s} instructions and
|
|
the corresponding check instructions @code{chk.s}.
|
|
The default setting is disabled.
|
|
|
|
@item -msched-br-in-data-spec
|
|
@itemx -mno-sched-br-in-data-spec
|
|
@opindex msched-br-in-data-spec
|
|
@opindex mno-sched-br-in-data-spec
|
|
(En/Dis)able speculative scheduling of the instructions that
|
|
are dependent on the data speculative loads before reload.
|
|
This is effective only with @option{-msched-br-data-spec} enabled.
|
|
The default setting is enabled.
|
|
|
|
@item -msched-ar-in-data-spec
|
|
@itemx -mno-sched-ar-in-data-spec
|
|
@opindex msched-ar-in-data-spec
|
|
@opindex mno-sched-ar-in-data-spec
|
|
(En/Dis)able speculative scheduling of the instructions that
|
|
are dependent on the data speculative loads after reload.
|
|
This is effective only with @option{-msched-ar-data-spec} enabled.
|
|
The default setting is enabled.
|
|
|
|
@item -msched-in-control-spec
|
|
@itemx -mno-sched-in-control-spec
|
|
@opindex msched-in-control-spec
|
|
@opindex mno-sched-in-control-spec
|
|
(En/Dis)able speculative scheduling of the instructions that
|
|
are dependent on the control speculative loads.
|
|
This is effective only with @option{-msched-control-spec} enabled.
|
|
The default setting is enabled.
|
|
|
|
@item -mno-sched-prefer-non-data-spec-insns
|
|
@itemx -msched-prefer-non-data-spec-insns
|
|
@opindex mno-sched-prefer-non-data-spec-insns
|
|
@opindex msched-prefer-non-data-spec-insns
|
|
If enabled, data-speculative instructions are chosen for schedule
|
|
only if there are no other choices at the moment. This makes
|
|
the use of the data speculation much more conservative.
|
|
The default setting is disabled.
|
|
|
|
@item -mno-sched-prefer-non-control-spec-insns
|
|
@itemx -msched-prefer-non-control-spec-insns
|
|
@opindex mno-sched-prefer-non-control-spec-insns
|
|
@opindex msched-prefer-non-control-spec-insns
|
|
If enabled, control-speculative instructions are chosen for schedule
|
|
only if there are no other choices at the moment. This makes
|
|
the use of the control speculation much more conservative.
|
|
The default setting is disabled.
|
|
|
|
@item -mno-sched-count-spec-in-critical-path
|
|
@itemx -msched-count-spec-in-critical-path
|
|
@opindex mno-sched-count-spec-in-critical-path
|
|
@opindex msched-count-spec-in-critical-path
|
|
If enabled, speculative dependencies are considered during
|
|
computation of the instructions priorities. This makes the use of the
|
|
speculation a bit more conservative.
|
|
The default setting is disabled.
|
|
|
|
@item -msched-spec-ldc
|
|
@opindex msched-spec-ldc
|
|
Use a simple data speculation check. This option is on by default.
|
|
|
|
@item -msched-control-spec-ldc
|
|
@opindex msched-spec-ldc
|
|
Use a simple check for control speculation. This option is on by default.
|
|
|
|
@item -msched-stop-bits-after-every-cycle
|
|
@opindex msched-stop-bits-after-every-cycle
|
|
Place a stop bit after every cycle when scheduling. This option is on
|
|
by default.
|
|
|
|
@item -msched-fp-mem-deps-zero-cost
|
|
@opindex msched-fp-mem-deps-zero-cost
|
|
Assume that floating-point stores and loads are not likely to cause a conflict
|
|
when placed into the same instruction group. This option is disabled by
|
|
default.
|
|
|
|
@item -msel-sched-dont-check-control-spec
|
|
@opindex msel-sched-dont-check-control-spec
|
|
Generate checks for control speculation in selective scheduling.
|
|
This flag is disabled by default.
|
|
|
|
@item -msched-max-memory-insns=@var{max-insns}
|
|
@opindex msched-max-memory-insns
|
|
Limit on the number of memory insns per instruction group, giving lower
|
|
priority to subsequent memory insns attempting to schedule in the same
|
|
instruction group. Frequently useful to prevent cache bank conflicts.
|
|
The default value is 1.
|
|
|
|
@item -msched-max-memory-insns-hard-limit
|
|
@opindex msched-max-memory-insns-hard-limit
|
|
Makes the limit specified by @option{msched-max-memory-insns} a hard limit,
|
|
disallowing more than that number in an instruction group.
|
|
Otherwise, the limit is ``soft'', meaning that non-memory operations
|
|
are preferred when the limit is reached, but memory operations may still
|
|
be scheduled.
|
|
|
|
@end table
|
|
|
|
@node LM32 Options
|
|
@subsection LM32 Options
|
|
@cindex LM32 options
|
|
|
|
These @option{-m} options are defined for the LatticeMico32 architecture:
|
|
|
|
@table @gcctabopt
|
|
@item -mbarrel-shift-enabled
|
|
@opindex mbarrel-shift-enabled
|
|
Enable barrel-shift instructions.
|
|
|
|
@item -mdivide-enabled
|
|
@opindex mdivide-enabled
|
|
Enable divide and modulus instructions.
|
|
|
|
@item -mmultiply-enabled
|
|
@opindex multiply-enabled
|
|
Enable multiply instructions.
|
|
|
|
@item -msign-extend-enabled
|
|
@opindex msign-extend-enabled
|
|
Enable sign extend instructions.
|
|
|
|
@item -muser-enabled
|
|
@opindex muser-enabled
|
|
Enable user-defined instructions.
|
|
|
|
@end table
|
|
|
|
@node M32C Options
|
|
@subsection M32C Options
|
|
@cindex M32C options
|
|
|
|
@table @gcctabopt
|
|
@item -mcpu=@var{name}
|
|
@opindex mcpu=
|
|
Select the CPU for which code is generated. @var{name} may be one of
|
|
@samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to
|
|
/60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for
|
|
the M32C/80 series.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Specifies that the program will be run on the simulator. This causes
|
|
an alternate runtime library to be linked in which supports, for
|
|
example, file I/O@. You must not use this option when generating
|
|
programs that will run on real hardware; you must provide your own
|
|
runtime library for whatever I/O functions are needed.
|
|
|
|
@item -memregs=@var{number}
|
|
@opindex memregs=
|
|
Specifies the number of memory-based pseudo-registers GCC uses
|
|
during code generation. These pseudo-registers are used like real
|
|
registers, so there is a tradeoff between GCC's ability to fit the
|
|
code into available registers, and the performance penalty of using
|
|
memory instead of registers. Note that all modules in a program must
|
|
be compiled with the same value for this option. Because of that, you
|
|
must not use this option with GCC's default runtime libraries.
|
|
|
|
@end table
|
|
|
|
@node M32R/D Options
|
|
@subsection M32R/D Options
|
|
@cindex M32R/D options
|
|
|
|
These @option{-m} options are defined for Renesas M32R/D architectures:
|
|
|
|
@table @gcctabopt
|
|
@item -m32r2
|
|
@opindex m32r2
|
|
Generate code for the M32R/2@.
|
|
|
|
@item -m32rx
|
|
@opindex m32rx
|
|
Generate code for the M32R/X@.
|
|
|
|
@item -m32r
|
|
@opindex m32r
|
|
Generate code for the M32R@. This is the default.
|
|
|
|
@item -mmodel=small
|
|
@opindex mmodel=small
|
|
Assume all objects live in the lower 16MB of memory (so that their addresses
|
|
can be loaded with the @code{ld24} instruction), and assume all subroutines
|
|
are reachable with the @code{bl} instruction.
|
|
This is the default.
|
|
|
|
The addressability of a particular object can be set with the
|
|
@code{model} attribute.
|
|
|
|
@item -mmodel=medium
|
|
@opindex mmodel=medium
|
|
Assume objects may be anywhere in the 32-bit address space (the compiler
|
|
generates @code{seth/add3} instructions to load their addresses), and
|
|
assume all subroutines are reachable with the @code{bl} instruction.
|
|
|
|
@item -mmodel=large
|
|
@opindex mmodel=large
|
|
Assume objects may be anywhere in the 32-bit address space (the compiler
|
|
generates @code{seth/add3} instructions to load their addresses), and
|
|
assume subroutines may not be reachable with the @code{bl} instruction
|
|
(the compiler generates the much slower @code{seth/add3/jl}
|
|
instruction sequence).
|
|
|
|
@item -msdata=none
|
|
@opindex msdata=none
|
|
Disable use of the small data area. Variables are put into
|
|
one of @code{.data}, @code{.bss}, or @code{.rodata} (unless the
|
|
@code{section} attribute has been specified).
|
|
This is the default.
|
|
|
|
The small data area consists of sections @code{.sdata} and @code{.sbss}.
|
|
Objects may be explicitly put in the small data area with the
|
|
@code{section} attribute using one of these sections.
|
|
|
|
@item -msdata=sdata
|
|
@opindex msdata=sdata
|
|
Put small global and static data in the small data area, but do not
|
|
generate special code to reference them.
|
|
|
|
@item -msdata=use
|
|
@opindex msdata=use
|
|
Put small global and static data in the small data area, and generate
|
|
special instructions to reference them.
|
|
|
|
@item -G @var{num}
|
|
@opindex G
|
|
@cindex smaller data references
|
|
Put global and static objects less than or equal to @var{num} bytes
|
|
into the small data or BSS sections instead of the normal data or BSS
|
|
sections. The default value of @var{num} is 8.
|
|
The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use}
|
|
for this option to have any effect.
|
|
|
|
All modules should be compiled with the same @option{-G @var{num}} value.
|
|
Compiling with different values of @var{num} may or may not work; if it
|
|
doesn't the linker gives an error message---incorrect code is not
|
|
generated.
|
|
|
|
@item -mdebug
|
|
@opindex mdebug
|
|
Makes the M32R-specific code in the compiler display some statistics
|
|
that might help in debugging programs.
|
|
|
|
@item -malign-loops
|
|
@opindex malign-loops
|
|
Align all loops to a 32-byte boundary.
|
|
|
|
@item -mno-align-loops
|
|
@opindex mno-align-loops
|
|
Do not enforce a 32-byte alignment for loops. This is the default.
|
|
|
|
@item -missue-rate=@var{number}
|
|
@opindex missue-rate=@var{number}
|
|
Issue @var{number} instructions per cycle. @var{number} can only be 1
|
|
or 2.
|
|
|
|
@item -mbranch-cost=@var{number}
|
|
@opindex mbranch-cost=@var{number}
|
|
@var{number} can only be 1 or 2. If it is 1 then branches are
|
|
preferred over conditional code, if it is 2, then the opposite applies.
|
|
|
|
@item -mflush-trap=@var{number}
|
|
@opindex mflush-trap=@var{number}
|
|
Specifies the trap number to use to flush the cache. The default is
|
|
12. Valid numbers are between 0 and 15 inclusive.
|
|
|
|
@item -mno-flush-trap
|
|
@opindex mno-flush-trap
|
|
Specifies that the cache cannot be flushed by using a trap.
|
|
|
|
@item -mflush-func=@var{name}
|
|
@opindex mflush-func=@var{name}
|
|
Specifies the name of the operating system function to call to flush
|
|
the cache. The default is @samp{_flush_cache}, but a function call
|
|
is only used if a trap is not available.
|
|
|
|
@item -mno-flush-func
|
|
@opindex mno-flush-func
|
|
Indicates that there is no OS function for flushing the cache.
|
|
|
|
@end table
|
|
|
|
@node M680x0 Options
|
|
@subsection M680x0 Options
|
|
@cindex M680x0 options
|
|
|
|
These are the @samp{-m} options defined for M680x0 and ColdFire processors.
|
|
The default settings depend on which architecture was selected when
|
|
the compiler was configured; the defaults for the most common choices
|
|
are given below.
|
|
|
|
@table @gcctabopt
|
|
@item -march=@var{arch}
|
|
@opindex march
|
|
Generate code for a specific M680x0 or ColdFire instruction set
|
|
architecture. Permissible values of @var{arch} for M680x0
|
|
architectures are: @samp{68000}, @samp{68010}, @samp{68020},
|
|
@samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire
|
|
architectures are selected according to Freescale's ISA classification
|
|
and the permissible values are: @samp{isaa}, @samp{isaaplus},
|
|
@samp{isab} and @samp{isac}.
|
|
|
|
GCC defines a macro @code{__mcf@var{arch}__} whenever it is generating
|
|
code for a ColdFire target. The @var{arch} in this macro is one of the
|
|
@option{-march} arguments given above.
|
|
|
|
When used together, @option{-march} and @option{-mtune} select code
|
|
that runs on a family of similar processors but that is optimized
|
|
for a particular microarchitecture.
|
|
|
|
@item -mcpu=@var{cpu}
|
|
@opindex mcpu
|
|
Generate code for a specific M680x0 or ColdFire processor.
|
|
The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020},
|
|
@samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332}
|
|
and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table
|
|
below, which also classifies the CPUs into families:
|
|
|
|
@multitable @columnfractions 0.20 0.80
|
|
@item @strong{Family} @tab @strong{@samp{-mcpu} arguments}
|
|
@item @samp{51} @tab @samp{51} @samp{51ac} @samp{51ag} @samp{51cn} @samp{51em} @samp{51je} @samp{51jf} @samp{51jg} @samp{51jm} @samp{51mm} @samp{51qe} @samp{51qm}
|
|
@item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206}
|
|
@item @samp{5206e} @tab @samp{5206e}
|
|
@item @samp{5208} @tab @samp{5207} @samp{5208}
|
|
@item @samp{5211a} @tab @samp{5210a} @samp{5211a}
|
|
@item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213}
|
|
@item @samp{5216} @tab @samp{5214} @samp{5216}
|
|
@item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235}
|
|
@item @samp{5225} @tab @samp{5224} @samp{5225}
|
|
@item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259}
|
|
@item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x}
|
|
@item @samp{5249} @tab @samp{5249}
|
|
@item @samp{5250} @tab @samp{5250}
|
|
@item @samp{5271} @tab @samp{5270} @samp{5271}
|
|
@item @samp{5272} @tab @samp{5272}
|
|
@item @samp{5275} @tab @samp{5274} @samp{5275}
|
|
@item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x}
|
|
@item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017}
|
|
@item @samp{5307} @tab @samp{5307}
|
|
@item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x}
|
|
@item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x}
|
|
@item @samp{5407} @tab @samp{5407}
|
|
@item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485}
|
|
@end multitable
|
|
|
|
@option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if
|
|
@var{arch} is compatible with @var{cpu}. Other combinations of
|
|
@option{-mcpu} and @option{-march} are rejected.
|
|
|
|
GCC defines the macro @code{__mcf_cpu_@var{cpu}} when ColdFire target
|
|
@var{cpu} is selected. It also defines @code{__mcf_family_@var{family}},
|
|
where the value of @var{family} is given by the table above.
|
|
|
|
@item -mtune=@var{tune}
|
|
@opindex mtune
|
|
Tune the code for a particular microarchitecture within the
|
|
constraints set by @option{-march} and @option{-mcpu}.
|
|
The M680x0 microarchitectures are: @samp{68000}, @samp{68010},
|
|
@samp{68020}, @samp{68030}, @samp{68040}, @samp{68060}
|
|
and @samp{cpu32}. The ColdFire microarchitectures
|
|
are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}.
|
|
|
|
You can also use @option{-mtune=68020-40} for code that needs
|
|
to run relatively well on 68020, 68030 and 68040 targets.
|
|
@option{-mtune=68020-60} is similar but includes 68060 targets
|
|
as well. These two options select the same tuning decisions as
|
|
@option{-m68020-40} and @option{-m68020-60} respectively.
|
|
|
|
GCC defines the macros @code{__mc@var{arch}} and @code{__mc@var{arch}__}
|
|
when tuning for 680x0 architecture @var{arch}. It also defines
|
|
@code{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std}
|
|
option is used. If GCC is tuning for a range of architectures,
|
|
as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60},
|
|
it defines the macros for every architecture in the range.
|
|
|
|
GCC also defines the macro @code{__m@var{uarch}__} when tuning for
|
|
ColdFire microarchitecture @var{uarch}, where @var{uarch} is one
|
|
of the arguments given above.
|
|
|
|
@item -m68000
|
|
@itemx -mc68000
|
|
@opindex m68000
|
|
@opindex mc68000
|
|
Generate output for a 68000. This is the default
|
|
when the compiler is configured for 68000-based systems.
|
|
It is equivalent to @option{-march=68000}.
|
|
|
|
Use this option for microcontrollers with a 68000 or EC000 core,
|
|
including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
|
|
|
|
@item -m68010
|
|
@opindex m68010
|
|
Generate output for a 68010. This is the default
|
|
when the compiler is configured for 68010-based systems.
|
|
It is equivalent to @option{-march=68010}.
|
|
|
|
@item -m68020
|
|
@itemx -mc68020
|
|
@opindex m68020
|
|
@opindex mc68020
|
|
Generate output for a 68020. This is the default
|
|
when the compiler is configured for 68020-based systems.
|
|
It is equivalent to @option{-march=68020}.
|
|
|
|
@item -m68030
|
|
@opindex m68030
|
|
Generate output for a 68030. This is the default when the compiler is
|
|
configured for 68030-based systems. It is equivalent to
|
|
@option{-march=68030}.
|
|
|
|
@item -m68040
|
|
@opindex m68040
|
|
Generate output for a 68040. This is the default when the compiler is
|
|
configured for 68040-based systems. It is equivalent to
|
|
@option{-march=68040}.
|
|
|
|
This option inhibits the use of 68881/68882 instructions that have to be
|
|
emulated by software on the 68040. Use this option if your 68040 does not
|
|
have code to emulate those instructions.
|
|
|
|
@item -m68060
|
|
@opindex m68060
|
|
Generate output for a 68060. This is the default when the compiler is
|
|
configured for 68060-based systems. It is equivalent to
|
|
@option{-march=68060}.
|
|
|
|
This option inhibits the use of 68020 and 68881/68882 instructions that
|
|
have to be emulated by software on the 68060. Use this option if your 68060
|
|
does not have code to emulate those instructions.
|
|
|
|
@item -mcpu32
|
|
@opindex mcpu32
|
|
Generate output for a CPU32. This is the default
|
|
when the compiler is configured for CPU32-based systems.
|
|
It is equivalent to @option{-march=cpu32}.
|
|
|
|
Use this option for microcontrollers with a
|
|
CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334,
|
|
68336, 68340, 68341, 68349 and 68360.
|
|
|
|
@item -m5200
|
|
@opindex m5200
|
|
Generate output for a 520X ColdFire CPU@. This is the default
|
|
when the compiler is configured for 520X-based systems.
|
|
It is equivalent to @option{-mcpu=5206}, and is now deprecated
|
|
in favor of that option.
|
|
|
|
Use this option for microcontroller with a 5200 core, including
|
|
the MCF5202, MCF5203, MCF5204 and MCF5206.
|
|
|
|
@item -m5206e
|
|
@opindex m5206e
|
|
Generate output for a 5206e ColdFire CPU@. The option is now
|
|
deprecated in favor of the equivalent @option{-mcpu=5206e}.
|
|
|
|
@item -m528x
|
|
@opindex m528x
|
|
Generate output for a member of the ColdFire 528X family.
|
|
The option is now deprecated in favor of the equivalent
|
|
@option{-mcpu=528x}.
|
|
|
|
@item -m5307
|
|
@opindex m5307
|
|
Generate output for a ColdFire 5307 CPU@. The option is now deprecated
|
|
in favor of the equivalent @option{-mcpu=5307}.
|
|
|
|
@item -m5407
|
|
@opindex m5407
|
|
Generate output for a ColdFire 5407 CPU@. The option is now deprecated
|
|
in favor of the equivalent @option{-mcpu=5407}.
|
|
|
|
@item -mcfv4e
|
|
@opindex mcfv4e
|
|
Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x).
|
|
This includes use of hardware floating-point instructions.
|
|
The option is equivalent to @option{-mcpu=547x}, and is now
|
|
deprecated in favor of that option.
|
|
|
|
@item -m68020-40
|
|
@opindex m68020-40
|
|
Generate output for a 68040, without using any of the new instructions.
|
|
This results in code that can run relatively efficiently on either a
|
|
68020/68881 or a 68030 or a 68040. The generated code does use the
|
|
68881 instructions that are emulated on the 68040.
|
|
|
|
The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}.
|
|
|
|
@item -m68020-60
|
|
@opindex m68020-60
|
|
Generate output for a 68060, without using any of the new instructions.
|
|
This results in code that can run relatively efficiently on either a
|
|
68020/68881 or a 68030 or a 68040. The generated code does use the
|
|
68881 instructions that are emulated on the 68060.
|
|
|
|
The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}.
|
|
|
|
@item -mhard-float
|
|
@itemx -m68881
|
|
@opindex mhard-float
|
|
@opindex m68881
|
|
Generate floating-point instructions. This is the default for 68020
|
|
and above, and for ColdFire devices that have an FPU@. It defines the
|
|
macro @code{__HAVE_68881__} on M680x0 targets and @code{__mcffpu__}
|
|
on ColdFire targets.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Do not generate floating-point instructions; use library calls instead.
|
|
This is the default for 68000, 68010, and 68832 targets. It is also
|
|
the default for ColdFire devices that have no FPU.
|
|
|
|
@item -mdiv
|
|
@itemx -mno-div
|
|
@opindex mdiv
|
|
@opindex mno-div
|
|
Generate (do not generate) ColdFire hardware divide and remainder
|
|
instructions. If @option{-march} is used without @option{-mcpu},
|
|
the default is ``on'' for ColdFire architectures and ``off'' for M680x0
|
|
architectures. Otherwise, the default is taken from the target CPU
|
|
(either the default CPU, or the one specified by @option{-mcpu}). For
|
|
example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for
|
|
@option{-mcpu=5206e}.
|
|
|
|
GCC defines the macro @code{__mcfhwdiv__} when this option is enabled.
|
|
|
|
@item -mshort
|
|
@opindex mshort
|
|
Consider type @code{int} to be 16 bits wide, like @code{short int}.
|
|
Additionally, parameters passed on the stack are also aligned to a
|
|
16-bit boundary even on targets whose API mandates promotion to 32-bit.
|
|
|
|
@item -mno-short
|
|
@opindex mno-short
|
|
Do not consider type @code{int} to be 16 bits wide. This is the default.
|
|
|
|
@item -mnobitfield
|
|
@itemx -mno-bitfield
|
|
@opindex mnobitfield
|
|
@opindex mno-bitfield
|
|
Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32}
|
|
and @option{-m5200} options imply @w{@option{-mnobitfield}}.
|
|
|
|
@item -mbitfield
|
|
@opindex mbitfield
|
|
Do use the bit-field instructions. The @option{-m68020} option implies
|
|
@option{-mbitfield}. This is the default if you use a configuration
|
|
designed for a 68020.
|
|
|
|
@item -mrtd
|
|
@opindex mrtd
|
|
Use a different function-calling convention, in which functions
|
|
that take a fixed number of arguments return with the @code{rtd}
|
|
instruction, which pops their arguments while returning. This
|
|
saves one instruction in the caller since there is no need to pop
|
|
the arguments there.
|
|
|
|
This calling convention is incompatible with the one normally
|
|
used on Unix, so you cannot use it if you need to call libraries
|
|
compiled with the Unix compiler.
|
|
|
|
Also, you must provide function prototypes for all functions that
|
|
take variable numbers of arguments (including @code{printf});
|
|
otherwise incorrect code is generated for calls to those
|
|
functions.
|
|
|
|
In addition, seriously incorrect code results if you call a
|
|
function with too many arguments. (Normally, extra arguments are
|
|
harmlessly ignored.)
|
|
|
|
The @code{rtd} instruction is supported by the 68010, 68020, 68030,
|
|
68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
|
|
|
|
@item -mno-rtd
|
|
@opindex mno-rtd
|
|
Do not use the calling conventions selected by @option{-mrtd}.
|
|
This is the default.
|
|
|
|
@item -malign-int
|
|
@itemx -mno-align-int
|
|
@opindex malign-int
|
|
@opindex mno-align-int
|
|
Control whether GCC aligns @code{int}, @code{long}, @code{long long},
|
|
@code{float}, @code{double}, and @code{long double} variables on a 32-bit
|
|
boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}).
|
|
Aligning variables on 32-bit boundaries produces code that runs somewhat
|
|
faster on processors with 32-bit busses at the expense of more memory.
|
|
|
|
@strong{Warning:} if you use the @option{-malign-int} switch, GCC
|
|
aligns structures containing the above types differently than
|
|
most published application binary interface specifications for the m68k.
|
|
|
|
@item -mpcrel
|
|
@opindex mpcrel
|
|
Use the pc-relative addressing mode of the 68000 directly, instead of
|
|
using a global offset table. At present, this option implies @option{-fpic},
|
|
allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is
|
|
not presently supported with @option{-mpcrel}, though this could be supported for
|
|
68020 and higher processors.
|
|
|
|
@item -mno-strict-align
|
|
@itemx -mstrict-align
|
|
@opindex mno-strict-align
|
|
@opindex mstrict-align
|
|
Do not (do) assume that unaligned memory references are handled by
|
|
the system.
|
|
|
|
@item -msep-data
|
|
Generate code that allows the data segment to be located in a different
|
|
area of memory from the text segment. This allows for execute-in-place in
|
|
an environment without virtual memory management. This option implies
|
|
@option{-fPIC}.
|
|
|
|
@item -mno-sep-data
|
|
Generate code that assumes that the data segment follows the text segment.
|
|
This is the default.
|
|
|
|
@item -mid-shared-library
|
|
Generate code that supports shared libraries via the library ID method.
|
|
This allows for execute-in-place and shared libraries in an environment
|
|
without virtual memory management. This option implies @option{-fPIC}.
|
|
|
|
@item -mno-id-shared-library
|
|
Generate code that doesn't assume ID-based shared libraries are being used.
|
|
This is the default.
|
|
|
|
@item -mshared-library-id=n
|
|
Specifies the identification number of the ID-based shared library being
|
|
compiled. Specifying a value of 0 generates more compact code; specifying
|
|
other values forces the allocation of that number to the current
|
|
library, but is no more space- or time-efficient than omitting this option.
|
|
|
|
@item -mxgot
|
|
@itemx -mno-xgot
|
|
@opindex mxgot
|
|
@opindex mno-xgot
|
|
When generating position-independent code for ColdFire, generate code
|
|
that works if the GOT has more than 8192 entries. This code is
|
|
larger and slower than code generated without this option. On M680x0
|
|
processors, this option is not needed; @option{-fPIC} suffices.
|
|
|
|
GCC normally uses a single instruction to load values from the GOT@.
|
|
While this is relatively efficient, it only works if the GOT
|
|
is smaller than about 64k. Anything larger causes the linker
|
|
to report an error such as:
|
|
|
|
@cindex relocation truncated to fit (ColdFire)
|
|
@smallexample
|
|
relocation truncated to fit: R_68K_GOT16O foobar
|
|
@end smallexample
|
|
|
|
If this happens, you should recompile your code with @option{-mxgot}.
|
|
It should then work with very large GOTs. However, code generated with
|
|
@option{-mxgot} is less efficient, since it takes 4 instructions to fetch
|
|
the value of a global symbol.
|
|
|
|
Note that some linkers, including newer versions of the GNU linker,
|
|
can create multiple GOTs and sort GOT entries. If you have such a linker,
|
|
you should only need to use @option{-mxgot} when compiling a single
|
|
object file that accesses more than 8192 GOT entries. Very few do.
|
|
|
|
These options have no effect unless GCC is generating
|
|
position-independent code.
|
|
|
|
@item -mlong-jump-table-offsets
|
|
@opindex mlong-jump-table-offsets
|
|
Use 32-bit offsets in @code{switch} tables. The default is to use
|
|
16-bit offsets.
|
|
|
|
@end table
|
|
|
|
@node MCore Options
|
|
@subsection MCore Options
|
|
@cindex MCore options
|
|
|
|
These are the @samp{-m} options defined for the Motorola M*Core
|
|
processors.
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mhardlit
|
|
@itemx -mno-hardlit
|
|
@opindex mhardlit
|
|
@opindex mno-hardlit
|
|
Inline constants into the code stream if it can be done in two
|
|
instructions or less.
|
|
|
|
@item -mdiv
|
|
@itemx -mno-div
|
|
@opindex mdiv
|
|
@opindex mno-div
|
|
Use the divide instruction. (Enabled by default).
|
|
|
|
@item -mrelax-immediate
|
|
@itemx -mno-relax-immediate
|
|
@opindex mrelax-immediate
|
|
@opindex mno-relax-immediate
|
|
Allow arbitrary-sized immediates in bit operations.
|
|
|
|
@item -mwide-bitfields
|
|
@itemx -mno-wide-bitfields
|
|
@opindex mwide-bitfields
|
|
@opindex mno-wide-bitfields
|
|
Always treat bit-fields as @code{int}-sized.
|
|
|
|
@item -m4byte-functions
|
|
@itemx -mno-4byte-functions
|
|
@opindex m4byte-functions
|
|
@opindex mno-4byte-functions
|
|
Force all functions to be aligned to a 4-byte boundary.
|
|
|
|
@item -mcallgraph-data
|
|
@itemx -mno-callgraph-data
|
|
@opindex mcallgraph-data
|
|
@opindex mno-callgraph-data
|
|
Emit callgraph information.
|
|
|
|
@item -mslow-bytes
|
|
@itemx -mno-slow-bytes
|
|
@opindex mslow-bytes
|
|
@opindex mno-slow-bytes
|
|
Prefer word access when reading byte quantities.
|
|
|
|
@item -mlittle-endian
|
|
@itemx -mbig-endian
|
|
@opindex mlittle-endian
|
|
@opindex mbig-endian
|
|
Generate code for a little-endian target.
|
|
|
|
@item -m210
|
|
@itemx -m340
|
|
@opindex m210
|
|
@opindex m340
|
|
Generate code for the 210 processor.
|
|
|
|
@item -mno-lsim
|
|
@opindex mno-lsim
|
|
Assume that runtime support has been provided and so omit the
|
|
simulator library (@file{libsim.a)} from the linker command line.
|
|
|
|
@item -mstack-increment=@var{size}
|
|
@opindex mstack-increment
|
|
Set the maximum amount for a single stack increment operation. Large
|
|
values can increase the speed of programs that contain functions
|
|
that need a large amount of stack space, but they can also trigger a
|
|
segmentation fault if the stack is extended too much. The default
|
|
value is 0x1000.
|
|
|
|
@end table
|
|
|
|
@node MeP Options
|
|
@subsection MeP Options
|
|
@cindex MeP options
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mabsdiff
|
|
@opindex mabsdiff
|
|
Enables the @code{abs} instruction, which is the absolute difference
|
|
between two registers.
|
|
|
|
@item -mall-opts
|
|
@opindex mall-opts
|
|
Enables all the optional instructions---average, multiply, divide, bit
|
|
operations, leading zero, absolute difference, min/max, clip, and
|
|
saturation.
|
|
|
|
|
|
@item -maverage
|
|
@opindex maverage
|
|
Enables the @code{ave} instruction, which computes the average of two
|
|
registers.
|
|
|
|
@item -mbased=@var{n}
|
|
@opindex mbased=
|
|
Variables of size @var{n} bytes or smaller are placed in the
|
|
@code{.based} section by default. Based variables use the @code{$tp}
|
|
register as a base register, and there is a 128-byte limit to the
|
|
@code{.based} section.
|
|
|
|
@item -mbitops
|
|
@opindex mbitops
|
|
Enables the bit operation instructions---bit test (@code{btstm}), set
|
|
(@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and
|
|
test-and-set (@code{tas}).
|
|
|
|
@item -mc=@var{name}
|
|
@opindex mc=
|
|
Selects which section constant data is placed in. @var{name} may
|
|
be @samp{tiny}, @samp{near}, or @samp{far}.
|
|
|
|
@item -mclip
|
|
@opindex mclip
|
|
Enables the @code{clip} instruction. Note that @option{-mclip} is not
|
|
useful unless you also provide @option{-mminmax}.
|
|
|
|
@item -mconfig=@var{name}
|
|
@opindex mconfig=
|
|
Selects one of the built-in core configurations. Each MeP chip has
|
|
one or more modules in it; each module has a core CPU and a variety of
|
|
coprocessors, optional instructions, and peripherals. The
|
|
@code{MeP-Integrator} tool, not part of GCC, provides these
|
|
configurations through this option; using this option is the same as
|
|
using all the corresponding command-line options. The default
|
|
configuration is @samp{default}.
|
|
|
|
@item -mcop
|
|
@opindex mcop
|
|
Enables the coprocessor instructions. By default, this is a 32-bit
|
|
coprocessor. Note that the coprocessor is normally enabled via the
|
|
@option{-mconfig=} option.
|
|
|
|
@item -mcop32
|
|
@opindex mcop32
|
|
Enables the 32-bit coprocessor's instructions.
|
|
|
|
@item -mcop64
|
|
@opindex mcop64
|
|
Enables the 64-bit coprocessor's instructions.
|
|
|
|
@item -mivc2
|
|
@opindex mivc2
|
|
Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor.
|
|
|
|
@item -mdc
|
|
@opindex mdc
|
|
Causes constant variables to be placed in the @code{.near} section.
|
|
|
|
@item -mdiv
|
|
@opindex mdiv
|
|
Enables the @code{div} and @code{divu} instructions.
|
|
|
|
@item -meb
|
|
@opindex meb
|
|
Generate big-endian code.
|
|
|
|
@item -mel
|
|
@opindex mel
|
|
Generate little-endian code.
|
|
|
|
@item -mio-volatile
|
|
@opindex mio-volatile
|
|
Tells the compiler that any variable marked with the @code{io}
|
|
attribute is to be considered volatile.
|
|
|
|
@item -ml
|
|
@opindex ml
|
|
Causes variables to be assigned to the @code{.far} section by default.
|
|
|
|
@item -mleadz
|
|
@opindex mleadz
|
|
Enables the @code{leadz} (leading zero) instruction.
|
|
|
|
@item -mm
|
|
@opindex mm
|
|
Causes variables to be assigned to the @code{.near} section by default.
|
|
|
|
@item -mminmax
|
|
@opindex mminmax
|
|
Enables the @code{min} and @code{max} instructions.
|
|
|
|
@item -mmult
|
|
@opindex mmult
|
|
Enables the multiplication and multiply-accumulate instructions.
|
|
|
|
@item -mno-opts
|
|
@opindex mno-opts
|
|
Disables all the optional instructions enabled by @option{-mall-opts}.
|
|
|
|
@item -mrepeat
|
|
@opindex mrepeat
|
|
Enables the @code{repeat} and @code{erepeat} instructions, used for
|
|
low-overhead looping.
|
|
|
|
@item -ms
|
|
@opindex ms
|
|
Causes all variables to default to the @code{.tiny} section. Note
|
|
that there is a 65536-byte limit to this section. Accesses to these
|
|
variables use the @code{%gp} base register.
|
|
|
|
@item -msatur
|
|
@opindex msatur
|
|
Enables the saturation instructions. Note that the compiler does not
|
|
currently generate these itself, but this option is included for
|
|
compatibility with other tools, like @code{as}.
|
|
|
|
@item -msdram
|
|
@opindex msdram
|
|
Link the SDRAM-based runtime instead of the default ROM-based runtime.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Link the simulator run-time libraries.
|
|
|
|
@item -msimnovec
|
|
@opindex msimnovec
|
|
Link the simulator runtime libraries, excluding built-in support
|
|
for reset and exception vectors and tables.
|
|
|
|
@item -mtf
|
|
@opindex mtf
|
|
Causes all functions to default to the @code{.far} section. Without
|
|
this option, functions default to the @code{.near} section.
|
|
|
|
@item -mtiny=@var{n}
|
|
@opindex mtiny=
|
|
Variables that are @var{n} bytes or smaller are allocated to the
|
|
@code{.tiny} section. These variables use the @code{$gp} base
|
|
register. The default for this option is 4, but note that there's a
|
|
65536-byte limit to the @code{.tiny} section.
|
|
|
|
@end table
|
|
|
|
@node MicroBlaze Options
|
|
@subsection MicroBlaze Options
|
|
@cindex MicroBlaze Options
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Use software emulation for floating point (default).
|
|
|
|
@item -mhard-float
|
|
@opindex mhard-float
|
|
Use hardware floating-point instructions.
|
|
|
|
@item -mmemcpy
|
|
@opindex mmemcpy
|
|
Do not optimize block moves, use @code{memcpy}.
|
|
|
|
@item -mno-clearbss
|
|
@opindex mno-clearbss
|
|
This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead.
|
|
|
|
@item -mcpu=@var{cpu-type}
|
|
@opindex mcpu=
|
|
Use features of, and schedule code for, the given CPU.
|
|
Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}},
|
|
where @var{X} is a major version, @var{YY} is the minor version, and
|
|
@var{Z} is compatibility code. Example values are @samp{v3.00.a},
|
|
@samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v5.00.b}, @samp{v6.00.a}.
|
|
|
|
@item -mxl-soft-mul
|
|
@opindex mxl-soft-mul
|
|
Use software multiply emulation (default).
|
|
|
|
@item -mxl-soft-div
|
|
@opindex mxl-soft-div
|
|
Use software emulation for divides (default).
|
|
|
|
@item -mxl-barrel-shift
|
|
@opindex mxl-barrel-shift
|
|
Use the hardware barrel shifter.
|
|
|
|
@item -mxl-pattern-compare
|
|
@opindex mxl-pattern-compare
|
|
Use pattern compare instructions.
|
|
|
|
@item -msmall-divides
|
|
@opindex msmall-divides
|
|
Use table lookup optimization for small signed integer divisions.
|
|
|
|
@item -mxl-stack-check
|
|
@opindex mxl-stack-check
|
|
This option is deprecated. Use @option{-fstack-check} instead.
|
|
|
|
@item -mxl-gp-opt
|
|
@opindex mxl-gp-opt
|
|
Use GP-relative @code{.sdata}/@code{.sbss} sections.
|
|
|
|
@item -mxl-multiply-high
|
|
@opindex mxl-multiply-high
|
|
Use multiply high instructions for high part of 32x32 multiply.
|
|
|
|
@item -mxl-float-convert
|
|
@opindex mxl-float-convert
|
|
Use hardware floating-point conversion instructions.
|
|
|
|
@item -mxl-float-sqrt
|
|
@opindex mxl-float-sqrt
|
|
Use hardware floating-point square root instruction.
|
|
|
|
@item -mbig-endian
|
|
@opindex mbig-endian
|
|
Generate code for a big-endian target.
|
|
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
Generate code for a little-endian target.
|
|
|
|
@item -mxl-reorder
|
|
@opindex mxl-reorder
|
|
Use reorder instructions (swap and byte reversed load/store).
|
|
|
|
@item -mxl-mode-@var{app-model}
|
|
Select application model @var{app-model}. Valid models are
|
|
@table @samp
|
|
@item executable
|
|
normal executable (default), uses startup code @file{crt0.o}.
|
|
|
|
@item xmdstub
|
|
for use with Xilinx Microprocessor Debugger (XMD) based
|
|
software intrusive debug agent called xmdstub. This uses startup file
|
|
@file{crt1.o} and sets the start address of the program to 0x800.
|
|
|
|
@item bootstrap
|
|
for applications that are loaded using a bootloader.
|
|
This model uses startup file @file{crt2.o} which does not contain a processor
|
|
reset vector handler. This is suitable for transferring control on a
|
|
processor reset to the bootloader rather than the application.
|
|
|
|
@item novectors
|
|
for applications that do not require any of the
|
|
MicroBlaze vectors. This option may be useful for applications running
|
|
within a monitoring application. This model uses @file{crt3.o} as a startup file.
|
|
@end table
|
|
|
|
Option @option{-xl-mode-@var{app-model}} is a deprecated alias for
|
|
@option{-mxl-mode-@var{app-model}}.
|
|
|
|
@end table
|
|
|
|
@node MIPS Options
|
|
@subsection MIPS Options
|
|
@cindex MIPS options
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -EB
|
|
@opindex EB
|
|
Generate big-endian code.
|
|
|
|
@item -EL
|
|
@opindex EL
|
|
Generate little-endian code. This is the default for @samp{mips*el-*-*}
|
|
configurations.
|
|
|
|
@item -march=@var{arch}
|
|
@opindex march
|
|
Generate code that runs on @var{arch}, which can be the name of a
|
|
generic MIPS ISA, or the name of a particular processor.
|
|
The ISA names are:
|
|
@samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4},
|
|
@samp{mips32}, @samp{mips32r2}, @samp{mips32r3}, @samp{mips32r5},
|
|
@samp{mips32r6}, @samp{mips64}, @samp{mips64r2}, @samp{mips64r3},
|
|
@samp{mips64r5} and @samp{mips64r6}.
|
|
The processor names are:
|
|
@samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc},
|
|
@samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd},
|
|
@samp{5kc}, @samp{5kf},
|
|
@samp{20kc},
|
|
@samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1},
|
|
@samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1},
|
|
@samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1}, @samp{34kn},
|
|
@samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2},
|
|
@samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1},
|
|
@samp{i6400},
|
|
@samp{interaptiv},
|
|
@samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a},
|
|
@samp{m4k},
|
|
@samp{m14k}, @samp{m14kc}, @samp{m14ke}, @samp{m14kec},
|
|
@samp{m5100}, @samp{m5101},
|
|
@samp{octeon}, @samp{octeon+}, @samp{octeon2}, @samp{octeon3},
|
|
@samp{orion},
|
|
@samp{p5600},
|
|
@samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400},
|
|
@samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r6000}, @samp{r8000},
|
|
@samp{rm7000}, @samp{rm9000},
|
|
@samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000},
|
|
@samp{sb1},
|
|
@samp{sr71000},
|
|
@samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300},
|
|
@samp{vr5000}, @samp{vr5400}, @samp{vr5500},
|
|
@samp{xlr} and @samp{xlp}.
|
|
The special value @samp{from-abi} selects the
|
|
most compatible architecture for the selected ABI (that is,
|
|
@samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@.
|
|
|
|
The native Linux/GNU toolchain also supports the value @samp{native},
|
|
which selects the best architecture option for the host processor.
|
|
@option{-march=native} has no effect if GCC does not recognize
|
|
the processor.
|
|
|
|
In processor names, a final @samp{000} can be abbreviated as @samp{k}
|
|
(for example, @option{-march=r2k}). Prefixes are optional, and
|
|
@samp{vr} may be written @samp{r}.
|
|
|
|
Names of the form @samp{@var{n}f2_1} refer to processors with
|
|
FPUs clocked at half the rate of the core, names of the form
|
|
@samp{@var{n}f1_1} refer to processors with FPUs clocked at the same
|
|
rate as the core, and names of the form @samp{@var{n}f3_2} refer to
|
|
processors with FPUs clocked a ratio of 3:2 with respect to the core.
|
|
For compatibility reasons, @samp{@var{n}f} is accepted as a synonym
|
|
for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are
|
|
accepted as synonyms for @samp{@var{n}f1_1}.
|
|
|
|
GCC defines two macros based on the value of this option. The first
|
|
is @code{_MIPS_ARCH}, which gives the name of target architecture, as
|
|
a string. The second has the form @code{_MIPS_ARCH_@var{foo}},
|
|
where @var{foo} is the capitalized value of @code{_MIPS_ARCH}@.
|
|
For example, @option{-march=r2000} sets @code{_MIPS_ARCH}
|
|
to @code{"r2000"} and defines the macro @code{_MIPS_ARCH_R2000}.
|
|
|
|
Note that the @code{_MIPS_ARCH} macro uses the processor names given
|
|
above. In other words, it has the full prefix and does not
|
|
abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi},
|
|
the macro names the resolved architecture (either @code{"mips1"} or
|
|
@code{"mips3"}). It names the default architecture when no
|
|
@option{-march} option is given.
|
|
|
|
@item -mtune=@var{arch}
|
|
@opindex mtune
|
|
Optimize for @var{arch}. Among other things, this option controls
|
|
the way instructions are scheduled, and the perceived cost of arithmetic
|
|
operations. The list of @var{arch} values is the same as for
|
|
@option{-march}.
|
|
|
|
When this option is not used, GCC optimizes for the processor
|
|
specified by @option{-march}. By using @option{-march} and
|
|
@option{-mtune} together, it is possible to generate code that
|
|
runs on a family of processors, but optimize the code for one
|
|
particular member of that family.
|
|
|
|
@option{-mtune} defines the macros @code{_MIPS_TUNE} and
|
|
@code{_MIPS_TUNE_@var{foo}}, which work in the same way as the
|
|
@option{-march} ones described above.
|
|
|
|
@item -mips1
|
|
@opindex mips1
|
|
Equivalent to @option{-march=mips1}.
|
|
|
|
@item -mips2
|
|
@opindex mips2
|
|
Equivalent to @option{-march=mips2}.
|
|
|
|
@item -mips3
|
|
@opindex mips3
|
|
Equivalent to @option{-march=mips3}.
|
|
|
|
@item -mips4
|
|
@opindex mips4
|
|
Equivalent to @option{-march=mips4}.
|
|
|
|
@item -mips32
|
|
@opindex mips32
|
|
Equivalent to @option{-march=mips32}.
|
|
|
|
@item -mips32r3
|
|
@opindex mips32r3
|
|
Equivalent to @option{-march=mips32r3}.
|
|
|
|
@item -mips32r5
|
|
@opindex mips32r5
|
|
Equivalent to @option{-march=mips32r5}.
|
|
|
|
@item -mips32r6
|
|
@opindex mips32r6
|
|
Equivalent to @option{-march=mips32r6}.
|
|
|
|
@item -mips64
|
|
@opindex mips64
|
|
Equivalent to @option{-march=mips64}.
|
|
|
|
@item -mips64r2
|
|
@opindex mips64r2
|
|
Equivalent to @option{-march=mips64r2}.
|
|
|
|
@item -mips64r3
|
|
@opindex mips64r3
|
|
Equivalent to @option{-march=mips64r3}.
|
|
|
|
@item -mips64r5
|
|
@opindex mips64r5
|
|
Equivalent to @option{-march=mips64r5}.
|
|
|
|
@item -mips64r6
|
|
@opindex mips64r6
|
|
Equivalent to @option{-march=mips64r6}.
|
|
|
|
@item -mips16
|
|
@itemx -mno-mips16
|
|
@opindex mips16
|
|
@opindex mno-mips16
|
|
Generate (do not generate) MIPS16 code. If GCC is targeting a
|
|
MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE@.
|
|
|
|
MIPS16 code generation can also be controlled on a per-function basis
|
|
by means of @code{mips16} and @code{nomips16} attributes.
|
|
@xref{Function Attributes}, for more information.
|
|
|
|
@item -mflip-mips16
|
|
@opindex mflip-mips16
|
|
Generate MIPS16 code on alternating functions. This option is provided
|
|
for regression testing of mixed MIPS16/non-MIPS16 code generation, and is
|
|
not intended for ordinary use in compiling user code.
|
|
|
|
@item -minterlink-compressed
|
|
@item -mno-interlink-compressed
|
|
@opindex minterlink-compressed
|
|
@opindex mno-interlink-compressed
|
|
Require (do not require) that code using the standard (uncompressed) MIPS ISA
|
|
be link-compatible with MIPS16 and microMIPS code, and vice versa.
|
|
|
|
For example, code using the standard ISA encoding cannot jump directly
|
|
to MIPS16 or microMIPS code; it must either use a call or an indirect jump.
|
|
@option{-minterlink-compressed} therefore disables direct jumps unless GCC
|
|
knows that the target of the jump is not compressed.
|
|
|
|
@item -minterlink-mips16
|
|
@itemx -mno-interlink-mips16
|
|
@opindex minterlink-mips16
|
|
@opindex mno-interlink-mips16
|
|
Aliases of @option{-minterlink-compressed} and
|
|
@option{-mno-interlink-compressed}. These options predate the microMIPS ASE
|
|
and are retained for backwards compatibility.
|
|
|
|
@item -mabi=32
|
|
@itemx -mabi=o64
|
|
@itemx -mabi=n32
|
|
@itemx -mabi=64
|
|
@itemx -mabi=eabi
|
|
@opindex mabi=32
|
|
@opindex mabi=o64
|
|
@opindex mabi=n32
|
|
@opindex mabi=64
|
|
@opindex mabi=eabi
|
|
Generate code for the given ABI@.
|
|
|
|
Note that the EABI has a 32-bit and a 64-bit variant. GCC normally
|
|
generates 64-bit code when you select a 64-bit architecture, but you
|
|
can use @option{-mgp32} to get 32-bit code instead.
|
|
|
|
For information about the O64 ABI, see
|
|
@uref{http://gcc.gnu.org/@/projects/@/mipso64-abi.html}.
|
|
|
|
GCC supports a variant of the o32 ABI in which floating-point registers
|
|
are 64 rather than 32 bits wide. You can select this combination with
|
|
@option{-mabi=32} @option{-mfp64}. This ABI relies on the @code{mthc1}
|
|
and @code{mfhc1} instructions and is therefore only supported for
|
|
MIPS32R2, MIPS32R3 and MIPS32R5 processors.
|
|
|
|
The register assignments for arguments and return values remain the
|
|
same, but each scalar value is passed in a single 64-bit register
|
|
rather than a pair of 32-bit registers. For example, scalar
|
|
floating-point values are returned in @samp{$f0} only, not a
|
|
@samp{$f0}/@samp{$f1} pair. The set of call-saved registers also
|
|
remains the same in that the even-numbered double-precision registers
|
|
are saved.
|
|
|
|
Two additional variants of the o32 ABI are supported to enable
|
|
a transition from 32-bit to 64-bit registers. These are FPXX
|
|
(@option{-mfpxx}) and FP64A (@option{-mfp64} @option{-mno-odd-spreg}).
|
|
The FPXX extension mandates that all code must execute correctly
|
|
when run using 32-bit or 64-bit registers. The code can be interlinked
|
|
with either FP32 or FP64, but not both.
|
|
The FP64A extension is similar to the FP64 extension but forbids the
|
|
use of odd-numbered single-precision registers. This can be used
|
|
in conjunction with the @code{FRE} mode of FPUs in MIPS32R5
|
|
processors and allows both FP32 and FP64A code to interlink and
|
|
run in the same process without changing FPU modes.
|
|
|
|
@item -mabicalls
|
|
@itemx -mno-abicalls
|
|
@opindex mabicalls
|
|
@opindex mno-abicalls
|
|
Generate (do not generate) code that is suitable for SVR4-style
|
|
dynamic objects. @option{-mabicalls} is the default for SVR4-based
|
|
systems.
|
|
|
|
@item -mshared
|
|
@itemx -mno-shared
|
|
Generate (do not generate) code that is fully position-independent,
|
|
and that can therefore be linked into shared libraries. This option
|
|
only affects @option{-mabicalls}.
|
|
|
|
All @option{-mabicalls} code has traditionally been position-independent,
|
|
regardless of options like @option{-fPIC} and @option{-fpic}. However,
|
|
as an extension, the GNU toolchain allows executables to use absolute
|
|
accesses for locally-binding symbols. It can also use shorter GP
|
|
initialization sequences and generate direct calls to locally-defined
|
|
functions. This mode is selected by @option{-mno-shared}.
|
|
|
|
@option{-mno-shared} depends on binutils 2.16 or higher and generates
|
|
objects that can only be linked by the GNU linker. However, the option
|
|
does not affect the ABI of the final executable; it only affects the ABI
|
|
of relocatable objects. Using @option{-mno-shared} generally makes
|
|
executables both smaller and quicker.
|
|
|
|
@option{-mshared} is the default.
|
|
|
|
@item -mplt
|
|
@itemx -mno-plt
|
|
@opindex mplt
|
|
@opindex mno-plt
|
|
Assume (do not assume) that the static and dynamic linkers
|
|
support PLTs and copy relocations. This option only affects
|
|
@option{-mno-shared -mabicalls}. For the n64 ABI, this option
|
|
has no effect without @option{-msym32}.
|
|
|
|
You can make @option{-mplt} the default by configuring
|
|
GCC with @option{--with-mips-plt}. The default is
|
|
@option{-mno-plt} otherwise.
|
|
|
|
@item -mxgot
|
|
@itemx -mno-xgot
|
|
@opindex mxgot
|
|
@opindex mno-xgot
|
|
Lift (do not lift) the usual restrictions on the size of the global
|
|
offset table.
|
|
|
|
GCC normally uses a single instruction to load values from the GOT@.
|
|
While this is relatively efficient, it only works if the GOT
|
|
is smaller than about 64k. Anything larger causes the linker
|
|
to report an error such as:
|
|
|
|
@cindex relocation truncated to fit (MIPS)
|
|
@smallexample
|
|
relocation truncated to fit: R_MIPS_GOT16 foobar
|
|
@end smallexample
|
|
|
|
If this happens, you should recompile your code with @option{-mxgot}.
|
|
This works with very large GOTs, although the code is also
|
|
less efficient, since it takes three instructions to fetch the
|
|
value of a global symbol.
|
|
|
|
Note that some linkers can create multiple GOTs. If you have such a
|
|
linker, you should only need to use @option{-mxgot} when a single object
|
|
file accesses more than 64k's worth of GOT entries. Very few do.
|
|
|
|
These options have no effect unless GCC is generating position
|
|
independent code.
|
|
|
|
@item -mgp32
|
|
@opindex mgp32
|
|
Assume that general-purpose registers are 32 bits wide.
|
|
|
|
@item -mgp64
|
|
@opindex mgp64
|
|
Assume that general-purpose registers are 64 bits wide.
|
|
|
|
@item -mfp32
|
|
@opindex mfp32
|
|
Assume that floating-point registers are 32 bits wide.
|
|
|
|
@item -mfp64
|
|
@opindex mfp64
|
|
Assume that floating-point registers are 64 bits wide.
|
|
|
|
@item -mfpxx
|
|
@opindex mfpxx
|
|
Do not assume the width of floating-point registers.
|
|
|
|
@item -mhard-float
|
|
@opindex mhard-float
|
|
Use floating-point coprocessor instructions.
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Do not use floating-point coprocessor instructions. Implement
|
|
floating-point calculations using library calls instead.
|
|
|
|
@item -mno-float
|
|
@opindex mno-float
|
|
Equivalent to @option{-msoft-float}, but additionally asserts that the
|
|
program being compiled does not perform any floating-point operations.
|
|
This option is presently supported only by some bare-metal MIPS
|
|
configurations, where it may select a special set of libraries
|
|
that lack all floating-point support (including, for example, the
|
|
floating-point @code{printf} formats).
|
|
If code compiled with @option{-mno-float} accidentally contains
|
|
floating-point operations, it is likely to suffer a link-time
|
|
or run-time failure.
|
|
|
|
@item -msingle-float
|
|
@opindex msingle-float
|
|
Assume that the floating-point coprocessor only supports single-precision
|
|
operations.
|
|
|
|
@item -mdouble-float
|
|
@opindex mdouble-float
|
|
Assume that the floating-point coprocessor supports double-precision
|
|
operations. This is the default.
|
|
|
|
@item -modd-spreg
|
|
@itemx -mno-odd-spreg
|
|
@opindex modd-spreg
|
|
@opindex mno-odd-spreg
|
|
Enable the use of odd-numbered single-precision floating-point registers
|
|
for the o32 ABI. This is the default for processors that are known to
|
|
support these registers. When using the o32 FPXX ABI, @option{-mno-odd-spreg}
|
|
is set by default.
|
|
|
|
@item -mabs=2008
|
|
@itemx -mabs=legacy
|
|
@opindex mabs=2008
|
|
@opindex mabs=legacy
|
|
These options control the treatment of the special not-a-number (NaN)
|
|
IEEE 754 floating-point data with the @code{abs.@i{fmt}} and
|
|
@code{neg.@i{fmt}} machine instructions.
|
|
|
|
By default or when @option{-mabs=legacy} is used the legacy
|
|
treatment is selected. In this case these instructions are considered
|
|
arithmetic and avoided where correct operation is required and the
|
|
input operand might be a NaN. A longer sequence of instructions that
|
|
manipulate the sign bit of floating-point datum manually is used
|
|
instead unless the @option{-ffinite-math-only} option has also been
|
|
specified.
|
|
|
|
The @option{-mabs=2008} option selects the IEEE 754-2008 treatment. In
|
|
this case these instructions are considered non-arithmetic and therefore
|
|
operating correctly in all cases, including in particular where the
|
|
input operand is a NaN. These instructions are therefore always used
|
|
for the respective operations.
|
|
|
|
@item -mnan=2008
|
|
@itemx -mnan=legacy
|
|
@opindex mnan=2008
|
|
@opindex mnan=legacy
|
|
These options control the encoding of the special not-a-number (NaN)
|
|
IEEE 754 floating-point data.
|
|
|
|
The @option{-mnan=legacy} option selects the legacy encoding. In this
|
|
case quiet NaNs (qNaNs) are denoted by the first bit of their trailing
|
|
significand field being 0, whereas signaling NaNs (sNaNs) are denoted
|
|
by the first bit of their trailing significand field being 1.
|
|
|
|
The @option{-mnan=2008} option selects the IEEE 754-2008 encoding. In
|
|
this case qNaNs are denoted by the first bit of their trailing
|
|
significand field being 1, whereas sNaNs are denoted by the first bit of
|
|
their trailing significand field being 0.
|
|
|
|
The default is @option{-mnan=legacy} unless GCC has been configured with
|
|
@option{--with-nan=2008}.
|
|
|
|
@item -mllsc
|
|
@itemx -mno-llsc
|
|
@opindex mllsc
|
|
@opindex mno-llsc
|
|
Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to
|
|
implement atomic memory built-in functions. When neither option is
|
|
specified, GCC uses the instructions if the target architecture
|
|
supports them.
|
|
|
|
@option{-mllsc} is useful if the runtime environment can emulate the
|
|
instructions and @option{-mno-llsc} can be useful when compiling for
|
|
nonstandard ISAs. You can make either option the default by
|
|
configuring GCC with @option{--with-llsc} and @option{--without-llsc}
|
|
respectively. @option{--with-llsc} is the default for some
|
|
configurations; see the installation documentation for details.
|
|
|
|
@item -mdsp
|
|
@itemx -mno-dsp
|
|
@opindex mdsp
|
|
@opindex mno-dsp
|
|
Use (do not use) revision 1 of the MIPS DSP ASE@.
|
|
@xref{MIPS DSP Built-in Functions}. This option defines the
|
|
preprocessor macro @code{__mips_dsp}. It also defines
|
|
@code{__mips_dsp_rev} to 1.
|
|
|
|
@item -mdspr2
|
|
@itemx -mno-dspr2
|
|
@opindex mdspr2
|
|
@opindex mno-dspr2
|
|
Use (do not use) revision 2 of the MIPS DSP ASE@.
|
|
@xref{MIPS DSP Built-in Functions}. This option defines the
|
|
preprocessor macros @code{__mips_dsp} and @code{__mips_dspr2}.
|
|
It also defines @code{__mips_dsp_rev} to 2.
|
|
|
|
@item -msmartmips
|
|
@itemx -mno-smartmips
|
|
@opindex msmartmips
|
|
@opindex mno-smartmips
|
|
Use (do not use) the MIPS SmartMIPS ASE.
|
|
|
|
@item -mpaired-single
|
|
@itemx -mno-paired-single
|
|
@opindex mpaired-single
|
|
@opindex mno-paired-single
|
|
Use (do not use) paired-single floating-point instructions.
|
|
@xref{MIPS Paired-Single Support}. This option requires
|
|
hardware floating-point support to be enabled.
|
|
|
|
@item -mdmx
|
|
@itemx -mno-mdmx
|
|
@opindex mdmx
|
|
@opindex mno-mdmx
|
|
Use (do not use) MIPS Digital Media Extension instructions.
|
|
This option can only be used when generating 64-bit code and requires
|
|
hardware floating-point support to be enabled.
|
|
|
|
@item -mips3d
|
|
@itemx -mno-mips3d
|
|
@opindex mips3d
|
|
@opindex mno-mips3d
|
|
Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}.
|
|
The option @option{-mips3d} implies @option{-mpaired-single}.
|
|
|
|
@item -mmicromips
|
|
@itemx -mno-micromips
|
|
@opindex mmicromips
|
|
@opindex mno-mmicromips
|
|
Generate (do not generate) microMIPS code.
|
|
|
|
MicroMIPS code generation can also be controlled on a per-function basis
|
|
by means of @code{micromips} and @code{nomicromips} attributes.
|
|
@xref{Function Attributes}, for more information.
|
|
|
|
@item -mmt
|
|
@itemx -mno-mt
|
|
@opindex mmt
|
|
@opindex mno-mt
|
|
Use (do not use) MT Multithreading instructions.
|
|
|
|
@item -mmcu
|
|
@itemx -mno-mcu
|
|
@opindex mmcu
|
|
@opindex mno-mcu
|
|
Use (do not use) the MIPS MCU ASE instructions.
|
|
|
|
@item -meva
|
|
@itemx -mno-eva
|
|
@opindex meva
|
|
@opindex mno-eva
|
|
Use (do not use) the MIPS Enhanced Virtual Addressing instructions.
|
|
|
|
@item -mvirt
|
|
@itemx -mno-virt
|
|
@opindex mvirt
|
|
@opindex mno-virt
|
|
Use (do not use) the MIPS Virtualization Application Specific instructions.
|
|
|
|
@item -mxpa
|
|
@itemx -mno-xpa
|
|
@opindex mxpa
|
|
@opindex mno-xpa
|
|
Use (do not use) the MIPS eXtended Physical Address (XPA) instructions.
|
|
|
|
@item -mlong64
|
|
@opindex mlong64
|
|
Force @code{long} types to be 64 bits wide. See @option{-mlong32} for
|
|
an explanation of the default and the way that the pointer size is
|
|
determined.
|
|
|
|
@item -mlong32
|
|
@opindex mlong32
|
|
Force @code{long}, @code{int}, and pointer types to be 32 bits wide.
|
|
|
|
The default size of @code{int}s, @code{long}s and pointers depends on
|
|
the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI
|
|
uses 64-bit @code{long}s, as does the 64-bit EABI; the others use
|
|
32-bit @code{long}s. Pointers are the same size as @code{long}s,
|
|
or the same size as integer registers, whichever is smaller.
|
|
|
|
@item -msym32
|
|
@itemx -mno-sym32
|
|
@opindex msym32
|
|
@opindex mno-sym32
|
|
Assume (do not assume) that all symbols have 32-bit values, regardless
|
|
of the selected ABI@. This option is useful in combination with
|
|
@option{-mabi=64} and @option{-mno-abicalls} because it allows GCC
|
|
to generate shorter and faster references to symbolic addresses.
|
|
|
|
@item -G @var{num}
|
|
@opindex G
|
|
Put definitions of externally-visible data in a small data section
|
|
if that data is no bigger than @var{num} bytes. GCC can then generate
|
|
more efficient accesses to the data; see @option{-mgpopt} for details.
|
|
|
|
The default @option{-G} option depends on the configuration.
|
|
|
|
@item -mlocal-sdata
|
|
@itemx -mno-local-sdata
|
|
@opindex mlocal-sdata
|
|
@opindex mno-local-sdata
|
|
Extend (do not extend) the @option{-G} behavior to local data too,
|
|
such as to static variables in C@. @option{-mlocal-sdata} is the
|
|
default for all configurations.
|
|
|
|
If the linker complains that an application is using too much small data,
|
|
you might want to try rebuilding the less performance-critical parts with
|
|
@option{-mno-local-sdata}. You might also want to build large
|
|
libraries with @option{-mno-local-sdata}, so that the libraries leave
|
|
more room for the main program.
|
|
|
|
@item -mextern-sdata
|
|
@itemx -mno-extern-sdata
|
|
@opindex mextern-sdata
|
|
@opindex mno-extern-sdata
|
|
Assume (do not assume) that externally-defined data is in
|
|
a small data section if the size of that data is within the @option{-G} limit.
|
|
@option{-mextern-sdata} is the default for all configurations.
|
|
|
|
If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G
|
|
@var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var}
|
|
that is no bigger than @var{num} bytes, you must make sure that @var{Var}
|
|
is placed in a small data section. If @var{Var} is defined by another
|
|
module, you must either compile that module with a high-enough
|
|
@option{-G} setting or attach a @code{section} attribute to @var{Var}'s
|
|
definition. If @var{Var} is common, you must link the application
|
|
with a high-enough @option{-G} setting.
|
|
|
|
The easiest way of satisfying these restrictions is to compile
|
|
and link every module with the same @option{-G} option. However,
|
|
you may wish to build a library that supports several different
|
|
small data limits. You can do this by compiling the library with
|
|
the highest supported @option{-G} setting and additionally using
|
|
@option{-mno-extern-sdata} to stop the library from making assumptions
|
|
about externally-defined data.
|
|
|
|
@item -mgpopt
|
|
@itemx -mno-gpopt
|
|
@opindex mgpopt
|
|
@opindex mno-gpopt
|
|
Use (do not use) GP-relative accesses for symbols that are known to be
|
|
in a small data section; see @option{-G}, @option{-mlocal-sdata} and
|
|
@option{-mextern-sdata}. @option{-mgpopt} is the default for all
|
|
configurations.
|
|
|
|
@option{-mno-gpopt} is useful for cases where the @code{$gp} register
|
|
might not hold the value of @code{_gp}. For example, if the code is
|
|
part of a library that might be used in a boot monitor, programs that
|
|
call boot monitor routines pass an unknown value in @code{$gp}.
|
|
(In such situations, the boot monitor itself is usually compiled
|
|
with @option{-G0}.)
|
|
|
|
@option{-mno-gpopt} implies @option{-mno-local-sdata} and
|
|
@option{-mno-extern-sdata}.
|
|
|
|
@item -membedded-data
|
|
@itemx -mno-embedded-data
|
|
@opindex membedded-data
|
|
@opindex mno-embedded-data
|
|
Allocate variables to the read-only data section first if possible, then
|
|
next in the small data section if possible, otherwise in data. This gives
|
|
slightly slower code than the default, but reduces the amount of RAM required
|
|
when executing, and thus may be preferred for some embedded systems.
|
|
|
|
@item -muninit-const-in-rodata
|
|
@itemx -mno-uninit-const-in-rodata
|
|
@opindex muninit-const-in-rodata
|
|
@opindex mno-uninit-const-in-rodata
|
|
Put uninitialized @code{const} variables in the read-only data section.
|
|
This option is only meaningful in conjunction with @option{-membedded-data}.
|
|
|
|
@item -mcode-readable=@var{setting}
|
|
@opindex mcode-readable
|
|
Specify whether GCC may generate code that reads from executable sections.
|
|
There are three possible settings:
|
|
|
|
@table @gcctabopt
|
|
@item -mcode-readable=yes
|
|
Instructions may freely access executable sections. This is the
|
|
default setting.
|
|
|
|
@item -mcode-readable=pcrel
|
|
MIPS16 PC-relative load instructions can access executable sections,
|
|
but other instructions must not do so. This option is useful on 4KSc
|
|
and 4KSd processors when the code TLBs have the Read Inhibit bit set.
|
|
It is also useful on processors that can be configured to have a dual
|
|
instruction/data SRAM interface and that, like the M4K, automatically
|
|
redirect PC-relative loads to the instruction RAM.
|
|
|
|
@item -mcode-readable=no
|
|
Instructions must not access executable sections. This option can be
|
|
useful on targets that are configured to have a dual instruction/data
|
|
SRAM interface but that (unlike the M4K) do not automatically redirect
|
|
PC-relative loads to the instruction RAM.
|
|
@end table
|
|
|
|
@item -msplit-addresses
|
|
@itemx -mno-split-addresses
|
|
@opindex msplit-addresses
|
|
@opindex mno-split-addresses
|
|
Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler
|
|
relocation operators. This option has been superseded by
|
|
@option{-mexplicit-relocs} but is retained for backwards compatibility.
|
|
|
|
@item -mexplicit-relocs
|
|
@itemx -mno-explicit-relocs
|
|
@opindex mexplicit-relocs
|
|
@opindex mno-explicit-relocs
|
|
Use (do not use) assembler relocation operators when dealing with symbolic
|
|
addresses. The alternative, selected by @option{-mno-explicit-relocs},
|
|
is to use assembler macros instead.
|
|
|
|
@option{-mexplicit-relocs} is the default if GCC was configured
|
|
to use an assembler that supports relocation operators.
|
|
|
|
@item -mcheck-zero-division
|
|
@itemx -mno-check-zero-division
|
|
@opindex mcheck-zero-division
|
|
@opindex mno-check-zero-division
|
|
Trap (do not trap) on integer division by zero.
|
|
|
|
The default is @option{-mcheck-zero-division}.
|
|
|
|
@item -mdivide-traps
|
|
@itemx -mdivide-breaks
|
|
@opindex mdivide-traps
|
|
@opindex mdivide-breaks
|
|
MIPS systems check for division by zero by generating either a
|
|
conditional trap or a break instruction. Using traps results in
|
|
smaller code, but is only supported on MIPS II and later. Also, some
|
|
versions of the Linux kernel have a bug that prevents trap from
|
|
generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to
|
|
allow conditional traps on architectures that support them and
|
|
@option{-mdivide-breaks} to force the use of breaks.
|
|
|
|
The default is usually @option{-mdivide-traps}, but this can be
|
|
overridden at configure time using @option{--with-divide=breaks}.
|
|
Divide-by-zero checks can be completely disabled using
|
|
@option{-mno-check-zero-division}.
|
|
|
|
@item -mmemcpy
|
|
@itemx -mno-memcpy
|
|
@opindex mmemcpy
|
|
@opindex mno-memcpy
|
|
Force (do not force) the use of @code{memcpy} for non-trivial block
|
|
moves. The default is @option{-mno-memcpy}, which allows GCC to inline
|
|
most constant-sized copies.
|
|
|
|
@item -mlong-calls
|
|
@itemx -mno-long-calls
|
|
@opindex mlong-calls
|
|
@opindex mno-long-calls
|
|
Disable (do not disable) use of the @code{jal} instruction. Calling
|
|
functions using @code{jal} is more efficient but requires the caller
|
|
and callee to be in the same 256 megabyte segment.
|
|
|
|
This option has no effect on abicalls code. The default is
|
|
@option{-mno-long-calls}.
|
|
|
|
@item -mmad
|
|
@itemx -mno-mad
|
|
@opindex mmad
|
|
@opindex mno-mad
|
|
Enable (disable) use of the @code{mad}, @code{madu} and @code{mul}
|
|
instructions, as provided by the R4650 ISA@.
|
|
|
|
@item -mimadd
|
|
@itemx -mno-imadd
|
|
@opindex mimadd
|
|
@opindex mno-imadd
|
|
Enable (disable) use of the @code{madd} and @code{msub} integer
|
|
instructions. The default is @option{-mimadd} on architectures
|
|
that support @code{madd} and @code{msub} except for the 74k
|
|
architecture where it was found to generate slower code.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Enable (disable) use of the floating-point multiply-accumulate
|
|
instructions, when they are available. The default is
|
|
@option{-mfused-madd}.
|
|
|
|
On the R8000 CPU when multiply-accumulate instructions are used,
|
|
the intermediate product is calculated to infinite precision
|
|
and is not subject to the FCSR Flush to Zero bit. This may be
|
|
undesirable in some circumstances. On other processors the result
|
|
is numerically identical to the equivalent computation using
|
|
separate multiply, add, subtract and negate instructions.
|
|
|
|
@item -nocpp
|
|
@opindex nocpp
|
|
Tell the MIPS assembler to not run its preprocessor over user
|
|
assembler files (with a @samp{.s} suffix) when assembling them.
|
|
|
|
@item -mfix-24k
|
|
@item -mno-fix-24k
|
|
@opindex mfix-24k
|
|
@opindex mno-fix-24k
|
|
Work around the 24K E48 (lost data on stores during refill) errata.
|
|
The workarounds are implemented by the assembler rather than by GCC@.
|
|
|
|
@item -mfix-r4000
|
|
@itemx -mno-fix-r4000
|
|
@opindex mfix-r4000
|
|
@opindex mno-fix-r4000
|
|
Work around certain R4000 CPU errata:
|
|
@itemize @minus
|
|
@item
|
|
A double-word or a variable shift may give an incorrect result if executed
|
|
immediately after starting an integer division.
|
|
@item
|
|
A double-word or a variable shift may give an incorrect result if executed
|
|
while an integer multiplication is in progress.
|
|
@item
|
|
An integer division may give an incorrect result if started in a delay slot
|
|
of a taken branch or a jump.
|
|
@end itemize
|
|
|
|
@item -mfix-r4400
|
|
@itemx -mno-fix-r4400
|
|
@opindex mfix-r4400
|
|
@opindex mno-fix-r4400
|
|
Work around certain R4400 CPU errata:
|
|
@itemize @minus
|
|
@item
|
|
A double-word or a variable shift may give an incorrect result if executed
|
|
immediately after starting an integer division.
|
|
@end itemize
|
|
|
|
@item -mfix-r10000
|
|
@itemx -mno-fix-r10000
|
|
@opindex mfix-r10000
|
|
@opindex mno-fix-r10000
|
|
Work around certain R10000 errata:
|
|
@itemize @minus
|
|
@item
|
|
@code{ll}/@code{sc} sequences may not behave atomically on revisions
|
|
prior to 3.0. They may deadlock on revisions 2.6 and earlier.
|
|
@end itemize
|
|
|
|
This option can only be used if the target architecture supports
|
|
branch-likely instructions. @option{-mfix-r10000} is the default when
|
|
@option{-march=r10000} is used; @option{-mno-fix-r10000} is the default
|
|
otherwise.
|
|
|
|
@item -mfix-rm7000
|
|
@itemx -mno-fix-rm7000
|
|
@opindex mfix-rm7000
|
|
Work around the RM7000 @code{dmult}/@code{dmultu} errata. The
|
|
workarounds are implemented by the assembler rather than by GCC@.
|
|
|
|
@item -mfix-vr4120
|
|
@itemx -mno-fix-vr4120
|
|
@opindex mfix-vr4120
|
|
Work around certain VR4120 errata:
|
|
@itemize @minus
|
|
@item
|
|
@code{dmultu} does not always produce the correct result.
|
|
@item
|
|
@code{div} and @code{ddiv} do not always produce the correct result if one
|
|
of the operands is negative.
|
|
@end itemize
|
|
The workarounds for the division errata rely on special functions in
|
|
@file{libgcc.a}. At present, these functions are only provided by
|
|
the @code{mips64vr*-elf} configurations.
|
|
|
|
Other VR4120 errata require a NOP to be inserted between certain pairs of
|
|
instructions. These errata are handled by the assembler, not by GCC itself.
|
|
|
|
@item -mfix-vr4130
|
|
@opindex mfix-vr4130
|
|
Work around the VR4130 @code{mflo}/@code{mfhi} errata. The
|
|
workarounds are implemented by the assembler rather than by GCC,
|
|
although GCC avoids using @code{mflo} and @code{mfhi} if the
|
|
VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi}
|
|
instructions are available instead.
|
|
|
|
@item -mfix-sb1
|
|
@itemx -mno-fix-sb1
|
|
@opindex mfix-sb1
|
|
Work around certain SB-1 CPU core errata.
|
|
(This flag currently works around the SB-1 revision 2
|
|
``F1'' and ``F2'' floating-point errata.)
|
|
|
|
@item -mr10k-cache-barrier=@var{setting}
|
|
@opindex mr10k-cache-barrier
|
|
Specify whether GCC should insert cache barriers to avoid the
|
|
side-effects of speculation on R10K processors.
|
|
|
|
In common with many processors, the R10K tries to predict the outcome
|
|
of a conditional branch and speculatively executes instructions from
|
|
the ``taken'' branch. It later aborts these instructions if the
|
|
predicted outcome is wrong. However, on the R10K, even aborted
|
|
instructions can have side effects.
|
|
|
|
This problem only affects kernel stores and, depending on the system,
|
|
kernel loads. As an example, a speculatively-executed store may load
|
|
the target memory into cache and mark the cache line as dirty, even if
|
|
the store itself is later aborted. If a DMA operation writes to the
|
|
same area of memory before the ``dirty'' line is flushed, the cached
|
|
data overwrites the DMA-ed data. See the R10K processor manual
|
|
for a full description, including other potential problems.
|
|
|
|
One workaround is to insert cache barrier instructions before every memory
|
|
access that might be speculatively executed and that might have side
|
|
effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}}
|
|
controls GCC's implementation of this workaround. It assumes that
|
|
aborted accesses to any byte in the following regions does not have
|
|
side effects:
|
|
|
|
@enumerate
|
|
@item
|
|
the memory occupied by the current function's stack frame;
|
|
|
|
@item
|
|
the memory occupied by an incoming stack argument;
|
|
|
|
@item
|
|
the memory occupied by an object with a link-time-constant address.
|
|
@end enumerate
|
|
|
|
It is the kernel's responsibility to ensure that speculative
|
|
accesses to these regions are indeed safe.
|
|
|
|
If the input program contains a function declaration such as:
|
|
|
|
@smallexample
|
|
void foo (void);
|
|
@end smallexample
|
|
|
|
then the implementation of @code{foo} must allow @code{j foo} and
|
|
@code{jal foo} to be executed speculatively. GCC honors this
|
|
restriction for functions it compiles itself. It expects non-GCC
|
|
functions (such as hand-written assembly code) to do the same.
|
|
|
|
The option has three forms:
|
|
|
|
@table @gcctabopt
|
|
@item -mr10k-cache-barrier=load-store
|
|
Insert a cache barrier before a load or store that might be
|
|
speculatively executed and that might have side effects even
|
|
if aborted.
|
|
|
|
@item -mr10k-cache-barrier=store
|
|
Insert a cache barrier before a store that might be speculatively
|
|
executed and that might have side effects even if aborted.
|
|
|
|
@item -mr10k-cache-barrier=none
|
|
Disable the insertion of cache barriers. This is the default setting.
|
|
@end table
|
|
|
|
@item -mflush-func=@var{func}
|
|
@itemx -mno-flush-func
|
|
@opindex mflush-func
|
|
Specifies the function to call to flush the I and D caches, or to not
|
|
call any such function. If called, the function must take the same
|
|
arguments as the common @code{_flush_func}, that is, the address of the
|
|
memory range for which the cache is being flushed, the size of the
|
|
memory range, and the number 3 (to flush both caches). The default
|
|
depends on the target GCC was configured for, but commonly is either
|
|
@code{_flush_func} or @code{__cpu_flush}.
|
|
|
|
@item mbranch-cost=@var{num}
|
|
@opindex mbranch-cost
|
|
Set the cost of branches to roughly @var{num} ``simple'' instructions.
|
|
This cost is only a heuristic and is not guaranteed to produce
|
|
consistent results across releases. A zero cost redundantly selects
|
|
the default, which is based on the @option{-mtune} setting.
|
|
|
|
@item -mbranch-likely
|
|
@itemx -mno-branch-likely
|
|
@opindex mbranch-likely
|
|
@opindex mno-branch-likely
|
|
Enable or disable use of Branch Likely instructions, regardless of the
|
|
default for the selected architecture. By default, Branch Likely
|
|
instructions may be generated if they are supported by the selected
|
|
architecture. An exception is for the MIPS32 and MIPS64 architectures
|
|
and processors that implement those architectures; for those, Branch
|
|
Likely instructions are not be generated by default because the MIPS32
|
|
and MIPS64 architectures specifically deprecate their use.
|
|
|
|
@item -mcompact-branches=never
|
|
@itemx -mcompact-branches=optimal
|
|
@itemx -mcompact-branches=always
|
|
@opindex mcompact-branches=never
|
|
@opindex mcompact-branches=optimal
|
|
@opindex mcompact-branches=always
|
|
These options control which form of branches will be generated. The
|
|
default is @option{-mcompact-branches=optimal}.
|
|
|
|
The @option{-mcompact-branches=never} option ensures that compact branch
|
|
instructions will never be generated.
|
|
|
|
The @option{-mcompact-branches=always} option ensures that a compact
|
|
branch instruction will be generated if available. If a compact branch
|
|
instruction is not available, a delay slot form of the branch will be
|
|
used instead.
|
|
|
|
This option is supported from MIPS Release 6 onwards.
|
|
|
|
The @option{-mcompact-branches=optimal} option will cause a delay slot
|
|
branch to be used if one is available in the current ISA and the delay
|
|
slot is successfully filled. If the delay slot is not filled, a compact
|
|
branch will be chosen if one is available.
|
|
|
|
@item -mfp-exceptions
|
|
@itemx -mno-fp-exceptions
|
|
@opindex mfp-exceptions
|
|
Specifies whether FP exceptions are enabled. This affects how
|
|
FP instructions are scheduled for some processors.
|
|
The default is that FP exceptions are
|
|
enabled.
|
|
|
|
For instance, on the SB-1, if FP exceptions are disabled, and we are emitting
|
|
64-bit code, then we can use both FP pipes. Otherwise, we can only use one
|
|
FP pipe.
|
|
|
|
@item -mvr4130-align
|
|
@itemx -mno-vr4130-align
|
|
@opindex mvr4130-align
|
|
The VR4130 pipeline is two-way superscalar, but can only issue two
|
|
instructions together if the first one is 8-byte aligned. When this
|
|
option is enabled, GCC aligns pairs of instructions that it
|
|
thinks should execute in parallel.
|
|
|
|
This option only has an effect when optimizing for the VR4130.
|
|
It normally makes code faster, but at the expense of making it bigger.
|
|
It is enabled by default at optimization level @option{-O3}.
|
|
|
|
@item -msynci
|
|
@itemx -mno-synci
|
|
@opindex msynci
|
|
Enable (disable) generation of @code{synci} instructions on
|
|
architectures that support it. The @code{synci} instructions (if
|
|
enabled) are generated when @code{__builtin___clear_cache} is
|
|
compiled.
|
|
|
|
This option defaults to @option{-mno-synci}, but the default can be
|
|
overridden by configuring GCC with @option{--with-synci}.
|
|
|
|
When compiling code for single processor systems, it is generally safe
|
|
to use @code{synci}. However, on many multi-core (SMP) systems, it
|
|
does not invalidate the instruction caches on all cores and may lead
|
|
to undefined behavior.
|
|
|
|
@item -mrelax-pic-calls
|
|
@itemx -mno-relax-pic-calls
|
|
@opindex mrelax-pic-calls
|
|
Try to turn PIC calls that are normally dispatched via register
|
|
@code{$25} into direct calls. This is only possible if the linker can
|
|
resolve the destination at link time and if the destination is within
|
|
range for a direct call.
|
|
|
|
@option{-mrelax-pic-calls} is the default if GCC was configured to use
|
|
an assembler and a linker that support the @code{.reloc} assembly
|
|
directive and @option{-mexplicit-relocs} is in effect. With
|
|
@option{-mno-explicit-relocs}, this optimization can be performed by the
|
|
assembler and the linker alone without help from the compiler.
|
|
|
|
@item -mmcount-ra-address
|
|
@itemx -mno-mcount-ra-address
|
|
@opindex mmcount-ra-address
|
|
@opindex mno-mcount-ra-address
|
|
Emit (do not emit) code that allows @code{_mcount} to modify the
|
|
calling function's return address. When enabled, this option extends
|
|
the usual @code{_mcount} interface with a new @var{ra-address}
|
|
parameter, which has type @code{intptr_t *} and is passed in register
|
|
@code{$12}. @code{_mcount} can then modify the return address by
|
|
doing both of the following:
|
|
@itemize
|
|
@item
|
|
Returning the new address in register @code{$31}.
|
|
@item
|
|
Storing the new address in @code{*@var{ra-address}},
|
|
if @var{ra-address} is nonnull.
|
|
@end itemize
|
|
|
|
The default is @option{-mno-mcount-ra-address}.
|
|
|
|
@item -mframe-header-opt
|
|
@itemx -mno-frame-header-opt
|
|
@opindex mframe-header-opt
|
|
Enable (disable) frame header optimization in the o32 ABI. When using the
|
|
o32 ABI, calling functions will allocate 16 bytes on the stack for the called
|
|
function to write out register arguments. When enabled, this optimization
|
|
will suppress the allocation of the frame header if it can be determined that
|
|
it is unused.
|
|
|
|
This optimization is off by default at all optimization levels.
|
|
|
|
@end table
|
|
|
|
@node MMIX Options
|
|
@subsection MMIX Options
|
|
@cindex MMIX Options
|
|
|
|
These options are defined for the MMIX:
|
|
|
|
@table @gcctabopt
|
|
@item -mlibfuncs
|
|
@itemx -mno-libfuncs
|
|
@opindex mlibfuncs
|
|
@opindex mno-libfuncs
|
|
Specify that intrinsic library functions are being compiled, passing all
|
|
values in registers, no matter the size.
|
|
|
|
@item -mepsilon
|
|
@itemx -mno-epsilon
|
|
@opindex mepsilon
|
|
@opindex mno-epsilon
|
|
Generate floating-point comparison instructions that compare with respect
|
|
to the @code{rE} epsilon register.
|
|
|
|
@item -mabi=mmixware
|
|
@itemx -mabi=gnu
|
|
@opindex mabi=mmixware
|
|
@opindex mabi=gnu
|
|
Generate code that passes function parameters and return values that (in
|
|
the called function) are seen as registers @code{$0} and up, as opposed to
|
|
the GNU ABI which uses global registers @code{$231} and up.
|
|
|
|
@item -mzero-extend
|
|
@itemx -mno-zero-extend
|
|
@opindex mzero-extend
|
|
@opindex mno-zero-extend
|
|
When reading data from memory in sizes shorter than 64 bits, use (do not
|
|
use) zero-extending load instructions by default, rather than
|
|
sign-extending ones.
|
|
|
|
@item -mknuthdiv
|
|
@itemx -mno-knuthdiv
|
|
@opindex mknuthdiv
|
|
@opindex mno-knuthdiv
|
|
Make the result of a division yielding a remainder have the same sign as
|
|
the divisor. With the default, @option{-mno-knuthdiv}, the sign of the
|
|
remainder follows the sign of the dividend. Both methods are
|
|
arithmetically valid, the latter being almost exclusively used.
|
|
|
|
@item -mtoplevel-symbols
|
|
@itemx -mno-toplevel-symbols
|
|
@opindex mtoplevel-symbols
|
|
@opindex mno-toplevel-symbols
|
|
Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly
|
|
code can be used with the @code{PREFIX} assembly directive.
|
|
|
|
@item -melf
|
|
@opindex melf
|
|
Generate an executable in the ELF format, rather than the default
|
|
@samp{mmo} format used by the @command{mmix} simulator.
|
|
|
|
@item -mbranch-predict
|
|
@itemx -mno-branch-predict
|
|
@opindex mbranch-predict
|
|
@opindex mno-branch-predict
|
|
Use (do not use) the probable-branch instructions, when static branch
|
|
prediction indicates a probable branch.
|
|
|
|
@item -mbase-addresses
|
|
@itemx -mno-base-addresses
|
|
@opindex mbase-addresses
|
|
@opindex mno-base-addresses
|
|
Generate (do not generate) code that uses @emph{base addresses}. Using a
|
|
base address automatically generates a request (handled by the assembler
|
|
and the linker) for a constant to be set up in a global register. The
|
|
register is used for one or more base address requests within the range 0
|
|
to 255 from the value held in the register. The generally leads to short
|
|
and fast code, but the number of different data items that can be
|
|
addressed is limited. This means that a program that uses lots of static
|
|
data may require @option{-mno-base-addresses}.
|
|
|
|
@item -msingle-exit
|
|
@itemx -mno-single-exit
|
|
@opindex msingle-exit
|
|
@opindex mno-single-exit
|
|
Force (do not force) generated code to have a single exit point in each
|
|
function.
|
|
@end table
|
|
|
|
@node MN10300 Options
|
|
@subsection MN10300 Options
|
|
@cindex MN10300 options
|
|
|
|
These @option{-m} options are defined for Matsushita MN10300 architectures:
|
|
|
|
@table @gcctabopt
|
|
@item -mmult-bug
|
|
@opindex mmult-bug
|
|
Generate code to avoid bugs in the multiply instructions for the MN10300
|
|
processors. This is the default.
|
|
|
|
@item -mno-mult-bug
|
|
@opindex mno-mult-bug
|
|
Do not generate code to avoid bugs in the multiply instructions for the
|
|
MN10300 processors.
|
|
|
|
@item -mam33
|
|
@opindex mam33
|
|
Generate code using features specific to the AM33 processor.
|
|
|
|
@item -mno-am33
|
|
@opindex mno-am33
|
|
Do not generate code using features specific to the AM33 processor. This
|
|
is the default.
|
|
|
|
@item -mam33-2
|
|
@opindex mam33-2
|
|
Generate code using features specific to the AM33/2.0 processor.
|
|
|
|
@item -mam34
|
|
@opindex mam34
|
|
Generate code using features specific to the AM34 processor.
|
|
|
|
@item -mtune=@var{cpu-type}
|
|
@opindex mtune
|
|
Use the timing characteristics of the indicated CPU type when
|
|
scheduling instructions. This does not change the targeted processor
|
|
type. The CPU type must be one of @samp{mn10300}, @samp{am33},
|
|
@samp{am33-2} or @samp{am34}.
|
|
|
|
@item -mreturn-pointer-on-d0
|
|
@opindex mreturn-pointer-on-d0
|
|
When generating a function that returns a pointer, return the pointer
|
|
in both @code{a0} and @code{d0}. Otherwise, the pointer is returned
|
|
only in @code{a0}, and attempts to call such functions without a prototype
|
|
result in errors. Note that this option is on by default; use
|
|
@option{-mno-return-pointer-on-d0} to disable it.
|
|
|
|
@item -mno-crt0
|
|
@opindex mno-crt0
|
|
Do not link in the C run-time initialization object file.
|
|
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
Indicate to the linker that it should perform a relaxation optimization pass
|
|
to shorten branches, calls and absolute memory addresses. This option only
|
|
has an effect when used on the command line for the final link step.
|
|
|
|
This option makes symbolic debugging impossible.
|
|
|
|
@item -mliw
|
|
@opindex mliw
|
|
Allow the compiler to generate @emph{Long Instruction Word}
|
|
instructions if the target is the @samp{AM33} or later. This is the
|
|
default. This option defines the preprocessor macro @code{__LIW__}.
|
|
|
|
@item -mnoliw
|
|
@opindex mnoliw
|
|
Do not allow the compiler to generate @emph{Long Instruction Word}
|
|
instructions. This option defines the preprocessor macro
|
|
@code{__NO_LIW__}.
|
|
|
|
@item -msetlb
|
|
@opindex msetlb
|
|
Allow the compiler to generate the @emph{SETLB} and @emph{Lcc}
|
|
instructions if the target is the @samp{AM33} or later. This is the
|
|
default. This option defines the preprocessor macro @code{__SETLB__}.
|
|
|
|
@item -mnosetlb
|
|
@opindex mnosetlb
|
|
Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc}
|
|
instructions. This option defines the preprocessor macro
|
|
@code{__NO_SETLB__}.
|
|
|
|
@end table
|
|
|
|
@node Moxie Options
|
|
@subsection Moxie Options
|
|
@cindex Moxie Options
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -meb
|
|
@opindex meb
|
|
Generate big-endian code. This is the default for @samp{moxie-*-*}
|
|
configurations.
|
|
|
|
@item -mel
|
|
@opindex mel
|
|
Generate little-endian code.
|
|
|
|
@item -mmul.x
|
|
@opindex mmul.x
|
|
Generate mul.x and umul.x instructions. This is the default for
|
|
@samp{moxiebox-*-*} configurations.
|
|
|
|
@item -mno-crt0
|
|
@opindex mno-crt0
|
|
Do not link in the C run-time initialization object file.
|
|
|
|
@end table
|
|
|
|
@node MSP430 Options
|
|
@subsection MSP430 Options
|
|
@cindex MSP430 Options
|
|
|
|
These options are defined for the MSP430:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -masm-hex
|
|
@opindex masm-hex
|
|
Force assembly output to always use hex constants. Normally such
|
|
constants are signed decimals, but this option is available for
|
|
testsuite and/or aesthetic purposes.
|
|
|
|
@item -mmcu=
|
|
@opindex mmcu=
|
|
Select the MCU to target. This is used to create a C preprocessor
|
|
symbol based upon the MCU name, converted to upper case and pre- and
|
|
post-fixed with @samp{__}. This in turn is used by the
|
|
@file{msp430.h} header file to select an MCU-specific supplementary
|
|
header file.
|
|
|
|
The option also sets the ISA to use. If the MCU name is one that is
|
|
known to only support the 430 ISA then that is selected, otherwise the
|
|
430X ISA is selected. A generic MCU name of @samp{msp430} can also be
|
|
used to select the 430 ISA. Similarly the generic @samp{msp430x} MCU
|
|
name selects the 430X ISA.
|
|
|
|
In addition an MCU-specific linker script is added to the linker
|
|
command line. The script's name is the name of the MCU with
|
|
@file{.ld} appended. Thus specifying @option{-mmcu=xxx} on the @command{gcc}
|
|
command line defines the C preprocessor symbol @code{__XXX__} and
|
|
cause the linker to search for a script called @file{xxx.ld}.
|
|
|
|
This option is also passed on to the assembler.
|
|
|
|
@item -mwarn-mcu
|
|
@itemx -mno-warn-mcu
|
|
@opindex mwarn-mcu
|
|
@opindex mno-warn-mcu
|
|
This option enables or disables warnings about conflicts between the
|
|
MCU name specified by the @option{-mmcu} option and the ISA set by the
|
|
@option{-mcpu} option and/or the hardware multiply support set by the
|
|
@option{-mhwmult} option. It also toggles warnings about unrecognized
|
|
MCU names. This option is on by default.
|
|
|
|
@item -mcpu=
|
|
@opindex mcpu=
|
|
Specifies the ISA to use. Accepted values are @samp{msp430},
|
|
@samp{msp430x} and @samp{msp430xv2}. This option is deprecated. The
|
|
@option{-mmcu=} option should be used to select the ISA.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Link to the simulator runtime libraries and linker script. Overrides
|
|
any scripts that would be selected by the @option{-mmcu=} option.
|
|
|
|
@item -mlarge
|
|
@opindex mlarge
|
|
Use large-model addressing (20-bit pointers, 32-bit @code{size_t}).
|
|
|
|
@item -msmall
|
|
@opindex msmall
|
|
Use small-model addressing (16-bit pointers, 16-bit @code{size_t}).
|
|
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
This option is passed to the assembler and linker, and allows the
|
|
linker to perform certain optimizations that cannot be done until
|
|
the final link.
|
|
|
|
@item mhwmult=
|
|
@opindex mhwmult=
|
|
Describes the type of hardware multiply supported by the target.
|
|
Accepted values are @samp{none} for no hardware multiply, @samp{16bit}
|
|
for the original 16-bit-only multiply supported by early MCUs.
|
|
@samp{32bit} for the 16/32-bit multiply supported by later MCUs and
|
|
@samp{f5series} for the 16/32-bit multiply supported by F5-series MCUs.
|
|
A value of @samp{auto} can also be given. This tells GCC to deduce
|
|
the hardware multiply support based upon the MCU name provided by the
|
|
@option{-mmcu} option. If no @option{-mmcu} option is specified or if
|
|
the MCU name is not recognized then no hardware multiply support is
|
|
assumed. @code{auto} is the default setting.
|
|
|
|
Hardware multiplies are normally performed by calling a library
|
|
routine. This saves space in the generated code. When compiling at
|
|
@option{-O3} or higher however the hardware multiplier is invoked
|
|
inline. This makes for bigger, but faster code.
|
|
|
|
The hardware multiply routines disable interrupts whilst running and
|
|
restore the previous interrupt state when they finish. This makes
|
|
them safe to use inside interrupt handlers as well as in normal code.
|
|
|
|
@item -minrt
|
|
@opindex minrt
|
|
Enable the use of a minimum runtime environment - no static
|
|
initializers or constructors. This is intended for memory-constrained
|
|
devices. The compiler includes special symbols in some objects
|
|
that tell the linker and runtime which code fragments are required.
|
|
|
|
@item -mcode-region=
|
|
@itemx -mdata-region=
|
|
@opindex mcode-region
|
|
@opindex mdata-region
|
|
These options tell the compiler where to place functions and data that
|
|
do not have one of the @code{lower}, @code{upper}, @code{either} or
|
|
@code{section} attributes. Possible values are @code{lower},
|
|
@code{upper}, @code{either} or @code{any}. The first three behave
|
|
like the corresponding attribute. The fourth possible value -
|
|
@code{any} - is the default. It leaves placement entirely up to the
|
|
linker script and how it assigns the standard sections
|
|
(@code{.text}, @code{.data}, etc) to the memory regions.
|
|
|
|
@item -msilicon-errata=
|
|
@opindex msilicon-errata
|
|
This option passes on a request to assembler to enable the fixes for
|
|
the named silicon errata.
|
|
|
|
@item -msilicon-errata-warn=
|
|
@opindex msilicon-errata-warn
|
|
This option passes on a request to the assembler to enable warning
|
|
messages when a silicon errata might need to be applied.
|
|
|
|
@end table
|
|
|
|
@node NDS32 Options
|
|
@subsection NDS32 Options
|
|
@cindex NDS32 Options
|
|
|
|
These options are defined for NDS32 implementations:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mbig-endian
|
|
@opindex mbig-endian
|
|
Generate code in big-endian mode.
|
|
|
|
@item -mlittle-endian
|
|
@opindex mlittle-endian
|
|
Generate code in little-endian mode.
|
|
|
|
@item -mreduced-regs
|
|
@opindex mreduced-regs
|
|
Use reduced-set registers for register allocation.
|
|
|
|
@item -mfull-regs
|
|
@opindex mfull-regs
|
|
Use full-set registers for register allocation.
|
|
|
|
@item -mcmov
|
|
@opindex mcmov
|
|
Generate conditional move instructions.
|
|
|
|
@item -mno-cmov
|
|
@opindex mno-cmov
|
|
Do not generate conditional move instructions.
|
|
|
|
@item -mperf-ext
|
|
@opindex mperf-ext
|
|
Generate performance extension instructions.
|
|
|
|
@item -mno-perf-ext
|
|
@opindex mno-perf-ext
|
|
Do not generate performance extension instructions.
|
|
|
|
@item -mv3push
|
|
@opindex mv3push
|
|
Generate v3 push25/pop25 instructions.
|
|
|
|
@item -mno-v3push
|
|
@opindex mno-v3push
|
|
Do not generate v3 push25/pop25 instructions.
|
|
|
|
@item -m16-bit
|
|
@opindex m16-bit
|
|
Generate 16-bit instructions.
|
|
|
|
@item -mno-16-bit
|
|
@opindex mno-16-bit
|
|
Do not generate 16-bit instructions.
|
|
|
|
@item -misr-vector-size=@var{num}
|
|
@opindex misr-vector-size
|
|
Specify the size of each interrupt vector, which must be 4 or 16.
|
|
|
|
@item -mcache-block-size=@var{num}
|
|
@opindex mcache-block-size
|
|
Specify the size of each cache block,
|
|
which must be a power of 2 between 4 and 512.
|
|
|
|
@item -march=@var{arch}
|
|
@opindex march
|
|
Specify the name of the target architecture.
|
|
|
|
@item -mcmodel=@var{code-model}
|
|
@opindex mcmodel
|
|
Set the code model to one of
|
|
@table @asis
|
|
@item @samp{small}
|
|
All the data and read-only data segments must be within 512KB addressing space.
|
|
The text segment must be within 16MB addressing space.
|
|
@item @samp{medium}
|
|
The data segment must be within 512KB while the read-only data segment can be
|
|
within 4GB addressing space. The text segment should be still within 16MB
|
|
addressing space.
|
|
@item @samp{large}
|
|
All the text and data segments can be within 4GB addressing space.
|
|
@end table
|
|
|
|
@item -mctor-dtor
|
|
@opindex mctor-dtor
|
|
Enable constructor/destructor feature.
|
|
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
Guide linker to relax instructions.
|
|
|
|
@end table
|
|
|
|
@node Nios II Options
|
|
@subsection Nios II Options
|
|
@cindex Nios II options
|
|
@cindex Altera Nios II options
|
|
|
|
These are the options defined for the Altera Nios II processor.
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -G @var{num}
|
|
@opindex G
|
|
@cindex smaller data references
|
|
Put global and static objects less than or equal to @var{num} bytes
|
|
into the small data or BSS sections instead of the normal data or BSS
|
|
sections. The default value of @var{num} is 8.
|
|
|
|
@item -mgpopt=@var{option}
|
|
@item -mgpopt
|
|
@itemx -mno-gpopt
|
|
@opindex mgpopt
|
|
@opindex mno-gpopt
|
|
Generate (do not generate) GP-relative accesses. The following
|
|
@var{option} names are recognized:
|
|
|
|
@table @samp
|
|
|
|
@item none
|
|
Do not generate GP-relative accesses.
|
|
|
|
@item local
|
|
Generate GP-relative accesses for small data objects that are not
|
|
external, weak, or uninitialized common symbols.
|
|
Also use GP-relative addressing for objects that
|
|
have been explicitly placed in a small data section via a @code{section}
|
|
attribute.
|
|
|
|
@item global
|
|
As for @samp{local}, but also generate GP-relative accesses for
|
|
small data objects that are external, weak, or common. If you use this option,
|
|
you must ensure that all parts of your program (including libraries) are
|
|
compiled with the same @option{-G} setting.
|
|
|
|
@item data
|
|
Generate GP-relative accesses for all data objects in the program. If you
|
|
use this option, the entire data and BSS segments
|
|
of your program must fit in 64K of memory and you must use an appropriate
|
|
linker script to allocate them within the addressable range of the
|
|
global pointer.
|
|
|
|
@item all
|
|
Generate GP-relative addresses for function pointers as well as data
|
|
pointers. If you use this option, the entire text, data, and BSS segments
|
|
of your program must fit in 64K of memory and you must use an appropriate
|
|
linker script to allocate them within the addressable range of the
|
|
global pointer.
|
|
|
|
@end table
|
|
|
|
@option{-mgpopt} is equivalent to @option{-mgpopt=local}, and
|
|
@option{-mno-gpopt} is equivalent to @option{-mgpopt=none}.
|
|
|
|
The default is @option{-mgpopt} except when @option{-fpic} or
|
|
@option{-fPIC} is specified to generate position-independent code.
|
|
Note that the Nios II ABI does not permit GP-relative accesses from
|
|
shared libraries.
|
|
|
|
You may need to specify @option{-mno-gpopt} explicitly when building
|
|
programs that include large amounts of small data, including large
|
|
GOT data sections. In this case, the 16-bit offset for GP-relative
|
|
addressing may not be large enough to allow access to the entire
|
|
small data section.
|
|
|
|
@item -mel
|
|
@itemx -meb
|
|
@opindex mel
|
|
@opindex meb
|
|
Generate little-endian (default) or big-endian (experimental) code,
|
|
respectively.
|
|
|
|
@item -march=@var{arch}
|
|
@opindex march
|
|
This specifies the name of the target Nios II architecture. GCC uses this
|
|
name to determine what kind of instructions it can emit when generating
|
|
assembly code. Permissible names are: @samp{r1}, @samp{r2}.
|
|
|
|
The preprocessor macro @code{__nios2_arch__} is available to programs,
|
|
with value 1 or 2, indicating the targeted ISA level.
|
|
|
|
@item -mbypass-cache
|
|
@itemx -mno-bypass-cache
|
|
@opindex mno-bypass-cache
|
|
@opindex mbypass-cache
|
|
Force all load and store instructions to always bypass cache by
|
|
using I/O variants of the instructions. The default is not to
|
|
bypass the cache.
|
|
|
|
@item -mno-cache-volatile
|
|
@itemx -mcache-volatile
|
|
@opindex mcache-volatile
|
|
@opindex mno-cache-volatile
|
|
Volatile memory access bypass the cache using the I/O variants of
|
|
the load and store instructions. The default is not to bypass the cache.
|
|
|
|
@item -mno-fast-sw-div
|
|
@itemx -mfast-sw-div
|
|
@opindex mno-fast-sw-div
|
|
@opindex mfast-sw-div
|
|
Do not use table-based fast divide for small numbers. The default
|
|
is to use the fast divide at @option{-O3} and above.
|
|
|
|
@item -mno-hw-mul
|
|
@itemx -mhw-mul
|
|
@itemx -mno-hw-mulx
|
|
@itemx -mhw-mulx
|
|
@itemx -mno-hw-div
|
|
@itemx -mhw-div
|
|
@opindex mno-hw-mul
|
|
@opindex mhw-mul
|
|
@opindex mno-hw-mulx
|
|
@opindex mhw-mulx
|
|
@opindex mno-hw-div
|
|
@opindex mhw-div
|
|
Enable or disable emitting @code{mul}, @code{mulx} and @code{div} family of
|
|
instructions by the compiler. The default is to emit @code{mul}
|
|
and not emit @code{div} and @code{mulx}.
|
|
|
|
@item -mbmx
|
|
@itemx -mno-bmx
|
|
@itemx -mcdx
|
|
@itemx -mno-cdx
|
|
Enable or disable generation of Nios II R2 BMX (bit manipulation) and
|
|
CDX (code density) instructions. Enabling these instructions also
|
|
requires @option{-march=r2}. Since these instructions are optional
|
|
extensions to the R2 architecture, the default is not to emit them.
|
|
|
|
@item -mcustom-@var{insn}=@var{N}
|
|
@itemx -mno-custom-@var{insn}
|
|
@opindex mcustom-@var{insn}
|
|
@opindex mno-custom-@var{insn}
|
|
Each @option{-mcustom-@var{insn}=@var{N}} option enables use of a
|
|
custom instruction with encoding @var{N} when generating code that uses
|
|
@var{insn}. For example, @option{-mcustom-fadds=253} generates custom
|
|
instruction 253 for single-precision floating-point add operations instead
|
|
of the default behavior of using a library call.
|
|
|
|
The following values of @var{insn} are supported. Except as otherwise
|
|
noted, floating-point operations are expected to be implemented with
|
|
normal IEEE 754 semantics and correspond directly to the C operators or the
|
|
equivalent GCC built-in functions (@pxref{Other Builtins}).
|
|
|
|
Single-precision floating point:
|
|
@table @asis
|
|
|
|
@item @samp{fadds}, @samp{fsubs}, @samp{fdivs}, @samp{fmuls}
|
|
Binary arithmetic operations.
|
|
|
|
@item @samp{fnegs}
|
|
Unary negation.
|
|
|
|
@item @samp{fabss}
|
|
Unary absolute value.
|
|
|
|
@item @samp{fcmpeqs}, @samp{fcmpges}, @samp{fcmpgts}, @samp{fcmples}, @samp{fcmplts}, @samp{fcmpnes}
|
|
Comparison operations.
|
|
|
|
@item @samp{fmins}, @samp{fmaxs}
|
|
Floating-point minimum and maximum. These instructions are only
|
|
generated if @option{-ffinite-math-only} is specified.
|
|
|
|
@item @samp{fsqrts}
|
|
Unary square root operation.
|
|
|
|
@item @samp{fcoss}, @samp{fsins}, @samp{ftans}, @samp{fatans}, @samp{fexps}, @samp{flogs}
|
|
Floating-point trigonometric and exponential functions. These instructions
|
|
are only generated if @option{-funsafe-math-optimizations} is also specified.
|
|
|
|
@end table
|
|
|
|
Double-precision floating point:
|
|
@table @asis
|
|
|
|
@item @samp{faddd}, @samp{fsubd}, @samp{fdivd}, @samp{fmuld}
|
|
Binary arithmetic operations.
|
|
|
|
@item @samp{fnegd}
|
|
Unary negation.
|
|
|
|
@item @samp{fabsd}
|
|
Unary absolute value.
|
|
|
|
@item @samp{fcmpeqd}, @samp{fcmpged}, @samp{fcmpgtd}, @samp{fcmpled}, @samp{fcmpltd}, @samp{fcmpned}
|
|
Comparison operations.
|
|
|
|
@item @samp{fmind}, @samp{fmaxd}
|
|
Double-precision minimum and maximum. These instructions are only
|
|
generated if @option{-ffinite-math-only} is specified.
|
|
|
|
@item @samp{fsqrtd}
|
|
Unary square root operation.
|
|
|
|
@item @samp{fcosd}, @samp{fsind}, @samp{ftand}, @samp{fatand}, @samp{fexpd}, @samp{flogd}
|
|
Double-precision trigonometric and exponential functions. These instructions
|
|
are only generated if @option{-funsafe-math-optimizations} is also specified.
|
|
|
|
@end table
|
|
|
|
Conversions:
|
|
@table @asis
|
|
@item @samp{fextsd}
|
|
Conversion from single precision to double precision.
|
|
|
|
@item @samp{ftruncds}
|
|
Conversion from double precision to single precision.
|
|
|
|
@item @samp{fixsi}, @samp{fixsu}, @samp{fixdi}, @samp{fixdu}
|
|
Conversion from floating point to signed or unsigned integer types, with
|
|
truncation towards zero.
|
|
|
|
@item @samp{round}
|
|
Conversion from single-precision floating point to signed integer,
|
|
rounding to the nearest integer and ties away from zero.
|
|
This corresponds to the @code{__builtin_lroundf} function when
|
|
@option{-fno-math-errno} is used.
|
|
|
|
@item @samp{floatis}, @samp{floatus}, @samp{floatid}, @samp{floatud}
|
|
Conversion from signed or unsigned integer types to floating-point types.
|
|
|
|
@end table
|
|
|
|
In addition, all of the following transfer instructions for internal
|
|
registers X and Y must be provided to use any of the double-precision
|
|
floating-point instructions. Custom instructions taking two
|
|
double-precision source operands expect the first operand in the
|
|
64-bit register X. The other operand (or only operand of a unary
|
|
operation) is given to the custom arithmetic instruction with the
|
|
least significant half in source register @var{src1} and the most
|
|
significant half in @var{src2}. A custom instruction that returns a
|
|
double-precision result returns the most significant 32 bits in the
|
|
destination register and the other half in 32-bit register Y.
|
|
GCC automatically generates the necessary code sequences to write
|
|
register X and/or read register Y when double-precision floating-point
|
|
instructions are used.
|
|
|
|
@table @asis
|
|
|
|
@item @samp{fwrx}
|
|
Write @var{src1} into the least significant half of X and @var{src2} into
|
|
the most significant half of X.
|
|
|
|
@item @samp{fwry}
|
|
Write @var{src1} into Y.
|
|
|
|
@item @samp{frdxhi}, @samp{frdxlo}
|
|
Read the most or least (respectively) significant half of X and store it in
|
|
@var{dest}.
|
|
|
|
@item @samp{frdy}
|
|
Read the value of Y and store it into @var{dest}.
|
|
@end table
|
|
|
|
Note that you can gain more local control over generation of Nios II custom
|
|
instructions by using the @code{target("custom-@var{insn}=@var{N}")}
|
|
and @code{target("no-custom-@var{insn}")} function attributes
|
|
(@pxref{Function Attributes})
|
|
or pragmas (@pxref{Function Specific Option Pragmas}).
|
|
|
|
@item -mcustom-fpu-cfg=@var{name}
|
|
@opindex mcustom-fpu-cfg
|
|
|
|
This option enables a predefined, named set of custom instruction encodings
|
|
(see @option{-mcustom-@var{insn}} above).
|
|
Currently, the following sets are defined:
|
|
|
|
@option{-mcustom-fpu-cfg=60-1} is equivalent to:
|
|
@gccoptlist{-mcustom-fmuls=252 @gol
|
|
-mcustom-fadds=253 @gol
|
|
-mcustom-fsubs=254 @gol
|
|
-fsingle-precision-constant}
|
|
|
|
@option{-mcustom-fpu-cfg=60-2} is equivalent to:
|
|
@gccoptlist{-mcustom-fmuls=252 @gol
|
|
-mcustom-fadds=253 @gol
|
|
-mcustom-fsubs=254 @gol
|
|
-mcustom-fdivs=255 @gol
|
|
-fsingle-precision-constant}
|
|
|
|
@option{-mcustom-fpu-cfg=72-3} is equivalent to:
|
|
@gccoptlist{-mcustom-floatus=243 @gol
|
|
-mcustom-fixsi=244 @gol
|
|
-mcustom-floatis=245 @gol
|
|
-mcustom-fcmpgts=246 @gol
|
|
-mcustom-fcmples=249 @gol
|
|
-mcustom-fcmpeqs=250 @gol
|
|
-mcustom-fcmpnes=251 @gol
|
|
-mcustom-fmuls=252 @gol
|
|
-mcustom-fadds=253 @gol
|
|
-mcustom-fsubs=254 @gol
|
|
-mcustom-fdivs=255 @gol
|
|
-fsingle-precision-constant}
|
|
|
|
Custom instruction assignments given by individual
|
|
@option{-mcustom-@var{insn}=} options override those given by
|
|
@option{-mcustom-fpu-cfg=}, regardless of the
|
|
order of the options on the command line.
|
|
|
|
Note that you can gain more local control over selection of a FPU
|
|
configuration by using the @code{target("custom-fpu-cfg=@var{name}")}
|
|
function attribute (@pxref{Function Attributes})
|
|
or pragma (@pxref{Function Specific Option Pragmas}).
|
|
|
|
@end table
|
|
|
|
These additional @samp{-m} options are available for the Altera Nios II
|
|
ELF (bare-metal) target:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mhal
|
|
@opindex mhal
|
|
Link with HAL BSP. This suppresses linking with the GCC-provided C runtime
|
|
startup and termination code, and is typically used in conjunction with
|
|
@option{-msys-crt0=} to specify the location of the alternate startup code
|
|
provided by the HAL BSP.
|
|
|
|
@item -msmallc
|
|
@opindex msmallc
|
|
Link with a limited version of the C library, @option{-lsmallc}, rather than
|
|
Newlib.
|
|
|
|
@item -msys-crt0=@var{startfile}
|
|
@opindex msys-crt0
|
|
@var{startfile} is the file name of the startfile (crt0) to use
|
|
when linking. This option is only useful in conjunction with @option{-mhal}.
|
|
|
|
@item -msys-lib=@var{systemlib}
|
|
@opindex msys-lib
|
|
@var{systemlib} is the library name of the library that provides
|
|
low-level system calls required by the C library,
|
|
e.g. @code{read} and @code{write}.
|
|
This option is typically used to link with a library provided by a HAL BSP.
|
|
|
|
@end table
|
|
|
|
@node Nvidia PTX Options
|
|
@subsection Nvidia PTX Options
|
|
@cindex Nvidia PTX options
|
|
@cindex nvptx options
|
|
|
|
These options are defined for Nvidia PTX:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -m32
|
|
@itemx -m64
|
|
@opindex m32
|
|
@opindex m64
|
|
Generate code for 32-bit or 64-bit ABI.
|
|
|
|
@item -mmainkernel
|
|
@opindex mmainkernel
|
|
Link in code for a __main kernel. This is for stand-alone instead of
|
|
offloading execution.
|
|
|
|
@item -moptimize
|
|
@opindex moptimize
|
|
Apply partitioned execution optimizations. This is the default when any
|
|
level of optimization is selected.
|
|
|
|
@item -msoft-stack
|
|
@opindex msoft-stack
|
|
Generate code that does not use @code{.local} memory
|
|
directly for stack storage. Instead, a per-warp stack pointer is
|
|
maintained explicitly. This enables variable-length stack allocation (with
|
|
variable-length arrays or @code{alloca}), and when global memory is used for
|
|
underlying storage, makes it possible to access automatic variables from other
|
|
threads, or with atomic instructions. This code generation variant is used
|
|
for OpenMP offloading, but the option is exposed on its own for the purpose
|
|
of testing the compiler; to generate code suitable for linking into programs
|
|
using OpenMP offloading, use option @option{-mgomp}.
|
|
|
|
@item -muniform-simt
|
|
@opindex muniform-simt
|
|
Switch to code generation variant that allows to execute all threads in each
|
|
warp, while maintaining memory state and side effects as if only one thread
|
|
in each warp was active outside of OpenMP SIMD regions. All atomic operations
|
|
and calls to runtime (malloc, free, vprintf) are conditionally executed (iff
|
|
current lane index equals the master lane index), and the register being
|
|
assigned is copied via a shuffle instruction from the master lane. Outside of
|
|
SIMD regions lane 0 is the master; inside, each thread sees itself as the
|
|
master. Shared memory array @code{int __nvptx_uni[]} stores all-zeros or
|
|
all-ones bitmasks for each warp, indicating current mode (0 outside of SIMD
|
|
regions). Each thread can bitwise-and the bitmask at position @code{tid.y}
|
|
with current lane index to compute the master lane index.
|
|
|
|
@item -mgomp
|
|
@opindex mgomp
|
|
Generate code for use in OpenMP offloading: enables @option{-msoft-stack} and
|
|
@option{-muniform-simt} options, and selects corresponding multilib variant.
|
|
|
|
@end table
|
|
|
|
@node PDP-11 Options
|
|
@subsection PDP-11 Options
|
|
@cindex PDP-11 Options
|
|
|
|
These options are defined for the PDP-11:
|
|
|
|
@table @gcctabopt
|
|
@item -mfpu
|
|
@opindex mfpu
|
|
Use hardware FPP floating point. This is the default. (FIS floating
|
|
point on the PDP-11/40 is not supported.)
|
|
|
|
@item -msoft-float
|
|
@opindex msoft-float
|
|
Do not use hardware floating point.
|
|
|
|
@item -mac0
|
|
@opindex mac0
|
|
Return floating-point results in ac0 (fr0 in Unix assembler syntax).
|
|
|
|
@item -mno-ac0
|
|
@opindex mno-ac0
|
|
Return floating-point results in memory. This is the default.
|
|
|
|
@item -m40
|
|
@opindex m40
|
|
Generate code for a PDP-11/40.
|
|
|
|
@item -m45
|
|
@opindex m45
|
|
Generate code for a PDP-11/45. This is the default.
|
|
|
|
@item -m10
|
|
@opindex m10
|
|
Generate code for a PDP-11/10.
|
|
|
|
@item -mbcopy-builtin
|
|
@opindex mbcopy-builtin
|
|
Use inline @code{movmemhi} patterns for copying memory. This is the
|
|
default.
|
|
|
|
@item -mbcopy
|
|
@opindex mbcopy
|
|
Do not use inline @code{movmemhi} patterns for copying memory.
|
|
|
|
@item -mint16
|
|
@itemx -mno-int32
|
|
@opindex mint16
|
|
@opindex mno-int32
|
|
Use 16-bit @code{int}. This is the default.
|
|
|
|
@item -mint32
|
|
@itemx -mno-int16
|
|
@opindex mint32
|
|
@opindex mno-int16
|
|
Use 32-bit @code{int}.
|
|
|
|
@item -mfloat64
|
|
@itemx -mno-float32
|
|
@opindex mfloat64
|
|
@opindex mno-float32
|
|
Use 64-bit @code{float}. This is the default.
|
|
|
|
@item -mfloat32
|
|
@itemx -mno-float64
|
|
@opindex mfloat32
|
|
@opindex mno-float64
|
|
Use 32-bit @code{float}.
|
|
|
|
@item -mabshi
|
|
@opindex mabshi
|
|
Use @code{abshi2} pattern. This is the default.
|
|
|
|
@item -mno-abshi
|
|
@opindex mno-abshi
|
|
Do not use @code{abshi2} pattern.
|
|
|
|
@item -mbranch-expensive
|
|
@opindex mbranch-expensive
|
|
Pretend that branches are expensive. This is for experimenting with
|
|
code generation only.
|
|
|
|
@item -mbranch-cheap
|
|
@opindex mbranch-cheap
|
|
Do not pretend that branches are expensive. This is the default.
|
|
|
|
@item -munix-asm
|
|
@opindex munix-asm
|
|
Use Unix assembler syntax. This is the default when configured for
|
|
@samp{pdp11-*-bsd}.
|
|
|
|
@item -mdec-asm
|
|
@opindex mdec-asm
|
|
Use DEC assembler syntax. This is the default when configured for any
|
|
PDP-11 target other than @samp{pdp11-*-bsd}.
|
|
@end table
|
|
|
|
@node picoChip Options
|
|
@subsection picoChip Options
|
|
@cindex picoChip options
|
|
|
|
These @samp{-m} options are defined for picoChip implementations:
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mae=@var{ae_type}
|
|
@opindex mcpu
|
|
Set the instruction set, register set, and instruction scheduling
|
|
parameters for array element type @var{ae_type}. Supported values
|
|
for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}.
|
|
|
|
@option{-mae=ANY} selects a completely generic AE type. Code
|
|
generated with this option runs on any of the other AE types. The
|
|
code is not as efficient as it would be if compiled for a specific
|
|
AE type, and some types of operation (e.g., multiplication) do not
|
|
work properly on all types of AE.
|
|
|
|
@option{-mae=MUL} selects a MUL AE type. This is the most useful AE type
|
|
for compiled code, and is the default.
|
|
|
|
@option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this
|
|
option may suffer from poor performance of byte (char) manipulation,
|
|
since the DSP AE does not provide hardware support for byte load/stores.
|
|
|
|
@item -msymbol-as-address
|
|
Enable the compiler to directly use a symbol name as an address in a
|
|
load/store instruction, without first loading it into a
|
|
register. Typically, the use of this option generates larger
|
|
programs, which run faster than when the option isn't used. However, the
|
|
results vary from program to program, so it is left as a user option,
|
|
rather than being permanently enabled.
|
|
|
|
@item -mno-inefficient-warnings
|
|
Disables warnings about the generation of inefficient code. These
|
|
warnings can be generated, for example, when compiling code that
|
|
performs byte-level memory operations on the MAC AE type. The MAC AE has
|
|
no hardware support for byte-level memory operations, so all byte
|
|
load/stores must be synthesized from word load/store operations. This is
|
|
inefficient and a warning is generated to indicate
|
|
that you should rewrite the code to avoid byte operations, or to target
|
|
an AE type that has the necessary hardware support. This option disables
|
|
these warnings.
|
|
|
|
@end table
|
|
|
|
@node PowerPC Options
|
|
@subsection PowerPC Options
|
|
@cindex PowerPC options
|
|
|
|
These are listed under @xref{RS/6000 and PowerPC Options}.
|
|
|
|
@node RL78 Options
|
|
@subsection RL78 Options
|
|
@cindex RL78 Options
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
Links in additional target libraries to support operation within a
|
|
simulator.
|
|
|
|
@item -mmul=none
|
|
@itemx -mmul=g10
|
|
@itemx -mmul=g13
|
|
@itemx -mmul=g14
|
|
@itemx -mmul=rl78
|
|
@opindex mmul
|
|
Specifies the type of hardware multiplication and division support to
|
|
be used. The simplest is @code{none}, which uses software for both
|
|
multiplication and division. This is the default. The @code{g13}
|
|
value is for the hardware multiply/divide peripheral found on the
|
|
RL78/G13 (S2 core) targets. The @code{g14} value selects the use of
|
|
the multiplication and division instructions supported by the RL78/G14
|
|
(S3 core) parts. The value @code{rl78} is an alias for @code{g14} and
|
|
the value @code{mg10} is an alias for @code{none}.
|
|
|
|
In addition a C preprocessor macro is defined, based upon the setting
|
|
of this option. Possible values are: @code{__RL78_MUL_NONE__},
|
|
@code{__RL78_MUL_G13__} or @code{__RL78_MUL_G14__}.
|
|
|
|
@item -mcpu=g10
|
|
@itemx -mcpu=g13
|
|
@itemx -mcpu=g14
|
|
@itemx -mcpu=rl78
|
|
@opindex mcpu
|
|
Specifies the RL78 core to target. The default is the G14 core, also
|
|
known as an S3 core or just RL78. The G13 or S2 core does not have
|
|
multiply or divide instructions, instead it uses a hardware peripheral
|
|
for these operations. The G10 or S1 core does not have register
|
|
banks, so it uses a different calling convention.
|
|
|
|
If this option is set it also selects the type of hardware multiply
|
|
support to use, unless this is overridden by an explicit
|
|
@option{-mmul=none} option on the command line. Thus specifying
|
|
@option{-mcpu=g13} enables the use of the G13 hardware multiply
|
|
peripheral and specifying @option{-mcpu=g10} disables the use of
|
|
hardware multiplications altogether.
|
|
|
|
Note, although the RL78/G14 core is the default target, specifying
|
|
@option{-mcpu=g14} or @option{-mcpu=rl78} on the command line does
|
|
change the behavior of the toolchain since it also enables G14
|
|
hardware multiply support. If these options are not specified on the
|
|
command line then software multiplication routines will be used even
|
|
though the code targets the RL78 core. This is for backwards
|
|
compatibility with older toolchains which did not have hardware
|
|
multiply and divide support.
|
|
|
|
In addition a C preprocessor macro is defined, based upon the setting
|
|
of this option. Possible values are: @code{__RL78_G10__},
|
|
@code{__RL78_G13__} or @code{__RL78_G14__}.
|
|
|
|
@item -mg10
|
|
@itemx -mg13
|
|
@itemx -mg14
|
|
@itemx -mrl78
|
|
@opindex mg10
|
|
@opindex mg13
|
|
@opindex mg14
|
|
@opindex mrl78
|
|
These are aliases for the corresponding @option{-mcpu=} option. They
|
|
are provided for backwards compatibility.
|
|
|
|
@item -mallregs
|
|
@opindex mallregs
|
|
Allow the compiler to use all of the available registers. By default
|
|
registers @code{r24..r31} are reserved for use in interrupt handlers.
|
|
With this option enabled these registers can be used in ordinary
|
|
functions as well.
|
|
|
|
@item -m64bit-doubles
|
|
@itemx -m32bit-doubles
|
|
@opindex m64bit-doubles
|
|
@opindex m32bit-doubles
|
|
Make the @code{double} data type be 64 bits (@option{-m64bit-doubles})
|
|
or 32 bits (@option{-m32bit-doubles}) in size. The default is
|
|
@option{-m32bit-doubles}.
|
|
|
|
@item -msave-mduc-in-interrupts
|
|
@item -mno-save-mduc-in-interrupts
|
|
@opindex msave-mduc-in-interrupts
|
|
@opindex mno-save-mduc-in-interrupts
|
|
Specifies that interrupt handler functions should preserve the
|
|
MDUC registers. This is only necessary if normal code might use
|
|
the MDUC registers, for example because it performs multiplication
|
|
and division operations. The default is to ignore the MDUC registers
|
|
as this makes the interrupt handlers faster. The target option -mg13
|
|
needs to be passed for this to work as this feature is only available
|
|
on the G13 target (S2 core). The MDUC registers will only be saved
|
|
if the interrupt handler performs a multiplication or division
|
|
operation or it calls another function.
|
|
|
|
@end table
|
|
|
|
@node RS/6000 and PowerPC Options
|
|
@subsection IBM RS/6000 and PowerPC Options
|
|
@cindex RS/6000 and PowerPC Options
|
|
@cindex IBM RS/6000 and PowerPC Options
|
|
|
|
These @samp{-m} options are defined for the IBM RS/6000 and PowerPC:
|
|
@table @gcctabopt
|
|
@item -mpowerpc-gpopt
|
|
@itemx -mno-powerpc-gpopt
|
|
@itemx -mpowerpc-gfxopt
|
|
@itemx -mno-powerpc-gfxopt
|
|
@need 800
|
|
@itemx -mpowerpc64
|
|
@itemx -mno-powerpc64
|
|
@itemx -mmfcrf
|
|
@itemx -mno-mfcrf
|
|
@itemx -mpopcntb
|
|
@itemx -mno-popcntb
|
|
@itemx -mpopcntd
|
|
@itemx -mno-popcntd
|
|
@itemx -mfprnd
|
|
@itemx -mno-fprnd
|
|
@need 800
|
|
@itemx -mcmpb
|
|
@itemx -mno-cmpb
|
|
@itemx -mmfpgpr
|
|
@itemx -mno-mfpgpr
|
|
@itemx -mhard-dfp
|
|
@itemx -mno-hard-dfp
|
|
@opindex mpowerpc-gpopt
|
|
@opindex mno-powerpc-gpopt
|
|
@opindex mpowerpc-gfxopt
|
|
@opindex mno-powerpc-gfxopt
|
|
@opindex mpowerpc64
|
|
@opindex mno-powerpc64
|
|
@opindex mmfcrf
|
|
@opindex mno-mfcrf
|
|
@opindex mpopcntb
|
|
@opindex mno-popcntb
|
|
@opindex mpopcntd
|
|
@opindex mno-popcntd
|
|
@opindex mfprnd
|
|
@opindex mno-fprnd
|
|
@opindex mcmpb
|
|
@opindex mno-cmpb
|
|
@opindex mmfpgpr
|
|
@opindex mno-mfpgpr
|
|
@opindex mhard-dfp
|
|
@opindex mno-hard-dfp
|
|
You use these options to specify which instructions are available on the
|
|
processor you are using. The default value of these options is
|
|
determined when configuring GCC@. Specifying the
|
|
@option{-mcpu=@var{cpu_type}} overrides the specification of these
|
|
options. We recommend you use the @option{-mcpu=@var{cpu_type}} option
|
|
rather than the options listed above.
|
|
|
|
Specifying @option{-mpowerpc-gpopt} allows
|
|
GCC to use the optional PowerPC architecture instructions in the
|
|
General Purpose group, including floating-point square root. Specifying
|
|
@option{-mpowerpc-gfxopt} allows GCC to
|
|
use the optional PowerPC architecture instructions in the Graphics
|
|
group, including floating-point select.
|
|
|
|
The @option{-mmfcrf} option allows GCC to generate the move from
|
|
condition register field instruction implemented on the POWER4
|
|
processor and other processors that support the PowerPC V2.01
|
|
architecture.
|
|
The @option{-mpopcntb} option allows GCC to generate the popcount and
|
|
double-precision FP reciprocal estimate instruction implemented on the
|
|
POWER5 processor and other processors that support the PowerPC V2.02
|
|
architecture.
|
|
The @option{-mpopcntd} option allows GCC to generate the popcount
|
|
instruction implemented on the POWER7 processor and other processors
|
|
that support the PowerPC V2.06 architecture.
|
|
The @option{-mfprnd} option allows GCC to generate the FP round to
|
|
integer instructions implemented on the POWER5+ processor and other
|
|
processors that support the PowerPC V2.03 architecture.
|
|
The @option{-mcmpb} option allows GCC to generate the compare bytes
|
|
instruction implemented on the POWER6 processor and other processors
|
|
that support the PowerPC V2.05 architecture.
|
|
The @option{-mmfpgpr} option allows GCC to generate the FP move to/from
|
|
general-purpose register instructions implemented on the POWER6X
|
|
processor and other processors that support the extended PowerPC V2.05
|
|
architecture.
|
|
The @option{-mhard-dfp} option allows GCC to generate the decimal
|
|
floating-point instructions implemented on some POWER processors.
|
|
|
|
The @option{-mpowerpc64} option allows GCC to generate the additional
|
|
64-bit instructions that are found in the full PowerPC64 architecture
|
|
and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to
|
|
@option{-mno-powerpc64}.
|
|
|
|
@item -mcpu=@var{cpu_type}
|
|
@opindex mcpu
|
|
Set architecture type, register usage, and
|
|
instruction scheduling parameters for machine type @var{cpu_type}.
|
|
Supported values for @var{cpu_type} are @samp{401}, @samp{403},
|
|
@samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp},
|
|
@samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603},
|
|
@samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740},
|
|
@samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823},
|
|
@samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2},
|
|
@samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500},
|
|
@samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5},
|
|
@samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+},
|
|
@samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8},
|
|
@samp{power9}, @samp{powerpc}, @samp{powerpc64}, @samp{powerpc64le},
|
|
and @samp{rs64}.
|
|
|
|
@option{-mcpu=powerpc}, @option{-mcpu=powerpc64}, and
|
|
@option{-mcpu=powerpc64le} specify pure 32-bit PowerPC (either
|
|
endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC
|
|
architecture machine types, with an appropriate, generic processor
|
|
model assumed for scheduling purposes.
|
|
|
|
The other options specify a specific processor. Code generated under
|
|
those options runs best on that processor, and may not run at all on
|
|
others.
|
|
|
|
The @option{-mcpu} options automatically enable or disable the
|
|
following options:
|
|
|
|
@gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol
|
|
-mpopcntb -mpopcntd -mpowerpc64 @gol
|
|
-mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol
|
|
-msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx @gol
|
|
-mcrypto -mdirect-move -mhtm -mpower8-fusion -mpower8-vector @gol
|
|
-mquad-memory -mquad-memory-atomic -mfloat128 -mfloat128-hardware}
|
|
|
|
The particular options set for any particular CPU varies between
|
|
compiler versions, depending on what setting seems to produce optimal
|
|
code for that CPU; it doesn't necessarily reflect the actual hardware's
|
|
capabilities. If you wish to set an individual option to a particular
|
|
value, you may specify it after the @option{-mcpu} option, like
|
|
@option{-mcpu=970 -mno-altivec}.
|
|
|
|
On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are
|
|
not enabled or disabled by the @option{-mcpu} option at present because
|
|
AIX does not have full support for these options. You may still
|
|
enable or disable them individually if you're sure it'll work in your
|
|
environment.
|
|
|
|
@item -mtune=@var{cpu_type}
|
|
@opindex mtune
|
|
Set the instruction scheduling parameters for machine type
|
|
@var{cpu_type}, but do not set the architecture type or register usage,
|
|
as @option{-mcpu=@var{cpu_type}} does. The same
|
|
values for @var{cpu_type} are used for @option{-mtune} as for
|
|
@option{-mcpu}. If both are specified, the code generated uses the
|
|
architecture and registers set by @option{-mcpu}, but the
|
|
scheduling parameters set by @option{-mtune}.
|
|
|
|
@item -mcmodel=small
|
|
@opindex mcmodel=small
|
|
Generate PowerPC64 code for the small model: The TOC is limited to
|
|
64k.
|
|
|
|
@item -mcmodel=medium
|
|
@opindex mcmodel=medium
|
|
Generate PowerPC64 code for the medium model: The TOC and other static
|
|
data may be up to a total of 4G in size.
|
|
|
|
@item -mcmodel=large
|
|
@opindex mcmodel=large
|
|
Generate PowerPC64 code for the large model: The TOC may be up to 4G
|
|
in size. Other data and code is only limited by the 64-bit address
|
|
space.
|
|
|
|
@item -maltivec
|
|
@itemx -mno-altivec
|
|
@opindex maltivec
|
|
@opindex mno-altivec
|
|
Generate code that uses (does not use) AltiVec instructions, and also
|
|
enable the use of built-in functions that allow more direct access to
|
|
the AltiVec instruction set. You may also need to set
|
|
@option{-mabi=altivec} to adjust the current ABI with AltiVec ABI
|
|
enhancements.
|
|
|
|
When @option{-maltivec} is used, rather than @option{-maltivec=le} or
|
|
@option{-maltivec=be}, the element order for AltiVec intrinsics such
|
|
as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert}
|
|
match array element order corresponding to the endianness of the
|
|
target. That is, element zero identifies the leftmost element in a
|
|
vector register when targeting a big-endian platform, and identifies
|
|
the rightmost element in a vector register when targeting a
|
|
little-endian platform.
|
|
|
|
@item -maltivec=be
|
|
@opindex maltivec=be
|
|
Generate AltiVec instructions using big-endian element order,
|
|
regardless of whether the target is big- or little-endian. This is
|
|
the default when targeting a big-endian platform.
|
|
|
|
The element order is used to interpret element numbers in AltiVec
|
|
intrinsics such as @code{vec_splat}, @code{vec_extract}, and
|
|
@code{vec_insert}. By default, these match array element order
|
|
corresponding to the endianness for the target.
|
|
|
|
@item -maltivec=le
|
|
@opindex maltivec=le
|
|
Generate AltiVec instructions using little-endian element order,
|
|
regardless of whether the target is big- or little-endian. This is
|
|
the default when targeting a little-endian platform. This option is
|
|
currently ignored when targeting a big-endian platform.
|
|
|
|
The element order is used to interpret element numbers in AltiVec
|
|
intrinsics such as @code{vec_splat}, @code{vec_extract}, and
|
|
@code{vec_insert}. By default, these match array element order
|
|
corresponding to the endianness for the target.
|
|
|
|
@item -mvrsave
|
|
@itemx -mno-vrsave
|
|
@opindex mvrsave
|
|
@opindex mno-vrsave
|
|
Generate VRSAVE instructions when generating AltiVec code.
|
|
|
|
@item -mgen-cell-microcode
|
|
@opindex mgen-cell-microcode
|
|
Generate Cell microcode instructions.
|
|
|
|
@item -mwarn-cell-microcode
|
|
@opindex mwarn-cell-microcode
|
|
Warn when a Cell microcode instruction is emitted. An example
|
|
of a Cell microcode instruction is a variable shift.
|
|
|
|
@item -msecure-plt
|
|
@opindex msecure-plt
|
|
Generate code that allows @command{ld} and @command{ld.so}
|
|
to build executables and shared
|
|
libraries with non-executable @code{.plt} and @code{.got} sections.
|
|
This is a PowerPC
|
|
32-bit SYSV ABI option.
|
|
|
|
@item -mbss-plt
|
|
@opindex mbss-plt
|
|
Generate code that uses a BSS @code{.plt} section that @command{ld.so}
|
|
fills in, and
|
|
requires @code{.plt} and @code{.got}
|
|
sections that are both writable and executable.
|
|
This is a PowerPC 32-bit SYSV ABI option.
|
|
|
|
@item -misel
|
|
@itemx -mno-isel
|
|
@opindex misel
|
|
@opindex mno-isel
|
|
This switch enables or disables the generation of ISEL instructions.
|
|
|
|
@item -misel=@var{yes/no}
|
|
This switch has been deprecated. Use @option{-misel} and
|
|
@option{-mno-isel} instead.
|
|
|
|
@item -mlra
|
|
@opindex mlra
|
|
Enable Local Register Allocation. By default the port uses LRA.
|
|
(i.e. @option{-mno-lra}).
|
|
|
|
@item -mspe
|
|
@itemx -mno-spe
|
|
@opindex mspe
|
|
@opindex mno-spe
|
|
This switch enables or disables the generation of SPE simd
|
|
instructions.
|
|
|
|
@item -mpaired
|
|
@itemx -mno-paired
|
|
@opindex mpaired
|
|
@opindex mno-paired
|
|
This switch enables or disables the generation of PAIRED simd
|
|
instructions.
|
|
|
|
@item -mspe=@var{yes/no}
|
|
This option has been deprecated. Use @option{-mspe} and
|
|
@option{-mno-spe} instead.
|
|
|
|
@item -mvsx
|
|
@itemx -mno-vsx
|
|
@opindex mvsx
|
|
@opindex mno-vsx
|
|
Generate code that uses (does not use) vector/scalar (VSX)
|
|
instructions, and also enable the use of built-in functions that allow
|
|
more direct access to the VSX instruction set.
|
|
|
|
@item -mcrypto
|
|
@itemx -mno-crypto
|
|
@opindex mcrypto
|
|
@opindex mno-crypto
|
|
Enable the use (disable) of the built-in functions that allow direct
|
|
access to the cryptographic instructions that were added in version
|
|
2.07 of the PowerPC ISA.
|
|
|
|
@item -mdirect-move
|
|
@itemx -mno-direct-move
|
|
@opindex mdirect-move
|
|
@opindex mno-direct-move
|
|
Generate code that uses (does not use) the instructions to move data
|
|
between the general purpose registers and the vector/scalar (VSX)
|
|
registers that were added in version 2.07 of the PowerPC ISA.
|
|
|
|
@item -mhtm
|
|
@itemx -mno-htm
|
|
@opindex mhtm
|
|
@opindex mno-htm
|
|
Enable (disable) the use of the built-in functions that allow direct
|
|
access to the Hardware Transactional Memory (HTM) instructions that
|
|
were added in version 2.07 of the PowerPC ISA.
|
|
|
|
@item -mpower8-fusion
|
|
@itemx -mno-power8-fusion
|
|
@opindex mpower8-fusion
|
|
@opindex mno-power8-fusion
|
|
Generate code that keeps (does not keeps) some integer operations
|
|
adjacent so that the instructions can be fused together on power8 and
|
|
later processors.
|
|
|
|
@item -mpower8-vector
|
|
@itemx -mno-power8-vector
|
|
@opindex mpower8-vector
|
|
@opindex mno-power8-vector
|
|
Generate code that uses (does not use) the vector and scalar
|
|
instructions that were added in version 2.07 of the PowerPC ISA. Also
|
|
enable the use of built-in functions that allow more direct access to
|
|
the vector instructions.
|
|
|
|
@item -mquad-memory
|
|
@itemx -mno-quad-memory
|
|
@opindex mquad-memory
|
|
@opindex mno-quad-memory
|
|
Generate code that uses (does not use) the non-atomic quad word memory
|
|
instructions. The @option{-mquad-memory} option requires use of
|
|
64-bit mode.
|
|
|
|
@item -mquad-memory-atomic
|
|
@itemx -mno-quad-memory-atomic
|
|
@opindex mquad-memory-atomic
|
|
@opindex mno-quad-memory-atomic
|
|
Generate code that uses (does not use) the atomic quad word memory
|
|
instructions. The @option{-mquad-memory-atomic} option requires use of
|
|
64-bit mode.
|
|
|
|
@item -mupper-regs-di
|
|
@itemx -mno-upper-regs-di
|
|
@opindex mupper-regs-di
|
|
@opindex mno-upper-regs-di
|
|
Generate code that uses (does not use) the scalar instructions that
|
|
target all 64 registers in the vector/scalar floating point register
|
|
set that were added in version 2.06 of the PowerPC ISA when processing
|
|
integers. @option{-mupper-regs-di} is turned on by default if you use
|
|
any of the @option{-mcpu=power7}, @option{-mcpu=power8},
|
|
@option{-mcpu=power9}, or @option{-mvsx} options.
|
|
|
|
@item -mupper-regs-df
|
|
@itemx -mno-upper-regs-df
|
|
@opindex mupper-regs-df
|
|
@opindex mno-upper-regs-df
|
|
Generate code that uses (does not use) the scalar double precision
|
|
instructions that target all 64 registers in the vector/scalar
|
|
floating point register set that were added in version 2.06 of the
|
|
PowerPC ISA. @option{-mupper-regs-df} is turned on by default if you
|
|
use any of the @option{-mcpu=power7}, @option{-mcpu=power8},
|
|
@option{-mcpu=power9}, or @option{-mvsx} options.
|
|
|
|
@item -mupper-regs-sf
|
|
@itemx -mno-upper-regs-sf
|
|
@opindex mupper-regs-sf
|
|
@opindex mno-upper-regs-sf
|
|
Generate code that uses (does not use) the scalar single precision
|
|
instructions that target all 64 registers in the vector/scalar
|
|
floating point register set that were added in version 2.07 of the
|
|
PowerPC ISA. @option{-mupper-regs-sf} is turned on by default if you
|
|
use either of the @option{-mcpu=power8}, @option{-mpower8-vector}, or
|
|
@option{-mcpu=power9} options.
|
|
|
|
@item -mupper-regs
|
|
@itemx -mno-upper-regs
|
|
@opindex mupper-regs
|
|
@opindex mno-upper-regs
|
|
Generate code that uses (does not use) the scalar
|
|
instructions that target all 64 registers in the vector/scalar
|
|
floating point register set, depending on the model of the machine.
|
|
|
|
If the @option{-mno-upper-regs} option is used, it turns off both
|
|
@option{-mupper-regs-sf} and @option{-mupper-regs-df} options.
|
|
|
|
@item -mfloat128
|
|
@itemx -mno-float128
|
|
@opindex mfloat128
|
|
@opindex mno-float128
|
|
Enable/disable the @var{__float128} keyword for IEEE 128-bit floating point
|
|
and use either software emulation for IEEE 128-bit floating point or
|
|
hardware instructions.
|
|
|
|
The VSX instruction set (@option{-mvsx}, @option{-mcpu=power7}, or
|
|
@option{-mcpu=power8}) must be enabled to use the @option{-mfloat128}
|
|
option. The @option{-mfloat128} option only works on PowerPC 64-bit
|
|
Linux systems.
|
|
|
|
If you use the ISA 3.0 instruction set (@option{-mcpu=power9}), the
|
|
@option{-mfloat128} option will also enable the generation of ISA 3.0
|
|
IEEE 128-bit floating point instructions. Otherwise, IEEE 128-bit
|
|
floating point will be done with software emulation.
|
|
|
|
@item -mfloat128-hardware
|
|
@itemx -mno-float128-hardware
|
|
@opindex mfloat128-hardware
|
|
@opindex mno-float128-hardware
|
|
Enable/disable using ISA 3.0 hardware instructions to support the
|
|
@var{__float128} data type.
|
|
|
|
If you use @option{-mfloat128-hardware}, it will enable the option
|
|
@option{-mfloat128} as well.
|
|
|
|
If you select ISA 3.0 instructions with @option{-mcpu=power9}, but do
|
|
not use either @option{-mfloat128} or @option{-mfloat128-hardware},
|
|
the IEEE 128-bit floating point support will not be enabled.
|
|
|
|
@item -mfloat-gprs=@var{yes/single/double/no}
|
|
@itemx -mfloat-gprs
|
|
@opindex mfloat-gprs
|
|
This switch enables or disables the generation of floating-point
|
|
operations on the general-purpose registers for architectures that
|
|
support it.
|
|
|
|
The argument @samp{yes} or @samp{single} enables the use of
|
|
single-precision floating-point operations.
|
|
|
|
The argument @samp{double} enables the use of single and
|
|
double-precision floating-point operations.
|
|
|
|
The argument @samp{no} disables floating-point operations on the
|
|
general-purpose registers.
|
|
|
|
This option is currently only available on the MPC854x.
|
|
|
|
@item -m32
|
|
@itemx -m64
|
|
@opindex m32
|
|
@opindex m64
|
|
Generate code for 32-bit or 64-bit environments of Darwin and SVR4
|
|
targets (including GNU/Linux). The 32-bit environment sets int, long
|
|
and pointer to 32 bits and generates code that runs on any PowerPC
|
|
variant. The 64-bit environment sets int to 32 bits and long and
|
|
pointer to 64 bits, and generates code for PowerPC64, as for
|
|
@option{-mpowerpc64}.
|
|
|
|
@item -mfull-toc
|
|
@itemx -mno-fp-in-toc
|
|
@itemx -mno-sum-in-toc
|
|
@itemx -mminimal-toc
|
|
@opindex mfull-toc
|
|
@opindex mno-fp-in-toc
|
|
@opindex mno-sum-in-toc
|
|
@opindex mminimal-toc
|
|
Modify generation of the TOC (Table Of Contents), which is created for
|
|
every executable file. The @option{-mfull-toc} option is selected by
|
|
default. In that case, GCC allocates at least one TOC entry for
|
|
each unique non-automatic variable reference in your program. GCC
|
|
also places floating-point constants in the TOC@. However, only
|
|
16,384 entries are available in the TOC@.
|
|
|
|
If you receive a linker error message that saying you have overflowed
|
|
the available TOC space, you can reduce the amount of TOC space used
|
|
with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options.
|
|
@option{-mno-fp-in-toc} prevents GCC from putting floating-point
|
|
constants in the TOC and @option{-mno-sum-in-toc} forces GCC to
|
|
generate code to calculate the sum of an address and a constant at
|
|
run time instead of putting that sum into the TOC@. You may specify one
|
|
or both of these options. Each causes GCC to produce very slightly
|
|
slower and larger code at the expense of conserving TOC space.
|
|
|
|
If you still run out of space in the TOC even when you specify both of
|
|
these options, specify @option{-mminimal-toc} instead. This option causes
|
|
GCC to make only one TOC entry for every file. When you specify this
|
|
option, GCC produces code that is slower and larger but which
|
|
uses extremely little TOC space. You may wish to use this option
|
|
only on files that contain less frequently-executed code.
|
|
|
|
@item -maix64
|
|
@itemx -maix32
|
|
@opindex maix64
|
|
@opindex maix32
|
|
Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit
|
|
@code{long} type, and the infrastructure needed to support them.
|
|
Specifying @option{-maix64} implies @option{-mpowerpc64},
|
|
while @option{-maix32} disables the 64-bit ABI and
|
|
implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}.
|
|
|
|
@item -mxl-compat
|
|
@itemx -mno-xl-compat
|
|
@opindex mxl-compat
|
|
@opindex mno-xl-compat
|
|
Produce code that conforms more closely to IBM XL compiler semantics
|
|
when using AIX-compatible ABI@. Pass floating-point arguments to
|
|
prototyped functions beyond the register save area (RSA) on the stack
|
|
in addition to argument FPRs. Do not assume that most significant
|
|
double in 128-bit long double value is properly rounded when comparing
|
|
values and converting to double. Use XL symbol names for long double
|
|
support routines.
|
|
|
|
The AIX calling convention was extended but not initially documented to
|
|
handle an obscure K&R C case of calling a function that takes the
|
|
address of its arguments with fewer arguments than declared. IBM XL
|
|
compilers access floating-point arguments that do not fit in the
|
|
RSA from the stack when a subroutine is compiled without
|
|
optimization. Because always storing floating-point arguments on the
|
|
stack is inefficient and rarely needed, this option is not enabled by
|
|
default and only is necessary when calling subroutines compiled by IBM
|
|
XL compilers without optimization.
|
|
|
|
@item -mpe
|
|
@opindex mpe
|
|
Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an
|
|
application written to use message passing with special startup code to
|
|
enable the application to run. The system must have PE installed in the
|
|
standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file
|
|
must be overridden with the @option{-specs=} option to specify the
|
|
appropriate directory location. The Parallel Environment does not
|
|
support threads, so the @option{-mpe} option and the @option{-pthread}
|
|
option are incompatible.
|
|
|
|
@item -malign-natural
|
|
@itemx -malign-power
|
|
@opindex malign-natural
|
|
@opindex malign-power
|
|
On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
|
|
@option{-malign-natural} overrides the ABI-defined alignment of larger
|
|
types, such as floating-point doubles, on their natural size-based boundary.
|
|
The option @option{-malign-power} instructs GCC to follow the ABI-specified
|
|
alignment rules. GCC defaults to the standard alignment defined in the ABI@.
|
|
|
|
On 64-bit Darwin, natural alignment is the default, and @option{-malign-power}
|
|
is not supported.
|
|
|
|
@item -msoft-float
|
|
@itemx -mhard-float
|
|
@opindex msoft-float
|
|
@opindex mhard-float
|
|
Generate code that does not use (uses) the floating-point register set.
|
|
Software floating-point emulation is provided if you use the
|
|
@option{-msoft-float} option, and pass the option to GCC when linking.
|
|
|
|
@item -msingle-float
|
|
@itemx -mdouble-float
|
|
@opindex msingle-float
|
|
@opindex mdouble-float
|
|
Generate code for single- or double-precision floating-point operations.
|
|
@option{-mdouble-float} implies @option{-msingle-float}.
|
|
|
|
@item -msimple-fpu
|
|
@opindex msimple-fpu
|
|
Do not generate @code{sqrt} and @code{div} instructions for hardware
|
|
floating-point unit.
|
|
|
|
@item -mfpu=@var{name}
|
|
@opindex mfpu
|
|
Specify type of floating-point unit. Valid values for @var{name} are
|
|
@samp{sp_lite} (equivalent to @option{-msingle-float -msimple-fpu}),
|
|
@samp{dp_lite} (equivalent to @option{-mdouble-float -msimple-fpu}),
|
|
@samp{sp_full} (equivalent to @option{-msingle-float}),
|
|
and @samp{dp_full} (equivalent to @option{-mdouble-float}).
|
|
|
|
@item -mxilinx-fpu
|
|
@opindex mxilinx-fpu
|
|
Perform optimizations for the floating-point unit on Xilinx PPC 405/440.
|
|
|
|
@item -mmultiple
|
|
@itemx -mno-multiple
|
|
@opindex mmultiple
|
|
@opindex mno-multiple
|
|
Generate code that uses (does not use) the load multiple word
|
|
instructions and the store multiple word instructions. These
|
|
instructions are generated by default on POWER systems, and not
|
|
generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian
|
|
PowerPC systems, since those instructions do not work when the
|
|
processor is in little-endian mode. The exceptions are PPC740 and
|
|
PPC750 which permit these instructions in little-endian mode.
|
|
|
|
@item -mstring
|
|
@itemx -mno-string
|
|
@opindex mstring
|
|
@opindex mno-string
|
|
Generate code that uses (does not use) the load string instructions
|
|
and the store string word instructions to save multiple registers and
|
|
do small block moves. These instructions are generated by default on
|
|
POWER systems, and not generated on PowerPC systems. Do not use
|
|
@option{-mstring} on little-endian PowerPC systems, since those
|
|
instructions do not work when the processor is in little-endian mode.
|
|
The exceptions are PPC740 and PPC750 which permit these instructions
|
|
in little-endian mode.
|
|
|
|
@item -mupdate
|
|
@itemx -mno-update
|
|
@opindex mupdate
|
|
@opindex mno-update
|
|
Generate code that uses (does not use) the load or store instructions
|
|
that update the base register to the address of the calculated memory
|
|
location. These instructions are generated by default. If you use
|
|
@option{-mno-update}, there is a small window between the time that the
|
|
stack pointer is updated and the address of the previous frame is
|
|
stored, which means code that walks the stack frame across interrupts or
|
|
signals may get corrupted data.
|
|
|
|
@item -mavoid-indexed-addresses
|
|
@itemx -mno-avoid-indexed-addresses
|
|
@opindex mavoid-indexed-addresses
|
|
@opindex mno-avoid-indexed-addresses
|
|
Generate code that tries to avoid (not avoid) the use of indexed load
|
|
or store instructions. These instructions can incur a performance
|
|
penalty on Power6 processors in certain situations, such as when
|
|
stepping through large arrays that cross a 16M boundary. This option
|
|
is enabled by default when targeting Power6 and disabled otherwise.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Generate code that uses (does not use) the floating-point multiply and
|
|
accumulate instructions. These instructions are generated by default
|
|
if hardware floating point is used. The machine-dependent
|
|
@option{-mfused-madd} option is now mapped to the machine-independent
|
|
@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is
|
|
mapped to @option{-ffp-contract=off}.
|
|
|
|
@item -mmulhw
|
|
@itemx -mno-mulhw
|
|
@opindex mmulhw
|
|
@opindex mno-mulhw
|
|
Generate code that uses (does not use) the half-word multiply and
|
|
multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors.
|
|
These instructions are generated by default when targeting those
|
|
processors.
|
|
|
|
@item -mdlmzb
|
|
@itemx -mno-dlmzb
|
|
@opindex mdlmzb
|
|
@opindex mno-dlmzb
|
|
Generate code that uses (does not use) the string-search @samp{dlmzb}
|
|
instruction on the IBM 405, 440, 464 and 476 processors. This instruction is
|
|
generated by default when targeting those processors.
|
|
|
|
@item -mno-bit-align
|
|
@itemx -mbit-align
|
|
@opindex mno-bit-align
|
|
@opindex mbit-align
|
|
On System V.4 and embedded PowerPC systems do not (do) force structures
|
|
and unions that contain bit-fields to be aligned to the base type of the
|
|
bit-field.
|
|
|
|
For example, by default a structure containing nothing but 8
|
|
@code{unsigned} bit-fields of length 1 is aligned to a 4-byte
|
|
boundary and has a size of 4 bytes. By using @option{-mno-bit-align},
|
|
the structure is aligned to a 1-byte boundary and is 1 byte in
|
|
size.
|
|
|
|
@item -mno-strict-align
|
|
@itemx -mstrict-align
|
|
@opindex mno-strict-align
|
|
@opindex mstrict-align
|
|
On System V.4 and embedded PowerPC systems do not (do) assume that
|
|
unaligned memory references are handled by the system.
|
|
|
|
@item -mrelocatable
|
|
@itemx -mno-relocatable
|
|
@opindex mrelocatable
|
|
@opindex mno-relocatable
|
|
Generate code that allows (does not allow) a static executable to be
|
|
relocated to a different address at run time. A simple embedded
|
|
PowerPC system loader should relocate the entire contents of
|
|
@code{.got2} and 4-byte locations listed in the @code{.fixup} section,
|
|
a table of 32-bit addresses generated by this option. For this to
|
|
work, all objects linked together must be compiled with
|
|
@option{-mrelocatable} or @option{-mrelocatable-lib}.
|
|
@option{-mrelocatable} code aligns the stack to an 8-byte boundary.
|
|
|
|
@item -mrelocatable-lib
|
|
@itemx -mno-relocatable-lib
|
|
@opindex mrelocatable-lib
|
|
@opindex mno-relocatable-lib
|
|
Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a
|
|
@code{.fixup} section to allow static executables to be relocated at
|
|
run time, but @option{-mrelocatable-lib} does not use the smaller stack
|
|
alignment of @option{-mrelocatable}. Objects compiled with
|
|
@option{-mrelocatable-lib} may be linked with objects compiled with
|
|
any combination of the @option{-mrelocatable} options.
|
|
|
|
@item -mno-toc
|
|
@itemx -mtoc
|
|
@opindex mno-toc
|
|
@opindex mtoc
|
|
On System V.4 and embedded PowerPC systems do not (do) assume that
|
|
register 2 contains a pointer to a global area pointing to the addresses
|
|
used in the program.
|
|
|
|
@item -mlittle
|
|
@itemx -mlittle-endian
|
|
@opindex mlittle
|
|
@opindex mlittle-endian
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
processor in little-endian mode. The @option{-mlittle-endian} option is
|
|
the same as @option{-mlittle}.
|
|
|
|
@item -mbig
|
|
@itemx -mbig-endian
|
|
@opindex mbig
|
|
@opindex mbig-endian
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
processor in big-endian mode. The @option{-mbig-endian} option is
|
|
the same as @option{-mbig}.
|
|
|
|
@item -mdynamic-no-pic
|
|
@opindex mdynamic-no-pic
|
|
On Darwin and Mac OS X systems, compile code so that it is not
|
|
relocatable, but that its external references are relocatable. The
|
|
resulting code is suitable for applications, but not shared
|
|
libraries.
|
|
|
|
@item -msingle-pic-base
|
|
@opindex msingle-pic-base
|
|
Treat the register used for PIC addressing as read-only, rather than
|
|
loading it in the prologue for each function. The runtime system is
|
|
responsible for initializing this register with an appropriate value
|
|
before execution begins.
|
|
|
|
@item -mprioritize-restricted-insns=@var{priority}
|
|
@opindex mprioritize-restricted-insns
|
|
This option controls the priority that is assigned to
|
|
dispatch-slot restricted instructions during the second scheduling
|
|
pass. The argument @var{priority} takes the value @samp{0}, @samp{1},
|
|
or @samp{2} to assign no, highest, or second-highest (respectively)
|
|
priority to dispatch-slot restricted
|
|
instructions.
|
|
|
|
@item -msched-costly-dep=@var{dependence_type}
|
|
@opindex msched-costly-dep
|
|
This option controls which dependences are considered costly
|
|
by the target during instruction scheduling. The argument
|
|
@var{dependence_type} takes one of the following values:
|
|
|
|
@table @asis
|
|
@item @samp{no}
|
|
No dependence is costly.
|
|
|
|
@item @samp{all}
|
|
All dependences are costly.
|
|
|
|
@item @samp{true_store_to_load}
|
|
A true dependence from store to load is costly.
|
|
|
|
@item @samp{store_to_load}
|
|
Any dependence from store to load is costly.
|
|
|
|
@item @var{number}
|
|
Any dependence for which the latency is greater than or equal to
|
|
@var{number} is costly.
|
|
@end table
|
|
|
|
@item -minsert-sched-nops=@var{scheme}
|
|
@opindex minsert-sched-nops
|
|
This option controls which NOP insertion scheme is used during
|
|
the second scheduling pass. The argument @var{scheme} takes one of the
|
|
following values:
|
|
|
|
@table @asis
|
|
@item @samp{no}
|
|
Don't insert NOPs.
|
|
|
|
@item @samp{pad}
|
|
Pad with NOPs any dispatch group that has vacant issue slots,
|
|
according to the scheduler's grouping.
|
|
|
|
@item @samp{regroup_exact}
|
|
Insert NOPs to force costly dependent insns into
|
|
separate groups. Insert exactly as many NOPs as needed to force an insn
|
|
to a new group, according to the estimated processor grouping.
|
|
|
|
@item @var{number}
|
|
Insert NOPs to force costly dependent insns into
|
|
separate groups. Insert @var{number} NOPs to force an insn to a new group.
|
|
@end table
|
|
|
|
@item -mcall-sysv
|
|
@opindex mcall-sysv
|
|
On System V.4 and embedded PowerPC systems compile code using calling
|
|
conventions that adhere to the March 1995 draft of the System V
|
|
Application Binary Interface, PowerPC processor supplement. This is the
|
|
default unless you configured GCC using @samp{powerpc-*-eabiaix}.
|
|
|
|
@item -mcall-sysv-eabi
|
|
@itemx -mcall-eabi
|
|
@opindex mcall-sysv-eabi
|
|
@opindex mcall-eabi
|
|
Specify both @option{-mcall-sysv} and @option{-meabi} options.
|
|
|
|
@item -mcall-sysv-noeabi
|
|
@opindex mcall-sysv-noeabi
|
|
Specify both @option{-mcall-sysv} and @option{-mno-eabi} options.
|
|
|
|
@item -mcall-aixdesc
|
|
@opindex m
|
|
On System V.4 and embedded PowerPC systems compile code for the AIX
|
|
operating system.
|
|
|
|
@item -mcall-linux
|
|
@opindex mcall-linux
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
Linux-based GNU system.
|
|
|
|
@item -mcall-freebsd
|
|
@opindex mcall-freebsd
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
FreeBSD operating system.
|
|
|
|
@item -mcall-netbsd
|
|
@opindex mcall-netbsd
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
NetBSD operating system.
|
|
|
|
@item -mcall-openbsd
|
|
@opindex mcall-netbsd
|
|
On System V.4 and embedded PowerPC systems compile code for the
|
|
OpenBSD operating system.
|
|
|
|
@item -maix-struct-return
|
|
@opindex maix-struct-return
|
|
Return all structures in memory (as specified by the AIX ABI)@.
|
|
|
|
@item -msvr4-struct-return
|
|
@opindex msvr4-struct-return
|
|
Return structures smaller than 8 bytes in registers (as specified by the
|
|
SVR4 ABI)@.
|
|
|
|
@item -mabi=@var{abi-type}
|
|
@opindex mabi
|
|
Extend the current ABI with a particular extension, or remove such extension.
|
|
Valid values are @samp{altivec}, @samp{no-altivec}, @samp{spe},
|
|
@samp{no-spe}, @samp{ibmlongdouble}, @samp{ieeelongdouble},
|
|
@samp{elfv1}, @samp{elfv2}@.
|
|
|
|
@item -mabi=spe
|
|
@opindex mabi=spe
|
|
Extend the current ABI with SPE ABI extensions. This does not change
|
|
the default ABI, instead it adds the SPE ABI extensions to the current
|
|
ABI@.
|
|
|
|
@item -mabi=no-spe
|
|
@opindex mabi=no-spe
|
|
Disable Book-E SPE ABI extensions for the current ABI@.
|
|
|
|
@item -mabi=ibmlongdouble
|
|
@opindex mabi=ibmlongdouble
|
|
Change the current ABI to use IBM extended-precision long double.
|
|
This is a PowerPC 32-bit SYSV ABI option.
|
|
|
|
@item -mabi=ieeelongdouble
|
|
@opindex mabi=ieeelongdouble
|
|
Change the current ABI to use IEEE extended-precision long double.
|
|
This is a PowerPC 32-bit Linux ABI option.
|
|
|
|
@item -mabi=elfv1
|
|
@opindex mabi=elfv1
|
|
Change the current ABI to use the ELFv1 ABI.
|
|
This is the default ABI for big-endian PowerPC 64-bit Linux.
|
|
Overriding the default ABI requires special system support and is
|
|
likely to fail in spectacular ways.
|
|
|
|
@item -mabi=elfv2
|
|
@opindex mabi=elfv2
|
|
Change the current ABI to use the ELFv2 ABI.
|
|
This is the default ABI for little-endian PowerPC 64-bit Linux.
|
|
Overriding the default ABI requires special system support and is
|
|
likely to fail in spectacular ways.
|
|
|
|
@item -mgnu-attribute
|
|
@itemx -mno-gnu-attribute
|
|
@opindex mgnu-attribute
|
|
@opindex mno-gnu-attribute
|
|
Emit .gnu_attribute assembly directives to set tag/value pairs in a
|
|
.gnu.attributes section that specify ABI variations in function
|
|
parameters or return values.
|
|
|
|
@item -mprototype
|
|
@itemx -mno-prototype
|
|
@opindex mprototype
|
|
@opindex mno-prototype
|
|
On System V.4 and embedded PowerPC systems assume that all calls to
|
|
variable argument functions are properly prototyped. Otherwise, the
|
|
compiler must insert an instruction before every non-prototyped call to
|
|
set or clear bit 6 of the condition code register (@code{CR}) to
|
|
indicate whether floating-point values are passed in the floating-point
|
|
registers in case the function takes variable arguments. With
|
|
@option{-mprototype}, only calls to prototyped variable argument functions
|
|
set or clear the bit.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
On embedded PowerPC systems, assume that the startup module is called
|
|
@file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and
|
|
@file{libc.a}. This is the default for @samp{powerpc-*-eabisim}
|
|
configurations.
|
|
|
|
@item -mmvme
|
|
@opindex mmvme
|
|
On embedded PowerPC systems, assume that the startup module is called
|
|
@file{crt0.o} and the standard C libraries are @file{libmvme.a} and
|
|
@file{libc.a}.
|
|
|
|
@item -mads
|
|
@opindex mads
|
|
On embedded PowerPC systems, assume that the startup module is called
|
|
@file{crt0.o} and the standard C libraries are @file{libads.a} and
|
|
@file{libc.a}.
|
|
|
|
@item -myellowknife
|
|
@opindex myellowknife
|
|
On embedded PowerPC systems, assume that the startup module is called
|
|
@file{crt0.o} and the standard C libraries are @file{libyk.a} and
|
|
@file{libc.a}.
|
|
|
|
@item -mvxworks
|
|
@opindex mvxworks
|
|
On System V.4 and embedded PowerPC systems, specify that you are
|
|
compiling for a VxWorks system.
|
|
|
|
@item -memb
|
|
@opindex memb
|
|
On embedded PowerPC systems, set the @code{PPC_EMB} bit in the ELF flags
|
|
header to indicate that @samp{eabi} extended relocations are used.
|
|
|
|
@item -meabi
|
|
@itemx -mno-eabi
|
|
@opindex meabi
|
|
@opindex mno-eabi
|
|
On System V.4 and embedded PowerPC systems do (do not) adhere to the
|
|
Embedded Applications Binary Interface (EABI), which is a set of
|
|
modifications to the System V.4 specifications. Selecting @option{-meabi}
|
|
means that the stack is aligned to an 8-byte boundary, a function
|
|
@code{__eabi} is called from @code{main} to set up the EABI
|
|
environment, and the @option{-msdata} option can use both @code{r2} and
|
|
@code{r13} to point to two separate small data areas. Selecting
|
|
@option{-mno-eabi} means that the stack is aligned to a 16-byte boundary,
|
|
no EABI initialization function is called from @code{main}, and the
|
|
@option{-msdata} option only uses @code{r13} to point to a single
|
|
small data area. The @option{-meabi} option is on by default if you
|
|
configured GCC using one of the @samp{powerpc*-*-eabi*} options.
|
|
|
|
@item -msdata=eabi
|
|
@opindex msdata=eabi
|
|
On System V.4 and embedded PowerPC systems, put small initialized
|
|
@code{const} global and static data in the @code{.sdata2} section, which
|
|
is pointed to by register @code{r2}. Put small initialized
|
|
non-@code{const} global and static data in the @code{.sdata} section,
|
|
which is pointed to by register @code{r13}. Put small uninitialized
|
|
global and static data in the @code{.sbss} section, which is adjacent to
|
|
the @code{.sdata} section. The @option{-msdata=eabi} option is
|
|
incompatible with the @option{-mrelocatable} option. The
|
|
@option{-msdata=eabi} option also sets the @option{-memb} option.
|
|
|
|
@item -msdata=sysv
|
|
@opindex msdata=sysv
|
|
On System V.4 and embedded PowerPC systems, put small global and static
|
|
data in the @code{.sdata} section, which is pointed to by register
|
|
@code{r13}. Put small uninitialized global and static data in the
|
|
@code{.sbss} section, which is adjacent to the @code{.sdata} section.
|
|
The @option{-msdata=sysv} option is incompatible with the
|
|
@option{-mrelocatable} option.
|
|
|
|
@item -msdata=default
|
|
@itemx -msdata
|
|
@opindex msdata=default
|
|
@opindex msdata
|
|
On System V.4 and embedded PowerPC systems, if @option{-meabi} is used,
|
|
compile code the same as @option{-msdata=eabi}, otherwise compile code the
|
|
same as @option{-msdata=sysv}.
|
|
|
|
@item -msdata=data
|
|
@opindex msdata=data
|
|
On System V.4 and embedded PowerPC systems, put small global
|
|
data in the @code{.sdata} section. Put small uninitialized global
|
|
data in the @code{.sbss} section. Do not use register @code{r13}
|
|
to address small data however. This is the default behavior unless
|
|
other @option{-msdata} options are used.
|
|
|
|
@item -msdata=none
|
|
@itemx -mno-sdata
|
|
@opindex msdata=none
|
|
@opindex mno-sdata
|
|
On embedded PowerPC systems, put all initialized global and static data
|
|
in the @code{.data} section, and all uninitialized data in the
|
|
@code{.bss} section.
|
|
|
|
@item -mblock-move-inline-limit=@var{num}
|
|
@opindex mblock-move-inline-limit
|
|
Inline all block moves (such as calls to @code{memcpy} or structure
|
|
copies) less than or equal to @var{num} bytes. The minimum value for
|
|
@var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit
|
|
targets. The default value is target-specific.
|
|
|
|
@item -G @var{num}
|
|
@opindex G
|
|
@cindex smaller data references (PowerPC)
|
|
@cindex .sdata/.sdata2 references (PowerPC)
|
|
On embedded PowerPC systems, put global and static items less than or
|
|
equal to @var{num} bytes into the small data or BSS sections instead of
|
|
the normal data or BSS section. By default, @var{num} is 8. The
|
|
@option{-G @var{num}} switch is also passed to the linker.
|
|
All modules should be compiled with the same @option{-G @var{num}} value.
|
|
|
|
@item -mregnames
|
|
@itemx -mno-regnames
|
|
@opindex mregnames
|
|
@opindex mno-regnames
|
|
On System V.4 and embedded PowerPC systems do (do not) emit register
|
|
names in the assembly language output using symbolic forms.
|
|
|
|
@item -mlongcall
|
|
@itemx -mno-longcall
|
|
@opindex mlongcall
|
|
@opindex mno-longcall
|
|
By default assume that all calls are far away so that a longer and more
|
|
expensive calling sequence is required. This is required for calls
|
|
farther than 32 megabytes (33,554,432 bytes) from the current location.
|
|
A short call is generated if the compiler knows
|
|
the call cannot be that far away. This setting can be overridden by
|
|
the @code{shortcall} function attribute, or by @code{#pragma
|
|
longcall(0)}.
|
|
|
|
Some linkers are capable of detecting out-of-range calls and generating
|
|
glue code on the fly. On these systems, long calls are unnecessary and
|
|
generate slower code. As of this writing, the AIX linker can do this,
|
|
as can the GNU linker for PowerPC/64. It is planned to add this feature
|
|
to the GNU linker for 32-bit PowerPC systems as well.
|
|
|
|
On Darwin/PPC systems, @code{#pragma longcall} generates @code{jbsr
|
|
callee, L42}, plus a @dfn{branch island} (glue code). The two target
|
|
addresses represent the callee and the branch island. The
|
|
Darwin/PPC linker prefers the first address and generates a @code{bl
|
|
callee} if the PPC @code{bl} instruction reaches the callee directly;
|
|
otherwise, the linker generates @code{bl L42} to call the branch
|
|
island. The branch island is appended to the body of the
|
|
calling function; it computes the full 32-bit address of the callee
|
|
and jumps to it.
|
|
|
|
On Mach-O (Darwin) systems, this option directs the compiler emit to
|
|
the glue for every direct call, and the Darwin linker decides whether
|
|
to use or discard it.
|
|
|
|
In the future, GCC may ignore all longcall specifications
|
|
when the linker is known to generate glue.
|
|
|
|
@item -mtls-markers
|
|
@itemx -mno-tls-markers
|
|
@opindex mtls-markers
|
|
@opindex mno-tls-markers
|
|
Mark (do not mark) calls to @code{__tls_get_addr} with a relocation
|
|
specifying the function argument. The relocation allows the linker to
|
|
reliably associate function call with argument setup instructions for
|
|
TLS optimization, which in turn allows GCC to better schedule the
|
|
sequence.
|
|
|
|
@item -mrecip
|
|
@itemx -mno-recip
|
|
@opindex mrecip
|
|
This option enables use of the reciprocal estimate and
|
|
reciprocal square root estimate instructions with additional
|
|
Newton-Raphson steps to increase precision instead of doing a divide or
|
|
square root and divide for floating-point arguments. You should use
|
|
the @option{-ffast-math} option when using @option{-mrecip} (or at
|
|
least @option{-funsafe-math-optimizations},
|
|
@option{-ffinite-math-only}, @option{-freciprocal-math} and
|
|
@option{-fno-trapping-math}). Note that while the throughput of the
|
|
sequence is generally higher than the throughput of the non-reciprocal
|
|
instruction, the precision of the sequence can be decreased by up to 2
|
|
ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square
|
|
roots.
|
|
|
|
@item -mrecip=@var{opt}
|
|
@opindex mrecip=opt
|
|
This option controls which reciprocal estimate instructions
|
|
may be used. @var{opt} is a comma-separated list of options, which may
|
|
be preceded by a @code{!} to invert the option:
|
|
|
|
@table @samp
|
|
|
|
@item all
|
|
Enable all estimate instructions.
|
|
|
|
@item default
|
|
Enable the default instructions, equivalent to @option{-mrecip}.
|
|
|
|
@item none
|
|
Disable all estimate instructions, equivalent to @option{-mno-recip}.
|
|
|
|
@item div
|
|
Enable the reciprocal approximation instructions for both
|
|
single and double precision.
|
|
|
|
@item divf
|
|
Enable the single-precision reciprocal approximation instructions.
|
|
|
|
@item divd
|
|
Enable the double-precision reciprocal approximation instructions.
|
|
|
|
@item rsqrt
|
|
Enable the reciprocal square root approximation instructions for both
|
|
single and double precision.
|
|
|
|
@item rsqrtf
|
|
Enable the single-precision reciprocal square root approximation instructions.
|
|
|
|
@item rsqrtd
|
|
Enable the double-precision reciprocal square root approximation instructions.
|
|
|
|
@end table
|
|
|
|
So, for example, @option{-mrecip=all,!rsqrtd} enables
|
|
all of the reciprocal estimate instructions, except for the
|
|
@code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions
|
|
which handle the double-precision reciprocal square root calculations.
|
|
|
|
@item -mrecip-precision
|
|
@itemx -mno-recip-precision
|
|
@opindex mrecip-precision
|
|
Assume (do not assume) that the reciprocal estimate instructions
|
|
provide higher-precision estimates than is mandated by the PowerPC
|
|
ABI. Selecting @option{-mcpu=power6}, @option{-mcpu=power7} or
|
|
@option{-mcpu=power8} automatically selects @option{-mrecip-precision}.
|
|
The double-precision square root estimate instructions are not generated by
|
|
default on low-precision machines, since they do not provide an
|
|
estimate that converges after three steps.
|
|
|
|
@item -mveclibabi=@var{type}
|
|
@opindex mveclibabi
|
|
Specifies the ABI type to use for vectorizing intrinsics using an
|
|
external library. The only type supported at present is @samp{mass},
|
|
which specifies to use IBM's Mathematical Acceleration Subsystem
|
|
(MASS) libraries for vectorizing intrinsics using external libraries.
|
|
GCC currently emits calls to @code{acosd2}, @code{acosf4},
|
|
@code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4},
|
|
@code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4},
|
|
@code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4},
|
|
@code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4},
|
|
@code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4},
|
|
@code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4},
|
|
@code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4},
|
|
@code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4},
|
|
@code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4},
|
|
@code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4},
|
|
@code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2},
|
|
@code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2},
|
|
@code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code
|
|
for power7. Both @option{-ftree-vectorize} and
|
|
@option{-funsafe-math-optimizations} must also be enabled. The MASS
|
|
libraries must be specified at link time.
|
|
|
|
@item -mfriz
|
|
@itemx -mno-friz
|
|
@opindex mfriz
|
|
Generate (do not generate) the @code{friz} instruction when the
|
|
@option{-funsafe-math-optimizations} option is used to optimize
|
|
rounding of floating-point values to 64-bit integer and back to floating
|
|
point. The @code{friz} instruction does not return the same value if
|
|
the floating-point number is too large to fit in an integer.
|
|
|
|
@item -mpointers-to-nested-functions
|
|
@itemx -mno-pointers-to-nested-functions
|
|
@opindex mpointers-to-nested-functions
|
|
Generate (do not generate) code to load up the static chain register
|
|
(@code{r11}) when calling through a pointer on AIX and 64-bit Linux
|
|
systems where a function pointer points to a 3-word descriptor giving
|
|
the function address, TOC value to be loaded in register @code{r2}, and
|
|
static chain value to be loaded in register @code{r11}. The
|
|
@option{-mpointers-to-nested-functions} is on by default. You cannot
|
|
call through pointers to nested functions or pointers
|
|
to functions compiled in other languages that use the static chain if
|
|
you use @option{-mno-pointers-to-nested-functions}.
|
|
|
|
@item -msave-toc-indirect
|
|
@itemx -mno-save-toc-indirect
|
|
@opindex msave-toc-indirect
|
|
Generate (do not generate) code to save the TOC value in the reserved
|
|
stack location in the function prologue if the function calls through
|
|
a pointer on AIX and 64-bit Linux systems. If the TOC value is not
|
|
saved in the prologue, it is saved just before the call through the
|
|
pointer. The @option{-mno-save-toc-indirect} option is the default.
|
|
|
|
@item -mcompat-align-parm
|
|
@itemx -mno-compat-align-parm
|
|
@opindex mcompat-align-parm
|
|
Generate (do not generate) code to pass structure parameters with a
|
|
maximum alignment of 64 bits, for compatibility with older versions
|
|
of GCC.
|
|
|
|
Older versions of GCC (prior to 4.9.0) incorrectly did not align a
|
|
structure parameter on a 128-bit boundary when that structure contained
|
|
a member requiring 128-bit alignment. This is corrected in more
|
|
recent versions of GCC. This option may be used to generate code
|
|
that is compatible with functions compiled with older versions of
|
|
GCC.
|
|
|
|
The @option{-mno-compat-align-parm} option is the default.
|
|
@end table
|
|
|
|
@node RX Options
|
|
@subsection RX Options
|
|
@cindex RX Options
|
|
|
|
These command-line options are defined for RX targets:
|
|
|
|
@table @gcctabopt
|
|
@item -m64bit-doubles
|
|
@itemx -m32bit-doubles
|
|
@opindex m64bit-doubles
|
|
@opindex m32bit-doubles
|
|
Make the @code{double} data type be 64 bits (@option{-m64bit-doubles})
|
|
or 32 bits (@option{-m32bit-doubles}) in size. The default is
|
|
@option{-m32bit-doubles}. @emph{Note} RX floating-point hardware only
|
|
works on 32-bit values, which is why the default is
|
|
@option{-m32bit-doubles}.
|
|
|
|
@item -fpu
|
|
@itemx -nofpu
|
|
@opindex fpu
|
|
@opindex nofpu
|
|
Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX
|
|
floating-point hardware. The default is enabled for the RX600
|
|
series and disabled for the RX200 series.
|
|
|
|
Floating-point instructions are only generated for 32-bit floating-point
|
|
values, however, so the FPU hardware is not used for doubles if the
|
|
@option{-m64bit-doubles} option is used.
|
|
|
|
@emph{Note} If the @option{-fpu} option is enabled then
|
|
@option{-funsafe-math-optimizations} is also enabled automatically.
|
|
This is because the RX FPU instructions are themselves unsafe.
|
|
|
|
@item -mcpu=@var{name}
|
|
@opindex mcpu
|
|
Selects the type of RX CPU to be targeted. Currently three types are
|
|
supported, the generic @samp{RX600} and @samp{RX200} series hardware and
|
|
the specific @samp{RX610} CPU. The default is @samp{RX600}.
|
|
|
|
The only difference between @samp{RX600} and @samp{RX610} is that the
|
|
@samp{RX610} does not support the @code{MVTIPL} instruction.
|
|
|
|
The @samp{RX200} series does not have a hardware floating-point unit
|
|
and so @option{-nofpu} is enabled by default when this type is
|
|
selected.
|
|
|
|
@item -mbig-endian-data
|
|
@itemx -mlittle-endian-data
|
|
@opindex mbig-endian-data
|
|
@opindex mlittle-endian-data
|
|
Store data (but not code) in the big-endian format. The default is
|
|
@option{-mlittle-endian-data}, i.e.@: to store data in the little-endian
|
|
format.
|
|
|
|
@item -msmall-data-limit=@var{N}
|
|
@opindex msmall-data-limit
|
|
Specifies the maximum size in bytes of global and static variables
|
|
which can be placed into the small data area. Using the small data
|
|
area can lead to smaller and faster code, but the size of area is
|
|
limited and it is up to the programmer to ensure that the area does
|
|
not overflow. Also when the small data area is used one of the RX's
|
|
registers (usually @code{r13}) is reserved for use pointing to this
|
|
area, so it is no longer available for use by the compiler. This
|
|
could result in slower and/or larger code if variables are pushed onto
|
|
the stack instead of being held in this register.
|
|
|
|
Note, common variables (variables that have not been initialized) and
|
|
constants are not placed into the small data area as they are assigned
|
|
to other sections in the output executable.
|
|
|
|
The default value is zero, which disables this feature. Note, this
|
|
feature is not enabled by default with higher optimization levels
|
|
(@option{-O2} etc) because of the potentially detrimental effects of
|
|
reserving a register. It is up to the programmer to experiment and
|
|
discover whether this feature is of benefit to their program. See the
|
|
description of the @option{-mpid} option for a description of how the
|
|
actual register to hold the small data area pointer is chosen.
|
|
|
|
@item -msim
|
|
@itemx -mno-sim
|
|
@opindex msim
|
|
@opindex mno-sim
|
|
Use the simulator runtime. The default is to use the libgloss
|
|
board-specific runtime.
|
|
|
|
@item -mas100-syntax
|
|
@itemx -mno-as100-syntax
|
|
@opindex mas100-syntax
|
|
@opindex mno-as100-syntax
|
|
When generating assembler output use a syntax that is compatible with
|
|
Renesas's AS100 assembler. This syntax can also be handled by the GAS
|
|
assembler, but it has some restrictions so it is not generated by default.
|
|
|
|
@item -mmax-constant-size=@var{N}
|
|
@opindex mmax-constant-size
|
|
Specifies the maximum size, in bytes, of a constant that can be used as
|
|
an operand in a RX instruction. Although the RX instruction set does
|
|
allow constants of up to 4 bytes in length to be used in instructions,
|
|
a longer value equates to a longer instruction. Thus in some
|
|
circumstances it can be beneficial to restrict the size of constants
|
|
that are used in instructions. Constants that are too big are instead
|
|
placed into a constant pool and referenced via register indirection.
|
|
|
|
The value @var{N} can be between 0 and 4. A value of 0 (the default)
|
|
or 4 means that constants of any size are allowed.
|
|
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
Enable linker relaxation. Linker relaxation is a process whereby the
|
|
linker attempts to reduce the size of a program by finding shorter
|
|
versions of various instructions. Disabled by default.
|
|
|
|
@item -mint-register=@var{N}
|
|
@opindex mint-register
|
|
Specify the number of registers to reserve for fast interrupt handler
|
|
functions. The value @var{N} can be between 0 and 4. A value of 1
|
|
means that register @code{r13} is reserved for the exclusive use
|
|
of fast interrupt handlers. A value of 2 reserves @code{r13} and
|
|
@code{r12}. A value of 3 reserves @code{r13}, @code{r12} and
|
|
@code{r11}, and a value of 4 reserves @code{r13} through @code{r10}.
|
|
A value of 0, the default, does not reserve any registers.
|
|
|
|
@item -msave-acc-in-interrupts
|
|
@opindex msave-acc-in-interrupts
|
|
Specifies that interrupt handler functions should preserve the
|
|
accumulator register. This is only necessary if normal code might use
|
|
the accumulator register, for example because it performs 64-bit
|
|
multiplications. The default is to ignore the accumulator as this
|
|
makes the interrupt handlers faster.
|
|
|
|
@item -mpid
|
|
@itemx -mno-pid
|
|
@opindex mpid
|
|
@opindex mno-pid
|
|
Enables the generation of position independent data. When enabled any
|
|
access to constant data is done via an offset from a base address
|
|
held in a register. This allows the location of constant data to be
|
|
determined at run time without requiring the executable to be
|
|
relocated, which is a benefit to embedded applications with tight
|
|
memory constraints. Data that can be modified is not affected by this
|
|
option.
|
|
|
|
Note, using this feature reserves a register, usually @code{r13}, for
|
|
the constant data base address. This can result in slower and/or
|
|
larger code, especially in complicated functions.
|
|
|
|
The actual register chosen to hold the constant data base address
|
|
depends upon whether the @option{-msmall-data-limit} and/or the
|
|
@option{-mint-register} command-line options are enabled. Starting
|
|
with register @code{r13} and proceeding downwards, registers are
|
|
allocated first to satisfy the requirements of @option{-mint-register},
|
|
then @option{-mpid} and finally @option{-msmall-data-limit}. Thus it
|
|
is possible for the small data area register to be @code{r8} if both
|
|
@option{-mint-register=4} and @option{-mpid} are specified on the
|
|
command line.
|
|
|
|
By default this feature is not enabled. The default can be restored
|
|
via the @option{-mno-pid} command-line option.
|
|
|
|
@item -mno-warn-multiple-fast-interrupts
|
|
@itemx -mwarn-multiple-fast-interrupts
|
|
@opindex mno-warn-multiple-fast-interrupts
|
|
@opindex mwarn-multiple-fast-interrupts
|
|
Prevents GCC from issuing a warning message if it finds more than one
|
|
fast interrupt handler when it is compiling a file. The default is to
|
|
issue a warning for each extra fast interrupt handler found, as the RX
|
|
only supports one such interrupt.
|
|
|
|
@item -mallow-string-insns
|
|
@itemx -mno-allow-string-insns
|
|
@opindex mallow-string-insns
|
|
@opindex mno-allow-string-insns
|
|
Enables or disables the use of the string manipulation instructions
|
|
@code{SMOVF}, @code{SCMPU}, @code{SMOVB}, @code{SMOVU}, @code{SUNTIL}
|
|
@code{SWHILE} and also the @code{RMPA} instruction. These
|
|
instructions may prefetch data, which is not safe to do if accessing
|
|
an I/O register. (See section 12.2.7 of the RX62N Group User's Manual
|
|
for more information).
|
|
|
|
The default is to allow these instructions, but it is not possible for
|
|
GCC to reliably detect all circumstances where a string instruction
|
|
might be used to access an I/O register, so their use cannot be
|
|
disabled automatically. Instead it is reliant upon the programmer to
|
|
use the @option{-mno-allow-string-insns} option if their program
|
|
accesses I/O space.
|
|
|
|
When the instructions are enabled GCC defines the C preprocessor
|
|
symbol @code{__RX_ALLOW_STRING_INSNS__}, otherwise it defines the
|
|
symbol @code{__RX_DISALLOW_STRING_INSNS__}.
|
|
|
|
@item -mjsr
|
|
@itemx -mno-jsr
|
|
@opindex mjsr
|
|
@opindex mno-jsr
|
|
Use only (or not only) @code{JSR} instructions to access functions.
|
|
This option can be used when code size exceeds the range of @code{BSR}
|
|
instructions. Note that @option{-mno-jsr} does not mean to not use
|
|
@code{JSR} but instead means that any type of branch may be used.
|
|
@end table
|
|
|
|
@emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}}
|
|
has special significance to the RX port when used with the
|
|
@code{interrupt} function attribute. This attribute indicates a
|
|
function intended to process fast interrupts. GCC ensures
|
|
that it only uses the registers @code{r10}, @code{r11}, @code{r12}
|
|
and/or @code{r13} and only provided that the normal use of the
|
|
corresponding registers have been restricted via the
|
|
@option{-ffixed-@var{reg}} or @option{-mint-register} command-line
|
|
options.
|
|
|
|
@node S/390 and zSeries Options
|
|
@subsection S/390 and zSeries Options
|
|
@cindex S/390 and zSeries Options
|
|
|
|
These are the @samp{-m} options defined for the S/390 and zSeries architecture.
|
|
|
|
@table @gcctabopt
|
|
@item -mhard-float
|
|
@itemx -msoft-float
|
|
@opindex mhard-float
|
|
@opindex msoft-float
|
|
Use (do not use) the hardware floating-point instructions and registers
|
|
for floating-point operations. When @option{-msoft-float} is specified,
|
|
functions in @file{libgcc.a} are used to perform floating-point
|
|
operations. When @option{-mhard-float} is specified, the compiler
|
|
generates IEEE floating-point instructions. This is the default.
|
|
|
|
@item -mhard-dfp
|
|
@itemx -mno-hard-dfp
|
|
@opindex mhard-dfp
|
|
@opindex mno-hard-dfp
|
|
Use (do not use) the hardware decimal-floating-point instructions for
|
|
decimal-floating-point operations. When @option{-mno-hard-dfp} is
|
|
specified, functions in @file{libgcc.a} are used to perform
|
|
decimal-floating-point operations. When @option{-mhard-dfp} is
|
|
specified, the compiler generates decimal-floating-point hardware
|
|
instructions. This is the default for @option{-march=z9-ec} or higher.
|
|
|
|
@item -mlong-double-64
|
|
@itemx -mlong-double-128
|
|
@opindex mlong-double-64
|
|
@opindex mlong-double-128
|
|
These switches control the size of @code{long double} type. A size
|
|
of 64 bits makes the @code{long double} type equivalent to the @code{double}
|
|
type. This is the default.
|
|
|
|
@item -mbackchain
|
|
@itemx -mno-backchain
|
|
@opindex mbackchain
|
|
@opindex mno-backchain
|
|
Store (do not store) the address of the caller's frame as backchain pointer
|
|
into the callee's stack frame.
|
|
A backchain may be needed to allow debugging using tools that do not understand
|
|
DWARF call frame information.
|
|
When @option{-mno-packed-stack} is in effect, the backchain pointer is stored
|
|
at the bottom of the stack frame; when @option{-mpacked-stack} is in effect,
|
|
the backchain is placed into the topmost word of the 96/160 byte register
|
|
save area.
|
|
|
|
In general, code compiled with @option{-mbackchain} is call-compatible with
|
|
code compiled with @option{-mmo-backchain}; however, use of the backchain
|
|
for debugging purposes usually requires that the whole binary is built with
|
|
@option{-mbackchain}. Note that the combination of @option{-mbackchain},
|
|
@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
|
|
to build a linux kernel use @option{-msoft-float}.
|
|
|
|
The default is to not maintain the backchain.
|
|
|
|
@item -mpacked-stack
|
|
@itemx -mno-packed-stack
|
|
@opindex mpacked-stack
|
|
@opindex mno-packed-stack
|
|
Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is
|
|
specified, the compiler uses the all fields of the 96/160 byte register save
|
|
area only for their default purpose; unused fields still take up stack space.
|
|
When @option{-mpacked-stack} is specified, register save slots are densely
|
|
packed at the top of the register save area; unused space is reused for other
|
|
purposes, allowing for more efficient use of the available stack space.
|
|
However, when @option{-mbackchain} is also in effect, the topmost word of
|
|
the save area is always used to store the backchain, and the return address
|
|
register is always saved two words below the backchain.
|
|
|
|
As long as the stack frame backchain is not used, code generated with
|
|
@option{-mpacked-stack} is call-compatible with code generated with
|
|
@option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for
|
|
S/390 or zSeries generated code that uses the stack frame backchain at run
|
|
time, not just for debugging purposes. Such code is not call-compatible
|
|
with code compiled with @option{-mpacked-stack}. Also, note that the
|
|
combination of @option{-mbackchain},
|
|
@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order
|
|
to build a linux kernel use @option{-msoft-float}.
|
|
|
|
The default is to not use the packed stack layout.
|
|
|
|
@item -msmall-exec
|
|
@itemx -mno-small-exec
|
|
@opindex msmall-exec
|
|
@opindex mno-small-exec
|
|
Generate (or do not generate) code using the @code{bras} instruction
|
|
to do subroutine calls.
|
|
This only works reliably if the total executable size does not
|
|
exceed 64k. The default is to use the @code{basr} instruction instead,
|
|
which does not have this limitation.
|
|
|
|
@item -m64
|
|
@itemx -m31
|
|
@opindex m64
|
|
@opindex m31
|
|
When @option{-m31} is specified, generate code compliant to the
|
|
GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate
|
|
code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in
|
|
particular to generate 64-bit instructions. For the @samp{s390}
|
|
targets, the default is @option{-m31}, while the @samp{s390x}
|
|
targets default to @option{-m64}.
|
|
|
|
@item -mzarch
|
|
@itemx -mesa
|
|
@opindex mzarch
|
|
@opindex mesa
|
|
When @option{-mzarch} is specified, generate code using the
|
|
instructions available on z/Architecture.
|
|
When @option{-mesa} is specified, generate code using the
|
|
instructions available on ESA/390. Note that @option{-mesa} is
|
|
not possible with @option{-m64}.
|
|
When generating code compliant to the GNU/Linux for S/390 ABI,
|
|
the default is @option{-mesa}. When generating code compliant
|
|
to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}.
|
|
|
|
@item -mhtm
|
|
@itemx -mno-htm
|
|
@opindex mhtm
|
|
@opindex mno-htm
|
|
The @option{-mhtm} option enables a set of builtins making use of
|
|
instructions available with the transactional execution facility
|
|
introduced with the IBM zEnterprise EC12 machine generation
|
|
@ref{S/390 System z Built-in Functions}.
|
|
@option{-mhtm} is enabled by default when using @option{-march=zEC12}.
|
|
|
|
@item -mvx
|
|
@itemx -mno-vx
|
|
@opindex mvx
|
|
@opindex mno-vx
|
|
When @option{-mvx} is specified, generate code using the instructions
|
|
available with the vector extension facility introduced with the IBM
|
|
z13 machine generation.
|
|
This option changes the ABI for some vector type values with regard to
|
|
alignment and calling conventions. In case vector type values are
|
|
being used in an ABI-relevant context a GAS @samp{.gnu_attribute}
|
|
command will be added to mark the resulting binary with the ABI used.
|
|
@option{-mvx} is enabled by default when using @option{-march=z13}.
|
|
|
|
@item -mzvector
|
|
@itemx -mno-zvector
|
|
@opindex mzvector
|
|
@opindex mno-zvector
|
|
The @option{-mzvector} option enables vector language extensions and
|
|
builtins using instructions available with the vector extension
|
|
facility introduced with the IBM z13 machine generation.
|
|
This option adds support for @samp{vector} to be used as a keyword to
|
|
define vector type variables and arguments. @samp{vector} is only
|
|
available when GNU extensions are enabled. It will not be expanded
|
|
when requesting strict standard compliance e.g. with @option{-std=c99}.
|
|
In addition to the GCC low-level builtins @option{-mzvector} enables
|
|
a set of builtins added for compatibility with AltiVec-style
|
|
implementations like Power and Cell. In order to make use of these
|
|
builtins the header file @file{vecintrin.h} needs to be included.
|
|
@option{-mzvector} is disabled by default.
|
|
|
|
@item -mmvcle
|
|
@itemx -mno-mvcle
|
|
@opindex mmvcle
|
|
@opindex mno-mvcle
|
|
Generate (or do not generate) code using the @code{mvcle} instruction
|
|
to perform block moves. When @option{-mno-mvcle} is specified,
|
|
use a @code{mvc} loop instead. This is the default unless optimizing for
|
|
size.
|
|
|
|
@item -mdebug
|
|
@itemx -mno-debug
|
|
@opindex mdebug
|
|
@opindex mno-debug
|
|
Print (or do not print) additional debug information when compiling.
|
|
The default is to not print debug information.
|
|
|
|
@item -march=@var{cpu-type}
|
|
@opindex march
|
|
Generate code that runs on @var{cpu-type}, which is the name of a
|
|
system representing a certain processor type. Possible values for
|
|
@var{cpu-type} are @samp{z900}/@samp{arch5}, @samp{z990}/@samp{arch6},
|
|
@samp{z9-109}, @samp{z9-ec}/@samp{arch7}, @samp{z10}/@samp{arch8},
|
|
@samp{z196}/@samp{arch9}, @samp{zEC12}, @samp{z13}/@samp{arch11}, and
|
|
@samp{native}.
|
|
|
|
The default is @option{-march=z900}. @samp{g5}/@samp{arch3} and
|
|
@samp{g6} are deprecated and will be removed with future releases.
|
|
|
|
Specifying @samp{native} as cpu type can be used to select the best
|
|
architecture option for the host processor.
|
|
@option{-march=native} has no effect if GCC does not recognize the
|
|
processor.
|
|
|
|
@item -mtune=@var{cpu-type}
|
|
@opindex mtune
|
|
Tune to @var{cpu-type} everything applicable about the generated code,
|
|
except for the ABI and the set of available instructions.
|
|
The list of @var{cpu-type} values is the same as for @option{-march}.
|
|
The default is the value used for @option{-march}.
|
|
|
|
@item -mtpf-trace
|
|
@itemx -mno-tpf-trace
|
|
@opindex mtpf-trace
|
|
@opindex mno-tpf-trace
|
|
Generate code that adds (does not add) in TPF OS specific branches to trace
|
|
routines in the operating system. This option is off by default, even
|
|
when compiling for the TPF OS@.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Generate code that uses (does not use) the floating-point multiply and
|
|
accumulate instructions. These instructions are generated by default if
|
|
hardware floating point is used.
|
|
|
|
@item -mwarn-framesize=@var{framesize}
|
|
@opindex mwarn-framesize
|
|
Emit a warning if the current function exceeds the given frame size. Because
|
|
this is a compile-time check it doesn't need to be a real problem when the program
|
|
runs. It is intended to identify functions that most probably cause
|
|
a stack overflow. It is useful to be used in an environment with limited stack
|
|
size e.g.@: the linux kernel.
|
|
|
|
@item -mwarn-dynamicstack
|
|
@opindex mwarn-dynamicstack
|
|
Emit a warning if the function calls @code{alloca} or uses dynamically-sized
|
|
arrays. This is generally a bad idea with a limited stack size.
|
|
|
|
@item -mstack-guard=@var{stack-guard}
|
|
@itemx -mstack-size=@var{stack-size}
|
|
@opindex mstack-guard
|
|
@opindex mstack-size
|
|
If these options are provided the S/390 back end emits additional instructions in
|
|
the function prologue that trigger a trap if the stack size is @var{stack-guard}
|
|
bytes above the @var{stack-size} (remember that the stack on S/390 grows downward).
|
|
If the @var{stack-guard} option is omitted the smallest power of 2 larger than
|
|
the frame size of the compiled function is chosen.
|
|
These options are intended to be used to help debugging stack overflow problems.
|
|
The additionally emitted code causes only little overhead and hence can also be
|
|
used in production-like systems without greater performance degradation. The given
|
|
values have to be exact powers of 2 and @var{stack-size} has to be greater than
|
|
@var{stack-guard} without exceeding 64k.
|
|
In order to be efficient the extra code makes the assumption that the stack starts
|
|
at an address aligned to the value given by @var{stack-size}.
|
|
The @var{stack-guard} option can only be used in conjunction with @var{stack-size}.
|
|
|
|
@item -mhotpatch=@var{pre-halfwords},@var{post-halfwords}
|
|
@opindex mhotpatch
|
|
If the hotpatch option is enabled, a ``hot-patching'' function
|
|
prologue is generated for all functions in the compilation unit.
|
|
The funtion label is prepended with the given number of two-byte
|
|
NOP instructions (@var{pre-halfwords}, maximum 1000000). After
|
|
the label, 2 * @var{post-halfwords} bytes are appended, using the
|
|
largest NOP like instructions the architecture allows (maximum
|
|
1000000).
|
|
|
|
If both arguments are zero, hotpatching is disabled.
|
|
|
|
This option can be overridden for individual functions with the
|
|
@code{hotpatch} attribute.
|
|
@end table
|
|
|
|
@node Score Options
|
|
@subsection Score Options
|
|
@cindex Score Options
|
|
|
|
These options are defined for Score implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -meb
|
|
@opindex meb
|
|
Compile code for big-endian mode. This is the default.
|
|
|
|
@item -mel
|
|
@opindex mel
|
|
Compile code for little-endian mode.
|
|
|
|
@item -mnhwloop
|
|
@opindex mnhwloop
|
|
Disable generation of @code{bcnz} instructions.
|
|
|
|
@item -muls
|
|
@opindex muls
|
|
Enable generation of unaligned load and store instructions.
|
|
|
|
@item -mmac
|
|
@opindex mmac
|
|
Enable the use of multiply-accumulate instructions. Disabled by default.
|
|
|
|
@item -mscore5
|
|
@opindex mscore5
|
|
Specify the SCORE5 as the target architecture.
|
|
|
|
@item -mscore5u
|
|
@opindex mscore5u
|
|
Specify the SCORE5U of the target architecture.
|
|
|
|
@item -mscore7
|
|
@opindex mscore7
|
|
Specify the SCORE7 as the target architecture. This is the default.
|
|
|
|
@item -mscore7d
|
|
@opindex mscore7d
|
|
Specify the SCORE7D as the target architecture.
|
|
@end table
|
|
|
|
@node SH Options
|
|
@subsection SH Options
|
|
|
|
These @samp{-m} options are defined for the SH implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -m1
|
|
@opindex m1
|
|
Generate code for the SH1.
|
|
|
|
@item -m2
|
|
@opindex m2
|
|
Generate code for the SH2.
|
|
|
|
@item -m2e
|
|
Generate code for the SH2e.
|
|
|
|
@item -m2a-nofpu
|
|
@opindex m2a-nofpu
|
|
Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way
|
|
that the floating-point unit is not used.
|
|
|
|
@item -m2a-single-only
|
|
@opindex m2a-single-only
|
|
Generate code for the SH2a-FPU, in such a way that no double-precision
|
|
floating-point operations are used.
|
|
|
|
@item -m2a-single
|
|
@opindex m2a-single
|
|
Generate code for the SH2a-FPU assuming the floating-point unit is in
|
|
single-precision mode by default.
|
|
|
|
@item -m2a
|
|
@opindex m2a
|
|
Generate code for the SH2a-FPU assuming the floating-point unit is in
|
|
double-precision mode by default.
|
|
|
|
@item -m3
|
|
@opindex m3
|
|
Generate code for the SH3.
|
|
|
|
@item -m3e
|
|
@opindex m3e
|
|
Generate code for the SH3e.
|
|
|
|
@item -m4-nofpu
|
|
@opindex m4-nofpu
|
|
Generate code for the SH4 without a floating-point unit.
|
|
|
|
@item -m4-single-only
|
|
@opindex m4-single-only
|
|
Generate code for the SH4 with a floating-point unit that only
|
|
supports single-precision arithmetic.
|
|
|
|
@item -m4-single
|
|
@opindex m4-single
|
|
Generate code for the SH4 assuming the floating-point unit is in
|
|
single-precision mode by default.
|
|
|
|
@item -m4
|
|
@opindex m4
|
|
Generate code for the SH4.
|
|
|
|
@item -m4-100
|
|
@opindex m4-100
|
|
Generate code for SH4-100.
|
|
|
|
@item -m4-100-nofpu
|
|
@opindex m4-100-nofpu
|
|
Generate code for SH4-100 in such a way that the
|
|
floating-point unit is not used.
|
|
|
|
@item -m4-100-single
|
|
@opindex m4-100-single
|
|
Generate code for SH4-100 assuming the floating-point unit is in
|
|
single-precision mode by default.
|
|
|
|
@item -m4-100-single-only
|
|
@opindex m4-100-single-only
|
|
Generate code for SH4-100 in such a way that no double-precision
|
|
floating-point operations are used.
|
|
|
|
@item -m4-200
|
|
@opindex m4-200
|
|
Generate code for SH4-200.
|
|
|
|
@item -m4-200-nofpu
|
|
@opindex m4-200-nofpu
|
|
Generate code for SH4-200 without in such a way that the
|
|
floating-point unit is not used.
|
|
|
|
@item -m4-200-single
|
|
@opindex m4-200-single
|
|
Generate code for SH4-200 assuming the floating-point unit is in
|
|
single-precision mode by default.
|
|
|
|
@item -m4-200-single-only
|
|
@opindex m4-200-single-only
|
|
Generate code for SH4-200 in such a way that no double-precision
|
|
floating-point operations are used.
|
|
|
|
@item -m4-300
|
|
@opindex m4-300
|
|
Generate code for SH4-300.
|
|
|
|
@item -m4-300-nofpu
|
|
@opindex m4-300-nofpu
|
|
Generate code for SH4-300 without in such a way that the
|
|
floating-point unit is not used.
|
|
|
|
@item -m4-300-single
|
|
@opindex m4-300-single
|
|
Generate code for SH4-300 in such a way that no double-precision
|
|
floating-point operations are used.
|
|
|
|
@item -m4-300-single-only
|
|
@opindex m4-300-single-only
|
|
Generate code for SH4-300 in such a way that no double-precision
|
|
floating-point operations are used.
|
|
|
|
@item -m4-340
|
|
@opindex m4-340
|
|
Generate code for SH4-340 (no MMU, no FPU).
|
|
|
|
@item -m4-500
|
|
@opindex m4-500
|
|
Generate code for SH4-500 (no FPU). Passes @option{-isa=sh4-nofpu} to the
|
|
assembler.
|
|
|
|
@item -m4a-nofpu
|
|
@opindex m4a-nofpu
|
|
Generate code for the SH4al-dsp, or for a SH4a in such a way that the
|
|
floating-point unit is not used.
|
|
|
|
@item -m4a-single-only
|
|
@opindex m4a-single-only
|
|
Generate code for the SH4a, in such a way that no double-precision
|
|
floating-point operations are used.
|
|
|
|
@item -m4a-single
|
|
@opindex m4a-single
|
|
Generate code for the SH4a assuming the floating-point unit is in
|
|
single-precision mode by default.
|
|
|
|
@item -m4a
|
|
@opindex m4a
|
|
Generate code for the SH4a.
|
|
|
|
@item -m4al
|
|
@opindex m4al
|
|
Same as @option{-m4a-nofpu}, except that it implicitly passes
|
|
@option{-dsp} to the assembler. GCC doesn't generate any DSP
|
|
instructions at the moment.
|
|
|
|
@item -mb
|
|
@opindex mb
|
|
Compile code for the processor in big-endian mode.
|
|
|
|
@item -ml
|
|
@opindex ml
|
|
Compile code for the processor in little-endian mode.
|
|
|
|
@item -mdalign
|
|
@opindex mdalign
|
|
Align doubles at 64-bit boundaries. Note that this changes the calling
|
|
conventions, and thus some functions from the standard C library do
|
|
not work unless you recompile it first with @option{-mdalign}.
|
|
|
|
@item -mrelax
|
|
@opindex mrelax
|
|
Shorten some address references at link time, when possible; uses the
|
|
linker option @option{-relax}.
|
|
|
|
@item -mbigtable
|
|
@opindex mbigtable
|
|
Use 32-bit offsets in @code{switch} tables. The default is to use
|
|
16-bit offsets.
|
|
|
|
@item -mbitops
|
|
@opindex mbitops
|
|
Enable the use of bit manipulation instructions on SH2A.
|
|
|
|
@item -mfmovd
|
|
@opindex mfmovd
|
|
Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for
|
|
alignment constraints.
|
|
|
|
@item -mrenesas
|
|
@opindex mrenesas
|
|
Comply with the calling conventions defined by Renesas.
|
|
|
|
@item -mno-renesas
|
|
@opindex mno-renesas
|
|
Comply with the calling conventions defined for GCC before the Renesas
|
|
conventions were available. This option is the default for all
|
|
targets of the SH toolchain.
|
|
|
|
@item -mnomacsave
|
|
@opindex mnomacsave
|
|
Mark the @code{MAC} register as call-clobbered, even if
|
|
@option{-mrenesas} is given.
|
|
|
|
@item -mieee
|
|
@itemx -mno-ieee
|
|
@opindex mieee
|
|
@opindex mno-ieee
|
|
Control the IEEE compliance of floating-point comparisons, which affects the
|
|
handling of cases where the result of a comparison is unordered. By default
|
|
@option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is
|
|
enabled @option{-mno-ieee} is implicitly set, which results in faster
|
|
floating-point greater-equal and less-equal comparisons. The implicit settings
|
|
can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}.
|
|
|
|
@item -minline-ic_invalidate
|
|
@opindex minline-ic_invalidate
|
|
Inline code to invalidate instruction cache entries after setting up
|
|
nested function trampolines.
|
|
This option has no effect if @option{-musermode} is in effect and the selected
|
|
code generation option (e.g. @option{-m4}) does not allow the use of the @code{icbi}
|
|
instruction.
|
|
If the selected code generation option does not allow the use of the @code{icbi}
|
|
instruction, and @option{-musermode} is not in effect, the inlined code
|
|
manipulates the instruction cache address array directly with an associative
|
|
write. This not only requires privileged mode at run time, but it also
|
|
fails if the cache line had been mapped via the TLB and has become unmapped.
|
|
|
|
@item -misize
|
|
@opindex misize
|
|
Dump instruction size and location in the assembly code.
|
|
|
|
@item -mpadstruct
|
|
@opindex mpadstruct
|
|
This option is deprecated. It pads structures to multiple of 4 bytes,
|
|
which is incompatible with the SH ABI@.
|
|
|
|
@item -matomic-model=@var{model}
|
|
@opindex matomic-model=@var{model}
|
|
Sets the model of atomic operations and additional parameters as a comma
|
|
separated list. For details on the atomic built-in functions see
|
|
@ref{__atomic Builtins}. The following models and parameters are supported:
|
|
|
|
@table @samp
|
|
|
|
@item none
|
|
Disable compiler generated atomic sequences and emit library calls for atomic
|
|
operations. This is the default if the target is not @code{sh*-*-linux*}.
|
|
|
|
@item soft-gusa
|
|
Generate GNU/Linux compatible gUSA software atomic sequences for the atomic
|
|
built-in functions. The generated atomic sequences require additional support
|
|
from the interrupt/exception handling code of the system and are only suitable
|
|
for SH3* and SH4* single-core systems. This option is enabled by default when
|
|
the target is @code{sh*-*-linux*} and SH3* or SH4*. When the target is SH4A,
|
|
this option also partially utilizes the hardware atomic instructions
|
|
@code{movli.l} and @code{movco.l} to create more efficient code, unless
|
|
@samp{strict} is specified.
|
|
|
|
@item soft-tcb
|
|
Generate software atomic sequences that use a variable in the thread control
|
|
block. This is a variation of the gUSA sequences which can also be used on
|
|
SH1* and SH2* targets. The generated atomic sequences require additional
|
|
support from the interrupt/exception handling code of the system and are only
|
|
suitable for single-core systems. When using this model, the @samp{gbr-offset=}
|
|
parameter has to be specified as well.
|
|
|
|
@item soft-imask
|
|
Generate software atomic sequences that temporarily disable interrupts by
|
|
setting @code{SR.IMASK = 1111}. This model works only when the program runs
|
|
in privileged mode and is only suitable for single-core systems. Additional
|
|
support from the interrupt/exception handling code of the system is not
|
|
required. This model is enabled by default when the target is
|
|
@code{sh*-*-linux*} and SH1* or SH2*.
|
|
|
|
@item hard-llcs
|
|
Generate hardware atomic sequences using the @code{movli.l} and @code{movco.l}
|
|
instructions only. This is only available on SH4A and is suitable for
|
|
multi-core systems. Since the hardware instructions support only 32 bit atomic
|
|
variables access to 8 or 16 bit variables is emulated with 32 bit accesses.
|
|
Code compiled with this option is also compatible with other software
|
|
atomic model interrupt/exception handling systems if executed on an SH4A
|
|
system. Additional support from the interrupt/exception handling code of the
|
|
system is not required for this model.
|
|
|
|
@item gbr-offset=
|
|
This parameter specifies the offset in bytes of the variable in the thread
|
|
control block structure that should be used by the generated atomic sequences
|
|
when the @samp{soft-tcb} model has been selected. For other models this
|
|
parameter is ignored. The specified value must be an integer multiple of four
|
|
and in the range 0-1020.
|
|
|
|
@item strict
|
|
This parameter prevents mixed usage of multiple atomic models, even if they
|
|
are compatible, and makes the compiler generate atomic sequences of the
|
|
specified model only.
|
|
|
|
@end table
|
|
|
|
@item -mtas
|
|
@opindex mtas
|
|
Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}.
|
|
Notice that depending on the particular hardware and software configuration
|
|
this can degrade overall performance due to the operand cache line flushes
|
|
that are implied by the @code{tas.b} instruction. On multi-core SH4A
|
|
processors the @code{tas.b} instruction must be used with caution since it
|
|
can result in data corruption for certain cache configurations.
|
|
|
|
@item -mprefergot
|
|
@opindex mprefergot
|
|
When generating position-independent code, emit function calls using
|
|
the Global Offset Table instead of the Procedure Linkage Table.
|
|
|
|
@item -musermode
|
|
@itemx -mno-usermode
|
|
@opindex musermode
|
|
@opindex mno-usermode
|
|
Don't allow (allow) the compiler generating privileged mode code. Specifying
|
|
@option{-musermode} also implies @option{-mno-inline-ic_invalidate} if the
|
|
inlined code would not work in user mode. @option{-musermode} is the default
|
|
when the target is @code{sh*-*-linux*}. If the target is SH1* or SH2*
|
|
@option{-musermode} has no effect, since there is no user mode.
|
|
|
|
@item -multcost=@var{number}
|
|
@opindex multcost=@var{number}
|
|
Set the cost to assume for a multiply insn.
|
|
|
|
@item -mdiv=@var{strategy}
|
|
@opindex mdiv=@var{strategy}
|
|
Set the division strategy to be used for integer division operations.
|
|
@var{strategy} can be one of:
|
|
|
|
@table @samp
|
|
|
|
@item call-div1
|
|
Calls a library function that uses the single-step division instruction
|
|
@code{div1} to perform the operation. Division by zero calculates an
|
|
unspecified result and does not trap. This is the default except for SH4,
|
|
SH2A and SHcompact.
|
|
|
|
@item call-fp
|
|
Calls a library function that performs the operation in double precision
|
|
floating point. Division by zero causes a floating-point exception. This is
|
|
the default for SHcompact with FPU. Specifying this for targets that do not
|
|
have a double precision FPU defaults to @code{call-div1}.
|
|
|
|
@item call-table
|
|
Calls a library function that uses a lookup table for small divisors and
|
|
the @code{div1} instruction with case distinction for larger divisors. Division
|
|
by zero calculates an unspecified result and does not trap. This is the default
|
|
for SH4. Specifying this for targets that do not have dynamic shift
|
|
instructions defaults to @code{call-div1}.
|
|
|
|
@end table
|
|
|
|
When a division strategy has not been specified the default strategy is
|
|
selected based on the current target. For SH2A the default strategy is to
|
|
use the @code{divs} and @code{divu} instructions instead of library function
|
|
calls.
|
|
|
|
@item -maccumulate-outgoing-args
|
|
@opindex maccumulate-outgoing-args
|
|
Reserve space once for outgoing arguments in the function prologue rather
|
|
than around each call. Generally beneficial for performance and size. Also
|
|
needed for unwinding to avoid changing the stack frame around conditional code.
|
|
|
|
@item -mdivsi3_libfunc=@var{name}
|
|
@opindex mdivsi3_libfunc=@var{name}
|
|
Set the name of the library function used for 32-bit signed division to
|
|
@var{name}.
|
|
This only affects the name used in the @samp{call} division strategies, and
|
|
the compiler still expects the same sets of input/output/clobbered registers as
|
|
if this option were not present.
|
|
|
|
@item -mfixed-range=@var{register-range}
|
|
@opindex mfixed-range
|
|
Generate code treating the given register range as fixed registers.
|
|
A fixed register is one that the register allocator can not use. This is
|
|
useful when compiling kernel code. A register range is specified as
|
|
two registers separated by a dash. Multiple register ranges can be
|
|
specified separated by a comma.
|
|
|
|
@item -mbranch-cost=@var{num}
|
|
@opindex mbranch-cost=@var{num}
|
|
Assume @var{num} to be the cost for a branch instruction. Higher numbers
|
|
make the compiler try to generate more branch-free code if possible.
|
|
If not specified the value is selected depending on the processor type that
|
|
is being compiled for.
|
|
|
|
@item -mzdcbranch
|
|
@itemx -mno-zdcbranch
|
|
@opindex mzdcbranch
|
|
@opindex mno-zdcbranch
|
|
Assume (do not assume) that zero displacement conditional branch instructions
|
|
@code{bt} and @code{bf} are fast. If @option{-mzdcbranch} is specified, the
|
|
compiler prefers zero displacement branch code sequences. This is
|
|
enabled by default when generating code for SH4 and SH4A. It can be explicitly
|
|
disabled by specifying @option{-mno-zdcbranch}.
|
|
|
|
@item -mcbranch-force-delay-slot
|
|
@opindex mcbranch-force-delay-slot
|
|
Force the usage of delay slots for conditional branches, which stuffs the delay
|
|
slot with a @code{nop} if a suitable instruction can't be found. By default
|
|
this option is disabled. It can be enabled to work around hardware bugs as
|
|
found in the original SH7055.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Generate code that uses (does not use) the floating-point multiply and
|
|
accumulate instructions. These instructions are generated by default
|
|
if hardware floating point is used. The machine-dependent
|
|
@option{-mfused-madd} option is now mapped to the machine-independent
|
|
@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is
|
|
mapped to @option{-ffp-contract=off}.
|
|
|
|
@item -mfsca
|
|
@itemx -mno-fsca
|
|
@opindex mfsca
|
|
@opindex mno-fsca
|
|
Allow or disallow the compiler to emit the @code{fsca} instruction for sine
|
|
and cosine approximations. The option @option{-mfsca} must be used in
|
|
combination with @option{-funsafe-math-optimizations}. It is enabled by default
|
|
when generating code for SH4A. Using @option{-mno-fsca} disables sine and cosine
|
|
approximations even if @option{-funsafe-math-optimizations} is in effect.
|
|
|
|
@item -mfsrra
|
|
@itemx -mno-fsrra
|
|
@opindex mfsrra
|
|
@opindex mno-fsrra
|
|
Allow or disallow the compiler to emit the @code{fsrra} instruction for
|
|
reciprocal square root approximations. The option @option{-mfsrra} must be used
|
|
in combination with @option{-funsafe-math-optimizations} and
|
|
@option{-ffinite-math-only}. It is enabled by default when generating code for
|
|
SH4A. Using @option{-mno-fsrra} disables reciprocal square root approximations
|
|
even if @option{-funsafe-math-optimizations} and @option{-ffinite-math-only} are
|
|
in effect.
|
|
|
|
@item -mpretend-cmove
|
|
@opindex mpretend-cmove
|
|
Prefer zero-displacement conditional branches for conditional move instruction
|
|
patterns. This can result in faster code on the SH4 processor.
|
|
|
|
@item -mfdpic
|
|
@opindex fdpic
|
|
Generate code using the FDPIC ABI.
|
|
|
|
@end table
|
|
|
|
@node Solaris 2 Options
|
|
@subsection Solaris 2 Options
|
|
@cindex Solaris 2 options
|
|
|
|
These @samp{-m} options are supported on Solaris 2:
|
|
|
|
@table @gcctabopt
|
|
@item -mclear-hwcap
|
|
@opindex mclear-hwcap
|
|
@option{-mclear-hwcap} tells the compiler to remove the hardware
|
|
capabilities generated by the Solaris assembler. This is only necessary
|
|
when object files use ISA extensions not supported by the current
|
|
machine, but check at runtime whether or not to use them.
|
|
|
|
@item -mimpure-text
|
|
@opindex mimpure-text
|
|
@option{-mimpure-text}, used in addition to @option{-shared}, tells
|
|
the compiler to not pass @option{-z text} to the linker when linking a
|
|
shared object. Using this option, you can link position-dependent
|
|
code into a shared object.
|
|
|
|
@option{-mimpure-text} suppresses the ``relocations remain against
|
|
allocatable but non-writable sections'' linker error message.
|
|
However, the necessary relocations trigger copy-on-write, and the
|
|
shared object is not actually shared across processes. Instead of
|
|
using @option{-mimpure-text}, you should compile all source code with
|
|
@option{-fpic} or @option{-fPIC}.
|
|
|
|
@end table
|
|
|
|
These switches are supported in addition to the above on Solaris 2:
|
|
|
|
@table @gcctabopt
|
|
@item -pthreads
|
|
@opindex pthreads
|
|
This is a synonym for @option{-pthread}.
|
|
@end table
|
|
|
|
@node SPARC Options
|
|
@subsection SPARC Options
|
|
@cindex SPARC options
|
|
|
|
These @samp{-m} options are supported on the SPARC:
|
|
|
|
@table @gcctabopt
|
|
@item -mno-app-regs
|
|
@itemx -mapp-regs
|
|
@opindex mno-app-regs
|
|
@opindex mapp-regs
|
|
Specify @option{-mapp-regs} to generate output using the global registers
|
|
2 through 4, which the SPARC SVR4 ABI reserves for applications. Like the
|
|
global register 1, each global register 2 through 4 is then treated as an
|
|
allocable register that is clobbered by function calls. This is the default.
|
|
|
|
To be fully SVR4 ABI-compliant at the cost of some performance loss,
|
|
specify @option{-mno-app-regs}. You should compile libraries and system
|
|
software with this option.
|
|
|
|
@item -mflat
|
|
@itemx -mno-flat
|
|
@opindex mflat
|
|
@opindex mno-flat
|
|
With @option{-mflat}, the compiler does not generate save/restore instructions
|
|
and uses a ``flat'' or single register window model. This model is compatible
|
|
with the regular register window model. The local registers and the input
|
|
registers (0--5) are still treated as ``call-saved'' registers and are
|
|
saved on the stack as needed.
|
|
|
|
With @option{-mno-flat} (the default), the compiler generates save/restore
|
|
instructions (except for leaf functions). This is the normal operating mode.
|
|
|
|
@item -mfpu
|
|
@itemx -mhard-float
|
|
@opindex mfpu
|
|
@opindex mhard-float
|
|
Generate output containing floating-point instructions. This is the
|
|
default.
|
|
|
|
@item -mno-fpu
|
|
@itemx -msoft-float
|
|
@opindex mno-fpu
|
|
@opindex msoft-float
|
|
Generate output containing library calls for floating point.
|
|
@strong{Warning:} the requisite libraries are not available for all SPARC
|
|
targets. Normally the facilities of the machine's usual C compiler are
|
|
used, but this cannot be done directly in cross-compilation. You must make
|
|
your own arrangements to provide suitable library functions for
|
|
cross-compilation. The embedded targets @samp{sparc-*-aout} and
|
|
@samp{sparclite-*-*} do provide software floating-point support.
|
|
|
|
@option{-msoft-float} changes the calling convention in the output file;
|
|
therefore, it is only useful if you compile @emph{all} of a program with
|
|
this option. In particular, you need to compile @file{libgcc.a}, the
|
|
library that comes with GCC, with @option{-msoft-float} in order for
|
|
this to work.
|
|
|
|
@item -mhard-quad-float
|
|
@opindex mhard-quad-float
|
|
Generate output containing quad-word (long double) floating-point
|
|
instructions.
|
|
|
|
@item -msoft-quad-float
|
|
@opindex msoft-quad-float
|
|
Generate output containing library calls for quad-word (long double)
|
|
floating-point instructions. The functions called are those specified
|
|
in the SPARC ABI@. This is the default.
|
|
|
|
As of this writing, there are no SPARC implementations that have hardware
|
|
support for the quad-word floating-point instructions. They all invoke
|
|
a trap handler for one of these instructions, and then the trap handler
|
|
emulates the effect of the instruction. Because of the trap handler overhead,
|
|
this is much slower than calling the ABI library routines. Thus the
|
|
@option{-msoft-quad-float} option is the default.
|
|
|
|
@item -mno-unaligned-doubles
|
|
@itemx -munaligned-doubles
|
|
@opindex mno-unaligned-doubles
|
|
@opindex munaligned-doubles
|
|
Assume that doubles have 8-byte alignment. This is the default.
|
|
|
|
With @option{-munaligned-doubles}, GCC assumes that doubles have 8-byte
|
|
alignment only if they are contained in another type, or if they have an
|
|
absolute address. Otherwise, it assumes they have 4-byte alignment.
|
|
Specifying this option avoids some rare compatibility problems with code
|
|
generated by other compilers. It is not the default because it results
|
|
in a performance loss, especially for floating-point code.
|
|
|
|
@item -muser-mode
|
|
@itemx -mno-user-mode
|
|
@opindex muser-mode
|
|
@opindex mno-user-mode
|
|
Do not generate code that can only run in supervisor mode. This is relevant
|
|
only for the @code{casa} instruction emitted for the LEON3 processor. This
|
|
is the default.
|
|
|
|
@item -mfaster-structs
|
|
@itemx -mno-faster-structs
|
|
@opindex mfaster-structs
|
|
@opindex mno-faster-structs
|
|
With @option{-mfaster-structs}, the compiler assumes that structures
|
|
should have 8-byte alignment. This enables the use of pairs of
|
|
@code{ldd} and @code{std} instructions for copies in structure
|
|
assignment, in place of twice as many @code{ld} and @code{st} pairs.
|
|
However, the use of this changed alignment directly violates the SPARC
|
|
ABI@. Thus, it's intended only for use on targets where the developer
|
|
acknowledges that their resulting code is not directly in line with
|
|
the rules of the ABI@.
|
|
|
|
@item -mstd-struct-return
|
|
@itemx -mno-std-struct-return
|
|
@opindex mstd-struct-return
|
|
@opindex mno-std-struct-return
|
|
With @option{-mstd-struct-return}, the compiler generates checking code
|
|
in functions returning structures or unions to detect size mismatches
|
|
between the two sides of function calls, as per the 32-bit ABI@.
|
|
|
|
The default is @option{-mno-std-struct-return}. This option has no effect
|
|
in 64-bit mode.
|
|
|
|
@item -mlra
|
|
@itemx -mno-lra
|
|
@opindex mlra
|
|
@opindex mno-lra
|
|
Enable Local Register Allocation. This is the default for SPARC since GCC 7
|
|
so @option{-mno-lra} needs to be passed to get old Reload.
|
|
|
|
@item -mcpu=@var{cpu_type}
|
|
@opindex mcpu
|
|
Set the instruction set, register set, and instruction scheduling parameters
|
|
for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
|
|
@samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc},
|
|
@samp{leon}, @samp{leon3}, @samp{leon3v7}, @samp{sparclite}, @samp{f930},
|
|
@samp{f934}, @samp{sparclite86x}, @samp{sparclet}, @samp{tsc701}, @samp{v9},
|
|
@samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2},
|
|
@samp{niagara3}, @samp{niagara4} and @samp{niagara7}.
|
|
|
|
Native Solaris and GNU/Linux toolchains also support the value @samp{native},
|
|
which selects the best architecture option for the host processor.
|
|
@option{-mcpu=native} has no effect if GCC does not recognize
|
|
the processor.
|
|
|
|
Default instruction scheduling parameters are used for values that select
|
|
an architecture and not an implementation. These are @samp{v7}, @samp{v8},
|
|
@samp{sparclite}, @samp{sparclet}, @samp{v9}.
|
|
|
|
Here is a list of each supported architecture and their supported
|
|
implementations.
|
|
|
|
@table @asis
|
|
@item v7
|
|
cypress, leon3v7
|
|
|
|
@item v8
|
|
supersparc, hypersparc, leon, leon3
|
|
|
|
@item sparclite
|
|
f930, f934, sparclite86x
|
|
|
|
@item sparclet
|
|
tsc701
|
|
|
|
@item v9
|
|
ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4, niagara7
|
|
@end table
|
|
|
|
By default (unless configured otherwise), GCC generates code for the V7
|
|
variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler
|
|
additionally optimizes it for the Cypress CY7C602 chip, as used in the
|
|
SPARCStation/SPARCServer 3xx series. This is also appropriate for the older
|
|
SPARCStation 1, 2, IPX etc.
|
|
|
|
With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC
|
|
architecture. The only difference from V7 code is that the compiler emits
|
|
the integer multiply and integer divide instructions which exist in SPARC-V8
|
|
but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally
|
|
optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and
|
|
2000 series.
|
|
|
|
With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of
|
|
the SPARC architecture. This adds the integer multiply, integer divide step
|
|
and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7.
|
|
With @option{-mcpu=f930}, the compiler additionally optimizes it for the
|
|
Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With
|
|
@option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu
|
|
MB86934 chip, which is the more recent SPARClite with FPU@.
|
|
|
|
With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of
|
|
the SPARC architecture. This adds the integer multiply, multiply/accumulate,
|
|
integer divide step and scan (@code{ffs}) instructions which exist in SPARClet
|
|
but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally
|
|
optimizes it for the TEMIC SPARClet chip.
|
|
|
|
With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC
|
|
architecture. This adds 64-bit integer and floating-point move instructions,
|
|
3 additional floating-point condition code registers and conditional move
|
|
instructions. With @option{-mcpu=ultrasparc}, the compiler additionally
|
|
optimizes it for the Sun UltraSPARC I/II/IIi chips. With
|
|
@option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the
|
|
Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With
|
|
@option{-mcpu=niagara}, the compiler additionally optimizes it for
|
|
Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler
|
|
additionally optimizes it for Sun UltraSPARC T2 chips. With
|
|
@option{-mcpu=niagara3}, the compiler additionally optimizes it for Sun
|
|
UltraSPARC T3 chips. With @option{-mcpu=niagara4}, the compiler
|
|
additionally optimizes it for Sun UltraSPARC T4 chips. With
|
|
@option{-mcpu=niagara7}, the compiler additionally optimizes it for
|
|
Oracle SPARC M7 chips.
|
|
|
|
@item -mtune=@var{cpu_type}
|
|
@opindex mtune
|
|
Set the instruction scheduling parameters for machine type
|
|
@var{cpu_type}, but do not set the instruction set or register set that the
|
|
option @option{-mcpu=@var{cpu_type}} does.
|
|
|
|
The same values for @option{-mcpu=@var{cpu_type}} can be used for
|
|
@option{-mtune=@var{cpu_type}}, but the only useful values are those
|
|
that select a particular CPU implementation. Those are
|
|
@samp{cypress}, @samp{supersparc}, @samp{hypersparc}, @samp{leon},
|
|
@samp{leon3}, @samp{leon3v7}, @samp{f930}, @samp{f934},
|
|
@samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc},
|
|
@samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, @samp{niagara3},
|
|
@samp{niagara4} and @samp{niagara7}. With native Solaris and
|
|
GNU/Linux toolchains, @samp{native} can also be used.
|
|
|
|
@item -mv8plus
|
|
@itemx -mno-v8plus
|
|
@opindex mv8plus
|
|
@opindex mno-v8plus
|
|
With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The
|
|
difference from the V8 ABI is that the global and out registers are
|
|
considered 64 bits wide. This is enabled by default on Solaris in 32-bit
|
|
mode for all SPARC-V9 processors.
|
|
|
|
@item -mvis
|
|
@itemx -mno-vis
|
|
@opindex mvis
|
|
@opindex mno-vis
|
|
With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC
|
|
Visual Instruction Set extensions. The default is @option{-mno-vis}.
|
|
|
|
@item -mvis2
|
|
@itemx -mno-vis2
|
|
@opindex mvis2
|
|
@opindex mno-vis2
|
|
With @option{-mvis2}, GCC generates code that takes advantage of
|
|
version 2.0 of the UltraSPARC Visual Instruction Set extensions. The
|
|
default is @option{-mvis2} when targeting a cpu that supports such
|
|
instructions, such as UltraSPARC-III and later. Setting @option{-mvis2}
|
|
also sets @option{-mvis}.
|
|
|
|
@item -mvis3
|
|
@itemx -mno-vis3
|
|
@opindex mvis3
|
|
@opindex mno-vis3
|
|
With @option{-mvis3}, GCC generates code that takes advantage of
|
|
version 3.0 of the UltraSPARC Visual Instruction Set extensions. The
|
|
default is @option{-mvis3} when targeting a cpu that supports such
|
|
instructions, such as niagara-3 and later. Setting @option{-mvis3}
|
|
also sets @option{-mvis2} and @option{-mvis}.
|
|
|
|
@item -mvis4
|
|
@itemx -mno-vis4
|
|
@opindex mvis4
|
|
@opindex mno-vis4
|
|
With @option{-mvis4}, GCC generates code that takes advantage of
|
|
version 4.0 of the UltraSPARC Visual Instruction Set extensions. The
|
|
default is @option{-mvis4} when targeting a cpu that supports such
|
|
instructions, such as niagara-7 and later. Setting @option{-mvis4}
|
|
also sets @option{-mvis3}, @option{-mvis2} and @option{-mvis}.
|
|
|
|
@item -mcbcond
|
|
@itemx -mno-cbcond
|
|
@opindex mcbcond
|
|
@opindex mno-cbcond
|
|
With @option{-mcbcond}, GCC generates code that takes advantage of the UltraSPARC
|
|
Compare-and-Branch-on-Condition instructions. The default is @option{-mcbcond}
|
|
when targeting a CPU that supports such instructions, such as Niagara-4 and
|
|
later.
|
|
|
|
@item -mfmaf
|
|
@itemx -mno-fmaf
|
|
@opindex mfmaf
|
|
@opindex mno-fmaf
|
|
With @option{-mfmaf}, GCC generates code that takes advantage of the UltraSPARC
|
|
Fused Multiply-Add Floating-point instructions. The default is @option{-mfmaf}
|
|
when targeting a CPU that supports such instructions, such as Niagara-3 and
|
|
later.
|
|
|
|
@item -mpopc
|
|
@itemx -mno-popc
|
|
@opindex mpopc
|
|
@opindex mno-popc
|
|
With @option{-mpopc}, GCC generates code that takes advantage of the UltraSPARC
|
|
Population Count instruction. The default is @option{-mpopc}
|
|
when targeting a CPU that supports such an instruction, such as Niagara-2 and
|
|
later.
|
|
|
|
@item -msubxc
|
|
@itemx -mno-subxc
|
|
@opindex msubxc
|
|
@opindex mno-subxc
|
|
With @option{-msubxc}, GCC generates code that takes advantage of the UltraSPARC
|
|
Subtract-Extended-with-Carry instruction. The default is @option{-msubxc}
|
|
when targeting a CPU that supports such an instruction, such as Niagara-7 and
|
|
later.
|
|
|
|
@item -mfix-at697f
|
|
@opindex mfix-at697f
|
|
Enable the documented workaround for the single erratum of the Atmel AT697F
|
|
processor (which corresponds to erratum #13 of the AT697E processor).
|
|
|
|
@item -mfix-ut699
|
|
@opindex mfix-ut699
|
|
Enable the documented workarounds for the floating-point errata and the data
|
|
cache nullify errata of the UT699 processor.
|
|
@end table
|
|
|
|
These @samp{-m} options are supported in addition to the above
|
|
on SPARC-V9 processors in 64-bit environments:
|
|
|
|
@table @gcctabopt
|
|
@item -m32
|
|
@itemx -m64
|
|
@opindex m32
|
|
@opindex m64
|
|
Generate code for a 32-bit or 64-bit environment.
|
|
The 32-bit environment sets int, long and pointer to 32 bits.
|
|
The 64-bit environment sets int to 32 bits and long and pointer
|
|
to 64 bits.
|
|
|
|
@item -mcmodel=@var{which}
|
|
@opindex mcmodel
|
|
Set the code model to one of
|
|
|
|
@table @samp
|
|
@item medlow
|
|
The Medium/Low code model: 64-bit addresses, programs
|
|
must be linked in the low 32 bits of memory. Programs can be statically
|
|
or dynamically linked.
|
|
|
|
@item medmid
|
|
The Medium/Middle code model: 64-bit addresses, programs
|
|
must be linked in the low 44 bits of memory, the text and data segments must
|
|
be less than 2GB in size and the data segment must be located within 2GB of
|
|
the text segment.
|
|
|
|
@item medany
|
|
The Medium/Anywhere code model: 64-bit addresses, programs
|
|
may be linked anywhere in memory, the text and data segments must be less
|
|
than 2GB in size and the data segment must be located within 2GB of the
|
|
text segment.
|
|
|
|
@item embmedany
|
|
The Medium/Anywhere code model for embedded systems:
|
|
64-bit addresses, the text and data segments must be less than 2GB in
|
|
size, both starting anywhere in memory (determined at link time). The
|
|
global register %g4 points to the base of the data segment. Programs
|
|
are statically linked and PIC is not supported.
|
|
@end table
|
|
|
|
@item -mmemory-model=@var{mem-model}
|
|
@opindex mmemory-model
|
|
Set the memory model in force on the processor to one of
|
|
|
|
@table @samp
|
|
@item default
|
|
The default memory model for the processor and operating system.
|
|
|
|
@item rmo
|
|
Relaxed Memory Order
|
|
|
|
@item pso
|
|
Partial Store Order
|
|
|
|
@item tso
|
|
Total Store Order
|
|
|
|
@item sc
|
|
Sequential Consistency
|
|
@end table
|
|
|
|
These memory models are formally defined in Appendix D of the SPARC-V9
|
|
architecture manual, as set in the processor's @code{PSTATE.MM} field.
|
|
|
|
@item -mstack-bias
|
|
@itemx -mno-stack-bias
|
|
@opindex mstack-bias
|
|
@opindex mno-stack-bias
|
|
With @option{-mstack-bias}, GCC assumes that the stack pointer, and
|
|
frame pointer if present, are offset by @minus{}2047 which must be added back
|
|
when making stack frame references. This is the default in 64-bit mode.
|
|
Otherwise, assume no such offset is present.
|
|
@end table
|
|
|
|
@node SPU Options
|
|
@subsection SPU Options
|
|
@cindex SPU options
|
|
|
|
These @samp{-m} options are supported on the SPU:
|
|
|
|
@table @gcctabopt
|
|
@item -mwarn-reloc
|
|
@itemx -merror-reloc
|
|
@opindex mwarn-reloc
|
|
@opindex merror-reloc
|
|
|
|
The loader for SPU does not handle dynamic relocations. By default, GCC
|
|
gives an error when it generates code that requires a dynamic
|
|
relocation. @option{-mno-error-reloc} disables the error,
|
|
@option{-mwarn-reloc} generates a warning instead.
|
|
|
|
@item -msafe-dma
|
|
@itemx -munsafe-dma
|
|
@opindex msafe-dma
|
|
@opindex munsafe-dma
|
|
|
|
Instructions that initiate or test completion of DMA must not be
|
|
reordered with respect to loads and stores of the memory that is being
|
|
accessed.
|
|
With @option{-munsafe-dma} you must use the @code{volatile} keyword to protect
|
|
memory accesses, but that can lead to inefficient code in places where the
|
|
memory is known to not change. Rather than mark the memory as volatile,
|
|
you can use @option{-msafe-dma} to tell the compiler to treat
|
|
the DMA instructions as potentially affecting all memory.
|
|
|
|
@item -mbranch-hints
|
|
@opindex mbranch-hints
|
|
|
|
By default, GCC generates a branch hint instruction to avoid
|
|
pipeline stalls for always-taken or probably-taken branches. A hint
|
|
is not generated closer than 8 instructions away from its branch.
|
|
There is little reason to disable them, except for debugging purposes,
|
|
or to make an object a little bit smaller.
|
|
|
|
@item -msmall-mem
|
|
@itemx -mlarge-mem
|
|
@opindex msmall-mem
|
|
@opindex mlarge-mem
|
|
|
|
By default, GCC generates code assuming that addresses are never larger
|
|
than 18 bits. With @option{-mlarge-mem} code is generated that assumes
|
|
a full 32-bit address.
|
|
|
|
@item -mstdmain
|
|
@opindex mstdmain
|
|
|
|
By default, GCC links against startup code that assumes the SPU-style
|
|
main function interface (which has an unconventional parameter list).
|
|
With @option{-mstdmain}, GCC links your program against startup
|
|
code that assumes a C99-style interface to @code{main}, including a
|
|
local copy of @code{argv} strings.
|
|
|
|
@item -mfixed-range=@var{register-range}
|
|
@opindex mfixed-range
|
|
Generate code treating the given register range as fixed registers.
|
|
A fixed register is one that the register allocator cannot use. This is
|
|
useful when compiling kernel code. A register range is specified as
|
|
two registers separated by a dash. Multiple register ranges can be
|
|
specified separated by a comma.
|
|
|
|
@item -mea32
|
|
@itemx -mea64
|
|
@opindex mea32
|
|
@opindex mea64
|
|
Compile code assuming that pointers to the PPU address space accessed
|
|
via the @code{__ea} named address space qualifier are either 32 or 64
|
|
bits wide. The default is 32 bits. As this is an ABI-changing option,
|
|
all object code in an executable must be compiled with the same setting.
|
|
|
|
@item -maddress-space-conversion
|
|
@itemx -mno-address-space-conversion
|
|
@opindex maddress-space-conversion
|
|
@opindex mno-address-space-conversion
|
|
Allow/disallow treating the @code{__ea} address space as superset
|
|
of the generic address space. This enables explicit type casts
|
|
between @code{__ea} and generic pointer as well as implicit
|
|
conversions of generic pointers to @code{__ea} pointers. The
|
|
default is to allow address space pointer conversions.
|
|
|
|
@item -mcache-size=@var{cache-size}
|
|
@opindex mcache-size
|
|
This option controls the version of libgcc that the compiler links to an
|
|
executable and selects a software-managed cache for accessing variables
|
|
in the @code{__ea} address space with a particular cache size. Possible
|
|
options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64}
|
|
and @samp{128}. The default cache size is 64KB.
|
|
|
|
@item -matomic-updates
|
|
@itemx -mno-atomic-updates
|
|
@opindex matomic-updates
|
|
@opindex mno-atomic-updates
|
|
This option controls the version of libgcc that the compiler links to an
|
|
executable and selects whether atomic updates to the software-managed
|
|
cache of PPU-side variables are used. If you use atomic updates, changes
|
|
to a PPU variable from SPU code using the @code{__ea} named address space
|
|
qualifier do not interfere with changes to other PPU variables residing
|
|
in the same cache line from PPU code. If you do not use atomic updates,
|
|
such interference may occur; however, writing back cache lines is
|
|
more efficient. The default behavior is to use atomic updates.
|
|
|
|
@item -mdual-nops
|
|
@itemx -mdual-nops=@var{n}
|
|
@opindex mdual-nops
|
|
By default, GCC inserts NOPs to increase dual issue when it expects
|
|
it to increase performance. @var{n} can be a value from 0 to 10. A
|
|
smaller @var{n} inserts fewer NOPs. 10 is the default, 0 is the
|
|
same as @option{-mno-dual-nops}. Disabled with @option{-Os}.
|
|
|
|
@item -mhint-max-nops=@var{n}
|
|
@opindex mhint-max-nops
|
|
Maximum number of NOPs to insert for a branch hint. A branch hint must
|
|
be at least 8 instructions away from the branch it is affecting. GCC
|
|
inserts up to @var{n} NOPs to enforce this, otherwise it does not
|
|
generate the branch hint.
|
|
|
|
@item -mhint-max-distance=@var{n}
|
|
@opindex mhint-max-distance
|
|
The encoding of the branch hint instruction limits the hint to be within
|
|
256 instructions of the branch it is affecting. By default, GCC makes
|
|
sure it is within 125.
|
|
|
|
@item -msafe-hints
|
|
@opindex msafe-hints
|
|
Work around a hardware bug that causes the SPU to stall indefinitely.
|
|
By default, GCC inserts the @code{hbrp} instruction to make sure
|
|
this stall won't happen.
|
|
|
|
@end table
|
|
|
|
@node System V Options
|
|
@subsection Options for System V
|
|
|
|
These additional options are available on System V Release 4 for
|
|
compatibility with other compilers on those systems:
|
|
|
|
@table @gcctabopt
|
|
@item -G
|
|
@opindex G
|
|
Create a shared object.
|
|
It is recommended that @option{-symbolic} or @option{-shared} be used instead.
|
|
|
|
@item -Qy
|
|
@opindex Qy
|
|
Identify the versions of each tool used by the compiler, in a
|
|
@code{.ident} assembler directive in the output.
|
|
|
|
@item -Qn
|
|
@opindex Qn
|
|
Refrain from adding @code{.ident} directives to the output file (this is
|
|
the default).
|
|
|
|
@item -YP,@var{dirs}
|
|
@opindex YP
|
|
Search the directories @var{dirs}, and no others, for libraries
|
|
specified with @option{-l}.
|
|
|
|
@item -Ym,@var{dir}
|
|
@opindex Ym
|
|
Look in the directory @var{dir} to find the M4 preprocessor.
|
|
The assembler uses this option.
|
|
@c This is supposed to go with a -Yd for predefined M4 macro files, but
|
|
@c the generic assembler that comes with Solaris takes just -Ym.
|
|
@end table
|
|
|
|
@node TILE-Gx Options
|
|
@subsection TILE-Gx Options
|
|
@cindex TILE-Gx options
|
|
|
|
These @samp{-m} options are supported on the TILE-Gx:
|
|
|
|
@table @gcctabopt
|
|
@item -mcmodel=small
|
|
@opindex mcmodel=small
|
|
Generate code for the small model. The distance for direct calls is
|
|
limited to 500M in either direction. PC-relative addresses are 32
|
|
bits. Absolute addresses support the full address range.
|
|
|
|
@item -mcmodel=large
|
|
@opindex mcmodel=large
|
|
Generate code for the large model. There is no limitation on call
|
|
distance, pc-relative addresses, or absolute addresses.
|
|
|
|
@item -mcpu=@var{name}
|
|
@opindex mcpu
|
|
Selects the type of CPU to be targeted. Currently the only supported
|
|
type is @samp{tilegx}.
|
|
|
|
@item -m32
|
|
@itemx -m64
|
|
@opindex m32
|
|
@opindex m64
|
|
Generate code for a 32-bit or 64-bit environment. The 32-bit
|
|
environment sets int, long, and pointer to 32 bits. The 64-bit
|
|
environment sets int to 32 bits and long and pointer to 64 bits.
|
|
|
|
@item -mbig-endian
|
|
@itemx -mlittle-endian
|
|
@opindex mbig-endian
|
|
@opindex mlittle-endian
|
|
Generate code in big/little endian mode, respectively.
|
|
@end table
|
|
|
|
@node TILEPro Options
|
|
@subsection TILEPro Options
|
|
@cindex TILEPro options
|
|
|
|
These @samp{-m} options are supported on the TILEPro:
|
|
|
|
@table @gcctabopt
|
|
@item -mcpu=@var{name}
|
|
@opindex mcpu
|
|
Selects the type of CPU to be targeted. Currently the only supported
|
|
type is @samp{tilepro}.
|
|
|
|
@item -m32
|
|
@opindex m32
|
|
Generate code for a 32-bit environment, which sets int, long, and
|
|
pointer to 32 bits. This is the only supported behavior so the flag
|
|
is essentially ignored.
|
|
@end table
|
|
|
|
@node V850 Options
|
|
@subsection V850 Options
|
|
@cindex V850 Options
|
|
|
|
These @samp{-m} options are defined for V850 implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -mlong-calls
|
|
@itemx -mno-long-calls
|
|
@opindex mlong-calls
|
|
@opindex mno-long-calls
|
|
Treat all calls as being far away (near). If calls are assumed to be
|
|
far away, the compiler always loads the function's address into a
|
|
register, and calls indirect through the pointer.
|
|
|
|
@item -mno-ep
|
|
@itemx -mep
|
|
@opindex mno-ep
|
|
@opindex mep
|
|
Do not optimize (do optimize) basic blocks that use the same index
|
|
pointer 4 or more times to copy pointer into the @code{ep} register, and
|
|
use the shorter @code{sld} and @code{sst} instructions. The @option{-mep}
|
|
option is on by default if you optimize.
|
|
|
|
@item -mno-prolog-function
|
|
@itemx -mprolog-function
|
|
@opindex mno-prolog-function
|
|
@opindex mprolog-function
|
|
Do not use (do use) external functions to save and restore registers
|
|
at the prologue and epilogue of a function. The external functions
|
|
are slower, but use less code space if more than one function saves
|
|
the same number of registers. The @option{-mprolog-function} option
|
|
is on by default if you optimize.
|
|
|
|
@item -mspace
|
|
@opindex mspace
|
|
Try to make the code as small as possible. At present, this just turns
|
|
on the @option{-mep} and @option{-mprolog-function} options.
|
|
|
|
@item -mtda=@var{n}
|
|
@opindex mtda
|
|
Put static or global variables whose size is @var{n} bytes or less into
|
|
the tiny data area that register @code{ep} points to. The tiny data
|
|
area can hold up to 256 bytes in total (128 bytes for byte references).
|
|
|
|
@item -msda=@var{n}
|
|
@opindex msda
|
|
Put static or global variables whose size is @var{n} bytes or less into
|
|
the small data area that register @code{gp} points to. The small data
|
|
area can hold up to 64 kilobytes.
|
|
|
|
@item -mzda=@var{n}
|
|
@opindex mzda
|
|
Put static or global variables whose size is @var{n} bytes or less into
|
|
the first 32 kilobytes of memory.
|
|
|
|
@item -mv850
|
|
@opindex mv850
|
|
Specify that the target processor is the V850.
|
|
|
|
@item -mv850e3v5
|
|
@opindex mv850e3v5
|
|
Specify that the target processor is the V850E3V5. The preprocessor
|
|
constant @code{__v850e3v5__} is defined if this option is used.
|
|
|
|
@item -mv850e2v4
|
|
@opindex mv850e2v4
|
|
Specify that the target processor is the V850E3V5. This is an alias for
|
|
the @option{-mv850e3v5} option.
|
|
|
|
@item -mv850e2v3
|
|
@opindex mv850e2v3
|
|
Specify that the target processor is the V850E2V3. The preprocessor
|
|
constant @code{__v850e2v3__} is defined if this option is used.
|
|
|
|
@item -mv850e2
|
|
@opindex mv850e2
|
|
Specify that the target processor is the V850E2. The preprocessor
|
|
constant @code{__v850e2__} is defined if this option is used.
|
|
|
|
@item -mv850e1
|
|
@opindex mv850e1
|
|
Specify that the target processor is the V850E1. The preprocessor
|
|
constants @code{__v850e1__} and @code{__v850e__} are defined if
|
|
this option is used.
|
|
|
|
@item -mv850es
|
|
@opindex mv850es
|
|
Specify that the target processor is the V850ES. This is an alias for
|
|
the @option{-mv850e1} option.
|
|
|
|
@item -mv850e
|
|
@opindex mv850e
|
|
Specify that the target processor is the V850E@. The preprocessor
|
|
constant @code{__v850e__} is defined if this option is used.
|
|
|
|
If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1}
|
|
nor @option{-mv850e2} nor @option{-mv850e2v3} nor @option{-mv850e3v5}
|
|
are defined then a default target processor is chosen and the
|
|
relevant @samp{__v850*__} preprocessor constant is defined.
|
|
|
|
The preprocessor constants @code{__v850} and @code{__v851__} are always
|
|
defined, regardless of which processor variant is the target.
|
|
|
|
@item -mdisable-callt
|
|
@itemx -mno-disable-callt
|
|
@opindex mdisable-callt
|
|
@opindex mno-disable-callt
|
|
This option suppresses generation of the @code{CALLT} instruction for the
|
|
v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850
|
|
architecture.
|
|
|
|
This option is enabled by default when the RH850 ABI is
|
|
in use (see @option{-mrh850-abi}), and disabled by default when the
|
|
GCC ABI is in use. If @code{CALLT} instructions are being generated
|
|
then the C preprocessor symbol @code{__V850_CALLT__} is defined.
|
|
|
|
@item -mrelax
|
|
@itemx -mno-relax
|
|
@opindex mrelax
|
|
@opindex mno-relax
|
|
Pass on (or do not pass on) the @option{-mrelax} command-line option
|
|
to the assembler.
|
|
|
|
@item -mlong-jumps
|
|
@itemx -mno-long-jumps
|
|
@opindex mlong-jumps
|
|
@opindex mno-long-jumps
|
|
Disable (or re-enable) the generation of PC-relative jump instructions.
|
|
|
|
@item -msoft-float
|
|
@itemx -mhard-float
|
|
@opindex msoft-float
|
|
@opindex mhard-float
|
|
Disable (or re-enable) the generation of hardware floating point
|
|
instructions. This option is only significant when the target
|
|
architecture is @samp{V850E2V3} or higher. If hardware floating point
|
|
instructions are being generated then the C preprocessor symbol
|
|
@code{__FPU_OK__} is defined, otherwise the symbol
|
|
@code{__NO_FPU__} is defined.
|
|
|
|
@item -mloop
|
|
@opindex mloop
|
|
Enables the use of the e3v5 LOOP instruction. The use of this
|
|
instruction is not enabled by default when the e3v5 architecture is
|
|
selected because its use is still experimental.
|
|
|
|
@item -mrh850-abi
|
|
@itemx -mghs
|
|
@opindex mrh850-abi
|
|
@opindex mghs
|
|
Enables support for the RH850 version of the V850 ABI. This is the
|
|
default. With this version of the ABI the following rules apply:
|
|
|
|
@itemize
|
|
@item
|
|
Integer sized structures and unions are returned via a memory pointer
|
|
rather than a register.
|
|
|
|
@item
|
|
Large structures and unions (more than 8 bytes in size) are passed by
|
|
value.
|
|
|
|
@item
|
|
Functions are aligned to 16-bit boundaries.
|
|
|
|
@item
|
|
The @option{-m8byte-align} command-line option is supported.
|
|
|
|
@item
|
|
The @option{-mdisable-callt} command-line option is enabled by
|
|
default. The @option{-mno-disable-callt} command-line option is not
|
|
supported.
|
|
@end itemize
|
|
|
|
When this version of the ABI is enabled the C preprocessor symbol
|
|
@code{__V850_RH850_ABI__} is defined.
|
|
|
|
@item -mgcc-abi
|
|
@opindex mgcc-abi
|
|
Enables support for the old GCC version of the V850 ABI. With this
|
|
version of the ABI the following rules apply:
|
|
|
|
@itemize
|
|
@item
|
|
Integer sized structures and unions are returned in register @code{r10}.
|
|
|
|
@item
|
|
Large structures and unions (more than 8 bytes in size) are passed by
|
|
reference.
|
|
|
|
@item
|
|
Functions are aligned to 32-bit boundaries, unless optimizing for
|
|
size.
|
|
|
|
@item
|
|
The @option{-m8byte-align} command-line option is not supported.
|
|
|
|
@item
|
|
The @option{-mdisable-callt} command-line option is supported but not
|
|
enabled by default.
|
|
@end itemize
|
|
|
|
When this version of the ABI is enabled the C preprocessor symbol
|
|
@code{__V850_GCC_ABI__} is defined.
|
|
|
|
@item -m8byte-align
|
|
@itemx -mno-8byte-align
|
|
@opindex m8byte-align
|
|
@opindex mno-8byte-align
|
|
Enables support for @code{double} and @code{long long} types to be
|
|
aligned on 8-byte boundaries. The default is to restrict the
|
|
alignment of all objects to at most 4-bytes. When
|
|
@option{-m8byte-align} is in effect the C preprocessor symbol
|
|
@code{__V850_8BYTE_ALIGN__} is defined.
|
|
|
|
@item -mbig-switch
|
|
@opindex mbig-switch
|
|
Generate code suitable for big switch tables. Use this option only if
|
|
the assembler/linker complain about out of range branches within a switch
|
|
table.
|
|
|
|
@item -mapp-regs
|
|
@opindex mapp-regs
|
|
This option causes r2 and r5 to be used in the code generated by
|
|
the compiler. This setting is the default.
|
|
|
|
@item -mno-app-regs
|
|
@opindex mno-app-regs
|
|
This option causes r2 and r5 to be treated as fixed registers.
|
|
|
|
@end table
|
|
|
|
@node VAX Options
|
|
@subsection VAX Options
|
|
@cindex VAX options
|
|
|
|
These @samp{-m} options are defined for the VAX:
|
|
|
|
@table @gcctabopt
|
|
@item -munix
|
|
@opindex munix
|
|
Do not output certain jump instructions (@code{aobleq} and so on)
|
|
that the Unix assembler for the VAX cannot handle across long
|
|
ranges.
|
|
|
|
@item -mgnu
|
|
@opindex mgnu
|
|
Do output those jump instructions, on the assumption that the
|
|
GNU assembler is being used.
|
|
|
|
@item -mg
|
|
@opindex mg
|
|
Output code for G-format floating-point numbers instead of D-format.
|
|
@end table
|
|
|
|
@node Visium Options
|
|
@subsection Visium Options
|
|
@cindex Visium options
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -mdebug
|
|
@opindex mdebug
|
|
A program which performs file I/O and is destined to run on an MCM target
|
|
should be linked with this option. It causes the libraries libc.a and
|
|
libdebug.a to be linked. The program should be run on the target under
|
|
the control of the GDB remote debugging stub.
|
|
|
|
@item -msim
|
|
@opindex msim
|
|
A program which performs file I/O and is destined to run on the simulator
|
|
should be linked with option. This causes libraries libc.a and libsim.a to
|
|
be linked.
|
|
|
|
@item -mfpu
|
|
@itemx -mhard-float
|
|
@opindex mfpu
|
|
@opindex mhard-float
|
|
Generate code containing floating-point instructions. This is the
|
|
default.
|
|
|
|
@item -mno-fpu
|
|
@itemx -msoft-float
|
|
@opindex mno-fpu
|
|
@opindex msoft-float
|
|
Generate code containing library calls for floating-point.
|
|
|
|
@option{-msoft-float} changes the calling convention in the output file;
|
|
therefore, it is only useful if you compile @emph{all} of a program with
|
|
this option. In particular, you need to compile @file{libgcc.a}, the
|
|
library that comes with GCC, with @option{-msoft-float} in order for
|
|
this to work.
|
|
|
|
@item -mcpu=@var{cpu_type}
|
|
@opindex mcpu
|
|
Set the instruction set, register set, and instruction scheduling parameters
|
|
for machine type @var{cpu_type}. Supported values for @var{cpu_type} are
|
|
@samp{mcm}, @samp{gr5} and @samp{gr6}.
|
|
|
|
@samp{mcm} is a synonym of @samp{gr5} present for backward compatibility.
|
|
|
|
By default (unless configured otherwise), GCC generates code for the GR5
|
|
variant of the Visium architecture.
|
|
|
|
With @option{-mcpu=gr6}, GCC generates code for the GR6 variant of the Visium
|
|
architecture. The only difference from GR5 code is that the compiler will
|
|
generate block move instructions.
|
|
|
|
@item -mtune=@var{cpu_type}
|
|
@opindex mtune
|
|
Set the instruction scheduling parameters for machine type @var{cpu_type},
|
|
but do not set the instruction set or register set that the option
|
|
@option{-mcpu=@var{cpu_type}} would.
|
|
|
|
@item -msv-mode
|
|
@opindex msv-mode
|
|
Generate code for the supervisor mode, where there are no restrictions on
|
|
the access to general registers. This is the default.
|
|
|
|
@item -muser-mode
|
|
@opindex muser-mode
|
|
Generate code for the user mode, where the access to some general registers
|
|
is forbidden: on the GR5, registers r24 to r31 cannot be accessed in this
|
|
mode; on the GR6, only registers r29 to r31 are affected.
|
|
@end table
|
|
|
|
@node VMS Options
|
|
@subsection VMS Options
|
|
|
|
These @samp{-m} options are defined for the VMS implementations:
|
|
|
|
@table @gcctabopt
|
|
@item -mvms-return-codes
|
|
@opindex mvms-return-codes
|
|
Return VMS condition codes from @code{main}. The default is to return POSIX-style
|
|
condition (e.g.@ error) codes.
|
|
|
|
@item -mdebug-main=@var{prefix}
|
|
@opindex mdebug-main=@var{prefix}
|
|
Flag the first routine whose name starts with @var{prefix} as the main
|
|
routine for the debugger.
|
|
|
|
@item -mmalloc64
|
|
@opindex mmalloc64
|
|
Default to 64-bit memory allocation routines.
|
|
|
|
@item -mpointer-size=@var{size}
|
|
@opindex mpointer-size=@var{size}
|
|
Set the default size of pointers. Possible options for @var{size} are
|
|
@samp{32} or @samp{short} for 32 bit pointers, @samp{64} or @samp{long}
|
|
for 64 bit pointers, and @samp{no} for supporting only 32 bit pointers.
|
|
The later option disables @code{pragma pointer_size}.
|
|
@end table
|
|
|
|
@node VxWorks Options
|
|
@subsection VxWorks Options
|
|
@cindex VxWorks Options
|
|
|
|
The options in this section are defined for all VxWorks targets.
|
|
Options specific to the target hardware are listed with the other
|
|
options for that target.
|
|
|
|
@table @gcctabopt
|
|
@item -mrtp
|
|
@opindex mrtp
|
|
GCC can generate code for both VxWorks kernels and real time processes
|
|
(RTPs). This option switches from the former to the latter. It also
|
|
defines the preprocessor macro @code{__RTP__}.
|
|
|
|
@item -non-static
|
|
@opindex non-static
|
|
Link an RTP executable against shared libraries rather than static
|
|
libraries. The options @option{-static} and @option{-shared} can
|
|
also be used for RTPs (@pxref{Link Options}); @option{-static}
|
|
is the default.
|
|
|
|
@item -Bstatic
|
|
@itemx -Bdynamic
|
|
@opindex Bstatic
|
|
@opindex Bdynamic
|
|
These options are passed down to the linker. They are defined for
|
|
compatibility with Diab.
|
|
|
|
@item -Xbind-lazy
|
|
@opindex Xbind-lazy
|
|
Enable lazy binding of function calls. This option is equivalent to
|
|
@option{-Wl,-z,now} and is defined for compatibility with Diab.
|
|
|
|
@item -Xbind-now
|
|
@opindex Xbind-now
|
|
Disable lazy binding of function calls. This option is the default and
|
|
is defined for compatibility with Diab.
|
|
@end table
|
|
|
|
@node x86 Options
|
|
@subsection x86 Options
|
|
@cindex x86 Options
|
|
|
|
These @samp{-m} options are defined for the x86 family of computers.
|
|
|
|
@table @gcctabopt
|
|
|
|
@item -march=@var{cpu-type}
|
|
@opindex march
|
|
Generate instructions for the machine type @var{cpu-type}. In contrast to
|
|
@option{-mtune=@var{cpu-type}}, which merely tunes the generated code
|
|
for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC
|
|
to generate code that may not run at all on processors other than the one
|
|
indicated. Specifying @option{-march=@var{cpu-type}} implies
|
|
@option{-mtune=@var{cpu-type}}.
|
|
|
|
The choices for @var{cpu-type} are:
|
|
|
|
@table @samp
|
|
@item native
|
|
This selects the CPU to generate code for at compilation time by determining
|
|
the processor type of the compiling machine. Using @option{-march=native}
|
|
enables all instruction subsets supported by the local machine (hence
|
|
the result might not run on different machines). Using @option{-mtune=native}
|
|
produces code optimized for the local machine under the constraints
|
|
of the selected instruction set.
|
|
|
|
@item i386
|
|
Original Intel i386 CPU@.
|
|
|
|
@item i486
|
|
Intel i486 CPU@. (No scheduling is implemented for this chip.)
|
|
|
|
@item i586
|
|
@itemx pentium
|
|
Intel Pentium CPU with no MMX support.
|
|
|
|
@item lakemont
|
|
Intel Lakemont MCU, based on Intel Pentium CPU.
|
|
|
|
@item pentium-mmx
|
|
Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support.
|
|
|
|
@item pentiumpro
|
|
Intel Pentium Pro CPU@.
|
|
|
|
@item i686
|
|
When used with @option{-march}, the Pentium Pro
|
|
instruction set is used, so the code runs on all i686 family chips.
|
|
When used with @option{-mtune}, it has the same meaning as @samp{generic}.
|
|
|
|
@item pentium2
|
|
Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set
|
|
support.
|
|
|
|
@item pentium3
|
|
@itemx pentium3m
|
|
Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction
|
|
set support.
|
|
|
|
@item pentium-m
|
|
Intel Pentium M; low-power version of Intel Pentium III CPU
|
|
with MMX, SSE and SSE2 instruction set support. Used by Centrino notebooks.
|
|
|
|
@item pentium4
|
|
@itemx pentium4m
|
|
Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support.
|
|
|
|
@item prescott
|
|
Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction
|
|
set support.
|
|
|
|
@item nocona
|
|
Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE,
|
|
SSE2 and SSE3 instruction set support.
|
|
|
|
@item core2
|
|
Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
|
|
instruction set support.
|
|
|
|
@item nehalem
|
|
Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
|
|
SSE4.1, SSE4.2 and POPCNT instruction set support.
|
|
|
|
@item westmere
|
|
Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
|
|
SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction set support.
|
|
|
|
@item sandybridge
|
|
Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
|
|
SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL instruction set support.
|
|
|
|
@item ivybridge
|
|
Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3,
|
|
SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C
|
|
instruction set support.
|
|
|
|
@item haswell
|
|
Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
|
|
SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
|
|
BMI, BMI2 and F16C instruction set support.
|
|
|
|
@item broadwell
|
|
Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
|
|
SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
|
|
BMI, BMI2, F16C, RDSEED, ADCX and PREFETCHW instruction set support.
|
|
|
|
@item skylake
|
|
Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
|
|
SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
|
|
BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC and
|
|
XSAVES instruction set support.
|
|
|
|
@item bonnell
|
|
Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3
|
|
instruction set support.
|
|
|
|
@item silvermont
|
|
Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3,
|
|
SSE4.1, SSE4.2, POPCNT, AES, PCLMUL and RDRND instruction set support.
|
|
|
|
@item knl
|
|
Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3,
|
|
SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
|
|
BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, AVX512F, AVX512PF, AVX512ER and
|
|
AVX512CD instruction set support.
|
|
|
|
@item skylake-avx512
|
|
Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3,
|
|
SSSE3, SSE4.1, SSE4.2, POPCNT, PKU, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA,
|
|
BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, CLFLUSHOPT, XSAVEC, XSAVES, AVX512F,
|
|
AVX512VL, AVX512BW, AVX512DQ and AVX512CD instruction set support.
|
|
|
|
@item k6
|
|
AMD K6 CPU with MMX instruction set support.
|
|
|
|
@item k6-2
|
|
@itemx k6-3
|
|
Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support.
|
|
|
|
@item athlon
|
|
@itemx athlon-tbird
|
|
AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions
|
|
support.
|
|
|
|
@item athlon-4
|
|
@itemx athlon-xp
|
|
@itemx athlon-mp
|
|
Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE
|
|
instruction set support.
|
|
|
|
@item k8
|
|
@itemx opteron
|
|
@itemx athlon64
|
|
@itemx athlon-fx
|
|
Processors based on the AMD K8 core with x86-64 instruction set support,
|
|
including the AMD Opteron, Athlon 64, and Athlon 64 FX processors.
|
|
(This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit
|
|
instruction set extensions.)
|
|
|
|
@item k8-sse3
|
|
@itemx opteron-sse3
|
|
@itemx athlon64-sse3
|
|
Improved versions of AMD K8 cores with SSE3 instruction set support.
|
|
|
|
@item amdfam10
|
|
@itemx barcelona
|
|
CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This
|
|
supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit
|
|
instruction set extensions.)
|
|
|
|
@item bdver1
|
|
CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This
|
|
supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A,
|
|
SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)
|
|
@item bdver2
|
|
AMD Family 15h core based CPUs with x86-64 instruction set support. (This
|
|
supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX,
|
|
SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set
|
|
extensions.)
|
|
@item bdver3
|
|
AMD Family 15h core based CPUs with x86-64 instruction set support. (This
|
|
supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES,
|
|
PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and
|
|
64-bit instruction set extensions.
|
|
@item bdver4
|
|
AMD Family 15h core based CPUs with x86-64 instruction set support. (This
|
|
supersets BMI, BMI2, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP,
|
|
AES, PCL_MUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1,
|
|
SSE4.2, ABM and 64-bit instruction set extensions.
|
|
|
|
@item znver1
|
|
AMD Family 17h core based CPUs with x86-64 instruction set support. (This
|
|
supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX,
|
|
SHA, CLZERO, AES, PCL_MUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3,
|
|
SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit
|
|
instruction set extensions.
|
|
|
|
@item btver1
|
|
CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This
|
|
supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit
|
|
instruction set extensions.)
|
|
|
|
@item btver2
|
|
CPUs based on AMD Family 16h cores with x86-64 instruction set support. This
|
|
includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES, SSE4.2, SSE4.1, CX16, ABM,
|
|
SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions.
|
|
|
|
@item winchip-c6
|
|
IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction
|
|
set support.
|
|
|
|
@item winchip2
|
|
IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@:
|
|
instruction set support.
|
|
|
|
@item c3
|
|
VIA C3 CPU with MMX and 3DNow!@: instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item c3-2
|
|
VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item c7
|
|
VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item samuel-2
|
|
VIA Eden Samuel 2 CPU with MMX and 3DNow!@: instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item nehemiah
|
|
VIA Eden Nehemiah CPU with MMX and SSE instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item esther
|
|
VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item eden-x2
|
|
VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3 instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item eden-x4
|
|
VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2,
|
|
AVX and AVX2 instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item nano
|
|
Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
|
|
instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item nano-1000
|
|
VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
|
|
instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item nano-2000
|
|
VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3
|
|
instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item nano-3000
|
|
VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1
|
|
instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item nano-x2
|
|
VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1
|
|
instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item nano-x4
|
|
VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1
|
|
instruction set support.
|
|
(No scheduling is implemented for this chip.)
|
|
|
|
@item geode
|
|
AMD Geode embedded processor with MMX and 3DNow!@: instruction set support.
|
|
@end table
|
|
|
|
@item -mtune=@var{cpu-type}
|
|
@opindex mtune
|
|
Tune to @var{cpu-type} everything applicable about the generated code, except
|
|
for the ABI and the set of available instructions.
|
|
While picking a specific @var{cpu-type} schedules things appropriately
|
|
for that particular chip, the compiler does not generate any code that
|
|
cannot run on the default machine type unless you use a
|
|
@option{-march=@var{cpu-type}} option.
|
|
For example, if GCC is configured for i686-pc-linux-gnu
|
|
then @option{-mtune=pentium4} generates code that is tuned for Pentium 4
|
|
but still runs on i686 machines.
|
|
|
|
The choices for @var{cpu-type} are the same as for @option{-march}.
|
|
In addition, @option{-mtune} supports 2 extra choices for @var{cpu-type}:
|
|
|
|
@table @samp
|
|
@item generic
|
|
Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors.
|
|
If you know the CPU on which your code will run, then you should use
|
|
the corresponding @option{-mtune} or @option{-march} option instead of
|
|
@option{-mtune=generic}. But, if you do not know exactly what CPU users
|
|
of your application will have, then you should use this option.
|
|
|
|
As new processors are deployed in the marketplace, the behavior of this
|
|
option will change. Therefore, if you upgrade to a newer version of
|
|
GCC, code generation controlled by this option will change to reflect
|
|
the processors
|
|
that are most common at the time that version of GCC is released.
|
|
|
|
There is no @option{-march=generic} option because @option{-march}
|
|
indicates the instruction set the compiler can use, and there is no
|
|
generic instruction set applicable to all processors. In contrast,
|
|
@option{-mtune} indicates the processor (or, in this case, collection of
|
|
processors) for which the code is optimized.
|
|
|
|
@item intel
|
|
Produce code optimized for the most current Intel processors, which are
|
|
Haswell and Silvermont for this version of GCC. If you know the CPU
|
|
on which your code will run, then you should use the corresponding
|
|
@option{-mtune} or @option{-march} option instead of @option{-mtune=intel}.
|
|
But, if you want your application performs better on both Haswell and
|
|
Silvermont, then you should use this option.
|
|
|
|
As new Intel processors are deployed in the marketplace, the behavior of
|
|
this option will change. Therefore, if you upgrade to a newer version of
|
|
GCC, code generation controlled by this option will change to reflect
|
|
the most current Intel processors at the time that version of GCC is
|
|
released.
|
|
|
|
There is no @option{-march=intel} option because @option{-march} indicates
|
|
the instruction set the compiler can use, and there is no common
|
|
instruction set applicable to all processors. In contrast,
|
|
@option{-mtune} indicates the processor (or, in this case, collection of
|
|
processors) for which the code is optimized.
|
|
@end table
|
|
|
|
@item -mcpu=@var{cpu-type}
|
|
@opindex mcpu
|
|
A deprecated synonym for @option{-mtune}.
|
|
|
|
@item -mfpmath=@var{unit}
|
|
@opindex mfpmath
|
|
Generate floating-point arithmetic for selected unit @var{unit}. The choices
|
|
for @var{unit} are:
|
|
|
|
@table @samp
|
|
@item 387
|
|
Use the standard 387 floating-point coprocessor present on the majority of chips and
|
|
emulated otherwise. Code compiled with this option runs almost everywhere.
|
|
The temporary results are computed in 80-bit precision instead of the precision
|
|
specified by the type, resulting in slightly different results compared to most
|
|
of other chips. See @option{-ffloat-store} for more detailed description.
|
|
|
|
This is the default choice for x86-32 targets.
|
|
|
|
@item sse
|
|
Use scalar floating-point instructions present in the SSE instruction set.
|
|
This instruction set is supported by Pentium III and newer chips,
|
|
and in the AMD line
|
|
by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE
|
|
instruction set supports only single-precision arithmetic, thus the double and
|
|
extended-precision arithmetic are still done using 387. A later version, present
|
|
only in Pentium 4 and AMD x86-64 chips, supports double-precision
|
|
arithmetic too.
|
|
|
|
For the x86-32 compiler, you must use @option{-march=@var{cpu-type}}, @option{-msse}
|
|
or @option{-msse2} switches to enable SSE extensions and make this option
|
|
effective. For the x86-64 compiler, these extensions are enabled by default.
|
|
|
|
The resulting code should be considerably faster in the majority of cases and avoid
|
|
the numerical instability problems of 387 code, but may break some existing
|
|
code that expects temporaries to be 80 bits.
|
|
|
|
This is the default choice for the x86-64 compiler.
|
|
|
|
@item sse,387
|
|
@itemx sse+387
|
|
@itemx both
|
|
Attempt to utilize both instruction sets at once. This effectively doubles the
|
|
amount of available registers, and on chips with separate execution units for
|
|
387 and SSE the execution resources too. Use this option with care, as it is
|
|
still experimental, because the GCC register allocator does not model separate
|
|
functional units well, resulting in unstable performance.
|
|
@end table
|
|
|
|
@item -masm=@var{dialect}
|
|
@opindex masm=@var{dialect}
|
|
Output assembly instructions using selected @var{dialect}. Also affects
|
|
which dialect is used for basic @code{asm} (@pxref{Basic Asm}) and
|
|
extended @code{asm} (@pxref{Extended Asm}). Supported choices (in dialect
|
|
order) are @samp{att} or @samp{intel}. The default is @samp{att}. Darwin does
|
|
not support @samp{intel}.
|
|
|
|
@item -mieee-fp
|
|
@itemx -mno-ieee-fp
|
|
@opindex mieee-fp
|
|
@opindex mno-ieee-fp
|
|
Control whether or not the compiler uses IEEE floating-point
|
|
comparisons. These correctly handle the case where the result of a
|
|
comparison is unordered.
|
|
|
|
@item -m80387
|
|
@item -mhard-float
|
|
@opindex 80387
|
|
@opindex mhard-float
|
|
Generate output containing 80387 instructions for floating point.
|
|
|
|
@item -mno-80387
|
|
@item -msoft-float
|
|
@opindex no-80387
|
|
@opindex msoft-float
|
|
Generate output containing library calls for floating point.
|
|
|
|
@strong{Warning:} the requisite libraries are not part of GCC@.
|
|
Normally the facilities of the machine's usual C compiler are used, but
|
|
this can't be done directly in cross-compilation. You must make your
|
|
own arrangements to provide suitable library functions for
|
|
cross-compilation.
|
|
|
|
On machines where a function returns floating-point results in the 80387
|
|
register stack, some floating-point opcodes may be emitted even if
|
|
@option{-msoft-float} is used.
|
|
|
|
@item -mno-fp-ret-in-387
|
|
@opindex mno-fp-ret-in-387
|
|
Do not use the FPU registers for return values of functions.
|
|
|
|
The usual calling convention has functions return values of types
|
|
@code{float} and @code{double} in an FPU register, even if there
|
|
is no FPU@. The idea is that the operating system should emulate
|
|
an FPU@.
|
|
|
|
The option @option{-mno-fp-ret-in-387} causes such values to be returned
|
|
in ordinary CPU registers instead.
|
|
|
|
@item -mno-fancy-math-387
|
|
@opindex mno-fancy-math-387
|
|
Some 387 emulators do not support the @code{sin}, @code{cos} and
|
|
@code{sqrt} instructions for the 387. Specify this option to avoid
|
|
generating those instructions. This option is the default on
|
|
OpenBSD and NetBSD@. This option is overridden when @option{-march}
|
|
indicates that the target CPU always has an FPU and so the
|
|
instruction does not need emulation. These
|
|
instructions are not generated unless you also use the
|
|
@option{-funsafe-math-optimizations} switch.
|
|
|
|
@item -malign-double
|
|
@itemx -mno-align-double
|
|
@opindex malign-double
|
|
@opindex mno-align-double
|
|
Control whether GCC aligns @code{double}, @code{long double}, and
|
|
@code{long long} variables on a two-word boundary or a one-word
|
|
boundary. Aligning @code{double} variables on a two-word boundary
|
|
produces code that runs somewhat faster on a Pentium at the
|
|
expense of more memory.
|
|
|
|
On x86-64, @option{-malign-double} is enabled by default.
|
|
|
|
@strong{Warning:} if you use the @option{-malign-double} switch,
|
|
structures containing the above types are aligned differently than
|
|
the published application binary interface specifications for the x86-32
|
|
and are not binary compatible with structures in code compiled
|
|
without that switch.
|
|
|
|
@item -m96bit-long-double
|
|
@itemx -m128bit-long-double
|
|
@opindex m96bit-long-double
|
|
@opindex m128bit-long-double
|
|
These switches control the size of @code{long double} type. The x86-32
|
|
application binary interface specifies the size to be 96 bits,
|
|
so @option{-m96bit-long-double} is the default in 32-bit mode.
|
|
|
|
Modern architectures (Pentium and newer) prefer @code{long double}
|
|
to be aligned to an 8- or 16-byte boundary. In arrays or structures
|
|
conforming to the ABI, this is not possible. So specifying
|
|
@option{-m128bit-long-double} aligns @code{long double}
|
|
to a 16-byte boundary by padding the @code{long double} with an additional
|
|
32-bit zero.
|
|
|
|
In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as
|
|
its ABI specifies that @code{long double} is aligned on 16-byte boundary.
|
|
|
|
Notice that neither of these options enable any extra precision over the x87
|
|
standard of 80 bits for a @code{long double}.
|
|
|
|
@strong{Warning:} if you override the default value for your target ABI, this
|
|
changes the size of
|
|
structures and arrays containing @code{long double} variables,
|
|
as well as modifying the function calling convention for functions taking
|
|
@code{long double}. Hence they are not binary-compatible
|
|
with code compiled without that switch.
|
|
|
|
@item -mlong-double-64
|
|
@itemx -mlong-double-80
|
|
@itemx -mlong-double-128
|
|
@opindex mlong-double-64
|
|
@opindex mlong-double-80
|
|
@opindex mlong-double-128
|
|
These switches control the size of @code{long double} type. A size
|
|
of 64 bits makes the @code{long double} type equivalent to the @code{double}
|
|
type. This is the default for 32-bit Bionic C library. A size
|
|
of 128 bits makes the @code{long double} type equivalent to the
|
|
@code{__float128} type. This is the default for 64-bit Bionic C library.
|
|
|
|
@strong{Warning:} if you override the default value for your target ABI, this
|
|
changes the size of
|
|
structures and arrays containing @code{long double} variables,
|
|
as well as modifying the function calling convention for functions taking
|
|
@code{long double}. Hence they are not binary-compatible
|
|
with code compiled without that switch.
|
|
|
|
@item -malign-data=@var{type}
|
|
@opindex malign-data
|
|
Control how GCC aligns variables. Supported values for @var{type} are
|
|
@samp{compat} uses increased alignment value compatible uses GCC 4.8
|
|
and earlier, @samp{abi} uses alignment value as specified by the
|
|
psABI, and @samp{cacheline} uses increased alignment value to match
|
|
the cache line size. @samp{compat} is the default.
|
|
|
|
@item -mlarge-data-threshold=@var{threshold}
|
|
@opindex mlarge-data-threshold
|
|
When @option{-mcmodel=medium} is specified, data objects larger than
|
|
@var{threshold} are placed in the large data section. This value must be the
|
|
same across all objects linked into the binary, and defaults to 65535.
|
|
|
|
@item -mrtd
|
|
@opindex mrtd
|
|
Use a different function-calling convention, in which functions that
|
|
take a fixed number of arguments return with the @code{ret @var{num}}
|
|
instruction, which pops their arguments while returning. This saves one
|
|
instruction in the caller since there is no need to pop the arguments
|
|
there.
|
|
|
|
You can specify that an individual function is called with this calling
|
|
sequence with the function attribute @code{stdcall}. You can also
|
|
override the @option{-mrtd} option by using the function attribute
|
|
@code{cdecl}. @xref{Function Attributes}.
|
|
|
|
@strong{Warning:} this calling convention is incompatible with the one
|
|
normally used on Unix, so you cannot use it if you need to call
|
|
libraries compiled with the Unix compiler.
|
|
|
|
Also, you must provide function prototypes for all functions that
|
|
take variable numbers of arguments (including @code{printf});
|
|
otherwise incorrect code is generated for calls to those
|
|
functions.
|
|
|
|
In addition, seriously incorrect code results if you call a
|
|
function with too many arguments. (Normally, extra arguments are
|
|
harmlessly ignored.)
|
|
|
|
@item -mregparm=@var{num}
|
|
@opindex mregparm
|
|
Control how many registers are used to pass integer arguments. By
|
|
default, no registers are used to pass arguments, and at most 3
|
|
registers can be used. You can control this behavior for a specific
|
|
function by using the function attribute @code{regparm}.
|
|
@xref{Function Attributes}.
|
|
|
|
@strong{Warning:} if you use this switch, and
|
|
@var{num} is nonzero, then you must build all modules with the same
|
|
value, including any libraries. This includes the system libraries and
|
|
startup modules.
|
|
|
|
@item -msseregparm
|
|
@opindex msseregparm
|
|
Use SSE register passing conventions for float and double arguments
|
|
and return values. You can control this behavior for a specific
|
|
function by using the function attribute @code{sseregparm}.
|
|
@xref{Function Attributes}.
|
|
|
|
@strong{Warning:} if you use this switch then you must build all
|
|
modules with the same value, including any libraries. This includes
|
|
the system libraries and startup modules.
|
|
|
|
@item -mvect8-ret-in-mem
|
|
@opindex mvect8-ret-in-mem
|
|
Return 8-byte vectors in memory instead of MMX registers. This is the
|
|
default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of the Sun
|
|
Studio compilers until version 12. Later compiler versions (starting
|
|
with Studio 12 Update@tie{}1) follow the ABI used by other x86 targets, which
|
|
is the default on Solaris@tie{}10 and later. @emph{Only} use this option if
|
|
you need to remain compatible with existing code produced by those
|
|
previous compiler versions or older versions of GCC@.
|
|
|
|
@item -mpc32
|
|
@itemx -mpc64
|
|
@itemx -mpc80
|
|
@opindex mpc32
|
|
@opindex mpc64
|
|
@opindex mpc80
|
|
|
|
Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32}
|
|
is specified, the significands of results of floating-point operations are
|
|
rounded to 24 bits (single precision); @option{-mpc64} rounds the
|
|
significands of results of floating-point operations to 53 bits (double
|
|
precision) and @option{-mpc80} rounds the significands of results of
|
|
floating-point operations to 64 bits (extended double precision), which is
|
|
the default. When this option is used, floating-point operations in higher
|
|
precisions are not available to the programmer without setting the FPU
|
|
control word explicitly.
|
|
|
|
Setting the rounding of floating-point operations to less than the default
|
|
80 bits can speed some programs by 2% or more. Note that some mathematical
|
|
libraries assume that extended-precision (80-bit) floating-point operations
|
|
are enabled by default; routines in such libraries could suffer significant
|
|
loss of accuracy, typically through so-called ``catastrophic cancellation'',
|
|
when this option is used to set the precision to less than extended precision.
|
|
|
|
@item -mstackrealign
|
|
@opindex mstackrealign
|
|
Realign the stack at entry. On the x86, the @option{-mstackrealign}
|
|
option generates an alternate prologue and epilogue that realigns the
|
|
run-time stack if necessary. This supports mixing legacy codes that keep
|
|
4-byte stack alignment with modern codes that keep 16-byte stack alignment for
|
|
SSE compatibility. See also the attribute @code{force_align_arg_pointer},
|
|
applicable to individual functions.
|
|
|
|
@item -mpreferred-stack-boundary=@var{num}
|
|
@opindex mpreferred-stack-boundary
|
|
Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
|
|
byte boundary. If @option{-mpreferred-stack-boundary} is not specified,
|
|
the default is 4 (16 bytes or 128 bits).
|
|
|
|
@strong{Warning:} When generating code for the x86-64 architecture with
|
|
SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be
|
|
used to keep the stack boundary aligned to 8 byte boundary. Since
|
|
x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and
|
|
intended to be used in controlled environment where stack space is
|
|
important limitation. This option leads to wrong code when functions
|
|
compiled with 16 byte stack alignment (such as functions from a standard
|
|
library) are called with misaligned stack. In this case, SSE
|
|
instructions may lead to misaligned memory access traps. In addition,
|
|
variable arguments are handled incorrectly for 16 byte aligned
|
|
objects (including x87 long double and __int128), leading to wrong
|
|
results. You must build all modules with
|
|
@option{-mpreferred-stack-boundary=3}, including any libraries. This
|
|
includes the system libraries and startup modules.
|
|
|
|
@item -mincoming-stack-boundary=@var{num}
|
|
@opindex mincoming-stack-boundary
|
|
Assume the incoming stack is aligned to a 2 raised to @var{num} byte
|
|
boundary. If @option{-mincoming-stack-boundary} is not specified,
|
|
the one specified by @option{-mpreferred-stack-boundary} is used.
|
|
|
|
On Pentium and Pentium Pro, @code{double} and @code{long double} values
|
|
should be aligned to an 8-byte boundary (see @option{-malign-double}) or
|
|
suffer significant run time performance penalties. On Pentium III, the
|
|
Streaming SIMD Extension (SSE) data type @code{__m128} may not work
|
|
properly if it is not 16-byte aligned.
|
|
|
|
To ensure proper alignment of this values on the stack, the stack boundary
|
|
must be as aligned as that required by any value stored on the stack.
|
|
Further, every function must be generated such that it keeps the stack
|
|
aligned. Thus calling a function compiled with a higher preferred
|
|
stack boundary from a function compiled with a lower preferred stack
|
|
boundary most likely misaligns the stack. It is recommended that
|
|
libraries that use callbacks always use the default setting.
|
|
|
|
This extra alignment does consume extra stack space, and generally
|
|
increases code size. Code that is sensitive to stack space usage, such
|
|
as embedded systems and operating system kernels, may want to reduce the
|
|
preferred alignment to @option{-mpreferred-stack-boundary=2}.
|
|
|
|
@need 200
|
|
@item -mmmx
|
|
@opindex mmmx
|
|
@need 200
|
|
@itemx -msse
|
|
@opindex msse
|
|
@need 200
|
|
@itemx -msse2
|
|
@opindex msse2
|
|
@need 200
|
|
@itemx -msse3
|
|
@opindex msse3
|
|
@need 200
|
|
@itemx -mssse3
|
|
@opindex mssse3
|
|
@need 200
|
|
@itemx -msse4
|
|
@opindex msse4
|
|
@need 200
|
|
@itemx -msse4a
|
|
@opindex msse4a
|
|
@need 200
|
|
@itemx -msse4.1
|
|
@opindex msse4.1
|
|
@need 200
|
|
@itemx -msse4.2
|
|
@opindex msse4.2
|
|
@need 200
|
|
@itemx -mavx
|
|
@opindex mavx
|
|
@need 200
|
|
@itemx -mavx2
|
|
@opindex mavx2
|
|
@need 200
|
|
@itemx -mavx512f
|
|
@opindex mavx512f
|
|
@need 200
|
|
@itemx -mavx512pf
|
|
@opindex mavx512pf
|
|
@need 200
|
|
@itemx -mavx512er
|
|
@opindex mavx512er
|
|
@need 200
|
|
@itemx -mavx512cd
|
|
@opindex mavx512cd
|
|
@need 200
|
|
@itemx -mavx512vl
|
|
@opindex mavx512vl
|
|
@need 200
|
|
@itemx -mavx512bw
|
|
@opindex mavx512bw
|
|
@need 200
|
|
@itemx -mavx512dq
|
|
@opindex mavx512dq
|
|
@need 200
|
|
@itemx -mavx512ifma
|
|
@opindex mavx512ifma
|
|
@need 200
|
|
@itemx -mavx512vbmi
|
|
@opindex mavx512vbmi
|
|
@need 200
|
|
@itemx -msha
|
|
@opindex msha
|
|
@need 200
|
|
@itemx -maes
|
|
@opindex maes
|
|
@need 200
|
|
@itemx -mpclmul
|
|
@opindex mpclmul
|
|
@need 200
|
|
@itemx -mclfushopt
|
|
@opindex mclfushopt
|
|
@need 200
|
|
@itemx -mfsgsbase
|
|
@opindex mfsgsbase
|
|
@need 200
|
|
@itemx -mrdrnd
|
|
@opindex mrdrnd
|
|
@need 200
|
|
@itemx -mf16c
|
|
@opindex mf16c
|
|
@need 200
|
|
@itemx -mfma
|
|
@opindex mfma
|
|
@need 200
|
|
@itemx -mfma4
|
|
@opindex mfma4
|
|
@need 200
|
|
@itemx -mprefetchwt1
|
|
@opindex mprefetchwt1
|
|
@need 200
|
|
@itemx -mxop
|
|
@opindex mxop
|
|
@need 200
|
|
@itemx -mlwp
|
|
@opindex mlwp
|
|
@need 200
|
|
@itemx -m3dnow
|
|
@opindex m3dnow
|
|
@need 200
|
|
@itemx -mpopcnt
|
|
@opindex mpopcnt
|
|
@need 200
|
|
@itemx -mabm
|
|
@opindex mabm
|
|
@need 200
|
|
@itemx -mbmi
|
|
@opindex mbmi
|
|
@need 200
|
|
@itemx -mbmi2
|
|
@need 200
|
|
@itemx -mlzcnt
|
|
@opindex mlzcnt
|
|
@need 200
|
|
@itemx -mfxsr
|
|
@opindex mfxsr
|
|
@need 200
|
|
@itemx -mxsave
|
|
@opindex mxsave
|
|
@need 200
|
|
@itemx -mxsaveopt
|
|
@opindex mxsaveopt
|
|
@need 200
|
|
@itemx -mxsavec
|
|
@opindex mxsavec
|
|
@need 200
|
|
@itemx -mxsaves
|
|
@opindex mxsaves
|
|
@need 200
|
|
@itemx -mrtm
|
|
@opindex mrtm
|
|
@need 200
|
|
@itemx -mtbm
|
|
@opindex mtbm
|
|
@need 200
|
|
@itemx -mmpx
|
|
@opindex mmpx
|
|
@need 200
|
|
@itemx -mmwaitx
|
|
@opindex mmwaitx
|
|
@need 200
|
|
@itemx -mclzero
|
|
@opindex mclzero
|
|
@itemx -mpku
|
|
@opindex mpku
|
|
These switches enable the use of instructions in the MMX, SSE,
|
|
SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AVX512F, AVX512PF, AVX512ER, AVX512CD,
|
|
SHA, AES, PCLMUL, FSGSBASE, RDRND, F16C, FMA, SSE4A, FMA4, XOP, LWP, ABM,
|
|
AVX512VL, AVX512BW, AVX512DQ, AVX512IFMA AVX512VBMI, BMI, BMI2, FXSR,
|
|
XSAVE, XSAVEOPT, LZCNT, RTM, MPX, MWAITX, PKU or 3DNow!@:
|
|
extended instruction sets. Each has a corresponding @option{-mno-} option
|
|
to disable use of these instructions.
|
|
|
|
These extensions are also available as built-in functions: see
|
|
@ref{x86 Built-in Functions}, for details of the functions enabled and
|
|
disabled by these switches.
|
|
|
|
To generate SSE/SSE2 instructions automatically from floating-point
|
|
code (as opposed to 387 instructions), see @option{-mfpmath=sse}.
|
|
|
|
GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it
|
|
generates new AVX instructions or AVX equivalence for all SSEx instructions
|
|
when needed.
|
|
|
|
These options enable GCC to use these extended instructions in
|
|
generated code, even without @option{-mfpmath=sse}. Applications that
|
|
perform run-time CPU detection must compile separate files for each
|
|
supported architecture, using the appropriate flags. In particular,
|
|
the file containing the CPU detection code should be compiled without
|
|
these options.
|
|
|
|
@item -mdump-tune-features
|
|
@opindex mdump-tune-features
|
|
This option instructs GCC to dump the names of the x86 performance
|
|
tuning features and default settings. The names can be used in
|
|
@option{-mtune-ctrl=@var{feature-list}}.
|
|
|
|
@item -mtune-ctrl=@var{feature-list}
|
|
@opindex mtune-ctrl=@var{feature-list}
|
|
This option is used to do fine grain control of x86 code generation features.
|
|
@var{feature-list} is a comma separated list of @var{feature} names. See also
|
|
@option{-mdump-tune-features}. When specified, the @var{feature} is turned
|
|
on if it is not preceded with @samp{^}, otherwise, it is turned off.
|
|
@option{-mtune-ctrl=@var{feature-list}} is intended to be used by GCC
|
|
developers. Using it may lead to code paths not covered by testing and can
|
|
potentially result in compiler ICEs or runtime errors.
|
|
|
|
@item -mno-default
|
|
@opindex mno-default
|
|
This option instructs GCC to turn off all tunable features. See also
|
|
@option{-mtune-ctrl=@var{feature-list}} and @option{-mdump-tune-features}.
|
|
|
|
@item -mcld
|
|
@opindex mcld
|
|
This option instructs GCC to emit a @code{cld} instruction in the prologue
|
|
of functions that use string instructions. String instructions depend on
|
|
the DF flag to select between autoincrement or autodecrement mode. While the
|
|
ABI specifies the DF flag to be cleared on function entry, some operating
|
|
systems violate this specification by not clearing the DF flag in their
|
|
exception dispatchers. The exception handler can be invoked with the DF flag
|
|
set, which leads to wrong direction mode when string instructions are used.
|
|
This option can be enabled by default on 32-bit x86 targets by configuring
|
|
GCC with the @option{--enable-cld} configure option. Generation of @code{cld}
|
|
instructions can be suppressed with the @option{-mno-cld} compiler option
|
|
in this case.
|
|
|
|
@item -mvzeroupper
|
|
@opindex mvzeroupper
|
|
This option instructs GCC to emit a @code{vzeroupper} instruction
|
|
before a transfer of control flow out of the function to minimize
|
|
the AVX to SSE transition penalty as well as remove unnecessary @code{zeroupper}
|
|
intrinsics.
|
|
|
|
@item -mprefer-avx128
|
|
@opindex mprefer-avx128
|
|
This option instructs GCC to use 128-bit AVX instructions instead of
|
|
256-bit AVX instructions in the auto-vectorizer.
|
|
|
|
@item -mcx16
|
|
@opindex mcx16
|
|
This option enables GCC to generate @code{CMPXCHG16B} instructions.
|
|
@code{CMPXCHG16B} allows for atomic operations on 128-bit double quadword
|
|
(or oword) data types.
|
|
This is useful for high-resolution counters that can be updated
|
|
by multiple processors (or cores). This instruction is generated as part of
|
|
atomic built-in functions: see @ref{__sync Builtins} or
|
|
@ref{__atomic Builtins} for details.
|
|
|
|
@item -msahf
|
|
@opindex msahf
|
|
This option enables generation of @code{SAHF} instructions in 64-bit code.
|
|
Early Intel Pentium 4 CPUs with Intel 64 support,
|
|
prior to the introduction of Pentium 4 G1 step in December 2005,
|
|
lacked the @code{LAHF} and @code{SAHF} instructions
|
|
which are supported by AMD64.
|
|
These are load and store instructions, respectively, for certain status flags.
|
|
In 64-bit mode, the @code{SAHF} instruction is used to optimize @code{fmod},
|
|
@code{drem}, and @code{remainder} built-in functions;
|
|
see @ref{Other Builtins} for details.
|
|
|
|
@item -mmovbe
|
|
@opindex mmovbe
|
|
This option enables use of the @code{movbe} instruction to implement
|
|
@code{__builtin_bswap32} and @code{__builtin_bswap64}.
|
|
|
|
@item -mcrc32
|
|
@opindex mcrc32
|
|
This option enables built-in functions @code{__builtin_ia32_crc32qi},
|
|
@code{__builtin_ia32_crc32hi}, @code{__builtin_ia32_crc32si} and
|
|
@code{__builtin_ia32_crc32di} to generate the @code{crc32} machine instruction.
|
|
|
|
@item -mrecip
|
|
@opindex mrecip
|
|
This option enables use of @code{RCPSS} and @code{RSQRTSS} instructions
|
|
(and their vectorized variants @code{RCPPS} and @code{RSQRTPS})
|
|
with an additional Newton-Raphson step
|
|
to increase precision instead of @code{DIVSS} and @code{SQRTSS}
|
|
(and their vectorized
|
|
variants) for single-precision floating-point arguments. These instructions
|
|
are generated only when @option{-funsafe-math-optimizations} is enabled
|
|
together with @option{-ffinite-math-only} and @option{-fno-trapping-math}.
|
|
Note that while the throughput of the sequence is higher than the throughput
|
|
of the non-reciprocal instruction, the precision of the sequence can be
|
|
decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
|
|
|
|
Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of @code{RSQRTSS}
|
|
(or @code{RSQRTPS}) already with @option{-ffast-math} (or the above option
|
|
combination), and doesn't need @option{-mrecip}.
|
|
|
|
Also note that GCC emits the above sequence with additional Newton-Raphson step
|
|
for vectorized single-float division and vectorized @code{sqrtf(@var{x})}
|
|
already with @option{-ffast-math} (or the above option combination), and
|
|
doesn't need @option{-mrecip}.
|
|
|
|
@item -mrecip=@var{opt}
|
|
@opindex mrecip=opt
|
|
This option controls which reciprocal estimate instructions
|
|
may be used. @var{opt} is a comma-separated list of options, which may
|
|
be preceded by a @samp{!} to invert the option:
|
|
|
|
@table @samp
|
|
@item all
|
|
Enable all estimate instructions.
|
|
|
|
@item default
|
|
Enable the default instructions, equivalent to @option{-mrecip}.
|
|
|
|
@item none
|
|
Disable all estimate instructions, equivalent to @option{-mno-recip}.
|
|
|
|
@item div
|
|
Enable the approximation for scalar division.
|
|
|
|
@item vec-div
|
|
Enable the approximation for vectorized division.
|
|
|
|
@item sqrt
|
|
Enable the approximation for scalar square root.
|
|
|
|
@item vec-sqrt
|
|
Enable the approximation for vectorized square root.
|
|
@end table
|
|
|
|
So, for example, @option{-mrecip=all,!sqrt} enables
|
|
all of the reciprocal approximations, except for square root.
|
|
|
|
@item -mveclibabi=@var{type}
|
|
@opindex mveclibabi
|
|
Specifies the ABI type to use for vectorizing intrinsics using an
|
|
external library. Supported values for @var{type} are @samp{svml}
|
|
for the Intel short
|
|
vector math library and @samp{acml} for the AMD math core library.
|
|
To use this option, both @option{-ftree-vectorize} and
|
|
@option{-funsafe-math-optimizations} have to be enabled, and an SVML or ACML
|
|
ABI-compatible library must be specified at link time.
|
|
|
|
GCC currently emits calls to @code{vmldExp2},
|
|
@code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2},
|
|
@code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2},
|
|
@code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2},
|
|
@code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2},
|
|
@code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104},
|
|
@code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4},
|
|
@code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4},
|
|
@code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4},
|
|
@code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding
|
|
function type when @option{-mveclibabi=svml} is used, and @code{__vrd2_sin},
|
|
@code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2},
|
|
@code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf},
|
|
@code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f},
|
|
@code{__vrs4_log10f} and @code{__vrs4_powf} for the corresponding function type
|
|
when @option{-mveclibabi=acml} is used.
|
|
|
|
@item -mabi=@var{name}
|
|
@opindex mabi
|
|
Generate code for the specified calling convention. Permissible values
|
|
are @samp{sysv} for the ABI used on GNU/Linux and other systems, and
|
|
@samp{ms} for the Microsoft ABI. The default is to use the Microsoft
|
|
ABI when targeting Microsoft Windows and the SysV ABI on all other systems.
|
|
You can control this behavior for specific functions by
|
|
using the function attributes @code{ms_abi} and @code{sysv_abi}.
|
|
@xref{Function Attributes}.
|
|
|
|
@item -mtls-dialect=@var{type}
|
|
@opindex mtls-dialect
|
|
Generate code to access thread-local storage using the @samp{gnu} or
|
|
@samp{gnu2} conventions. @samp{gnu} is the conservative default;
|
|
@samp{gnu2} is more efficient, but it may add compile- and run-time
|
|
requirements that cannot be satisfied on all systems.
|
|
|
|
@item -mpush-args
|
|
@itemx -mno-push-args
|
|
@opindex mpush-args
|
|
@opindex mno-push-args
|
|
Use PUSH operations to store outgoing parameters. This method is shorter
|
|
and usually equally fast as method using SUB/MOV operations and is enabled
|
|
by default. In some cases disabling it may improve performance because of
|
|
improved scheduling and reduced dependencies.
|
|
|
|
@item -maccumulate-outgoing-args
|
|
@opindex maccumulate-outgoing-args
|
|
If enabled, the maximum amount of space required for outgoing arguments is
|
|
computed in the function prologue. This is faster on most modern CPUs
|
|
because of reduced dependencies, improved scheduling and reduced stack usage
|
|
when the preferred stack boundary is not equal to 2. The drawback is a notable
|
|
increase in code size. This switch implies @option{-mno-push-args}.
|
|
|
|
@item -mthreads
|
|
@opindex mthreads
|
|
Support thread-safe exception handling on MinGW. Programs that rely
|
|
on thread-safe exception handling must compile and link all code with the
|
|
@option{-mthreads} option. When compiling, @option{-mthreads} defines
|
|
@option{-D_MT}; when linking, it links in a special thread helper library
|
|
@option{-lmingwthrd} which cleans up per-thread exception-handling data.
|
|
|
|
@item -mms-bitfields
|
|
@itemx -mno-ms-bitfields
|
|
@opindex mms-bitfields
|
|
@opindex mno-ms-bitfields
|
|
|
|
Enable/disable bit-field layout compatible with the native Microsoft
|
|
Windows compiler.
|
|
|
|
If @code{packed} is used on a structure, or if bit-fields are used,
|
|
it may be that the Microsoft ABI lays out the structure differently
|
|
than the way GCC normally does. Particularly when moving packed
|
|
data between functions compiled with GCC and the native Microsoft compiler
|
|
(either via function call or as data in a file), it may be necessary to access
|
|
either format.
|
|
|
|
This option is enabled by default for Microsoft Windows
|
|
targets. This behavior can also be controlled locally by use of variable
|
|
or type attributes. For more information, see @ref{x86 Variable Attributes}
|
|
and @ref{x86 Type Attributes}.
|
|
|
|
The Microsoft structure layout algorithm is fairly simple with the exception
|
|
of the bit-field packing.
|
|
The padding and alignment of members of structures and whether a bit-field
|
|
can straddle a storage-unit boundary are determine by these rules:
|
|
|
|
@enumerate
|
|
@item Structure members are stored sequentially in the order in which they are
|
|
declared: the first member has the lowest memory address and the last member
|
|
the highest.
|
|
|
|
@item Every data object has an alignment requirement. The alignment requirement
|
|
for all data except structures, unions, and arrays is either the size of the
|
|
object or the current packing size (specified with either the
|
|
@code{aligned} attribute or the @code{pack} pragma),
|
|
whichever is less. For structures, unions, and arrays,
|
|
the alignment requirement is the largest alignment requirement of its members.
|
|
Every object is allocated an offset so that:
|
|
|
|
@smallexample
|
|
offset % alignment_requirement == 0
|
|
@end smallexample
|
|
|
|
@item Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation
|
|
unit if the integral types are the same size and if the next bit-field fits
|
|
into the current allocation unit without crossing the boundary imposed by the
|
|
common alignment requirements of the bit-fields.
|
|
@end enumerate
|
|
|
|
MSVC interprets zero-length bit-fields in the following ways:
|
|
|
|
@enumerate
|
|
@item If a zero-length bit-field is inserted between two bit-fields that
|
|
are normally coalesced, the bit-fields are not coalesced.
|
|
|
|
For example:
|
|
|
|
@smallexample
|
|
struct
|
|
@{
|
|
unsigned long bf_1 : 12;
|
|
unsigned long : 0;
|
|
unsigned long bf_2 : 12;
|
|
@} t1;
|
|
@end smallexample
|
|
|
|
@noindent
|
|
The size of @code{t1} is 8 bytes with the zero-length bit-field. If the
|
|
zero-length bit-field were removed, @code{t1}'s size would be 4 bytes.
|
|
|
|
@item If a zero-length bit-field is inserted after a bit-field, @code{foo}, and the
|
|
alignment of the zero-length bit-field is greater than the member that follows it,
|
|
@code{bar}, @code{bar} is aligned as the type of the zero-length bit-field.
|
|
|
|
For example:
|
|
|
|
@smallexample
|
|
struct
|
|
@{
|
|
char foo : 4;
|
|
short : 0;
|
|
char bar;
|
|
@} t2;
|
|
|
|
struct
|
|
@{
|
|
char foo : 4;
|
|
short : 0;
|
|
double bar;
|
|
@} t3;
|
|
@end smallexample
|
|
|
|
@noindent
|
|
For @code{t2}, @code{bar} is placed at offset 2, rather than offset 1.
|
|
Accordingly, the size of @code{t2} is 4. For @code{t3}, the zero-length
|
|
bit-field does not affect the alignment of @code{bar} or, as a result, the size
|
|
of the structure.
|
|
|
|
Taking this into account, it is important to note the following:
|
|
|
|
@enumerate
|
|
@item If a zero-length bit-field follows a normal bit-field, the type of the
|
|
zero-length bit-field may affect the alignment of the structure as whole. For
|
|
example, @code{t2} has a size of 4 bytes, since the zero-length bit-field follows a
|
|
normal bit-field, and is of type short.
|
|
|
|
@item Even if a zero-length bit-field is not followed by a normal bit-field, it may
|
|
still affect the alignment of the structure:
|
|
|
|
@smallexample
|
|
struct
|
|
@{
|
|
char foo : 6;
|
|
long : 0;
|
|
@} t4;
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Here, @code{t4} takes up 4 bytes.
|
|
@end enumerate
|
|
|
|
@item Zero-length bit-fields following non-bit-field members are ignored:
|
|
|
|
@smallexample
|
|
struct
|
|
@{
|
|
char foo;
|
|
long : 0;
|
|
char bar;
|
|
@} t5;
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Here, @code{t5} takes up 2 bytes.
|
|
@end enumerate
|
|
|
|
|
|
@item -mno-align-stringops
|
|
@opindex mno-align-stringops
|
|
Do not align the destination of inlined string operations. This switch reduces
|
|
code size and improves performance in case the destination is already aligned,
|
|
but GCC doesn't know about it.
|
|
|
|
@item -minline-all-stringops
|
|
@opindex minline-all-stringops
|
|
By default GCC inlines string operations only when the destination is
|
|
known to be aligned to least a 4-byte boundary.
|
|
This enables more inlining and increases code
|
|
size, but may improve performance of code that depends on fast
|
|
@code{memcpy}, @code{strlen},
|
|
and @code{memset} for short lengths.
|
|
|
|
@item -minline-stringops-dynamically
|
|
@opindex minline-stringops-dynamically
|
|
For string operations of unknown size, use run-time checks with
|
|
inline code for small blocks and a library call for large blocks.
|
|
|
|
@item -mstringop-strategy=@var{alg}
|
|
@opindex mstringop-strategy=@var{alg}
|
|
Override the internal decision heuristic for the particular algorithm to use
|
|
for inlining string operations. The allowed values for @var{alg} are:
|
|
|
|
@table @samp
|
|
@item rep_byte
|
|
@itemx rep_4byte
|
|
@itemx rep_8byte
|
|
Expand using i386 @code{rep} prefix of the specified size.
|
|
|
|
@item byte_loop
|
|
@itemx loop
|
|
@itemx unrolled_loop
|
|
Expand into an inline loop.
|
|
|
|
@item libcall
|
|
Always use a library call.
|
|
@end table
|
|
|
|
@item -mmemcpy-strategy=@var{strategy}
|
|
@opindex mmemcpy-strategy=@var{strategy}
|
|
Override the internal decision heuristic to decide if @code{__builtin_memcpy}
|
|
should be inlined and what inline algorithm to use when the expected size
|
|
of the copy operation is known. @var{strategy}
|
|
is a comma-separated list of @var{alg}:@var{max_size}:@var{dest_align} triplets.
|
|
@var{alg} is specified in @option{-mstringop-strategy}, @var{max_size} specifies
|
|
the max byte size with which inline algorithm @var{alg} is allowed. For the last
|
|
triplet, the @var{max_size} must be @code{-1}. The @var{max_size} of the triplets
|
|
in the list must be specified in increasing order. The minimal byte size for
|
|
@var{alg} is @code{0} for the first triplet and @code{@var{max_size} + 1} of the
|
|
preceding range.
|
|
|
|
@item -mmemset-strategy=@var{strategy}
|
|
@opindex mmemset-strategy=@var{strategy}
|
|
The option is similar to @option{-mmemcpy-strategy=} except that it is to control
|
|
@code{__builtin_memset} expansion.
|
|
|
|
@item -momit-leaf-frame-pointer
|
|
@opindex momit-leaf-frame-pointer
|
|
Don't keep the frame pointer in a register for leaf functions. This
|
|
avoids the instructions to save, set up, and restore frame pointers and
|
|
makes an extra register available in leaf functions. The option
|
|
@option{-fomit-leaf-frame-pointer} removes the frame pointer for leaf functions,
|
|
which might make debugging harder.
|
|
|
|
@item -mtls-direct-seg-refs
|
|
@itemx -mno-tls-direct-seg-refs
|
|
@opindex mtls-direct-seg-refs
|
|
Controls whether TLS variables may be accessed with offsets from the
|
|
TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit),
|
|
or whether the thread base pointer must be added. Whether or not this
|
|
is valid depends on the operating system, and whether it maps the
|
|
segment to cover the entire TLS area.
|
|
|
|
For systems that use the GNU C Library, the default is on.
|
|
|
|
@item -msse2avx
|
|
@itemx -mno-sse2avx
|
|
@opindex msse2avx
|
|
Specify that the assembler should encode SSE instructions with VEX
|
|
prefix. The option @option{-mavx} turns this on by default.
|
|
|
|
@item -mfentry
|
|
@itemx -mno-fentry
|
|
@opindex mfentry
|
|
If profiling is active (@option{-pg}), put the profiling
|
|
counter call before the prologue.
|
|
Note: On x86 architectures the attribute @code{ms_hook_prologue}
|
|
isn't possible at the moment for @option{-mfentry} and @option{-pg}.
|
|
|
|
@item -mrecord-mcount
|
|
@itemx -mno-record-mcount
|
|
@opindex mrecord-mcount
|
|
If profiling is active (@option{-pg}), generate a __mcount_loc section
|
|
that contains pointers to each profiling call. This is useful for
|
|
automatically patching and out calls.
|
|
|
|
@item -mnop-mcount
|
|
@itemx -mno-nop-mcount
|
|
@opindex mnop-mcount
|
|
If profiling is active (@option{-pg}), generate the calls to
|
|
the profiling functions as NOPs. This is useful when they
|
|
should be patched in later dynamically. This is likely only
|
|
useful together with @option{-mrecord-mcount}.
|
|
|
|
@item -mskip-rax-setup
|
|
@itemx -mno-skip-rax-setup
|
|
@opindex mskip-rax-setup
|
|
When generating code for the x86-64 architecture with SSE extensions
|
|
disabled, @option{-mskip-rax-setup} can be used to skip setting up RAX
|
|
register when there are no variable arguments passed in vector registers.
|
|
|
|
@strong{Warning:} Since RAX register is used to avoid unnecessarily
|
|
saving vector registers on stack when passing variable arguments, the
|
|
impacts of this option are callees may waste some stack space,
|
|
misbehave or jump to a random location. GCC 4.4 or newer don't have
|
|
those issues, regardless the RAX register value.
|
|
|
|
@item -m8bit-idiv
|
|
@itemx -mno-8bit-idiv
|
|
@opindex m8bit-idiv
|
|
On some processors, like Intel Atom, 8-bit unsigned integer divide is
|
|
much faster than 32-bit/64-bit integer divide. This option generates a
|
|
run-time check. If both dividend and divisor are within range of 0
|
|
to 255, 8-bit unsigned integer divide is used instead of
|
|
32-bit/64-bit integer divide.
|
|
|
|
@item -mavx256-split-unaligned-load
|
|
@itemx -mavx256-split-unaligned-store
|
|
@opindex mavx256-split-unaligned-load
|
|
@opindex mavx256-split-unaligned-store
|
|
Split 32-byte AVX unaligned load and store.
|
|
|
|
@item -mstack-protector-guard=@var{guard}
|
|
@opindex mstack-protector-guard=@var{guard}
|
|
Generate stack protection code using canary at @var{guard}. Supported
|
|
locations are @samp{global} for global canary or @samp{tls} for per-thread
|
|
canary in the TLS block (the default). This option has effect only when
|
|
@option{-fstack-protector} or @option{-fstack-protector-all} is specified.
|
|
|
|
@item -mmitigate-rop
|
|
@opindex mmitigate-rop
|
|
Try to avoid generating code sequences that contain unintended return
|
|
opcodes, to mitigate against certain forms of attack. At the moment,
|
|
this option is limited in what it can do and should not be relied
|
|
on to provide serious protection.
|
|
|
|
@item -mgeneral-regs-only
|
|
@opindex mgeneral-regs-only
|
|
Generate code that uses only the general-purpose registers. This
|
|
prevents the compiler from using floating-point, vector, mask and bound
|
|
registers.
|
|
|
|
@end table
|
|
|
|
These @samp{-m} switches are supported in addition to the above
|
|
on x86-64 processors in 64-bit environments.
|
|
|
|
@table @gcctabopt
|
|
@item -m32
|
|
@itemx -m64
|
|
@itemx -mx32
|
|
@itemx -m16
|
|
@itemx -miamcu
|
|
@opindex m32
|
|
@opindex m64
|
|
@opindex mx32
|
|
@opindex m16
|
|
@opindex miamcu
|
|
Generate code for a 16-bit, 32-bit or 64-bit environment.
|
|
The @option{-m32} option sets @code{int}, @code{long}, and pointer types
|
|
to 32 bits, and
|
|
generates code that runs on any i386 system.
|
|
|
|
The @option{-m64} option sets @code{int} to 32 bits and @code{long} and pointer
|
|
types to 64 bits, and generates code for the x86-64 architecture.
|
|
For Darwin only the @option{-m64} option also turns off the @option{-fno-pic}
|
|
and @option{-mdynamic-no-pic} options.
|
|
|
|
The @option{-mx32} option sets @code{int}, @code{long}, and pointer types
|
|
to 32 bits, and
|
|
generates code for the x86-64 architecture.
|
|
|
|
The @option{-m16} option is the same as @option{-m32}, except for that
|
|
it outputs the @code{.code16gcc} assembly directive at the beginning of
|
|
the assembly output so that the binary can run in 16-bit mode.
|
|
|
|
The @option{-miamcu} option generates code which conforms to Intel MCU
|
|
psABI. It requires the @option{-m32} option to be turned on.
|
|
|
|
@item -mno-red-zone
|
|
@opindex mno-red-zone
|
|
Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated
|
|
by the x86-64 ABI; it is a 128-byte area beyond the location of the
|
|
stack pointer that is not modified by signal or interrupt handlers
|
|
and therefore can be used for temporary data without adjusting the stack
|
|
pointer. The flag @option{-mno-red-zone} disables this red zone.
|
|
|
|
@item -mcmodel=small
|
|
@opindex mcmodel=small
|
|
Generate code for the small code model: the program and its symbols must
|
|
be linked in the lower 2 GB of the address space. Pointers are 64 bits.
|
|
Programs can be statically or dynamically linked. This is the default
|
|
code model.
|
|
|
|
@item -mcmodel=kernel
|
|
@opindex mcmodel=kernel
|
|
Generate code for the kernel code model. The kernel runs in the
|
|
negative 2 GB of the address space.
|
|
This model has to be used for Linux kernel code.
|
|
|
|
@item -mcmodel=medium
|
|
@opindex mcmodel=medium
|
|
Generate code for the medium model: the program is linked in the lower 2
|
|
GB of the address space. Small symbols are also placed there. Symbols
|
|
with sizes larger than @option{-mlarge-data-threshold} are put into
|
|
large data or BSS sections and can be located above 2GB. Programs can
|
|
be statically or dynamically linked.
|
|
|
|
@item -mcmodel=large
|
|
@opindex mcmodel=large
|
|
Generate code for the large model. This model makes no assumptions
|
|
about addresses and sizes of sections.
|
|
|
|
@item -maddress-mode=long
|
|
@opindex maddress-mode=long
|
|
Generate code for long address mode. This is only supported for 64-bit
|
|
and x32 environments. It is the default address mode for 64-bit
|
|
environments.
|
|
|
|
@item -maddress-mode=short
|
|
@opindex maddress-mode=short
|
|
Generate code for short address mode. This is only supported for 32-bit
|
|
and x32 environments. It is the default address mode for 32-bit and
|
|
x32 environments.
|
|
@end table
|
|
|
|
@node x86 Windows Options
|
|
@subsection x86 Windows Options
|
|
@cindex x86 Windows Options
|
|
@cindex Windows Options for x86
|
|
|
|
These additional options are available for Microsoft Windows targets:
|
|
|
|
@table @gcctabopt
|
|
@item -mconsole
|
|
@opindex mconsole
|
|
This option
|
|
specifies that a console application is to be generated, by
|
|
instructing the linker to set the PE header subsystem type
|
|
required for console applications.
|
|
This option is available for Cygwin and MinGW targets and is
|
|
enabled by default on those targets.
|
|
|
|
@item -mdll
|
|
@opindex mdll
|
|
This option is available for Cygwin and MinGW targets. It
|
|
specifies that a DLL---a dynamic link library---is to be
|
|
generated, enabling the selection of the required runtime
|
|
startup object and entry point.
|
|
|
|
@item -mnop-fun-dllimport
|
|
@opindex mnop-fun-dllimport
|
|
This option is available for Cygwin and MinGW targets. It
|
|
specifies that the @code{dllimport} attribute should be ignored.
|
|
|
|
@item -mthread
|
|
@opindex mthread
|
|
This option is available for MinGW targets. It specifies
|
|
that MinGW-specific thread support is to be used.
|
|
|
|
@item -municode
|
|
@opindex municode
|
|
This option is available for MinGW-w64 targets. It causes
|
|
the @code{UNICODE} preprocessor macro to be predefined, and
|
|
chooses Unicode-capable runtime startup code.
|
|
|
|
@item -mwin32
|
|
@opindex mwin32
|
|
This option is available for Cygwin and MinGW targets. It
|
|
specifies that the typical Microsoft Windows predefined macros are to
|
|
be set in the pre-processor, but does not influence the choice
|
|
of runtime library/startup code.
|
|
|
|
@item -mwindows
|
|
@opindex mwindows
|
|
This option is available for Cygwin and MinGW targets. It
|
|
specifies that a GUI application is to be generated by
|
|
instructing the linker to set the PE header subsystem type
|
|
appropriately.
|
|
|
|
@item -fno-set-stack-executable
|
|
@opindex fno-set-stack-executable
|
|
This option is available for MinGW targets. It specifies that
|
|
the executable flag for the stack used by nested functions isn't
|
|
set. This is necessary for binaries running in kernel mode of
|
|
Microsoft Windows, as there the User32 API, which is used to set executable
|
|
privileges, isn't available.
|
|
|
|
@item -fwritable-relocated-rdata
|
|
@opindex fno-writable-relocated-rdata
|
|
This option is available for MinGW and Cygwin targets. It specifies
|
|
that relocated-data in read-only section is put into the @code{.data}
|
|
section. This is a necessary for older runtimes not supporting
|
|
modification of @code{.rdata} sections for pseudo-relocation.
|
|
|
|
@item -mpe-aligned-commons
|
|
@opindex mpe-aligned-commons
|
|
This option is available for Cygwin and MinGW targets. It
|
|
specifies that the GNU extension to the PE file format that
|
|
permits the correct alignment of COMMON variables should be
|
|
used when generating code. It is enabled by default if
|
|
GCC detects that the target assembler found during configuration
|
|
supports the feature.
|
|
@end table
|
|
|
|
See also under @ref{x86 Options} for standard options.
|
|
|
|
@node Xstormy16 Options
|
|
@subsection Xstormy16 Options
|
|
@cindex Xstormy16 Options
|
|
|
|
These options are defined for Xstormy16:
|
|
|
|
@table @gcctabopt
|
|
@item -msim
|
|
@opindex msim
|
|
Choose startup files and linker script suitable for the simulator.
|
|
@end table
|
|
|
|
@node Xtensa Options
|
|
@subsection Xtensa Options
|
|
@cindex Xtensa Options
|
|
|
|
These options are supported for Xtensa targets:
|
|
|
|
@table @gcctabopt
|
|
@item -mconst16
|
|
@itemx -mno-const16
|
|
@opindex mconst16
|
|
@opindex mno-const16
|
|
Enable or disable use of @code{CONST16} instructions for loading
|
|
constant values. The @code{CONST16} instruction is currently not a
|
|
standard option from Tensilica. When enabled, @code{CONST16}
|
|
instructions are always used in place of the standard @code{L32R}
|
|
instructions. The use of @code{CONST16} is enabled by default only if
|
|
the @code{L32R} instruction is not available.
|
|
|
|
@item -mfused-madd
|
|
@itemx -mno-fused-madd
|
|
@opindex mfused-madd
|
|
@opindex mno-fused-madd
|
|
Enable or disable use of fused multiply/add and multiply/subtract
|
|
instructions in the floating-point option. This has no effect if the
|
|
floating-point option is not also enabled. Disabling fused multiply/add
|
|
and multiply/subtract instructions forces the compiler to use separate
|
|
instructions for the multiply and add/subtract operations. This may be
|
|
desirable in some cases where strict IEEE 754-compliant results are
|
|
required: the fused multiply add/subtract instructions do not round the
|
|
intermediate result, thereby producing results with @emph{more} bits of
|
|
precision than specified by the IEEE standard. Disabling fused multiply
|
|
add/subtract instructions also ensures that the program output is not
|
|
sensitive to the compiler's ability to combine multiply and add/subtract
|
|
operations.
|
|
|
|
@item -mserialize-volatile
|
|
@itemx -mno-serialize-volatile
|
|
@opindex mserialize-volatile
|
|
@opindex mno-serialize-volatile
|
|
When this option is enabled, GCC inserts @code{MEMW} instructions before
|
|
@code{volatile} memory references to guarantee sequential consistency.
|
|
The default is @option{-mserialize-volatile}. Use
|
|
@option{-mno-serialize-volatile} to omit the @code{MEMW} instructions.
|
|
|
|
@item -mforce-no-pic
|
|
@opindex mforce-no-pic
|
|
For targets, like GNU/Linux, where all user-mode Xtensa code must be
|
|
position-independent code (PIC), this option disables PIC for compiling
|
|
kernel code.
|
|
|
|
@item -mtext-section-literals
|
|
@itemx -mno-text-section-literals
|
|
@opindex mtext-section-literals
|
|
@opindex mno-text-section-literals
|
|
These options control the treatment of literal pools. The default is
|
|
@option{-mno-text-section-literals}, which places literals in a separate
|
|
section in the output file. This allows the literal pool to be placed
|
|
in a data RAM/ROM, and it also allows the linker to combine literal
|
|
pools from separate object files to remove redundant literals and
|
|
improve code size. With @option{-mtext-section-literals}, the literals
|
|
are interspersed in the text section in order to keep them as close as
|
|
possible to their references. This may be necessary for large assembly
|
|
files. Literals for each function are placed right before that function.
|
|
|
|
@item -mauto-litpools
|
|
@itemx -mno-auto-litpools
|
|
@opindex mauto-litpools
|
|
@opindex mno-auto-litpools
|
|
These options control the treatment of literal pools. The default is
|
|
@option{-mno-auto-litpools}, which places literals in a separate
|
|
section in the output file unless @option{-mtext-section-literals} is
|
|
used. With @option{-mauto-litpools} the literals are interspersed in
|
|
the text section by the assembler. Compiler does not produce explicit
|
|
@code{.literal} directives and loads literals into registers with
|
|
@code{MOVI} instructions instead of @code{L32R} to let the assembler
|
|
do relaxation and place literals as necessary. This option allows
|
|
assembler to create several literal pools per function and assemble
|
|
very big functions, which may not be possible with
|
|
@option{-mtext-section-literals}.
|
|
|
|
@item -mtarget-align
|
|
@itemx -mno-target-align
|
|
@opindex mtarget-align
|
|
@opindex mno-target-align
|
|
When this option is enabled, GCC instructs the assembler to
|
|
automatically align instructions to reduce branch penalties at the
|
|
expense of some code density. The assembler attempts to widen density
|
|
instructions to align branch targets and the instructions following call
|
|
instructions. If there are not enough preceding safe density
|
|
instructions to align a target, no widening is performed. The
|
|
default is @option{-mtarget-align}. These options do not affect the
|
|
treatment of auto-aligned instructions like @code{LOOP}, which the
|
|
assembler always aligns, either by widening density instructions or
|
|
by inserting NOP instructions.
|
|
|
|
@item -mlongcalls
|
|
@itemx -mno-longcalls
|
|
@opindex mlongcalls
|
|
@opindex mno-longcalls
|
|
When this option is enabled, GCC instructs the assembler to translate
|
|
direct calls to indirect calls unless it can determine that the target
|
|
of a direct call is in the range allowed by the call instruction. This
|
|
translation typically occurs for calls to functions in other source
|
|
files. Specifically, the assembler translates a direct @code{CALL}
|
|
instruction into an @code{L32R} followed by a @code{CALLX} instruction.
|
|
The default is @option{-mno-longcalls}. This option should be used in
|
|
programs where the call target can potentially be out of range. This
|
|
option is implemented in the assembler, not the compiler, so the
|
|
assembly code generated by GCC still shows direct call
|
|
instructions---look at the disassembled object code to see the actual
|
|
instructions. Note that the assembler uses an indirect call for
|
|
every cross-file call, not just those that really are out of range.
|
|
@end table
|
|
|
|
@node zSeries Options
|
|
@subsection zSeries Options
|
|
@cindex zSeries options
|
|
|
|
These are listed under @xref{S/390 and zSeries Options}.
|
|
|
|
|
|
@c man end
|
|
|
|
@node Spec Files
|
|
@section Specifying Subprocesses and the Switches to Pass to Them
|
|
@cindex Spec Files
|
|
|
|
@command{gcc} is a driver program. It performs its job by invoking a
|
|
sequence of other programs to do the work of compiling, assembling and
|
|
linking. GCC interprets its command-line parameters and uses these to
|
|
deduce which programs it should invoke, and which command-line options
|
|
it ought to place on their command lines. This behavior is controlled
|
|
by @dfn{spec strings}. In most cases there is one spec string for each
|
|
program that GCC can invoke, but a few programs have multiple spec
|
|
strings to control their behavior. The spec strings built into GCC can
|
|
be overridden by using the @option{-specs=} command-line switch to specify
|
|
a spec file.
|
|
|
|
@dfn{Spec files} are plain-text files that are used to construct spec
|
|
strings. They consist of a sequence of directives separated by blank
|
|
lines. The type of directive is determined by the first non-whitespace
|
|
character on the line, which can be one of the following:
|
|
|
|
@table @code
|
|
@item %@var{command}
|
|
Issues a @var{command} to the spec file processor. The commands that can
|
|
appear here are:
|
|
|
|
@table @code
|
|
@item %include <@var{file}>
|
|
@cindex @code{%include}
|
|
Search for @var{file} and insert its text at the current point in the
|
|
specs file.
|
|
|
|
@item %include_noerr <@var{file}>
|
|
@cindex @code{%include_noerr}
|
|
Just like @samp{%include}, but do not generate an error message if the include
|
|
file cannot be found.
|
|
|
|
@item %rename @var{old_name} @var{new_name}
|
|
@cindex @code{%rename}
|
|
Rename the spec string @var{old_name} to @var{new_name}.
|
|
|
|
@end table
|
|
|
|
@item *[@var{spec_name}]:
|
|
This tells the compiler to create, override or delete the named spec
|
|
string. All lines after this directive up to the next directive or
|
|
blank line are considered to be the text for the spec string. If this
|
|
results in an empty string then the spec is deleted. (Or, if the
|
|
spec did not exist, then nothing happens.) Otherwise, if the spec
|
|
does not currently exist a new spec is created. If the spec does
|
|
exist then its contents are overridden by the text of this
|
|
directive, unless the first character of that text is the @samp{+}
|
|
character, in which case the text is appended to the spec.
|
|
|
|
@item [@var{suffix}]:
|
|
Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive
|
|
and up to the next directive or blank line are considered to make up the
|
|
spec string for the indicated suffix. When the compiler encounters an
|
|
input file with the named suffix, it processes the spec string in
|
|
order to work out how to compile that file. For example:
|
|
|
|
@smallexample
|
|
.ZZ:
|
|
z-compile -input %i
|
|
@end smallexample
|
|
|
|
This says that any input file whose name ends in @samp{.ZZ} should be
|
|
passed to the program @samp{z-compile}, which should be invoked with the
|
|
command-line switch @option{-input} and with the result of performing the
|
|
@samp{%i} substitution. (See below.)
|
|
|
|
As an alternative to providing a spec string, the text following a
|
|
suffix directive can be one of the following:
|
|
|
|
@table @code
|
|
@item @@@var{language}
|
|
This says that the suffix is an alias for a known @var{language}. This is
|
|
similar to using the @option{-x} command-line switch to GCC to specify a
|
|
language explicitly. For example:
|
|
|
|
@smallexample
|
|
.ZZ:
|
|
@@c++
|
|
@end smallexample
|
|
|
|
Says that .ZZ files are, in fact, C++ source files.
|
|
|
|
@item #@var{name}
|
|
This causes an error messages saying:
|
|
|
|
@smallexample
|
|
@var{name} compiler not installed on this system.
|
|
@end smallexample
|
|
@end table
|
|
|
|
GCC already has an extensive list of suffixes built into it.
|
|
This directive adds an entry to the end of the list of suffixes, but
|
|
since the list is searched from the end backwards, it is effectively
|
|
possible to override earlier entries using this technique.
|
|
|
|
@end table
|
|
|
|
GCC has the following spec strings built into it. Spec files can
|
|
override these strings or create their own. Note that individual
|
|
targets can also add their own spec strings to this list.
|
|
|
|
@smallexample
|
|
asm Options to pass to the assembler
|
|
asm_final Options to pass to the assembler post-processor
|
|
cpp Options to pass to the C preprocessor
|
|
cc1 Options to pass to the C compiler
|
|
cc1plus Options to pass to the C++ compiler
|
|
endfile Object files to include at the end of the link
|
|
link Options to pass to the linker
|
|
lib Libraries to include on the command line to the linker
|
|
libgcc Decides which GCC support library to pass to the linker
|
|
linker Sets the name of the linker
|
|
predefines Defines to be passed to the C preprocessor
|
|
signed_char Defines to pass to CPP to say whether @code{char} is signed
|
|
by default
|
|
startfile Object files to include at the start of the link
|
|
@end smallexample
|
|
|
|
Here is a small example of a spec file:
|
|
|
|
@smallexample
|
|
%rename lib old_lib
|
|
|
|
*lib:
|
|
--start-group -lgcc -lc -leval1 --end-group %(old_lib)
|
|
@end smallexample
|
|
|
|
This example renames the spec called @samp{lib} to @samp{old_lib} and
|
|
then overrides the previous definition of @samp{lib} with a new one.
|
|
The new definition adds in some extra command-line options before
|
|
including the text of the old definition.
|
|
|
|
@dfn{Spec strings} are a list of command-line options to be passed to their
|
|
corresponding program. In addition, the spec strings can contain
|
|
@samp{%}-prefixed sequences to substitute variable text or to
|
|
conditionally insert text into the command line. Using these constructs
|
|
it is possible to generate quite complex command lines.
|
|
|
|
Here is a table of all defined @samp{%}-sequences for spec
|
|
strings. Note that spaces are not generated automatically around the
|
|
results of expanding these sequences. Therefore you can concatenate them
|
|
together or combine them with constant text in a single argument.
|
|
|
|
@table @code
|
|
@item %%
|
|
Substitute one @samp{%} into the program name or argument.
|
|
|
|
@item %i
|
|
Substitute the name of the input file being processed.
|
|
|
|
@item %b
|
|
Substitute the basename of the input file being processed.
|
|
This is the substring up to (and not including) the last period
|
|
and not including the directory.
|
|
|
|
@item %B
|
|
This is the same as @samp{%b}, but include the file suffix (text after
|
|
the last period).
|
|
|
|
@item %d
|
|
Marks the argument containing or following the @samp{%d} as a
|
|
temporary file name, so that that file is deleted if GCC exits
|
|
successfully. Unlike @samp{%g}, this contributes no text to the
|
|
argument.
|
|
|
|
@item %g@var{suffix}
|
|
Substitute a file name that has suffix @var{suffix} and is chosen
|
|
once per compilation, and mark the argument in the same way as
|
|
@samp{%d}. To reduce exposure to denial-of-service attacks, the file
|
|
name is now chosen in a way that is hard to predict even when previously
|
|
chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s}
|
|
might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches
|
|
the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is
|
|
treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g}
|
|
was simply substituted with a file name chosen once per compilation,
|
|
without regard to any appended suffix (which was therefore treated
|
|
just like ordinary text), making such attacks more likely to succeed.
|
|
|
|
@item %u@var{suffix}
|
|
Like @samp{%g}, but generates a new temporary file name
|
|
each time it appears instead of once per compilation.
|
|
|
|
@item %U@var{suffix}
|
|
Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a
|
|
new one if there is no such last file name. In the absence of any
|
|
@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share
|
|
the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s}
|
|
involves the generation of two distinct file names, one
|
|
for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was
|
|
simply substituted with a file name chosen for the previous @samp{%u},
|
|
without regard to any appended suffix.
|
|
|
|
@item %j@var{suffix}
|
|
Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is
|
|
writable, and if @option{-save-temps} is not used;
|
|
otherwise, substitute the name
|
|
of a temporary file, just like @samp{%u}. This temporary file is not
|
|
meant for communication between processes, but rather as a junk
|
|
disposal mechanism.
|
|
|
|
@item %|@var{suffix}
|
|
@itemx %m@var{suffix}
|
|
Like @samp{%g}, except if @option{-pipe} is in effect. In that case
|
|
@samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at
|
|
all. These are the two most common ways to instruct a program that it
|
|
should read from standard input or write to standard output. If you
|
|
need something more elaborate you can use an @samp{%@{pipe:@code{X}@}}
|
|
construct: see for example @file{f/lang-specs.h}.
|
|
|
|
@item %.@var{SUFFIX}
|
|
Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args
|
|
when it is subsequently output with @samp{%*}. @var{SUFFIX} is
|
|
terminated by the next space or %.
|
|
|
|
@item %w
|
|
Marks the argument containing or following the @samp{%w} as the
|
|
designated output file of this compilation. This puts the argument
|
|
into the sequence of arguments that @samp{%o} substitutes.
|
|
|
|
@item %o
|
|
Substitutes the names of all the output files, with spaces
|
|
automatically placed around them. You should write spaces
|
|
around the @samp{%o} as well or the results are undefined.
|
|
@samp{%o} is for use in the specs for running the linker.
|
|
Input files whose names have no recognized suffix are not compiled
|
|
at all, but they are included among the output files, so they are
|
|
linked.
|
|
|
|
@item %O
|
|
Substitutes the suffix for object files. Note that this is
|
|
handled specially when it immediately follows @samp{%g, %u, or %U},
|
|
because of the need for those to form complete file names. The
|
|
handling is such that @samp{%O} is treated exactly as if it had already
|
|
been substituted, except that @samp{%g, %u, and %U} do not currently
|
|
support additional @var{suffix} characters following @samp{%O} as they do
|
|
following, for example, @samp{.o}.
|
|
|
|
@item %p
|
|
Substitutes the standard macro predefinitions for the
|
|
current target machine. Use this when running @command{cpp}.
|
|
|
|
@item %P
|
|
Like @samp{%p}, but puts @samp{__} before and after the name of each
|
|
predefined macro, except for macros that start with @samp{__} or with
|
|
@samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO
|
|
C@.
|
|
|
|
@item %I
|
|
Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}),
|
|
@option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}),
|
|
@option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options)
|
|
and @option{-imultilib} as necessary.
|
|
|
|
@item %s
|
|
Current argument is the name of a library or startup file of some sort.
|
|
Search for that file in a standard list of directories and substitute
|
|
the full name found. The current working directory is included in the
|
|
list of directories scanned.
|
|
|
|
@item %T
|
|
Current argument is the name of a linker script. Search for that file
|
|
in the current list of directories to scan for libraries. If the file
|
|
is located insert a @option{--script} option into the command line
|
|
followed by the full path name found. If the file is not found then
|
|
generate an error message. Note: the current working directory is not
|
|
searched.
|
|
|
|
@item %e@var{str}
|
|
Print @var{str} as an error message. @var{str} is terminated by a newline.
|
|
Use this when inconsistent options are detected.
|
|
|
|
@item %(@var{name})
|
|
Substitute the contents of spec string @var{name} at this point.
|
|
|
|
@item %x@{@var{option}@}
|
|
Accumulate an option for @samp{%X}.
|
|
|
|
@item %X
|
|
Output the accumulated linker options specified by @option{-Wl} or a @samp{%x}
|
|
spec string.
|
|
|
|
@item %Y
|
|
Output the accumulated assembler options specified by @option{-Wa}.
|
|
|
|
@item %Z
|
|
Output the accumulated preprocessor options specified by @option{-Wp}.
|
|
|
|
@item %a
|
|
Process the @code{asm} spec. This is used to compute the
|
|
switches to be passed to the assembler.
|
|
|
|
@item %A
|
|
Process the @code{asm_final} spec. This is a spec string for
|
|
passing switches to an assembler post-processor, if such a program is
|
|
needed.
|
|
|
|
@item %l
|
|
Process the @code{link} spec. This is the spec for computing the
|
|
command line passed to the linker. Typically it makes use of the
|
|
@samp{%L %G %S %D and %E} sequences.
|
|
|
|
@item %D
|
|
Dump out a @option{-L} option for each directory that GCC believes might
|
|
contain startup files. If the target supports multilibs then the
|
|
current multilib directory is prepended to each of these paths.
|
|
|
|
@item %L
|
|
Process the @code{lib} spec. This is a spec string for deciding which
|
|
libraries are included on the command line to the linker.
|
|
|
|
@item %G
|
|
Process the @code{libgcc} spec. This is a spec string for deciding
|
|
which GCC support library is included on the command line to the linker.
|
|
|
|
@item %S
|
|
Process the @code{startfile} spec. This is a spec for deciding which
|
|
object files are the first ones passed to the linker. Typically
|
|
this might be a file named @file{crt0.o}.
|
|
|
|
@item %E
|
|
Process the @code{endfile} spec. This is a spec string that specifies
|
|
the last object files that are passed to the linker.
|
|
|
|
@item %C
|
|
Process the @code{cpp} spec. This is used to construct the arguments
|
|
to be passed to the C preprocessor.
|
|
|
|
@item %1
|
|
Process the @code{cc1} spec. This is used to construct the options to be
|
|
passed to the actual C compiler (@command{cc1}).
|
|
|
|
@item %2
|
|
Process the @code{cc1plus} spec. This is used to construct the options to be
|
|
passed to the actual C++ compiler (@command{cc1plus}).
|
|
|
|
@item %*
|
|
Substitute the variable part of a matched option. See below.
|
|
Note that each comma in the substituted string is replaced by
|
|
a single space.
|
|
|
|
@item %<@code{S}
|
|
Remove all occurrences of @code{-S} from the command line. Note---this
|
|
command is position dependent. @samp{%} commands in the spec string
|
|
before this one see @code{-S}, @samp{%} commands in the spec string
|
|
after this one do not.
|
|
|
|
@item %:@var{function}(@var{args})
|
|
Call the named function @var{function}, passing it @var{args}.
|
|
@var{args} is first processed as a nested spec string, then split
|
|
into an argument vector in the usual fashion. The function returns
|
|
a string which is processed as if it had appeared literally as part
|
|
of the current spec.
|
|
|
|
The following built-in spec functions are provided:
|
|
|
|
@table @code
|
|
@item @code{getenv}
|
|
The @code{getenv} spec function takes two arguments: an environment
|
|
variable name and a string. If the environment variable is not
|
|
defined, a fatal error is issued. Otherwise, the return value is the
|
|
value of the environment variable concatenated with the string. For
|
|
example, if @env{TOPDIR} is defined as @file{/path/to/top}, then:
|
|
|
|
@smallexample
|
|
%:getenv(TOPDIR /include)
|
|
@end smallexample
|
|
|
|
expands to @file{/path/to/top/include}.
|
|
|
|
@item @code{if-exists}
|
|
The @code{if-exists} spec function takes one argument, an absolute
|
|
pathname to a file. If the file exists, @code{if-exists} returns the
|
|
pathname. Here is a small example of its usage:
|
|
|
|
@smallexample
|
|
*startfile:
|
|
crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
|
|
@end smallexample
|
|
|
|
@item @code{if-exists-else}
|
|
The @code{if-exists-else} spec function is similar to the @code{if-exists}
|
|
spec function, except that it takes two arguments. The first argument is
|
|
an absolute pathname to a file. If the file exists, @code{if-exists-else}
|
|
returns the pathname. If it does not exist, it returns the second argument.
|
|
This way, @code{if-exists-else} can be used to select one file or another,
|
|
based on the existence of the first. Here is a small example of its usage:
|
|
|
|
@smallexample
|
|
*startfile:
|
|
crt0%O%s %:if-exists(crti%O%s) \
|
|
%:if-exists-else(crtbeginT%O%s crtbegin%O%s)
|
|
@end smallexample
|
|
|
|
@item @code{replace-outfile}
|
|
The @code{replace-outfile} spec function takes two arguments. It looks for the
|
|
first argument in the outfiles array and replaces it with the second argument. Here
|
|
is a small example of its usage:
|
|
|
|
@smallexample
|
|
%@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@}
|
|
@end smallexample
|
|
|
|
@item @code{remove-outfile}
|
|
The @code{remove-outfile} spec function takes one argument. It looks for the
|
|
first argument in the outfiles array and removes it. Here is a small example
|
|
its usage:
|
|
|
|
@smallexample
|
|
%:remove-outfile(-lm)
|
|
@end smallexample
|
|
|
|
@item @code{pass-through-libs}
|
|
The @code{pass-through-libs} spec function takes any number of arguments. It
|
|
finds any @option{-l} options and any non-options ending in @file{.a} (which it
|
|
assumes are the names of linker input library archive files) and returns a
|
|
result containing all the found arguments each prepended by
|
|
@option{-plugin-opt=-pass-through=} and joined by spaces. This list is
|
|
intended to be passed to the LTO linker plugin.
|
|
|
|
@smallexample
|
|
%:pass-through-libs(%G %L %G)
|
|
@end smallexample
|
|
|
|
@item @code{print-asm-header}
|
|
The @code{print-asm-header} function takes no arguments and simply
|
|
prints a banner like:
|
|
|
|
@smallexample
|
|
Assembler options
|
|
=================
|
|
|
|
Use "-Wa,OPTION" to pass "OPTION" to the assembler.
|
|
@end smallexample
|
|
|
|
It is used to separate compiler options from assembler options
|
|
in the @option{--target-help} output.
|
|
@end table
|
|
|
|
@item %@{@code{S}@}
|
|
Substitutes the @code{-S} switch, if that switch is given to GCC@.
|
|
If that switch is not specified, this substitutes nothing. Note that
|
|
the leading dash is omitted when specifying this option, and it is
|
|
automatically inserted if the substitution is performed. Thus the spec
|
|
string @samp{%@{foo@}} matches the command-line option @option{-foo}
|
|
and outputs the command-line option @option{-foo}.
|
|
|
|
@item %W@{@code{S}@}
|
|
Like %@{@code{S}@} but mark last argument supplied within as a file to be
|
|
deleted on failure.
|
|
|
|
@item %@{@code{S}*@}
|
|
Substitutes all the switches specified to GCC whose names start
|
|
with @code{-S}, but which also take an argument. This is used for
|
|
switches like @option{-o}, @option{-D}, @option{-I}, etc.
|
|
GCC considers @option{-o foo} as being
|
|
one switch whose name starts with @samp{o}. %@{o*@} substitutes this
|
|
text, including the space. Thus two arguments are generated.
|
|
|
|
@item %@{@code{S}*&@code{T}*@}
|
|
Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options
|
|
(the order of @code{S} and @code{T} in the spec is not significant).
|
|
There can be any number of ampersand-separated variables; for each the
|
|
wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}.
|
|
|
|
@item %@{@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if the @option{-S} switch is given to GCC@.
|
|
|
|
@item %@{!@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@.
|
|
|
|
@item %@{@code{S}*:@code{X}@}
|
|
Substitutes @code{X} if one or more switches whose names start with
|
|
@code{-S} are specified to GCC@. Normally @code{X} is substituted only
|
|
once, no matter how many such switches appeared. However, if @code{%*}
|
|
appears somewhere in @code{X}, then @code{X} is substituted once
|
|
for each matching switch, with the @code{%*} replaced by the part of
|
|
that switch matching the @code{*}.
|
|
|
|
If @code{%*} appears as the last part of a spec sequence then a space
|
|
is added after the end of the last substitution. If there is more
|
|
text in the sequence, however, then a space is not generated. This
|
|
allows the @code{%*} substitution to be used as part of a larger
|
|
string. For example, a spec string like this:
|
|
|
|
@smallexample
|
|
%@{mcu=*:--script=%*/memory.ld@}
|
|
@end smallexample
|
|
|
|
@noindent
|
|
when matching an option like @option{-mcu=newchip} produces:
|
|
|
|
@smallexample
|
|
--script=newchip/memory.ld
|
|
@end smallexample
|
|
|
|
@item %@{.@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if processing a file with suffix @code{S}.
|
|
|
|
@item %@{!.@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}.
|
|
|
|
@item %@{,@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if processing a file for language @code{S}.
|
|
|
|
@item %@{!,@code{S}:@code{X}@}
|
|
Substitutes @code{X}, if not processing a file for language @code{S}.
|
|
|
|
@item %@{@code{S}|@code{P}:@code{X}@}
|
|
Substitutes @code{X} if either @code{-S} or @code{-P} is given to
|
|
GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and
|
|
@code{*} sequences as well, although they have a stronger binding than
|
|
the @samp{|}. If @code{%*} appears in @code{X}, all of the
|
|
alternatives must be starred, and only the first matching alternative
|
|
is substituted.
|
|
|
|
For example, a spec string like this:
|
|
|
|
@smallexample
|
|
%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@}
|
|
@end smallexample
|
|
|
|
@noindent
|
|
outputs the following command-line options from the following input
|
|
command-line options:
|
|
|
|
@smallexample
|
|
fred.c -foo -baz
|
|
jim.d -bar -boggle
|
|
-d fred.c -foo -baz -boggle
|
|
-d jim.d -bar -baz -boggle
|
|
@end smallexample
|
|
|
|
@item %@{S:X; T:Y; :D@}
|
|
|
|
If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is
|
|
given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can
|
|
be as many clauses as you need. This may be combined with @code{.},
|
|
@code{,}, @code{!}, @code{|}, and @code{*} as needed.
|
|
|
|
|
|
@end table
|
|
|
|
The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar
|
|
construct may contain other nested @samp{%} constructs or spaces, or
|
|
even newlines. They are processed as usual, as described above.
|
|
Trailing white space in @code{X} is ignored. White space may also
|
|
appear anywhere on the left side of the colon in these constructs,
|
|
except between @code{.} or @code{*} and the corresponding word.
|
|
|
|
The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are
|
|
handled specifically in these constructs. If another value of
|
|
@option{-O} or the negated form of a @option{-f}, @option{-m}, or
|
|
@option{-W} switch is found later in the command line, the earlier
|
|
switch value is ignored, except with @{@code{S}*@} where @code{S} is
|
|
just one letter, which passes all matching options.
|
|
|
|
The character @samp{|} at the beginning of the predicate text is used to
|
|
indicate that a command should be piped to the following command, but
|
|
only if @option{-pipe} is specified.
|
|
|
|
It is built into GCC which switches take arguments and which do not.
|
|
(You might think it would be useful to generalize this to allow each
|
|
compiler's spec to say which switches take arguments. But this cannot
|
|
be done in a consistent fashion. GCC cannot even decide which input
|
|
files have been specified without knowing which switches take arguments,
|
|
and it must know which input files to compile in order to tell which
|
|
compilers to run).
|
|
|
|
GCC also knows implicitly that arguments starting in @option{-l} are to be
|
|
treated as compiler output files, and passed to the linker in their
|
|
proper position among the other output files.
|
|
|
|
@node Environment Variables
|
|
@section Environment Variables Affecting GCC
|
|
@cindex environment variables
|
|
|
|
@c man begin ENVIRONMENT
|
|
This section describes several environment variables that affect how GCC
|
|
operates. Some of them work by specifying directories or prefixes to use
|
|
when searching for various kinds of files. Some are used to specify other
|
|
aspects of the compilation environment.
|
|
|
|
Note that you can also specify places to search using options such as
|
|
@option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These
|
|
take precedence over places specified using environment variables, which
|
|
in turn take precedence over those specified by the configuration of GCC@.
|
|
@xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint,
|
|
GNU Compiler Collection (GCC) Internals}.
|
|
|
|
@table @env
|
|
@item LANG
|
|
@itemx LC_CTYPE
|
|
@c @itemx LC_COLLATE
|
|
@itemx LC_MESSAGES
|
|
@c @itemx LC_MONETARY
|
|
@c @itemx LC_NUMERIC
|
|
@c @itemx LC_TIME
|
|
@itemx LC_ALL
|
|
@findex LANG
|
|
@findex LC_CTYPE
|
|
@c @findex LC_COLLATE
|
|
@findex LC_MESSAGES
|
|
@c @findex LC_MONETARY
|
|
@c @findex LC_NUMERIC
|
|
@c @findex LC_TIME
|
|
@findex LC_ALL
|
|
@cindex locale
|
|
These environment variables control the way that GCC uses
|
|
localization information which allows GCC to work with different
|
|
national conventions. GCC inspects the locale categories
|
|
@env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do
|
|
so. These locale categories can be set to any value supported by your
|
|
installation. A typical value is @samp{en_GB.UTF-8} for English in the United
|
|
Kingdom encoded in UTF-8.
|
|
|
|
The @env{LC_CTYPE} environment variable specifies character
|
|
classification. GCC uses it to determine the character boundaries in
|
|
a string; this is needed for some multibyte encodings that contain quote
|
|
and escape characters that are otherwise interpreted as a string
|
|
end or escape.
|
|
|
|
The @env{LC_MESSAGES} environment variable specifies the language to
|
|
use in diagnostic messages.
|
|
|
|
If the @env{LC_ALL} environment variable is set, it overrides the value
|
|
of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE}
|
|
and @env{LC_MESSAGES} default to the value of the @env{LANG}
|
|
environment variable. If none of these variables are set, GCC
|
|
defaults to traditional C English behavior.
|
|
|
|
@item TMPDIR
|
|
@findex TMPDIR
|
|
If @env{TMPDIR} is set, it specifies the directory to use for temporary
|
|
files. GCC uses temporary files to hold the output of one stage of
|
|
compilation which is to be used as input to the next stage: for example,
|
|
the output of the preprocessor, which is the input to the compiler
|
|
proper.
|
|
|
|
@item GCC_COMPARE_DEBUG
|
|
@findex GCC_COMPARE_DEBUG
|
|
Setting @env{GCC_COMPARE_DEBUG} is nearly equivalent to passing
|
|
@option{-fcompare-debug} to the compiler driver. See the documentation
|
|
of this option for more details.
|
|
|
|
@item GCC_EXEC_PREFIX
|
|
@findex GCC_EXEC_PREFIX
|
|
If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the
|
|
names of the subprograms executed by the compiler. No slash is added
|
|
when this prefix is combined with the name of a subprogram, but you can
|
|
specify a prefix that ends with a slash if you wish.
|
|
|
|
If @env{GCC_EXEC_PREFIX} is not set, GCC attempts to figure out
|
|
an appropriate prefix to use based on the pathname it is invoked with.
|
|
|
|
If GCC cannot find the subprogram using the specified prefix, it
|
|
tries looking in the usual places for the subprogram.
|
|
|
|
The default value of @env{GCC_EXEC_PREFIX} is
|
|
@file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to
|
|
the installed compiler. In many cases @var{prefix} is the value
|
|
of @code{prefix} when you ran the @file{configure} script.
|
|
|
|
Other prefixes specified with @option{-B} take precedence over this prefix.
|
|
|
|
This prefix is also used for finding files such as @file{crt0.o} that are
|
|
used for linking.
|
|
|
|
In addition, the prefix is used in an unusual way in finding the
|
|
directories to search for header files. For each of the standard
|
|
directories whose name normally begins with @samp{/usr/local/lib/gcc}
|
|
(more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries
|
|
replacing that beginning with the specified prefix to produce an
|
|
alternate directory name. Thus, with @option{-Bfoo/}, GCC searches
|
|
@file{foo/bar} just before it searches the standard directory
|
|
@file{/usr/local/lib/bar}.
|
|
If a standard directory begins with the configured
|
|
@var{prefix} then the value of @var{prefix} is replaced by
|
|
@env{GCC_EXEC_PREFIX} when looking for header files.
|
|
|
|
@item COMPILER_PATH
|
|
@findex COMPILER_PATH
|
|
The value of @env{COMPILER_PATH} is a colon-separated list of
|
|
directories, much like @env{PATH}. GCC tries the directories thus
|
|
specified when searching for subprograms, if it can't find the
|
|
subprograms using @env{GCC_EXEC_PREFIX}.
|
|
|
|
@item LIBRARY_PATH
|
|
@findex LIBRARY_PATH
|
|
The value of @env{LIBRARY_PATH} is a colon-separated list of
|
|
directories, much like @env{PATH}. When configured as a native compiler,
|
|
GCC tries the directories thus specified when searching for special
|
|
linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking
|
|
using GCC also uses these directories when searching for ordinary
|
|
libraries for the @option{-l} option (but directories specified with
|
|
@option{-L} come first).
|
|
|
|
@item LANG
|
|
@findex LANG
|
|
@cindex locale definition
|
|
This variable is used to pass locale information to the compiler. One way in
|
|
which this information is used is to determine the character set to be used
|
|
when character literals, string literals and comments are parsed in C and C++.
|
|
When the compiler is configured to allow multibyte characters,
|
|
the following values for @env{LANG} are recognized:
|
|
|
|
@table @samp
|
|
@item C-JIS
|
|
Recognize JIS characters.
|
|
@item C-SJIS
|
|
Recognize SJIS characters.
|
|
@item C-EUCJP
|
|
Recognize EUCJP characters.
|
|
@end table
|
|
|
|
If @env{LANG} is not defined, or if it has some other value, then the
|
|
compiler uses @code{mblen} and @code{mbtowc} as defined by the default locale to
|
|
recognize and translate multibyte characters.
|
|
@end table
|
|
|
|
@noindent
|
|
Some additional environment variables affect the behavior of the
|
|
preprocessor.
|
|
|
|
@include cppenv.texi
|
|
|
|
@c man end
|
|
|
|
@node Precompiled Headers
|
|
@section Using Precompiled Headers
|
|
@cindex precompiled headers
|
|
@cindex speed of compilation
|
|
|
|
Often large projects have many header files that are included in every
|
|
source file. The time the compiler takes to process these header files
|
|
over and over again can account for nearly all of the time required to
|
|
build the project. To make builds faster, GCC allows you to
|
|
@dfn{precompile} a header file.
|
|
|
|
To create a precompiled header file, simply compile it as you would any
|
|
other file, if necessary using the @option{-x} option to make the driver
|
|
treat it as a C or C++ header file. You may want to use a
|
|
tool like @command{make} to keep the precompiled header up-to-date when
|
|
the headers it contains change.
|
|
|
|
A precompiled header file is searched for when @code{#include} is
|
|
seen in the compilation. As it searches for the included file
|
|
(@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the
|
|
compiler looks for a precompiled header in each directory just before it
|
|
looks for the include file in that directory. The name searched for is
|
|
the name specified in the @code{#include} with @samp{.gch} appended. If
|
|
the precompiled header file can't be used, it is ignored.
|
|
|
|
For instance, if you have @code{#include "all.h"}, and you have
|
|
@file{all.h.gch} in the same directory as @file{all.h}, then the
|
|
precompiled header file is used if possible, and the original
|
|
header is used otherwise.
|
|
|
|
Alternatively, you might decide to put the precompiled header file in a
|
|
directory and use @option{-I} to ensure that directory is searched
|
|
before (or instead of) the directory containing the original header.
|
|
Then, if you want to check that the precompiled header file is always
|
|
used, you can put a file of the same name as the original header in this
|
|
directory containing an @code{#error} command.
|
|
|
|
This also works with @option{-include}. So yet another way to use
|
|
precompiled headers, good for projects not designed with precompiled
|
|
header files in mind, is to simply take most of the header files used by
|
|
a project, include them from another header file, precompile that header
|
|
file, and @option{-include} the precompiled header. If the header files
|
|
have guards against multiple inclusion, they are skipped because
|
|
they've already been included (in the precompiled header).
|
|
|
|
If you need to precompile the same header file for different
|
|
languages, targets, or compiler options, you can instead make a
|
|
@emph{directory} named like @file{all.h.gch}, and put each precompiled
|
|
header in the directory, perhaps using @option{-o}. It doesn't matter
|
|
what you call the files in the directory; every precompiled header in
|
|
the directory is considered. The first precompiled header
|
|
encountered in the directory that is valid for this compilation is
|
|
used; they're searched in no particular order.
|
|
|
|
There are many other possibilities, limited only by your imagination,
|
|
good sense, and the constraints of your build system.
|
|
|
|
A precompiled header file can be used only when these conditions apply:
|
|
|
|
@itemize
|
|
@item
|
|
Only one precompiled header can be used in a particular compilation.
|
|
|
|
@item
|
|
A precompiled header can't be used once the first C token is seen. You
|
|
can have preprocessor directives before a precompiled header; you cannot
|
|
include a precompiled header from inside another header.
|
|
|
|
@item
|
|
The precompiled header file must be produced for the same language as
|
|
the current compilation. You can't use a C precompiled header for a C++
|
|
compilation.
|
|
|
|
@item
|
|
The precompiled header file must have been produced by the same compiler
|
|
binary as the current compilation is using.
|
|
|
|
@item
|
|
Any macros defined before the precompiled header is included must
|
|
either be defined in the same way as when the precompiled header was
|
|
generated, or must not affect the precompiled header, which usually
|
|
means that they don't appear in the precompiled header at all.
|
|
|
|
The @option{-D} option is one way to define a macro before a
|
|
precompiled header is included; using a @code{#define} can also do it.
|
|
There are also some options that define macros implicitly, like
|
|
@option{-O} and @option{-Wdeprecated}; the same rule applies to macros
|
|
defined this way.
|
|
|
|
@item If debugging information is output when using the precompiled
|
|
header, using @option{-g} or similar, the same kind of debugging information
|
|
must have been output when building the precompiled header. However,
|
|
a precompiled header built using @option{-g} can be used in a compilation
|
|
when no debugging information is being output.
|
|
|
|
@item The same @option{-m} options must generally be used when building
|
|
and using the precompiled header. @xref{Submodel Options},
|
|
for any cases where this rule is relaxed.
|
|
|
|
@item Each of the following options must be the same when building and using
|
|
the precompiled header:
|
|
|
|
@gccoptlist{-fexceptions}
|
|
|
|
@item
|
|
Some other command-line options starting with @option{-f},
|
|
@option{-p}, or @option{-O} must be defined in the same way as when
|
|
the precompiled header was generated. At present, it's not clear
|
|
which options are safe to change and which are not; the safest choice
|
|
is to use exactly the same options when generating and using the
|
|
precompiled header. The following are known to be safe:
|
|
|
|
@gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol
|
|
-fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol
|
|
-fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol
|
|
-pedantic-errors}
|
|
|
|
@end itemize
|
|
|
|
For all of these except the last, the compiler automatically
|
|
ignores the precompiled header if the conditions aren't met. If you
|
|
find an option combination that doesn't work and doesn't cause the
|
|
precompiled header to be ignored, please consider filing a bug report,
|
|
see @ref{Bugs}.
|
|
|
|
If you do use differing options when generating and using the
|
|
precompiled header, the actual behavior is a mixture of the
|
|
behavior for the options. For instance, if you use @option{-g} to
|
|
generate the precompiled header but not when using it, you may or may
|
|
not get debugging information for routines in the precompiled header.
|