12611 lines
575 KiB
Plaintext
12611 lines
575 KiB
Plaintext
@c Copyright (C) 1988-2022 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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@node Target Macros
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@chapter Target Description Macros and Functions
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@cindex machine description macros
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@cindex target description macros
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@cindex macros, target description
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@cindex @file{tm.h} macros
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In addition to the file @file{@var{machine}.md}, a machine description
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includes a C header file conventionally given the name
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@file{@var{machine}.h} and a C source file named @file{@var{machine}.c}.
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The header file defines numerous macros that convey the information
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about the target machine that does not fit into the scheme of the
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@file{.md} file. The file @file{tm.h} should be a link to
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@file{@var{machine}.h}. The header file @file{config.h} includes
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@file{tm.h} and most compiler source files include @file{config.h}. The
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source file defines a variable @code{targetm}, which is a structure
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containing pointers to functions and data relating to the target
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machine. @file{@var{machine}.c} should also contain their definitions,
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if they are not defined elsewhere in GCC, and other functions called
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through the macros defined in the @file{.h} file.
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@menu
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* Target Structure:: The @code{targetm} variable.
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* Driver:: Controlling how the driver runs the compilation passes.
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* Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}.
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* Per-Function Data:: Defining data structures for per-function information.
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* Storage Layout:: Defining sizes and alignments of data.
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* Type Layout:: Defining sizes and properties of basic user data types.
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* Registers:: Naming and describing the hardware registers.
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* Register Classes:: Defining the classes of hardware registers.
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* Stack and Calling:: Defining which way the stack grows and by how much.
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* Varargs:: Defining the varargs macros.
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* Trampolines:: Code set up at run time to enter a nested function.
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* Library Calls:: Controlling how library routines are implicitly called.
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* Addressing Modes:: Defining addressing modes valid for memory operands.
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* Anchored Addresses:: Defining how @option{-fsection-anchors} should work.
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* Condition Code:: Defining how insns update the condition code.
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* Costs:: Defining relative costs of different operations.
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* Scheduling:: Adjusting the behavior of the instruction scheduler.
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* Sections:: Dividing storage into text, data, and other sections.
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* PIC:: Macros for position independent code.
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* Assembler Format:: Defining how to write insns and pseudo-ops to output.
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* Debugging Info:: Defining the format of debugging output.
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* Floating Point:: Handling floating point for cross-compilers.
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* Mode Switching:: Insertion of mode-switching instructions.
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* Target Attributes:: Defining target-specific uses of @code{__attribute__}.
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* Emulated TLS:: Emulated TLS support.
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* MIPS Coprocessors:: MIPS coprocessor support and how to customize it.
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* PCH Target:: Validity checking for precompiled headers.
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* C++ ABI:: Controlling C++ ABI changes.
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* D Language and ABI:: Controlling D ABI changes.
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* Named Address Spaces:: Adding support for named address spaces
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* Misc:: Everything else.
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@end menu
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@node Target Structure
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@section The Global @code{targetm} Variable
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@cindex target hooks
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@cindex target functions
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@deftypevar {struct gcc_target} targetm
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The target @file{.c} file must define the global @code{targetm} variable
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which contains pointers to functions and data relating to the target
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machine. The variable is declared in @file{target.h};
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@file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is
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used to initialize the variable, and macros for the default initializers
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for elements of the structure. The @file{.c} file should override those
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macros for which the default definition is inappropriate. For example:
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@smallexample
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#include "target.h"
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#include "target-def.h"
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/* @r{Initialize the GCC target structure.} */
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#undef TARGET_COMP_TYPE_ATTRIBUTES
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#define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes
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struct gcc_target targetm = TARGET_INITIALIZER;
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@end smallexample
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@end deftypevar
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Where a macro should be defined in the @file{.c} file in this manner to
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form part of the @code{targetm} structure, it is documented below as a
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``Target Hook'' with a prototype. Many macros will change in future
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from being defined in the @file{.h} file to being part of the
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@code{targetm} structure.
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Similarly, there is a @code{targetcm} variable for hooks that are
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specific to front ends for C-family languages, documented as ``C
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Target Hook''. This is declared in @file{c-family/c-target.h}, the
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initializer @code{TARGETCM_INITIALIZER} in
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@file{c-family/c-target-def.h}. If targets initialize @code{targetcm}
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themselves, they should set @code{target_has_targetcm=yes} in
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@file{config.gcc}; otherwise a default definition is used.
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Similarly, there is a @code{targetm_common} variable for hooks that
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are shared between the compiler driver and the compilers proper,
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documented as ``Common Target Hook''. This is declared in
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@file{common/common-target.h}, the initializer
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@code{TARGETM_COMMON_INITIALIZER} in
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@file{common/common-target-def.h}. If targets initialize
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@code{targetm_common} themselves, they should set
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@code{target_has_targetm_common=yes} in @file{config.gcc}; otherwise a
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default definition is used.
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Similarly, there is a @code{targetdm} variable for hooks that are
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specific to the D language front end, documented as ``D Target Hook''.
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This is declared in @file{d/d-target.h}, the initializer
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@code{TARGETDM_INITIALIZER} in @file{d/d-target-def.h}. If targets
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initialize @code{targetdm} themselves, they should set
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@code{target_has_targetdm=yes} in @file{config.gcc}; otherwise a default
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definition is used.
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@node Driver
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@section Controlling the Compilation Driver, @file{gcc}
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@cindex driver
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@cindex controlling the compilation driver
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@c prevent bad page break with this line
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You can control the compilation driver.
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@defmac DRIVER_SELF_SPECS
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A list of specs for the driver itself. It should be a suitable
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initializer for an array of strings, with no surrounding braces.
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The driver applies these specs to its own command line between loading
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default @file{specs} files (but not command-line specified ones) and
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choosing the multilib directory or running any subcommands. It
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applies them in the order given, so each spec can depend on the
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options added by earlier ones. It is also possible to remove options
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using @samp{%<@var{option}} in the usual way.
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This macro can be useful when a port has several interdependent target
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options. It provides a way of standardizing the command line so
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that the other specs are easier to write.
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Do not define this macro if it does not need to do anything.
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@end defmac
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@defmac OPTION_DEFAULT_SPECS
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A list of specs used to support configure-time default options (i.e.@:
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@option{--with} options) in the driver. It should be a suitable initializer
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for an array of structures, each containing two strings, without the
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outermost pair of surrounding braces.
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The first item in the pair is the name of the default. This must match
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the code in @file{config.gcc} for the target. The second item is a spec
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to apply if a default with this name was specified. The string
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@samp{%(VALUE)} in the spec will be replaced by the value of the default
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everywhere it occurs.
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The driver will apply these specs to its own command line between loading
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default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using
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the same mechanism as @code{DRIVER_SELF_SPECS}.
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Do not define this macro if it does not need to do anything.
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@end defmac
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@defmac CPP_SPEC
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A C string constant that tells the GCC driver program options to
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pass to CPP@. It can also specify how to translate options you
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give to GCC into options for GCC to pass to the CPP@.
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Do not define this macro if it does not need to do anything.
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@end defmac
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@defmac CPLUSPLUS_CPP_SPEC
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This macro is just like @code{CPP_SPEC}, but is used for C++, rather
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than C@. If you do not define this macro, then the value of
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@code{CPP_SPEC} (if any) will be used instead.
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@end defmac
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@defmac CC1_SPEC
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A C string constant that tells the GCC driver program options to
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pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language
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front ends.
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It can also specify how to translate options you give to GCC into options
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for GCC to pass to front ends.
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Do not define this macro if it does not need to do anything.
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@end defmac
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@defmac CC1PLUS_SPEC
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A C string constant that tells the GCC driver program options to
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pass to @code{cc1plus}. It can also specify how to translate options you
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give to GCC into options for GCC to pass to the @code{cc1plus}.
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Do not define this macro if it does not need to do anything.
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Note that everything defined in CC1_SPEC is already passed to
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@code{cc1plus} so there is no need to duplicate the contents of
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CC1_SPEC in CC1PLUS_SPEC@.
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@end defmac
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@defmac ASM_SPEC
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A C string constant that tells the GCC driver program options to
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pass to the assembler. It can also specify how to translate options
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you give to GCC into options for GCC to pass to the assembler.
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See the file @file{sun3.h} for an example of this.
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Do not define this macro if it does not need to do anything.
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@end defmac
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@defmac ASM_FINAL_SPEC
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A C string constant that tells the GCC driver program how to
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run any programs which cleanup after the normal assembler.
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Normally, this is not needed. See the file @file{mips.h} for
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an example of this.
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Do not define this macro if it does not need to do anything.
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@end defmac
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@defmac AS_NEEDS_DASH_FOR_PIPED_INPUT
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Define this macro, with no value, if the driver should give the assembler
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an argument consisting of a single dash, @option{-}, to instruct it to
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read from its standard input (which will be a pipe connected to the
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output of the compiler proper). This argument is given after any
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@option{-o} option specifying the name of the output file.
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If you do not define this macro, the assembler is assumed to read its
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standard input if given no non-option arguments. If your assembler
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cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct;
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see @file{mips.h} for instance.
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@end defmac
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@defmac LINK_SPEC
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A C string constant that tells the GCC driver program options to
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pass to the linker. It can also specify how to translate options you
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give to GCC into options for GCC to pass to the linker.
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Do not define this macro if it does not need to do anything.
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@end defmac
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@defmac LIB_SPEC
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Another C string constant used much like @code{LINK_SPEC}. The difference
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between the two is that @code{LIB_SPEC} is used at the end of the
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command given to the linker.
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If this macro is not defined, a default is provided that
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loads the standard C library from the usual place. See @file{gcc.cc}.
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@end defmac
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@defmac LIBGCC_SPEC
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Another C string constant that tells the GCC driver program
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how and when to place a reference to @file{libgcc.a} into the
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linker command line. This constant is placed both before and after
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the value of @code{LIB_SPEC}.
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If this macro is not defined, the GCC driver provides a default that
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passes the string @option{-lgcc} to the linker.
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@end defmac
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@defmac REAL_LIBGCC_SPEC
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By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the
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@code{LIBGCC_SPEC} is not directly used by the driver program but is
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instead modified to refer to different versions of @file{libgcc.a}
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depending on the values of the command line flags @option{-static},
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@option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On
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targets where these modifications are inappropriate, define
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@code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the
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driver how to place a reference to @file{libgcc} on the link command
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line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified.
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@end defmac
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@defmac USE_LD_AS_NEEDED
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A macro that controls the modifications to @code{LIBGCC_SPEC}
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mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be
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generated that uses @option{--as-needed} or equivalent options and the
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shared @file{libgcc} in place of the
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static exception handler library, when linking without any of
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@code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}.
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@end defmac
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@defmac LINK_EH_SPEC
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If defined, this C string constant is added to @code{LINK_SPEC}.
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When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects
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the modifications to @code{LIBGCC_SPEC} mentioned in
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@code{REAL_LIBGCC_SPEC}.
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@end defmac
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@defmac STARTFILE_SPEC
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Another C string constant used much like @code{LINK_SPEC}. The
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difference between the two is that @code{STARTFILE_SPEC} is used at
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the very beginning of the command given to the linker.
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If this macro is not defined, a default is provided that loads the
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standard C startup file from the usual place. See @file{gcc.cc}.
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@end defmac
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@defmac ENDFILE_SPEC
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Another C string constant used much like @code{LINK_SPEC}. The
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difference between the two is that @code{ENDFILE_SPEC} is used at
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the very end of the command given to the linker.
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Do not define this macro if it does not need to do anything.
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@end defmac
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@defmac THREAD_MODEL_SPEC
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GCC @code{-v} will print the thread model GCC was configured to use.
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However, this doesn't work on platforms that are multilibbed on thread
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models, such as AIX 4.3. On such platforms, define
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@code{THREAD_MODEL_SPEC} such that it evaluates to a string without
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blanks that names one of the recognized thread models. @code{%*}, the
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default value of this macro, will expand to the value of
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@code{thread_file} set in @file{config.gcc}.
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@end defmac
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@defmac SYSROOT_SUFFIX_SPEC
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Define this macro to add a suffix to the target sysroot when GCC is
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configured with a sysroot. This will cause GCC to search for usr/lib,
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et al, within sysroot+suffix.
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@end defmac
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@defmac SYSROOT_HEADERS_SUFFIX_SPEC
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Define this macro to add a headers_suffix to the target sysroot when
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GCC is configured with a sysroot. This will cause GCC to pass the
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updated sysroot+headers_suffix to CPP, causing it to search for
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usr/include, et al, within sysroot+headers_suffix.
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@end defmac
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@defmac EXTRA_SPECS
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Define this macro to provide additional specifications to put in the
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@file{specs} file that can be used in various specifications like
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@code{CC1_SPEC}.
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The definition should be an initializer for an array of structures,
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containing a string constant, that defines the specification name, and a
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string constant that provides the specification.
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Do not define this macro if it does not need to do anything.
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@code{EXTRA_SPECS} is useful when an architecture contains several
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related targets, which have various @code{@dots{}_SPECS} which are similar
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to each other, and the maintainer would like one central place to keep
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these definitions.
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For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to
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define either @code{_CALL_SYSV} when the System V calling sequence is
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used or @code{_CALL_AIX} when the older AIX-based calling sequence is
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used.
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The @file{config/rs6000/rs6000.h} target file defines:
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@smallexample
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#define EXTRA_SPECS \
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@{ "cpp_sysv_default", CPP_SYSV_DEFAULT @},
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#define CPP_SYS_DEFAULT ""
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@end smallexample
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The @file{config/rs6000/sysv.h} target file defines:
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@smallexample
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#undef CPP_SPEC
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#define CPP_SPEC \
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"%@{posix: -D_POSIX_SOURCE @} \
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%@{mcall-sysv: -D_CALL_SYSV @} \
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%@{!mcall-sysv: %(cpp_sysv_default) @} \
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%@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}"
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#undef CPP_SYSV_DEFAULT
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#define CPP_SYSV_DEFAULT "-D_CALL_SYSV"
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@end smallexample
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while the @file{config/rs6000/eabiaix.h} target file defines
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@code{CPP_SYSV_DEFAULT} as:
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@smallexample
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#undef CPP_SYSV_DEFAULT
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#define CPP_SYSV_DEFAULT "-D_CALL_AIX"
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@end smallexample
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@end defmac
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@defmac LINK_LIBGCC_SPECIAL_1
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Define this macro if the driver program should find the library
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@file{libgcc.a}. If you do not define this macro, the driver program will pass
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the argument @option{-lgcc} to tell the linker to do the search.
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@end defmac
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@defmac LINK_GCC_C_SEQUENCE_SPEC
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The sequence in which libgcc and libc are specified to the linker.
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By default this is @code{%G %L %G}.
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@end defmac
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@defmac POST_LINK_SPEC
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Define this macro to add additional steps to be executed after linker.
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The default value of this macro is empty string.
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@end defmac
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@defmac LINK_COMMAND_SPEC
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A C string constant giving the complete command line need to execute the
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linker. When you do this, you will need to update your port each time a
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change is made to the link command line within @file{gcc.cc}. Therefore,
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define this macro only if you need to completely redefine the command
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line for invoking the linker and there is no other way to accomplish
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the effect you need. Overriding this macro may be avoidable by overriding
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@code{LINK_GCC_C_SEQUENCE_SPEC} instead.
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@end defmac
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@deftypevr {Common Target Hook} bool TARGET_ALWAYS_STRIP_DOTDOT
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True if @file{..} components should always be removed from directory names
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computed relative to GCC's internal directories, false (default) if such
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components should be preserved and directory names containing them passed
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to other tools such as the linker.
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@end deftypevr
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@defmac MULTILIB_DEFAULTS
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Define this macro as a C expression for the initializer of an array of
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string to tell the driver program which options are defaults for this
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target and thus do not need to be handled specially when using
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@code{MULTILIB_OPTIONS}.
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Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in
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the target makefile fragment or if none of the options listed in
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@code{MULTILIB_OPTIONS} are set by default.
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@xref{Target Fragment}.
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@end defmac
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@defmac RELATIVE_PREFIX_NOT_LINKDIR
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Define this macro to tell @command{gcc} that it should only translate
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a @option{-B} prefix into a @option{-L} linker option if the prefix
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indicates an absolute file name.
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@end defmac
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@defmac MD_EXEC_PREFIX
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If defined, this macro is an additional prefix to try after
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@code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched
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when the compiler is built as a cross
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compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it
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to the list of directories used to find the assembler in @file{configure.ac}.
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@end defmac
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@defmac STANDARD_STARTFILE_PREFIX
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Define this macro as a C string constant if you wish to override the
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standard choice of @code{libdir} as the default prefix to
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try when searching for startup files such as @file{crt0.o}.
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@code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler
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is built as a cross compiler.
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@end defmac
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@defmac STANDARD_STARTFILE_PREFIX_1
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|
Define this macro as a C string constant if you wish to override the
|
|
standard choice of @code{/lib} as a prefix to try after the default prefix
|
|
when searching for startup files such as @file{crt0.o}.
|
|
@code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler
|
|
is built as a cross compiler.
|
|
@end defmac
|
|
|
|
@defmac STANDARD_STARTFILE_PREFIX_2
|
|
Define this macro as a C string constant if you wish to override the
|
|
standard choice of @code{/lib} as yet another prefix to try after the
|
|
default prefix when searching for startup files such as @file{crt0.o}.
|
|
@code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler
|
|
is built as a cross compiler.
|
|
@end defmac
|
|
|
|
@defmac MD_STARTFILE_PREFIX
|
|
If defined, this macro supplies an additional prefix to try after the
|
|
standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the
|
|
compiler is built as a cross compiler.
|
|
@end defmac
|
|
|
|
@defmac MD_STARTFILE_PREFIX_1
|
|
If defined, this macro supplies yet another prefix to try after the
|
|
standard prefixes. It is not searched when the compiler is built as a
|
|
cross compiler.
|
|
@end defmac
|
|
|
|
@defmac INIT_ENVIRONMENT
|
|
Define this macro as a C string constant if you wish to set environment
|
|
variables for programs called by the driver, such as the assembler and
|
|
loader. The driver passes the value of this macro to @code{putenv} to
|
|
initialize the necessary environment variables.
|
|
@end defmac
|
|
|
|
@defmac LOCAL_INCLUDE_DIR
|
|
Define this macro as a C string constant if you wish to override the
|
|
standard choice of @file{/usr/local/include} as the default prefix to
|
|
try when searching for local header files. @code{LOCAL_INCLUDE_DIR}
|
|
comes before @code{NATIVE_SYSTEM_HEADER_DIR} (set in
|
|
@file{config.gcc}, normally @file{/usr/include}) in the search order.
|
|
|
|
Cross compilers do not search either @file{/usr/local/include} or its
|
|
replacement.
|
|
@end defmac
|
|
|
|
@defmac NATIVE_SYSTEM_HEADER_COMPONENT
|
|
The ``component'' corresponding to @code{NATIVE_SYSTEM_HEADER_DIR}.
|
|
See @code{INCLUDE_DEFAULTS}, below, for the description of components.
|
|
If you do not define this macro, no component is used.
|
|
@end defmac
|
|
|
|
@defmac INCLUDE_DEFAULTS
|
|
Define this macro if you wish to override the entire default search path
|
|
for include files. For a native compiler, the default search path
|
|
usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR},
|
|
@code{GPLUSPLUS_INCLUDE_DIR}, and
|
|
@code{NATIVE_SYSTEM_HEADER_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR}
|
|
and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile},
|
|
and specify private search areas for GCC@. The directory
|
|
@code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs.
|
|
|
|
The definition should be an initializer for an array of structures.
|
|
Each array element should have four elements: the directory name (a
|
|
string constant), the component name (also a string constant), a flag
|
|
for C++-only directories,
|
|
and a flag showing that the includes in the directory don't need to be
|
|
wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of
|
|
the array with a null element.
|
|
|
|
The component name denotes what GNU package the include file is part of,
|
|
if any, in all uppercase letters. For example, it might be @samp{GCC}
|
|
or @samp{BINUTILS}. If the package is part of a vendor-supplied
|
|
operating system, code the component name as @samp{0}.
|
|
|
|
For example, here is the definition used for VAX/VMS:
|
|
|
|
@smallexample
|
|
#define INCLUDE_DEFAULTS \
|
|
@{ \
|
|
@{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \
|
|
@{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \
|
|
@{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \
|
|
@{ ".", 0, 0, 0@}, \
|
|
@{ 0, 0, 0, 0@} \
|
|
@}
|
|
@end smallexample
|
|
@end defmac
|
|
|
|
Here is the order of prefixes tried for exec files:
|
|
|
|
@enumerate
|
|
@item
|
|
Any prefixes specified by the user with @option{-B}.
|
|
|
|
@item
|
|
The environment variable @code{GCC_EXEC_PREFIX} or, if @code{GCC_EXEC_PREFIX}
|
|
is not set and the compiler has not been installed in the configure-time
|
|
@var{prefix}, the location in which the compiler has actually been installed.
|
|
|
|
@item
|
|
The directories specified by the environment variable @code{COMPILER_PATH}.
|
|
|
|
@item
|
|
The macro @code{STANDARD_EXEC_PREFIX}, if the compiler has been installed
|
|
in the configured-time @var{prefix}.
|
|
|
|
@item
|
|
The location @file{/usr/libexec/gcc/}, but only if this is a native compiler.
|
|
|
|
@item
|
|
The location @file{/usr/lib/gcc/}, but only if this is a native compiler.
|
|
|
|
@item
|
|
The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native
|
|
compiler.
|
|
@end enumerate
|
|
|
|
Here is the order of prefixes tried for startfiles:
|
|
|
|
@enumerate
|
|
@item
|
|
Any prefixes specified by the user with @option{-B}.
|
|
|
|
@item
|
|
The environment variable @code{GCC_EXEC_PREFIX} or its automatically determined
|
|
value based on the installed toolchain location.
|
|
|
|
@item
|
|
The directories specified by the environment variable @code{LIBRARY_PATH}
|
|
(or port-specific name; native only, cross compilers do not use this).
|
|
|
|
@item
|
|
The macro @code{STANDARD_EXEC_PREFIX}, but only if the toolchain is installed
|
|
in the configured @var{prefix} or this is a native compiler.
|
|
|
|
@item
|
|
The location @file{/usr/lib/gcc/}, but only if this is a native compiler.
|
|
|
|
@item
|
|
The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native
|
|
compiler.
|
|
|
|
@item
|
|
The macro @code{MD_STARTFILE_PREFIX}, if defined, but only if this is a
|
|
native compiler, or we have a target system root.
|
|
|
|
@item
|
|
The macro @code{MD_STARTFILE_PREFIX_1}, if defined, but only if this is a
|
|
native compiler, or we have a target system root.
|
|
|
|
@item
|
|
The macro @code{STANDARD_STARTFILE_PREFIX}, with any sysroot modifications.
|
|
If this path is relative it will be prefixed by @code{GCC_EXEC_PREFIX} and
|
|
the machine suffix or @code{STANDARD_EXEC_PREFIX} and the machine suffix.
|
|
|
|
@item
|
|
The macro @code{STANDARD_STARTFILE_PREFIX_1}, but only if this is a native
|
|
compiler, or we have a target system root. The default for this macro is
|
|
@file{/lib/}.
|
|
|
|
@item
|
|
The macro @code{STANDARD_STARTFILE_PREFIX_2}, but only if this is a native
|
|
compiler, or we have a target system root. The default for this macro is
|
|
@file{/usr/lib/}.
|
|
@end enumerate
|
|
|
|
@node Run-time Target
|
|
@section Run-time Target Specification
|
|
@cindex run-time target specification
|
|
@cindex predefined macros
|
|
@cindex target specifications
|
|
|
|
@c prevent bad page break with this line
|
|
Here are run-time target specifications.
|
|
|
|
@defmac TARGET_CPU_CPP_BUILTINS ()
|
|
This function-like macro expands to a block of code that defines
|
|
built-in preprocessor macros and assertions for the target CPU, using
|
|
the functions @code{builtin_define}, @code{builtin_define_std} and
|
|
@code{builtin_assert}. When the front end
|
|
calls this macro it provides a trailing semicolon, and since it has
|
|
finished command line option processing your code can use those
|
|
results freely.
|
|
|
|
@code{builtin_assert} takes a string in the form you pass to the
|
|
command-line option @option{-A}, such as @code{cpu=mips}, and creates
|
|
the assertion. @code{builtin_define} takes a string in the form
|
|
accepted by option @option{-D} and unconditionally defines the macro.
|
|
|
|
@code{builtin_define_std} takes a string representing the name of an
|
|
object-like macro. If it doesn't lie in the user's namespace,
|
|
@code{builtin_define_std} defines it unconditionally. Otherwise, it
|
|
defines a version with two leading underscores, and another version
|
|
with two leading and trailing underscores, and defines the original
|
|
only if an ISO standard was not requested on the command line. For
|
|
example, passing @code{unix} defines @code{__unix}, @code{__unix__}
|
|
and possibly @code{unix}; passing @code{_mips} defines @code{__mips},
|
|
@code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64}
|
|
defines only @code{_ABI64}.
|
|
|
|
You can also test for the C dialect being compiled. The variable
|
|
@code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus}
|
|
or @code{clk_objective_c}. Note that if we are preprocessing
|
|
assembler, this variable will be @code{clk_c} but the function-like
|
|
macro @code{preprocessing_asm_p()} will return true, so you might want
|
|
to check for that first. If you need to check for strict ANSI, the
|
|
variable @code{flag_iso} can be used. The function-like macro
|
|
@code{preprocessing_trad_p()} can be used to check for traditional
|
|
preprocessing.
|
|
@end defmac
|
|
|
|
@defmac TARGET_OS_CPP_BUILTINS ()
|
|
Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
|
|
and is used for the target operating system instead.
|
|
@end defmac
|
|
|
|
@defmac TARGET_OBJFMT_CPP_BUILTINS ()
|
|
Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional
|
|
and is used for the target object format. @file{elfos.h} uses this
|
|
macro to define @code{__ELF__}, so you probably do not need to define
|
|
it yourself.
|
|
@end defmac
|
|
|
|
@deftypevar {extern int} target_flags
|
|
This variable is declared in @file{options.h}, which is included before
|
|
any target-specific headers.
|
|
@end deftypevar
|
|
|
|
@deftypevr {Common Target Hook} int TARGET_DEFAULT_TARGET_FLAGS
|
|
This variable specifies the initial value of @code{target_flags}.
|
|
Its default setting is 0.
|
|
@end deftypevr
|
|
|
|
@cindex optional hardware or system features
|
|
@cindex features, optional, in system conventions
|
|
|
|
@deftypefn {Common Target Hook} bool TARGET_HANDLE_OPTION (struct gcc_options *@var{opts}, struct gcc_options *@var{opts_set}, const struct cl_decoded_option *@var{decoded}, location_t @var{loc})
|
|
This hook is called whenever the user specifies one of the
|
|
target-specific options described by the @file{.opt} definition files
|
|
(@pxref{Options}). It has the opportunity to do some option-specific
|
|
processing and should return true if the option is valid. The default
|
|
definition does nothing but return true.
|
|
|
|
@var{decoded} specifies the option and its arguments. @var{opts} and
|
|
@var{opts_set} are the @code{gcc_options} structures to be used for
|
|
storing option state, and @var{loc} is the location at which the
|
|
option was passed (@code{UNKNOWN_LOCATION} except for options passed
|
|
via attributes).
|
|
@end deftypefn
|
|
|
|
@deftypefn {C Target Hook} bool TARGET_HANDLE_C_OPTION (size_t @var{code}, const char *@var{arg}, int @var{value})
|
|
This target hook is called whenever the user specifies one of the
|
|
target-specific C language family options described by the @file{.opt}
|
|
definition files(@pxref{Options}). It has the opportunity to do some
|
|
option-specific processing and should return true if the option is
|
|
valid. The arguments are like for @code{TARGET_HANDLE_OPTION}. The
|
|
default definition does nothing but return false.
|
|
|
|
In general, you should use @code{TARGET_HANDLE_OPTION} to handle
|
|
options. However, if processing an option requires routines that are
|
|
only available in the C (and related language) front ends, then you
|
|
should use @code{TARGET_HANDLE_C_OPTION} instead.
|
|
@end deftypefn
|
|
|
|
@deftypefn {C Target Hook} tree TARGET_OBJC_CONSTRUCT_STRING_OBJECT (tree @var{string})
|
|
Targets may provide a string object type that can be used within
|
|
and between C, C++ and their respective Objective-C dialects.
|
|
A string object might, for example, embed encoding and length information.
|
|
These objects are considered opaque to the compiler and handled as references.
|
|
An ideal implementation makes the composition of the string object
|
|
match that of the Objective-C @code{NSString} (@code{NXString} for GNUStep),
|
|
allowing efficient interworking between C-only and Objective-C code.
|
|
If a target implements string objects then this hook should return a
|
|
reference to such an object constructed from the normal `C' string
|
|
representation provided in @var{string}.
|
|
At present, the hook is used by Objective-C only, to obtain a
|
|
common-format string object when the target provides one.
|
|
@end deftypefn
|
|
|
|
@deftypefn {C Target Hook} void TARGET_OBJC_DECLARE_UNRESOLVED_CLASS_REFERENCE (const char *@var{classname})
|
|
Declare that Objective C class @var{classname} is referenced
|
|
by the current TU.
|
|
@end deftypefn
|
|
|
|
@deftypefn {C Target Hook} void TARGET_OBJC_DECLARE_CLASS_DEFINITION (const char *@var{classname})
|
|
Declare that Objective C class @var{classname} is defined
|
|
by the current TU.
|
|
@end deftypefn
|
|
|
|
@deftypefn {C Target Hook} bool TARGET_STRING_OBJECT_REF_TYPE_P (const_tree @var{stringref})
|
|
If a target implements string objects then this hook should return
|
|
@code{true} if @var{stringref} is a valid reference to such an object.
|
|
@end deftypefn
|
|
|
|
@deftypefn {C Target Hook} void TARGET_CHECK_STRING_OBJECT_FORMAT_ARG (tree @var{format_arg}, tree @var{args_list})
|
|
If a target implements string objects then this hook should
|
|
provide a facility to check the function arguments in @var{args_list}
|
|
against the format specifiers in @var{format_arg} where the type of
|
|
@var{format_arg} is one recognized as a valid string reference type.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE (void)
|
|
This target function is similar to the hook @code{TARGET_OPTION_OVERRIDE}
|
|
but is called when the optimize level is changed via an attribute or
|
|
pragma or when it is reset at the end of the code affected by the
|
|
attribute or pragma. It is not called at the beginning of compilation
|
|
when @code{TARGET_OPTION_OVERRIDE} is called so if you want to perform these
|
|
actions then, you should have @code{TARGET_OPTION_OVERRIDE} call
|
|
@code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE}.
|
|
@end deftypefn
|
|
|
|
@defmac C_COMMON_OVERRIDE_OPTIONS
|
|
This is similar to the @code{TARGET_OPTION_OVERRIDE} hook
|
|
but is only used in the C
|
|
language frontends (C, Objective-C, C++, Objective-C++) and so can be
|
|
used to alter option flag variables which only exist in those
|
|
frontends.
|
|
@end defmac
|
|
|
|
@deftypevr {Common Target Hook} {const struct default_options *} TARGET_OPTION_OPTIMIZATION_TABLE
|
|
Some machines may desire to change what optimizations are performed for
|
|
various optimization levels. This variable, if defined, describes
|
|
options to enable at particular sets of optimization levels. These
|
|
options are processed once
|
|
just after the optimization level is determined and before the remainder
|
|
of the command options have been parsed, so may be overridden by other
|
|
options passed explicitly.
|
|
|
|
This processing is run once at program startup and when the optimization
|
|
options are changed via @code{#pragma GCC optimize} or by using the
|
|
@code{optimize} attribute.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Common Target Hook} void TARGET_OPTION_INIT_STRUCT (struct gcc_options *@var{opts})
|
|
Set target-dependent initial values of fields in @var{opts}.
|
|
@end deftypefn
|
|
|
|
@defmac SWITCHABLE_TARGET
|
|
Some targets need to switch between substantially different subtargets
|
|
during compilation. For example, the MIPS target has one subtarget for
|
|
the traditional MIPS architecture and another for MIPS16. Source code
|
|
can switch between these two subarchitectures using the @code{mips16}
|
|
and @code{nomips16} attributes.
|
|
|
|
Such subtargets can differ in things like the set of available
|
|
registers, the set of available instructions, the costs of various
|
|
operations, and so on. GCC caches a lot of this type of information
|
|
in global variables, and recomputing them for each subtarget takes a
|
|
significant amount of time. The compiler therefore provides a facility
|
|
for maintaining several versions of the global variables and quickly
|
|
switching between them; see @file{target-globals.h} for details.
|
|
|
|
Define this macro to 1 if your target needs this facility. The default
|
|
is 0.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_FLOAT_EXCEPTIONS_ROUNDING_SUPPORTED_P (void)
|
|
Returns true if the target supports IEEE 754 floating-point exceptions
|
|
and rounding modes, false otherwise. This is intended to relate to the
|
|
@code{float} and @code{double} types, but not necessarily @code{long double}.
|
|
By default, returns true if the @code{adddf3} instruction pattern is
|
|
available and false otherwise, on the assumption that hardware floating
|
|
point supports exceptions and rounding modes but software floating point
|
|
does not.
|
|
@end deftypefn
|
|
|
|
@node Per-Function Data
|
|
@section Defining data structures for per-function information.
|
|
@cindex per-function data
|
|
@cindex data structures
|
|
|
|
If the target needs to store information on a per-function basis, GCC
|
|
provides a macro and a couple of variables to allow this. Note, just
|
|
using statics to store the information is a bad idea, since GCC supports
|
|
nested functions, so you can be halfway through encoding one function
|
|
when another one comes along.
|
|
|
|
GCC defines a data structure called @code{struct function} which
|
|
contains all of the data specific to an individual function. This
|
|
structure contains a field called @code{machine} whose type is
|
|
@code{struct machine_function *}, which can be used by targets to point
|
|
to their own specific data.
|
|
|
|
If a target needs per-function specific data it should define the type
|
|
@code{struct machine_function} and also the macro @code{INIT_EXPANDERS}.
|
|
This macro should be used to initialize the function pointer
|
|
@code{init_machine_status}. This pointer is explained below.
|
|
|
|
One typical use of per-function, target specific data is to create an
|
|
RTX to hold the register containing the function's return address. This
|
|
RTX can then be used to implement the @code{__builtin_return_address}
|
|
function, for level 0.
|
|
|
|
Note---earlier implementations of GCC used a single data area to hold
|
|
all of the per-function information. Thus when processing of a nested
|
|
function began the old per-function data had to be pushed onto a
|
|
stack, and when the processing was finished, it had to be popped off the
|
|
stack. GCC used to provide function pointers called
|
|
@code{save_machine_status} and @code{restore_machine_status} to handle
|
|
the saving and restoring of the target specific information. Since the
|
|
single data area approach is no longer used, these pointers are no
|
|
longer supported.
|
|
|
|
@defmac INIT_EXPANDERS
|
|
Macro called to initialize any target specific information. This macro
|
|
is called once per function, before generation of any RTL has begun.
|
|
The intention of this macro is to allow the initialization of the
|
|
function pointer @code{init_machine_status}.
|
|
@end defmac
|
|
|
|
@deftypevar {void (*)(struct function *)} init_machine_status
|
|
If this function pointer is non-@code{NULL} it will be called once per
|
|
function, before function compilation starts, in order to allow the
|
|
target to perform any target specific initialization of the
|
|
@code{struct function} structure. It is intended that this would be
|
|
used to initialize the @code{machine} of that structure.
|
|
|
|
@code{struct machine_function} structures are expected to be freed by GC@.
|
|
Generally, any memory that they reference must be allocated by using
|
|
GC allocation, including the structure itself.
|
|
@end deftypevar
|
|
|
|
@node Storage Layout
|
|
@section Storage Layout
|
|
@cindex storage layout
|
|
|
|
Note that the definitions of the macros in this table which are sizes or
|
|
alignments measured in bits do not need to be constant. They can be C
|
|
expressions that refer to static variables, such as the @code{target_flags}.
|
|
@xref{Run-time Target}.
|
|
|
|
@defmac BITS_BIG_ENDIAN
|
|
Define this macro to have the value 1 if the most significant bit in a
|
|
byte has the lowest number; otherwise define it to have the value zero.
|
|
This means that bit-field instructions count from the most significant
|
|
bit. If the machine has no bit-field instructions, then this must still
|
|
be defined, but it doesn't matter which value it is defined to. This
|
|
macro need not be a constant.
|
|
|
|
This macro does not affect the way structure fields are packed into
|
|
bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}.
|
|
@end defmac
|
|
|
|
@defmac BYTES_BIG_ENDIAN
|
|
Define this macro to have the value 1 if the most significant byte in a
|
|
word has the lowest number. This macro need not be a constant.
|
|
@end defmac
|
|
|
|
@defmac WORDS_BIG_ENDIAN
|
|
Define this macro to have the value 1 if, in a multiword object, the
|
|
most significant word has the lowest number. This applies to both
|
|
memory locations and registers; see @code{REG_WORDS_BIG_ENDIAN} if the
|
|
order of words in memory is not the same as the order in registers. This
|
|
macro need not be a constant.
|
|
@end defmac
|
|
|
|
@defmac REG_WORDS_BIG_ENDIAN
|
|
On some machines, the order of words in a multiword object differs between
|
|
registers in memory. In such a situation, define this macro to describe
|
|
the order of words in a register. The macro @code{WORDS_BIG_ENDIAN} controls
|
|
the order of words in memory.
|
|
@end defmac
|
|
|
|
@defmac FLOAT_WORDS_BIG_ENDIAN
|
|
Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or
|
|
@code{TFmode} floating point numbers are stored in memory with the word
|
|
containing the sign bit at the lowest address; otherwise define it to
|
|
have the value 0. This macro need not be a constant.
|
|
|
|
You need not define this macro if the ordering is the same as for
|
|
multi-word integers.
|
|
@end defmac
|
|
|
|
@defmac BITS_PER_WORD
|
|
Number of bits in a word. If you do not define this macro, the default
|
|
is @code{BITS_PER_UNIT * UNITS_PER_WORD}.
|
|
@end defmac
|
|
|
|
@defmac MAX_BITS_PER_WORD
|
|
Maximum number of bits in a word. If this is undefined, the default is
|
|
@code{BITS_PER_WORD}. Otherwise, it is the constant value that is the
|
|
largest value that @code{BITS_PER_WORD} can have at run-time.
|
|
@end defmac
|
|
|
|
@defmac UNITS_PER_WORD
|
|
Number of storage units in a word; normally the size of a general-purpose
|
|
register, a power of two from 1 or 8.
|
|
@end defmac
|
|
|
|
@defmac MIN_UNITS_PER_WORD
|
|
Minimum number of units in a word. If this is undefined, the default is
|
|
@code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the
|
|
smallest value that @code{UNITS_PER_WORD} can have at run-time.
|
|
@end defmac
|
|
|
|
@defmac POINTER_SIZE
|
|
Width of a pointer, in bits. You must specify a value no wider than the
|
|
width of @code{Pmode}. If it is not equal to the width of @code{Pmode},
|
|
you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify
|
|
a value the default is @code{BITS_PER_WORD}.
|
|
@end defmac
|
|
|
|
@defmac POINTERS_EXTEND_UNSIGNED
|
|
A C expression that determines how pointers should be extended from
|
|
@code{ptr_mode} to either @code{Pmode} or @code{word_mode}. It is
|
|
greater than zero if pointers should be zero-extended, zero if they
|
|
should be sign-extended, and negative if some other sort of conversion
|
|
is needed. In the last case, the extension is done by the target's
|
|
@code{ptr_extend} instruction.
|
|
|
|
You need not define this macro if the @code{ptr_mode}, @code{Pmode}
|
|
and @code{word_mode} are all the same width.
|
|
@end defmac
|
|
|
|
@defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type})
|
|
A macro to update @var{m} and @var{unsignedp} when an object whose type
|
|
is @var{type} and which has the specified mode and signedness is to be
|
|
stored in a register. This macro is only called when @var{type} is a
|
|
scalar type.
|
|
|
|
On most RISC machines, which only have operations that operate on a full
|
|
register, define this macro to set @var{m} to @code{word_mode} if
|
|
@var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most
|
|
cases, only integer modes should be widened because wider-precision
|
|
floating-point operations are usually more expensive than their narrower
|
|
counterparts.
|
|
|
|
For most machines, the macro definition does not change @var{unsignedp}.
|
|
However, some machines, have instructions that preferentially handle
|
|
either signed or unsigned quantities of certain modes. For example, on
|
|
the DEC Alpha, 32-bit loads from memory and 32-bit add instructions
|
|
sign-extend the result to 64 bits. On such machines, set
|
|
@var{unsignedp} according to which kind of extension is more efficient.
|
|
|
|
Do not define this macro if it would never modify @var{m}.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} {enum flt_eval_method} TARGET_C_EXCESS_PRECISION (enum excess_precision_type @var{type})
|
|
Return a value, with the same meaning as the C99 macro
|
|
@code{FLT_EVAL_METHOD} that describes which excess precision should be
|
|
applied. @var{type} is either @code{EXCESS_PRECISION_TYPE_IMPLICIT},
|
|
@code{EXCESS_PRECISION_TYPE_FAST},
|
|
@code{EXCESS_PRECISION_TYPE_STANDARD}, or
|
|
@code{EXCESS_PRECISION_TYPE_FLOAT16}. For
|
|
@code{EXCESS_PRECISION_TYPE_IMPLICIT}, the target should return which
|
|
precision and range operations will be implictly evaluated in regardless
|
|
of the excess precision explicitly added. For
|
|
@code{EXCESS_PRECISION_TYPE_STANDARD},
|
|
@code{EXCESS_PRECISION_TYPE_FLOAT16}, and
|
|
@code{EXCESS_PRECISION_TYPE_FAST}, the target should return the
|
|
explicit excess precision that should be added depending on the
|
|
value set for @option{-fexcess-precision=@r{[}standard@r{|}fast@r{]}}.
|
|
Note that unpredictable explicit excess precision does not make sense,
|
|
so a target should never return @code{FLT_EVAL_METHOD_UNPREDICTABLE}
|
|
when @var{type} is @code{EXCESS_PRECISION_TYPE_STANDARD},
|
|
@code{EXCESS_PRECISION_TYPE_FLOAT16} or
|
|
@code{EXCESS_PRECISION_TYPE_FAST}.
|
|
@end deftypefn
|
|
Return a value, with the same meaning as the C99 macro
|
|
@code{FLT_EVAL_METHOD} that describes which excess precision should be
|
|
applied.
|
|
|
|
@deftypefn {Target Hook} machine_mode TARGET_PROMOTE_FUNCTION_MODE (const_tree @var{type}, machine_mode @var{mode}, int *@var{punsignedp}, const_tree @var{funtype}, int @var{for_return})
|
|
Like @code{PROMOTE_MODE}, but it is applied to outgoing function arguments or
|
|
function return values. The target hook should return the new mode
|
|
and possibly change @code{*@var{punsignedp}} if the promotion should
|
|
change signedness. This function is called only for scalar @emph{or
|
|
pointer} types.
|
|
|
|
@var{for_return} allows to distinguish the promotion of arguments and
|
|
return values. If it is @code{1}, a return value is being promoted and
|
|
@code{TARGET_FUNCTION_VALUE} must perform the same promotions done here.
|
|
If it is @code{2}, the returned mode should be that of the register in
|
|
which an incoming parameter is copied, or the outgoing result is computed;
|
|
then the hook should return the same mode as @code{promote_mode}, though
|
|
the signedness may be different.
|
|
|
|
@var{type} can be NULL when promoting function arguments of libcalls.
|
|
|
|
The default is to not promote arguments and return values. You can
|
|
also define the hook to @code{default_promote_function_mode_always_promote}
|
|
if you would like to apply the same rules given by @code{PROMOTE_MODE}.
|
|
@end deftypefn
|
|
|
|
@defmac PARM_BOUNDARY
|
|
Normal alignment required for function parameters on the stack, in
|
|
bits. All stack parameters receive at least this much alignment
|
|
regardless of data type. On most machines, this is the same as the
|
|
size of an integer.
|
|
@end defmac
|
|
|
|
@defmac STACK_BOUNDARY
|
|
Define this macro to the minimum alignment enforced by hardware for the
|
|
stack pointer on this machine. The definition is a C expression for the
|
|
desired alignment (measured in bits). This value is used as a default
|
|
if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines,
|
|
this should be the same as @code{PARM_BOUNDARY}.
|
|
@end defmac
|
|
|
|
@defmac PREFERRED_STACK_BOUNDARY
|
|
Define this macro if you wish to preserve a certain alignment for the
|
|
stack pointer, greater than what the hardware enforces. The definition
|
|
is a C expression for the desired alignment (measured in bits). This
|
|
macro must evaluate to a value equal to or larger than
|
|
@code{STACK_BOUNDARY}.
|
|
@end defmac
|
|
|
|
@defmac INCOMING_STACK_BOUNDARY
|
|
Define this macro if the incoming stack boundary may be different
|
|
from @code{PREFERRED_STACK_BOUNDARY}. This macro must evaluate
|
|
to a value equal to or larger than @code{STACK_BOUNDARY}.
|
|
@end defmac
|
|
|
|
@defmac FUNCTION_BOUNDARY
|
|
Alignment required for a function entry point, in bits.
|
|
@end defmac
|
|
|
|
@defmac BIGGEST_ALIGNMENT
|
|
Biggest alignment that any data type can require on this machine, in
|
|
bits. Note that this is not the biggest alignment that is supported,
|
|
just the biggest alignment that, when violated, may cause a fault.
|
|
@end defmac
|
|
|
|
@deftypevr {Target Hook} HOST_WIDE_INT TARGET_ABSOLUTE_BIGGEST_ALIGNMENT
|
|
If defined, this target hook specifies the absolute biggest alignment
|
|
that a type or variable can have on this machine, otherwise,
|
|
@code{BIGGEST_ALIGNMENT} is used.
|
|
@end deftypevr
|
|
|
|
@defmac MALLOC_ABI_ALIGNMENT
|
|
Alignment, in bits, a C conformant malloc implementation has to
|
|
provide. If not defined, the default value is @code{BITS_PER_WORD}.
|
|
@end defmac
|
|
|
|
@defmac ATTRIBUTE_ALIGNED_VALUE
|
|
Alignment used by the @code{__attribute__ ((aligned))} construct. If
|
|
not defined, the default value is @code{BIGGEST_ALIGNMENT}.
|
|
@end defmac
|
|
|
|
@defmac MINIMUM_ATOMIC_ALIGNMENT
|
|
If defined, the smallest alignment, in bits, that can be given to an
|
|
object that can be referenced in one operation, without disturbing any
|
|
nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger
|
|
on machines that don't have byte or half-word store operations.
|
|
@end defmac
|
|
|
|
@defmac BIGGEST_FIELD_ALIGNMENT
|
|
Biggest alignment that any structure or union field can require on this
|
|
machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for
|
|
structure and union fields only, unless the field alignment has been set
|
|
by the @code{__attribute__ ((aligned (@var{n})))} construct.
|
|
@end defmac
|
|
|
|
@defmac ADJUST_FIELD_ALIGN (@var{field}, @var{type}, @var{computed})
|
|
An expression for the alignment of a structure field @var{field} of
|
|
type @var{type} if the alignment computed in the usual way (including
|
|
applying of @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the
|
|
alignment) is @var{computed}. It overrides alignment only if the
|
|
field alignment has not been set by the
|
|
@code{__attribute__ ((aligned (@var{n})))} construct. Note that @var{field}
|
|
may be @code{NULL_TREE} in case we just query for the minimum alignment
|
|
of a field of type @var{type} in structure context.
|
|
@end defmac
|
|
|
|
@defmac MAX_STACK_ALIGNMENT
|
|
Biggest stack alignment guaranteed by the backend. Use this macro
|
|
to specify the maximum alignment of a variable on stack.
|
|
|
|
If not defined, the default value is @code{STACK_BOUNDARY}.
|
|
|
|
@c FIXME: The default should be @code{PREFERRED_STACK_BOUNDARY}.
|
|
@c But the fix for PR 32893 indicates that we can only guarantee
|
|
@c maximum stack alignment on stack up to @code{STACK_BOUNDARY}, not
|
|
@c @code{PREFERRED_STACK_BOUNDARY}, if stack alignment isn't supported.
|
|
@end defmac
|
|
|
|
@defmac MAX_OFILE_ALIGNMENT
|
|
Biggest alignment supported by the object file format of this machine.
|
|
Use this macro to limit the alignment which can be specified using the
|
|
@code{__attribute__ ((aligned (@var{n})))} construct for functions and
|
|
objects with static storage duration. The alignment of automatic
|
|
objects may exceed the object file format maximum up to the maximum
|
|
supported by GCC. If not defined, the default value is
|
|
@code{BIGGEST_ALIGNMENT}.
|
|
|
|
On systems that use ELF, the default (in @file{config/elfos.h}) is
|
|
the largest supported 32-bit ELF section alignment representable on
|
|
a 32-bit host e.g.@: @samp{(((uint64_t) 1 << 28) * 8)}.
|
|
On 32-bit ELF the largest supported section alignment in bits is
|
|
@samp{(0x80000000 * 8)}, but this is not representable on 32-bit hosts.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_LOWER_LOCAL_DECL_ALIGNMENT (tree @var{decl})
|
|
Define this hook to lower alignment of local, parm or result
|
|
decl @samp{(@var{decl})}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} HOST_WIDE_INT TARGET_STATIC_RTX_ALIGNMENT (machine_mode @var{mode})
|
|
This hook returns the preferred alignment in bits for a
|
|
statically-allocated rtx, such as a constant pool entry. @var{mode}
|
|
is the mode of the rtx. The default implementation returns
|
|
@samp{GET_MODE_ALIGNMENT (@var{mode})}.
|
|
@end deftypefn
|
|
|
|
@defmac DATA_ALIGNMENT (@var{type}, @var{basic-align})
|
|
If defined, a C expression to compute the alignment for a variable in
|
|
the static store. @var{type} is the data type, and @var{basic-align} is
|
|
the alignment that the object would ordinarily have. The value of this
|
|
macro is used instead of that alignment to align the object.
|
|
|
|
If this macro is not defined, then @var{basic-align} is used.
|
|
|
|
@findex strcpy
|
|
One use of this macro is to increase alignment of medium-size data to
|
|
make it all fit in fewer cache lines. Another is to cause character
|
|
arrays to be word-aligned so that @code{strcpy} calls that copy
|
|
constants to character arrays can be done inline.
|
|
@end defmac
|
|
|
|
@defmac DATA_ABI_ALIGNMENT (@var{type}, @var{basic-align})
|
|
Similar to @code{DATA_ALIGNMENT}, but for the cases where the ABI mandates
|
|
some alignment increase, instead of optimization only purposes. E.g.@
|
|
AMD x86-64 psABI says that variables with array type larger than 15 bytes
|
|
must be aligned to 16 byte boundaries.
|
|
|
|
If this macro is not defined, then @var{basic-align} is used.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} HOST_WIDE_INT TARGET_CONSTANT_ALIGNMENT (const_tree @var{constant}, HOST_WIDE_INT @var{basic_align})
|
|
This hook returns the alignment in bits of a constant that is being
|
|
placed in memory. @var{constant} is the constant and @var{basic_align}
|
|
is the alignment that the object would ordinarily have.
|
|
|
|
The default definition just returns @var{basic_align}.
|
|
|
|
The typical use of this hook is to increase alignment for string
|
|
constants to be word aligned so that @code{strcpy} calls that copy
|
|
constants can be done inline. The function
|
|
@code{constant_alignment_word_strings} provides such a definition.
|
|
@end deftypefn
|
|
|
|
@defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align})
|
|
If defined, a C expression to compute the alignment for a variable in
|
|
the local store. @var{type} is the data type, and @var{basic-align} is
|
|
the alignment that the object would ordinarily have. The value of this
|
|
macro is used instead of that alignment to align the object.
|
|
|
|
If this macro is not defined, then @var{basic-align} is used.
|
|
|
|
One use of this macro is to increase alignment of medium-size data to
|
|
make it all fit in fewer cache lines.
|
|
|
|
If the value of this macro has a type, it should be an unsigned type.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} HOST_WIDE_INT TARGET_VECTOR_ALIGNMENT (const_tree @var{type})
|
|
This hook can be used to define the alignment for a vector of type
|
|
@var{type}, in order to comply with a platform ABI. The default is to
|
|
require natural alignment for vector types. The alignment returned by
|
|
this hook must be a power-of-two multiple of the default alignment of
|
|
the vector element type.
|
|
@end deftypefn
|
|
|
|
@defmac STACK_SLOT_ALIGNMENT (@var{type}, @var{mode}, @var{basic-align})
|
|
If defined, a C expression to compute the alignment for stack slot.
|
|
@var{type} is the data type, @var{mode} is the widest mode available,
|
|
and @var{basic-align} is the alignment that the slot would ordinarily
|
|
have. The value of this macro is used instead of that alignment to
|
|
align the slot.
|
|
|
|
If this macro is not defined, then @var{basic-align} is used when
|
|
@var{type} is @code{NULL}. Otherwise, @code{LOCAL_ALIGNMENT} will
|
|
be used.
|
|
|
|
This macro is to set alignment of stack slot to the maximum alignment
|
|
of all possible modes which the slot may have.
|
|
|
|
If the value of this macro has a type, it should be an unsigned type.
|
|
@end defmac
|
|
|
|
@defmac LOCAL_DECL_ALIGNMENT (@var{decl})
|
|
If defined, a C expression to compute the alignment for a local
|
|
variable @var{decl}.
|
|
|
|
If this macro is not defined, then
|
|
@code{LOCAL_ALIGNMENT (TREE_TYPE (@var{decl}), DECL_ALIGN (@var{decl}))}
|
|
is used.
|
|
|
|
One use of this macro is to increase alignment of medium-size data to
|
|
make it all fit in fewer cache lines.
|
|
|
|
If the value of this macro has a type, it should be an unsigned type.
|
|
@end defmac
|
|
|
|
@defmac MINIMUM_ALIGNMENT (@var{exp}, @var{mode}, @var{align})
|
|
If defined, a C expression to compute the minimum required alignment
|
|
for dynamic stack realignment purposes for @var{exp} (a type or decl),
|
|
@var{mode}, assuming normal alignment @var{align}.
|
|
|
|
If this macro is not defined, then @var{align} will be used.
|
|
@end defmac
|
|
|
|
@defmac EMPTY_FIELD_BOUNDARY
|
|
Alignment in bits to be given to a structure bit-field that follows an
|
|
empty field such as @code{int : 0;}.
|
|
|
|
If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro.
|
|
@end defmac
|
|
|
|
@defmac STRUCTURE_SIZE_BOUNDARY
|
|
Number of bits which any structure or union's size must be a multiple of.
|
|
Each structure or union's size is rounded up to a multiple of this.
|
|
|
|
If you do not define this macro, the default is the same as
|
|
@code{BITS_PER_UNIT}.
|
|
@end defmac
|
|
|
|
@defmac STRICT_ALIGNMENT
|
|
Define this macro to be the value 1 if instructions will fail to work
|
|
if given data not on the nominal alignment. If instructions will merely
|
|
go slower in that case, define this macro as 0.
|
|
@end defmac
|
|
|
|
@defmac PCC_BITFIELD_TYPE_MATTERS
|
|
Define this if you wish to imitate the way many other C compilers handle
|
|
alignment of bit-fields and the structures that contain them.
|
|
|
|
The behavior is that the type written for a named bit-field (@code{int},
|
|
@code{short}, or other integer type) imposes an alignment for the entire
|
|
structure, as if the structure really did contain an ordinary field of
|
|
that type. In addition, the bit-field is placed within the structure so
|
|
that it would fit within such a field, not crossing a boundary for it.
|
|
|
|
Thus, on most machines, a named bit-field whose type is written as
|
|
@code{int} would not cross a four-byte boundary, and would force
|
|
four-byte alignment for the whole structure. (The alignment used may
|
|
not be four bytes; it is controlled by the other alignment parameters.)
|
|
|
|
An unnamed bit-field will not affect the alignment of the containing
|
|
structure.
|
|
|
|
If the macro is defined, its definition should be a C expression;
|
|
a nonzero value for the expression enables this behavior.
|
|
|
|
Note that if this macro is not defined, or its value is zero, some
|
|
bit-fields may cross more than one alignment boundary. The compiler can
|
|
support such references if there are @samp{insv}, @samp{extv}, and
|
|
@samp{extzv} insns that can directly reference memory.
|
|
|
|
The other known way of making bit-fields work is to define
|
|
@code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}.
|
|
Then every structure can be accessed with fullwords.
|
|
|
|
Unless the machine has bit-field instructions or you define
|
|
@code{STRUCTURE_SIZE_BOUNDARY} that way, you must define
|
|
@code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value.
|
|
|
|
If your aim is to make GCC use the same conventions for laying out
|
|
bit-fields as are used by another compiler, here is how to investigate
|
|
what the other compiler does. Compile and run this program:
|
|
|
|
@smallexample
|
|
struct foo1
|
|
@{
|
|
char x;
|
|
char :0;
|
|
char y;
|
|
@};
|
|
|
|
struct foo2
|
|
@{
|
|
char x;
|
|
int :0;
|
|
char y;
|
|
@};
|
|
|
|
main ()
|
|
@{
|
|
printf ("Size of foo1 is %d\n",
|
|
sizeof (struct foo1));
|
|
printf ("Size of foo2 is %d\n",
|
|
sizeof (struct foo2));
|
|
exit (0);
|
|
@}
|
|
@end smallexample
|
|
|
|
If this prints 2 and 5, then the compiler's behavior is what you would
|
|
get from @code{PCC_BITFIELD_TYPE_MATTERS}.
|
|
@end defmac
|
|
|
|
@defmac BITFIELD_NBYTES_LIMITED
|
|
Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited
|
|
to aligning a bit-field within the structure.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ALIGN_ANON_BITFIELD (void)
|
|
When @code{PCC_BITFIELD_TYPE_MATTERS} is true this hook will determine
|
|
whether unnamed bitfields affect the alignment of the containing
|
|
structure. The hook should return true if the structure should inherit
|
|
the alignment requirements of an unnamed bitfield's type.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_NARROW_VOLATILE_BITFIELD (void)
|
|
This target hook should return @code{true} if accesses to volatile bitfields
|
|
should use the narrowest mode possible. It should return @code{false} if
|
|
these accesses should use the bitfield container type.
|
|
|
|
The default is @code{false}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_MEMBER_TYPE_FORCES_BLK (const_tree @var{field}, machine_mode @var{mode})
|
|
Return true if a structure, union or array containing @var{field} should
|
|
be accessed using @code{BLKMODE}.
|
|
|
|
If @var{field} is the only field in the structure, @var{mode} is its
|
|
mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the
|
|
case where structures of one field would require the structure's mode to
|
|
retain the field's mode.
|
|
|
|
Normally, this is not needed.
|
|
@end deftypefn
|
|
|
|
@defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified})
|
|
Define this macro as an expression for the alignment of a type (given
|
|
by @var{type} as a tree node) if the alignment computed in the usual
|
|
way is @var{computed} and the alignment explicitly specified was
|
|
@var{specified}.
|
|
|
|
The default is to use @var{specified} if it is larger; otherwise, use
|
|
the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT}
|
|
@end defmac
|
|
|
|
@defmac MAX_FIXED_MODE_SIZE
|
|
An integer expression for the size in bits of the largest integer
|
|
machine mode that should actually be used. All integer machine modes of
|
|
this size or smaller can be used for structures and unions with the
|
|
appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE
|
|
(DImode)} is assumed.
|
|
@end defmac
|
|
|
|
@defmac STACK_SAVEAREA_MODE (@var{save_level})
|
|
If defined, an expression of type @code{machine_mode} that
|
|
specifies the mode of the save area operand of a
|
|
@code{save_stack_@var{level}} named pattern (@pxref{Standard Names}).
|
|
@var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or
|
|
@code{SAVE_NONLOCAL} and selects which of the three named patterns is
|
|
having its mode specified.
|
|
|
|
You need not define this macro if it always returns @code{Pmode}. You
|
|
would most commonly define this macro if the
|
|
@code{save_stack_@var{level}} patterns need to support both a 32- and a
|
|
64-bit mode.
|
|
@end defmac
|
|
|
|
@defmac STACK_SIZE_MODE
|
|
If defined, an expression of type @code{machine_mode} that
|
|
specifies the mode of the size increment operand of an
|
|
@code{allocate_stack} named pattern (@pxref{Standard Names}).
|
|
|
|
You need not define this macro if it always returns @code{word_mode}.
|
|
You would most commonly define this macro if the @code{allocate_stack}
|
|
pattern needs to support both a 32- and a 64-bit mode.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} scalar_int_mode TARGET_LIBGCC_CMP_RETURN_MODE (void)
|
|
This target hook should return the mode to be used for the return value
|
|
of compare instructions expanded to libgcc calls. If not defined
|
|
@code{word_mode} is returned which is the right choice for a majority of
|
|
targets.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} scalar_int_mode TARGET_LIBGCC_SHIFT_COUNT_MODE (void)
|
|
This target hook should return the mode to be used for the shift count operand
|
|
of shift instructions expanded to libgcc calls. If not defined
|
|
@code{word_mode} is returned which is the right choice for a majority of
|
|
targets.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} scalar_int_mode TARGET_UNWIND_WORD_MODE (void)
|
|
Return machine mode to be used for @code{_Unwind_Word} type.
|
|
The default is to use @code{word_mode}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (const_tree @var{record_type})
|
|
This target hook returns @code{true} if bit-fields in the given
|
|
@var{record_type} are to be laid out following the rules of Microsoft
|
|
Visual C/C++, namely: (i) a bit-field won't share the same storage
|
|
unit with the previous bit-field if their underlying types have
|
|
different sizes, and the bit-field will be aligned to the highest
|
|
alignment of the underlying types of itself and of the previous
|
|
bit-field; (ii) a zero-sized bit-field will affect the alignment of
|
|
the whole enclosing structure, even if it is unnamed; except that
|
|
(iii) a zero-sized bit-field will be disregarded unless it follows
|
|
another bit-field of nonzero size. If this hook returns @code{true},
|
|
other macros that control bit-field layout are ignored.
|
|
|
|
When a bit-field is inserted into a packed record, the whole size
|
|
of the underlying type is used by one or more same-size adjacent
|
|
bit-fields (that is, if its long:3, 32 bits is used in the record,
|
|
and any additional adjacent long bit-fields are packed into the same
|
|
chunk of 32 bits. However, if the size changes, a new field of that
|
|
size is allocated). In an unpacked record, this is the same as using
|
|
alignment, but not equivalent when packing.
|
|
|
|
If both MS bit-fields and @samp{__attribute__((packed))} are used,
|
|
the latter will take precedence. If @samp{__attribute__((packed))} is
|
|
used on a single field when MS bit-fields are in use, it will take
|
|
precedence for that field, but the alignment of the rest of the structure
|
|
may affect its placement.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_DECIMAL_FLOAT_SUPPORTED_P (void)
|
|
Returns true if the target supports decimal floating point.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_FIXED_POINT_SUPPORTED_P (void)
|
|
Returns true if the target supports fixed-point arithmetic.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_EXPAND_TO_RTL_HOOK (void)
|
|
This hook is called just before expansion into rtl, allowing the target
|
|
to perform additional initializations or analysis before the expansion.
|
|
For example, the rs6000 port uses it to allocate a scratch stack slot
|
|
for use in copying SDmode values between memory and floating point
|
|
registers whenever the function being expanded has any SDmode
|
|
usage.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_INSTANTIATE_DECLS (void)
|
|
This hook allows the backend to perform additional instantiations on rtl
|
|
that are not actually in any insns yet, but will be later.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_MANGLE_TYPE (const_tree @var{type})
|
|
If your target defines any fundamental types, or any types your target
|
|
uses should be mangled differently from the default, define this hook
|
|
to return the appropriate encoding for these types as part of a C++
|
|
mangled name. The @var{type} argument is the tree structure representing
|
|
the type to be mangled. The hook may be applied to trees which are
|
|
not target-specific fundamental types; it should return @code{NULL}
|
|
for all such types, as well as arguments it does not recognize. If the
|
|
return value is not @code{NULL}, it must point to a statically-allocated
|
|
string constant.
|
|
|
|
Target-specific fundamental types might be new fundamental types or
|
|
qualified versions of ordinary fundamental types. Encode new
|
|
fundamental types as @samp{@w{u @var{n} @var{name}}}, where @var{name}
|
|
is the name used for the type in source code, and @var{n} is the
|
|
length of @var{name} in decimal. Encode qualified versions of
|
|
ordinary types as @samp{@w{U @var{n} @var{name} @var{code}}}, where
|
|
@var{name} is the name used for the type qualifier in source code,
|
|
@var{n} is the length of @var{name} as above, and @var{code} is the
|
|
code used to represent the unqualified version of this type. (See
|
|
@code{write_builtin_type} in @file{cp/mangle.cc} for the list of
|
|
codes.) In both cases the spaces are for clarity; do not include any
|
|
spaces in your string.
|
|
|
|
This hook is applied to types prior to typedef resolution. If the mangled
|
|
name for a particular type depends only on that type's main variant, you
|
|
can perform typedef resolution yourself using @code{TYPE_MAIN_VARIANT}
|
|
before mangling.
|
|
|
|
The default version of this hook always returns @code{NULL}, which is
|
|
appropriate for a target that does not define any new fundamental
|
|
types.
|
|
@end deftypefn
|
|
|
|
@node Type Layout
|
|
@section Layout of Source Language Data Types
|
|
|
|
These macros define the sizes and other characteristics of the standard
|
|
basic data types used in programs being compiled. Unlike the macros in
|
|
the previous section, these apply to specific features of C and related
|
|
languages, rather than to fundamental aspects of storage layout.
|
|
|
|
@defmac INT_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{int} on the
|
|
target machine. If you don't define this, the default is one word.
|
|
@end defmac
|
|
|
|
@defmac SHORT_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{short} on the
|
|
target machine. If you don't define this, the default is half a word.
|
|
(If this would be less than one storage unit, it is rounded up to one
|
|
unit.)
|
|
@end defmac
|
|
|
|
@defmac LONG_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{long} on the
|
|
target machine. If you don't define this, the default is one word.
|
|
@end defmac
|
|
|
|
@defmac ADA_LONG_TYPE_SIZE
|
|
On some machines, the size used for the Ada equivalent of the type
|
|
@code{long} by a native Ada compiler differs from that used by C@. In
|
|
that situation, define this macro to be a C expression to be used for
|
|
the size of that type. If you don't define this, the default is the
|
|
value of @code{LONG_TYPE_SIZE}.
|
|
@end defmac
|
|
|
|
@defmac LONG_LONG_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{long long} on the
|
|
target machine. If you don't define this, the default is two
|
|
words. If you want to support GNU Ada on your machine, the value of this
|
|
macro must be at least 64.
|
|
@end defmac
|
|
|
|
@defmac CHAR_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{char} on the
|
|
target machine. If you don't define this, the default is
|
|
@code{BITS_PER_UNIT}.
|
|
@end defmac
|
|
|
|
@defmac BOOL_TYPE_SIZE
|
|
A C expression for the size in bits of the C++ type @code{bool} and
|
|
C99 type @code{_Bool} on the target machine. If you don't define
|
|
this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}.
|
|
@end defmac
|
|
|
|
@defmac FLOAT_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{float} on the
|
|
target machine. If you don't define this, the default is one word.
|
|
@end defmac
|
|
|
|
@defmac DOUBLE_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{double} on the
|
|
target machine. If you don't define this, the default is two
|
|
words.
|
|
@end defmac
|
|
|
|
@defmac LONG_DOUBLE_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{long double} on
|
|
the target machine. If you don't define this, the default is two
|
|
words.
|
|
@end defmac
|
|
|
|
@defmac SHORT_FRACT_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{short _Fract} on
|
|
the target machine. If you don't define this, the default is
|
|
@code{BITS_PER_UNIT}.
|
|
@end defmac
|
|
|
|
@defmac FRACT_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{_Fract} on
|
|
the target machine. If you don't define this, the default is
|
|
@code{BITS_PER_UNIT * 2}.
|
|
@end defmac
|
|
|
|
@defmac LONG_FRACT_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{long _Fract} on
|
|
the target machine. If you don't define this, the default is
|
|
@code{BITS_PER_UNIT * 4}.
|
|
@end defmac
|
|
|
|
@defmac LONG_LONG_FRACT_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{long long _Fract} on
|
|
the target machine. If you don't define this, the default is
|
|
@code{BITS_PER_UNIT * 8}.
|
|
@end defmac
|
|
|
|
@defmac SHORT_ACCUM_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{short _Accum} on
|
|
the target machine. If you don't define this, the default is
|
|
@code{BITS_PER_UNIT * 2}.
|
|
@end defmac
|
|
|
|
@defmac ACCUM_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{_Accum} on
|
|
the target machine. If you don't define this, the default is
|
|
@code{BITS_PER_UNIT * 4}.
|
|
@end defmac
|
|
|
|
@defmac LONG_ACCUM_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{long _Accum} on
|
|
the target machine. If you don't define this, the default is
|
|
@code{BITS_PER_UNIT * 8}.
|
|
@end defmac
|
|
|
|
@defmac LONG_LONG_ACCUM_TYPE_SIZE
|
|
A C expression for the size in bits of the type @code{long long _Accum} on
|
|
the target machine. If you don't define this, the default is
|
|
@code{BITS_PER_UNIT * 16}.
|
|
@end defmac
|
|
|
|
@defmac LIBGCC2_GNU_PREFIX
|
|
This macro corresponds to the @code{TARGET_LIBFUNC_GNU_PREFIX} target
|
|
hook and should be defined if that hook is overriden to be true. It
|
|
causes function names in libgcc to be changed to use a @code{__gnu_}
|
|
prefix for their name rather than the default @code{__}. A port which
|
|
uses this macro should also arrange to use @file{t-gnu-prefix} in
|
|
the libgcc @file{config.host}.
|
|
@end defmac
|
|
|
|
@defmac WIDEST_HARDWARE_FP_SIZE
|
|
A C expression for the size in bits of the widest floating-point format
|
|
supported by the hardware. If you define this macro, you must specify a
|
|
value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}.
|
|
If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE}
|
|
is the default.
|
|
@end defmac
|
|
|
|
@defmac DEFAULT_SIGNED_CHAR
|
|
An expression whose value is 1 or 0, according to whether the type
|
|
@code{char} should be signed or unsigned by default. The user can
|
|
always override this default with the options @option{-fsigned-char}
|
|
and @option{-funsigned-char}.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_DEFAULT_SHORT_ENUMS (void)
|
|
This target hook should return true if the compiler should give an
|
|
@code{enum} type only as many bytes as it takes to represent the range
|
|
of possible values of that type. It should return false if all
|
|
@code{enum} types should be allocated like @code{int}.
|
|
|
|
The default is to return false.
|
|
@end deftypefn
|
|
|
|
@defmac SIZE_TYPE
|
|
A C expression for a string describing the name of the data type to use
|
|
for size values. The typedef name @code{size_t} is defined using the
|
|
contents of the string.
|
|
|
|
The string can contain more than one keyword. If so, separate them with
|
|
spaces, and write first any length keyword, then @code{unsigned} if
|
|
appropriate, and finally @code{int}. The string must exactly match one
|
|
of the data type names defined in the function
|
|
@code{c_common_nodes_and_builtins} in the file @file{c-family/c-common.cc}.
|
|
You may not omit @code{int} or change the order---that would cause the
|
|
compiler to crash on startup.
|
|
|
|
If you don't define this macro, the default is @code{"long unsigned
|
|
int"}.
|
|
@end defmac
|
|
|
|
@defmac SIZETYPE
|
|
GCC defines internal types (@code{sizetype}, @code{ssizetype},
|
|
@code{bitsizetype} and @code{sbitsizetype}) for expressions
|
|
dealing with size. This macro is a C expression for a string describing
|
|
the name of the data type from which the precision of @code{sizetype}
|
|
is extracted.
|
|
|
|
The string has the same restrictions as @code{SIZE_TYPE} string.
|
|
|
|
If you don't define this macro, the default is @code{SIZE_TYPE}.
|
|
@end defmac
|
|
|
|
@defmac PTRDIFF_TYPE
|
|
A C expression for a string describing the name of the data type to use
|
|
for the result of subtracting two pointers. The typedef name
|
|
@code{ptrdiff_t} is defined using the contents of the string. See
|
|
@code{SIZE_TYPE} above for more information.
|
|
|
|
If you don't define this macro, the default is @code{"long int"}.
|
|
@end defmac
|
|
|
|
@defmac WCHAR_TYPE
|
|
A C expression for a string describing the name of the data type to use
|
|
for wide characters. The typedef name @code{wchar_t} is defined using
|
|
the contents of the string. See @code{SIZE_TYPE} above for more
|
|
information.
|
|
|
|
If you don't define this macro, the default is @code{"int"}.
|
|
@end defmac
|
|
|
|
@defmac WCHAR_TYPE_SIZE
|
|
A C expression for the size in bits of the data type for wide
|
|
characters. This is used in @code{cpp}, which cannot make use of
|
|
@code{WCHAR_TYPE}.
|
|
@end defmac
|
|
|
|
@defmac WINT_TYPE
|
|
A C expression for a string describing the name of the data type to
|
|
use for wide characters passed to @code{printf} and returned from
|
|
@code{getwc}. The typedef name @code{wint_t} is defined using the
|
|
contents of the string. See @code{SIZE_TYPE} above for more
|
|
information.
|
|
|
|
If you don't define this macro, the default is @code{"unsigned int"}.
|
|
@end defmac
|
|
|
|
@defmac INTMAX_TYPE
|
|
A C expression for a string describing the name of the data type that
|
|
can represent any value of any standard or extended signed integer type.
|
|
The typedef name @code{intmax_t} is defined using the contents of the
|
|
string. See @code{SIZE_TYPE} above for more information.
|
|
|
|
If you don't define this macro, the default is the first of
|
|
@code{"int"}, @code{"long int"}, or @code{"long long int"} that has as
|
|
much precision as @code{long long int}.
|
|
@end defmac
|
|
|
|
@defmac UINTMAX_TYPE
|
|
A C expression for a string describing the name of the data type that
|
|
can represent any value of any standard or extended unsigned integer
|
|
type. The typedef name @code{uintmax_t} is defined using the contents
|
|
of the string. See @code{SIZE_TYPE} above for more information.
|
|
|
|
If you don't define this macro, the default is the first of
|
|
@code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long
|
|
unsigned int"} that has as much precision as @code{long long unsigned
|
|
int}.
|
|
@end defmac
|
|
|
|
@defmac SIG_ATOMIC_TYPE
|
|
@defmacx INT8_TYPE
|
|
@defmacx INT16_TYPE
|
|
@defmacx INT32_TYPE
|
|
@defmacx INT64_TYPE
|
|
@defmacx UINT8_TYPE
|
|
@defmacx UINT16_TYPE
|
|
@defmacx UINT32_TYPE
|
|
@defmacx UINT64_TYPE
|
|
@defmacx INT_LEAST8_TYPE
|
|
@defmacx INT_LEAST16_TYPE
|
|
@defmacx INT_LEAST32_TYPE
|
|
@defmacx INT_LEAST64_TYPE
|
|
@defmacx UINT_LEAST8_TYPE
|
|
@defmacx UINT_LEAST16_TYPE
|
|
@defmacx UINT_LEAST32_TYPE
|
|
@defmacx UINT_LEAST64_TYPE
|
|
@defmacx INT_FAST8_TYPE
|
|
@defmacx INT_FAST16_TYPE
|
|
@defmacx INT_FAST32_TYPE
|
|
@defmacx INT_FAST64_TYPE
|
|
@defmacx UINT_FAST8_TYPE
|
|
@defmacx UINT_FAST16_TYPE
|
|
@defmacx UINT_FAST32_TYPE
|
|
@defmacx UINT_FAST64_TYPE
|
|
@defmacx INTPTR_TYPE
|
|
@defmacx UINTPTR_TYPE
|
|
C expressions for the standard types @code{sig_atomic_t},
|
|
@code{int8_t}, @code{int16_t}, @code{int32_t}, @code{int64_t},
|
|
@code{uint8_t}, @code{uint16_t}, @code{uint32_t}, @code{uint64_t},
|
|
@code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t},
|
|
@code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t},
|
|
@code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t},
|
|
@code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t},
|
|
@code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t},
|
|
@code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t}. See
|
|
@code{SIZE_TYPE} above for more information.
|
|
|
|
If any of these macros evaluates to a null pointer, the corresponding
|
|
type is not supported; if GCC is configured to provide
|
|
@code{<stdint.h>} in such a case, the header provided may not conform
|
|
to C99, depending on the type in question. The defaults for all of
|
|
these macros are null pointers.
|
|
@end defmac
|
|
|
|
@defmac TARGET_PTRMEMFUNC_VBIT_LOCATION
|
|
The C++ compiler represents a pointer-to-member-function with a struct
|
|
that looks like:
|
|
|
|
@smallexample
|
|
struct @{
|
|
union @{
|
|
void (*fn)();
|
|
ptrdiff_t vtable_index;
|
|
@};
|
|
ptrdiff_t delta;
|
|
@};
|
|
@end smallexample
|
|
|
|
@noindent
|
|
The C++ compiler must use one bit to indicate whether the function that
|
|
will be called through a pointer-to-member-function is virtual.
|
|
Normally, we assume that the low-order bit of a function pointer must
|
|
always be zero. Then, by ensuring that the vtable_index is odd, we can
|
|
distinguish which variant of the union is in use. But, on some
|
|
platforms function pointers can be odd, and so this doesn't work. In
|
|
that case, we use the low-order bit of the @code{delta} field, and shift
|
|
the remainder of the @code{delta} field to the left.
|
|
|
|
GCC will automatically make the right selection about where to store
|
|
this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
|
|
However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
|
|
set such that functions always start at even addresses, but the lowest
|
|
bit of pointers to functions indicate whether the function at that
|
|
address is in ARM or Thumb mode. If this is the case of your
|
|
architecture, you should define this macro to
|
|
@code{ptrmemfunc_vbit_in_delta}.
|
|
|
|
In general, you should not have to define this macro. On architectures
|
|
in which function addresses are always even, according to
|
|
@code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
|
|
@code{ptrmemfunc_vbit_in_pfn}.
|
|
@end defmac
|
|
|
|
@defmac TARGET_VTABLE_USES_DESCRIPTORS
|
|
Normally, the C++ compiler uses function pointers in vtables. This
|
|
macro allows the target to change to use ``function descriptors''
|
|
instead. Function descriptors are found on targets for whom a
|
|
function pointer is actually a small data structure. Normally the
|
|
data structure consists of the actual code address plus a data
|
|
pointer to which the function's data is relative.
|
|
|
|
If vtables are used, the value of this macro should be the number
|
|
of words that the function descriptor occupies.
|
|
@end defmac
|
|
|
|
@defmac TARGET_VTABLE_ENTRY_ALIGN
|
|
By default, the vtable entries are void pointers, the so the alignment
|
|
is the same as pointer alignment. The value of this macro specifies
|
|
the alignment of the vtable entry in bits. It should be defined only
|
|
when special alignment is necessary. */
|
|
@end defmac
|
|
|
|
@defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE
|
|
There are a few non-descriptor entries in the vtable at offsets below
|
|
zero. If these entries must be padded (say, to preserve the alignment
|
|
specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number
|
|
of words in each data entry.
|
|
@end defmac
|
|
|
|
@node Registers
|
|
@section Register Usage
|
|
@cindex register usage
|
|
|
|
This section explains how to describe what registers the target machine
|
|
has, and how (in general) they can be used.
|
|
|
|
The description of which registers a specific instruction can use is
|
|
done with register classes; see @ref{Register Classes}. For information
|
|
on using registers to access a stack frame, see @ref{Frame Registers}.
|
|
For passing values in registers, see @ref{Register Arguments}.
|
|
For returning values in registers, see @ref{Scalar Return}.
|
|
|
|
@menu
|
|
* Register Basics:: Number and kinds of registers.
|
|
* Allocation Order:: Order in which registers are allocated.
|
|
* Values in Registers:: What kinds of values each reg can hold.
|
|
* Leaf Functions:: Renumbering registers for leaf functions.
|
|
* Stack Registers:: Handling a register stack such as 80387.
|
|
@end menu
|
|
|
|
@node Register Basics
|
|
@subsection Basic Characteristics of Registers
|
|
|
|
@c prevent bad page break with this line
|
|
Registers have various characteristics.
|
|
|
|
@defmac FIRST_PSEUDO_REGISTER
|
|
Number of hardware registers known to the compiler. They receive
|
|
numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first
|
|
pseudo register's number really is assigned the number
|
|
@code{FIRST_PSEUDO_REGISTER}.
|
|
@end defmac
|
|
|
|
@defmac FIXED_REGISTERS
|
|
@cindex fixed register
|
|
An initializer that says which registers are used for fixed purposes
|
|
all throughout the compiled code and are therefore not available for
|
|
general allocation. These would include the stack pointer, the frame
|
|
pointer (except on machines where that can be used as a general
|
|
register when no frame pointer is needed), the program counter on
|
|
machines where that is considered one of the addressable registers,
|
|
and any other numbered register with a standard use.
|
|
|
|
This information is expressed as a sequence of numbers, separated by
|
|
commas and surrounded by braces. The @var{n}th number is 1 if
|
|
register @var{n} is fixed, 0 otherwise.
|
|
|
|
The table initialized from this macro, and the table initialized by
|
|
the following one, may be overridden at run time either automatically,
|
|
by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by
|
|
the user with the command options @option{-ffixed-@var{reg}},
|
|
@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}.
|
|
@end defmac
|
|
|
|
@defmac CALL_USED_REGISTERS
|
|
@cindex call-used register
|
|
@cindex call-clobbered register
|
|
@cindex call-saved register
|
|
Like @code{FIXED_REGISTERS} but has 1 for each register that is
|
|
clobbered (in general) by function calls as well as for fixed
|
|
registers. This macro therefore identifies the registers that are not
|
|
available for general allocation of values that must live across
|
|
function calls.
|
|
|
|
If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler
|
|
automatically saves it on function entry and restores it on function
|
|
exit, if the register is used within the function.
|
|
|
|
Exactly one of @code{CALL_USED_REGISTERS} and @code{CALL_REALLY_USED_REGISTERS}
|
|
must be defined. Modern ports should define @code{CALL_REALLY_USED_REGISTERS}.
|
|
@end defmac
|
|
|
|
@defmac CALL_REALLY_USED_REGISTERS
|
|
@cindex call-used register
|
|
@cindex call-clobbered register
|
|
@cindex call-saved register
|
|
Like @code{CALL_USED_REGISTERS} except this macro doesn't require
|
|
that the entire set of @code{FIXED_REGISTERS} be included.
|
|
(@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}).
|
|
|
|
Exactly one of @code{CALL_USED_REGISTERS} and @code{CALL_REALLY_USED_REGISTERS}
|
|
must be defined. Modern ports should define @code{CALL_REALLY_USED_REGISTERS}.
|
|
@end defmac
|
|
|
|
@cindex call-used register
|
|
@cindex call-clobbered register
|
|
@cindex call-saved register
|
|
@deftypefn {Target Hook} {const predefined_function_abi &} TARGET_FNTYPE_ABI (const_tree @var{type})
|
|
Return the ABI used by a function with type @var{type}; see the
|
|
definition of @code{predefined_function_abi} for details of the ABI
|
|
descriptor. Targets only need to define this hook if they support
|
|
interoperability between several ABIs in the same translation unit.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const predefined_function_abi &} TARGET_INSN_CALLEE_ABI (const rtx_insn *@var{insn})
|
|
This hook returns a description of the ABI used by the target of
|
|
call instruction @var{insn}; see the definition of
|
|
@code{predefined_function_abi} for details of the ABI descriptor.
|
|
Only the global function @code{insn_callee_abi} should call this hook
|
|
directly.
|
|
|
|
Targets only need to define this hook if they support
|
|
interoperability between several ABIs in the same translation unit.
|
|
@end deftypefn
|
|
|
|
@cindex call-used register
|
|
@cindex call-clobbered register
|
|
@cindex call-saved register
|
|
@deftypefn {Target Hook} bool TARGET_HARD_REGNO_CALL_PART_CLOBBERED (unsigned int @var{abi_id}, unsigned int @var{regno}, machine_mode @var{mode})
|
|
ABIs usually specify that calls must preserve the full contents
|
|
of a particular register, or that calls can alter any part of a
|
|
particular register. This information is captured by the target macro
|
|
@code{CALL_REALLY_USED_REGISTERS}. However, some ABIs specify that calls
|
|
must preserve certain bits of a particular register but can alter others.
|
|
This hook should return true if this applies to at least one of the
|
|
registers in @samp{(reg:@var{mode} @var{regno})}, and if as a result the
|
|
call would alter part of the @var{mode} value. For example, if a call
|
|
preserves the low 32 bits of a 64-bit hard register @var{regno} but can
|
|
clobber the upper 32 bits, this hook should return true for a 64-bit mode
|
|
but false for a 32-bit mode.
|
|
|
|
The value of @var{abi_id} comes from the @code{predefined_function_abi}
|
|
structure that describes the ABI of the call; see the definition of the
|
|
structure for more details. If (as is usual) the target uses the same ABI
|
|
for all functions in a translation unit, @var{abi_id} is always 0.
|
|
|
|
The default implementation returns false, which is correct
|
|
for targets that don't have partly call-clobbered registers.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_GET_MULTILIB_ABI_NAME (void)
|
|
This hook returns name of multilib ABI name.
|
|
@end deftypefn
|
|
|
|
@findex fixed_regs
|
|
@findex call_used_regs
|
|
@findex global_regs
|
|
@findex reg_names
|
|
@findex reg_class_contents
|
|
@deftypefn {Target Hook} void TARGET_CONDITIONAL_REGISTER_USAGE (void)
|
|
This hook may conditionally modify five variables
|
|
@code{fixed_regs}, @code{call_used_regs}, @code{global_regs},
|
|
@code{reg_names}, and @code{reg_class_contents}, to take into account
|
|
any dependence of these register sets on target flags. The first three
|
|
of these are of type @code{char []} (interpreted as boolean vectors).
|
|
@code{global_regs} is a @code{const char *[]}, and
|
|
@code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is
|
|
called, @code{fixed_regs}, @code{call_used_regs},
|
|
@code{reg_class_contents}, and @code{reg_names} have been initialized
|
|
from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS},
|
|
@code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively.
|
|
@code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}},
|
|
@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}
|
|
command options have been applied.
|
|
|
|
@cindex disabling certain registers
|
|
@cindex controlling register usage
|
|
If the usage of an entire class of registers depends on the target
|
|
flags, you may indicate this to GCC by using this macro to modify
|
|
@code{fixed_regs} and @code{call_used_regs} to 1 for each of the
|
|
registers in the classes which should not be used by GCC@. Also make
|
|
@code{define_register_constraint}s return @code{NO_REGS} for constraints
|
|
that shouldn't be used.
|
|
|
|
(However, if this class is not included in @code{GENERAL_REGS} and all
|
|
of the insn patterns whose constraints permit this class are
|
|
controlled by target switches, then GCC will automatically avoid using
|
|
these registers when the target switches are opposed to them.)
|
|
@end deftypefn
|
|
|
|
@defmac INCOMING_REGNO (@var{out})
|
|
Define this macro if the target machine has register windows. This C
|
|
expression returns the register number as seen by the called function
|
|
corresponding to the register number @var{out} as seen by the calling
|
|
function. Return @var{out} if register number @var{out} is not an
|
|
outbound register.
|
|
@end defmac
|
|
|
|
@defmac OUTGOING_REGNO (@var{in})
|
|
Define this macro if the target machine has register windows. This C
|
|
expression returns the register number as seen by the calling function
|
|
corresponding to the register number @var{in} as seen by the called
|
|
function. Return @var{in} if register number @var{in} is not an inbound
|
|
register.
|
|
@end defmac
|
|
|
|
@defmac LOCAL_REGNO (@var{regno})
|
|
Define this macro if the target machine has register windows. This C
|
|
expression returns true if the register is call-saved but is in the
|
|
register window. Unlike most call-saved registers, such registers
|
|
need not be explicitly restored on function exit or during non-local
|
|
gotos.
|
|
@end defmac
|
|
|
|
@defmac PC_REGNUM
|
|
If the program counter has a register number, define this as that
|
|
register number. Otherwise, do not define it.
|
|
@end defmac
|
|
|
|
@node Allocation Order
|
|
@subsection Order of Allocation of Registers
|
|
@cindex order of register allocation
|
|
@cindex register allocation order
|
|
|
|
@c prevent bad page break with this line
|
|
Registers are allocated in order.
|
|
|
|
@defmac REG_ALLOC_ORDER
|
|
If defined, an initializer for a vector of integers, containing the
|
|
numbers of hard registers in the order in which GCC should prefer
|
|
to use them (from most preferred to least).
|
|
|
|
If this macro is not defined, registers are used lowest numbered first
|
|
(all else being equal).
|
|
|
|
One use of this macro is on machines where the highest numbered
|
|
registers must always be saved and the save-multiple-registers
|
|
instruction supports only sequences of consecutive registers. On such
|
|
machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists
|
|
the highest numbered allocable register first.
|
|
@end defmac
|
|
|
|
@defmac ADJUST_REG_ALLOC_ORDER
|
|
A C statement (sans semicolon) to choose the order in which to allocate
|
|
hard registers for pseudo-registers local to a basic block.
|
|
|
|
Store the desired register order in the array @code{reg_alloc_order}.
|
|
Element 0 should be the register to allocate first; element 1, the next
|
|
register; and so on.
|
|
|
|
The macro body should not assume anything about the contents of
|
|
@code{reg_alloc_order} before execution of the macro.
|
|
|
|
On most machines, it is not necessary to define this macro.
|
|
@end defmac
|
|
|
|
@defmac HONOR_REG_ALLOC_ORDER
|
|
Normally, IRA tries to estimate the costs for saving a register in the
|
|
prologue and restoring it in the epilogue. This discourages it from
|
|
using call-saved registers. If a machine wants to ensure that IRA
|
|
allocates registers in the order given by REG_ALLOC_ORDER even if some
|
|
call-saved registers appear earlier than call-used ones, then define this
|
|
macro as a C expression to nonzero. Default is 0.
|
|
@end defmac
|
|
|
|
@defmac IRA_HARD_REGNO_ADD_COST_MULTIPLIER (@var{regno})
|
|
In some case register allocation order is not enough for the
|
|
Integrated Register Allocator (@acronym{IRA}) to generate a good code.
|
|
If this macro is defined, it should return a floating point value
|
|
based on @var{regno}. The cost of using @var{regno} for a pseudo will
|
|
be increased by approximately the pseudo's usage frequency times the
|
|
value returned by this macro. Not defining this macro is equivalent
|
|
to having it always return @code{0.0}.
|
|
|
|
On most machines, it is not necessary to define this macro.
|
|
@end defmac
|
|
|
|
@node Values in Registers
|
|
@subsection How Values Fit in Registers
|
|
|
|
This section discusses the macros that describe which kinds of values
|
|
(specifically, which machine modes) each register can hold, and how many
|
|
consecutive registers are needed for a given mode.
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_HARD_REGNO_NREGS (unsigned int @var{regno}, machine_mode @var{mode})
|
|
This hook returns the number of consecutive hard registers, starting
|
|
at register number @var{regno}, required to hold a value of mode
|
|
@var{mode}. This hook must never return zero, even if a register
|
|
cannot hold the requested mode - indicate that with
|
|
@code{TARGET_HARD_REGNO_MODE_OK} and/or
|
|
@code{TARGET_CAN_CHANGE_MODE_CLASS} instead.
|
|
|
|
The default definition returns the number of words in @var{mode}.
|
|
@end deftypefn
|
|
|
|
@defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode})
|
|
A C expression that is nonzero if a value of mode @var{mode}, stored
|
|
in memory, ends with padding that causes it to take up more space than
|
|
in registers starting at register number @var{regno} (as determined by
|
|
multiplying GCC's notion of the size of the register when containing
|
|
this mode by the number of registers returned by
|
|
@code{TARGET_HARD_REGNO_NREGS}). By default this is zero.
|
|
|
|
For example, if a floating-point value is stored in three 32-bit
|
|
registers but takes up 128 bits in memory, then this would be
|
|
nonzero.
|
|
|
|
This macros only needs to be defined if there are cases where
|
|
@code{subreg_get_info}
|
|
would otherwise wrongly determine that a @code{subreg} can be
|
|
represented by an offset to the register number, when in fact such a
|
|
@code{subreg} would contain some of the padding not stored in
|
|
registers and so not be representable.
|
|
@end defmac
|
|
|
|
@defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode})
|
|
For values of @var{regno} and @var{mode} for which
|
|
@code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression
|
|
returning the greater number of registers required to hold the value
|
|
including any padding. In the example above, the value would be four.
|
|
@end defmac
|
|
|
|
@defmac REGMODE_NATURAL_SIZE (@var{mode})
|
|
Define this macro if the natural size of registers that hold values
|
|
of mode @var{mode} is not the word size. It is a C expression that
|
|
should give the natural size in bytes for the specified mode. It is
|
|
used by the register allocator to try to optimize its results. This
|
|
happens for example on SPARC 64-bit where the natural size of
|
|
floating-point registers is still 32-bit.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_HARD_REGNO_MODE_OK (unsigned int @var{regno}, machine_mode @var{mode})
|
|
This hook returns true if it is permissible to store a value
|
|
of mode @var{mode} in hard register number @var{regno} (or in several
|
|
registers starting with that one). The default definition returns true
|
|
unconditionally.
|
|
|
|
You need not include code to check for the numbers of fixed registers,
|
|
because the allocation mechanism considers them to be always occupied.
|
|
|
|
@cindex register pairs
|
|
On some machines, double-precision values must be kept in even/odd
|
|
register pairs. You can implement that by defining this hook to reject
|
|
odd register numbers for such modes.
|
|
|
|
The minimum requirement for a mode to be OK in a register is that the
|
|
@samp{mov@var{mode}} instruction pattern support moves between the
|
|
register and other hard register in the same class and that moving a
|
|
value into the register and back out not alter it.
|
|
|
|
Since the same instruction used to move @code{word_mode} will work for
|
|
all narrower integer modes, it is not necessary on any machine for
|
|
this hook to distinguish between these modes, provided you define
|
|
patterns @samp{movhi}, etc., to take advantage of this. This is
|
|
useful because of the interaction between @code{TARGET_HARD_REGNO_MODE_OK}
|
|
and @code{TARGET_MODES_TIEABLE_P}; it is very desirable for all integer
|
|
modes to be tieable.
|
|
|
|
Many machines have special registers for floating point arithmetic.
|
|
Often people assume that floating point machine modes are allowed only
|
|
in floating point registers. This is not true. Any registers that
|
|
can hold integers can safely @emph{hold} a floating point machine
|
|
mode, whether or not floating arithmetic can be done on it in those
|
|
registers. Integer move instructions can be used to move the values.
|
|
|
|
On some machines, though, the converse is true: fixed-point machine
|
|
modes may not go in floating registers. This is true if the floating
|
|
registers normalize any value stored in them, because storing a
|
|
non-floating value there would garble it. In this case,
|
|
@code{TARGET_HARD_REGNO_MODE_OK} should reject fixed-point machine modes in
|
|
floating registers. But if the floating registers do not automatically
|
|
normalize, if you can store any bit pattern in one and retrieve it
|
|
unchanged without a trap, then any machine mode may go in a floating
|
|
register, so you can define this hook to say so.
|
|
|
|
The primary significance of special floating registers is rather that
|
|
they are the registers acceptable in floating point arithmetic
|
|
instructions. However, this is of no concern to
|
|
@code{TARGET_HARD_REGNO_MODE_OK}. You handle it by writing the proper
|
|
constraints for those instructions.
|
|
|
|
On some machines, the floating registers are especially slow to access,
|
|
so that it is better to store a value in a stack frame than in such a
|
|
register if floating point arithmetic is not being done. As long as the
|
|
floating registers are not in class @code{GENERAL_REGS}, they will not
|
|
be used unless some pattern's constraint asks for one.
|
|
@end deftypefn
|
|
|
|
@defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to})
|
|
A C expression that is nonzero if it is OK to rename a hard register
|
|
@var{from} to another hard register @var{to}.
|
|
|
|
One common use of this macro is to prevent renaming of a register to
|
|
another register that is not saved by a prologue in an interrupt
|
|
handler.
|
|
|
|
The default is always nonzero.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_MODES_TIEABLE_P (machine_mode @var{mode1}, machine_mode @var{mode2})
|
|
This hook returns true if a value of mode @var{mode1} is accessible
|
|
in mode @var{mode2} without copying.
|
|
|
|
If @code{TARGET_HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and
|
|
@code{TARGET_HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always
|
|
the same for any @var{r}, then
|
|
@code{TARGET_MODES_TIEABLE_P (@var{mode1}, @var{mode2})}
|
|
should be true. If they differ for any @var{r}, you should define
|
|
this hook to return false unless some other mechanism ensures the
|
|
accessibility of the value in a narrower mode.
|
|
|
|
You should define this hook to return true in as many cases as
|
|
possible since doing so will allow GCC to perform better register
|
|
allocation. The default definition returns true unconditionally.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_HARD_REGNO_SCRATCH_OK (unsigned int @var{regno})
|
|
This target hook should return @code{true} if it is OK to use a hard register
|
|
@var{regno} as scratch reg in peephole2.
|
|
|
|
One common use of this macro is to prevent using of a register that
|
|
is not saved by a prologue in an interrupt handler.
|
|
|
|
The default version of this hook always returns @code{true}.
|
|
@end deftypefn
|
|
|
|
@defmac AVOID_CCMODE_COPIES
|
|
Define this macro if the compiler should avoid copies to/from @code{CCmode}
|
|
registers. You should only define this macro if support for copying to/from
|
|
@code{CCmode} is incomplete.
|
|
@end defmac
|
|
|
|
@node Leaf Functions
|
|
@subsection Handling Leaf Functions
|
|
|
|
@cindex leaf functions
|
|
@cindex functions, leaf
|
|
On some machines, a leaf function (i.e., one which makes no calls) can run
|
|
more efficiently if it does not make its own register window. Often this
|
|
means it is required to receive its arguments in the registers where they
|
|
are passed by the caller, instead of the registers where they would
|
|
normally arrive.
|
|
|
|
The special treatment for leaf functions generally applies only when
|
|
other conditions are met; for example, often they may use only those
|
|
registers for its own variables and temporaries. We use the term ``leaf
|
|
function'' to mean a function that is suitable for this special
|
|
handling, so that functions with no calls are not necessarily ``leaf
|
|
functions''.
|
|
|
|
GCC assigns register numbers before it knows whether the function is
|
|
suitable for leaf function treatment. So it needs to renumber the
|
|
registers in order to output a leaf function. The following macros
|
|
accomplish this.
|
|
|
|
@defmac LEAF_REGISTERS
|
|
Name of a char vector, indexed by hard register number, which
|
|
contains 1 for a register that is allowable in a candidate for leaf
|
|
function treatment.
|
|
|
|
If leaf function treatment involves renumbering the registers, then the
|
|
registers marked here should be the ones before renumbering---those that
|
|
GCC would ordinarily allocate. The registers which will actually be
|
|
used in the assembler code, after renumbering, should not be marked with 1
|
|
in this vector.
|
|
|
|
Define this macro only if the target machine offers a way to optimize
|
|
the treatment of leaf functions.
|
|
@end defmac
|
|
|
|
@defmac LEAF_REG_REMAP (@var{regno})
|
|
A C expression whose value is the register number to which @var{regno}
|
|
should be renumbered, when a function is treated as a leaf function.
|
|
|
|
If @var{regno} is a register number which should not appear in a leaf
|
|
function before renumbering, then the expression should yield @minus{}1, which
|
|
will cause the compiler to abort.
|
|
|
|
Define this macro only if the target machine offers a way to optimize the
|
|
treatment of leaf functions, and registers need to be renumbered to do
|
|
this.
|
|
@end defmac
|
|
|
|
@findex current_function_is_leaf
|
|
@findex current_function_uses_only_leaf_regs
|
|
@code{TARGET_ASM_FUNCTION_PROLOGUE} and
|
|
@code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions
|
|
specially. They can test the C variable @code{current_function_is_leaf}
|
|
which is nonzero for leaf functions. @code{current_function_is_leaf} is
|
|
set prior to local register allocation and is valid for the remaining
|
|
compiler passes. They can also test the C variable
|
|
@code{current_function_uses_only_leaf_regs} which is nonzero for leaf
|
|
functions which only use leaf registers.
|
|
@code{current_function_uses_only_leaf_regs} is valid after all passes
|
|
that modify the instructions have been run and is only useful if
|
|
@code{LEAF_REGISTERS} is defined.
|
|
@c changed this to fix overfull. ALSO: why the "it" at the beginning
|
|
@c of the next paragraph?! --mew 2feb93
|
|
|
|
@node Stack Registers
|
|
@subsection Registers That Form a Stack
|
|
|
|
There are special features to handle computers where some of the
|
|
``registers'' form a stack. Stack registers are normally written by
|
|
pushing onto the stack, and are numbered relative to the top of the
|
|
stack.
|
|
|
|
Currently, GCC can only handle one group of stack-like registers, and
|
|
they must be consecutively numbered. Furthermore, the existing
|
|
support for stack-like registers is specific to the 80387 floating
|
|
point coprocessor. If you have a new architecture that uses
|
|
stack-like registers, you will need to do substantial work on
|
|
@file{reg-stack.cc} and write your machine description to cooperate
|
|
with it, as well as defining these macros.
|
|
|
|
@defmac STACK_REGS
|
|
Define this if the machine has any stack-like registers.
|
|
@end defmac
|
|
|
|
@defmac STACK_REG_COVER_CLASS
|
|
This is a cover class containing the stack registers. Define this if
|
|
the machine has any stack-like registers.
|
|
@end defmac
|
|
|
|
@defmac FIRST_STACK_REG
|
|
The number of the first stack-like register. This one is the top
|
|
of the stack.
|
|
@end defmac
|
|
|
|
@defmac LAST_STACK_REG
|
|
The number of the last stack-like register. This one is the bottom of
|
|
the stack.
|
|
@end defmac
|
|
|
|
@node Register Classes
|
|
@section Register Classes
|
|
@cindex register class definitions
|
|
@cindex class definitions, register
|
|
|
|
On many machines, the numbered registers are not all equivalent.
|
|
For example, certain registers may not be allowed for indexed addressing;
|
|
certain registers may not be allowed in some instructions. These machine
|
|
restrictions are described to the compiler using @dfn{register classes}.
|
|
|
|
You define a number of register classes, giving each one a name and saying
|
|
which of the registers belong to it. Then you can specify register classes
|
|
that are allowed as operands to particular instruction patterns.
|
|
|
|
@findex ALL_REGS
|
|
@findex NO_REGS
|
|
In general, each register will belong to several classes. In fact, one
|
|
class must be named @code{ALL_REGS} and contain all the registers. Another
|
|
class must be named @code{NO_REGS} and contain no registers. Often the
|
|
union of two classes will be another class; however, this is not required.
|
|
|
|
@findex GENERAL_REGS
|
|
One of the classes must be named @code{GENERAL_REGS}. There is nothing
|
|
terribly special about the name, but the operand constraint letters
|
|
@samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is
|
|
the same as @code{ALL_REGS}, just define it as a macro which expands
|
|
to @code{ALL_REGS}.
|
|
|
|
Order the classes so that if class @var{x} is contained in class @var{y}
|
|
then @var{x} has a lower class number than @var{y}.
|
|
|
|
The way classes other than @code{GENERAL_REGS} are specified in operand
|
|
constraints is through machine-dependent operand constraint letters.
|
|
You can define such letters to correspond to various classes, then use
|
|
them in operand constraints.
|
|
|
|
You must define the narrowest register classes for allocatable
|
|
registers, so that each class either has no subclasses, or that for
|
|
some mode, the move cost between registers within the class is
|
|
cheaper than moving a register in the class to or from memory
|
|
(@pxref{Costs}).
|
|
|
|
You should define a class for the union of two classes whenever some
|
|
instruction allows both classes. For example, if an instruction allows
|
|
either a floating point (coprocessor) register or a general register for a
|
|
certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS}
|
|
which includes both of them. Otherwise you will get suboptimal code,
|
|
or even internal compiler errors when reload cannot find a register in the
|
|
class computed via @code{reg_class_subunion}.
|
|
|
|
You must also specify certain redundant information about the register
|
|
classes: for each class, which classes contain it and which ones are
|
|
contained in it; for each pair of classes, the largest class contained
|
|
in their union.
|
|
|
|
When a value occupying several consecutive registers is expected in a
|
|
certain class, all the registers used must belong to that class.
|
|
Therefore, register classes cannot be used to enforce a requirement for
|
|
a register pair to start with an even-numbered register. The way to
|
|
specify this requirement is with @code{TARGET_HARD_REGNO_MODE_OK}.
|
|
|
|
Register classes used for input-operands of bitwise-and or shift
|
|
instructions have a special requirement: each such class must have, for
|
|
each fixed-point machine mode, a subclass whose registers can transfer that
|
|
mode to or from memory. For example, on some machines, the operations for
|
|
single-byte values (@code{QImode}) are limited to certain registers. When
|
|
this is so, each register class that is used in a bitwise-and or shift
|
|
instruction must have a subclass consisting of registers from which
|
|
single-byte values can be loaded or stored. This is so that
|
|
@code{PREFERRED_RELOAD_CLASS} can always have a possible value to return.
|
|
|
|
@deftp {Data type} {enum reg_class}
|
|
An enumerated type that must be defined with all the register class names
|
|
as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS}
|
|
must be the last register class, followed by one more enumerated value,
|
|
@code{LIM_REG_CLASSES}, which is not a register class but rather
|
|
tells how many classes there are.
|
|
|
|
Each register class has a number, which is the value of casting
|
|
the class name to type @code{int}. The number serves as an index
|
|
in many of the tables described below.
|
|
@end deftp
|
|
|
|
@defmac N_REG_CLASSES
|
|
The number of distinct register classes, defined as follows:
|
|
|
|
@smallexample
|
|
#define N_REG_CLASSES (int) LIM_REG_CLASSES
|
|
@end smallexample
|
|
@end defmac
|
|
|
|
@defmac REG_CLASS_NAMES
|
|
An initializer containing the names of the register classes as C string
|
|
constants. These names are used in writing some of the debugging dumps.
|
|
@end defmac
|
|
|
|
@defmac REG_CLASS_CONTENTS
|
|
An initializer containing the contents of the register classes, as integers
|
|
which are bit masks. The @var{n}th integer specifies the contents of class
|
|
@var{n}. The way the integer @var{mask} is interpreted is that
|
|
register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1.
|
|
|
|
When the machine has more than 32 registers, an integer does not suffice.
|
|
Then the integers are replaced by sub-initializers, braced groupings containing
|
|
several integers. Each sub-initializer must be suitable as an initializer
|
|
for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}.
|
|
In this situation, the first integer in each sub-initializer corresponds to
|
|
registers 0 through 31, the second integer to registers 32 through 63, and
|
|
so on.
|
|
@end defmac
|
|
|
|
@defmac REGNO_REG_CLASS (@var{regno})
|
|
A C expression whose value is a register class containing hard register
|
|
@var{regno}. In general there is more than one such class; choose a class
|
|
which is @dfn{minimal}, meaning that no smaller class also contains the
|
|
register.
|
|
@end defmac
|
|
|
|
@defmac BASE_REG_CLASS
|
|
A macro whose definition is the name of the class to which a valid
|
|
base register must belong. A base register is one used in an address
|
|
which is the register value plus a displacement.
|
|
@end defmac
|
|
|
|
@defmac MODE_BASE_REG_CLASS (@var{mode})
|
|
This is a variation of the @code{BASE_REG_CLASS} macro which allows
|
|
the selection of a base register in a mode dependent manner. If
|
|
@var{mode} is VOIDmode then it should return the same value as
|
|
@code{BASE_REG_CLASS}.
|
|
@end defmac
|
|
|
|
@defmac MODE_BASE_REG_REG_CLASS (@var{mode})
|
|
A C expression whose value is the register class to which a valid
|
|
base register must belong in order to be used in a base plus index
|
|
register address. You should define this macro if base plus index
|
|
addresses have different requirements than other base register uses.
|
|
@end defmac
|
|
|
|
@defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{address_space}, @var{outer_code}, @var{index_code})
|
|
A C expression whose value is the register class to which a valid
|
|
base register for a memory reference in mode @var{mode} to address
|
|
space @var{address_space} must belong. @var{outer_code} and @var{index_code}
|
|
define the context in which the base register occurs. @var{outer_code} is
|
|
the code of the immediately enclosing expression (@code{MEM} for the top level
|
|
of an address, @code{ADDRESS} for something that occurs in an
|
|
@code{address_operand}). @var{index_code} is the code of the corresponding
|
|
index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise.
|
|
@end defmac
|
|
|
|
@defmac INDEX_REG_CLASS
|
|
A macro whose definition is the name of the class to which a valid
|
|
index register must belong. An index register is one used in an
|
|
address where its value is either multiplied by a scale factor or
|
|
added to another register (as well as added to a displacement).
|
|
@end defmac
|
|
|
|
@defmac REGNO_OK_FOR_BASE_P (@var{num})
|
|
A C expression which is nonzero if register number @var{num} is
|
|
suitable for use as a base register in operand addresses.
|
|
@end defmac
|
|
|
|
@defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode})
|
|
A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that
|
|
that expression may examine the mode of the memory reference in
|
|
@var{mode}. You should define this macro if the mode of the memory
|
|
reference affects whether a register may be used as a base register. If
|
|
you define this macro, the compiler will use it instead of
|
|
@code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for
|
|
addresses that appear outside a @code{MEM}, i.e., as an
|
|
@code{address_operand}.
|
|
@end defmac
|
|
|
|
@defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode})
|
|
A C expression which is nonzero if register number @var{num} is suitable for
|
|
use as a base register in base plus index operand addresses, accessing
|
|
memory in mode @var{mode}. It may be either a suitable hard register or a
|
|
pseudo register that has been allocated such a hard register. You should
|
|
define this macro if base plus index addresses have different requirements
|
|
than other base register uses.
|
|
|
|
Use of this macro is deprecated; please use the more general
|
|
@code{REGNO_MODE_CODE_OK_FOR_BASE_P}.
|
|
@end defmac
|
|
|
|
@defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{address_space}, @var{outer_code}, @var{index_code})
|
|
A C expression which is nonzero if register number @var{num} is
|
|
suitable for use as a base register in operand addresses, accessing
|
|
memory in mode @var{mode} in address space @var{address_space}.
|
|
This is similar to @code{REGNO_MODE_OK_FOR_BASE_P}, except
|
|
that that expression may examine the context in which the register
|
|
appears in the memory reference. @var{outer_code} is the code of the
|
|
immediately enclosing expression (@code{MEM} if at the top level of the
|
|
address, @code{ADDRESS} for something that occurs in an
|
|
@code{address_operand}). @var{index_code} is the code of the
|
|
corresponding index expression if @var{outer_code} is @code{PLUS};
|
|
@code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses
|
|
that appear outside a @code{MEM}, i.e., as an @code{address_operand}.
|
|
@end defmac
|
|
|
|
@defmac REGNO_OK_FOR_INDEX_P (@var{num})
|
|
A C expression which is nonzero if register number @var{num} is
|
|
suitable for use as an index register in operand addresses. It may be
|
|
either a suitable hard register or a pseudo register that has been
|
|
allocated such a hard register.
|
|
|
|
The difference between an index register and a base register is that
|
|
the index register may be scaled. If an address involves the sum of
|
|
two registers, neither one of them scaled, then either one may be
|
|
labeled the ``base'' and the other the ``index''; but whichever
|
|
labeling is used must fit the machine's constraints of which registers
|
|
may serve in each capacity. The compiler will try both labelings,
|
|
looking for one that is valid, and will reload one or both registers
|
|
only if neither labeling works.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} reg_class_t TARGET_PREFERRED_RENAME_CLASS (reg_class_t @var{rclass})
|
|
A target hook that places additional preference on the register
|
|
class to use when it is necessary to rename a register in class
|
|
@var{rclass} to another class, or perhaps @var{NO_REGS}, if no
|
|
preferred register class is found or hook @code{preferred_rename_class}
|
|
is not implemented.
|
|
Sometimes returning a more restrictive class makes better code. For
|
|
example, on ARM, thumb-2 instructions using @code{LO_REGS} may be
|
|
smaller than instructions using @code{GENERIC_REGS}. By returning
|
|
@code{LO_REGS} from @code{preferred_rename_class}, code size can
|
|
be reduced.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} reg_class_t TARGET_PREFERRED_RELOAD_CLASS (rtx @var{x}, reg_class_t @var{rclass})
|
|
A target hook that places additional restrictions on the register class
|
|
to use when it is necessary to copy value @var{x} into a register in class
|
|
@var{rclass}. The value is a register class; perhaps @var{rclass}, or perhaps
|
|
another, smaller class.
|
|
|
|
The default version of this hook always returns value of @code{rclass} argument.
|
|
|
|
Sometimes returning a more restrictive class makes better code. For
|
|
example, on the 68000, when @var{x} is an integer constant that is in range
|
|
for a @samp{moveq} instruction, the value of this macro is always
|
|
@code{DATA_REGS} as long as @var{rclass} includes the data registers.
|
|
Requiring a data register guarantees that a @samp{moveq} will be used.
|
|
|
|
One case where @code{TARGET_PREFERRED_RELOAD_CLASS} must not return
|
|
@var{rclass} is if @var{x} is a legitimate constant which cannot be
|
|
loaded into some register class. By returning @code{NO_REGS} you can
|
|
force @var{x} into a memory location. For example, rs6000 can load
|
|
immediate values into general-purpose registers, but does not have an
|
|
instruction for loading an immediate value into a floating-point
|
|
register, so @code{TARGET_PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
|
|
@var{x} is a floating-point constant. If the constant can't be loaded
|
|
into any kind of register, code generation will be better if
|
|
@code{TARGET_LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
|
|
of using @code{TARGET_PREFERRED_RELOAD_CLASS}.
|
|
|
|
If an insn has pseudos in it after register allocation, reload will go
|
|
through the alternatives and call repeatedly @code{TARGET_PREFERRED_RELOAD_CLASS}
|
|
to find the best one. Returning @code{NO_REGS}, in this case, makes
|
|
reload add a @code{!} in front of the constraint: the x86 back-end uses
|
|
this feature to discourage usage of 387 registers when math is done in
|
|
the SSE registers (and vice versa).
|
|
@end deftypefn
|
|
|
|
@defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class})
|
|
A C expression that places additional restrictions on the register class
|
|
to use when it is necessary to copy value @var{x} into a register in class
|
|
@var{class}. The value is a register class; perhaps @var{class}, or perhaps
|
|
another, smaller class. On many machines, the following definition is
|
|
safe:
|
|
|
|
@smallexample
|
|
#define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS
|
|
@end smallexample
|
|
|
|
Sometimes returning a more restrictive class makes better code. For
|
|
example, on the 68000, when @var{x} is an integer constant that is in range
|
|
for a @samp{moveq} instruction, the value of this macro is always
|
|
@code{DATA_REGS} as long as @var{class} includes the data registers.
|
|
Requiring a data register guarantees that a @samp{moveq} will be used.
|
|
|
|
One case where @code{PREFERRED_RELOAD_CLASS} must not return
|
|
@var{class} is if @var{x} is a legitimate constant which cannot be
|
|
loaded into some register class. By returning @code{NO_REGS} you can
|
|
force @var{x} into a memory location. For example, rs6000 can load
|
|
immediate values into general-purpose registers, but does not have an
|
|
instruction for loading an immediate value into a floating-point
|
|
register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when
|
|
@var{x} is a floating-point constant. If the constant cannot be loaded
|
|
into any kind of register, code generation will be better if
|
|
@code{TARGET_LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead
|
|
of using @code{TARGET_PREFERRED_RELOAD_CLASS}.
|
|
|
|
If an insn has pseudos in it after register allocation, reload will go
|
|
through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS}
|
|
to find the best one. Returning @code{NO_REGS}, in this case, makes
|
|
reload add a @code{!} in front of the constraint: the x86 back-end uses
|
|
this feature to discourage usage of 387 registers when math is done in
|
|
the SSE registers (and vice versa).
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} reg_class_t TARGET_PREFERRED_OUTPUT_RELOAD_CLASS (rtx @var{x}, reg_class_t @var{rclass})
|
|
Like @code{TARGET_PREFERRED_RELOAD_CLASS}, but for output reloads instead of
|
|
input reloads.
|
|
|
|
The default version of this hook always returns value of @code{rclass}
|
|
argument.
|
|
|
|
You can also use @code{TARGET_PREFERRED_OUTPUT_RELOAD_CLASS} to discourage
|
|
reload from using some alternatives, like @code{TARGET_PREFERRED_RELOAD_CLASS}.
|
|
@end deftypefn
|
|
|
|
@defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class})
|
|
A C expression that places additional restrictions on the register class
|
|
to use when it is necessary to be able to hold a value of mode
|
|
@var{mode} in a reload register for which class @var{class} would
|
|
ordinarily be used.
|
|
|
|
Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when
|
|
there are certain modes that simply cannot go in certain reload classes.
|
|
|
|
The value is a register class; perhaps @var{class}, or perhaps another,
|
|
smaller class.
|
|
|
|
Don't define this macro unless the target machine has limitations which
|
|
require the macro to do something nontrivial.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} reg_class_t TARGET_SECONDARY_RELOAD (bool @var{in_p}, rtx @var{x}, reg_class_t @var{reload_class}, machine_mode @var{reload_mode}, secondary_reload_info *@var{sri})
|
|
Many machines have some registers that cannot be copied directly to or
|
|
from memory or even from other types of registers. An example is the
|
|
@samp{MQ} register, which on most machines, can only be copied to or
|
|
from general registers, but not memory. Below, we shall be using the
|
|
term 'intermediate register' when a move operation cannot be performed
|
|
directly, but has to be done by copying the source into the intermediate
|
|
register first, and then copying the intermediate register to the
|
|
destination. An intermediate register always has the same mode as
|
|
source and destination. Since it holds the actual value being copied,
|
|
reload might apply optimizations to re-use an intermediate register
|
|
and eliding the copy from the source when it can determine that the
|
|
intermediate register still holds the required value.
|
|
|
|
Another kind of secondary reload is required on some machines which
|
|
allow copying all registers to and from memory, but require a scratch
|
|
register for stores to some memory locations (e.g., those with symbolic
|
|
address on the RT, and those with certain symbolic address on the SPARC
|
|
when compiling PIC)@. Scratch registers need not have the same mode
|
|
as the value being copied, and usually hold a different value than
|
|
that being copied. Special patterns in the md file are needed to
|
|
describe how the copy is performed with the help of the scratch register;
|
|
these patterns also describe the number, register class(es) and mode(s)
|
|
of the scratch register(s).
|
|
|
|
In some cases, both an intermediate and a scratch register are required.
|
|
|
|
For input reloads, this target hook is called with nonzero @var{in_p},
|
|
and @var{x} is an rtx that needs to be copied to a register of class
|
|
@var{reload_class} in @var{reload_mode}. For output reloads, this target
|
|
hook is called with zero @var{in_p}, and a register of class @var{reload_class}
|
|
needs to be copied to rtx @var{x} in @var{reload_mode}.
|
|
|
|
If copying a register of @var{reload_class} from/to @var{x} requires
|
|
an intermediate register, the hook @code{secondary_reload} should
|
|
return the register class required for this intermediate register.
|
|
If no intermediate register is required, it should return NO_REGS.
|
|
If more than one intermediate register is required, describe the one
|
|
that is closest in the copy chain to the reload register.
|
|
|
|
If scratch registers are needed, you also have to describe how to
|
|
perform the copy from/to the reload register to/from this
|
|
closest intermediate register. Or if no intermediate register is
|
|
required, but still a scratch register is needed, describe the
|
|
copy from/to the reload register to/from the reload operand @var{x}.
|
|
|
|
You do this by setting @code{sri->icode} to the instruction code of a pattern
|
|
in the md file which performs the move. Operands 0 and 1 are the output
|
|
and input of this copy, respectively. Operands from operand 2 onward are
|
|
for scratch operands. These scratch operands must have a mode, and a
|
|
single-register-class
|
|
@c [later: or memory]
|
|
output constraint.
|
|
|
|
When an intermediate register is used, the @code{secondary_reload}
|
|
hook will be called again to determine how to copy the intermediate
|
|
register to/from the reload operand @var{x}, so your hook must also
|
|
have code to handle the register class of the intermediate operand.
|
|
|
|
@c [For later: maybe we'll allow multi-alternative reload patterns -
|
|
@c the port maintainer could name a mov<mode> pattern that has clobbers -
|
|
@c and match the constraints of input and output to determine the required
|
|
@c alternative. A restriction would be that constraints used to match
|
|
@c against reloads registers would have to be written as register class
|
|
@c constraints, or we need a new target macro / hook that tells us if an
|
|
@c arbitrary constraint can match an unknown register of a given class.
|
|
@c Such a macro / hook would also be useful in other places.]
|
|
|
|
|
|
@var{x} might be a pseudo-register or a @code{subreg} of a
|
|
pseudo-register, which could either be in a hard register or in memory.
|
|
Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
|
|
in memory and the hard register number if it is in a register.
|
|
|
|
Scratch operands in memory (constraint @code{"=m"} / @code{"=&m"}) are
|
|
currently not supported. For the time being, you will have to continue
|
|
to use @code{TARGET_SECONDARY_MEMORY_NEEDED} for that purpose.
|
|
|
|
@code{copy_cost} also uses this target hook to find out how values are
|
|
copied. If you want it to include some extra cost for the need to allocate
|
|
(a) scratch register(s), set @code{sri->extra_cost} to the additional cost.
|
|
Or if two dependent moves are supposed to have a lower cost than the sum
|
|
of the individual moves due to expected fortuitous scheduling and/or special
|
|
forwarding logic, you can set @code{sri->extra_cost} to a negative amount.
|
|
@end deftypefn
|
|
|
|
@defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
|
|
@defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
|
|
@defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x})
|
|
These macros are obsolete, new ports should use the target hook
|
|
@code{TARGET_SECONDARY_RELOAD} instead.
|
|
|
|
These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD}
|
|
target hook. Older ports still define these macros to indicate to the
|
|
reload phase that it may
|
|
need to allocate at least one register for a reload in addition to the
|
|
register to contain the data. Specifically, if copying @var{x} to a
|
|
register @var{class} in @var{mode} requires an intermediate register,
|
|
you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the
|
|
largest register class all of whose registers can be used as
|
|
intermediate registers or scratch registers.
|
|
|
|
If copying a register @var{class} in @var{mode} to @var{x} requires an
|
|
intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS}
|
|
was supposed to be defined to return the largest register
|
|
class required. If the
|
|
requirements for input and output reloads were the same, the macro
|
|
@code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both
|
|
macros identically.
|
|
|
|
The values returned by these macros are often @code{GENERAL_REGS}.
|
|
Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x}
|
|
can be directly copied to or from a register of @var{class} in
|
|
@var{mode} without requiring a scratch register. Do not define this
|
|
macro if it would always return @code{NO_REGS}.
|
|
|
|
If a scratch register is required (either with or without an
|
|
intermediate register), you were supposed to define patterns for
|
|
@samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required
|
|
(@pxref{Standard Names}. These patterns, which were normally
|
|
implemented with a @code{define_expand}, should be similar to the
|
|
@samp{mov@var{m}} patterns, except that operand 2 is the scratch
|
|
register.
|
|
|
|
These patterns need constraints for the reload register and scratch
|
|
register that
|
|
contain a single register class. If the original reload register (whose
|
|
class is @var{class}) can meet the constraint given in the pattern, the
|
|
value returned by these macros is used for the class of the scratch
|
|
register. Otherwise, two additional reload registers are required.
|
|
Their classes are obtained from the constraints in the insn pattern.
|
|
|
|
@var{x} might be a pseudo-register or a @code{subreg} of a
|
|
pseudo-register, which could either be in a hard register or in memory.
|
|
Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is
|
|
in memory and the hard register number if it is in a register.
|
|
|
|
These macros should not be used in the case where a particular class of
|
|
registers can only be copied to memory and not to another class of
|
|
registers. In that case, secondary reload registers are not needed and
|
|
would not be helpful. Instead, a stack location must be used to perform
|
|
the copy and the @code{mov@var{m}} pattern should use memory as an
|
|
intermediate storage. This case often occurs between floating-point and
|
|
general registers.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SECONDARY_MEMORY_NEEDED (machine_mode @var{mode}, reg_class_t @var{class1}, reg_class_t @var{class2})
|
|
Certain machines have the property that some registers cannot be copied
|
|
to some other registers without using memory. Define this hook on
|
|
those machines to return true if objects of mode @var{m} in registers
|
|
of @var{class1} can only be copied to registers of class @var{class2} by
|
|
storing a register of @var{class1} into memory and loading that memory
|
|
location into a register of @var{class2}. The default definition returns
|
|
false for all inputs.
|
|
@end deftypefn
|
|
|
|
@defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode})
|
|
Normally when @code{TARGET_SECONDARY_MEMORY_NEEDED} is defined, the compiler
|
|
allocates a stack slot for a memory location needed for register copies.
|
|
If this macro is defined, the compiler instead uses the memory location
|
|
defined by this macro.
|
|
|
|
Do not define this macro if you do not define
|
|
@code{TARGET_SECONDARY_MEMORY_NEEDED}.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} machine_mode TARGET_SECONDARY_MEMORY_NEEDED_MODE (machine_mode @var{mode})
|
|
If @code{TARGET_SECONDARY_MEMORY_NEEDED} tells the compiler to use memory
|
|
when moving between two particular registers of mode @var{mode},
|
|
this hook specifies the mode that the memory should have.
|
|
|
|
The default depends on @code{TARGET_LRA_P}. Without LRA, the default
|
|
is to use a word-sized mode for integral modes that are smaller than a
|
|
a word. This is right thing to do on most machines because it ensures
|
|
that all bits of the register are copied and prevents accesses to the
|
|
registers in a narrower mode, which some machines prohibit for
|
|
floating-point registers.
|
|
|
|
However, this default behavior is not correct on some machines, such as
|
|
the DEC Alpha, that store short integers in floating-point registers
|
|
differently than in integer registers. On those machines, the default
|
|
widening will not work correctly and you must define this hook to
|
|
suppress that widening in some cases. See the file @file{alpha.cc} for
|
|
details.
|
|
|
|
With LRA, the default is to use @var{mode} unmodified.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SELECT_EARLY_REMAT_MODES (sbitmap @var{modes})
|
|
On some targets, certain modes cannot be held in registers around a
|
|
standard ABI call and are relatively expensive to spill to the stack.
|
|
The early rematerialization pass can help in such cases by aggressively
|
|
recomputing values after calls, so that they don't need to be spilled.
|
|
|
|
This hook returns the set of such modes by setting the associated bits
|
|
in @var{modes}. The default implementation selects no modes, which has
|
|
the effect of disabling the early rematerialization pass.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CLASS_LIKELY_SPILLED_P (reg_class_t @var{rclass})
|
|
A target hook which returns @code{true} if pseudos that have been assigned
|
|
to registers of class @var{rclass} would likely be spilled because
|
|
registers of @var{rclass} are needed for spill registers.
|
|
|
|
The default version of this target hook returns @code{true} if @var{rclass}
|
|
has exactly one register and @code{false} otherwise. On most machines, this
|
|
default should be used. For generally register-starved machines, such as
|
|
i386, or machines with right register constraints, such as SH, this hook
|
|
can be used to avoid excessive spilling.
|
|
|
|
This hook is also used by some of the global intra-procedural code
|
|
transformations to throtle code motion, to avoid increasing register
|
|
pressure.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {unsigned char} TARGET_CLASS_MAX_NREGS (reg_class_t @var{rclass}, machine_mode @var{mode})
|
|
A target hook returns the maximum number of consecutive registers
|
|
of class @var{rclass} needed to hold a value of mode @var{mode}.
|
|
|
|
This is closely related to the macro @code{TARGET_HARD_REGNO_NREGS}.
|
|
In fact, the value returned by @code{TARGET_CLASS_MAX_NREGS (@var{rclass},
|
|
@var{mode})} target hook should be the maximum value of
|
|
@code{TARGET_HARD_REGNO_NREGS (@var{regno}, @var{mode})} for all @var{regno}
|
|
values in the class @var{rclass}.
|
|
|
|
This target hook helps control the handling of multiple-word values
|
|
in the reload pass.
|
|
|
|
The default version of this target hook returns the size of @var{mode}
|
|
in words.
|
|
@end deftypefn
|
|
|
|
@defmac CLASS_MAX_NREGS (@var{class}, @var{mode})
|
|
A C expression for the maximum number of consecutive registers
|
|
of class @var{class} needed to hold a value of mode @var{mode}.
|
|
|
|
This is closely related to the macro @code{TARGET_HARD_REGNO_NREGS}. In fact,
|
|
the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})}
|
|
should be the maximum value of @code{TARGET_HARD_REGNO_NREGS (@var{regno},
|
|
@var{mode})} for all @var{regno} values in the class @var{class}.
|
|
|
|
This macro helps control the handling of multiple-word values
|
|
in the reload pass.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CAN_CHANGE_MODE_CLASS (machine_mode @var{from}, machine_mode @var{to}, reg_class_t @var{rclass})
|
|
This hook returns true if it is possible to bitcast values held in
|
|
registers of class @var{rclass} from mode @var{from} to mode @var{to}
|
|
and if doing so preserves the low-order bits that are common to both modes.
|
|
The result is only meaningful if @var{rclass} has registers that can hold
|
|
both @code{from} and @code{to}. The default implementation returns true.
|
|
|
|
As an example of when such bitcasting is invalid, loading 32-bit integer or
|
|
floating-point objects into floating-point registers on Alpha extends them
|
|
to 64 bits. Therefore loading a 64-bit object and then storing it as a
|
|
32-bit object does not store the low-order 32 bits, as would be the case
|
|
for a normal register. Therefore, @file{alpha.h} defines
|
|
@code{TARGET_CAN_CHANGE_MODE_CLASS} to return:
|
|
|
|
@smallexample
|
|
(GET_MODE_SIZE (from) == GET_MODE_SIZE (to)
|
|
|| !reg_classes_intersect_p (FLOAT_REGS, rclass))
|
|
@end smallexample
|
|
|
|
Even if storing from a register in mode @var{to} would be valid,
|
|
if both @var{from} and @code{raw_reg_mode} for @var{rclass} are wider
|
|
than @code{word_mode}, then we must prevent @var{to} narrowing the
|
|
mode. This happens when the middle-end assumes that it can load
|
|
or store pieces of an @var{N}-word pseudo, and that the pseudo will
|
|
eventually be allocated to @var{N} @code{word_mode} hard registers.
|
|
Failure to prevent this kind of mode change will result in the
|
|
entire @code{raw_reg_mode} being modified instead of the partial
|
|
value that the middle-end intended.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} reg_class_t TARGET_IRA_CHANGE_PSEUDO_ALLOCNO_CLASS (int, @var{reg_class_t}, @var{reg_class_t})
|
|
A target hook which can change allocno class for given pseudo from
|
|
allocno and best class calculated by IRA.
|
|
|
|
The default version of this target hook always returns given class.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_LRA_P (void)
|
|
A target hook which returns true if we use LRA instead of reload pass.
|
|
|
|
The default version of this target hook returns true. New ports
|
|
should use LRA, and existing ports are encouraged to convert.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_REGISTER_PRIORITY (int)
|
|
A target hook which returns the register priority number to which the
|
|
register @var{hard_regno} belongs to. The bigger the number, the
|
|
more preferable the hard register usage (when all other conditions are
|
|
the same). This hook can be used to prefer some hard register over
|
|
others in LRA. For example, some x86-64 register usage needs
|
|
additional prefix which makes instructions longer. The hook can
|
|
return lower priority number for such registers make them less favorable
|
|
and as result making the generated code smaller.
|
|
|
|
The default version of this target hook returns always zero.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_REGISTER_USAGE_LEVELING_P (void)
|
|
A target hook which returns true if we need register usage leveling.
|
|
That means if a few hard registers are equally good for the
|
|
assignment, we choose the least used hard register. The register
|
|
usage leveling may be profitable for some targets. Don't use the
|
|
usage leveling for targets with conditional execution or targets
|
|
with big register files as it hurts if-conversion and cross-jumping
|
|
optimizations.
|
|
|
|
The default version of this target hook returns always false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_DIFFERENT_ADDR_DISPLACEMENT_P (void)
|
|
A target hook which returns true if an address with the same structure
|
|
can have different maximal legitimate displacement. For example, the
|
|
displacement can depend on memory mode or on operand combinations in
|
|
the insn.
|
|
|
|
The default version of this target hook returns always false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CANNOT_SUBSTITUTE_MEM_EQUIV_P (rtx @var{subst})
|
|
A target hook which returns @code{true} if @var{subst} can't
|
|
substitute safely pseudos with equivalent memory values during
|
|
register allocation.
|
|
The default version of this target hook returns @code{false}.
|
|
On most machines, this default should be used. For generally
|
|
machines with non orthogonal register usage for addressing, such
|
|
as SH, this hook can be used to avoid excessive spilling.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_LEGITIMIZE_ADDRESS_DISPLACEMENT (rtx *@var{offset1}, rtx *@var{offset2}, poly_int64 @var{orig_offset}, machine_mode @var{mode})
|
|
This hook tries to split address offset @var{orig_offset} into
|
|
two parts: one that should be added to the base address to create
|
|
a local anchor point, and an additional offset that can be applied
|
|
to the anchor to address a value of mode @var{mode}. The idea is that
|
|
the local anchor could be shared by other accesses to nearby locations.
|
|
|
|
The hook returns true if it succeeds, storing the offset of the
|
|
anchor from the base in @var{offset1} and the offset of the final address
|
|
from the anchor in @var{offset2}. The default implementation returns false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} reg_class_t TARGET_SPILL_CLASS (reg_class_t, @var{machine_mode})
|
|
This hook defines a class of registers which could be used for spilling
|
|
pseudos of the given mode and class, or @code{NO_REGS} if only memory
|
|
should be used. Not defining this hook is equivalent to returning
|
|
@code{NO_REGS} for all inputs.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ADDITIONAL_ALLOCNO_CLASS_P (reg_class_t)
|
|
This hook should return @code{true} if given class of registers should
|
|
be an allocno class in any way. Usually RA uses only one register
|
|
class from all classes containing the same register set. In some
|
|
complicated cases, you need to have two or more such classes as
|
|
allocno ones for RA correct work. Not defining this hook is
|
|
equivalent to returning @code{false} for all inputs.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} scalar_int_mode TARGET_CSTORE_MODE (enum insn_code @var{icode})
|
|
This hook defines the machine mode to use for the boolean result of
|
|
conditional store patterns. The ICODE argument is the instruction code
|
|
for the cstore being performed. Not definiting this hook is the same
|
|
as accepting the mode encoded into operand 0 of the cstore expander
|
|
patterns.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_COMPUTE_PRESSURE_CLASSES (enum reg_class *@var{pressure_classes})
|
|
A target hook which lets a backend compute the set of pressure classes to
|
|
be used by those optimization passes which take register pressure into
|
|
account, as opposed to letting IRA compute them. It returns the number of
|
|
register classes stored in the array @var{pressure_classes}.
|
|
@end deftypefn
|
|
|
|
@node Stack and Calling
|
|
@section Stack Layout and Calling Conventions
|
|
@cindex calling conventions
|
|
|
|
@c prevent bad page break with this line
|
|
This describes the stack layout and calling conventions.
|
|
|
|
@menu
|
|
* Frame Layout::
|
|
* Exception Handling::
|
|
* Stack Checking::
|
|
* Frame Registers::
|
|
* Elimination::
|
|
* Stack Arguments::
|
|
* Register Arguments::
|
|
* Scalar Return::
|
|
* Aggregate Return::
|
|
* Caller Saves::
|
|
* Function Entry::
|
|
* Profiling::
|
|
* Tail Calls::
|
|
* Shrink-wrapping separate components::
|
|
* Stack Smashing Protection::
|
|
* Miscellaneous Register Hooks::
|
|
@end menu
|
|
|
|
@node Frame Layout
|
|
@subsection Basic Stack Layout
|
|
@cindex stack frame layout
|
|
@cindex frame layout
|
|
|
|
@c prevent bad page break with this line
|
|
Here is the basic stack layout.
|
|
|
|
@defmac STACK_GROWS_DOWNWARD
|
|
Define this macro to be true if pushing a word onto the stack moves the stack
|
|
pointer to a smaller address, and false otherwise.
|
|
@end defmac
|
|
|
|
@defmac STACK_PUSH_CODE
|
|
This macro defines the operation used when something is pushed
|
|
on the stack. In RTL, a push operation will be
|
|
@code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})}
|
|
|
|
The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC},
|
|
and @code{POST_INC}. Which of these is correct depends on
|
|
the stack direction and on whether the stack pointer points
|
|
to the last item on the stack or whether it points to the
|
|
space for the next item on the stack.
|
|
|
|
The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is
|
|
true, which is almost always right, and @code{PRE_INC} otherwise,
|
|
which is often wrong.
|
|
@end defmac
|
|
|
|
@defmac FRAME_GROWS_DOWNWARD
|
|
Define this macro to nonzero value if the addresses of local variable slots
|
|
are at negative offsets from the frame pointer.
|
|
@end defmac
|
|
|
|
@defmac ARGS_GROW_DOWNWARD
|
|
Define this macro if successive arguments to a function occupy decreasing
|
|
addresses on the stack.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} HOST_WIDE_INT TARGET_STARTING_FRAME_OFFSET (void)
|
|
This hook returns the offset from the frame pointer to the first local
|
|
variable slot to be allocated. If @code{FRAME_GROWS_DOWNWARD}, it is the
|
|
offset to @emph{end} of the first slot allocated, otherwise it is the
|
|
offset to @emph{beginning} of the first slot allocated. The default
|
|
implementation returns 0.
|
|
@end deftypefn
|
|
|
|
@defmac STACK_ALIGNMENT_NEEDED
|
|
Define to zero to disable final alignment of the stack during reload.
|
|
The nonzero default for this macro is suitable for most ports.
|
|
|
|
On ports where @code{TARGET_STARTING_FRAME_OFFSET} is nonzero or where there
|
|
is a register save block following the local block that doesn't require
|
|
alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable
|
|
stack alignment and do it in the backend.
|
|
@end defmac
|
|
|
|
@defmac STACK_POINTER_OFFSET
|
|
Offset from the stack pointer register to the first location at which
|
|
outgoing arguments are placed. If not specified, the default value of
|
|
zero is used. This is the proper value for most machines.
|
|
|
|
If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
|
|
the first location at which outgoing arguments are placed.
|
|
@end defmac
|
|
|
|
@defmac FIRST_PARM_OFFSET (@var{fundecl})
|
|
Offset from the argument pointer register to the first argument's
|
|
address. On some machines it may depend on the data type of the
|
|
function.
|
|
|
|
If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above
|
|
the first argument's address.
|
|
@end defmac
|
|
|
|
@defmac STACK_DYNAMIC_OFFSET (@var{fundecl})
|
|
Offset from the stack pointer register to an item dynamically allocated
|
|
on the stack, e.g., by @code{alloca}.
|
|
|
|
The default value for this macro is @code{STACK_POINTER_OFFSET} plus the
|
|
length of the outgoing arguments. The default is correct for most
|
|
machines. See @file{function.cc} for details.
|
|
@end defmac
|
|
|
|
@defmac INITIAL_FRAME_ADDRESS_RTX
|
|
A C expression whose value is RTL representing the address of the initial
|
|
stack frame. This address is passed to @code{RETURN_ADDR_RTX} and
|
|
@code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable
|
|
default value will be used. Define this macro in order to make frame pointer
|
|
elimination work in the presence of @code{__builtin_frame_address (count)} and
|
|
@code{__builtin_return_address (count)} for @code{count} not equal to zero.
|
|
@end defmac
|
|
|
|
@defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr})
|
|
A C expression whose value is RTL representing the address in a stack
|
|
frame where the pointer to the caller's frame is stored. Assume that
|
|
@var{frameaddr} is an RTL expression for the address of the stack frame
|
|
itself.
|
|
|
|
If you don't define this macro, the default is to return the value
|
|
of @var{frameaddr}---that is, the stack frame address is also the
|
|
address of the stack word that points to the previous frame.
|
|
@end defmac
|
|
|
|
@defmac SETUP_FRAME_ADDRESSES
|
|
A C expression that produces the machine-specific code to
|
|
setup the stack so that arbitrary frames can be accessed. For example,
|
|
on the SPARC, we must flush all of the register windows to the stack
|
|
before we can access arbitrary stack frames. You will seldom need to
|
|
define this macro. The default is to do nothing.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_BUILTIN_SETJMP_FRAME_VALUE (void)
|
|
This target hook should return an rtx that is used to store
|
|
the address of the current frame into the built in @code{setjmp} buffer.
|
|
The default value, @code{virtual_stack_vars_rtx}, is correct for most
|
|
machines. One reason you may need to define this target hook is if
|
|
@code{hard_frame_pointer_rtx} is the appropriate value on your machine.
|
|
@end deftypefn
|
|
|
|
@defmac FRAME_ADDR_RTX (@var{frameaddr})
|
|
A C expression whose value is RTL representing the value of the frame
|
|
address for the current frame. @var{frameaddr} is the frame pointer
|
|
of the current frame. This is used for __builtin_frame_address.
|
|
You need only define this macro if the frame address is not the same
|
|
as the frame pointer. Most machines do not need to define it.
|
|
@end defmac
|
|
|
|
@defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr})
|
|
A C expression whose value is RTL representing the value of the return
|
|
address for the frame @var{count} steps up from the current frame, after
|
|
the prologue. @var{frameaddr} is the frame pointer of the @var{count}
|
|
frame, or the frame pointer of the @var{count} @minus{} 1 frame if
|
|
@code{RETURN_ADDR_IN_PREVIOUS_FRAME} is nonzero.
|
|
|
|
The value of the expression must always be the correct address when
|
|
@var{count} is zero, but may be @code{NULL_RTX} if there is no way to
|
|
determine the return address of other frames.
|
|
@end defmac
|
|
|
|
@defmac RETURN_ADDR_IN_PREVIOUS_FRAME
|
|
Define this macro to nonzero value if the return address of a particular
|
|
stack frame is accessed from the frame pointer of the previous stack
|
|
frame. The zero default for this macro is suitable for most ports.
|
|
@end defmac
|
|
|
|
@defmac INCOMING_RETURN_ADDR_RTX
|
|
A C expression whose value is RTL representing the location of the
|
|
incoming return address at the beginning of any function, before the
|
|
prologue. This RTL is either a @code{REG}, indicating that the return
|
|
value is saved in @samp{REG}, or a @code{MEM} representing a location in
|
|
the stack.
|
|
|
|
You only need to define this macro if you want to support call frame
|
|
debugging information like that provided by DWARF 2.
|
|
|
|
If this RTL is a @code{REG}, you should also define
|
|
@code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}.
|
|
@end defmac
|
|
|
|
@defmac DWARF_ALT_FRAME_RETURN_COLUMN
|
|
A C expression whose value is an integer giving a DWARF 2 column
|
|
number that may be used as an alternative return column. The column
|
|
must not correspond to any gcc hard register (that is, it must not
|
|
be in the range of @code{DWARF_FRAME_REGNUM}).
|
|
|
|
This macro can be useful if @code{DWARF_FRAME_RETURN_COLUMN} is set to a
|
|
general register, but an alternative column needs to be used for signal
|
|
frames. Some targets have also used different frame return columns
|
|
over time.
|
|
@end defmac
|
|
|
|
@defmac DWARF_ZERO_REG
|
|
A C expression whose value is an integer giving a DWARF 2 register
|
|
number that is considered to always have the value zero. This should
|
|
only be defined if the target has an architected zero register, and
|
|
someone decided it was a good idea to use that register number to
|
|
terminate the stack backtrace. New ports should avoid this.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_DWARF_HANDLE_FRAME_UNSPEC (const char *@var{label}, rtx @var{pattern}, int @var{index})
|
|
This target hook allows the backend to emit frame-related insns that
|
|
contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging
|
|
info engine will invoke it on insns of the form
|
|
@smallexample
|
|
(set (reg) (unspec [@dots{}] UNSPEC_INDEX))
|
|
@end smallexample
|
|
and
|
|
@smallexample
|
|
(set (reg) (unspec_volatile [@dots{}] UNSPECV_INDEX)).
|
|
@end smallexample
|
|
to let the backend emit the call frame instructions. @var{label} is
|
|
the CFI label attached to the insn, @var{pattern} is the pattern of
|
|
the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_DWARF_POLY_INDETERMINATE_VALUE (unsigned int @var{i}, unsigned int *@var{factor}, int *@var{offset})
|
|
Express the value of @code{poly_int} indeterminate @var{i} as a DWARF
|
|
expression, with @var{i} counting from 1. Return the number of a DWARF
|
|
register @var{R} and set @samp{*@var{factor}} and @samp{*@var{offset}} such
|
|
that the value of the indeterminate is:
|
|
@smallexample
|
|
value_of(@var{R}) / @var{factor} - @var{offset}
|
|
@end smallexample
|
|
|
|
A target only needs to define this hook if it sets
|
|
@samp{NUM_POLY_INT_COEFFS} to a value greater than 1.
|
|
@end deftypefn
|
|
|
|
@defmac INCOMING_FRAME_SP_OFFSET
|
|
A C expression whose value is an integer giving the offset, in bytes,
|
|
from the value of the stack pointer register to the top of the stack
|
|
frame at the beginning of any function, before the prologue. The top of
|
|
the frame is defined to be the value of the stack pointer in the
|
|
previous frame, just before the call instruction.
|
|
|
|
You only need to define this macro if you want to support call frame
|
|
debugging information like that provided by DWARF 2.
|
|
@end defmac
|
|
|
|
@defmac DEFAULT_INCOMING_FRAME_SP_OFFSET
|
|
Like @code{INCOMING_FRAME_SP_OFFSET}, but must be the same for all
|
|
functions of the same ABI, and when using GAS @code{.cfi_*} directives
|
|
must also agree with the default CFI GAS emits. Define this macro
|
|
only if @code{INCOMING_FRAME_SP_OFFSET} can have different values
|
|
between different functions of the same ABI or when
|
|
@code{INCOMING_FRAME_SP_OFFSET} does not agree with GAS default CFI.
|
|
@end defmac
|
|
|
|
@defmac ARG_POINTER_CFA_OFFSET (@var{fundecl})
|
|
A C expression whose value is an integer giving the offset, in bytes,
|
|
from the argument pointer to the canonical frame address (cfa). The
|
|
final value should coincide with that calculated by
|
|
@code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable
|
|
during virtual register instantiation.
|
|
|
|
The default value for this macro is
|
|
@code{FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size},
|
|
which is correct for most machines; in general, the arguments are found
|
|
immediately before the stack frame. Note that this is not the case on
|
|
some targets that save registers into the caller's frame, such as SPARC
|
|
and rs6000, and so such targets need to define this macro.
|
|
|
|
You only need to define this macro if the default is incorrect, and you
|
|
want to support call frame debugging information like that provided by
|
|
DWARF 2.
|
|
@end defmac
|
|
|
|
@defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl})
|
|
If defined, a C expression whose value is an integer giving the offset
|
|
in bytes from the frame pointer to the canonical frame address (cfa).
|
|
The final value should coincide with that calculated by
|
|
@code{INCOMING_FRAME_SP_OFFSET}.
|
|
|
|
Normally the CFA is calculated as an offset from the argument pointer,
|
|
via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is
|
|
variable due to the ABI, this may not be possible. If this macro is
|
|
defined, it implies that the virtual register instantiation should be
|
|
based on the frame pointer instead of the argument pointer. Only one
|
|
of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET}
|
|
should be defined.
|
|
@end defmac
|
|
|
|
@defmac CFA_FRAME_BASE_OFFSET (@var{fundecl})
|
|
If defined, a C expression whose value is an integer giving the offset
|
|
in bytes from the canonical frame address (cfa) to the frame base used
|
|
in DWARF 2 debug information. The default is zero. A different value
|
|
may reduce the size of debug information on some ports.
|
|
@end defmac
|
|
|
|
@node Exception Handling
|
|
@subsection Exception Handling Support
|
|
@cindex exception handling
|
|
|
|
@defmac EH_RETURN_DATA_REGNO (@var{N})
|
|
A C expression whose value is the @var{N}th register number used for
|
|
data by exception handlers, or @code{INVALID_REGNUM} if fewer than
|
|
@var{N} registers are usable.
|
|
|
|
The exception handling library routines communicate with the exception
|
|
handlers via a set of agreed upon registers. Ideally these registers
|
|
should be call-clobbered; it is possible to use call-saved registers,
|
|
but may negatively impact code size. The target must support at least
|
|
2 data registers, but should define 4 if there are enough free registers.
|
|
|
|
You must define this macro if you want to support call frame exception
|
|
handling like that provided by DWARF 2.
|
|
@end defmac
|
|
|
|
@defmac EH_RETURN_STACKADJ_RTX
|
|
A C expression whose value is RTL representing a location in which
|
|
to store a stack adjustment to be applied before function return.
|
|
This is used to unwind the stack to an exception handler's call frame.
|
|
It will be assigned zero on code paths that return normally.
|
|
|
|
Typically this is a call-clobbered hard register that is otherwise
|
|
untouched by the epilogue, but could also be a stack slot.
|
|
|
|
Do not define this macro if the stack pointer is saved and restored
|
|
by the regular prolog and epilog code in the call frame itself; in
|
|
this case, the exception handling library routines will update the
|
|
stack location to be restored in place. Otherwise, you must define
|
|
this macro if you want to support call frame exception handling like
|
|
that provided by DWARF 2.
|
|
@end defmac
|
|
|
|
@defmac EH_RETURN_HANDLER_RTX
|
|
A C expression whose value is RTL representing a location in which
|
|
to store the address of an exception handler to which we should
|
|
return. It will not be assigned on code paths that return normally.
|
|
|
|
Typically this is the location in the call frame at which the normal
|
|
return address is stored. For targets that return by popping an
|
|
address off the stack, this might be a memory address just below
|
|
the @emph{target} call frame rather than inside the current call
|
|
frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already
|
|
been assigned, so it may be used to calculate the location of the
|
|
target call frame.
|
|
|
|
Some targets have more complex requirements than storing to an
|
|
address calculable during initial code generation. In that case
|
|
the @code{eh_return} instruction pattern should be used instead.
|
|
|
|
If you want to support call frame exception handling, you must
|
|
define either this macro or the @code{eh_return} instruction pattern.
|
|
@end defmac
|
|
|
|
@defmac RETURN_ADDR_OFFSET
|
|
If defined, an integer-valued C expression for which rtl will be generated
|
|
to add it to the exception handler address before it is searched in the
|
|
exception handling tables, and to subtract it again from the address before
|
|
using it to return to the exception handler.
|
|
@end defmac
|
|
|
|
@defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global})
|
|
This macro chooses the encoding of pointers embedded in the exception
|
|
handling sections. If at all possible, this should be defined such
|
|
that the exception handling section will not require dynamic relocations,
|
|
and so may be read-only.
|
|
|
|
@var{code} is 0 for data, 1 for code labels, 2 for function pointers.
|
|
@var{global} is true if the symbol may be affected by dynamic relocations.
|
|
The macro should return a combination of the @code{DW_EH_PE_*} defines
|
|
as found in @file{dwarf2.h}.
|
|
|
|
If this macro is not defined, pointers will not be encoded but
|
|
represented directly.
|
|
@end defmac
|
|
|
|
@defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done})
|
|
This macro allows the target to emit whatever special magic is required
|
|
to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}.
|
|
Generic code takes care of pc-relative and indirect encodings; this must
|
|
be defined if the target uses text-relative or data-relative encodings.
|
|
|
|
This is a C statement that branches to @var{done} if the format was
|
|
handled. @var{encoding} is the format chosen, @var{size} is the number
|
|
of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF}
|
|
to be emitted.
|
|
@end defmac
|
|
|
|
@defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs})
|
|
This macro allows the target to add CPU and operating system specific
|
|
code to the call-frame unwinder for use when there is no unwind data
|
|
available. The most common reason to implement this macro is to unwind
|
|
through signal frames.
|
|
|
|
This macro is called from @code{uw_frame_state_for} in
|
|
@file{unwind-dw2.c}, @file{unwind-dw2-xtensa.c} and
|
|
@file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
|
|
@var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra}
|
|
for the address of the code being executed and @code{context->cfa} for
|
|
the stack pointer value. If the frame can be decoded, the register
|
|
save addresses should be updated in @var{fs} and the macro should
|
|
evaluate to @code{_URC_NO_REASON}. If the frame cannot be decoded,
|
|
the macro should evaluate to @code{_URC_END_OF_STACK}.
|
|
|
|
For proper signal handling in Java this macro is accompanied by
|
|
@code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers.
|
|
@end defmac
|
|
|
|
@defmac MD_HANDLE_UNWABI (@var{context}, @var{fs})
|
|
This macro allows the target to add operating system specific code to the
|
|
call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive,
|
|
usually used for signal or interrupt frames.
|
|
|
|
This macro is called from @code{uw_update_context} in libgcc's
|
|
@file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context};
|
|
@var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi}
|
|
for the abi and context in the @code{.unwabi} directive. If the
|
|
@code{.unwabi} directive can be handled, the register save addresses should
|
|
be updated in @var{fs}.
|
|
@end defmac
|
|
|
|
@defmac TARGET_USES_WEAK_UNWIND_INFO
|
|
A C expression that evaluates to true if the target requires unwind
|
|
info to be given comdat linkage. Define it to be @code{1} if comdat
|
|
linkage is necessary. The default is @code{0}.
|
|
@end defmac
|
|
|
|
@node Stack Checking
|
|
@subsection Specifying How Stack Checking is Done
|
|
|
|
GCC will check that stack references are within the boundaries of the
|
|
stack, if the option @option{-fstack-check} is specified, in one of
|
|
three ways:
|
|
|
|
@enumerate
|
|
@item
|
|
If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
|
|
will assume that you have arranged for full stack checking to be done
|
|
at appropriate places in the configuration files. GCC will not do
|
|
other special processing.
|
|
|
|
@item
|
|
If @code{STACK_CHECK_BUILTIN} is zero and the value of the
|
|
@code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume
|
|
that you have arranged for static stack checking (checking of the
|
|
static stack frame of functions) to be done at appropriate places
|
|
in the configuration files. GCC will only emit code to do dynamic
|
|
stack checking (checking on dynamic stack allocations) using the third
|
|
approach below.
|
|
|
|
@item
|
|
If neither of the above are true, GCC will generate code to periodically
|
|
``probe'' the stack pointer using the values of the macros defined below.
|
|
@end enumerate
|
|
|
|
If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined,
|
|
GCC will change its allocation strategy for large objects if the option
|
|
@option{-fstack-check} is specified: they will always be allocated
|
|
dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes.
|
|
|
|
@defmac STACK_CHECK_BUILTIN
|
|
A nonzero value if stack checking is done by the configuration files in a
|
|
machine-dependent manner. You should define this macro if stack checking
|
|
is required by the ABI of your machine or if you would like to do stack
|
|
checking in some more efficient way than the generic approach. The default
|
|
value of this macro is zero.
|
|
@end defmac
|
|
|
|
@defmac STACK_CHECK_STATIC_BUILTIN
|
|
A nonzero value if static stack checking is done by the configuration files
|
|
in a machine-dependent manner. You should define this macro if you would
|
|
like to do static stack checking in some more efficient way than the generic
|
|
approach. The default value of this macro is zero.
|
|
@end defmac
|
|
|
|
@defmac STACK_CHECK_PROBE_INTERVAL_EXP
|
|
An integer specifying the interval at which GCC must generate stack probe
|
|
instructions, defined as 2 raised to this integer. You will normally
|
|
define this macro so that the interval be no larger than the size of
|
|
the ``guard pages'' at the end of a stack area. The default value
|
|
of 12 (4096-byte interval) is suitable for most systems.
|
|
@end defmac
|
|
|
|
@defmac STACK_CHECK_MOVING_SP
|
|
An integer which is nonzero if GCC should move the stack pointer page by page
|
|
when doing probes. This can be necessary on systems where the stack pointer
|
|
contains the bottom address of the memory area accessible to the executing
|
|
thread at any point in time. In this situation an alternate signal stack
|
|
is required in order to be able to recover from a stack overflow. The
|
|
default value of this macro is zero.
|
|
@end defmac
|
|
|
|
@defmac STACK_CHECK_PROTECT
|
|
The number of bytes of stack needed to recover from a stack overflow, for
|
|
languages where such a recovery is supported. The default value of 4KB/8KB
|
|
with the @code{setjmp}/@code{longjmp}-based exception handling mechanism and
|
|
8KB/12KB with other exception handling mechanisms should be adequate for most
|
|
architectures and operating systems.
|
|
@end defmac
|
|
|
|
The following macros are relevant only if neither STACK_CHECK_BUILTIN
|
|
nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether
|
|
in the opposite case.
|
|
|
|
@defmac STACK_CHECK_MAX_FRAME_SIZE
|
|
The maximum size of a stack frame, in bytes. GCC will generate probe
|
|
instructions in non-leaf functions to ensure at least this many bytes of
|
|
stack are available. If a stack frame is larger than this size, stack
|
|
checking will not be reliable and GCC will issue a warning. The
|
|
default is chosen so that GCC only generates one instruction on most
|
|
systems. You should normally not change the default value of this macro.
|
|
@end defmac
|
|
|
|
@defmac STACK_CHECK_FIXED_FRAME_SIZE
|
|
GCC uses this value to generate the above warning message. It
|
|
represents the amount of fixed frame used by a function, not including
|
|
space for any callee-saved registers, temporaries and user variables.
|
|
You need only specify an upper bound for this amount and will normally
|
|
use the default of four words.
|
|
@end defmac
|
|
|
|
@defmac STACK_CHECK_MAX_VAR_SIZE
|
|
The maximum size, in bytes, of an object that GCC will place in the
|
|
fixed area of the stack frame when the user specifies
|
|
@option{-fstack-check}.
|
|
GCC computed the default from the values of the above macros and you will
|
|
normally not need to override that default.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} HOST_WIDE_INT TARGET_STACK_CLASH_PROTECTION_ALLOCA_PROBE_RANGE (void)
|
|
Some targets have an ABI defined interval for which no probing needs to be done.
|
|
When a probe does need to be done this same interval is used as the probe distance
|
|
up when doing stack clash protection for alloca.
|
|
On such targets this value can be set to override the default probing up interval.
|
|
Define this variable to return nonzero if such a probe range is required or zero otherwise.
|
|
Defining this hook also requires your functions which make use of alloca to have at least 8 byes
|
|
of outgoing arguments. If this is not the case the stack will be corrupted.
|
|
You need not define this macro if it would always have the value zero.
|
|
@end deftypefn
|
|
|
|
@need 2000
|
|
@node Frame Registers
|
|
@subsection Registers That Address the Stack Frame
|
|
|
|
@c prevent bad page break with this line
|
|
This discusses registers that address the stack frame.
|
|
|
|
@defmac STACK_POINTER_REGNUM
|
|
The register number of the stack pointer register, which must also be a
|
|
fixed register according to @code{FIXED_REGISTERS}. On most machines,
|
|
the hardware determines which register this is.
|
|
@end defmac
|
|
|
|
@defmac FRAME_POINTER_REGNUM
|
|
The register number of the frame pointer register, which is used to
|
|
access automatic variables in the stack frame. On some machines, the
|
|
hardware determines which register this is. On other machines, you can
|
|
choose any register you wish for this purpose.
|
|
@end defmac
|
|
|
|
@defmac HARD_FRAME_POINTER_REGNUM
|
|
On some machines the offset between the frame pointer and starting
|
|
offset of the automatic variables is not known until after register
|
|
allocation has been done (for example, because the saved registers are
|
|
between these two locations). On those machines, define
|
|
@code{FRAME_POINTER_REGNUM} the number of a special, fixed register to
|
|
be used internally until the offset is known, and define
|
|
@code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number
|
|
used for the frame pointer.
|
|
|
|
You should define this macro only in the very rare circumstances when it
|
|
is not possible to calculate the offset between the frame pointer and
|
|
the automatic variables until after register allocation has been
|
|
completed. When this macro is defined, you must also indicate in your
|
|
definition of @code{ELIMINABLE_REGS} how to eliminate
|
|
@code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM}
|
|
or @code{STACK_POINTER_REGNUM}.
|
|
|
|
Do not define this macro if it would be the same as
|
|
@code{FRAME_POINTER_REGNUM}.
|
|
@end defmac
|
|
|
|
@defmac ARG_POINTER_REGNUM
|
|
The register number of the arg pointer register, which is used to access
|
|
the function's argument list. On some machines, this is the same as the
|
|
frame pointer register. On some machines, the hardware determines which
|
|
register this is. On other machines, you can choose any register you
|
|
wish for this purpose. If this is not the same register as the frame
|
|
pointer register, then you must mark it as a fixed register according to
|
|
@code{FIXED_REGISTERS}, or arrange to be able to eliminate it
|
|
(@pxref{Elimination}).
|
|
@end defmac
|
|
|
|
@defmac HARD_FRAME_POINTER_IS_FRAME_POINTER
|
|
Define this to a preprocessor constant that is nonzero if
|
|
@code{hard_frame_pointer_rtx} and @code{frame_pointer_rtx} should be
|
|
the same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM
|
|
== FRAME_POINTER_REGNUM)}; you only need to define this macro if that
|
|
definition is not suitable for use in preprocessor conditionals.
|
|
@end defmac
|
|
|
|
@defmac HARD_FRAME_POINTER_IS_ARG_POINTER
|
|
Define this to a preprocessor constant that is nonzero if
|
|
@code{hard_frame_pointer_rtx} and @code{arg_pointer_rtx} should be the
|
|
same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM ==
|
|
ARG_POINTER_REGNUM)}; you only need to define this macro if that
|
|
definition is not suitable for use in preprocessor conditionals.
|
|
@end defmac
|
|
|
|
@defmac RETURN_ADDRESS_POINTER_REGNUM
|
|
The register number of the return address pointer register, which is used to
|
|
access the current function's return address from the stack. On some
|
|
machines, the return address is not at a fixed offset from the frame
|
|
pointer or stack pointer or argument pointer. This register can be defined
|
|
to point to the return address on the stack, and then be converted by
|
|
@code{ELIMINABLE_REGS} into either the frame pointer or stack pointer.
|
|
|
|
Do not define this macro unless there is no other way to get the return
|
|
address from the stack.
|
|
@end defmac
|
|
|
|
@defmac STATIC_CHAIN_REGNUM
|
|
@defmacx STATIC_CHAIN_INCOMING_REGNUM
|
|
Register numbers used for passing a function's static chain pointer. If
|
|
register windows are used, the register number as seen by the called
|
|
function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register
|
|
number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If
|
|
these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need
|
|
not be defined.
|
|
|
|
The static chain register need not be a fixed register.
|
|
|
|
If the static chain is passed in memory, these macros should not be
|
|
defined; instead, the @code{TARGET_STATIC_CHAIN} hook should be used.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_STATIC_CHAIN (const_tree @var{fndecl_or_type}, bool @var{incoming_p})
|
|
This hook replaces the use of @code{STATIC_CHAIN_REGNUM} et al for
|
|
targets that may use different static chain locations for different
|
|
nested functions. This may be required if the target has function
|
|
attributes that affect the calling conventions of the function and
|
|
those calling conventions use different static chain locations.
|
|
|
|
The default version of this hook uses @code{STATIC_CHAIN_REGNUM} et al.
|
|
|
|
If the static chain is passed in memory, this hook should be used to
|
|
provide rtx giving @code{mem} expressions that denote where they are stored.
|
|
Often the @code{mem} expression as seen by the caller will be at an offset
|
|
from the stack pointer and the @code{mem} expression as seen by the callee
|
|
will be at an offset from the frame pointer.
|
|
@findex stack_pointer_rtx
|
|
@findex frame_pointer_rtx
|
|
@findex arg_pointer_rtx
|
|
The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and
|
|
@code{arg_pointer_rtx} will have been initialized and should be used
|
|
to refer to those items.
|
|
@end deftypefn
|
|
|
|
@defmac DWARF_FRAME_REGISTERS
|
|
This macro specifies the maximum number of hard registers that can be
|
|
saved in a call frame. This is used to size data structures used in
|
|
DWARF2 exception handling.
|
|
|
|
Prior to GCC 3.0, this macro was needed in order to establish a stable
|
|
exception handling ABI in the face of adding new hard registers for ISA
|
|
extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
|
|
in the number of hard registers. Nevertheless, this macro can still be
|
|
used to reduce the runtime memory requirements of the exception handling
|
|
routines, which can be substantial if the ISA contains a lot of
|
|
registers that are not call-saved.
|
|
|
|
If this macro is not defined, it defaults to
|
|
@code{FIRST_PSEUDO_REGISTER}.
|
|
@end defmac
|
|
|
|
@defmac PRE_GCC3_DWARF_FRAME_REGISTERS
|
|
|
|
This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided
|
|
for backward compatibility in pre GCC 3.0 compiled code.
|
|
|
|
If this macro is not defined, it defaults to
|
|
@code{DWARF_FRAME_REGISTERS}.
|
|
@end defmac
|
|
|
|
@defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno})
|
|
|
|
Define this macro if the target's representation for dwarf registers
|
|
is different than the internal representation for unwind column.
|
|
Given a dwarf register, this macro should return the internal unwind
|
|
column number to use instead.
|
|
@end defmac
|
|
|
|
@defmac DWARF_FRAME_REGNUM (@var{regno})
|
|
|
|
Define this macro if the target's representation for dwarf registers
|
|
used in .eh_frame or .debug_frame is different from that used in other
|
|
debug info sections. Given a GCC hard register number, this macro
|
|
should return the .eh_frame register number. The default is
|
|
@code{DBX_REGISTER_NUMBER (@var{regno})}.
|
|
|
|
@end defmac
|
|
|
|
@defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh})
|
|
|
|
Define this macro to map register numbers held in the call frame info
|
|
that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that
|
|
should be output in .debug_frame (@code{@var{for_eh}} is zero) and
|
|
.eh_frame (@code{@var{for_eh}} is nonzero). The default is to
|
|
return @code{@var{regno}}.
|
|
|
|
@end defmac
|
|
|
|
@defmac REG_VALUE_IN_UNWIND_CONTEXT
|
|
|
|
Define this macro if the target stores register values as
|
|
@code{_Unwind_Word} type in unwind context. It should be defined if
|
|
target register size is larger than the size of @code{void *}. The
|
|
default is to store register values as @code{void *} type.
|
|
|
|
@end defmac
|
|
|
|
@defmac ASSUME_EXTENDED_UNWIND_CONTEXT
|
|
|
|
Define this macro to be 1 if the target always uses extended unwind
|
|
context with version, args_size and by_value fields. If it is undefined,
|
|
it will be defined to 1 when @code{REG_VALUE_IN_UNWIND_CONTEXT} is
|
|
defined and 0 otherwise.
|
|
|
|
@end defmac
|
|
|
|
@defmac DWARF_LAZY_REGISTER_VALUE (@var{regno}, @var{value})
|
|
Define this macro if the target has pseudo DWARF registers whose
|
|
values need to be computed lazily on demand by the unwinder (such as when
|
|
referenced in a CFA expression). The macro returns true if @var{regno}
|
|
is such a register and stores its value in @samp{*@var{value}} if so.
|
|
@end defmac
|
|
|
|
@node Elimination
|
|
@subsection Eliminating Frame Pointer and Arg Pointer
|
|
|
|
@c prevent bad page break with this line
|
|
This is about eliminating the frame pointer and arg pointer.
|
|
|
|
@deftypefn {Target Hook} bool TARGET_FRAME_POINTER_REQUIRED (void)
|
|
This target hook should return @code{true} if a function must have and use
|
|
a frame pointer. This target hook is called in the reload pass. If its return
|
|
value is @code{true} the function will have a frame pointer.
|
|
|
|
This target hook can in principle examine the current function and decide
|
|
according to the facts, but on most machines the constant @code{false} or the
|
|
constant @code{true} suffices. Use @code{false} when the machine allows code
|
|
to be generated with no frame pointer, and doing so saves some time or space.
|
|
Use @code{true} when there is no possible advantage to avoiding a frame
|
|
pointer.
|
|
|
|
In certain cases, the compiler does not know how to produce valid code
|
|
without a frame pointer. The compiler recognizes those cases and
|
|
automatically gives the function a frame pointer regardless of what
|
|
@code{targetm.frame_pointer_required} returns. You don't need to worry about
|
|
them.
|
|
|
|
In a function that does not require a frame pointer, the frame pointer
|
|
register can be allocated for ordinary usage, unless you mark it as a
|
|
fixed register. See @code{FIXED_REGISTERS} for more information.
|
|
|
|
Default return value is @code{false}.
|
|
@end deftypefn
|
|
|
|
@defmac ELIMINABLE_REGS
|
|
This macro specifies a table of register pairs used to eliminate
|
|
unneeded registers that point into the stack frame.
|
|
|
|
The definition of this macro is a list of structure initializations, each
|
|
of which specifies an original and replacement register.
|
|
|
|
On some machines, the position of the argument pointer is not known until
|
|
the compilation is completed. In such a case, a separate hard register
|
|
must be used for the argument pointer. This register can be eliminated by
|
|
replacing it with either the frame pointer or the argument pointer,
|
|
depending on whether or not the frame pointer has been eliminated.
|
|
|
|
In this case, you might specify:
|
|
@smallexample
|
|
#define ELIMINABLE_REGS \
|
|
@{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \
|
|
@{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \
|
|
@{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@}
|
|
@end smallexample
|
|
|
|
Note that the elimination of the argument pointer with the stack pointer is
|
|
specified first since that is the preferred elimination.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CAN_ELIMINATE (const int @var{from_reg}, const int @var{to_reg})
|
|
This target hook should return @code{true} if the compiler is allowed to
|
|
try to replace register number @var{from_reg} with register number
|
|
@var{to_reg}. This target hook will usually be @code{true}, since most of the
|
|
cases preventing register elimination are things that the compiler already
|
|
knows about.
|
|
|
|
Default return value is @code{true}.
|
|
@end deftypefn
|
|
|
|
@defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var})
|
|
This macro returns the initial difference between the specified pair
|
|
of registers. The value would be computed from information
|
|
such as the result of @code{get_frame_size ()} and the tables of
|
|
registers @code{df_regs_ever_live_p} and @code{call_used_regs}.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_COMPUTE_FRAME_LAYOUT (void)
|
|
This target hook is called once each time the frame layout needs to be
|
|
recalculated. The calculations can be cached by the target and can then
|
|
be used by @code{INITIAL_ELIMINATION_OFFSET} instead of re-computing the
|
|
layout on every invocation of that hook. This is particularly useful
|
|
for targets that have an expensive frame layout function. Implementing
|
|
this callback is optional.
|
|
@end deftypefn
|
|
|
|
@node Stack Arguments
|
|
@subsection Passing Function Arguments on the Stack
|
|
@cindex arguments on stack
|
|
@cindex stack arguments
|
|
|
|
The macros in this section control how arguments are passed
|
|
on the stack. See the following section for other macros that
|
|
control passing certain arguments in registers.
|
|
|
|
@deftypefn {Target Hook} bool TARGET_PROMOTE_PROTOTYPES (const_tree @var{fntype})
|
|
This target hook returns @code{true} if an argument declared in a
|
|
prototype as an integral type smaller than @code{int} should actually be
|
|
passed as an @code{int}. In addition to avoiding errors in certain
|
|
cases of mismatch, it also makes for better code on certain machines.
|
|
The default is to not promote prototypes.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_PUSH_ARGUMENT (unsigned int @var{npush})
|
|
This target hook returns @code{true} if push instructions will be
|
|
used to pass outgoing arguments. When the push instruction usage is
|
|
optional, @var{npush} is nonzero to indicate the number of bytes to
|
|
push. Otherwise, @var{npush} is zero. If the target machine does not
|
|
have a push instruction or push instruction should be avoided,
|
|
@code{false} should be returned. That directs GCC to use an alternate
|
|
strategy: to allocate the entire argument block and then store the
|
|
arguments into it. If this target hook may return @code{true},
|
|
@code{PUSH_ROUNDING} must be defined.
|
|
@end deftypefn
|
|
|
|
@defmac PUSH_ARGS_REVERSED
|
|
A C expression. If nonzero, function arguments will be evaluated from
|
|
last to first, rather than from first to last. If this macro is not
|
|
defined, it defaults to @code{PUSH_ARGS} on targets where the stack
|
|
and args grow in opposite directions, and 0 otherwise.
|
|
@end defmac
|
|
|
|
@defmac PUSH_ROUNDING (@var{npushed})
|
|
A C expression that is the number of bytes actually pushed onto the
|
|
stack when an instruction attempts to push @var{npushed} bytes.
|
|
|
|
On some machines, the definition
|
|
|
|
@smallexample
|
|
#define PUSH_ROUNDING(BYTES) (BYTES)
|
|
@end smallexample
|
|
|
|
@noindent
|
|
will suffice. But on other machines, instructions that appear
|
|
to push one byte actually push two bytes in an attempt to maintain
|
|
alignment. Then the definition should be
|
|
|
|
@smallexample
|
|
#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
|
|
@end smallexample
|
|
|
|
If the value of this macro has a type, it should be an unsigned type.
|
|
@end defmac
|
|
|
|
@findex outgoing_args_size
|
|
@findex crtl->outgoing_args_size
|
|
@defmac ACCUMULATE_OUTGOING_ARGS
|
|
A C expression. If nonzero, the maximum amount of space required for outgoing arguments
|
|
will be computed and placed into
|
|
@code{crtl->outgoing_args_size}. No space will be pushed
|
|
onto the stack for each call; instead, the function prologue should
|
|
increase the stack frame size by this amount.
|
|
|
|
Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS}
|
|
is not proper.
|
|
@end defmac
|
|
|
|
@defmac REG_PARM_STACK_SPACE (@var{fndecl})
|
|
Define this macro if functions should assume that stack space has been
|
|
allocated for arguments even when their values are passed in
|
|
registers.
|
|
|
|
The value of this macro is the size, in bytes, of the area reserved for
|
|
arguments passed in registers for the function represented by @var{fndecl},
|
|
which can be zero if GCC is calling a library function.
|
|
The argument @var{fndecl} can be the FUNCTION_DECL, or the type itself
|
|
of the function.
|
|
|
|
This space can be allocated by the caller, or be a part of the
|
|
machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says
|
|
which.
|
|
@end defmac
|
|
@c above is overfull. not sure what to do. --mew 5feb93 did
|
|
@c something, not sure if it looks good. --mew 10feb93
|
|
|
|
@defmac INCOMING_REG_PARM_STACK_SPACE (@var{fndecl})
|
|
Like @code{REG_PARM_STACK_SPACE}, but for incoming register arguments.
|
|
Define this macro if space guaranteed when compiling a function body
|
|
is different to space required when making a call, a situation that
|
|
can arise with K&R style function definitions.
|
|
@end defmac
|
|
|
|
@defmac OUTGOING_REG_PARM_STACK_SPACE (@var{fntype})
|
|
Define this to a nonzero value if it is the responsibility of the
|
|
caller to allocate the area reserved for arguments passed in registers
|
|
when calling a function of @var{fntype}. @var{fntype} may be NULL
|
|
if the function called is a library function.
|
|
|
|
If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls
|
|
whether the space for these arguments counts in the value of
|
|
@code{crtl->outgoing_args_size}.
|
|
@end defmac
|
|
|
|
@defmac STACK_PARMS_IN_REG_PARM_AREA
|
|
Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the
|
|
stack parameters don't skip the area specified by it.
|
|
@c i changed this, makes more sens and it should have taken care of the
|
|
@c overfull.. not as specific, tho. --mew 5feb93
|
|
|
|
Normally, when a parameter is not passed in registers, it is placed on the
|
|
stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro
|
|
suppresses this behavior and causes the parameter to be passed on the
|
|
stack in its natural location.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} poly_int64 TARGET_RETURN_POPS_ARGS (tree @var{fundecl}, tree @var{funtype}, poly_int64 @var{size})
|
|
This target hook returns the number of bytes of its own arguments that
|
|
a function pops on returning, or 0 if the function pops no arguments
|
|
and the caller must therefore pop them all after the function returns.
|
|
|
|
@var{fundecl} is a C variable whose value is a tree node that describes
|
|
the function in question. Normally it is a node of type
|
|
@code{FUNCTION_DECL} that describes the declaration of the function.
|
|
From this you can obtain the @code{DECL_ATTRIBUTES} of the function.
|
|
|
|
@var{funtype} is a C variable whose value is a tree node that
|
|
describes the function in question. Normally it is a node of type
|
|
@code{FUNCTION_TYPE} that describes the data type of the function.
|
|
From this it is possible to obtain the data types of the value and
|
|
arguments (if known).
|
|
|
|
When a call to a library function is being considered, @var{fundecl}
|
|
will contain an identifier node for the library function. Thus, if
|
|
you need to distinguish among various library functions, you can do so
|
|
by their names. Note that ``library function'' in this context means
|
|
a function used to perform arithmetic, whose name is known specially
|
|
in the compiler and was not mentioned in the C code being compiled.
|
|
|
|
@var{size} is the number of bytes of arguments passed on the
|
|
stack. If a variable number of bytes is passed, it is zero, and
|
|
argument popping will always be the responsibility of the calling function.
|
|
|
|
On the VAX, all functions always pop their arguments, so the definition
|
|
of this macro is @var{size}. On the 68000, using the standard
|
|
calling convention, no functions pop their arguments, so the value of
|
|
the macro is always 0 in this case. But an alternative calling
|
|
convention is available in which functions that take a fixed number of
|
|
arguments pop them but other functions (such as @code{printf}) pop
|
|
nothing (the caller pops all). When this convention is in use,
|
|
@var{funtype} is examined to determine whether a function takes a fixed
|
|
number of arguments.
|
|
@end deftypefn
|
|
|
|
@defmac CALL_POPS_ARGS (@var{cum})
|
|
A C expression that should indicate the number of bytes a call sequence
|
|
pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS}
|
|
when compiling a function call.
|
|
|
|
@var{cum} is the variable in which all arguments to the called function
|
|
have been accumulated.
|
|
|
|
On certain architectures, such as the SH5, a call trampoline is used
|
|
that pops certain registers off the stack, depending on the arguments
|
|
that have been passed to the function. Since this is a property of the
|
|
call site, not of the called function, @code{RETURN_POPS_ARGS} is not
|
|
appropriate.
|
|
@end defmac
|
|
|
|
@node Register Arguments
|
|
@subsection Passing Arguments in Registers
|
|
@cindex arguments in registers
|
|
@cindex registers arguments
|
|
|
|
This section describes the macros which let you control how various
|
|
types of arguments are passed in registers or how they are arranged in
|
|
the stack.
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_FUNCTION_ARG (cumulative_args_t @var{ca}, const function_arg_info @var{&arg})
|
|
Return an RTX indicating whether function argument @var{arg} is passed
|
|
in a register and if so, which register. Argument @var{ca} summarizes all
|
|
the previous arguments.
|
|
|
|
The return value is usually either a @code{reg} RTX for the hard
|
|
register in which to pass the argument, or zero to pass the argument
|
|
on the stack.
|
|
|
|
The value of the expression can also be a @code{parallel} RTX@. This is
|
|
used when an argument is passed in multiple locations. The mode of the
|
|
@code{parallel} should be the mode of the entire argument. The
|
|
@code{parallel} holds any number of @code{expr_list} pairs; each one
|
|
describes where part of the argument is passed. In each
|
|
@code{expr_list} the first operand must be a @code{reg} RTX for the hard
|
|
register in which to pass this part of the argument, and the mode of the
|
|
register RTX indicates how large this part of the argument is. The
|
|
second operand of the @code{expr_list} is a @code{const_int} which gives
|
|
the offset in bytes into the entire argument of where this part starts.
|
|
As a special exception the first @code{expr_list} in the @code{parallel}
|
|
RTX may have a first operand of zero. This indicates that the entire
|
|
argument is also stored on the stack.
|
|
|
|
The last time this hook is called, it is called with @code{MODE ==
|
|
VOIDmode}, and its result is passed to the @code{call} or @code{call_value}
|
|
pattern as operands 2 and 3 respectively.
|
|
|
|
@cindex @file{stdarg.h} and register arguments
|
|
The usual way to make the ISO library @file{stdarg.h} work on a
|
|
machine where some arguments are usually passed in registers, is to
|
|
cause nameless arguments to be passed on the stack instead. This is
|
|
done by making @code{TARGET_FUNCTION_ARG} return 0 whenever
|
|
@var{named} is @code{false}.
|
|
|
|
@cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{TARGET_FUNCTION_ARG}
|
|
@cindex @code{REG_PARM_STACK_SPACE}, and @code{TARGET_FUNCTION_ARG}
|
|
You may use the hook @code{targetm.calls.must_pass_in_stack}
|
|
in the definition of this macro to determine if this argument is of a
|
|
type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE}
|
|
is not defined and @code{TARGET_FUNCTION_ARG} returns nonzero for such an
|
|
argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is
|
|
defined, the argument will be computed in the stack and then loaded into
|
|
a register.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_MUST_PASS_IN_STACK (const function_arg_info @var{&arg})
|
|
This target hook should return @code{true} if we should not pass @var{arg}
|
|
solely in registers. The file @file{expr.h} defines a
|
|
definition that is usually appropriate, refer to @file{expr.h} for additional
|
|
documentation.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_FUNCTION_INCOMING_ARG (cumulative_args_t @var{ca}, const function_arg_info @var{&arg})
|
|
Define this hook if the caller and callee on the target have different
|
|
views of where arguments are passed. Also define this hook if there are
|
|
functions that are never directly called, but are invoked by the hardware
|
|
and which have nonstandard calling conventions.
|
|
|
|
In this case @code{TARGET_FUNCTION_ARG} computes the register in
|
|
which the caller passes the value, and
|
|
@code{TARGET_FUNCTION_INCOMING_ARG} should be defined in a similar
|
|
fashion to tell the function being called where the arguments will
|
|
arrive.
|
|
|
|
@code{TARGET_FUNCTION_INCOMING_ARG} can also return arbitrary address
|
|
computation using hard register, which can be forced into a register,
|
|
so that it can be used to pass special arguments.
|
|
|
|
If @code{TARGET_FUNCTION_INCOMING_ARG} is not defined,
|
|
@code{TARGET_FUNCTION_ARG} serves both purposes.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_USE_PSEUDO_PIC_REG (void)
|
|
This hook should return 1 in case pseudo register should be created
|
|
for pic_offset_table_rtx during function expand.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_INIT_PIC_REG (void)
|
|
Perform a target dependent initialization of pic_offset_table_rtx.
|
|
This hook is called at the start of register allocation.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_ARG_PARTIAL_BYTES (cumulative_args_t @var{cum}, const function_arg_info @var{&arg})
|
|
This target hook returns the number of bytes at the beginning of an
|
|
argument that must be put in registers. The value must be zero for
|
|
arguments that are passed entirely in registers or that are entirely
|
|
pushed on the stack.
|
|
|
|
On some machines, certain arguments must be passed partially in
|
|
registers and partially in memory. On these machines, typically the
|
|
first few words of arguments are passed in registers, and the rest
|
|
on the stack. If a multi-word argument (a @code{double} or a
|
|
structure) crosses that boundary, its first few words must be passed
|
|
in registers and the rest must be pushed. This macro tells the
|
|
compiler when this occurs, and how many bytes should go in registers.
|
|
|
|
@code{TARGET_FUNCTION_ARG} for these arguments should return the first
|
|
register to be used by the caller for this argument; likewise
|
|
@code{TARGET_FUNCTION_INCOMING_ARG}, for the called function.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_PASS_BY_REFERENCE (cumulative_args_t @var{cum}, const function_arg_info @var{&arg})
|
|
This target hook should return @code{true} if argument @var{arg} at the
|
|
position indicated by @var{cum} should be passed by reference. This
|
|
predicate is queried after target independent reasons for being
|
|
passed by reference, such as @code{TREE_ADDRESSABLE (@var{arg}.type)}.
|
|
|
|
If the hook returns true, a copy of that argument is made in memory and a
|
|
pointer to the argument is passed instead of the argument itself.
|
|
The pointer is passed in whatever way is appropriate for passing a pointer
|
|
to that type.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CALLEE_COPIES (cumulative_args_t @var{cum}, const function_arg_info @var{&arg})
|
|
The function argument described by the parameters to this hook is
|
|
known to be passed by reference. The hook should return true if the
|
|
function argument should be copied by the callee instead of copied
|
|
by the caller.
|
|
|
|
For any argument for which the hook returns true, if it can be
|
|
determined that the argument is not modified, then a copy need
|
|
not be generated.
|
|
|
|
The default version of this hook always returns false.
|
|
@end deftypefn
|
|
|
|
@defmac CUMULATIVE_ARGS
|
|
A C type for declaring a variable that is used as the first argument
|
|
of @code{TARGET_FUNCTION_ARG} and other related values. For some
|
|
target machines, the type @code{int} suffices and can hold the number
|
|
of bytes of argument so far.
|
|
|
|
There is no need to record in @code{CUMULATIVE_ARGS} anything about the
|
|
arguments that have been passed on the stack. The compiler has other
|
|
variables to keep track of that. For target machines on which all
|
|
arguments are passed on the stack, there is no need to store anything in
|
|
@code{CUMULATIVE_ARGS}; however, the data structure must exist and
|
|
should not be empty, so use @code{int}.
|
|
@end defmac
|
|
|
|
@defmac OVERRIDE_ABI_FORMAT (@var{fndecl})
|
|
If defined, this macro is called before generating any code for a
|
|
function, but after the @var{cfun} descriptor for the function has been
|
|
created. The back end may use this macro to update @var{cfun} to
|
|
reflect an ABI other than that which would normally be used by default.
|
|
If the compiler is generating code for a compiler-generated function,
|
|
@var{fndecl} may be @code{NULL}.
|
|
@end defmac
|
|
|
|
@defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args})
|
|
A C statement (sans semicolon) for initializing the variable
|
|
@var{cum} for the state at the beginning of the argument list. The
|
|
variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype}
|
|
is the tree node for the data type of the function which will receive
|
|
the args, or 0 if the args are to a compiler support library function.
|
|
For direct calls that are not libcalls, @var{fndecl} contain the
|
|
declaration node of the function. @var{fndecl} is also set when
|
|
@code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function
|
|
being compiled. @var{n_named_args} is set to the number of named
|
|
arguments, including a structure return address if it is passed as a
|
|
parameter, when making a call. When processing incoming arguments,
|
|
@var{n_named_args} is set to @minus{}1.
|
|
|
|
When processing a call to a compiler support library function,
|
|
@var{libname} identifies which one. It is a @code{symbol_ref} rtx which
|
|
contains the name of the function, as a string. @var{libname} is 0 when
|
|
an ordinary C function call is being processed. Thus, each time this
|
|
macro is called, either @var{libname} or @var{fntype} is nonzero, but
|
|
never both of them at once.
|
|
@end defmac
|
|
|
|
@defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname})
|
|
Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls,
|
|
it gets a @code{MODE} argument instead of @var{fntype}, that would be
|
|
@code{NULL}. @var{indirect} would always be zero, too. If this macro
|
|
is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname,
|
|
0)} is used instead.
|
|
@end defmac
|
|
|
|
@defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname})
|
|
Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of
|
|
finding the arguments for the function being compiled. If this macro is
|
|
undefined, @code{INIT_CUMULATIVE_ARGS} is used instead.
|
|
|
|
The value passed for @var{libname} is always 0, since library routines
|
|
with special calling conventions are never compiled with GCC@. The
|
|
argument @var{libname} exists for symmetry with
|
|
@code{INIT_CUMULATIVE_ARGS}.
|
|
@c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe.
|
|
@c --mew 5feb93 i switched the order of the sentences. --mew 10feb93
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_FUNCTION_ARG_ADVANCE (cumulative_args_t @var{ca}, const function_arg_info @var{&arg})
|
|
This hook updates the summarizer variable pointed to by @var{ca} to
|
|
advance past argument @var{arg} in the argument list. Once this is done,
|
|
the variable @var{cum} is suitable for analyzing the @emph{following}
|
|
argument with @code{TARGET_FUNCTION_ARG}, etc.
|
|
|
|
This hook need not do anything if the argument in question was passed
|
|
on the stack. The compiler knows how to track the amount of stack space
|
|
used for arguments without any special help.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} HOST_WIDE_INT TARGET_FUNCTION_ARG_OFFSET (machine_mode @var{mode}, const_tree @var{type})
|
|
This hook returns the number of bytes to add to the offset of an
|
|
argument of type @var{type} and mode @var{mode} when passed in memory.
|
|
This is needed for the SPU, which passes @code{char} and @code{short}
|
|
arguments in the preferred slot that is in the middle of the quad word
|
|
instead of starting at the top. The default implementation returns 0.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} pad_direction TARGET_FUNCTION_ARG_PADDING (machine_mode @var{mode}, const_tree @var{type})
|
|
This hook determines whether, and in which direction, to pad out
|
|
an argument of mode @var{mode} and type @var{type}. It returns
|
|
@code{PAD_UPWARD} to insert padding above the argument, @code{PAD_DOWNWARD}
|
|
to insert padding below the argument, or @code{PAD_NONE} to inhibit padding.
|
|
|
|
The @emph{amount} of padding is not controlled by this hook, but by
|
|
@code{TARGET_FUNCTION_ARG_ROUND_BOUNDARY}. It is always just enough
|
|
to reach the next multiple of that boundary.
|
|
|
|
This hook has a default definition that is right for most systems.
|
|
For little-endian machines, the default is to pad upward. For
|
|
big-endian machines, the default is to pad downward for an argument of
|
|
constant size shorter than an @code{int}, and upward otherwise.
|
|
@end deftypefn
|
|
|
|
@defmac PAD_VARARGS_DOWN
|
|
If defined, a C expression which determines whether the default
|
|
implementation of va_arg will attempt to pad down before reading the
|
|
next argument, if that argument is smaller than its aligned space as
|
|
controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such
|
|
arguments are padded down if @code{BYTES_BIG_ENDIAN} is true.
|
|
@end defmac
|
|
|
|
@defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first})
|
|
Specify padding for the last element of a block move between registers and
|
|
memory. @var{first} is nonzero if this is the only element. Defining this
|
|
macro allows better control of register function parameters on big-endian
|
|
machines, without using @code{PARALLEL} rtl. In particular,
|
|
@code{MUST_PASS_IN_STACK} need not test padding and mode of types in
|
|
registers, as there is no longer a "wrong" part of a register; For example,
|
|
a three byte aggregate may be passed in the high part of a register if so
|
|
required.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_FUNCTION_ARG_BOUNDARY (machine_mode @var{mode}, const_tree @var{type})
|
|
This hook returns the alignment boundary, in bits, of an argument
|
|
with the specified mode and type. The default hook returns
|
|
@code{PARM_BOUNDARY} for all arguments.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_FUNCTION_ARG_ROUND_BOUNDARY (machine_mode @var{mode}, const_tree @var{type})
|
|
Normally, the size of an argument is rounded up to @code{PARM_BOUNDARY},
|
|
which is the default value for this hook. You can define this hook to
|
|
return a different value if an argument size must be rounded to a larger
|
|
value.
|
|
@end deftypefn
|
|
|
|
@defmac FUNCTION_ARG_REGNO_P (@var{regno})
|
|
A C expression that is nonzero if @var{regno} is the number of a hard
|
|
register in which function arguments are sometimes passed. This does
|
|
@emph{not} include implicit arguments such as the static chain and
|
|
the structure-value address. On many machines, no registers can be
|
|
used for this purpose since all function arguments are pushed on the
|
|
stack.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SPLIT_COMPLEX_ARG (const_tree @var{type})
|
|
This hook should return true if parameter of type @var{type} are passed
|
|
as two scalar parameters. By default, GCC will attempt to pack complex
|
|
arguments into the target's word size. Some ABIs require complex arguments
|
|
to be split and treated as their individual components. For example, on
|
|
AIX64, complex floats should be passed in a pair of floating point
|
|
registers, even though a complex float would fit in one 64-bit floating
|
|
point register.
|
|
|
|
The default value of this hook is @code{NULL}, which is treated as always
|
|
false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_BUILD_BUILTIN_VA_LIST (void)
|
|
This hook returns a type node for @code{va_list} for the target.
|
|
The default version of the hook returns @code{void*}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_ENUM_VA_LIST_P (int @var{idx}, const char **@var{pname}, tree *@var{ptree})
|
|
This target hook is used in function @code{c_common_nodes_and_builtins}
|
|
to iterate through the target specific builtin types for va_list. The
|
|
variable @var{idx} is used as iterator. @var{pname} has to be a pointer
|
|
to a @code{const char *} and @var{ptree} a pointer to a @code{tree} typed
|
|
variable.
|
|
The arguments @var{pname} and @var{ptree} are used to store the result of
|
|
this macro and are set to the name of the va_list builtin type and its
|
|
internal type.
|
|
If the return value of this macro is zero, then there is no more element.
|
|
Otherwise the @var{IDX} should be increased for the next call of this
|
|
macro to iterate through all types.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_FN_ABI_VA_LIST (tree @var{fndecl})
|
|
This hook returns the va_list type of the calling convention specified by
|
|
@var{fndecl}.
|
|
The default version of this hook returns @code{va_list_type_node}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_CANONICAL_VA_LIST_TYPE (tree @var{type})
|
|
This hook returns the va_list type of the calling convention specified by the
|
|
type of @var{type}. If @var{type} is not a valid va_list type, it returns
|
|
@code{NULL_TREE}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_GIMPLIFY_VA_ARG_EXPR (tree @var{valist}, tree @var{type}, gimple_seq *@var{pre_p}, gimple_seq *@var{post_p})
|
|
This hook performs target-specific gimplification of
|
|
@code{VA_ARG_EXPR}. The first two parameters correspond to the
|
|
arguments to @code{va_arg}; the latter two are as in
|
|
@code{gimplify.cc:gimplify_expr}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_VALID_POINTER_MODE (scalar_int_mode @var{mode})
|
|
Define this to return nonzero if the port can handle pointers
|
|
with machine mode @var{mode}. The default version of this
|
|
hook returns true for both @code{ptr_mode} and @code{Pmode}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_REF_MAY_ALIAS_ERRNO (ao_ref *@var{ref})
|
|
Define this to return nonzero if the memory reference @var{ref}
|
|
may alias with the system C library errno location. The default
|
|
version of this hook assumes the system C library errno location
|
|
is either a declaration of type int or accessed by dereferencing
|
|
a pointer to int.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} machine_mode TARGET_TRANSLATE_MODE_ATTRIBUTE (machine_mode @var{mode})
|
|
Define this hook if during mode attribute processing, the port should
|
|
translate machine_mode @var{mode} to another mode. For example, rs6000's
|
|
@code{KFmode}, when it is the same as @code{TFmode}.
|
|
|
|
The default version of the hook returns that mode that was passed in.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SCALAR_MODE_SUPPORTED_P (scalar_mode @var{mode})
|
|
Define this to return nonzero if the port is prepared to handle
|
|
insns involving scalar mode @var{mode}. For a scalar mode to be
|
|
considered supported, all the basic arithmetic and comparisons
|
|
must work.
|
|
|
|
The default version of this hook returns true for any mode
|
|
required to handle the basic C types (as defined by the port).
|
|
Included here are the double-word arithmetic supported by the
|
|
code in @file{optabs.cc}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_VECTOR_MODE_SUPPORTED_P (machine_mode @var{mode})
|
|
Define this to return nonzero if the port is prepared to handle
|
|
insns involving vector mode @var{mode}. At the very least, it
|
|
must have move patterns for this mode.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_COMPATIBLE_VECTOR_TYPES_P (const_tree @var{type1}, const_tree @var{type2})
|
|
Return true if there is no target-specific reason for treating
|
|
vector types @var{type1} and @var{type2} as distinct types. The caller
|
|
has already checked for target-independent reasons, meaning that the
|
|
types are known to have the same mode, to have the same number of elements,
|
|
and to have what the caller considers to be compatible element types.
|
|
|
|
The main reason for defining this hook is to reject pairs of types
|
|
that are handled differently by the target's calling convention.
|
|
For example, when a new @var{N}-bit vector architecture is added
|
|
to a target, the target may want to handle normal @var{N}-bit
|
|
@code{VECTOR_TYPE} arguments and return values in the same way as
|
|
before, to maintain backwards compatibility. However, it may also
|
|
provide new, architecture-specific @code{VECTOR_TYPE}s that are passed
|
|
and returned in a more efficient way. It is then important to maintain
|
|
a distinction between the ``normal'' @code{VECTOR_TYPE}s and the new
|
|
architecture-specific ones.
|
|
|
|
The default implementation returns true, which is correct for most targets.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} opt_machine_mode TARGET_ARRAY_MODE (machine_mode @var{mode}, unsigned HOST_WIDE_INT @var{nelems})
|
|
Return the mode that GCC should use for an array that has
|
|
@var{nelems} elements, with each element having mode @var{mode}.
|
|
Return no mode if the target has no special requirements. In the
|
|
latter case, GCC looks for an integer mode of the appropriate size
|
|
if available and uses BLKmode otherwise. Usually the search for the
|
|
integer mode is limited to @code{MAX_FIXED_MODE_SIZE}, but the
|
|
@code{TARGET_ARRAY_MODE_SUPPORTED_P} hook allows a larger mode to be
|
|
used in specific cases.
|
|
|
|
The main use of this hook is to specify that an array of vectors should
|
|
also have a vector mode. The default implementation returns no mode.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ARRAY_MODE_SUPPORTED_P (machine_mode @var{mode}, unsigned HOST_WIDE_INT @var{nelems})
|
|
Return true if GCC should try to use a scalar mode to store an array
|
|
of @var{nelems} elements, given that each element has mode @var{mode}.
|
|
Returning true here overrides the usual @code{MAX_FIXED_MODE} limit
|
|
and allows GCC to use any defined integer mode.
|
|
|
|
One use of this hook is to support vector load and store operations
|
|
that operate on several homogeneous vectors. For example, ARM NEON
|
|
has operations like:
|
|
|
|
@smallexample
|
|
int8x8x3_t vld3_s8 (const int8_t *)
|
|
@end smallexample
|
|
|
|
where the return type is defined as:
|
|
|
|
@smallexample
|
|
typedef struct int8x8x3_t
|
|
@{
|
|
int8x8_t val[3];
|
|
@} int8x8x3_t;
|
|
@end smallexample
|
|
|
|
If this hook allows @code{val} to have a scalar mode, then
|
|
@code{int8x8x3_t} can have the same mode. GCC can then store
|
|
@code{int8x8x3_t}s in registers rather than forcing them onto the stack.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P (scalar_float_mode @var{mode})
|
|
Define this to return nonzero if libgcc provides support for the
|
|
floating-point mode @var{mode}, which is known to pass
|
|
@code{TARGET_SCALAR_MODE_SUPPORTED_P}. The default version of this
|
|
hook returns true for all of @code{SFmode}, @code{DFmode},
|
|
@code{XFmode} and @code{TFmode}, if such modes exist.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} opt_scalar_float_mode TARGET_FLOATN_MODE (int @var{n}, bool @var{extended})
|
|
Define this to return the machine mode to use for the type
|
|
@code{_Float@var{n}}, if @var{extended} is false, or the type
|
|
@code{_Float@var{n}x}, if @var{extended} is true. If such a type is not
|
|
supported, return @code{opt_scalar_float_mode ()}. The default version of
|
|
this hook returns @code{SFmode} for @code{_Float32}, @code{DFmode} for
|
|
@code{_Float64} and @code{_Float32x} and @code{TFmode} for
|
|
@code{_Float128}, if those modes exist and satisfy the requirements for
|
|
those types and pass @code{TARGET_SCALAR_MODE_SUPPORTED_P} and
|
|
@code{TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P}; for @code{_Float64x}, it
|
|
returns the first of @code{XFmode} and @code{TFmode} that exists and
|
|
satisfies the same requirements; for other types, it returns
|
|
@code{opt_scalar_float_mode ()}. The hook is only called for values
|
|
of @var{n} and @var{extended} that are valid according to
|
|
ISO/IEC TS 18661-3:2015; that is, @var{n} is one of 32, 64, 128, or,
|
|
if @var{extended} is false, 16 or greater than 128 and a multiple of 32.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_FLOATN_BUILTIN_P (int @var{func})
|
|
Define this to return true if the @code{_Float@var{n}} and
|
|
@code{_Float@var{n}x} built-in functions should implicitly enable the
|
|
built-in function without the @code{__builtin_} prefix in addition to the
|
|
normal built-in function with the @code{__builtin_} prefix. The default is
|
|
to only enable built-in functions without the @code{__builtin_} prefix for
|
|
the GNU C langauge. In strict ANSI/ISO mode, the built-in function without
|
|
the @code{__builtin_} prefix is not enabled. The argument @code{FUNC} is the
|
|
@code{enum built_in_function} id of the function to be enabled.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P (machine_mode @var{mode})
|
|
Define this to return nonzero for machine modes for which the port has
|
|
small register classes. If this target hook returns nonzero for a given
|
|
@var{mode}, the compiler will try to minimize the lifetime of registers
|
|
in @var{mode}. The hook may be called with @code{VOIDmode} as argument.
|
|
In this case, the hook is expected to return nonzero if it returns nonzero
|
|
for any mode.
|
|
|
|
On some machines, it is risky to let hard registers live across arbitrary
|
|
insns. Typically, these machines have instructions that require values
|
|
to be in specific registers (like an accumulator), and reload will fail
|
|
if the required hard register is used for another purpose across such an
|
|
insn.
|
|
|
|
Passes before reload do not know which hard registers will be used
|
|
in an instruction, but the machine modes of the registers set or used in
|
|
the instruction are already known. And for some machines, register
|
|
classes are small for, say, integer registers but not for floating point
|
|
registers. For example, the AMD x86-64 architecture requires specific
|
|
registers for the legacy x86 integer instructions, but there are many
|
|
SSE registers for floating point operations. On such targets, a good
|
|
strategy may be to return nonzero from this hook for @code{INTEGRAL_MODE_P}
|
|
machine modes but zero for the SSE register classes.
|
|
|
|
The default version of this hook returns false for any mode. It is always
|
|
safe to redefine this hook to return with a nonzero value. But if you
|
|
unnecessarily define it, you will reduce the amount of optimizations
|
|
that can be performed in some cases. If you do not define this hook
|
|
to return a nonzero value when it is required, the compiler will run out
|
|
of spill registers and print a fatal error message.
|
|
@end deftypefn
|
|
|
|
@node Scalar Return
|
|
@subsection How Scalar Function Values Are Returned
|
|
@cindex return values in registers
|
|
@cindex values, returned by functions
|
|
@cindex scalars, returned as values
|
|
|
|
This section discusses the macros that control returning scalars as
|
|
values---values that can fit in registers.
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_FUNCTION_VALUE (const_tree @var{ret_type}, const_tree @var{fn_decl_or_type}, bool @var{outgoing})
|
|
|
|
Define this to return an RTX representing the place where a function
|
|
returns or receives a value of data type @var{ret_type}, a tree node
|
|
representing a data type. @var{fn_decl_or_type} is a tree node
|
|
representing @code{FUNCTION_DECL} or @code{FUNCTION_TYPE} of a
|
|
function being called. If @var{outgoing} is false, the hook should
|
|
compute the register in which the caller will see the return value.
|
|
Otherwise, the hook should return an RTX representing the place where
|
|
a function returns a value.
|
|
|
|
On many machines, only @code{TYPE_MODE (@var{ret_type})} is relevant.
|
|
(Actually, on most machines, scalar values are returned in the same
|
|
place regardless of mode.) The value of the expression is usually a
|
|
@code{reg} RTX for the hard register where the return value is stored.
|
|
The value can also be a @code{parallel} RTX, if the return value is in
|
|
multiple places. See @code{TARGET_FUNCTION_ARG} for an explanation of the
|
|
@code{parallel} form. Note that the callee will populate every
|
|
location specified in the @code{parallel}, but if the first element of
|
|
the @code{parallel} contains the whole return value, callers will use
|
|
that element as the canonical location and ignore the others. The m68k
|
|
port uses this type of @code{parallel} to return pointers in both
|
|
@samp{%a0} (the canonical location) and @samp{%d0}.
|
|
|
|
If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply
|
|
the same promotion rules specified in @code{PROMOTE_MODE} if
|
|
@var{valtype} is a scalar type.
|
|
|
|
If the precise function being called is known, @var{func} is a tree
|
|
node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null
|
|
pointer. This makes it possible to use a different value-returning
|
|
convention for specific functions when all their calls are
|
|
known.
|
|
|
|
Some target machines have ``register windows'' so that the register in
|
|
which a function returns its value is not the same as the one in which
|
|
the caller sees the value. For such machines, you should return
|
|
different RTX depending on @var{outgoing}.
|
|
|
|
@code{TARGET_FUNCTION_VALUE} is not used for return values with
|
|
aggregate data types, because these are returned in another way. See
|
|
@code{TARGET_STRUCT_VALUE_RTX} and related macros, below.
|
|
@end deftypefn
|
|
|
|
@defmac FUNCTION_VALUE (@var{valtype}, @var{func})
|
|
This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for
|
|
a new target instead.
|
|
@end defmac
|
|
|
|
@defmac LIBCALL_VALUE (@var{mode})
|
|
A C expression to create an RTX representing the place where a library
|
|
function returns a value of mode @var{mode}.
|
|
|
|
Note that ``library function'' in this context means a compiler
|
|
support routine, used to perform arithmetic, whose name is known
|
|
specially by the compiler and was not mentioned in the C code being
|
|
compiled.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_LIBCALL_VALUE (machine_mode @var{mode}, const_rtx @var{fun})
|
|
Define this hook if the back-end needs to know the name of the libcall
|
|
function in order to determine where the result should be returned.
|
|
|
|
The mode of the result is given by @var{mode} and the name of the called
|
|
library function is given by @var{fun}. The hook should return an RTX
|
|
representing the place where the library function result will be returned.
|
|
|
|
If this hook is not defined, then LIBCALL_VALUE will be used.
|
|
@end deftypefn
|
|
|
|
@defmac FUNCTION_VALUE_REGNO_P (@var{regno})
|
|
A C expression that is nonzero if @var{regno} is the number of a hard
|
|
register in which the values of called function may come back.
|
|
|
|
A register whose use for returning values is limited to serving as the
|
|
second of a pair (for a value of type @code{double}, say) need not be
|
|
recognized by this macro. So for most machines, this definition
|
|
suffices:
|
|
|
|
@smallexample
|
|
#define FUNCTION_VALUE_REGNO_P(N) ((N) == 0)
|
|
@end smallexample
|
|
|
|
If the machine has register windows, so that the caller and the called
|
|
function use different registers for the return value, this macro
|
|
should recognize only the caller's register numbers.
|
|
|
|
This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE_REGNO_P}
|
|
for a new target instead.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_FUNCTION_VALUE_REGNO_P (const unsigned int @var{regno})
|
|
A target hook that return @code{true} if @var{regno} is the number of a hard
|
|
register in which the values of called function may come back.
|
|
|
|
A register whose use for returning values is limited to serving as the
|
|
second of a pair (for a value of type @code{double}, say) need not be
|
|
recognized by this target hook.
|
|
|
|
If the machine has register windows, so that the caller and the called
|
|
function use different registers for the return value, this target hook
|
|
should recognize only the caller's register numbers.
|
|
|
|
If this hook is not defined, then FUNCTION_VALUE_REGNO_P will be used.
|
|
@end deftypefn
|
|
|
|
@defmac APPLY_RESULT_SIZE
|
|
Define this macro if @samp{untyped_call} and @samp{untyped_return}
|
|
need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for
|
|
saving and restoring an arbitrary return value.
|
|
@end defmac
|
|
|
|
@deftypevr {Target Hook} bool TARGET_OMIT_STRUCT_RETURN_REG
|
|
Normally, when a function returns a structure by memory, the address
|
|
is passed as an invisible pointer argument, but the compiler also
|
|
arranges to return the address from the function like it would a normal
|
|
pointer return value. Define this to true if that behavior is
|
|
undesirable on your target.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} bool TARGET_RETURN_IN_MSB (const_tree @var{type})
|
|
This hook should return true if values of type @var{type} are returned
|
|
at the most significant end of a register (in other words, if they are
|
|
padded at the least significant end). You can assume that @var{type}
|
|
is returned in a register; the caller is required to check this.
|
|
|
|
Note that the register provided by @code{TARGET_FUNCTION_VALUE} must
|
|
be able to hold the complete return value. For example, if a 1-, 2-
|
|
or 3-byte structure is returned at the most significant end of a
|
|
4-byte register, @code{TARGET_FUNCTION_VALUE} should provide an
|
|
@code{SImode} rtx.
|
|
@end deftypefn
|
|
|
|
@node Aggregate Return
|
|
@subsection How Large Values Are Returned
|
|
@cindex aggregates as return values
|
|
@cindex large return values
|
|
@cindex returning aggregate values
|
|
@cindex structure value address
|
|
|
|
When a function value's mode is @code{BLKmode} (and in some other
|
|
cases), the value is not returned according to
|
|
@code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the
|
|
caller passes the address of a block of memory in which the value
|
|
should be stored. This address is called the @dfn{structure value
|
|
address}.
|
|
|
|
This section describes how to control returning structure values in
|
|
memory.
|
|
|
|
@deftypefn {Target Hook} bool TARGET_RETURN_IN_MEMORY (const_tree @var{type}, const_tree @var{fntype})
|
|
This target hook should return a nonzero value to say to return the
|
|
function value in memory, just as large structures are always returned.
|
|
Here @var{type} will be the data type of the value, and @var{fntype}
|
|
will be the type of the function doing the returning, or @code{NULL} for
|
|
libcalls.
|
|
|
|
Note that values of mode @code{BLKmode} must be explicitly handled
|
|
by this function. Also, the option @option{-fpcc-struct-return}
|
|
takes effect regardless of this macro. On most systems, it is
|
|
possible to leave the hook undefined; this causes a default
|
|
definition to be used, whose value is the constant 1 for @code{BLKmode}
|
|
values, and 0 otherwise.
|
|
|
|
Do not use this hook to indicate that structures and unions should always
|
|
be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN}
|
|
to indicate this.
|
|
@end deftypefn
|
|
|
|
@defmac DEFAULT_PCC_STRUCT_RETURN
|
|
Define this macro to be 1 if all structure and union return values must be
|
|
in memory. Since this results in slower code, this should be defined
|
|
only if needed for compatibility with other compilers or with an ABI@.
|
|
If you define this macro to be 0, then the conventions used for structure
|
|
and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY}
|
|
target hook.
|
|
|
|
If not defined, this defaults to the value 1.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_STRUCT_VALUE_RTX (tree @var{fndecl}, int @var{incoming})
|
|
This target hook should return the location of the structure value
|
|
address (normally a @code{mem} or @code{reg}), or 0 if the address is
|
|
passed as an ``invisible'' first argument. Note that @var{fndecl} may
|
|
be @code{NULL}, for libcalls. You do not need to define this target
|
|
hook if the address is always passed as an ``invisible'' first
|
|
argument.
|
|
|
|
On some architectures the place where the structure value address
|
|
is found by the called function is not the same place that the
|
|
caller put it. This can be due to register windows, or it could
|
|
be because the function prologue moves it to a different place.
|
|
@var{incoming} is @code{1} or @code{2} when the location is needed in
|
|
the context of the called function, and @code{0} in the context of
|
|
the caller.
|
|
|
|
If @var{incoming} is nonzero and the address is to be found on the
|
|
stack, return a @code{mem} which refers to the frame pointer. If
|
|
@var{incoming} is @code{2}, the result is being used to fetch the
|
|
structure value address at the beginning of a function. If you need
|
|
to emit adjusting code, you should do it at this point.
|
|
@end deftypefn
|
|
|
|
@defmac PCC_STATIC_STRUCT_RETURN
|
|
Define this macro if the usual system convention on the target machine
|
|
for returning structures and unions is for the called function to return
|
|
the address of a static variable containing the value.
|
|
|
|
Do not define this if the usual system convention is for the caller to
|
|
pass an address to the subroutine.
|
|
|
|
This macro has effect in @option{-fpcc-struct-return} mode, but it does
|
|
nothing when you use @option{-freg-struct-return} mode.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} fixed_size_mode TARGET_GET_RAW_RESULT_MODE (int @var{regno})
|
|
This target hook returns the mode to be used when accessing raw return
|
|
registers in @code{__builtin_return}. Define this macro if the value
|
|
in @var{reg_raw_mode} is not correct.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} fixed_size_mode TARGET_GET_RAW_ARG_MODE (int @var{regno})
|
|
This target hook returns the mode to be used when accessing raw argument
|
|
registers in @code{__builtin_apply_args}. Define this macro if the value
|
|
in @var{reg_raw_mode} is not correct.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_EMPTY_RECORD_P (const_tree @var{type})
|
|
This target hook returns true if the type is an empty record. The default
|
|
is to return @code{false}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_WARN_PARAMETER_PASSING_ABI (cumulative_args_t @var{ca}, tree @var{type})
|
|
This target hook warns about the change in empty class parameter passing
|
|
ABI.
|
|
@end deftypefn
|
|
|
|
@node Caller Saves
|
|
@subsection Caller-Saves Register Allocation
|
|
|
|
If you enable it, GCC can save registers around function calls. This
|
|
makes it possible to use call-clobbered registers to hold variables that
|
|
must live across calls.
|
|
|
|
@defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs})
|
|
A C expression specifying which mode is required for saving @var{nregs}
|
|
of a pseudo-register in call-clobbered hard register @var{regno}. If
|
|
@var{regno} is unsuitable for caller save, @code{VOIDmode} should be
|
|
returned. For most machines this macro need not be defined since GCC
|
|
will select the smallest suitable mode.
|
|
@end defmac
|
|
|
|
@node Function Entry
|
|
@subsection Function Entry and Exit
|
|
@cindex function entry and exit
|
|
@cindex prologue
|
|
@cindex epilogue
|
|
|
|
This section describes the macros that output function entry
|
|
(@dfn{prologue}) and exit (@dfn{epilogue}) code.
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY (FILE *@var{file}, unsigned HOST_WIDE_INT @var{patch_area_size}, bool @var{record_p})
|
|
Generate a patchable area at the function start, consisting of
|
|
@var{patch_area_size} NOP instructions. If the target supports named
|
|
sections and if @var{record_p} is true, insert a pointer to the current
|
|
location in the table of patchable functions. The default implementation
|
|
of the hook places the table of pointers in the special section named
|
|
@code{__patchable_function_entries}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file})
|
|
If defined, a function that outputs the assembler code for entry to a
|
|
function. The prologue is responsible for setting up the stack frame,
|
|
initializing the frame pointer register, saving registers that must be
|
|
saved, and allocating @var{size} additional bytes of storage for the
|
|
local variables. @var{file} is a stdio stream to which the assembler
|
|
code should be output.
|
|
|
|
The label for the beginning of the function need not be output by this
|
|
macro. That has already been done when the macro is run.
|
|
|
|
@findex regs_ever_live
|
|
To determine which registers to save, the macro can refer to the array
|
|
@code{regs_ever_live}: element @var{r} is nonzero if hard register
|
|
@var{r} is used anywhere within the function. This implies the function
|
|
prologue should save register @var{r}, provided it is not one of the
|
|
call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use
|
|
@code{regs_ever_live}.)
|
|
|
|
On machines that have ``register windows'', the function entry code does
|
|
not save on the stack the registers that are in the windows, even if
|
|
they are supposed to be preserved by function calls; instead it takes
|
|
appropriate steps to ``push'' the register stack, if any non-call-used
|
|
registers are used in the function.
|
|
|
|
@findex frame_pointer_needed
|
|
On machines where functions may or may not have frame-pointers, the
|
|
function entry code must vary accordingly; it must set up the frame
|
|
pointer if one is wanted, and not otherwise. To determine whether a
|
|
frame pointer is in wanted, the macro can refer to the variable
|
|
@code{frame_pointer_needed}. The variable's value will be 1 at run
|
|
time in a function that needs a frame pointer. @xref{Elimination}.
|
|
|
|
The function entry code is responsible for allocating any stack space
|
|
required for the function. This stack space consists of the regions
|
|
listed below. In most cases, these regions are allocated in the
|
|
order listed, with the last listed region closest to the top of the
|
|
stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and
|
|
the highest address if it is not defined). You can use a different order
|
|
for a machine if doing so is more convenient or required for
|
|
compatibility reasons. Except in cases where required by standard
|
|
or by a debugger, there is no reason why the stack layout used by GCC
|
|
need agree with that used by other compilers for a machine.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file})
|
|
If defined, a function that outputs assembler code at the end of a
|
|
prologue. This should be used when the function prologue is being
|
|
emitted as RTL, and you have some extra assembler that needs to be
|
|
emitted. @xref{prologue instruction pattern}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file})
|
|
If defined, a function that outputs assembler code at the start of an
|
|
epilogue. This should be used when the function epilogue is being
|
|
emitted as RTL, and you have some extra assembler that needs to be
|
|
emitted. @xref{epilogue instruction pattern}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file})
|
|
If defined, a function that outputs the assembler code for exit from a
|
|
function. The epilogue is responsible for restoring the saved
|
|
registers and stack pointer to their values when the function was
|
|
called, and returning control to the caller. This macro takes the
|
|
same argument as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the
|
|
registers to restore are determined from @code{regs_ever_live} and
|
|
@code{CALL_USED_REGISTERS} in the same way.
|
|
|
|
On some machines, there is a single instruction that does all the work
|
|
of returning from the function. On these machines, give that
|
|
instruction the name @samp{return} and do not define the macro
|
|
@code{TARGET_ASM_FUNCTION_EPILOGUE} at all.
|
|
|
|
Do not define a pattern named @samp{return} if you want the
|
|
@code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target
|
|
switches to control whether return instructions or epilogues are used,
|
|
define a @samp{return} pattern with a validity condition that tests the
|
|
target switches appropriately. If the @samp{return} pattern's validity
|
|
condition is false, epilogues will be used.
|
|
|
|
On machines where functions may or may not have frame-pointers, the
|
|
function exit code must vary accordingly. Sometimes the code for these
|
|
two cases is completely different. To determine whether a frame pointer
|
|
is wanted, the macro can refer to the variable
|
|
@code{frame_pointer_needed}. The variable's value will be 1 when compiling
|
|
a function that needs a frame pointer.
|
|
|
|
Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and
|
|
@code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially.
|
|
The C variable @code{current_function_is_leaf} is nonzero for such a
|
|
function. @xref{Leaf Functions}.
|
|
|
|
On some machines, some functions pop their arguments on exit while
|
|
others leave that for the caller to do. For example, the 68020 when
|
|
given @option{-mrtd} pops arguments in functions that take a fixed
|
|
number of arguments.
|
|
|
|
@findex pops_args
|
|
@findex crtl->args.pops_args
|
|
Your definition of the macro @code{RETURN_POPS_ARGS} decides which
|
|
functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE}
|
|
needs to know what was decided. The number of bytes of the current
|
|
function's arguments that this function should pop is available in
|
|
@code{crtl->args.pops_args}. @xref{Scalar Return}.
|
|
@end deftypefn
|
|
|
|
@itemize @bullet
|
|
@item
|
|
@findex pretend_args_size
|
|
@findex crtl->args.pretend_args_size
|
|
A region of @code{crtl->args.pretend_args_size} bytes of
|
|
uninitialized space just underneath the first argument arriving on the
|
|
stack. (This may not be at the very start of the allocated stack region
|
|
if the calling sequence has pushed anything else since pushing the stack
|
|
arguments. But usually, on such machines, nothing else has been pushed
|
|
yet, because the function prologue itself does all the pushing.) This
|
|
region is used on machines where an argument may be passed partly in
|
|
registers and partly in memory, and, in some cases to support the
|
|
features in @code{<stdarg.h>}.
|
|
|
|
@item
|
|
An area of memory used to save certain registers used by the function.
|
|
The size of this area, which may also include space for such things as
|
|
the return address and pointers to previous stack frames, is
|
|
machine-specific and usually depends on which registers have been used
|
|
in the function. Machines with register windows often do not require
|
|
a save area.
|
|
|
|
@item
|
|
A region of at least @var{size} bytes, possibly rounded up to an allocation
|
|
boundary, to contain the local variables of the function. On some machines,
|
|
this region and the save area may occur in the opposite order, with the
|
|
save area closer to the top of the stack.
|
|
|
|
@item
|
|
@cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames
|
|
Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of
|
|
@code{crtl->outgoing_args_size} bytes to be used for outgoing
|
|
argument lists of the function. @xref{Stack Arguments}.
|
|
@end itemize
|
|
|
|
@defmac EXIT_IGNORE_STACK
|
|
Define this macro as a C expression that is nonzero if the return
|
|
instruction or the function epilogue ignores the value of the stack
|
|
pointer; in other words, if it is safe to delete an instruction to
|
|
adjust the stack pointer before a return from the function. The
|
|
default is 0.
|
|
|
|
Note that this macro's value is relevant only for functions for which
|
|
frame pointers are maintained. It is never safe to delete a final
|
|
stack adjustment in a function that has no frame pointer, and the
|
|
compiler knows this regardless of @code{EXIT_IGNORE_STACK}.
|
|
@end defmac
|
|
|
|
@defmac EPILOGUE_USES (@var{regno})
|
|
Define this macro as a C expression that is nonzero for registers that are
|
|
used by the epilogue or the @samp{return} pattern. The stack and frame
|
|
pointer registers are already assumed to be used as needed.
|
|
@end defmac
|
|
|
|
@defmac EH_USES (@var{regno})
|
|
Define this macro as a C expression that is nonzero for registers that are
|
|
used by the exception handling mechanism, and so should be considered live
|
|
on entry to an exception edge.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_MI_THUNK (FILE *@var{file}, tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, HOST_WIDE_INT @var{vcall_offset}, tree @var{function})
|
|
A function that outputs the assembler code for a thunk
|
|
function, used to implement C++ virtual function calls with multiple
|
|
inheritance. The thunk acts as a wrapper around a virtual function,
|
|
adjusting the implicit object parameter before handing control off to
|
|
the real function.
|
|
|
|
First, emit code to add the integer @var{delta} to the location that
|
|
contains the incoming first argument. Assume that this argument
|
|
contains a pointer, and is the one used to pass the @code{this} pointer
|
|
in C++. This is the incoming argument @emph{before} the function prologue,
|
|
e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of
|
|
all other incoming arguments.
|
|
|
|
Then, if @var{vcall_offset} is nonzero, an additional adjustment should be
|
|
made after adding @code{delta}. In particular, if @var{p} is the
|
|
adjusted pointer, the following adjustment should be made:
|
|
|
|
@smallexample
|
|
p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)]
|
|
@end smallexample
|
|
|
|
After the additions, emit code to jump to @var{function}, which is a
|
|
@code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does
|
|
not touch the return address. Hence returning from @var{FUNCTION} will
|
|
return to whoever called the current @samp{thunk}.
|
|
|
|
The effect must be as if @var{function} had been called directly with
|
|
the adjusted first argument. This macro is responsible for emitting all
|
|
of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE}
|
|
and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked.
|
|
|
|
The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function}
|
|
have already been extracted from it.) It might possibly be useful on
|
|
some targets, but probably not.
|
|
|
|
If you do not define this macro, the target-independent code in the C++
|
|
front end will generate a less efficient heavyweight thunk that calls
|
|
@var{function} instead of jumping to it. The generic approach does
|
|
not support varargs.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ASM_CAN_OUTPUT_MI_THUNK (const_tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, HOST_WIDE_INT @var{vcall_offset}, const_tree @var{function})
|
|
A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able
|
|
to output the assembler code for the thunk function specified by the
|
|
arguments it is passed, and false otherwise. In the latter case, the
|
|
generic approach will be used by the C++ front end, with the limitations
|
|
previously exposed.
|
|
@end deftypefn
|
|
|
|
@node Profiling
|
|
@subsection Generating Code for Profiling
|
|
@cindex profiling, code generation
|
|
|
|
These macros will help you generate code for profiling.
|
|
|
|
@defmac FUNCTION_PROFILER (@var{file}, @var{labelno})
|
|
A C statement or compound statement to output to @var{file} some
|
|
assembler code to call the profiling subroutine @code{mcount}.
|
|
|
|
@findex mcount
|
|
The details of how @code{mcount} expects to be called are determined by
|
|
your operating system environment, not by GCC@. To figure them out,
|
|
compile a small program for profiling using the system's installed C
|
|
compiler and look at the assembler code that results.
|
|
|
|
Older implementations of @code{mcount} expect the address of a counter
|
|
variable to be loaded into some register. The name of this variable is
|
|
@samp{LP} followed by the number @var{labelno}, so you would generate
|
|
the name using @samp{LP%d} in a @code{fprintf}.
|
|
@end defmac
|
|
|
|
@defmac PROFILE_HOOK
|
|
A C statement or compound statement to output to @var{file} some assembly
|
|
code to call the profiling subroutine @code{mcount} even the target does
|
|
not support profiling.
|
|
@end defmac
|
|
|
|
@defmac NO_PROFILE_COUNTERS
|
|
Define this macro to be an expression with a nonzero value if the
|
|
@code{mcount} subroutine on your system does not need a counter variable
|
|
allocated for each function. This is true for almost all modern
|
|
implementations. If you define this macro, you must not use the
|
|
@var{labelno} argument to @code{FUNCTION_PROFILER}.
|
|
@end defmac
|
|
|
|
@defmac PROFILE_BEFORE_PROLOGUE
|
|
Define this macro if the code for function profiling should come before
|
|
the function prologue. Normally, the profiling code comes after.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_KEEP_LEAF_WHEN_PROFILED (void)
|
|
This target hook returns true if the target wants the leaf flag for
|
|
the current function to stay true even if it calls mcount. This might
|
|
make sense for targets using the leaf flag only to determine whether a
|
|
stack frame needs to be generated or not and for which the call to
|
|
mcount is generated before the function prologue.
|
|
@end deftypefn
|
|
|
|
@node Tail Calls
|
|
@subsection Permitting tail calls
|
|
@cindex tail calls
|
|
|
|
@deftypefn {Target Hook} bool TARGET_FUNCTION_OK_FOR_SIBCALL (tree @var{decl}, tree @var{exp})
|
|
True if it is OK to do sibling call optimization for the specified
|
|
call expression @var{exp}. @var{decl} will be the called function,
|
|
or @code{NULL} if this is an indirect call.
|
|
|
|
It is not uncommon for limitations of calling conventions to prevent
|
|
tail calls to functions outside the current unit of translation, or
|
|
during PIC compilation. The hook is used to enforce these restrictions,
|
|
as the @code{sibcall} md pattern cannot fail, or fall over to a
|
|
``normal'' call. The criteria for successful sibling call optimization
|
|
may vary greatly between different architectures.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_EXTRA_LIVE_ON_ENTRY (bitmap @var{regs})
|
|
Add any hard registers to @var{regs} that are live on entry to the
|
|
function. This hook only needs to be defined to provide registers that
|
|
cannot be found by examination of FUNCTION_ARG_REGNO_P, the callee saved
|
|
registers, STATIC_CHAIN_INCOMING_REGNUM, STATIC_CHAIN_REGNUM,
|
|
TARGET_STRUCT_VALUE_RTX, FRAME_POINTER_REGNUM, EH_USES,
|
|
FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SET_UP_BY_PROLOGUE (struct hard_reg_set_container *@var{})
|
|
This hook should add additional registers that are computed by the prologue
|
|
to the hard regset for shrink-wrapping optimization purposes.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_WARN_FUNC_RETURN (tree)
|
|
True if a function's return statements should be checked for matching
|
|
the function's return type. This includes checking for falling off the end
|
|
of a non-void function. Return false if no such check should be made.
|
|
@end deftypefn
|
|
|
|
@node Shrink-wrapping separate components
|
|
@subsection Shrink-wrapping separate components
|
|
@cindex shrink-wrapping separate components
|
|
|
|
The prologue may perform a variety of target dependent tasks such as
|
|
saving callee-saved registers, saving the return address, aligning the
|
|
stack, creating a stack frame, initializing the PIC register, setting
|
|
up the static chain, etc.
|
|
|
|
On some targets some of these tasks may be independent of others and
|
|
thus may be shrink-wrapped separately. These independent tasks are
|
|
referred to as components and are handled generically by the target
|
|
independent parts of GCC.
|
|
|
|
Using the following hooks those prologue or epilogue components can be
|
|
shrink-wrapped separately, so that the initialization (and possibly
|
|
teardown) those components do is not done as frequently on execution
|
|
paths where this would unnecessary.
|
|
|
|
What exactly those components are is up to the target code; the generic
|
|
code treats them abstractly, as a bit in an @code{sbitmap}. These
|
|
@code{sbitmap}s are allocated by the @code{shrink_wrap.get_separate_components}
|
|
and @code{shrink_wrap.components_for_bb} hooks, and deallocated by the
|
|
generic code.
|
|
|
|
@deftypefn {Target Hook} sbitmap TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS (void)
|
|
This hook should return an @code{sbitmap} with the bits set for those
|
|
components that can be separately shrink-wrapped in the current function.
|
|
Return @code{NULL} if the current function should not get any separate
|
|
shrink-wrapping.
|
|
Don't define this hook if it would always return @code{NULL}.
|
|
If it is defined, the other hooks in this group have to be defined as well.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} sbitmap TARGET_SHRINK_WRAP_COMPONENTS_FOR_BB (basic_block)
|
|
This hook should return an @code{sbitmap} with the bits set for those
|
|
components where either the prologue component has to be executed before
|
|
the @code{basic_block}, or the epilogue component after it, or both.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SHRINK_WRAP_DISQUALIFY_COMPONENTS (sbitmap @var{components}, edge @var{e}, sbitmap @var{edge_components}, bool @var{is_prologue})
|
|
This hook should clear the bits in the @var{components} bitmap for those
|
|
components in @var{edge_components} that the target cannot handle on edge
|
|
@var{e}, where @var{is_prologue} says if this is for a prologue or an
|
|
epilogue instead.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS (sbitmap)
|
|
Emit prologue insns for the components indicated by the parameter.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS (sbitmap)
|
|
Emit epilogue insns for the components indicated by the parameter.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SHRINK_WRAP_SET_HANDLED_COMPONENTS (sbitmap)
|
|
Mark the components in the parameter as handled, so that the
|
|
@code{prologue} and @code{epilogue} named patterns know to ignore those
|
|
components. The target code should not hang on to the @code{sbitmap}, it
|
|
will be deleted after this call.
|
|
@end deftypefn
|
|
|
|
@node Stack Smashing Protection
|
|
@subsection Stack smashing protection
|
|
@cindex stack smashing protection
|
|
|
|
@deftypefn {Target Hook} tree TARGET_STACK_PROTECT_GUARD (void)
|
|
This hook returns a @code{DECL} node for the external variable to use
|
|
for the stack protection guard. This variable is initialized by the
|
|
runtime to some random value and is used to initialize the guard value
|
|
that is placed at the top of the local stack frame. The type of this
|
|
variable must be @code{ptr_type_node}.
|
|
|
|
The default version of this hook creates a variable called
|
|
@samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_STACK_PROTECT_FAIL (void)
|
|
This hook returns a @code{CALL_EXPR} that alerts the runtime that the
|
|
stack protect guard variable has been modified. This expression should
|
|
involve a call to a @code{noreturn} function.
|
|
|
|
The default version of this hook invokes a function called
|
|
@samp{__stack_chk_fail}, taking no arguments. This function is
|
|
normally defined in @file{libgcc2.c}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_STACK_PROTECT_RUNTIME_ENABLED_P (void)
|
|
Returns true if the target wants GCC's default stack protect runtime support,
|
|
otherwise return false. The default implementation always returns true.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Common Target Hook} bool TARGET_SUPPORTS_SPLIT_STACK (bool @var{report}, struct gcc_options *@var{opts})
|
|
Whether this target supports splitting the stack when the options
|
|
described in @var{opts} have been passed. This is called
|
|
after options have been parsed, so the target may reject splitting
|
|
the stack in some configurations. The default version of this hook
|
|
returns false. If @var{report} is true, this function may issue a warning
|
|
or error; if @var{report} is false, it must simply return a value
|
|
@end deftypefn
|
|
|
|
@deftypefn {Common Target Hook} {vec<const char *>} TARGET_GET_VALID_OPTION_VALUES (int @var{option_code}, const char *@var{prefix})
|
|
The hook is used for options that have a non-trivial list of
|
|
possible option values. OPTION_CODE is option code of opt_code
|
|
enum type. PREFIX is used for bash completion and allows an implementation
|
|
to return more specific completion based on the prefix. All string values
|
|
should be allocated from heap memory and consumers should release them.
|
|
The result will be pruned to cases with PREFIX if not NULL.
|
|
@end deftypefn
|
|
|
|
@node Miscellaneous Register Hooks
|
|
@subsection Miscellaneous register hooks
|
|
@cindex miscellaneous register hooks
|
|
|
|
@deftypevr {Target Hook} bool TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS
|
|
Set to true if each call that binds to a local definition explicitly
|
|
clobbers or sets all non-fixed registers modified by performing the call.
|
|
That is, by the call pattern itself, or by code that might be inserted by the
|
|
linker (e.g.@: stubs, veneers, branch islands), but not including those
|
|
modifiable by the callee. The affected registers may be mentioned explicitly
|
|
in the call pattern, or included as clobbers in CALL_INSN_FUNCTION_USAGE.
|
|
The default version of this hook is set to false. The purpose of this hook
|
|
is to enable the fipa-ra optimization.
|
|
@end deftypevr
|
|
|
|
@node Varargs
|
|
@section Implementing the Varargs Macros
|
|
@cindex varargs implementation
|
|
|
|
GCC comes with an implementation of @code{<varargs.h>} and
|
|
@code{<stdarg.h>} that work without change on machines that pass arguments
|
|
on the stack. Other machines require their own implementations of
|
|
varargs, and the two machine independent header files must have
|
|
conditionals to include it.
|
|
|
|
ISO @code{<stdarg.h>} differs from traditional @code{<varargs.h>} mainly in
|
|
the calling convention for @code{va_start}. The traditional
|
|
implementation takes just one argument, which is the variable in which
|
|
to store the argument pointer. The ISO implementation of
|
|
@code{va_start} takes an additional second argument. The user is
|
|
supposed to write the last named argument of the function here.
|
|
|
|
However, @code{va_start} should not use this argument. The way to find
|
|
the end of the named arguments is with the built-in functions described
|
|
below.
|
|
|
|
@defmac __builtin_saveregs ()
|
|
Use this built-in function to save the argument registers in memory so
|
|
that the varargs mechanism can access them. Both ISO and traditional
|
|
versions of @code{va_start} must use @code{__builtin_saveregs}, unless
|
|
you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead.
|
|
|
|
On some machines, @code{__builtin_saveregs} is open-coded under the
|
|
control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On
|
|
other machines, it calls a routine written in assembler language,
|
|
found in @file{libgcc2.c}.
|
|
|
|
Code generated for the call to @code{__builtin_saveregs} appears at the
|
|
beginning of the function, as opposed to where the call to
|
|
@code{__builtin_saveregs} is written, regardless of what the code is.
|
|
This is because the registers must be saved before the function starts
|
|
to use them for its own purposes.
|
|
@c i rewrote the first sentence above to fix an overfull hbox. --mew
|
|
@c 10feb93
|
|
@end defmac
|
|
|
|
@defmac __builtin_next_arg (@var{lastarg})
|
|
This builtin returns the address of the first anonymous stack
|
|
argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it
|
|
returns the address of the location above the first anonymous stack
|
|
argument. Use it in @code{va_start} to initialize the pointer for
|
|
fetching arguments from the stack. Also use it in @code{va_start} to
|
|
verify that the second parameter @var{lastarg} is the last named argument
|
|
of the current function.
|
|
@end defmac
|
|
|
|
@defmac __builtin_classify_type (@var{object})
|
|
Since each machine has its own conventions for which data types are
|
|
passed in which kind of register, your implementation of @code{va_arg}
|
|
has to embody these conventions. The easiest way to categorize the
|
|
specified data type is to use @code{__builtin_classify_type} together
|
|
with @code{sizeof} and @code{__alignof__}.
|
|
|
|
@code{__builtin_classify_type} ignores the value of @var{object},
|
|
considering only its data type. It returns an integer describing what
|
|
kind of type that is---integer, floating, pointer, structure, and so on.
|
|
|
|
The file @file{typeclass.h} defines an enumeration that you can use to
|
|
interpret the values of @code{__builtin_classify_type}.
|
|
@end defmac
|
|
|
|
These machine description macros help implement varargs:
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN_SAVEREGS (void)
|
|
If defined, this hook produces the machine-specific code for a call to
|
|
@code{__builtin_saveregs}. This code will be moved to the very
|
|
beginning of the function, before any parameter access are made. The
|
|
return value of this function should be an RTX that contains the value
|
|
to use as the return of @code{__builtin_saveregs}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SETUP_INCOMING_VARARGS (cumulative_args_t @var{args_so_far}, const function_arg_info @var{&arg}, int *@var{pretend_args_size}, int @var{second_time})
|
|
This target hook offers an alternative to using
|
|
@code{__builtin_saveregs} and defining the hook
|
|
@code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous
|
|
register arguments into the stack so that all the arguments appear to
|
|
have been passed consecutively on the stack. Once this is done, you can
|
|
use the standard implementation of varargs that works for machines that
|
|
pass all their arguments on the stack.
|
|
|
|
The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data
|
|
structure, containing the values that are obtained after processing the
|
|
named arguments. The argument @var{arg} describes the last of these named
|
|
arguments.
|
|
|
|
The target hook should do two things: first, push onto the stack all the
|
|
argument registers @emph{not} used for the named arguments, and second,
|
|
store the size of the data thus pushed into the @code{int}-valued
|
|
variable pointed to by @var{pretend_args_size}. The value that you
|
|
store here will serve as additional offset for setting up the stack
|
|
frame.
|
|
|
|
Because you must generate code to push the anonymous arguments at
|
|
compile time without knowing their data types,
|
|
@code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that
|
|
have just a single category of argument register and use it uniformly
|
|
for all data types.
|
|
|
|
If the argument @var{second_time} is nonzero, it means that the
|
|
arguments of the function are being analyzed for the second time. This
|
|
happens for an inline function, which is not actually compiled until the
|
|
end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should
|
|
not generate any instructions in this case.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_STRICT_ARGUMENT_NAMING (cumulative_args_t @var{ca})
|
|
Define this hook to return @code{true} if the location where a function
|
|
argument is passed depends on whether or not it is a named argument.
|
|
|
|
This hook controls how the @var{named} argument to @code{TARGET_FUNCTION_ARG}
|
|
is set for varargs and stdarg functions. If this hook returns
|
|
@code{true}, the @var{named} argument is always true for named
|
|
arguments, and false for unnamed arguments. If it returns @code{false},
|
|
but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true},
|
|
then all arguments are treated as named. Otherwise, all named arguments
|
|
except the last are treated as named.
|
|
|
|
You need not define this hook if it always returns @code{false}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_CALL_ARGS (rtx, @var{tree})
|
|
While generating RTL for a function call, this target hook is invoked once
|
|
for each argument passed to the function, either a register returned by
|
|
@code{TARGET_FUNCTION_ARG} or a memory location. It is called just
|
|
before the point where argument registers are stored. The type of the
|
|
function to be called is also passed as the second argument; it is
|
|
@code{NULL_TREE} for libcalls. The @code{TARGET_END_CALL_ARGS} hook is
|
|
invoked just after the code to copy the return reg has been emitted.
|
|
This functionality can be used to perform special setup of call argument
|
|
registers if a target needs it.
|
|
For functions without arguments, the hook is called once with @code{pc_rtx}
|
|
passed instead of an argument register.
|
|
Most ports do not need to implement anything for this hook.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_END_CALL_ARGS (void)
|
|
This target hook is invoked while generating RTL for a function call,
|
|
just after the point where the return reg is copied into a pseudo. It
|
|
signals that all the call argument and return registers for the just
|
|
emitted call are now no longer in use.
|
|
Most ports do not need to implement anything for this hook.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_PRETEND_OUTGOING_VARARGS_NAMED (cumulative_args_t @var{ca})
|
|
If you need to conditionally change ABIs so that one works with
|
|
@code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither
|
|
@code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was
|
|
defined, then define this hook to return @code{true} if
|
|
@code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise.
|
|
Otherwise, you should not define this hook.
|
|
@end deftypefn
|
|
|
|
@node Trampolines
|
|
@section Support for Nested Functions
|
|
@cindex support for nested functions
|
|
@cindex trampolines for nested functions
|
|
@cindex descriptors for nested functions
|
|
@cindex nested functions, support for
|
|
|
|
Taking the address of a nested function requires special compiler
|
|
handling to ensure that the static chain register is loaded when
|
|
the function is invoked via an indirect call.
|
|
|
|
GCC has traditionally supported nested functions by creating an
|
|
executable @dfn{trampoline} at run time when the address of a nested
|
|
function is taken. This is a small piece of code which normally
|
|
resides on the stack, in the stack frame of the containing function.
|
|
The trampoline loads the static chain register and then jumps to the
|
|
real address of the nested function.
|
|
|
|
The use of trampolines requires an executable stack, which is a
|
|
security risk. To avoid this problem, GCC also supports another
|
|
strategy: using descriptors for nested functions. Under this model,
|
|
taking the address of a nested function results in a pointer to a
|
|
non-executable function descriptor object. Initializing the static chain
|
|
from the descriptor is handled at indirect call sites.
|
|
|
|
On some targets, including HPPA and IA-64, function descriptors may be
|
|
mandated by the ABI or be otherwise handled in a target-specific way
|
|
by the back end in its code generation strategy for indirect calls.
|
|
GCC also provides its own generic descriptor implementation to support the
|
|
@option{-fno-trampolines} option. In this case runtime detection of
|
|
function descriptors at indirect call sites relies on descriptor
|
|
pointers being tagged with a bit that is never set in bare function
|
|
addresses. Since GCC's generic function descriptors are
|
|
not ABI-compliant, this option is typically used only on a
|
|
per-language basis (notably by Ada) or when it can otherwise be
|
|
applied to the whole program.
|
|
|
|
For languages other than Ada, the @code{-ftrampolines} and
|
|
@code{-fno-trampolines} options currently have no effect, and
|
|
trampolines are always generated on platforms that need them
|
|
for nested functions.
|
|
|
|
Define the following hook if your backend either implements ABI-specified
|
|
descriptor support, or can use GCC's generic descriptor implementation
|
|
for nested functions.
|
|
|
|
@deftypevr {Target Hook} int TARGET_CUSTOM_FUNCTION_DESCRIPTORS
|
|
If the target can use GCC's generic descriptor mechanism for nested
|
|
functions, define this hook to a power of 2 representing an unused bit
|
|
in function pointers which can be used to differentiate descriptors at
|
|
run time. This value gives the number of bytes by which descriptor
|
|
pointers are misaligned compared to function pointers. For example, on
|
|
targets that require functions to be aligned to a 4-byte boundary, a
|
|
value of either 1 or 2 is appropriate unless the architecture already
|
|
reserves the bit for another purpose, such as on ARM.
|
|
|
|
Define this hook to 0 if the target implements ABI support for
|
|
function descriptors in its standard calling sequence, like for example
|
|
HPPA or IA-64.
|
|
|
|
Using descriptors for nested functions
|
|
eliminates the need for trampolines that reside on the stack and require
|
|
it to be made executable.
|
|
@end deftypevr
|
|
|
|
The following macros tell GCC how to generate code to allocate and
|
|
initialize an executable trampoline. You can also use this interface
|
|
if your back end needs to create ABI-specified non-executable descriptors; in
|
|
this case the "trampoline" created is the descriptor containing data only.
|
|
|
|
The instructions in an executable trampoline must do two things: load
|
|
a constant address into the static chain register, and jump to the real
|
|
address of the nested function. On CISC machines such as the m68k,
|
|
this requires two instructions, a move immediate and a jump. Then the
|
|
two addresses exist in the trampoline as word-long immediate operands.
|
|
On RISC machines, it is often necessary to load each address into a
|
|
register in two parts. Then pieces of each address form separate
|
|
immediate operands.
|
|
|
|
The code generated to initialize the trampoline must store the variable
|
|
parts---the static chain value and the function address---into the
|
|
immediate operands of the instructions. On a CISC machine, this is
|
|
simply a matter of copying each address to a memory reference at the
|
|
proper offset from the start of the trampoline. On a RISC machine, it
|
|
may be necessary to take out pieces of the address and store them
|
|
separately.
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_TRAMPOLINE_TEMPLATE (FILE *@var{f})
|
|
This hook is called by @code{assemble_trampoline_template} to output,
|
|
on the stream @var{f}, assembler code for a block of data that contains
|
|
the constant parts of a trampoline. This code should not include a
|
|
label---the label is taken care of automatically.
|
|
|
|
If you do not define this hook, it means no template is needed
|
|
for the target. Do not define this hook on systems where the block move
|
|
code to copy the trampoline into place would be larger than the code
|
|
to generate it on the spot.
|
|
@end deftypefn
|
|
|
|
@defmac TRAMPOLINE_SECTION
|
|
Return the section into which the trampoline template is to be placed
|
|
(@pxref{Sections}). The default value is @code{readonly_data_section}.
|
|
@end defmac
|
|
|
|
@defmac TRAMPOLINE_SIZE
|
|
A C expression for the size in bytes of the trampoline, as an integer.
|
|
@end defmac
|
|
|
|
@defmac TRAMPOLINE_ALIGNMENT
|
|
Alignment required for trampolines, in bits.
|
|
|
|
If you don't define this macro, the value of @code{FUNCTION_ALIGNMENT}
|
|
is used for aligning trampolines.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_TRAMPOLINE_INIT (rtx @var{m_tramp}, tree @var{fndecl}, rtx @var{static_chain})
|
|
This hook is called to initialize a trampoline.
|
|
@var{m_tramp} is an RTX for the memory block for the trampoline; @var{fndecl}
|
|
is the @code{FUNCTION_DECL} for the nested function; @var{static_chain} is an
|
|
RTX for the static chain value that should be passed to the function
|
|
when it is called.
|
|
|
|
If the target defines @code{TARGET_ASM_TRAMPOLINE_TEMPLATE}, then the
|
|
first thing this hook should do is emit a block move into @var{m_tramp}
|
|
from the memory block returned by @code{assemble_trampoline_template}.
|
|
Note that the block move need only cover the constant parts of the
|
|
trampoline. If the target isolates the variable parts of the trampoline
|
|
to the end, not all @code{TRAMPOLINE_SIZE} bytes need be copied.
|
|
|
|
If the target requires any other actions, such as flushing caches
|
|
(possibly calling function maybe_emit_call_builtin___clear_cache) or
|
|
enabling stack execution, these actions should be performed after
|
|
initializing the trampoline proper.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_EMIT_CALL_BUILTIN___CLEAR_CACHE (rtx @var{begin}, rtx @var{end})
|
|
On targets that do not define a @code{clear_cache} insn expander,
|
|
but that define the @code{CLEAR_CACHE_INSN} macro,
|
|
maybe_emit_call_builtin___clear_cache relies on this target hook
|
|
to clear an address range in the instruction cache.
|
|
|
|
The default implementation calls the @code{__clear_cache} builtin,
|
|
taking the assembler name from the builtin declaration. Overriding
|
|
definitions may call alternate functions, with alternate calling
|
|
conventions, or emit alternate RTX to perform the job.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_TRAMPOLINE_ADJUST_ADDRESS (rtx @var{addr})
|
|
This hook should perform any machine-specific adjustment in
|
|
the address of the trampoline. Its argument contains the address of the
|
|
memory block that was passed to @code{TARGET_TRAMPOLINE_INIT}. In case
|
|
the address to be used for a function call should be different from the
|
|
address at which the template was stored, the different address should
|
|
be returned; otherwise @var{addr} should be returned unchanged.
|
|
If this hook is not defined, @var{addr} will be used for function calls.
|
|
@end deftypefn
|
|
|
|
Implementing trampolines is difficult on many machines because they have
|
|
separate instruction and data caches. Writing into a stack location
|
|
fails to clear the memory in the instruction cache, so when the program
|
|
jumps to that location, it executes the old contents.
|
|
|
|
Here are two possible solutions. One is to clear the relevant parts of
|
|
the instruction cache whenever a trampoline is set up. The other is to
|
|
make all trampolines identical, by having them jump to a standard
|
|
subroutine. The former technique makes trampoline execution faster; the
|
|
latter makes initialization faster.
|
|
|
|
To clear the instruction cache when a trampoline is initialized, define
|
|
the following macro.
|
|
|
|
@defmac CLEAR_INSN_CACHE (@var{beg}, @var{end})
|
|
If defined, expands to a C expression clearing the @emph{instruction
|
|
cache} in the specified interval. The definition of this macro would
|
|
typically be a series of @code{asm} statements. Both @var{beg} and
|
|
@var{end} are pointer expressions.
|
|
@end defmac
|
|
|
|
To use a standard subroutine, define the following macro. In addition,
|
|
you must make sure that the instructions in a trampoline fill an entire
|
|
cache line with identical instructions, or else ensure that the
|
|
beginning of the trampoline code is always aligned at the same point in
|
|
its cache line. Look in @file{m68k.h} as a guide.
|
|
|
|
@defmac TRANSFER_FROM_TRAMPOLINE
|
|
Define this macro if trampolines need a special subroutine to do their
|
|
work. The macro should expand to a series of @code{asm} statements
|
|
which will be compiled with GCC@. They go in a library function named
|
|
@code{__transfer_from_trampoline}.
|
|
|
|
If you need to avoid executing the ordinary prologue code of a compiled
|
|
C function when you jump to the subroutine, you can do so by placing a
|
|
special label of your own in the assembler code. Use one @code{asm}
|
|
statement to generate an assembler label, and another to make the label
|
|
global. Then trampolines can use that label to jump directly to your
|
|
special assembler code.
|
|
@end defmac
|
|
|
|
@node Library Calls
|
|
@section Implicit Calls to Library Routines
|
|
@cindex library subroutine names
|
|
@cindex @file{libgcc.a}
|
|
|
|
@c prevent bad page break with this line
|
|
Here is an explanation of implicit calls to library routines.
|
|
|
|
@defmac DECLARE_LIBRARY_RENAMES
|
|
This macro, if defined, should expand to a piece of C code that will get
|
|
expanded when compiling functions for libgcc.a. It can be used to
|
|
provide alternate names for GCC's internal library functions if there
|
|
are ABI-mandated names that the compiler should provide.
|
|
@end defmac
|
|
|
|
@findex set_optab_libfunc
|
|
@findex init_one_libfunc
|
|
@deftypefn {Target Hook} void TARGET_INIT_LIBFUNCS (void)
|
|
This hook should declare additional library routines or rename
|
|
existing ones, using the functions @code{set_optab_libfunc} and
|
|
@code{init_one_libfunc} defined in @file{optabs.cc}.
|
|
@code{init_optabs} calls this macro after initializing all the normal
|
|
library routines.
|
|
|
|
The default is to do nothing. Most ports don't need to define this hook.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_LIBFUNC_GNU_PREFIX
|
|
If false (the default), internal library routines start with two
|
|
underscores. If set to true, these routines start with @code{__gnu_}
|
|
instead. E.g., @code{__muldi3} changes to @code{__gnu_muldi3}. This
|
|
currently only affects functions defined in @file{libgcc2.c}. If this
|
|
is set to true, the @file{tm.h} file must also
|
|
@code{#define LIBGCC2_GNU_PREFIX}.
|
|
@end deftypevr
|
|
|
|
@defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison})
|
|
This macro should return @code{true} if the library routine that
|
|
implements the floating point comparison operator @var{comparison} in
|
|
mode @var{mode} will return a boolean, and @var{false} if it will
|
|
return a tristate.
|
|
|
|
GCC's own floating point libraries return tristates from the
|
|
comparison operators, so the default returns false always. Most ports
|
|
don't need to define this macro.
|
|
@end defmac
|
|
|
|
@defmac TARGET_LIB_INT_CMP_BIASED
|
|
This macro should evaluate to @code{true} if the integer comparison
|
|
functions (like @code{__cmpdi2}) return 0 to indicate that the first
|
|
operand is smaller than the second, 1 to indicate that they are equal,
|
|
and 2 to indicate that the first operand is greater than the second.
|
|
If this macro evaluates to @code{false} the comparison functions return
|
|
@minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines
|
|
in @file{libgcc.a}, you do not need to define this macro.
|
|
@end defmac
|
|
|
|
@defmac TARGET_HAS_NO_HW_DIVIDE
|
|
This macro should be defined if the target has no hardware divide
|
|
instructions. If this macro is defined, GCC will use an algorithm which
|
|
make use of simple logical and arithmetic operations for 64-bit
|
|
division. If the macro is not defined, GCC will use an algorithm which
|
|
make use of a 64-bit by 32-bit divide primitive.
|
|
@end defmac
|
|
|
|
@cindex @code{EDOM}, implicit usage
|
|
@findex matherr
|
|
@defmac TARGET_EDOM
|
|
The value of @code{EDOM} on the target machine, as a C integer constant
|
|
expression. If you don't define this macro, GCC does not attempt to
|
|
deposit the value of @code{EDOM} into @code{errno} directly. Look in
|
|
@file{/usr/include/errno.h} to find the value of @code{EDOM} on your
|
|
system.
|
|
|
|
If you do not define @code{TARGET_EDOM}, then compiled code reports
|
|
domain errors by calling the library function and letting it report the
|
|
error. If mathematical functions on your system use @code{matherr} when
|
|
there is an error, then you should leave @code{TARGET_EDOM} undefined so
|
|
that @code{matherr} is used normally.
|
|
@end defmac
|
|
|
|
@cindex @code{errno}, implicit usage
|
|
@defmac GEN_ERRNO_RTX
|
|
Define this macro as a C expression to create an rtl expression that
|
|
refers to the global ``variable'' @code{errno}. (On certain systems,
|
|
@code{errno} may not actually be a variable.) If you don't define this
|
|
macro, a reasonable default is used.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_LIBC_HAS_FUNCTION (enum function_class @var{fn_class}, tree @var{type})
|
|
This hook determines whether a function from a class of functions
|
|
@var{fn_class} is present in the target C library. If @var{type} is NULL,
|
|
the caller asks for support for all standard (float, double, long double)
|
|
types. If @var{type} is non-NULL, the caller asks for support for a
|
|
specific type.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_LIBC_HAS_FAST_FUNCTION (int @var{fcode})
|
|
This hook determines whether a function from a class of functions
|
|
@code{(enum function_class)}@var{fcode} has a fast implementation.
|
|
@end deftypefn
|
|
|
|
@defmac NEXT_OBJC_RUNTIME
|
|
Set this macro to 1 to use the "NeXT" Objective-C message sending conventions
|
|
by default. This calling convention involves passing the object, the selector
|
|
and the method arguments all at once to the method-lookup library function.
|
|
This is the usual setting when targeting Darwin/Mac OS X systems, which have
|
|
the NeXT runtime installed.
|
|
|
|
If the macro is set to 0, the "GNU" Objective-C message sending convention
|
|
will be used by default. This convention passes just the object and the
|
|
selector to the method-lookup function, which returns a pointer to the method.
|
|
|
|
In either case, it remains possible to select code-generation for the alternate
|
|
scheme, by means of compiler command line switches.
|
|
@end defmac
|
|
|
|
@node Addressing Modes
|
|
@section Addressing Modes
|
|
@cindex addressing modes
|
|
|
|
@c prevent bad page break with this line
|
|
This is about addressing modes.
|
|
|
|
@defmac HAVE_PRE_INCREMENT
|
|
@defmacx HAVE_PRE_DECREMENT
|
|
@defmacx HAVE_POST_INCREMENT
|
|
@defmacx HAVE_POST_DECREMENT
|
|
A C expression that is nonzero if the machine supports pre-increment,
|
|
pre-decrement, post-increment, or post-decrement addressing respectively.
|
|
@end defmac
|
|
|
|
@defmac HAVE_PRE_MODIFY_DISP
|
|
@defmacx HAVE_POST_MODIFY_DISP
|
|
A C expression that is nonzero if the machine supports pre- or
|
|
post-address side-effect generation involving constants other than
|
|
the size of the memory operand.
|
|
@end defmac
|
|
|
|
@defmac HAVE_PRE_MODIFY_REG
|
|
@defmacx HAVE_POST_MODIFY_REG
|
|
A C expression that is nonzero if the machine supports pre- or
|
|
post-address side-effect generation involving a register displacement.
|
|
@end defmac
|
|
|
|
@defmac CONSTANT_ADDRESS_P (@var{x})
|
|
A C expression that is 1 if the RTX @var{x} is a constant which
|
|
is a valid address. On most machines the default definition of
|
|
@code{(CONSTANT_P (@var{x}) && GET_CODE (@var{x}) != CONST_DOUBLE)}
|
|
is acceptable, but a few machines are more restrictive as to which
|
|
constant addresses are supported.
|
|
@end defmac
|
|
|
|
@defmac CONSTANT_P (@var{x})
|
|
@code{CONSTANT_P}, which is defined by target-independent code,
|
|
accepts integer-values expressions whose values are not explicitly
|
|
known, such as @code{symbol_ref}, @code{label_ref}, and @code{high}
|
|
expressions and @code{const} arithmetic expressions, in addition to
|
|
@code{const_int} and @code{const_double} expressions.
|
|
@end defmac
|
|
|
|
@defmac MAX_REGS_PER_ADDRESS
|
|
A number, the maximum number of registers that can appear in a valid
|
|
memory address. Note that it is up to you to specify a value equal to
|
|
the maximum number that @code{TARGET_LEGITIMATE_ADDRESS_P} would ever
|
|
accept.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_LEGITIMATE_ADDRESS_P (machine_mode @var{mode}, rtx @var{x}, bool @var{strict})
|
|
A function that returns whether @var{x} (an RTX) is a legitimate memory
|
|
address on the target machine for a memory operand of mode @var{mode}.
|
|
|
|
Legitimate addresses are defined in two variants: a strict variant and a
|
|
non-strict one. The @var{strict} parameter chooses which variant is
|
|
desired by the caller.
|
|
|
|
The strict variant is used in the reload pass. It must be defined so
|
|
that any pseudo-register that has not been allocated a hard register is
|
|
considered a memory reference. This is because in contexts where some
|
|
kind of register is required, a pseudo-register with no hard register
|
|
must be rejected. For non-hard registers, the strict variant should look
|
|
up the @code{reg_renumber} array; it should then proceed using the hard
|
|
register number in the array, or treat the pseudo as a memory reference
|
|
if the array holds @code{-1}.
|
|
|
|
The non-strict variant is used in other passes. It must be defined to
|
|
accept all pseudo-registers in every context where some kind of
|
|
register is required.
|
|
|
|
Normally, constant addresses which are the sum of a @code{symbol_ref}
|
|
and an integer are stored inside a @code{const} RTX to mark them as
|
|
constant. Therefore, there is no need to recognize such sums
|
|
specifically as legitimate addresses. Normally you would simply
|
|
recognize any @code{const} as legitimate.
|
|
|
|
Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant
|
|
sums that are not marked with @code{const}. It assumes that a naked
|
|
@code{plus} indicates indexing. If so, then you @emph{must} reject such
|
|
naked constant sums as illegitimate addresses, so that none of them will
|
|
be given to @code{PRINT_OPERAND_ADDRESS}.
|
|
|
|
@cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation
|
|
On some machines, whether a symbolic address is legitimate depends on
|
|
the section that the address refers to. On these machines, define the
|
|
target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information
|
|
into the @code{symbol_ref}, and then check for it here. When you see a
|
|
@code{const}, you will have to look inside it to find the
|
|
@code{symbol_ref} in order to determine the section. @xref{Assembler
|
|
Format}.
|
|
|
|
@cindex @code{GO_IF_LEGITIMATE_ADDRESS}
|
|
Some ports are still using a deprecated legacy substitute for
|
|
this hook, the @code{GO_IF_LEGITIMATE_ADDRESS} macro. This macro
|
|
has this syntax:
|
|
|
|
@example
|
|
#define GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label})
|
|
@end example
|
|
|
|
@noindent
|
|
and should @code{goto @var{label}} if the address @var{x} is a valid
|
|
address on the target machine for a memory operand of mode @var{mode}.
|
|
|
|
@findex REG_OK_STRICT
|
|
Compiler source files that want to use the strict variant of this
|
|
macro define the macro @code{REG_OK_STRICT}. You should use an
|
|
@code{#ifdef REG_OK_STRICT} conditional to define the strict variant in
|
|
that case and the non-strict variant otherwise.
|
|
|
|
Using the hook is usually simpler because it limits the number of
|
|
files that are recompiled when changes are made.
|
|
@end deftypefn
|
|
|
|
@defmac TARGET_MEM_CONSTRAINT
|
|
A single character to be used instead of the default @code{'m'}
|
|
character for general memory addresses. This defines the constraint
|
|
letter which matches the memory addresses accepted by
|
|
@code{TARGET_LEGITIMATE_ADDRESS_P}. Define this macro if you want to
|
|
support new address formats in your back end without changing the
|
|
semantics of the @code{'m'} constraint. This is necessary in order to
|
|
preserve functionality of inline assembly constructs using the
|
|
@code{'m'} constraint.
|
|
@end defmac
|
|
|
|
@defmac FIND_BASE_TERM (@var{x})
|
|
A C expression to determine the base term of address @var{x},
|
|
or to provide a simplified version of @var{x} from which @file{alias.cc}
|
|
can easily find the base term. This macro is used in only two places:
|
|
@code{find_base_value} and @code{find_base_term} in @file{alias.cc}.
|
|
|
|
It is always safe for this macro to not be defined. It exists so
|
|
that alias analysis can understand machine-dependent addresses.
|
|
|
|
The typical use of this macro is to handle addresses containing
|
|
a label_ref or symbol_ref within an UNSPEC@.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_LEGITIMIZE_ADDRESS (rtx @var{x}, rtx @var{oldx}, machine_mode @var{mode})
|
|
This hook is given an invalid memory address @var{x} for an
|
|
operand of mode @var{mode} and should try to return a valid memory
|
|
address.
|
|
|
|
@findex break_out_memory_refs
|
|
@var{x} will always be the result of a call to @code{break_out_memory_refs},
|
|
and @var{oldx} will be the operand that was given to that function to produce
|
|
@var{x}.
|
|
|
|
The code of the hook should not alter the substructure of
|
|
@var{x}. If it transforms @var{x} into a more legitimate form, it
|
|
should return the new @var{x}.
|
|
|
|
It is not necessary for this hook to come up with a legitimate address,
|
|
with the exception of native TLS addresses (@pxref{Emulated TLS}).
|
|
The compiler has standard ways of doing so in all cases. In fact, if
|
|
the target supports only emulated TLS, it
|
|
is safe to omit this hook or make it return @var{x} if it cannot find
|
|
a valid way to legitimize the address. But often a machine-dependent
|
|
strategy can generate better code.
|
|
@end deftypefn
|
|
|
|
@defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win})
|
|
A C compound statement that attempts to replace @var{x}, which is an address
|
|
that needs reloading, with a valid memory address for an operand of mode
|
|
@var{mode}. @var{win} will be a C statement label elsewhere in the code.
|
|
It is not necessary to define this macro, but it might be useful for
|
|
performance reasons.
|
|
|
|
For example, on the i386, it is sometimes possible to use a single
|
|
reload register instead of two by reloading a sum of two pseudo
|
|
registers into a register. On the other hand, for number of RISC
|
|
processors offsets are limited so that often an intermediate address
|
|
needs to be generated in order to address a stack slot. By defining
|
|
@code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses
|
|
generated for adjacent some stack slots can be made identical, and thus
|
|
be shared.
|
|
|
|
@emph{Note}: This macro should be used with caution. It is necessary
|
|
to know something of how reload works in order to effectively use this,
|
|
and it is quite easy to produce macros that build in too much knowledge
|
|
of reload internals.
|
|
|
|
@emph{Note}: This macro must be able to reload an address created by a
|
|
previous invocation of this macro. If it fails to handle such addresses
|
|
then the compiler may generate incorrect code or abort.
|
|
|
|
@findex push_reload
|
|
The macro definition should use @code{push_reload} to indicate parts that
|
|
need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually
|
|
suitable to be passed unaltered to @code{push_reload}.
|
|
|
|
The code generated by this macro must not alter the substructure of
|
|
@var{x}. If it transforms @var{x} into a more legitimate form, it
|
|
should assign @var{x} (which will always be a C variable) a new value.
|
|
This also applies to parts that you change indirectly by calling
|
|
@code{push_reload}.
|
|
|
|
@findex strict_memory_address_p
|
|
The macro definition may use @code{strict_memory_address_p} to test if
|
|
the address has become legitimate.
|
|
|
|
@findex copy_rtx
|
|
If you want to change only a part of @var{x}, one standard way of doing
|
|
this is to use @code{copy_rtx}. Note, however, that it unshares only a
|
|
single level of rtl. Thus, if the part to be changed is not at the
|
|
top level, you'll need to replace first the top level.
|
|
It is not necessary for this macro to come up with a legitimate
|
|
address; but often a machine-dependent strategy can generate better code.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_MODE_DEPENDENT_ADDRESS_P (const_rtx @var{addr}, addr_space_t @var{addrspace})
|
|
This hook returns @code{true} if memory address @var{addr} in address
|
|
space @var{addrspace} can have
|
|
different meanings depending on the machine mode of the memory
|
|
reference it is used for or if the address is valid for some modes
|
|
but not others.
|
|
|
|
Autoincrement and autodecrement addresses typically have mode-dependent
|
|
effects because the amount of the increment or decrement is the size
|
|
of the operand being addressed. Some machines have other mode-dependent
|
|
addresses. Many RISC machines have no mode-dependent addresses.
|
|
|
|
You may assume that @var{addr} is a valid address for the machine.
|
|
|
|
The default version of this hook returns @code{false}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_LEGITIMATE_CONSTANT_P (machine_mode @var{mode}, rtx @var{x})
|
|
This hook returns true if @var{x} is a legitimate constant for a
|
|
@var{mode}-mode immediate operand on the target machine. You can assume that
|
|
@var{x} satisfies @code{CONSTANT_P}, so you need not check this.
|
|
|
|
The default definition returns true.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_PRECOMPUTE_TLS_P (machine_mode @var{mode}, rtx @var{x})
|
|
This hook returns true if @var{x} is a TLS operand on the target
|
|
machine that should be pre-computed when used as the argument in a call.
|
|
You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
|
|
check this.
|
|
|
|
The default definition returns false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_DELEGITIMIZE_ADDRESS (rtx @var{x})
|
|
This hook is used to undo the possibly obfuscating effects of the
|
|
@code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target
|
|
macros. Some backend implementations of these macros wrap symbol
|
|
references inside an @code{UNSPEC} rtx to represent PIC or similar
|
|
addressing modes. This target hook allows GCC's optimizers to understand
|
|
the semantics of these opaque @code{UNSPEC}s by converting them back
|
|
into their original form.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CONST_NOT_OK_FOR_DEBUG_P (rtx @var{x})
|
|
This hook should return true if @var{x} should not be emitted into
|
|
debug sections.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CANNOT_FORCE_CONST_MEM (machine_mode @var{mode}, rtx @var{x})
|
|
This hook should return true if @var{x} is of a form that cannot (or
|
|
should not) be spilled to the constant pool. @var{mode} is the mode
|
|
of @var{x}.
|
|
|
|
The default version of this hook returns false.
|
|
|
|
The primary reason to define this hook is to prevent reload from
|
|
deciding that a non-legitimate constant would be better reloaded
|
|
from the constant pool instead of spilling and reloading a register
|
|
holding the constant. This restriction is often true of addresses
|
|
of TLS symbols for various targets.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_USE_BLOCKS_FOR_CONSTANT_P (machine_mode @var{mode}, const_rtx @var{x})
|
|
This hook should return true if pool entries for constant @var{x} can
|
|
be placed in an @code{object_block} structure. @var{mode} is the mode
|
|
of @var{x}.
|
|
|
|
The default version returns false for all constants.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_USE_BLOCKS_FOR_DECL_P (const_tree @var{decl})
|
|
This hook should return true if pool entries for @var{decl} should
|
|
be placed in an @code{object_block} structure.
|
|
|
|
The default version returns true for all decls.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_BUILTIN_RECIPROCAL (tree @var{fndecl})
|
|
This hook should return the DECL of a function that implements the
|
|
reciprocal of the machine-specific builtin function @var{fndecl}, or
|
|
@code{NULL_TREE} if such a function is not available.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD (void)
|
|
This hook should return the DECL of a function @var{f} that given an
|
|
address @var{addr} as an argument returns a mask @var{m} that can be
|
|
used to extract from two vectors the relevant data that resides in
|
|
@var{addr} in case @var{addr} is not properly aligned.
|
|
|
|
The autovectorizer, when vectorizing a load operation from an address
|
|
@var{addr} that may be unaligned, will generate two vector loads from
|
|
the two aligned addresses around @var{addr}. It then generates a
|
|
@code{REALIGN_LOAD} operation to extract the relevant data from the
|
|
two loaded vectors. The first two arguments to @code{REALIGN_LOAD},
|
|
@var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and
|
|
the third argument, @var{OFF}, defines how the data will be extracted
|
|
from these two vectors: if @var{OFF} is 0, then the returned vector is
|
|
@var{v2}; otherwise, the returned vector is composed from the last
|
|
@var{VS}-@var{OFF} elements of @var{v1} concatenated to the first
|
|
@var{OFF} elements of @var{v2}.
|
|
|
|
If this hook is defined, the autovectorizer will generate a call
|
|
to @var{f} (using the DECL tree that this hook returns) and will
|
|
use the return value of @var{f} as the argument @var{OFF} to
|
|
@code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f}
|
|
should comply with the semantics expected by @code{REALIGN_LOAD}
|
|
described above.
|
|
If this hook is not defined, then @var{addr} will be used as
|
|
the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low
|
|
log2(@var{VS}) @minus{} 1 bits of @var{addr} will be considered.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST (enum vect_cost_for_stmt @var{type_of_cost}, tree @var{vectype}, int @var{misalign})
|
|
Returns cost of different scalar or vector statements for vectorization cost model.
|
|
For vector memory operations the cost may depend on type (@var{vectype}) and
|
|
misalignment value (@var{misalign}).
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} poly_uint64 TARGET_VECTORIZE_PREFERRED_VECTOR_ALIGNMENT (const_tree @var{type})
|
|
This hook returns the preferred alignment in bits for accesses to
|
|
vectors of type @var{type} in vectorized code. This might be less than
|
|
or greater than the ABI-defined value returned by
|
|
@code{TARGET_VECTOR_ALIGNMENT}. It can be equal to the alignment of
|
|
a single element, in which case the vectorizer will not try to optimize
|
|
for alignment.
|
|
|
|
The default hook returns @code{TYPE_ALIGN (@var{type})}, which is
|
|
correct for most targets.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_VECTORIZE_VECTOR_ALIGNMENT_REACHABLE (const_tree @var{type}, bool @var{is_packed})
|
|
Return true if vector alignment is reachable (by peeling N iterations)
|
|
for the given scalar type @var{type}. @var{is_packed} is false if the scalar
|
|
access using @var{type} is known to be naturally aligned.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_VECTORIZE_VEC_PERM_CONST (machine_mode @var{mode}, rtx @var{output}, rtx @var{in0}, rtx @var{in1}, const vec_perm_indices @var{&sel})
|
|
This hook is used to test whether the target can permute up to two
|
|
vectors of mode @var{mode} using the permutation vector @code{sel}, and
|
|
also to emit such a permutation. In the former case @var{in0}, @var{in1}
|
|
and @var{out} are all null. In the latter case @var{in0} and @var{in1} are
|
|
the source vectors and @var{out} is the destination vector; all three are
|
|
operands of mode @var{mode}. @var{in1} is the same as @var{in0} if
|
|
@var{sel} describes a permutation on one vector instead of two.
|
|
|
|
Return true if the operation is possible, emitting instructions for it
|
|
if rtxes are provided.
|
|
|
|
@cindex @code{vec_perm@var{m}} instruction pattern
|
|
If the hook returns false for a mode with multibyte elements, GCC will
|
|
try the equivalent byte operation. If that also fails, it will try forcing
|
|
the selector into a register and using the @var{vec_perm@var{mode}}
|
|
instruction pattern. There is no need for the hook to handle these two
|
|
implementation approaches itself.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION (unsigned @var{code}, tree @var{vec_type_out}, tree @var{vec_type_in})
|
|
This hook should return the decl of a function that implements the
|
|
vectorized variant of the function with the @code{combined_fn} code
|
|
@var{code} or @code{NULL_TREE} if such a function is not available.
|
|
The return type of the vectorized function shall be of vector type
|
|
@var{vec_type_out} and the argument types should be @var{vec_type_in}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MD_VECTORIZED_FUNCTION (tree @var{fndecl}, tree @var{vec_type_out}, tree @var{vec_type_in})
|
|
This hook should return the decl of a function that implements the
|
|
vectorized variant of target built-in function @code{fndecl}. The
|
|
return type of the vectorized function shall be of vector type
|
|
@var{vec_type_out} and the argument types should be @var{vec_type_in}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT (machine_mode @var{mode}, const_tree @var{type}, int @var{misalignment}, bool @var{is_packed})
|
|
This hook should return true if the target supports misaligned vector
|
|
store/load of a specific factor denoted in the @var{misalignment}
|
|
parameter. The vector store/load should be of machine mode @var{mode} and
|
|
the elements in the vectors should be of type @var{type}. @var{is_packed}
|
|
parameter is true if the memory access is defined in a packed struct.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} machine_mode TARGET_VECTORIZE_PREFERRED_SIMD_MODE (scalar_mode @var{mode})
|
|
This hook should return the preferred mode for vectorizing scalar
|
|
mode @var{mode}. The default is
|
|
equal to @code{word_mode}, because the vectorizer can do some
|
|
transformations even in absence of specialized @acronym{SIMD} hardware.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} machine_mode TARGET_VECTORIZE_SPLIT_REDUCTION (machine_mode)
|
|
This hook should return the preferred mode to split the final reduction
|
|
step on @var{mode} to. The reduction is then carried out reducing upper
|
|
against lower halves of vectors recursively until the specified mode is
|
|
reached. The default is @var{mode} which means no splitting.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_VECTORIZE_AUTOVECTORIZE_VECTOR_MODES (vector_modes *@var{modes}, bool @var{all})
|
|
If using the mode returned by @code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE}
|
|
is not the only approach worth considering, this hook should add one mode to
|
|
@var{modes} for each useful alternative approach. These modes are then
|
|
passed to @code{TARGET_VECTORIZE_RELATED_MODE} to obtain the vector mode
|
|
for a given element mode.
|
|
|
|
The modes returned in @var{modes} should use the smallest element mode
|
|
possible for the vectorization approach that they represent, preferring
|
|
integer modes over floating-poing modes in the event of a tie. The first
|
|
mode should be the @code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE} for its
|
|
element mode.
|
|
|
|
If @var{all} is true, add suitable vector modes even when they are generally
|
|
not expected to be worthwhile.
|
|
|
|
The hook returns a bitmask of flags that control how the modes in
|
|
@var{modes} are used. The flags are:
|
|
@table @code
|
|
@item VECT_COMPARE_COSTS
|
|
Tells the loop vectorizer to try all the provided modes and pick the one
|
|
with the lowest cost. By default the vectorizer will choose the first
|
|
mode that works.
|
|
@end table
|
|
|
|
The hook does not need to do anything if the vector returned by
|
|
@code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE} is the only one relevant
|
|
for autovectorization. The default implementation adds no modes and
|
|
returns 0.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} opt_machine_mode TARGET_VECTORIZE_RELATED_MODE (machine_mode @var{vector_mode}, scalar_mode @var{element_mode}, poly_uint64 @var{nunits})
|
|
If a piece of code is using vector mode @var{vector_mode} and also wants
|
|
to operate on elements of mode @var{element_mode}, return the vector mode
|
|
it should use for those elements. If @var{nunits} is nonzero, ensure that
|
|
the mode has exactly @var{nunits} elements, otherwise pick whichever vector
|
|
size pairs the most naturally with @var{vector_mode}. Return an empty
|
|
@code{opt_machine_mode} if there is no supported vector mode with the
|
|
required properties.
|
|
|
|
There is no prescribed way of handling the case in which @var{nunits}
|
|
is zero. One common choice is to pick a vector mode with the same size
|
|
as @var{vector_mode}; this is the natural choice if the target has a
|
|
fixed vector size. Another option is to choose a vector mode with the
|
|
same number of elements as @var{vector_mode}; this is the natural choice
|
|
if the target has a fixed number of elements. Alternatively, the hook
|
|
might choose a middle ground, such as trying to keep the number of
|
|
elements as similar as possible while applying maximum and minimum
|
|
vector sizes.
|
|
|
|
The default implementation uses @code{mode_for_vector} to find the
|
|
requested mode, returning a mode with the same size as @var{vector_mode}
|
|
when @var{nunits} is zero. This is the correct behavior for most targets.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} opt_machine_mode TARGET_VECTORIZE_GET_MASK_MODE (machine_mode @var{mode})
|
|
Return the mode to use for a vector mask that holds one boolean
|
|
result for each element of vector mode @var{mode}. The returned mask mode
|
|
can be a vector of integers (class @code{MODE_VECTOR_INT}), a vector of
|
|
booleans (class @code{MODE_VECTOR_BOOL}) or a scalar integer (class
|
|
@code{MODE_INT}). Return an empty @code{opt_machine_mode} if no such
|
|
mask mode exists.
|
|
|
|
The default implementation returns a @code{MODE_VECTOR_INT} with the
|
|
same size and number of elements as @var{mode}, if such a mode exists.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_VECTORIZE_EMPTY_MASK_IS_EXPENSIVE (unsigned @var{ifn})
|
|
This hook returns true if masked internal function @var{ifn} (really of
|
|
type @code{internal_fn}) should be considered expensive when the mask is
|
|
all zeros. GCC can then try to branch around the instruction instead.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {class vector_costs *} TARGET_VECTORIZE_CREATE_COSTS (vec_info *@var{vinfo}, bool @var{costing_for_scalar})
|
|
This hook should initialize target-specific data structures in preparation
|
|
for modeling the costs of vectorizing a loop or basic block. The default
|
|
allocates three unsigned integers for accumulating costs for the prologue,
|
|
body, and epilogue of the loop or basic block. If @var{loop_info} is
|
|
non-NULL, it identifies the loop being vectorized; otherwise a single block
|
|
is being vectorized. If @var{costing_for_scalar} is true, it indicates the
|
|
current cost model is for the scalar version of a loop or block; otherwise
|
|
it is for the vector version.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_GATHER (const_tree @var{mem_vectype}, const_tree @var{index_type}, int @var{scale})
|
|
Target builtin that implements vector gather operation. @var{mem_vectype}
|
|
is the vector type of the load and @var{index_type} is scalar type of
|
|
the index, scaled by @var{scale}.
|
|
The default is @code{NULL_TREE} which means to not vectorize gather
|
|
loads.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_SCATTER (const_tree @var{vectype}, const_tree @var{index_type}, int @var{scale})
|
|
Target builtin that implements vector scatter operation. @var{vectype}
|
|
is the vector type of the store and @var{index_type} is scalar type of
|
|
the index, scaled by @var{scale}.
|
|
The default is @code{NULL_TREE} which means to not vectorize scatter
|
|
stores.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SIMD_CLONE_COMPUTE_VECSIZE_AND_SIMDLEN (struct cgraph_node *@var{}, struct cgraph_simd_clone *@var{}, @var{tree}, @var{int})
|
|
This hook should set @var{vecsize_mangle}, @var{vecsize_int}, @var{vecsize_float}
|
|
fields in @var{simd_clone} structure pointed by @var{clone_info} argument and also
|
|
@var{simdlen} field if it was previously 0.
|
|
The hook should return 0 if SIMD clones shouldn't be emitted,
|
|
or number of @var{vecsize_mangle} variants that should be emitted.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SIMD_CLONE_ADJUST (struct cgraph_node *@var{})
|
|
This hook should add implicit @code{attribute(target("..."))} attribute
|
|
to SIMD clone @var{node} if needed.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SIMD_CLONE_USABLE (struct cgraph_node *@var{})
|
|
This hook should return -1 if SIMD clone @var{node} shouldn't be used
|
|
in vectorized loops in current function, or non-negative number if it is
|
|
usable. In that case, the smaller the number is, the more desirable it is
|
|
to use it.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SIMT_VF (void)
|
|
Return number of threads in SIMT thread group on the target.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_OMP_DEVICE_KIND_ARCH_ISA (enum omp_device_kind_arch_isa @var{trait}, const char *@var{name})
|
|
Return 1 if @var{trait} @var{name} is present in the OpenMP context's
|
|
device trait set, return 0 if not present in any OpenMP context in the
|
|
whole translation unit, or -1 if not present in the current OpenMP context
|
|
but might be present in another OpenMP context in the same TU.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_GOACC_VALIDATE_DIMS (tree @var{decl}, int *@var{dims}, int @var{fn_level}, unsigned @var{used})
|
|
This hook should check the launch dimensions provided for an OpenACC
|
|
compute region, or routine. Defaulted values are represented as -1
|
|
and non-constant values as 0. The @var{fn_level} is negative for the
|
|
function corresponding to the compute region. For a routine it is the
|
|
outermost level at which partitioned execution may be spawned. The hook
|
|
should verify non-default values. If DECL is NULL, global defaults
|
|
are being validated and unspecified defaults should be filled in.
|
|
Diagnostics should be issued as appropriate. Return
|
|
true, if changes have been made. You must override this hook to
|
|
provide dimensions larger than 1.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_GOACC_DIM_LIMIT (int @var{axis})
|
|
This hook should return the maximum size of a particular dimension,
|
|
or zero if unbounded.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_GOACC_FORK_JOIN (gcall *@var{call}, const int *@var{dims}, bool @var{is_fork})
|
|
This hook can be used to convert IFN_GOACC_FORK and IFN_GOACC_JOIN
|
|
function calls to target-specific gimple, or indicate whether they
|
|
should be retained. It is executed during the oacc_device_lower pass.
|
|
It should return true, if the call should be retained. It should
|
|
return false, if it is to be deleted (either because target-specific
|
|
gimple has been inserted before it, or there is no need for it).
|
|
The default hook returns false, if there are no RTL expanders for them.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_GOACC_REDUCTION (gcall *@var{call})
|
|
This hook is used by the oacc_transform pass to expand calls to the
|
|
@var{GOACC_REDUCTION} internal function, into a sequence of gimple
|
|
instructions. @var{call} is gimple statement containing the call to
|
|
the function. This hook removes statement @var{call} after the
|
|
expanded sequence has been inserted. This hook is also responsible
|
|
for allocating any storage for reductions when necessary.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_PREFERRED_ELSE_VALUE (unsigned @var{ifn}, tree @var{type}, unsigned @var{nops}, tree *@var{ops})
|
|
This hook returns the target's preferred final argument for a call
|
|
to conditional internal function @var{ifn} (really of type
|
|
@code{internal_fn}). @var{type} specifies the return type of the
|
|
function and @var{ops} are the operands to the conditional operation,
|
|
of which there are @var{nops}.
|
|
|
|
For example, if @var{ifn} is @code{IFN_COND_ADD}, the hook returns
|
|
a value of type @var{type} that should be used when @samp{@var{ops}[0]}
|
|
and @samp{@var{ops}[1]} are conditionally added together.
|
|
|
|
This hook is only relevant if the target supports conditional patterns
|
|
like @code{cond_add@var{m}}. The default implementation returns a zero
|
|
constant of type @var{type}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_GOACC_ADJUST_PRIVATE_DECL (location_t @var{loc}, tree @var{var}, int @var{level})
|
|
This hook, if defined, is used by accelerator target back-ends to adjust
|
|
OpenACC variable declarations that should be made private to the given
|
|
parallelism level (i.e. @code{GOMP_DIM_GANG}, @code{GOMP_DIM_WORKER} or
|
|
@code{GOMP_DIM_VECTOR}). A typical use for this hook is to force variable
|
|
declarations at the @code{gang} level to reside in GPU shared memory.
|
|
@var{loc} may be used for diagnostic purposes.
|
|
|
|
You may also use the @code{TARGET_GOACC_EXPAND_VAR_DECL} hook if the
|
|
adjusted variable declaration needs to be expanded to RTL in a non-standard
|
|
way.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_GOACC_EXPAND_VAR_DECL (tree @var{var})
|
|
This hook, if defined, is used by accelerator target back-ends to expand
|
|
specially handled kinds of @code{VAR_DECL} expressions. A particular use is
|
|
to place variables with specific attributes inside special accelarator
|
|
memories. A return value of @code{NULL} indicates that the target does not
|
|
handle this @code{VAR_DECL}, and normal RTL expanding is resumed.
|
|
|
|
Only define this hook if your accelerator target needs to expand certain
|
|
@code{VAR_DECL} nodes in a way that differs from the default. You can also adjust
|
|
private variables at OpenACC device-lowering time using the
|
|
@code{TARGET_GOACC_ADJUST_PRIVATE_DECL} target hook.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_GOACC_CREATE_WORKER_BROADCAST_RECORD (tree @var{rec}, bool @var{sender}, const char *@var{name}, unsigned HOST_WIDE_INT @var{offset})
|
|
Create a record used to propagate local-variable state from an active
|
|
worker to other workers. A possible implementation might adjust the type
|
|
of REC to place the new variable in shared GPU memory.
|
|
|
|
Presence of this target hook indicates that middle end neutering/broadcasting
|
|
be used.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_GOACC_SHARED_MEM_LAYOUT (unsigned HOST_WIDE_INT *@var{}, unsigned HOST_WIDE_INT *@var{}, @var{int[]}, unsigned @var{HOST_WIDE_INT[]}, unsigned @var{HOST_WIDE_INT[]})
|
|
Lay out a fixed shared-memory region on the target. The LO and HI
|
|
arguments should be set to a range of addresses that can be used for worker
|
|
broadcasting. The dimensions, reduction size and gang-private size
|
|
arguments are for the current offload region.
|
|
@end deftypefn
|
|
|
|
@node Anchored Addresses
|
|
@section Anchored Addresses
|
|
@cindex anchored addresses
|
|
@cindex @option{-fsection-anchors}
|
|
|
|
GCC usually addresses every static object as a separate entity.
|
|
For example, if we have:
|
|
|
|
@smallexample
|
|
static int a, b, c;
|
|
int foo (void) @{ return a + b + c; @}
|
|
@end smallexample
|
|
|
|
the code for @code{foo} will usually calculate three separate symbolic
|
|
addresses: those of @code{a}, @code{b} and @code{c}. On some targets,
|
|
it would be better to calculate just one symbolic address and access
|
|
the three variables relative to it. The equivalent pseudocode would
|
|
be something like:
|
|
|
|
@smallexample
|
|
int foo (void)
|
|
@{
|
|
register int *xr = &x;
|
|
return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
|
|
@}
|
|
@end smallexample
|
|
|
|
(which isn't valid C). We refer to shared addresses like @code{x} as
|
|
``section anchors''. Their use is controlled by @option{-fsection-anchors}.
|
|
|
|
The hooks below describe the target properties that GCC needs to know
|
|
in order to make effective use of section anchors. It won't use
|
|
section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET}
|
|
or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value.
|
|
|
|
@deftypevr {Target Hook} HOST_WIDE_INT TARGET_MIN_ANCHOR_OFFSET
|
|
The minimum offset that should be applied to a section anchor.
|
|
On most targets, it should be the smallest offset that can be
|
|
applied to a base register while still giving a legitimate address
|
|
for every mode. The default value is 0.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} HOST_WIDE_INT TARGET_MAX_ANCHOR_OFFSET
|
|
Like @code{TARGET_MIN_ANCHOR_OFFSET}, but the maximum (inclusive)
|
|
offset that should be applied to section anchors. The default
|
|
value is 0.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_ANCHOR (rtx @var{x})
|
|
Write the assembly code to define section anchor @var{x}, which is a
|
|
@code{SYMBOL_REF} for which @samp{SYMBOL_REF_ANCHOR_P (@var{x})} is true.
|
|
The hook is called with the assembly output position set to the beginning
|
|
of @code{SYMBOL_REF_BLOCK (@var{x})}.
|
|
|
|
If @code{ASM_OUTPUT_DEF} is available, the hook's default definition uses
|
|
it to define the symbol as @samp{. + SYMBOL_REF_BLOCK_OFFSET (@var{x})}.
|
|
If @code{ASM_OUTPUT_DEF} is not available, the hook's default definition
|
|
is @code{NULL}, which disables the use of section anchors altogether.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_USE_ANCHORS_FOR_SYMBOL_P (const_rtx @var{x})
|
|
Return true if GCC should attempt to use anchors to access @code{SYMBOL_REF}
|
|
@var{x}. You can assume @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})} and
|
|
@samp{!SYMBOL_REF_ANCHOR_P (@var{x})}.
|
|
|
|
The default version is correct for most targets, but you might need to
|
|
intercept this hook to handle things like target-specific attributes
|
|
or target-specific sections.
|
|
@end deftypefn
|
|
|
|
@node Condition Code
|
|
@section Condition Code Status
|
|
@cindex condition code status
|
|
|
|
Condition codes in GCC are represented as registers,
|
|
which provides better schedulability for
|
|
architectures that do have a condition code register, but on which
|
|
most instructions do not affect it. The latter category includes
|
|
most RISC machines.
|
|
|
|
Implicit clobbering would pose a strong restriction on the placement of
|
|
the definition and use of the condition code. In the past the definition
|
|
and use were always adjacent. However, recent changes to support trapping
|
|
arithmetic may result in the definition and user being in different blocks.
|
|
Thus, there may be a @code{NOTE_INSN_BASIC_BLOCK} between them. Additionally,
|
|
the definition may be the source of exception handling edges.
|
|
|
|
These restrictions can prevent important
|
|
optimizations on some machines. For example, on the IBM RS/6000, there
|
|
is a delay for taken branches unless the condition code register is set
|
|
three instructions earlier than the conditional branch. The instruction
|
|
scheduler cannot perform this optimization if it is not permitted to
|
|
separate the definition and use of the condition code register.
|
|
|
|
If there is a specific
|
|
condition code register in the machine, use a hard register. If the
|
|
condition code or comparison result can be placed in any general register,
|
|
or if there are multiple condition registers, use a pseudo register.
|
|
Registers used to store the condition code value will usually have a mode
|
|
that is in class @code{MODE_CC}.
|
|
|
|
Alternatively, you can use @code{BImode} if the comparison operator is
|
|
specified already in the compare instruction. In this case, you are not
|
|
interested in most macros in this section.
|
|
|
|
@menu
|
|
* MODE_CC Condition Codes:: Modern representation of condition codes.
|
|
@end menu
|
|
|
|
@node MODE_CC Condition Codes
|
|
@subsection Representation of condition codes using registers
|
|
@findex CCmode
|
|
@findex MODE_CC
|
|
|
|
@defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y})
|
|
On many machines, the condition code may be produced by other instructions
|
|
than compares, for example the branch can use directly the condition
|
|
code set by a subtract instruction. However, on some machines
|
|
when the condition code is set this way some bits (such as the overflow
|
|
bit) are not set in the same way as a test instruction, so that a different
|
|
branch instruction must be used for some conditional branches. When
|
|
this happens, use the machine mode of the condition code register to
|
|
record different formats of the condition code register. Modes can
|
|
also be used to record which compare instruction (e.g.@: a signed or an
|
|
unsigned comparison) produced the condition codes.
|
|
|
|
If other modes than @code{CCmode} are required, add them to
|
|
@file{@var{machine}-modes.def} and define @code{SELECT_CC_MODE} to choose
|
|
a mode given an operand of a compare. This is needed because the modes
|
|
have to be chosen not only during RTL generation but also, for example,
|
|
by instruction combination. The result of @code{SELECT_CC_MODE} should
|
|
be consistent with the mode used in the patterns; for example to support
|
|
the case of the add on the SPARC discussed above, we have the pattern
|
|
|
|
@smallexample
|
|
(define_insn ""
|
|
[(set (reg:CCNZ 0)
|
|
(compare:CCNZ
|
|
(plus:SI (match_operand:SI 0 "register_operand" "%r")
|
|
(match_operand:SI 1 "arith_operand" "rI"))
|
|
(const_int 0)))]
|
|
""
|
|
"@dots{}")
|
|
@end smallexample
|
|
|
|
@noindent
|
|
together with a @code{SELECT_CC_MODE} that returns @code{CCNZmode}
|
|
for comparisons whose argument is a @code{plus}:
|
|
|
|
@smallexample
|
|
#define SELECT_CC_MODE(OP,X,Y) \
|
|
(GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \
|
|
? ((OP == LT || OP == LE || OP == GT || OP == GE) \
|
|
? CCFPEmode : CCFPmode) \
|
|
: ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \
|
|
|| GET_CODE (X) == NEG || GET_CODE (x) == ASHIFT) \
|
|
? CCNZmode : CCmode))
|
|
@end smallexample
|
|
|
|
Another reason to use modes is to retain information on which operands
|
|
were used by the comparison; see @code{REVERSIBLE_CC_MODE} later in
|
|
this section.
|
|
|
|
You should define this macro if and only if you define extra CC modes
|
|
in @file{@var{machine}-modes.def}.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_CANONICALIZE_COMPARISON (int *@var{code}, rtx *@var{op0}, rtx *@var{op1}, bool @var{op0_preserve_value})
|
|
On some machines not all possible comparisons are defined, but you can
|
|
convert an invalid comparison into a valid one. For example, the Alpha
|
|
does not have a @code{GT} comparison, but you can use an @code{LT}
|
|
comparison instead and swap the order of the operands.
|
|
|
|
On such machines, implement this hook to do any required conversions.
|
|
@var{code} is the initial comparison code and @var{op0} and @var{op1}
|
|
are the left and right operands of the comparison, respectively. If
|
|
@var{op0_preserve_value} is @code{true} the implementation is not
|
|
allowed to change the value of @var{op0} since the value might be used
|
|
in RTXs which aren't comparisons. E.g. the implementation is not
|
|
allowed to swap operands in that case.
|
|
|
|
GCC will not assume that the comparison resulting from this macro is
|
|
valid but will see if the resulting insn matches a pattern in the
|
|
@file{md} file.
|
|
|
|
You need not to implement this hook if it would never change the
|
|
comparison code or operands.
|
|
@end deftypefn
|
|
|
|
@defmac REVERSIBLE_CC_MODE (@var{mode})
|
|
A C expression whose value is one if it is always safe to reverse a
|
|
comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE}
|
|
can ever return @var{mode} for a floating-point inequality comparison,
|
|
then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero.
|
|
|
|
You need not define this macro if it would always returns zero or if the
|
|
floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}.
|
|
For example, here is the definition used on the SPARC, where floating-point
|
|
inequality comparisons are given either @code{CCFPEmode} or @code{CCFPmode}:
|
|
|
|
@smallexample
|
|
#define REVERSIBLE_CC_MODE(MODE) \
|
|
((MODE) != CCFPEmode && (MODE) != CCFPmode)
|
|
@end smallexample
|
|
@end defmac
|
|
|
|
@defmac REVERSE_CONDITION (@var{code}, @var{mode})
|
|
A C expression whose value is reversed condition code of the @var{code} for
|
|
comparison done in CC_MODE @var{mode}. The macro is used only in case
|
|
@code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case
|
|
machine has some non-standard way how to reverse certain conditionals. For
|
|
instance in case all floating point conditions are non-trapping, compiler may
|
|
freely convert unordered compares to ordered ones. Then definition may look
|
|
like:
|
|
|
|
@smallexample
|
|
#define REVERSE_CONDITION(CODE, MODE) \
|
|
((MODE) != CCFPmode ? reverse_condition (CODE) \
|
|
: reverse_condition_maybe_unordered (CODE))
|
|
@end smallexample
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_FIXED_CONDITION_CODE_REGS (unsigned int *@var{p1}, unsigned int *@var{p2})
|
|
On targets which use a hard
|
|
register rather than a pseudo-register to hold condition codes, the
|
|
regular CSE passes are often not able to identify cases in which the
|
|
hard register is set to a common value. Use this hook to enable a
|
|
small pass which optimizes such cases. This hook should return true
|
|
to enable this pass, and it should set the integers to which its
|
|
arguments point to the hard register numbers used for condition codes.
|
|
When there is only one such register, as is true on most systems, the
|
|
integer pointed to by @var{p2} should be set to
|
|
@code{INVALID_REGNUM}.
|
|
|
|
The default version of this hook returns false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} machine_mode TARGET_CC_MODES_COMPATIBLE (machine_mode @var{m1}, machine_mode @var{m2})
|
|
On targets which use multiple condition code modes in class
|
|
@code{MODE_CC}, it is sometimes the case that a comparison can be
|
|
validly done in more than one mode. On such a system, define this
|
|
target hook to take two mode arguments and to return a mode in which
|
|
both comparisons may be validly done. If there is no such mode,
|
|
return @code{VOIDmode}.
|
|
|
|
The default version of this hook checks whether the modes are the
|
|
same. If they are, it returns that mode. If they are different, it
|
|
returns @code{VOIDmode}.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} {unsigned int} TARGET_FLAGS_REGNUM
|
|
If the target has a dedicated flags register, and it needs to use the
|
|
post-reload comparison elimination pass, or the delay slot filler pass,
|
|
then this value should be set appropriately.
|
|
@end deftypevr
|
|
|
|
@node Costs
|
|
@section Describing Relative Costs of Operations
|
|
@cindex costs of instructions
|
|
@cindex relative costs
|
|
@cindex speed of instructions
|
|
|
|
These macros let you describe the relative speed of various operations
|
|
on the target machine.
|
|
|
|
@defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to})
|
|
A C expression for the cost of moving data of mode @var{mode} from a
|
|
register in class @var{from} to one in class @var{to}. The classes are
|
|
expressed using the enumeration values such as @code{GENERAL_REGS}. A
|
|
value of 2 is the default; other values are interpreted relative to
|
|
that.
|
|
|
|
It is not required that the cost always equal 2 when @var{from} is the
|
|
same as @var{to}; on some machines it is expensive to move between
|
|
registers if they are not general registers.
|
|
|
|
If reload sees an insn consisting of a single @code{set} between two
|
|
hard registers, and if @code{REGISTER_MOVE_COST} applied to their
|
|
classes returns a value of 2, reload does not check to ensure that the
|
|
constraints of the insn are met. Setting a cost of other than 2 will
|
|
allow reload to verify that the constraints are met. You should do this
|
|
if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
|
|
|
|
These macros are obsolete, new ports should use the target hook
|
|
@code{TARGET_REGISTER_MOVE_COST} instead.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} int TARGET_REGISTER_MOVE_COST (machine_mode @var{mode}, reg_class_t @var{from}, reg_class_t @var{to})
|
|
This target hook should return the cost of moving data of mode @var{mode}
|
|
from a register in class @var{from} to one in class @var{to}. The classes
|
|
are expressed using the enumeration values such as @code{GENERAL_REGS}.
|
|
A value of 2 is the default; other values are interpreted relative to
|
|
that.
|
|
|
|
It is not required that the cost always equal 2 when @var{from} is the
|
|
same as @var{to}; on some machines it is expensive to move between
|
|
registers if they are not general registers.
|
|
|
|
If reload sees an insn consisting of a single @code{set} between two
|
|
hard registers, and if @code{TARGET_REGISTER_MOVE_COST} applied to their
|
|
classes returns a value of 2, reload does not check to ensure that the
|
|
constraints of the insn are met. Setting a cost of other than 2 will
|
|
allow reload to verify that the constraints are met. You should do this
|
|
if the @samp{mov@var{m}} pattern's constraints do not allow such copying.
|
|
|
|
The default version of this function returns 2.
|
|
@end deftypefn
|
|
|
|
@defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in})
|
|
A C expression for the cost of moving data of mode @var{mode} between a
|
|
register of class @var{class} and memory; @var{in} is zero if the value
|
|
is to be written to memory, nonzero if it is to be read in. This cost
|
|
is relative to those in @code{REGISTER_MOVE_COST}. If moving between
|
|
registers and memory is more expensive than between two registers, you
|
|
should define this macro to express the relative cost.
|
|
|
|
If you do not define this macro, GCC uses a default cost of 4 plus
|
|
the cost of copying via a secondary reload register, if one is
|
|
needed. If your machine requires a secondary reload register to copy
|
|
between memory and a register of @var{class} but the reload mechanism is
|
|
more complex than copying via an intermediate, define this macro to
|
|
reflect the actual cost of the move.
|
|
|
|
GCC defines the function @code{memory_move_secondary_cost} if
|
|
secondary reloads are needed. It computes the costs due to copying via
|
|
a secondary register. If your machine copies from memory using a
|
|
secondary register in the conventional way but the default base value of
|
|
4 is not correct for your machine, define this macro to add some other
|
|
value to the result of that function. The arguments to that function
|
|
are the same as to this macro.
|
|
|
|
These macros are obsolete, new ports should use the target hook
|
|
@code{TARGET_MEMORY_MOVE_COST} instead.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} int TARGET_MEMORY_MOVE_COST (machine_mode @var{mode}, reg_class_t @var{rclass}, bool @var{in})
|
|
This target hook should return the cost of moving data of mode @var{mode}
|
|
between a register of class @var{rclass} and memory; @var{in} is @code{false}
|
|
if the value is to be written to memory, @code{true} if it is to be read in.
|
|
This cost is relative to those in @code{TARGET_REGISTER_MOVE_COST}.
|
|
If moving between registers and memory is more expensive than between two
|
|
registers, you should add this target hook to express the relative cost.
|
|
|
|
If you do not add this target hook, GCC uses a default cost of 4 plus
|
|
the cost of copying via a secondary reload register, if one is
|
|
needed. If your machine requires a secondary reload register to copy
|
|
between memory and a register of @var{rclass} but the reload mechanism is
|
|
more complex than copying via an intermediate, use this target hook to
|
|
reflect the actual cost of the move.
|
|
|
|
GCC defines the function @code{memory_move_secondary_cost} if
|
|
secondary reloads are needed. It computes the costs due to copying via
|
|
a secondary register. If your machine copies from memory using a
|
|
secondary register in the conventional way but the default base value of
|
|
4 is not correct for your machine, use this target hook to add some other
|
|
value to the result of that function. The arguments to that function
|
|
are the same as to this target hook.
|
|
@end deftypefn
|
|
|
|
@defmac BRANCH_COST (@var{speed_p}, @var{predictable_p})
|
|
A C expression for the cost of a branch instruction. A value of 1 is
|
|
the default; other values are interpreted relative to that. Parameter
|
|
@var{speed_p} is true when the branch in question should be optimized
|
|
for speed. When it is false, @code{BRANCH_COST} should return a value
|
|
optimal for code size rather than performance. @var{predictable_p} is
|
|
true for well-predicted branches. On many architectures the
|
|
@code{BRANCH_COST} can be reduced then.
|
|
@end defmac
|
|
|
|
Here are additional macros which do not specify precise relative costs,
|
|
but only that certain actions are more expensive than GCC would
|
|
ordinarily expect.
|
|
|
|
@defmac SLOW_BYTE_ACCESS
|
|
Define this macro as a C expression which is nonzero if accessing less
|
|
than a word of memory (i.e.@: a @code{char} or a @code{short}) is no
|
|
faster than accessing a word of memory, i.e., if such access
|
|
require more than one instruction or if there is no difference in cost
|
|
between byte and (aligned) word loads.
|
|
|
|
When this macro is not defined, the compiler will access a field by
|
|
finding the smallest containing object; when it is defined, a fullword
|
|
load will be used if alignment permits. Unless bytes accesses are
|
|
faster than word accesses, using word accesses is preferable since it
|
|
may eliminate subsequent memory access if subsequent accesses occur to
|
|
other fields in the same word of the structure, but to different bytes.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SLOW_UNALIGNED_ACCESS (machine_mode @var{mode}, unsigned int @var{align})
|
|
This hook returns true if memory accesses described by the
|
|
@var{mode} and @var{alignment} parameters have a cost many times greater
|
|
than aligned accesses, for example if they are emulated in a trap handler.
|
|
This hook is invoked only for unaligned accesses, i.e.@: when
|
|
@code{@var{alignment} < GET_MODE_ALIGNMENT (@var{mode})}.
|
|
|
|
When this hook returns true, the compiler will act as if
|
|
@code{STRICT_ALIGNMENT} were true when generating code for block
|
|
moves. This can cause significantly more instructions to be produced.
|
|
Therefore, do not make this hook return true if unaligned accesses only
|
|
add a cycle or two to the time for a memory access.
|
|
|
|
The hook must return true whenever @code{STRICT_ALIGNMENT} is true.
|
|
The default implementation returns @code{STRICT_ALIGNMENT}.
|
|
@end deftypefn
|
|
|
|
@defmac MOVE_RATIO (@var{speed})
|
|
The threshold of number of scalar memory-to-memory move insns, @emph{below}
|
|
which a sequence of insns should be generated instead of a
|
|
string move insn or a library call. Increasing the value will always
|
|
make code faster, but eventually incurs high cost in increased code size.
|
|
|
|
Note that on machines where the corresponding move insn is a
|
|
@code{define_expand} that emits a sequence of insns, this macro counts
|
|
the number of such sequences.
|
|
|
|
The parameter @var{speed} is true if the code is currently being
|
|
optimized for speed rather than size.
|
|
|
|
If you don't define this, a reasonable default is used.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_USE_BY_PIECES_INFRASTRUCTURE_P (unsigned HOST_WIDE_INT @var{size}, unsigned int @var{alignment}, enum by_pieces_operation @var{op}, bool @var{speed_p})
|
|
GCC will attempt several strategies when asked to copy between
|
|
two areas of memory, or to set, clear or store to memory, for example
|
|
when copying a @code{struct}. The @code{by_pieces} infrastructure
|
|
implements such memory operations as a sequence of load, store or move
|
|
insns. Alternate strategies are to expand the
|
|
@code{cpymem} or @code{setmem} optabs, to emit a library call, or to emit
|
|
unit-by-unit, loop-based operations.
|
|
|
|
This target hook should return true if, for a memory operation with a
|
|
given @var{size} and @var{alignment}, using the @code{by_pieces}
|
|
infrastructure is expected to result in better code generation.
|
|
Both @var{size} and @var{alignment} are measured in terms of storage
|
|
units.
|
|
|
|
The parameter @var{op} is one of: @code{CLEAR_BY_PIECES},
|
|
@code{MOVE_BY_PIECES}, @code{SET_BY_PIECES}, @code{STORE_BY_PIECES} or
|
|
@code{COMPARE_BY_PIECES}. These describe the type of memory operation
|
|
under consideration.
|
|
|
|
The parameter @var{speed_p} is true if the code is currently being
|
|
optimized for speed rather than size.
|
|
|
|
Returning true for higher values of @var{size} can improve code generation
|
|
for speed if the target does not provide an implementation of the
|
|
@code{cpymem} or @code{setmem} standard names, if the @code{cpymem} or
|
|
@code{setmem} implementation would be more expensive than a sequence of
|
|
insns, or if the overhead of a library call would dominate that of
|
|
the body of the memory operation.
|
|
|
|
Returning true for higher values of @code{size} may also cause an increase
|
|
in code size, for example where the number of insns emitted to perform a
|
|
move would be greater than that of a library call.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_OVERLAP_OP_BY_PIECES_P (void)
|
|
This target hook should return true if when the @code{by_pieces}
|
|
infrastructure is used, an offset adjusted unaligned memory operation
|
|
in the smallest integer mode for the last piece operation of a memory
|
|
region can be generated to avoid doing more than one smaller operations.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_COMPARE_BY_PIECES_BRANCH_RATIO (machine_mode @var{mode})
|
|
When expanding a block comparison in MODE, gcc can try to reduce the
|
|
number of branches at the expense of more memory operations. This hook
|
|
allows the target to override the default choice. It should return the
|
|
factor by which branches should be reduced over the plain expansion with
|
|
one comparison per @var{mode}-sized piece. A port can also prevent a
|
|
particular mode from being used for block comparisons by returning a
|
|
negative number from this hook.
|
|
@end deftypefn
|
|
|
|
@defmac MOVE_MAX_PIECES
|
|
A C expression used by @code{move_by_pieces} to determine the largest unit
|
|
a load or store used to copy memory is. Defaults to @code{MOVE_MAX}.
|
|
@end defmac
|
|
|
|
@defmac STORE_MAX_PIECES
|
|
A C expression used by @code{store_by_pieces} to determine the largest unit
|
|
a store used to memory is. Defaults to @code{MOVE_MAX_PIECES}, or two times
|
|
the size of @code{HOST_WIDE_INT}, whichever is smaller.
|
|
@end defmac
|
|
|
|
@defmac COMPARE_MAX_PIECES
|
|
A C expression used by @code{compare_by_pieces} to determine the largest unit
|
|
a load or store used to compare memory is. Defaults to
|
|
@code{MOVE_MAX_PIECES}.
|
|
@end defmac
|
|
|
|
@defmac CLEAR_RATIO (@var{speed})
|
|
The threshold of number of scalar move insns, @emph{below} which a sequence
|
|
of insns should be generated to clear memory instead of a string clear insn
|
|
or a library call. Increasing the value will always make code faster, but
|
|
eventually incurs high cost in increased code size.
|
|
|
|
The parameter @var{speed} is true if the code is currently being
|
|
optimized for speed rather than size.
|
|
|
|
If you don't define this, a reasonable default is used.
|
|
@end defmac
|
|
|
|
@defmac SET_RATIO (@var{speed})
|
|
The threshold of number of scalar move insns, @emph{below} which a sequence
|
|
of insns should be generated to set memory to a constant value, instead of
|
|
a block set insn or a library call.
|
|
Increasing the value will always make code faster, but
|
|
eventually incurs high cost in increased code size.
|
|
|
|
The parameter @var{speed} is true if the code is currently being
|
|
optimized for speed rather than size.
|
|
|
|
If you don't define this, it defaults to the value of @code{MOVE_RATIO}.
|
|
@end defmac
|
|
|
|
@defmac USE_LOAD_POST_INCREMENT (@var{mode})
|
|
A C expression used to determine whether a load postincrement is a good
|
|
thing to use for a given mode. Defaults to the value of
|
|
@code{HAVE_POST_INCREMENT}.
|
|
@end defmac
|
|
|
|
@defmac USE_LOAD_POST_DECREMENT (@var{mode})
|
|
A C expression used to determine whether a load postdecrement is a good
|
|
thing to use for a given mode. Defaults to the value of
|
|
@code{HAVE_POST_DECREMENT}.
|
|
@end defmac
|
|
|
|
@defmac USE_LOAD_PRE_INCREMENT (@var{mode})
|
|
A C expression used to determine whether a load preincrement is a good
|
|
thing to use for a given mode. Defaults to the value of
|
|
@code{HAVE_PRE_INCREMENT}.
|
|
@end defmac
|
|
|
|
@defmac USE_LOAD_PRE_DECREMENT (@var{mode})
|
|
A C expression used to determine whether a load predecrement is a good
|
|
thing to use for a given mode. Defaults to the value of
|
|
@code{HAVE_PRE_DECREMENT}.
|
|
@end defmac
|
|
|
|
@defmac USE_STORE_POST_INCREMENT (@var{mode})
|
|
A C expression used to determine whether a store postincrement is a good
|
|
thing to use for a given mode. Defaults to the value of
|
|
@code{HAVE_POST_INCREMENT}.
|
|
@end defmac
|
|
|
|
@defmac USE_STORE_POST_DECREMENT (@var{mode})
|
|
A C expression used to determine whether a store postdecrement is a good
|
|
thing to use for a given mode. Defaults to the value of
|
|
@code{HAVE_POST_DECREMENT}.
|
|
@end defmac
|
|
|
|
@defmac USE_STORE_PRE_INCREMENT (@var{mode})
|
|
This macro is used to determine whether a store preincrement is a good
|
|
thing to use for a given mode. Defaults to the value of
|
|
@code{HAVE_PRE_INCREMENT}.
|
|
@end defmac
|
|
|
|
@defmac USE_STORE_PRE_DECREMENT (@var{mode})
|
|
This macro is used to determine whether a store predecrement is a good
|
|
thing to use for a given mode. Defaults to the value of
|
|
@code{HAVE_PRE_DECREMENT}.
|
|
@end defmac
|
|
|
|
@defmac NO_FUNCTION_CSE
|
|
Define this macro to be true if it is as good or better to call a constant
|
|
function address than to call an address kept in a register.
|
|
@end defmac
|
|
|
|
@defmac LOGICAL_OP_NON_SHORT_CIRCUIT
|
|
Define this macro if a non-short-circuit operation produced by
|
|
@samp{fold_range_test ()} is optimal. This macro defaults to true if
|
|
@code{BRANCH_COST} is greater than or equal to the value 2.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_OPTAB_SUPPORTED_P (int @var{op}, machine_mode @var{mode1}, machine_mode @var{mode2}, optimization_type @var{opt_type})
|
|
Return true if the optimizers should use optab @var{op} with
|
|
modes @var{mode1} and @var{mode2} for optimization type @var{opt_type}.
|
|
The optab is known to have an associated @file{.md} instruction
|
|
whose C condition is true. @var{mode2} is only meaningful for conversion
|
|
optabs; for direct optabs it is a copy of @var{mode1}.
|
|
|
|
For example, when called with @var{op} equal to @code{rint_optab} and
|
|
@var{mode1} equal to @code{DFmode}, the hook should say whether the
|
|
optimizers should use optab @code{rintdf2}.
|
|
|
|
The default hook returns true for all inputs.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_RTX_COSTS (rtx @var{x}, machine_mode @var{mode}, int @var{outer_code}, int @var{opno}, int *@var{total}, bool @var{speed})
|
|
This target hook describes the relative costs of RTL expressions.
|
|
|
|
The cost may depend on the precise form of the expression, which is
|
|
available for examination in @var{x}, and the fact that @var{x} appears
|
|
as operand @var{opno} of an expression with rtx code @var{outer_code}.
|
|
That is, the hook can assume that there is some rtx @var{y} such
|
|
that @samp{GET_CODE (@var{y}) == @var{outer_code}} and such that
|
|
either (a) @samp{XEXP (@var{y}, @var{opno}) == @var{x}} or
|
|
(b) @samp{XVEC (@var{y}, @var{opno})} contains @var{x}.
|
|
|
|
@var{mode} is @var{x}'s machine mode, or for cases like @code{const_int} that
|
|
do not have a mode, the mode in which @var{x} is used.
|
|
|
|
In implementing this hook, you can use the construct
|
|
@code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast
|
|
instructions.
|
|
|
|
On entry to the hook, @code{*@var{total}} contains a default estimate
|
|
for the cost of the expression. The hook should modify this value as
|
|
necessary. Traditionally, the default costs are @code{COSTS_N_INSNS (5)}
|
|
for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus
|
|
operations, and @code{COSTS_N_INSNS (1)} for all other operations.
|
|
|
|
When optimizing for code size, i.e.@: when @code{speed} is
|
|
false, this target hook should be used to estimate the relative
|
|
size cost of an expression, again relative to @code{COSTS_N_INSNS}.
|
|
|
|
The hook returns true when all subexpressions of @var{x} have been
|
|
processed, and false when @code{rtx_cost} should recurse.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_ADDRESS_COST (rtx @var{address}, machine_mode @var{mode}, addr_space_t @var{as}, bool @var{speed})
|
|
This hook computes the cost of an addressing mode that contains
|
|
@var{address}. If not defined, the cost is computed from
|
|
the @var{address} expression and the @code{TARGET_RTX_COST} hook.
|
|
|
|
For most CISC machines, the default cost is a good approximation of the
|
|
true cost of the addressing mode. However, on RISC machines, all
|
|
instructions normally have the same length and execution time. Hence
|
|
all addresses will have equal costs.
|
|
|
|
In cases where more than one form of an address is known, the form with
|
|
the lowest cost will be used. If multiple forms have the same, lowest,
|
|
cost, the one that is the most complex will be used.
|
|
|
|
For example, suppose an address that is equal to the sum of a register
|
|
and a constant is used twice in the same basic block. When this macro
|
|
is not defined, the address will be computed in a register and memory
|
|
references will be indirect through that register. On machines where
|
|
the cost of the addressing mode containing the sum is no higher than
|
|
that of a simple indirect reference, this will produce an additional
|
|
instruction and possibly require an additional register. Proper
|
|
specification of this macro eliminates this overhead for such machines.
|
|
|
|
This hook is never called with an invalid address.
|
|
|
|
On machines where an address involving more than one register is as
|
|
cheap as an address computation involving only one register, defining
|
|
@code{TARGET_ADDRESS_COST} to reflect this can cause two registers to
|
|
be live over a region of code where only one would have been if
|
|
@code{TARGET_ADDRESS_COST} were not defined in that manner. This effect
|
|
should be considered in the definition of this macro. Equivalent costs
|
|
should probably only be given to addresses with different numbers of
|
|
registers on machines with lots of registers.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_INSN_COST (rtx_insn *@var{insn}, bool @var{speed})
|
|
This target hook describes the relative costs of RTL instructions.
|
|
|
|
In implementing this hook, you can use the construct
|
|
@code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast
|
|
instructions.
|
|
|
|
When optimizing for code size, i.e.@: when @code{speed} is
|
|
false, this target hook should be used to estimate the relative
|
|
size cost of an expression, again relative to @code{COSTS_N_INSNS}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_MAX_NOCE_IFCVT_SEQ_COST (edge @var{e})
|
|
This hook returns a value in the same units as @code{TARGET_RTX_COSTS},
|
|
giving the maximum acceptable cost for a sequence generated by the RTL
|
|
if-conversion pass when conditional execution is not available.
|
|
The RTL if-conversion pass attempts to convert conditional operations
|
|
that would require a branch to a series of unconditional operations and
|
|
@code{mov@var{mode}cc} insns. This hook returns the maximum cost of the
|
|
unconditional instructions and the @code{mov@var{mode}cc} insns.
|
|
RTL if-conversion is cancelled if the cost of the converted sequence
|
|
is greater than the value returned by this hook.
|
|
|
|
@code{e} is the edge between the basic block containing the conditional
|
|
branch to the basic block which would be executed if the condition
|
|
were true.
|
|
|
|
The default implementation of this hook uses the
|
|
@code{max-rtl-if-conversion-[un]predictable} parameters if they are set,
|
|
and uses a multiple of @code{BRANCH_COST} otherwise.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_NOCE_CONVERSION_PROFITABLE_P (rtx_insn *@var{seq}, struct noce_if_info *@var{if_info})
|
|
This hook returns true if the instruction sequence @code{seq} is a good
|
|
candidate as a replacement for the if-convertible sequence described in
|
|
@code{if_info}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_NEW_ADDRESS_PROFITABLE_P (rtx @var{memref}, rtx_insn * @var{insn}, rtx @var{new_addr})
|
|
Return @code{true} if it is profitable to replace the address in
|
|
@var{memref} with @var{new_addr}. This allows targets to prevent the
|
|
scheduler from undoing address optimizations. The instruction containing the
|
|
memref is @var{insn}. The default implementation returns @code{true}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_NO_SPECULATION_IN_DELAY_SLOTS_P (void)
|
|
This predicate controls the use of the eager delay slot filler to disallow
|
|
speculatively executed instructions being placed in delay slots. Targets
|
|
such as certain MIPS architectures possess both branches with and without
|
|
delay slots. As the eager delay slot filler can decrease performance,
|
|
disabling it is beneficial when ordinary branches are available. Use of
|
|
delay slot branches filled using the basic filler is often still desirable
|
|
as the delay slot can hide a pipeline bubble.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} HOST_WIDE_INT TARGET_ESTIMATED_POLY_VALUE (poly_int64 @var{val}, poly_value_estimate_kind @var{kind})
|
|
Return an estimate of the runtime value of @var{val}, for use in
|
|
things like cost calculations or profiling frequencies. @var{kind} is used
|
|
to ask for the minimum, maximum, and likely estimates of the value through
|
|
the @code{POLY_VALUE_MIN}, @code{POLY_VALUE_MAX} and
|
|
@code{POLY_VALUE_LIKELY} values. The default
|
|
implementation returns the lowest possible value of @var{val}.
|
|
@end deftypefn
|
|
|
|
@node Scheduling
|
|
@section Adjusting the Instruction Scheduler
|
|
|
|
The instruction scheduler may need a fair amount of machine-specific
|
|
adjustment in order to produce good code. GCC provides several target
|
|
hooks for this purpose. It is usually enough to define just a few of
|
|
them: try the first ones in this list first.
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void)
|
|
This hook returns the maximum number of instructions that can ever
|
|
issue at the same time on the target machine. The default is one.
|
|
Although the insn scheduler can define itself the possibility of issue
|
|
an insn on the same cycle, the value can serve as an additional
|
|
constraint to issue insns on the same simulated processor cycle (see
|
|
hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}).
|
|
This value must be constant over the entire compilation. If you need
|
|
it to vary depending on what the instructions are, you must use
|
|
@samp{TARGET_SCHED_VARIABLE_ISSUE}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx_insn *@var{insn}, int @var{more})
|
|
This hook is executed by the scheduler after it has scheduled an insn
|
|
from the ready list. It should return the number of insns which can
|
|
still be issued in the current cycle. The default is
|
|
@samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and
|
|
@code{USE}, which normally are not counted against the issue rate.
|
|
You should define this hook if some insns take more machine resources
|
|
than others, so that fewer insns can follow them in the same cycle.
|
|
@var{file} is either a null pointer, or a stdio stream to write any
|
|
debug output to. @var{verbose} is the verbose level provided by
|
|
@option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that
|
|
was scheduled.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx_insn *@var{insn}, int @var{dep_type1}, rtx_insn *@var{dep_insn}, int @var{cost}, unsigned int @var{dw})
|
|
This function corrects the value of @var{cost} based on the
|
|
relationship between @var{insn} and @var{dep_insn} through a
|
|
dependence of type dep_type, and strength @var{dw}. It should return the new
|
|
value. The default is to make no adjustment to @var{cost}. This can be
|
|
used for example to specify to the scheduler using the traditional pipeline
|
|
description that an output- or anti-dependence does not incur the same cost
|
|
as a data-dependence. If the scheduler using the automaton based pipeline
|
|
description, the cost of anti-dependence is zero and the cost of
|
|
output-dependence is maximum of one and the difference of latency
|
|
times of the first and the second insns. If these values are not
|
|
acceptable, you could use the hook to modify them too. See also
|
|
@pxref{Processor pipeline description}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx_insn *@var{insn}, int @var{priority})
|
|
This hook adjusts the integer scheduling priority @var{priority} of
|
|
@var{insn}. It should return the new priority. Increase the priority to
|
|
execute @var{insn} earlier, reduce the priority to execute @var{insn}
|
|
later. Do not define this hook if you do not need to adjust the
|
|
scheduling priorities of insns.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx_insn **@var{ready}, int *@var{n_readyp}, int @var{clock})
|
|
This hook is executed by the scheduler after it has scheduled the ready
|
|
list, to allow the machine description to reorder it (for example to
|
|
combine two small instructions together on @samp{VLIW} machines).
|
|
@var{file} is either a null pointer, or a stdio stream to write any
|
|
debug output to. @var{verbose} is the verbose level provided by
|
|
@option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready
|
|
list of instructions that are ready to be scheduled. @var{n_readyp} is
|
|
a pointer to the number of elements in the ready list. The scheduler
|
|
reads the ready list in reverse order, starting with
|
|
@var{ready}[@var{*n_readyp} @minus{} 1] and going to @var{ready}[0]. @var{clock}
|
|
is the timer tick of the scheduler. You may modify the ready list and
|
|
the number of ready insns. The return value is the number of insns that
|
|
can issue this cycle; normally this is just @code{issue_rate}. See also
|
|
@samp{TARGET_SCHED_REORDER2}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx_insn **@var{ready}, int *@var{n_readyp}, int @var{clock})
|
|
Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That
|
|
function is called whenever the scheduler starts a new cycle. This one
|
|
is called once per iteration over a cycle, immediately after
|
|
@samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and
|
|
return the number of insns to be scheduled in the same cycle. Defining
|
|
this hook can be useful if there are frequent situations where
|
|
scheduling one insn causes other insns to become ready in the same
|
|
cycle. These other insns can then be taken into account properly.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SCHED_MACRO_FUSION_P (void)
|
|
This hook is used to check whether target platform supports macro fusion.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SCHED_MACRO_FUSION_PAIR_P (rtx_insn *@var{prev}, rtx_insn *@var{curr})
|
|
This hook is used to check whether two insns should be macro fused for
|
|
a target microarchitecture. If this hook returns true for the given insn pair
|
|
(@var{prev} and @var{curr}), the scheduler will put them into a sched
|
|
group, and they will not be scheduled apart. The two insns will be either
|
|
two SET insns or a compare and a conditional jump and this hook should
|
|
validate any dependencies needed to fuse the two insns together.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK (rtx_insn *@var{head}, rtx_insn *@var{tail})
|
|
This hook is called after evaluation forward dependencies of insns in
|
|
chain given by two parameter values (@var{head} and @var{tail}
|
|
correspondingly) but before insns scheduling of the insn chain. For
|
|
example, it can be used for better insn classification if it requires
|
|
analysis of dependencies. This hook can use backward and forward
|
|
dependencies of the insn scheduler because they are already
|
|
calculated.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready})
|
|
This hook is executed by the scheduler at the beginning of each block of
|
|
instructions that are to be scheduled. @var{file} is either a null
|
|
pointer, or a stdio stream to write any debug output to. @var{verbose}
|
|
is the verbose level provided by @option{-fsched-verbose-@var{n}}.
|
|
@var{max_ready} is the maximum number of insns in the current scheduling
|
|
region that can be live at the same time. This can be used to allocate
|
|
scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose})
|
|
This hook is executed by the scheduler at the end of each block of
|
|
instructions that are to be scheduled. It can be used to perform
|
|
cleanup of any actions done by the other scheduling hooks. @var{file}
|
|
is either a null pointer, or a stdio stream to write any debug output
|
|
to. @var{verbose} is the verbose level provided by
|
|
@option{-fsched-verbose-@var{n}}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_INIT_GLOBAL (FILE *@var{file}, int @var{verbose}, int @var{old_max_uid})
|
|
This hook is executed by the scheduler after function level initializations.
|
|
@var{file} is either a null pointer, or a stdio stream to write any debug output to.
|
|
@var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
|
|
@var{old_max_uid} is the maximum insn uid when scheduling begins.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FINISH_GLOBAL (FILE *@var{file}, int @var{verbose})
|
|
This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}.
|
|
@var{file} is either a null pointer, or a stdio stream to write any debug output to.
|
|
@var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_SCHED_DFA_PRE_CYCLE_INSN (void)
|
|
The hook returns an RTL insn. The automaton state used in the
|
|
pipeline hazard recognizer is changed as if the insn were scheduled
|
|
when the new simulated processor cycle starts. Usage of the hook may
|
|
simplify the automaton pipeline description for some @acronym{VLIW}
|
|
processors. If the hook is defined, it is used only for the automaton
|
|
based pipeline description. The default is not to change the state
|
|
when the new simulated processor cycle starts.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void)
|
|
The hook can be used to initialize data used by the previous hook.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {rtx_insn *} TARGET_SCHED_DFA_POST_CYCLE_INSN (void)
|
|
The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
|
|
to changed the state as if the insn were scheduled when the new
|
|
simulated processor cycle finishes.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void)
|
|
The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but
|
|
used to initialize data used by the previous hook.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_DFA_PRE_ADVANCE_CYCLE (void)
|
|
The hook to notify target that the current simulated cycle is about to finish.
|
|
The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used
|
|
to change the state in more complicated situations - e.g., when advancing
|
|
state on a single insn is not enough.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_DFA_POST_ADVANCE_CYCLE (void)
|
|
The hook to notify target that new simulated cycle has just started.
|
|
The hook is analogous to @samp{TARGET_SCHED_DFA_POST_CYCLE_INSN} but used
|
|
to change the state in more complicated situations - e.g., when advancing
|
|
state on a single insn is not enough.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void)
|
|
This hook controls better choosing an insn from the ready insn queue
|
|
for the @acronym{DFA}-based insn scheduler. Usually the scheduler
|
|
chooses the first insn from the queue. If the hook returns a positive
|
|
value, an additional scheduler code tries all permutations of
|
|
@samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()}
|
|
subsequent ready insns to choose an insn whose issue will result in
|
|
maximal number of issued insns on the same cycle. For the
|
|
@acronym{VLIW} processor, the code could actually solve the problem of
|
|
packing simple insns into the @acronym{VLIW} insn. Of course, if the
|
|
rules of @acronym{VLIW} packing are described in the automaton.
|
|
|
|
This code also could be used for superscalar @acronym{RISC}
|
|
processors. Let us consider a superscalar @acronym{RISC} processor
|
|
with 3 pipelines. Some insns can be executed in pipelines @var{A} or
|
|
@var{B}, some insns can be executed only in pipelines @var{B} or
|
|
@var{C}, and one insn can be executed in pipeline @var{B}. The
|
|
processor may issue the 1st insn into @var{A} and the 2nd one into
|
|
@var{B}. In this case, the 3rd insn will wait for freeing @var{B}
|
|
until the next cycle. If the scheduler issues the 3rd insn the first,
|
|
the processor could issue all 3 insns per cycle.
|
|
|
|
Actually this code demonstrates advantages of the automaton based
|
|
pipeline hazard recognizer. We try quickly and easy many insn
|
|
schedules to choose the best one.
|
|
|
|
The default is no multipass scheduling.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD (rtx_insn *@var{insn}, int @var{ready_index})
|
|
|
|
This hook controls what insns from the ready insn queue will be
|
|
considered for the multipass insn scheduling. If the hook returns
|
|
zero for @var{insn}, the insn will be considered in multipass scheduling.
|
|
Positive return values will remove @var{insn} from consideration on
|
|
the current round of multipass scheduling.
|
|
Negative return values will remove @var{insn} from consideration for given
|
|
number of cycles.
|
|
Backends should be careful about returning non-zero for highest priority
|
|
instruction at position 0 in the ready list. @var{ready_index} is passed
|
|
to allow backends make correct judgements.
|
|
|
|
The default is that any ready insns can be chosen to be issued.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BEGIN (void *@var{data}, signed char *@var{ready_try}, int @var{n_ready}, bool @var{first_cycle_insn_p})
|
|
This hook prepares the target backend for a new round of multipass
|
|
scheduling.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_ISSUE (void *@var{data}, signed char *@var{ready_try}, int @var{n_ready}, rtx_insn *@var{insn}, const void *@var{prev_data})
|
|
This hook is called when multipass scheduling evaluates instruction INSN.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BACKTRACK (const void *@var{data}, signed char *@var{ready_try}, int @var{n_ready})
|
|
This is called when multipass scheduling backtracks from evaluation of
|
|
an instruction.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_END (const void *@var{data})
|
|
This hook notifies the target about the result of the concluded current
|
|
round of multipass scheduling.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_INIT (void *@var{data})
|
|
This hook initializes target-specific data used in multipass scheduling.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_FINI (void *@var{data})
|
|
This hook finalizes target-specific data used in multipass scheduling.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_DFA_NEW_CYCLE (FILE *@var{dump}, int @var{verbose}, rtx_insn *@var{insn}, int @var{last_clock}, int @var{clock}, int *@var{sort_p})
|
|
This hook is called by the insn scheduler before issuing @var{insn}
|
|
on cycle @var{clock}. If the hook returns nonzero,
|
|
@var{insn} is not issued on this processor cycle. Instead,
|
|
the processor cycle is advanced. If *@var{sort_p}
|
|
is zero, the insn ready queue is not sorted on the new cycle
|
|
start as usually. @var{dump} and @var{verbose} specify the file and
|
|
verbosity level to use for debugging output.
|
|
@var{last_clock} and @var{clock} are, respectively, the
|
|
processor cycle on which the previous insn has been issued,
|
|
and the current processor cycle.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SCHED_IS_COSTLY_DEPENDENCE (struct _dep *@var{_dep}, int @var{cost}, int @var{distance})
|
|
This hook is used to define which dependences are considered costly by
|
|
the target, so costly that it is not advisable to schedule the insns that
|
|
are involved in the dependence too close to one another. The parameters
|
|
to this hook are as follows: The first parameter @var{_dep} is the dependence
|
|
being evaluated. The second parameter @var{cost} is the cost of the
|
|
dependence as estimated by the scheduler, and the third
|
|
parameter @var{distance} is the distance in cycles between the two insns.
|
|
The hook returns @code{true} if considering the distance between the two
|
|
insns the dependence between them is considered costly by the target,
|
|
and @code{false} otherwise.
|
|
|
|
Defining this hook can be useful in multiple-issue out-of-order machines,
|
|
where (a) it's practically hopeless to predict the actual data/resource
|
|
delays, however: (b) there's a better chance to predict the actual grouping
|
|
that will be formed, and (c) correctly emulating the grouping can be very
|
|
important. In such targets one may want to allow issuing dependent insns
|
|
closer to one another---i.e., closer than the dependence distance; however,
|
|
not in cases of ``costly dependences'', which this hooks allows to define.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_H_I_D_EXTENDED (void)
|
|
This hook is called by the insn scheduler after emitting a new instruction to
|
|
the instruction stream. The hook notifies a target backend to extend its
|
|
per instruction data structures.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {void *} TARGET_SCHED_ALLOC_SCHED_CONTEXT (void)
|
|
Return a pointer to a store large enough to hold target scheduling context.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_INIT_SCHED_CONTEXT (void *@var{tc}, bool @var{clean_p})
|
|
Initialize store pointed to by @var{tc} to hold target scheduling context.
|
|
It @var{clean_p} is true then initialize @var{tc} as if scheduler is at the
|
|
beginning of the block. Otherwise, copy the current context into @var{tc}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_CONTEXT (void *@var{tc})
|
|
Copy target scheduling context pointed to by @var{tc} to the current context.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_CLEAR_SCHED_CONTEXT (void *@var{tc})
|
|
Deallocate internal data in target scheduling context pointed to by @var{tc}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FREE_SCHED_CONTEXT (void *@var{tc})
|
|
Deallocate a store for target scheduling context pointed to by @var{tc}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_SPECULATE_INSN (rtx_insn *@var{insn}, unsigned int @var{dep_status}, rtx *@var{new_pat})
|
|
This hook is called by the insn scheduler when @var{insn} has only
|
|
speculative dependencies and therefore can be scheduled speculatively.
|
|
The hook is used to check if the pattern of @var{insn} has a speculative
|
|
version and, in case of successful check, to generate that speculative
|
|
pattern. The hook should return 1, if the instruction has a speculative form,
|
|
or @minus{}1, if it doesn't. @var{request} describes the type of requested
|
|
speculation. If the return value equals 1 then @var{new_pat} is assigned
|
|
the generated speculative pattern.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SCHED_NEEDS_BLOCK_P (unsigned int @var{dep_status})
|
|
This hook is called by the insn scheduler during generation of recovery code
|
|
for @var{insn}. It should return @code{true}, if the corresponding check
|
|
instruction should branch to recovery code, or @code{false} otherwise.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_SCHED_GEN_SPEC_CHECK (rtx_insn *@var{insn}, rtx_insn *@var{label}, unsigned int @var{ds})
|
|
This hook is called by the insn scheduler to generate a pattern for recovery
|
|
check instruction. If @var{mutate_p} is zero, then @var{insn} is a
|
|
speculative instruction for which the check should be generated.
|
|
@var{label} is either a label of a basic block, where recovery code should
|
|
be emitted, or a null pointer, when requested check doesn't branch to
|
|
recovery code (a simple check). If @var{mutate_p} is nonzero, then
|
|
a pattern for a branchy check corresponding to a simple check denoted by
|
|
@var{insn} should be generated. In this case @var{label} can't be null.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_FLAGS (struct spec_info_def *@var{spec_info})
|
|
This hook is used by the insn scheduler to find out what features should be
|
|
enabled/used.
|
|
The structure *@var{spec_info} should be filled in by the target.
|
|
The structure describes speculation types that can be used in the scheduler.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SCHED_CAN_SPECULATE_INSN (rtx_insn *@var{insn})
|
|
Some instructions should never be speculated by the schedulers, usually
|
|
because the instruction is too expensive to get this wrong. Often such
|
|
instructions have long latency, and often they are not fully modeled in the
|
|
pipeline descriptions. This hook should return @code{false} if @var{insn}
|
|
should not be speculated.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_SMS_RES_MII (struct ddg *@var{g})
|
|
This hook is called by the swing modulo scheduler to calculate a
|
|
resource-based lower bound which is based on the resources available in
|
|
the machine and the resources required by each instruction. The target
|
|
backend can use @var{g} to calculate such bound. A very simple lower
|
|
bound will be used in case this hook is not implemented: the total number
|
|
of instructions divided by the issue rate.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SCHED_DISPATCH (rtx_insn *@var{insn}, int @var{x})
|
|
This hook is called by Haifa Scheduler. It returns true if dispatch scheduling
|
|
is supported in hardware and the condition specified in the parameter is true.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_DISPATCH_DO (rtx_insn *@var{insn}, int @var{x})
|
|
This hook is called by Haifa Scheduler. It performs the operation specified
|
|
in its second parameter.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_SCHED_EXPOSED_PIPELINE
|
|
True if the processor has an exposed pipeline, which means that not just
|
|
the order of instructions is important for correctness when scheduling, but
|
|
also the latencies of operations.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} int TARGET_SCHED_REASSOCIATION_WIDTH (unsigned int @var{opc}, machine_mode @var{mode})
|
|
This hook is called by tree reassociator to determine a level of
|
|
parallelism required in output calculations chain.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SCHED_FUSION_PRIORITY (rtx_insn *@var{insn}, int @var{max_pri}, int *@var{fusion_pri}, int *@var{pri})
|
|
This hook is called by scheduling fusion pass. It calculates fusion
|
|
priorities for each instruction passed in by parameter. The priorities
|
|
are returned via pointer parameters.
|
|
|
|
@var{insn} is the instruction whose priorities need to be calculated.
|
|
@var{max_pri} is the maximum priority can be returned in any cases.
|
|
@var{fusion_pri} is the pointer parameter through which @var{insn}'s
|
|
fusion priority should be calculated and returned.
|
|
@var{pri} is the pointer parameter through which @var{insn}'s priority
|
|
should be calculated and returned.
|
|
|
|
Same @var{fusion_pri} should be returned for instructions which should
|
|
be scheduled together. Different @var{pri} should be returned for
|
|
instructions with same @var{fusion_pri}. @var{fusion_pri} is the major
|
|
sort key, @var{pri} is the minor sort key. All instructions will be
|
|
scheduled according to the two priorities. All priorities calculated
|
|
should be between 0 (exclusive) and @var{max_pri} (inclusive). To avoid
|
|
false dependencies, @var{fusion_pri} of instructions which need to be
|
|
scheduled together should be smaller than @var{fusion_pri} of irrelevant
|
|
instructions.
|
|
|
|
Given below example:
|
|
|
|
@smallexample
|
|
ldr r10, [r1, 4]
|
|
add r4, r4, r10
|
|
ldr r15, [r2, 8]
|
|
sub r5, r5, r15
|
|
ldr r11, [r1, 0]
|
|
add r4, r4, r11
|
|
ldr r16, [r2, 12]
|
|
sub r5, r5, r16
|
|
@end smallexample
|
|
|
|
On targets like ARM/AArch64, the two pairs of consecutive loads should be
|
|
merged. Since peephole2 pass can't help in this case unless consecutive
|
|
loads are actually next to each other in instruction flow. That's where
|
|
this scheduling fusion pass works. This hook calculates priority for each
|
|
instruction based on its fustion type, like:
|
|
|
|
@smallexample
|
|
ldr r10, [r1, 4] ; fusion_pri=99, pri=96
|
|
add r4, r4, r10 ; fusion_pri=100, pri=100
|
|
ldr r15, [r2, 8] ; fusion_pri=98, pri=92
|
|
sub r5, r5, r15 ; fusion_pri=100, pri=100
|
|
ldr r11, [r1, 0] ; fusion_pri=99, pri=100
|
|
add r4, r4, r11 ; fusion_pri=100, pri=100
|
|
ldr r16, [r2, 12] ; fusion_pri=98, pri=88
|
|
sub r5, r5, r16 ; fusion_pri=100, pri=100
|
|
@end smallexample
|
|
|
|
Scheduling fusion pass then sorts all ready to issue instructions according
|
|
to the priorities. As a result, instructions of same fusion type will be
|
|
pushed together in instruction flow, like:
|
|
|
|
@smallexample
|
|
ldr r11, [r1, 0]
|
|
ldr r10, [r1, 4]
|
|
ldr r15, [r2, 8]
|
|
ldr r16, [r2, 12]
|
|
add r4, r4, r10
|
|
sub r5, r5, r15
|
|
add r4, r4, r11
|
|
sub r5, r5, r16
|
|
@end smallexample
|
|
|
|
Now peephole2 pass can simply merge the two pairs of loads.
|
|
|
|
Since scheduling fusion pass relies on peephole2 to do real fusion
|
|
work, it is only enabled by default when peephole2 is in effect.
|
|
|
|
This is firstly introduced on ARM/AArch64 targets, please refer to
|
|
the hook implementation for how different fusion types are supported.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_EXPAND_DIVMOD_LIBFUNC (rtx @var{libfunc}, machine_mode @var{mode}, rtx @var{op0}, rtx @var{op1}, rtx *@var{quot}, rtx *@var{rem})
|
|
Define this hook for enabling divmod transform if the port does not have
|
|
hardware divmod insn but defines target-specific divmod libfuncs.
|
|
@end deftypefn
|
|
|
|
@node Sections
|
|
@section Dividing the Output into Sections (Texts, Data, @dots{})
|
|
@c the above section title is WAY too long. maybe cut the part between
|
|
@c the (...)? --mew 10feb93
|
|
|
|
An object file is divided into sections containing different types of
|
|
data. In the most common case, there are three sections: the @dfn{text
|
|
section}, which holds instructions and read-only data; the @dfn{data
|
|
section}, which holds initialized writable data; and the @dfn{bss
|
|
section}, which holds uninitialized data. Some systems have other kinds
|
|
of sections.
|
|
|
|
@file{varasm.cc} provides several well-known sections, such as
|
|
@code{text_section}, @code{data_section} and @code{bss_section}.
|
|
The normal way of controlling a @code{@var{foo}_section} variable
|
|
is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro,
|
|
as described below. The macros are only read once, when @file{varasm.cc}
|
|
initializes itself, so their values must be run-time constants.
|
|
They may however depend on command-line flags.
|
|
|
|
@emph{Note:} Some run-time files, such @file{crtstuff.c}, also make
|
|
use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them
|
|
to be string literals.
|
|
|
|
Some assemblers require a different string to be written every time a
|
|
section is selected. If your assembler falls into this category, you
|
|
should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use
|
|
@code{get_unnamed_section} to set up the sections.
|
|
|
|
You must always create a @code{text_section}, either by defining
|
|
@code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section}
|
|
in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of
|
|
@code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not
|
|
create a distinct @code{readonly_data_section}, the default is to
|
|
reuse @code{text_section}.
|
|
|
|
All the other @file{varasm.cc} sections are optional, and are null
|
|
if the target does not provide them.
|
|
|
|
@defmac TEXT_SECTION_ASM_OP
|
|
A C expression whose value is a string, including spacing, containing the
|
|
assembler operation that should precede instructions and read-only data.
|
|
Normally @code{"\t.text"} is right.
|
|
@end defmac
|
|
|
|
@defmac HOT_TEXT_SECTION_NAME
|
|
If defined, a C string constant for the name of the section containing most
|
|
frequently executed functions of the program. If not defined, GCC will provide
|
|
a default definition if the target supports named sections.
|
|
@end defmac
|
|
|
|
@defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME
|
|
If defined, a C string constant for the name of the section containing unlikely
|
|
executed functions in the program.
|
|
@end defmac
|
|
|
|
@defmac DATA_SECTION_ASM_OP
|
|
A C expression whose value is a string, including spacing, containing the
|
|
assembler operation to identify the following data as writable initialized
|
|
data. Normally @code{"\t.data"} is right.
|
|
@end defmac
|
|
|
|
@defmac SDATA_SECTION_ASM_OP
|
|
If defined, a C expression whose value is a string, including spacing,
|
|
containing the assembler operation to identify the following data as
|
|
initialized, writable small data.
|
|
@end defmac
|
|
|
|
@defmac READONLY_DATA_SECTION_ASM_OP
|
|
A C expression whose value is a string, including spacing, containing the
|
|
assembler operation to identify the following data as read-only initialized
|
|
data.
|
|
@end defmac
|
|
|
|
@defmac BSS_SECTION_ASM_OP
|
|
If defined, a C expression whose value is a string, including spacing,
|
|
containing the assembler operation to identify the following data as
|
|
uninitialized global data. If not defined, and
|
|
@code{ASM_OUTPUT_ALIGNED_BSS} not defined,
|
|
uninitialized global data will be output in the data section if
|
|
@option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be
|
|
used.
|
|
@end defmac
|
|
|
|
@defmac SBSS_SECTION_ASM_OP
|
|
If defined, a C expression whose value is a string, including spacing,
|
|
containing the assembler operation to identify the following data as
|
|
uninitialized, writable small data.
|
|
@end defmac
|
|
|
|
@defmac TLS_COMMON_ASM_OP
|
|
If defined, a C expression whose value is a string containing the
|
|
assembler operation to identify the following data as thread-local
|
|
common data. The default is @code{".tls_common"}.
|
|
@end defmac
|
|
|
|
@defmac TLS_SECTION_ASM_FLAG
|
|
If defined, a C expression whose value is a character constant
|
|
containing the flag used to mark a section as a TLS section. The
|
|
default is @code{'T'}.
|
|
@end defmac
|
|
|
|
@defmac INIT_SECTION_ASM_OP
|
|
If defined, a C expression whose value is a string, including spacing,
|
|
containing the assembler operation to identify the following data as
|
|
initialization code. If not defined, GCC will assume such a section does
|
|
not exist. This section has no corresponding @code{init_section}
|
|
variable; it is used entirely in runtime code.
|
|
@end defmac
|
|
|
|
@defmac FINI_SECTION_ASM_OP
|
|
If defined, a C expression whose value is a string, including spacing,
|
|
containing the assembler operation to identify the following data as
|
|
finalization code. If not defined, GCC will assume such a section does
|
|
not exist. This section has no corresponding @code{fini_section}
|
|
variable; it is used entirely in runtime code.
|
|
@end defmac
|
|
|
|
@defmac INIT_ARRAY_SECTION_ASM_OP
|
|
If defined, a C expression whose value is a string, including spacing,
|
|
containing the assembler operation to identify the following data as
|
|
part of the @code{.init_array} (or equivalent) section. If not
|
|
defined, GCC will assume such a section does not exist. Do not define
|
|
both this macro and @code{INIT_SECTION_ASM_OP}.
|
|
@end defmac
|
|
|
|
@defmac FINI_ARRAY_SECTION_ASM_OP
|
|
If defined, a C expression whose value is a string, including spacing,
|
|
containing the assembler operation to identify the following data as
|
|
part of the @code{.fini_array} (or equivalent) section. If not
|
|
defined, GCC will assume such a section does not exist. Do not define
|
|
both this macro and @code{FINI_SECTION_ASM_OP}.
|
|
@end defmac
|
|
|
|
@defmac MACH_DEP_SECTION_ASM_FLAG
|
|
If defined, a C expression whose value is a character constant
|
|
containing the flag used to mark a machine-dependent section. This
|
|
corresponds to the @code{SECTION_MACH_DEP} section flag.
|
|
@end defmac
|
|
|
|
@defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function})
|
|
If defined, an ASM statement that switches to a different section
|
|
via @var{section_op}, calls @var{function}, and switches back to
|
|
the text section. This is used in @file{crtstuff.c} if
|
|
@code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls
|
|
to initialization and finalization functions from the init and fini
|
|
sections. By default, this macro uses a simple function call. Some
|
|
ports need hand-crafted assembly code to avoid dependencies on
|
|
registers initialized in the function prologue or to ensure that
|
|
constant pools don't end up too far way in the text section.
|
|
@end defmac
|
|
|
|
@defmac TARGET_LIBGCC_SDATA_SECTION
|
|
If defined, a string which names the section into which small
|
|
variables defined in crtstuff and libgcc should go. This is useful
|
|
when the target has options for optimizing access to small data, and
|
|
you want the crtstuff and libgcc routines to be conservative in what
|
|
they expect of your application yet liberal in what your application
|
|
expects. For example, for targets with a @code{.sdata} section (like
|
|
MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't
|
|
require small data support from your application, but use this macro
|
|
to put small data into @code{.sdata} so that your application can
|
|
access these variables whether it uses small data or not.
|
|
@end defmac
|
|
|
|
@defmac FORCE_CODE_SECTION_ALIGN
|
|
If defined, an ASM statement that aligns a code section to some
|
|
arbitrary boundary. This is used to force all fragments of the
|
|
@code{.init} and @code{.fini} sections to have to same alignment
|
|
and thus prevent the linker from having to add any padding.
|
|
@end defmac
|
|
|
|
@defmac JUMP_TABLES_IN_TEXT_SECTION
|
|
Define this macro to be an expression with a nonzero value if jump
|
|
tables (for @code{tablejump} insns) should be output in the text
|
|
section, along with the assembler instructions. Otherwise, the
|
|
readonly data section is used.
|
|
|
|
This macro is irrelevant if there is no separate readonly data section.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_INIT_SECTIONS (void)
|
|
Define this hook if you need to do something special to set up the
|
|
@file{varasm.cc} sections, or if your target has some special sections
|
|
of its own that you need to create.
|
|
|
|
GCC calls this hook after processing the command line, but before writing
|
|
any assembly code, and before calling any of the section-returning hooks
|
|
described below.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_ASM_RELOC_RW_MASK (void)
|
|
Return a mask describing how relocations should be treated when
|
|
selecting sections. Bit 1 should be set if global relocations
|
|
should be placed in a read-write section; bit 0 should be set if
|
|
local relocations should be placed in a read-write section.
|
|
|
|
The default version of this function returns 3 when @option{-fpic}
|
|
is in effect, and 0 otherwise. The hook is typically redefined
|
|
when the target cannot support (some kinds of) dynamic relocations
|
|
in read-only sections even in executables.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ASM_GENERATE_PIC_ADDR_DIFF_VEC (void)
|
|
Return true to generate ADDR_DIF_VEC table
|
|
or false to generate ADDR_VEC table for jumps in case of -fPIC.
|
|
|
|
The default version of this function returns true if flag_pic
|
|
equals true and false otherwise
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align})
|
|
Return the section into which @var{exp} should be placed. You can
|
|
assume that @var{exp} is either a @code{VAR_DECL} node or a constant of
|
|
some sort. @var{reloc} indicates whether the initial value of @var{exp}
|
|
requires link-time relocations. Bit 0 is set when variable contains
|
|
local relocations only, while bit 1 is set for global relocations.
|
|
@var{align} is the constant alignment in bits.
|
|
|
|
The default version of this function takes care of putting read-only
|
|
variables in @code{readonly_data_section}.
|
|
|
|
See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}.
|
|
@end deftypefn
|
|
|
|
@defmac USE_SELECT_SECTION_FOR_FUNCTIONS
|
|
Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called
|
|
for @code{FUNCTION_DECL}s as well as for variables and constants.
|
|
|
|
In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the
|
|
function has been determined to be likely to be called, and nonzero if
|
|
it is unlikely to be called.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc})
|
|
Build up a unique section name, expressed as a @code{STRING_CST} node,
|
|
and assign it to @samp{DECL_SECTION_NAME (@var{decl})}.
|
|
As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether
|
|
the initial value of @var{exp} requires link-time relocations.
|
|
|
|
The default version of this function appends the symbol name to the
|
|
ELF section name that would normally be used for the symbol. For
|
|
example, the function @code{foo} would be placed in @code{.text.foo}.
|
|
Whatever the actual target object format, this is often good enough.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_RODATA_SECTION (tree @var{decl}, bool @var{relocatable})
|
|
Return the readonly data or reloc readonly data section associated with
|
|
@samp{DECL_SECTION_NAME (@var{decl})}. @var{relocatable} selects the latter
|
|
over the former.
|
|
The default version of this function selects @code{.gnu.linkonce.r.name} if
|
|
the function's section is @code{.gnu.linkonce.t.name}, @code{.rodata.name}
|
|
or @code{.data.rel.ro.name} if function is in @code{.text.name}, and
|
|
the normal readonly-data or reloc readonly data section otherwise.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_ASM_MERGEABLE_RODATA_PREFIX
|
|
Usually, the compiler uses the prefix @code{".rodata"} to construct
|
|
section names for mergeable constant data. Define this macro to override
|
|
the string if a different section name should be used.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} {section *} TARGET_ASM_TM_CLONE_TABLE_SECTION (void)
|
|
Return the section that should be used for transactional memory clone
|
|
tables.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_RTX_SECTION (machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align})
|
|
Return the section into which a constant @var{x}, of mode @var{mode},
|
|
should be placed. You can assume that @var{x} is some kind of
|
|
constant in RTL@. The argument @var{mode} is redundant except in the
|
|
case of a @code{const_int} rtx. @var{align} is the constant alignment
|
|
in bits.
|
|
|
|
The default version of this function takes care of putting symbolic
|
|
constants in @code{flag_pic} mode in @code{data_section} and everything
|
|
else in @code{readonly_data_section}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_MANGLE_DECL_ASSEMBLER_NAME (tree @var{decl}, tree @var{id})
|
|
Define this hook if you need to postprocess the assembler name generated
|
|
by target-independent code. The @var{id} provided to this hook will be
|
|
the computed name (e.g., the macro @code{DECL_NAME} of the @var{decl} in C,
|
|
or the mangled name of the @var{decl} in C++). The return value of the
|
|
hook is an @code{IDENTIFIER_NODE} for the appropriate mangled name on
|
|
your target system. The default implementation of this hook just
|
|
returns the @var{id} provided.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, rtx @var{rtl}, int @var{new_decl_p})
|
|
Define this hook if references to a symbol or a constant must be
|
|
treated differently depending on something about the variable or
|
|
function named by the symbol (such as what section it is in).
|
|
|
|
The hook is executed immediately after rtl has been created for
|
|
@var{decl}, which may be a variable or function declaration or
|
|
an entry in the constant pool. In either case, @var{rtl} is the
|
|
rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})}
|
|
in this hook; that field may not have been initialized yet.
|
|
|
|
In the case of a constant, it is safe to assume that the rtl is
|
|
a @code{mem} whose address is a @code{symbol_ref}. Most decls
|
|
will also have this form, but that is not guaranteed. Global
|
|
register variables, for instance, will have a @code{reg} for their
|
|
rtl. (Normally the right thing to do with such unusual rtl is
|
|
leave it alone.)
|
|
|
|
The @var{new_decl_p} argument will be true if this is the first time
|
|
that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will
|
|
be false for subsequent invocations, which will happen for duplicate
|
|
declarations. Whether or not anything must be done for the duplicate
|
|
declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}.
|
|
@var{new_decl_p} is always true when the hook is called for a constant.
|
|
|
|
@cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO}
|
|
The usual thing for this hook to do is to record flags in the
|
|
@code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}.
|
|
Historically, the name string was modified if it was necessary to
|
|
encode more than one bit of information, but this practice is now
|
|
discouraged; use @code{SYMBOL_REF_FLAGS}.
|
|
|
|
The default definition of this hook, @code{default_encode_section_info}
|
|
in @file{varasm.cc}, sets a number of commonly-useful bits in
|
|
@code{SYMBOL_REF_FLAGS}. Check whether the default does what you need
|
|
before overriding it.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_STRIP_NAME_ENCODING (const char *@var{name})
|
|
Decode @var{name} and return the real name part, sans
|
|
the characters that @code{TARGET_ENCODE_SECTION_INFO}
|
|
may have added.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (const_tree @var{exp})
|
|
Returns true if @var{exp} should be placed into a ``small data'' section.
|
|
The default version of this hook always returns false.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_HAVE_SRODATA_SECTION
|
|
Contains the value true if the target places read-only
|
|
``small data'' into a separate section. The default value is false.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} bool TARGET_PROFILE_BEFORE_PROLOGUE (void)
|
|
It returns true if target wants profile code emitted before prologue.
|
|
|
|
The default version of this hook use the target macro
|
|
@code{PROFILE_BEFORE_PROLOGUE}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (const_tree @var{exp})
|
|
Returns true if @var{exp} names an object for which name resolution
|
|
rules must resolve to the current ``module'' (dynamic shared library
|
|
or executable image).
|
|
|
|
The default version of this hook implements the name resolution rules
|
|
for ELF, which has a looser model of global name binding than other
|
|
currently supported object file formats.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_HAVE_TLS
|
|
Contains the value true if the target supports thread-local storage.
|
|
The default value is false.
|
|
@end deftypevr
|
|
|
|
|
|
@node PIC
|
|
@section Position Independent Code
|
|
@cindex position independent code
|
|
@cindex PIC
|
|
|
|
This section describes macros that help implement generation of position
|
|
independent code. Simply defining these macros is not enough to
|
|
generate valid PIC; you must also add support to the hook
|
|
@code{TARGET_LEGITIMATE_ADDRESS_P} and to the macro
|
|
@code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}. You
|
|
must modify the definition of @samp{movsi} to do something appropriate
|
|
when the source operand contains a symbolic address. You may also
|
|
need to alter the handling of switch statements so that they use
|
|
relative addresses.
|
|
@c i rearranged the order of the macros above to try to force one of
|
|
@c them to the next line, to eliminate an overfull hbox. --mew 10feb93
|
|
|
|
@defmac PIC_OFFSET_TABLE_REGNUM
|
|
The register number of the register used to address a table of static
|
|
data addresses in memory. In some cases this register is defined by a
|
|
processor's ``application binary interface'' (ABI)@. When this macro
|
|
is defined, RTL is generated for this register once, as with the stack
|
|
pointer and frame pointer registers. If this macro is not defined, it
|
|
is up to the machine-dependent files to allocate such a register (if
|
|
necessary). Note that this register must be fixed when in use (e.g.@:
|
|
when @code{flag_pic} is true).
|
|
@end defmac
|
|
|
|
@defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED
|
|
A C expression that is nonzero if the register defined by
|
|
@code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. If not defined,
|
|
the default is zero. Do not define
|
|
this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined.
|
|
@end defmac
|
|
|
|
@defmac LEGITIMATE_PIC_OPERAND_P (@var{x})
|
|
A C expression that is nonzero if @var{x} is a legitimate immediate
|
|
operand on the target machine when generating position independent code.
|
|
You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not
|
|
check this. You can also assume @var{flag_pic} is true, so you need not
|
|
check it either. You need not define this macro if all constants
|
|
(including @code{SYMBOL_REF}) can be immediate operands when generating
|
|
position independent code.
|
|
@end defmac
|
|
|
|
@node Assembler Format
|
|
@section Defining the Output Assembler Language
|
|
|
|
This section describes macros whose principal purpose is to describe how
|
|
to write instructions in assembler language---rather than what the
|
|
instructions do.
|
|
|
|
@menu
|
|
* File Framework:: Structural information for the assembler file.
|
|
* Data Output:: Output of constants (numbers, strings, addresses).
|
|
* Uninitialized Data:: Output of uninitialized variables.
|
|
* Label Output:: Output and generation of labels.
|
|
* Initialization:: General principles of initialization
|
|
and termination routines.
|
|
* Macros for Initialization::
|
|
Specific macros that control the handling of
|
|
initialization and termination routines.
|
|
* Instruction Output:: Output of actual instructions.
|
|
* Dispatch Tables:: Output of jump tables.
|
|
* Exception Region Output:: Output of exception region code.
|
|
* Alignment Output:: Pseudo ops for alignment and skipping data.
|
|
@end menu
|
|
|
|
@node File Framework
|
|
@subsection The Overall Framework of an Assembler File
|
|
@cindex assembler format
|
|
@cindex output of assembler code
|
|
|
|
@c prevent bad page break with this line
|
|
This describes the overall framework of an assembly file.
|
|
|
|
@findex default_file_start
|
|
@deftypefn {Target Hook} void TARGET_ASM_FILE_START (void)
|
|
Output to @code{asm_out_file} any text which the assembler expects to
|
|
find at the beginning of a file. The default behavior is controlled
|
|
by two flags, documented below. Unless your target's assembler is
|
|
quite unusual, if you override the default, you should call
|
|
@code{default_file_start} at some point in your target hook. This
|
|
lets other target files rely on these variables.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_ASM_FILE_START_APP_OFF
|
|
If this flag is true, the text of the macro @code{ASM_APP_OFF} will be
|
|
printed as the very first line in the assembly file, unless
|
|
@option{-fverbose-asm} is in effect. (If that macro has been defined
|
|
to the empty string, this variable has no effect.) With the normal
|
|
definition of @code{ASM_APP_OFF}, the effect is to notify the GNU
|
|
assembler that it need not bother stripping comments or extra
|
|
whitespace from its input. This allows it to work a bit faster.
|
|
|
|
The default is false. You should not set it to true unless you have
|
|
verified that your port does not generate any extra whitespace or
|
|
comments that will cause GAS to issue errors in NO_APP mode.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} bool TARGET_ASM_FILE_START_FILE_DIRECTIVE
|
|
If this flag is true, @code{output_file_directive} will be called
|
|
for the primary source file, immediately after printing
|
|
@code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect
|
|
this to be done. The default is false.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_FILE_END (void)
|
|
Output to @code{asm_out_file} any text which the assembler expects
|
|
to find at the end of a file. The default is to output nothing.
|
|
@end deftypefn
|
|
|
|
@deftypefun void file_end_indicate_exec_stack ()
|
|
Some systems use a common convention, the @samp{.note.GNU-stack}
|
|
special section, to indicate whether or not an object file relies on
|
|
the stack being executable. If your system uses this convention, you
|
|
should define @code{TARGET_ASM_FILE_END} to this function. If you
|
|
need to do other things in that hook, have your hook function call
|
|
this function.
|
|
@end deftypefun
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_LTO_START (void)
|
|
Output to @code{asm_out_file} any text which the assembler expects
|
|
to find at the start of an LTO section. The default is to output
|
|
nothing.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_LTO_END (void)
|
|
Output to @code{asm_out_file} any text which the assembler expects
|
|
to find at the end of an LTO section. The default is to output
|
|
nothing.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_CODE_END (void)
|
|
Output to @code{asm_out_file} any text which is needed before emitting
|
|
unwind info and debug info at the end of a file. Some targets emit
|
|
here PIC setup thunks that cannot be emitted at the end of file,
|
|
because they couldn't have unwind info then. The default is to output
|
|
nothing.
|
|
@end deftypefn
|
|
|
|
@defmac ASM_COMMENT_START
|
|
A C string constant describing how to begin a comment in the target
|
|
assembler language. The compiler assumes that the comment will end at
|
|
the end of the line.
|
|
@end defmac
|
|
|
|
@defmac ASM_APP_ON
|
|
A C string constant for text to be output before each @code{asm}
|
|
statement or group of consecutive ones. Normally this is
|
|
@code{"#APP"}, which is a comment that has no effect on most
|
|
assemblers but tells the GNU assembler that it must check the lines
|
|
that follow for all valid assembler constructs.
|
|
@end defmac
|
|
|
|
@defmac ASM_APP_OFF
|
|
A C string constant for text to be output after each @code{asm}
|
|
statement or group of consecutive ones. Normally this is
|
|
@code{"#NO_APP"}, which tells the GNU assembler to resume making the
|
|
time-saving assumptions that are valid for ordinary compiler output.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name})
|
|
A C statement to output COFF information or DWARF debugging information
|
|
which indicates that filename @var{name} is the current source file to
|
|
the stdio stream @var{stream}.
|
|
|
|
This macro need not be defined if the standard form of output
|
|
for the file format in use is appropriate.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_SOURCE_FILENAME (FILE *@var{file}, const char *@var{name})
|
|
Output DWARF debugging information which indicates that filename
|
|
@var{name} is the current source file to the stdio stream @var{file}.
|
|
|
|
This target hook need not be defined if the standard form of output
|
|
for the file format in use is appropriate.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_IDENT (const char *@var{name})
|
|
Output a string based on @var{name}, suitable for the @samp{#ident}
|
|
directive, or the equivalent directive or pragma in non-C-family languages.
|
|
If this hook is not defined, nothing is output for the @samp{#ident}
|
|
directive.
|
|
@end deftypefn
|
|
|
|
@defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string})
|
|
A C statement to output the string @var{string} to the stdio stream
|
|
@var{stream}. If you do not call the function @code{output_quoted_string}
|
|
in your config files, GCC will only call it to output filenames to
|
|
the assembler source. So you can use it to canonicalize the format
|
|
of the filename using this macro.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, tree @var{decl})
|
|
Output assembly directives to switch to section @var{name}. The section
|
|
should have attributes as specified by @var{flags}, which is a bit mask
|
|
of the @code{SECTION_*} flags defined in @file{output.h}. If @var{decl}
|
|
is non-NULL, it is the @code{VAR_DECL} or @code{FUNCTION_DECL} with which
|
|
this section is associated.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ASM_ELF_FLAGS_NUMERIC (unsigned int @var{flags}, unsigned int *@var{num})
|
|
This hook can be used to encode ELF section flags for which no letter
|
|
code has been defined in the assembler. It is called by
|
|
@code{default_asm_named_section} whenever the section flags need to be
|
|
emitted in the assembler output. If the hook returns true, then the
|
|
numerical value for ELF section flags should be calculated from
|
|
@var{flags} and saved in @var{*num}; the value is printed out instead of the
|
|
normal sequence of letter codes. If the hook is not defined, or if it
|
|
returns false, then @var{num} is ignored and the traditional letter sequence
|
|
is emitted.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_SECTION (tree @var{decl}, enum node_frequency @var{freq}, bool @var{startup}, bool @var{exit})
|
|
Return preferred text (sub)section for function @var{decl}.
|
|
Main purpose of this function is to separate cold, normal and hot
|
|
functions. @var{startup} is true when function is known to be used only
|
|
at startup (from static constructors or it is @code{main()}).
|
|
@var{exit} is true when function is known to be used only at exit
|
|
(from static destructors).
|
|
Return NULL if function should go to default text section.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_SWITCHED_TEXT_SECTIONS (FILE *@var{file}, tree @var{decl}, bool @var{new_is_cold})
|
|
Used by the target to emit any assembler directives or additional
|
|
labels needed when a function is partitioned between different
|
|
sections. Output should be written to @var{file}. The function
|
|
decl is available as @var{decl} and the new section is `cold' if
|
|
@var{new_is_cold} is @code{true}.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Common Target Hook} bool TARGET_HAVE_NAMED_SECTIONS
|
|
This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}.
|
|
It must not be modified by command-line option processing.
|
|
@end deftypevr
|
|
|
|
@anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}
|
|
@deftypevr {Target Hook} bool TARGET_HAVE_SWITCHABLE_BSS_SECTIONS
|
|
This flag is true if we can create zeroed data by switching to a BSS
|
|
section and then using @code{ASM_OUTPUT_SKIP} to allocate the space.
|
|
This is true on most ELF targets.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc})
|
|
Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION}
|
|
based on a variable or function decl, a section name, and whether or not the
|
|
declaration's initializer may contain runtime relocations. @var{decl} may be
|
|
null, in which case read-write data should be assumed.
|
|
|
|
The default version of this function handles choosing code vs data,
|
|
read-only vs read-write data, and @code{flag_pic}. You should only
|
|
need to override this if your target has special flags that might be
|
|
set via @code{__attribute__}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_RECORD_GCC_SWITCHES (const char *@var{})
|
|
Provides the target with the ability to record the gcc command line
|
|
switches provided as argument.
|
|
|
|
By default this hook is set to NULL, but an example implementation is
|
|
provided for ELF based targets. Called @var{elf_record_gcc_switches},
|
|
it records the switches as ASCII text inside a new, string mergeable
|
|
section in the assembler output file. The name of the new section is
|
|
provided by the @code{TARGET_ASM_RECORD_GCC_SWITCHES_SECTION} target
|
|
hook.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_ASM_RECORD_GCC_SWITCHES_SECTION
|
|
This is the name of the section that will be created by the example
|
|
ELF implementation of the @code{TARGET_ASM_RECORD_GCC_SWITCHES} target
|
|
hook.
|
|
@end deftypevr
|
|
|
|
@need 2000
|
|
@node Data Output
|
|
@subsection Output of Data
|
|
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_PSI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_PDI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_PTI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_PSI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_PDI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_PTI_OP
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP
|
|
These hooks specify assembly directives for creating certain kinds
|
|
of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a
|
|
byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an
|
|
aligned two-byte object, and so on. Any of the hooks may be
|
|
@code{NULL}, indicating that no suitable directive is available.
|
|
|
|
The compiler will print these strings at the start of a new line,
|
|
followed immediately by the object's initial value. In most cases,
|
|
the string should contain a tab, a pseudo-op, and then another tab.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p})
|
|
The @code{assemble_integer} function uses this hook to output an
|
|
integer object. @var{x} is the object's value, @var{size} is its size
|
|
in bytes and @var{aligned_p} indicates whether it is aligned. The
|
|
function should return @code{true} if it was able to output the
|
|
object. If it returns false, @code{assemble_integer} will try to
|
|
split the object into smaller parts.
|
|
|
|
The default implementation of this hook will use the
|
|
@code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false}
|
|
when the relevant string is @code{NULL}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_DECL_END (void)
|
|
Define this hook if the target assembler requires a special marker to
|
|
terminate an initialized variable declaration.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA (FILE *@var{file}, rtx @var{x})
|
|
A target hook to recognize @var{rtx} patterns that @code{output_addr_const}
|
|
can't deal with, and output assembly code to @var{file} corresponding to
|
|
the pattern @var{x}. This may be used to allow machine-dependent
|
|
@code{UNSPEC}s to appear within constants.
|
|
|
|
If target hook fails to recognize a pattern, it must return @code{false},
|
|
so that a standard error message is printed. If it prints an error message
|
|
itself, by calling, for example, @code{output_operand_lossage}, it may just
|
|
return @code{true}.
|
|
@end deftypefn
|
|
|
|
@defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len})
|
|
A C statement to output to the stdio stream @var{stream} an assembler
|
|
instruction to assemble a string constant containing the @var{len}
|
|
bytes at @var{ptr}. @var{ptr} will be a C expression of type
|
|
@code{char *} and @var{len} a C expression of type @code{int}.
|
|
|
|
If the assembler has a @code{.ascii} pseudo-op as found in the
|
|
Berkeley Unix assembler, do not define the macro
|
|
@code{ASM_OUTPUT_ASCII}.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n})
|
|
A C statement to output word @var{n} of a function descriptor for
|
|
@var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS}
|
|
is defined, and is otherwise unused.
|
|
@end defmac
|
|
|
|
@defmac CONSTANT_POOL_BEFORE_FUNCTION
|
|
You may define this macro as a C expression. You should define the
|
|
expression to have a nonzero value if GCC should output the constant
|
|
pool for a function before the code for the function, or a zero value if
|
|
GCC should output the constant pool after the function. If you do
|
|
not define this macro, the usual case, GCC will output the constant
|
|
pool before the function.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size})
|
|
A C statement to output assembler commands to define the start of the
|
|
constant pool for a function. @var{funname} is a string giving
|
|
the name of the function. Should the return type of the function
|
|
be required, it can be obtained via @var{fundecl}. @var{size}
|
|
is the size, in bytes, of the constant pool that will be written
|
|
immediately after this call.
|
|
|
|
If no constant-pool prefix is required, the usual case, this macro need
|
|
not be defined.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto})
|
|
A C statement (with or without semicolon) to output a constant in the
|
|
constant pool, if it needs special treatment. (This macro need not do
|
|
anything for RTL expressions that can be output normally.)
|
|
|
|
The argument @var{file} is the standard I/O stream to output the
|
|
assembler code on. @var{x} is the RTL expression for the constant to
|
|
output, and @var{mode} is the machine mode (in case @var{x} is a
|
|
@samp{const_int}). @var{align} is the required alignment for the value
|
|
@var{x}; you should output an assembler directive to force this much
|
|
alignment.
|
|
|
|
The argument @var{labelno} is a number to use in an internal label for
|
|
the address of this pool entry. The definition of this macro is
|
|
responsible for outputting the label definition at the proper place.
|
|
Here is how to do this:
|
|
|
|
@smallexample
|
|
@code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno});
|
|
@end smallexample
|
|
|
|
When you output a pool entry specially, you should end with a
|
|
@code{goto} to the label @var{jumpto}. This will prevent the same pool
|
|
entry from being output a second time in the usual manner.
|
|
|
|
You need not define this macro if it would do nothing.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size})
|
|
A C statement to output assembler commands to at the end of the constant
|
|
pool for a function. @var{funname} is a string giving the name of the
|
|
function. Should the return type of the function be required, you can
|
|
obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the
|
|
constant pool that GCC wrote immediately before this call.
|
|
|
|
If no constant-pool epilogue is required, the usual case, you need not
|
|
define this macro.
|
|
@end defmac
|
|
|
|
@defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}, @var{STR})
|
|
Define this macro as a C expression which is nonzero if @var{C} is
|
|
used as a logical line separator by the assembler. @var{STR} points
|
|
to the position in the string where @var{C} was found; this can be used if
|
|
a line separator uses multiple characters.
|
|
|
|
If you do not define this macro, the default is that only
|
|
the character @samp{;} is treated as a logical line separator.
|
|
@end defmac
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN
|
|
@deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN
|
|
These target hooks are C string constants, describing the syntax in the
|
|
assembler for grouping arithmetic expressions. If not overridden, they
|
|
default to normal parentheses, which is correct for most assemblers.
|
|
@end deftypevr
|
|
|
|
These macros are provided by @file{real.h} for writing the definitions
|
|
of @code{ASM_OUTPUT_DOUBLE} and the like:
|
|
|
|
@defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l})
|
|
@defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l})
|
|
@defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l})
|
|
@defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l})
|
|
@defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l})
|
|
@defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l})
|
|
These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the
|
|
target's floating point representation, and store its bit pattern in
|
|
the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and
|
|
@code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a
|
|
simple @code{long int}. For the others, it should be an array of
|
|
@code{long int}. The number of elements in this array is determined
|
|
by the size of the desired target floating point data type: 32 bits of
|
|
it go in each @code{long int} array element. Each array element holds
|
|
32 bits of the result, even if @code{long int} is wider than 32 bits
|
|
on the host machine.
|
|
|
|
The array element values are designed so that you can print them out
|
|
using @code{fprintf} in the order they should appear in the target
|
|
machine's memory.
|
|
@end defmac
|
|
|
|
@node Uninitialized Data
|
|
@subsection Output of Uninitialized Variables
|
|
|
|
Each of the macros in this section is used to do the whole job of
|
|
outputting a single uninitialized variable.
|
|
|
|
@defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} the assembler definition of a common-label named
|
|
@var{name} whose size is @var{size} bytes. The variable @var{rounded}
|
|
is the size rounded up to whatever alignment the caller wants. It is
|
|
possible that @var{size} may be zero, for instance if a struct with no
|
|
other member than a zero-length array is defined. In this case, the
|
|
backend must output a symbol definition that allocates at least one
|
|
byte, both so that the address of the resulting object does not compare
|
|
equal to any other, and because some object formats cannot even express
|
|
the concept of a zero-sized common symbol, as that is how they represent
|
|
an ordinary undefined external.
|
|
|
|
Use the expression @code{assemble_name (@var{stream}, @var{name})} to
|
|
output the name itself; before and after that, output the additional
|
|
assembler syntax for defining the name, and a newline.
|
|
|
|
This macro controls how the assembler definitions of uninitialized
|
|
common global variables are output.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment})
|
|
Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a
|
|
separate, explicit argument. If you define this macro, it is used in
|
|
place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in
|
|
handling the required alignment of the variable. The alignment is specified
|
|
as the number of bits.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
|
|
Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the
|
|
variable to be output, if there is one, or @code{NULL_TREE} if there
|
|
is no corresponding variable. If you define this macro, GCC will use it
|
|
in place of both @code{ASM_OUTPUT_COMMON} and
|
|
@code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see
|
|
the variable's decl in order to chose what to output.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} the assembler definition of uninitialized global @var{decl} named
|
|
@var{name} whose size is @var{size} bytes. The variable @var{alignment}
|
|
is the alignment specified as the number of bits.
|
|
|
|
Try to use function @code{asm_output_aligned_bss} defined in file
|
|
@file{varasm.cc} when defining this macro. If unable, use the expression
|
|
@code{assemble_name (@var{stream}, @var{name})} to output the name itself;
|
|
before and after that, output the additional assembler syntax for defining
|
|
the name, and a newline.
|
|
|
|
There are two ways of handling global BSS@. One is to define this macro.
|
|
The other is to have @code{TARGET_ASM_SELECT_SECTION} return a
|
|
switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}).
|
|
You do not need to do both.
|
|
|
|
Some languages do not have @code{common} data, and require a
|
|
non-common form of global BSS in order to handle uninitialized globals
|
|
efficiently. C++ is one example of this. However, if the target does
|
|
not support global BSS, the front end may choose to make globals
|
|
common in order to save space in the object file.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} the assembler definition of a local-common-label named
|
|
@var{name} whose size is @var{size} bytes. The variable @var{rounded}
|
|
is the size rounded up to whatever alignment the caller wants.
|
|
|
|
Use the expression @code{assemble_name (@var{stream}, @var{name})} to
|
|
output the name itself; before and after that, output the additional
|
|
assembler syntax for defining the name, and a newline.
|
|
|
|
This macro controls how the assembler definitions of uninitialized
|
|
static variables are output.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment})
|
|
Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a
|
|
separate, explicit argument. If you define this macro, it is used in
|
|
place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in
|
|
handling the required alignment of the variable. The alignment is specified
|
|
as the number of bits.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment})
|
|
Like @code{ASM_OUTPUT_ALIGNED_LOCAL} except that @var{decl} of the
|
|
variable to be output, if there is one, or @code{NULL_TREE} if there
|
|
is no corresponding variable. If you define this macro, GCC will use it
|
|
in place of both @code{ASM_OUTPUT_LOCAL} and
|
|
@code{ASM_OUTPUT_ALIGNED_LOCAL}. Define this macro when you need to see
|
|
the variable's decl in order to chose what to output.
|
|
@end defmac
|
|
|
|
@node Label Output
|
|
@subsection Output and Generation of Labels
|
|
|
|
@c prevent bad page break with this line
|
|
This is about outputting labels.
|
|
|
|
@findex assemble_name
|
|
@defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} the assembler definition of a label named @var{name}.
|
|
Use the expression @code{assemble_name (@var{stream}, @var{name})} to
|
|
output the name itself; before and after that, output the additional
|
|
assembler syntax for defining the name, and a newline. A default
|
|
definition of this macro is provided which is correct for most systems.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_FUNCTION_LABEL (@var{stream}, @var{name}, @var{decl})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} the assembler definition of a label named @var{name} of
|
|
a function.
|
|
Use the expression @code{assemble_name (@var{stream}, @var{name})} to
|
|
output the name itself; before and after that, output the additional
|
|
assembler syntax for defining the name, and a newline. A default
|
|
definition of this macro is provided which is correct for most systems.
|
|
|
|
If this macro is not defined, then the function name is defined in the
|
|
usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
|
|
@end defmac
|
|
|
|
@findex assemble_name_raw
|
|
@defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name})
|
|
Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known
|
|
to refer to a compiler-generated label. The default definition uses
|
|
@code{assemble_name_raw}, which is like @code{assemble_name} except
|
|
that it is more efficient.
|
|
@end defmac
|
|
|
|
@defmac SIZE_ASM_OP
|
|
A C string containing the appropriate assembler directive to specify the
|
|
size of a symbol, without any arguments. On systems that use ELF, the
|
|
default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other
|
|
systems, the default is not to define this macro.
|
|
|
|
Define this macro only if it is correct to use the default definitions
|
|
of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE}
|
|
for your system. If you need your own custom definitions of those
|
|
macros, or if you do not need explicit symbol sizes at all, do not
|
|
define this macro.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} a directive telling the assembler that the size of the
|
|
symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}.
|
|
If you define @code{SIZE_ASM_OP}, a default definition of this macro is
|
|
provided.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} a directive telling the assembler to calculate the size of
|
|
the symbol @var{name} by subtracting its address from the current
|
|
address.
|
|
|
|
If you define @code{SIZE_ASM_OP}, a default definition of this macro is
|
|
provided. The default assumes that the assembler recognizes a special
|
|
@samp{.} symbol as referring to the current address, and can calculate
|
|
the difference between this and another symbol. If your assembler does
|
|
not recognize @samp{.} or cannot do calculations with it, you will need
|
|
to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique.
|
|
@end defmac
|
|
|
|
@defmac NO_DOLLAR_IN_LABEL
|
|
Define this macro if the assembler does not accept the character
|
|
@samp{$} in label names. By default constructors and destructors in
|
|
G++ have @samp{$} in the identifiers. If this macro is defined,
|
|
@samp{.} is used instead.
|
|
@end defmac
|
|
|
|
@defmac NO_DOT_IN_LABEL
|
|
Define this macro if the assembler does not accept the character
|
|
@samp{.} in label names. By default constructors and destructors in G++
|
|
have names that use @samp{.}. If this macro is defined, these names
|
|
are rewritten to avoid @samp{.}.
|
|
@end defmac
|
|
|
|
@defmac TYPE_ASM_OP
|
|
A C string containing the appropriate assembler directive to specify the
|
|
type of a symbol, without any arguments. On systems that use ELF, the
|
|
default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other
|
|
systems, the default is not to define this macro.
|
|
|
|
Define this macro only if it is correct to use the default definition of
|
|
@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
|
|
custom definition of this macro, or if you do not need explicit symbol
|
|
types at all, do not define this macro.
|
|
@end defmac
|
|
|
|
@defmac TYPE_OPERAND_FMT
|
|
A C string which specifies (using @code{printf} syntax) the format of
|
|
the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the
|
|
default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems,
|
|
the default is not to define this macro.
|
|
|
|
Define this macro only if it is correct to use the default definition of
|
|
@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own
|
|
custom definition of this macro, or if you do not need explicit symbol
|
|
types at all, do not define this macro.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} a directive telling the assembler that the type of the
|
|
symbol @var{name} is @var{type}. @var{type} is a C string; currently,
|
|
that string is always either @samp{"function"} or @samp{"object"}, but
|
|
you should not count on this.
|
|
|
|
If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default
|
|
definition of this macro is provided.
|
|
@end defmac
|
|
|
|
@defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} any text necessary for declaring the name @var{name} of a
|
|
function which is being defined. This macro is responsible for
|
|
outputting the label definition (perhaps using
|
|
@code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the
|
|
@code{FUNCTION_DECL} tree node representing the function.
|
|
|
|
If this macro is not defined, then the function name is defined in the
|
|
usual manner as a label (by means of @code{ASM_OUTPUT_FUNCTION_LABEL}).
|
|
|
|
You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
|
|
of this macro.
|
|
@end defmac
|
|
|
|
@defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} any text necessary for declaring the size of a function
|
|
which is being defined. The argument @var{name} is the name of the
|
|
function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node
|
|
representing the function.
|
|
|
|
If this macro is not defined, then the function size is not defined.
|
|
|
|
You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
|
|
of this macro.
|
|
@end defmac
|
|
|
|
@defmac ASM_DECLARE_COLD_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} any text necessary for declaring the name @var{name} of a
|
|
cold function partition which is being defined. This macro is responsible
|
|
for outputting the label definition (perhaps using
|
|
@code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the
|
|
@code{FUNCTION_DECL} tree node representing the function.
|
|
|
|
If this macro is not defined, then the cold partition name is defined in the
|
|
usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
|
|
|
|
You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition
|
|
of this macro.
|
|
@end defmac
|
|
|
|
@defmac ASM_DECLARE_COLD_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} any text necessary for declaring the size of a cold function
|
|
partition which is being defined. The argument @var{name} is the name of the
|
|
cold partition of the function. The argument @var{decl} is the
|
|
@code{FUNCTION_DECL} tree node representing the function.
|
|
|
|
If this macro is not defined, then the partition size is not defined.
|
|
|
|
You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition
|
|
of this macro.
|
|
@end defmac
|
|
|
|
@defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} any text necessary for declaring the name @var{name} of an
|
|
initialized variable which is being defined. This macro must output the
|
|
label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument
|
|
@var{decl} is the @code{VAR_DECL} tree node representing the variable.
|
|
|
|
If this macro is not defined, then the variable name is defined in the
|
|
usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}).
|
|
|
|
You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or
|
|
@code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_DECLARE_CONSTANT_NAME (FILE *@var{file}, const char *@var{name}, const_tree @var{expr}, HOST_WIDE_INT @var{size})
|
|
A target hook to output to the stdio stream @var{file} any text necessary
|
|
for declaring the name @var{name} of a constant which is being defined. This
|
|
target hook is responsible for outputting the label definition (perhaps using
|
|
@code{assemble_label}). The argument @var{exp} is the value of the constant,
|
|
and @var{size} is the size of the constant in bytes. The @var{name}
|
|
will be an internal label.
|
|
|
|
The default version of this target hook, define the @var{name} in the
|
|
usual manner as a label (by means of @code{assemble_label}).
|
|
|
|
You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in this target hook.
|
|
@end deftypefn
|
|
|
|
@defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} any text necessary for claiming a register @var{regno}
|
|
for a global variable @var{decl} with name @var{name}.
|
|
|
|
If you don't define this macro, that is equivalent to defining it to do
|
|
nothing.
|
|
@end defmac
|
|
|
|
@defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend})
|
|
A C statement (sans semicolon) to finish up declaring a variable name
|
|
once the compiler has processed its initializer fully and thus has had a
|
|
chance to determine the size of an array when controlled by an
|
|
initializer. This is used on systems where it's necessary to declare
|
|
something about the size of the object.
|
|
|
|
If you don't define this macro, that is equivalent to defining it to do
|
|
nothing.
|
|
|
|
You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or
|
|
@code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name})
|
|
This target hook is a function to output to the stdio stream
|
|
@var{stream} some commands that will make the label @var{name} global;
|
|
that is, available for reference from other files.
|
|
|
|
The default implementation relies on a proper definition of
|
|
@code{GLOBAL_ASM_OP}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_DECL_NAME (FILE *@var{stream}, tree @var{decl})
|
|
This target hook is a function to output to the stdio stream
|
|
@var{stream} some commands that will make the name associated with @var{decl}
|
|
global; that is, available for reference from other files.
|
|
|
|
The default implementation uses the TARGET_ASM_GLOBALIZE_LABEL target hook.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_UNDEFINED_DECL (FILE *@var{stream}, const char *@var{name}, const_tree @var{decl})
|
|
This target hook is a function to output to the stdio stream
|
|
@var{stream} some commands that will declare the name associated with
|
|
@var{decl} which is not defined in the current translation unit. Most
|
|
assemblers do not require anything to be output in this case.
|
|
@end deftypefn
|
|
|
|
@defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} some commands that will make the label @var{name} weak;
|
|
that is, available for reference from other files but only used if
|
|
no other definition is available. Use the expression
|
|
@code{assemble_name (@var{stream}, @var{name})} to output the name
|
|
itself; before and after that, output the additional assembler syntax
|
|
for making that name weak, and a newline.
|
|
|
|
If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not
|
|
support weak symbols and you should not define the @code{SUPPORTS_WEAK}
|
|
macro.
|
|
@end defmac
|
|
|
|
@defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value})
|
|
Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and
|
|
@code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function
|
|
or variable decl. If @var{value} is not @code{NULL}, this C statement
|
|
should output to the stdio stream @var{stream} assembler code which
|
|
defines (equates) the weak symbol @var{name} to have the value
|
|
@var{value}. If @var{value} is @code{NULL}, it should output commands
|
|
to make @var{name} weak.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value})
|
|
Outputs a directive that enables @var{name} to be used to refer to
|
|
symbol @var{value} with weak-symbol semantics. @code{decl} is the
|
|
declaration of @code{name}.
|
|
@end defmac
|
|
|
|
@defmac SUPPORTS_WEAK
|
|
A preprocessor constant expression which evaluates to true if the target
|
|
supports weak symbols.
|
|
|
|
If you don't define this macro, @file{defaults.h} provides a default
|
|
definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL}
|
|
is defined, the default definition is @samp{1}; otherwise, it is @samp{0}.
|
|
@end defmac
|
|
|
|
@defmac TARGET_SUPPORTS_WEAK
|
|
A C expression which evaluates to true if the target supports weak symbols.
|
|
|
|
If you don't define this macro, @file{defaults.h} provides a default
|
|
definition. The default definition is @samp{(SUPPORTS_WEAK)}. Define
|
|
this macro if you want to control weak symbol support with a compiler
|
|
flag such as @option{-melf}.
|
|
@end defmac
|
|
|
|
@defmac MAKE_DECL_ONE_ONLY (@var{decl})
|
|
A C statement (sans semicolon) to mark @var{decl} to be emitted as a
|
|
public symbol such that extra copies in multiple translation units will
|
|
be discarded by the linker. Define this macro if your object file
|
|
format provides support for this concept, such as the @samp{COMDAT}
|
|
section flags in the Microsoft Windows PE/COFF format, and this support
|
|
requires changes to @var{decl}, such as putting it in a separate section.
|
|
@end defmac
|
|
|
|
@defmac SUPPORTS_ONE_ONLY
|
|
A C expression which evaluates to true if the target supports one-only
|
|
semantics.
|
|
|
|
If you don't define this macro, @file{varasm.cc} provides a default
|
|
definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default
|
|
definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if
|
|
you want to control one-only symbol support with a compiler flag, or if
|
|
setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to
|
|
be emitted as one-only.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, int @var{visibility})
|
|
This target hook is a function to output to @var{asm_out_file} some
|
|
commands that will make the symbol(s) associated with @var{decl} have
|
|
hidden, protected or internal visibility as specified by @var{visibility}.
|
|
@end deftypefn
|
|
|
|
@defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC
|
|
A C expression that evaluates to true if the target's linker expects
|
|
that weak symbols do not appear in a static archive's table of contents.
|
|
The default is @code{0}.
|
|
|
|
Leaving weak symbols out of an archive's table of contents means that,
|
|
if a symbol will only have a definition in one translation unit and
|
|
will have undefined references from other translation units, that
|
|
symbol should not be weak. Defining this macro to be nonzero will
|
|
thus have the effect that certain symbols that would normally be weak
|
|
(explicit template instantiations, and vtables for polymorphic classes
|
|
with noninline key methods) will instead be nonweak.
|
|
|
|
The C++ ABI requires this macro to be zero. Define this macro for
|
|
targets where full C++ ABI compliance is impossible and where linker
|
|
restrictions require weak symbols to be left out of a static archive's
|
|
table of contents.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} any text necessary for declaring the name of an external
|
|
symbol named @var{name} which is referenced in this compilation but
|
|
not defined. The value of @var{decl} is the tree node for the
|
|
declaration.
|
|
|
|
This macro need not be defined if it does not need to output anything.
|
|
The GNU assembler and most Unix assemblers don't require anything.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_EXTERNAL_LIBCALL (rtx @var{symref})
|
|
This target hook is a function to output to @var{asm_out_file} an assembler
|
|
pseudo-op to declare a library function name external. The name of the
|
|
library function is given by @var{symref}, which is a @code{symbol_ref}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_MARK_DECL_PRESERVED (const char *@var{symbol})
|
|
This target hook is a function to output to @var{asm_out_file} an assembler
|
|
directive to annotate @var{symbol} as used. The Darwin target uses the
|
|
.no_dead_code_strip directive.
|
|
@end deftypefn
|
|
|
|
@defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name})
|
|
A C statement (sans semicolon) to output to the stdio stream
|
|
@var{stream} a reference in assembler syntax to a label named
|
|
@var{name}. This should add @samp{_} to the front of the name, if that
|
|
is customary on your operating system, as it is in most Berkeley Unix
|
|
systems. This macro is used in @code{assemble_name}.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} tree TARGET_MANGLE_ASSEMBLER_NAME (const char *@var{name})
|
|
Given a symbol @var{name}, perform same mangling as @code{varasm.cc}'s
|
|
@code{assemble_name}, but in memory rather than to a file stream, returning
|
|
result as an @code{IDENTIFIER_NODE}. Required for correct LTO symtabs. The
|
|
default implementation calls the @code{TARGET_STRIP_NAME_ENCODING} hook and
|
|
then prepends the @code{USER_LABEL_PREFIX}, if any.
|
|
@end deftypefn
|
|
|
|
@defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym})
|
|
A C statement (sans semicolon) to output a reference to
|
|
@code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name}
|
|
will be used to output the name of the symbol. This macro may be used
|
|
to modify the way a symbol is referenced depending on information
|
|
encoded by @code{TARGET_ENCODE_SECTION_INFO}.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf})
|
|
A C statement (sans semicolon) to output a reference to @var{buf}, the
|
|
result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined,
|
|
@code{assemble_name} will be used to output the name of the symbol.
|
|
This macro is not used by @code{output_asm_label}, or the @code{%l}
|
|
specifier that calls it; the intention is that this macro should be set
|
|
when it is necessary to output a label differently when its address is
|
|
being taken.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_INTERNAL_LABEL (FILE *@var{stream}, const char *@var{prefix}, unsigned long @var{labelno})
|
|
A function to output to the stdio stream @var{stream} a label whose
|
|
name is made from the string @var{prefix} and the number @var{labelno}.
|
|
|
|
It is absolutely essential that these labels be distinct from the labels
|
|
used for user-level functions and variables. Otherwise, certain programs
|
|
will have name conflicts with internal labels.
|
|
|
|
It is desirable to exclude internal labels from the symbol table of the
|
|
object file. Most assemblers have a naming convention for labels that
|
|
should be excluded; on many systems, the letter @samp{L} at the
|
|
beginning of a label has this effect. You should find out what
|
|
convention your system uses, and follow it.
|
|
|
|
The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}.
|
|
@end deftypefn
|
|
|
|
@defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num})
|
|
A C statement to output to the stdio stream @var{stream} a debug info
|
|
label whose name is made from the string @var{prefix} and the number
|
|
@var{num}. This is useful for VLIW targets, where debug info labels
|
|
may need to be treated differently than branch target labels. On some
|
|
systems, branch target labels must be at the beginning of instruction
|
|
bundles, but debug info labels can occur in the middle of instruction
|
|
bundles.
|
|
|
|
If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be
|
|
used.
|
|
@end defmac
|
|
|
|
@defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num})
|
|
A C statement to store into the string @var{string} a label whose name
|
|
is made from the string @var{prefix} and the number @var{num}.
|
|
|
|
This string, when output subsequently by @code{assemble_name}, should
|
|
produce the output that @code{(*targetm.asm_out.internal_label)} would produce
|
|
with the same @var{prefix} and @var{num}.
|
|
|
|
If the string begins with @samp{*}, then @code{assemble_name} will
|
|
output the rest of the string unchanged. It is often convenient for
|
|
@code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the
|
|
string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets
|
|
to output the string, and may change it. (Of course,
|
|
@code{ASM_OUTPUT_LABELREF} is also part of your machine description, so
|
|
you should know what it does on your machine.)
|
|
@end defmac
|
|
|
|
@defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number})
|
|
A C expression to assign to @var{outvar} (which is a variable of type
|
|
@code{char *}) a newly allocated string made from the string
|
|
@var{name} and the number @var{number}, with some suitable punctuation
|
|
added. Use @code{alloca} to get space for the string.
|
|
|
|
The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to
|
|
produce an assembler label for an internal static variable whose name is
|
|
@var{name}. Therefore, the string must be such as to result in valid
|
|
assembler code. The argument @var{number} is different each time this
|
|
macro is executed; it prevents conflicts between similarly-named
|
|
internal static variables in different scopes.
|
|
|
|
Ideally this string should not be a valid C identifier, to prevent any
|
|
conflict with the user's own symbols. Most assemblers allow periods
|
|
or percent signs in assembler symbols; putting at least one of these
|
|
between the name and the number will suffice.
|
|
|
|
If this macro is not defined, a default definition will be provided
|
|
which is correct for most systems.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value})
|
|
A C statement to output to the stdio stream @var{stream} assembler code
|
|
which defines (equates) the symbol @var{name} to have the value @var{value}.
|
|
|
|
@findex SET_ASM_OP
|
|
If @code{SET_ASM_OP} is defined, a default definition is provided which is
|
|
correct for most systems.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value})
|
|
A C statement to output to the stdio stream @var{stream} assembler code
|
|
which defines (equates) the symbol whose tree node is @var{decl_of_name}
|
|
to have the value of the tree node @var{decl_of_value}. This macro will
|
|
be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if
|
|
the tree nodes are available.
|
|
|
|
@findex SET_ASM_OP
|
|
If @code{SET_ASM_OP} is defined, a default definition is provided which is
|
|
correct for most systems.
|
|
@end defmac
|
|
|
|
@defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value})
|
|
A C statement that evaluates to true if the assembler code which defines
|
|
(equates) the symbol whose tree node is @var{decl_of_name} to have the value
|
|
of the tree node @var{decl_of_value} should be emitted near the end of the
|
|
current compilation unit. The default is to not defer output of defines.
|
|
This macro affects defines output by @samp{ASM_OUTPUT_DEF} and
|
|
@samp{ASM_OUTPUT_DEF_FROM_DECLS}.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value})
|
|
A C statement to output to the stdio stream @var{stream} assembler code
|
|
which defines (equates) the weak symbol @var{name} to have the value
|
|
@var{value}. If @var{value} is @code{NULL}, it defines @var{name} as
|
|
an undefined weak symbol.
|
|
|
|
Define this macro if the target only supports weak aliases; define
|
|
@code{ASM_OUTPUT_DEF} instead if possible.
|
|
@end defmac
|
|
|
|
@defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name})
|
|
Define this macro to override the default assembler names used for
|
|
Objective-C methods.
|
|
|
|
The default name is a unique method number followed by the name of the
|
|
class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of
|
|
the category is also included in the assembler name (e.g.@:
|
|
@samp{_1_Foo_Bar}).
|
|
|
|
These names are safe on most systems, but make debugging difficult since
|
|
the method's selector is not present in the name. Therefore, particular
|
|
systems define other ways of computing names.
|
|
|
|
@var{buf} is an expression of type @code{char *} which gives you a
|
|
buffer in which to store the name; its length is as long as
|
|
@var{class_name}, @var{cat_name} and @var{sel_name} put together, plus
|
|
50 characters extra.
|
|
|
|
The argument @var{is_inst} specifies whether the method is an instance
|
|
method or a class method; @var{class_name} is the name of the class;
|
|
@var{cat_name} is the name of the category (or @code{NULL} if the method is not
|
|
in a category); and @var{sel_name} is the name of the selector.
|
|
|
|
On systems where the assembler can handle quoted names, you can use this
|
|
macro to provide more human-readable names.
|
|
@end defmac
|
|
|
|
@node Initialization
|
|
@subsection How Initialization Functions Are Handled
|
|
@cindex initialization routines
|
|
@cindex termination routines
|
|
@cindex constructors, output of
|
|
@cindex destructors, output of
|
|
|
|
The compiled code for certain languages includes @dfn{constructors}
|
|
(also called @dfn{initialization routines})---functions to initialize
|
|
data in the program when the program is started. These functions need
|
|
to be called before the program is ``started''---that is to say, before
|
|
@code{main} is called.
|
|
|
|
Compiling some languages generates @dfn{destructors} (also called
|
|
@dfn{termination routines}) that should be called when the program
|
|
terminates.
|
|
|
|
To make the initialization and termination functions work, the compiler
|
|
must output something in the assembler code to cause those functions to
|
|
be called at the appropriate time. When you port the compiler to a new
|
|
system, you need to specify how to do this.
|
|
|
|
There are two major ways that GCC currently supports the execution of
|
|
initialization and termination functions. Each way has two variants.
|
|
Much of the structure is common to all four variations.
|
|
|
|
@findex __CTOR_LIST__
|
|
@findex __DTOR_LIST__
|
|
The linker must build two lists of these functions---a list of
|
|
initialization functions, called @code{__CTOR_LIST__}, and a list of
|
|
termination functions, called @code{__DTOR_LIST__}.
|
|
|
|
Each list always begins with an ignored function pointer (which may hold
|
|
0, @minus{}1, or a count of the function pointers after it, depending on
|
|
the environment). This is followed by a series of zero or more function
|
|
pointers to constructors (or destructors), followed by a function
|
|
pointer containing zero.
|
|
|
|
Depending on the operating system and its executable file format, either
|
|
@file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup
|
|
time and exit time. Constructors are called in reverse order of the
|
|
list; destructors in forward order.
|
|
|
|
The best way to handle static constructors works only for object file
|
|
formats which provide arbitrarily-named sections. A section is set
|
|
aside for a list of constructors, and another for a list of destructors.
|
|
Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each
|
|
object file that defines an initialization function also puts a word in
|
|
the constructor section to point to that function. The linker
|
|
accumulates all these words into one contiguous @samp{.ctors} section.
|
|
Termination functions are handled similarly.
|
|
|
|
This method will be chosen as the default by @file{target-def.h} if
|
|
@code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not
|
|
support arbitrary sections, but does support special designated
|
|
constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP}
|
|
and @code{DTORS_SECTION_ASM_OP} to achieve the same effect.
|
|
|
|
When arbitrary sections are available, there are two variants, depending
|
|
upon how the code in @file{crtstuff.c} is called. On systems that
|
|
support a @dfn{.init} section which is executed at program startup,
|
|
parts of @file{crtstuff.c} are compiled into that section. The
|
|
program is linked by the @command{gcc} driver like this:
|
|
|
|
@smallexample
|
|
ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o
|
|
@end smallexample
|
|
|
|
The prologue of a function (@code{__init}) appears in the @code{.init}
|
|
section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise
|
|
for the function @code{__fini} in the @dfn{.fini} section. Normally these
|
|
files are provided by the operating system or by the GNU C library, but
|
|
are provided by GCC for a few targets.
|
|
|
|
The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets)
|
|
compiled from @file{crtstuff.c}. They contain, among other things, code
|
|
fragments within the @code{.init} and @code{.fini} sections that branch
|
|
to routines in the @code{.text} section. The linker will pull all parts
|
|
of a section together, which results in a complete @code{__init} function
|
|
that invokes the routines we need at startup.
|
|
|
|
To use this variant, you must define the @code{INIT_SECTION_ASM_OP}
|
|
macro properly.
|
|
|
|
If no init section is available, when GCC compiles any function called
|
|
@code{main} (or more accurately, any function designated as a program
|
|
entry point by the language front end calling @code{expand_main_function}),
|
|
it inserts a procedure call to @code{__main} as the first executable code
|
|
after the function prologue. The @code{__main} function is defined
|
|
in @file{libgcc2.c} and runs the global constructors.
|
|
|
|
In file formats that don't support arbitrary sections, there are again
|
|
two variants. In the simplest variant, the GNU linker (GNU @code{ld})
|
|
and an `a.out' format must be used. In this case,
|
|
@code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs}
|
|
entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__},
|
|
and with the address of the void function containing the initialization
|
|
code as its value. The GNU linker recognizes this as a request to add
|
|
the value to a @dfn{set}; the values are accumulated, and are eventually
|
|
placed in the executable as a vector in the format described above, with
|
|
a leading (ignored) count and a trailing zero element.
|
|
@code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init
|
|
section is available, the absence of @code{INIT_SECTION_ASM_OP} causes
|
|
the compilation of @code{main} to call @code{__main} as above, starting
|
|
the initialization process.
|
|
|
|
The last variant uses neither arbitrary sections nor the GNU linker.
|
|
This is preferable when you want to do dynamic linking and when using
|
|
file formats which the GNU linker does not support, such as `ECOFF'@. In
|
|
this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and
|
|
termination functions are recognized simply by their names. This requires
|
|
an extra program in the linkage step, called @command{collect2}. This program
|
|
pretends to be the linker, for use with GCC; it does its job by running
|
|
the ordinary linker, but also arranges to include the vectors of
|
|
initialization and termination functions. These functions are called
|
|
via @code{__main} as described above. In order to use this method,
|
|
@code{use_collect2} must be defined in the target in @file{config.gcc}.
|
|
|
|
@ifinfo
|
|
The following section describes the specific macros that control and
|
|
customize the handling of initialization and termination functions.
|
|
@end ifinfo
|
|
|
|
@node Macros for Initialization
|
|
@subsection Macros Controlling Initialization Routines
|
|
|
|
Here are the macros that control how the compiler handles initialization
|
|
and termination functions:
|
|
|
|
@defmac INIT_SECTION_ASM_OP
|
|
If defined, a C string constant, including spacing, for the assembler
|
|
operation to identify the following data as initialization code. If not
|
|
defined, GCC will assume such a section does not exist. When you are
|
|
using special sections for initialization and termination functions, this
|
|
macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to
|
|
run the initialization functions.
|
|
@end defmac
|
|
|
|
@defmac HAS_INIT_SECTION
|
|
If defined, @code{main} will not call @code{__main} as described above.
|
|
This macro should be defined for systems that control start-up code
|
|
on a symbol-by-symbol basis, such as OSF/1, and should not
|
|
be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}.
|
|
@end defmac
|
|
|
|
@defmac LD_INIT_SWITCH
|
|
If defined, a C string constant for a switch that tells the linker that
|
|
the following symbol is an initialization routine.
|
|
@end defmac
|
|
|
|
@defmac LD_FINI_SWITCH
|
|
If defined, a C string constant for a switch that tells the linker that
|
|
the following symbol is a finalization routine.
|
|
@end defmac
|
|
|
|
@defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func})
|
|
If defined, a C statement that will write a function that can be
|
|
automatically called when a shared library is loaded. The function
|
|
should call @var{func}, which takes no arguments. If not defined, and
|
|
the object format requires an explicit initialization function, then a
|
|
function called @code{_GLOBAL__DI} will be generated.
|
|
|
|
This function and the following one are used by collect2 when linking a
|
|
shared library that needs constructors or destructors, or has DWARF2
|
|
exception tables embedded in the code.
|
|
@end defmac
|
|
|
|
@defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func})
|
|
If defined, a C statement that will write a function that can be
|
|
automatically called when a shared library is unloaded. The function
|
|
should call @var{func}, which takes no arguments. If not defined, and
|
|
the object format requires an explicit finalization function, then a
|
|
function called @code{_GLOBAL__DD} will be generated.
|
|
@end defmac
|
|
|
|
@defmac INVOKE__main
|
|
If defined, @code{main} will call @code{__main} despite the presence of
|
|
@code{INIT_SECTION_ASM_OP}. This macro should be defined for systems
|
|
where the init section is not actually run automatically, but is still
|
|
useful for collecting the lists of constructors and destructors.
|
|
@end defmac
|
|
|
|
@defmac SUPPORTS_INIT_PRIORITY
|
|
If nonzero, the C++ @code{init_priority} attribute is supported and the
|
|
compiler should emit instructions to control the order of initialization
|
|
of objects. If zero, the compiler will issue an error message upon
|
|
encountering an @code{init_priority} attribute.
|
|
@end defmac
|
|
|
|
@deftypevr {Target Hook} bool TARGET_HAVE_CTORS_DTORS
|
|
This value is true if the target supports some ``native'' method of
|
|
collecting constructors and destructors to be run at startup and exit.
|
|
It is false if we must use @command{collect2}.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} bool TARGET_DTORS_FROM_CXA_ATEXIT
|
|
This value is true if the target wants destructors to be queued to be
|
|
run from __cxa_atexit. If this is the case then, for each priority level,
|
|
a new constructor will be entered that registers the destructors for that
|
|
level with __cxa_atexit (and there will be no destructors emitted).
|
|
It is false the method implied by @code{have_ctors_dtors} is used.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority})
|
|
If defined, a function that outputs assembler code to arrange to call
|
|
the function referenced by @var{symbol} at initialization time.
|
|
|
|
Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking
|
|
no arguments and with no return value. If the target supports initialization
|
|
priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY};
|
|
otherwise it must be @code{DEFAULT_INIT_PRIORITY}.
|
|
|
|
If this macro is not defined by the target, a suitable default will
|
|
be chosen if (1) the target supports arbitrary section names, (2) the
|
|
target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2}
|
|
is not defined.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority})
|
|
This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination
|
|
functions rather than initialization functions.
|
|
@end deftypefn
|
|
|
|
If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine
|
|
generated for the generated object file will have static linkage.
|
|
|
|
If your system uses @command{collect2} as the means of processing
|
|
constructors, then that program normally uses @command{nm} to scan
|
|
an object file for constructor functions to be called.
|
|
|
|
On certain kinds of systems, you can define this macro to make
|
|
@command{collect2} work faster (and, in some cases, make it work at all):
|
|
|
|
@defmac OBJECT_FORMAT_COFF
|
|
Define this macro if the system uses COFF (Common Object File Format)
|
|
object files, so that @command{collect2} can assume this format and scan
|
|
object files directly for dynamic constructor/destructor functions.
|
|
|
|
This macro is effective only in a native compiler; @command{collect2} as
|
|
part of a cross compiler always uses @command{nm} for the target machine.
|
|
@end defmac
|
|
|
|
@defmac REAL_NM_FILE_NAME
|
|
Define this macro as a C string constant containing the file name to use
|
|
to execute @command{nm}. The default is to search the path normally for
|
|
@command{nm}.
|
|
@end defmac
|
|
|
|
@defmac NM_FLAGS
|
|
@command{collect2} calls @command{nm} to scan object files for static
|
|
constructors and destructors and LTO info. By default, @option{-n} is
|
|
passed. Define @code{NM_FLAGS} to a C string constant if other options
|
|
are needed to get the same output format as GNU @command{nm -n}
|
|
produces.
|
|
@end defmac
|
|
|
|
If your system supports shared libraries and has a program to list the
|
|
dynamic dependencies of a given library or executable, you can define
|
|
these macros to enable support for running initialization and
|
|
termination functions in shared libraries:
|
|
|
|
@defmac LDD_SUFFIX
|
|
Define this macro to a C string constant containing the name of the program
|
|
which lists dynamic dependencies, like @command{ldd} under SunOS 4.
|
|
@end defmac
|
|
|
|
@defmac PARSE_LDD_OUTPUT (@var{ptr})
|
|
Define this macro to be C code that extracts filenames from the output
|
|
of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable
|
|
of type @code{char *} that points to the beginning of a line of output
|
|
from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the
|
|
code must advance @var{ptr} to the beginning of the filename on that
|
|
line. Otherwise, it must set @var{ptr} to @code{NULL}.
|
|
@end defmac
|
|
|
|
@defmac SHLIB_SUFFIX
|
|
Define this macro to a C string constant containing the default shared
|
|
library extension of the target (e.g., @samp{".so"}). @command{collect2}
|
|
strips version information after this suffix when generating global
|
|
constructor and destructor names. This define is only needed on targets
|
|
that use @command{collect2} to process constructors and destructors.
|
|
@end defmac
|
|
|
|
@node Instruction Output
|
|
@subsection Output of Assembler Instructions
|
|
|
|
@c prevent bad page break with this line
|
|
This describes assembler instruction output.
|
|
|
|
@defmac REGISTER_NAMES
|
|
A C initializer containing the assembler's names for the machine
|
|
registers, each one as a C string constant. This is what translates
|
|
register numbers in the compiler into assembler language.
|
|
@end defmac
|
|
|
|
@defmac ADDITIONAL_REGISTER_NAMES
|
|
If defined, a C initializer for an array of structures containing a name
|
|
and a register number. This macro defines additional names for hard
|
|
registers, thus allowing the @code{asm} option in declarations to refer
|
|
to registers using alternate names.
|
|
@end defmac
|
|
|
|
@defmac OVERLAPPING_REGISTER_NAMES
|
|
If defined, a C initializer for an array of structures containing a
|
|
name, a register number and a count of the number of consecutive
|
|
machine registers the name overlaps. This macro defines additional
|
|
names for hard registers, thus allowing the @code{asm} option in
|
|
declarations to refer to registers using alternate names. Unlike
|
|
@code{ADDITIONAL_REGISTER_NAMES}, this macro should be used when the
|
|
register name implies multiple underlying registers.
|
|
|
|
This macro should be used when it is important that a clobber in an
|
|
@code{asm} statement clobbers all the underlying values implied by the
|
|
register name. For example, on ARM, clobbering the double-precision
|
|
VFP register ``d0'' implies clobbering both single-precision registers
|
|
``s0'' and ``s1''.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr})
|
|
Define this macro if you are using an unusual assembler that
|
|
requires different names for the machine instructions.
|
|
|
|
The definition is a C statement or statements which output an
|
|
assembler instruction opcode to the stdio stream @var{stream}. The
|
|
macro-operand @var{ptr} is a variable of type @code{char *} which
|
|
points to the opcode name in its ``internal'' form---the form that is
|
|
written in the machine description. The definition should output the
|
|
opcode name to @var{stream}, performing any translation you desire, and
|
|
increment the variable @var{ptr} to point at the end of the opcode
|
|
so that it will not be output twice.
|
|
|
|
In fact, your macro definition may process less than the entire opcode
|
|
name, or more than the opcode name; but if you want to process text
|
|
that includes @samp{%}-sequences to substitute operands, you must take
|
|
care of the substitution yourself. Just be sure to increment
|
|
@var{ptr} over whatever text should not be output normally.
|
|
|
|
@findex recog_data.operand
|
|
If you need to look at the operand values, they can be found as the
|
|
elements of @code{recog_data.operand}.
|
|
|
|
If the macro definition does nothing, the instruction is output
|
|
in the usual way.
|
|
@end defmac
|
|
|
|
@defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands})
|
|
If defined, a C statement to be executed just prior to the output of
|
|
assembler code for @var{insn}, to modify the extracted operands so
|
|
they will be output differently.
|
|
|
|
Here the argument @var{opvec} is the vector containing the operands
|
|
extracted from @var{insn}, and @var{noperands} is the number of
|
|
elements of the vector which contain meaningful data for this insn.
|
|
The contents of this vector are what will be used to convert the insn
|
|
template into assembler code, so you can change the assembler output
|
|
by changing the contents of the vector.
|
|
|
|
This macro is useful when various assembler syntaxes share a single
|
|
file of instruction patterns; by defining this macro differently, you
|
|
can cause a large class of instructions to be output differently (such
|
|
as with rearranged operands). Naturally, variations in assembler
|
|
syntax affecting individual insn patterns ought to be handled by
|
|
writing conditional output routines in those patterns.
|
|
|
|
If this macro is not defined, it is equivalent to a null statement.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_FINAL_POSTSCAN_INSN (FILE *@var{file}, rtx_insn *@var{insn}, rtx *@var{opvec}, int @var{noperands})
|
|
If defined, this target hook is a function which is executed just after the
|
|
output of assembler code for @var{insn}, to change the mode of the assembler
|
|
if necessary.
|
|
|
|
Here the argument @var{opvec} is the vector containing the operands
|
|
extracted from @var{insn}, and @var{noperands} is the number of
|
|
elements of the vector which contain meaningful data for this insn.
|
|
The contents of this vector are what was used to convert the insn
|
|
template into assembler code, so you can change the assembler mode
|
|
by checking the contents of the vector.
|
|
@end deftypefn
|
|
|
|
@defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code})
|
|
A C compound statement to output to stdio stream @var{stream} the
|
|
assembler syntax for an instruction operand @var{x}. @var{x} is an
|
|
RTL expression.
|
|
|
|
@var{code} is a value that can be used to specify one of several ways
|
|
of printing the operand. It is used when identical operands must be
|
|
printed differently depending on the context. @var{code} comes from
|
|
the @samp{%} specification that was used to request printing of the
|
|
operand. If the specification was just @samp{%@var{digit}} then
|
|
@var{code} is 0; if the specification was @samp{%@var{ltr}
|
|
@var{digit}} then @var{code} is the ASCII code for @var{ltr}.
|
|
|
|
@findex reg_names
|
|
If @var{x} is a register, this macro should print the register's name.
|
|
The names can be found in an array @code{reg_names} whose type is
|
|
@code{char *[]}. @code{reg_names} is initialized from
|
|
@code{REGISTER_NAMES}.
|
|
|
|
When the machine description has a specification @samp{%@var{punct}}
|
|
(a @samp{%} followed by a punctuation character), this macro is called
|
|
with a null pointer for @var{x} and the punctuation character for
|
|
@var{code}.
|
|
@end defmac
|
|
|
|
@defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code})
|
|
A C expression which evaluates to true if @var{code} is a valid
|
|
punctuation character for use in the @code{PRINT_OPERAND} macro. If
|
|
@code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no
|
|
punctuation characters (except for the standard one, @samp{%}) are used
|
|
in this way.
|
|
@end defmac
|
|
|
|
@defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x})
|
|
A C compound statement to output to stdio stream @var{stream} the
|
|
assembler syntax for an instruction operand that is a memory reference
|
|
whose address is @var{x}. @var{x} is an RTL expression.
|
|
|
|
@cindex @code{TARGET_ENCODE_SECTION_INFO} usage
|
|
On some machines, the syntax for a symbolic address depends on the
|
|
section that the address refers to. On these machines, define the hook
|
|
@code{TARGET_ENCODE_SECTION_INFO} to store the information into the
|
|
@code{symbol_ref}, and then check for it here. @xref{Assembler
|
|
Format}.
|
|
@end defmac
|
|
|
|
@findex dbr_sequence_length
|
|
@defmac DBR_OUTPUT_SEQEND (@var{file})
|
|
A C statement, to be executed after all slot-filler instructions have
|
|
been output. If necessary, call @code{dbr_sequence_length} to
|
|
determine the number of slots filled in a sequence (zero if not
|
|
currently outputting a sequence), to decide how many no-ops to output,
|
|
or whatever.
|
|
|
|
Don't define this macro if it has nothing to do, but it is helpful in
|
|
reading assembly output if the extent of the delay sequence is made
|
|
explicit (e.g.@: with white space).
|
|
@end defmac
|
|
|
|
@findex final_sequence
|
|
Note that output routines for instructions with delay slots must be
|
|
prepared to deal with not being output as part of a sequence
|
|
(i.e.@: when the scheduling pass is not run, or when no slot fillers could be
|
|
found.) The variable @code{final_sequence} is null when not
|
|
processing a sequence, otherwise it contains the @code{sequence} rtx
|
|
being output.
|
|
|
|
@findex asm_fprintf
|
|
@defmac REGISTER_PREFIX
|
|
@defmacx LOCAL_LABEL_PREFIX
|
|
@defmacx USER_LABEL_PREFIX
|
|
@defmacx IMMEDIATE_PREFIX
|
|
If defined, C string expressions to be used for the @samp{%R}, @samp{%L},
|
|
@samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see
|
|
@file{final.cc}). These are useful when a single @file{md} file must
|
|
support multiple assembler formats. In that case, the various @file{tm.h}
|
|
files can define these macros differently.
|
|
@end defmac
|
|
|
|
@defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format})
|
|
If defined this macro should expand to a series of @code{case}
|
|
statements which will be parsed inside the @code{switch} statement of
|
|
the @code{asm_fprintf} function. This allows targets to define extra
|
|
printf formats which may useful when generating their assembler
|
|
statements. Note that uppercase letters are reserved for future
|
|
generic extensions to asm_fprintf, and so are not available to target
|
|
specific code. The output file is given by the parameter @var{file}.
|
|
The varargs input pointer is @var{argptr} and the rest of the format
|
|
string, starting the character after the one that is being switched
|
|
upon, is pointed to by @var{format}.
|
|
@end defmac
|
|
|
|
@defmac ASSEMBLER_DIALECT
|
|
If your target supports multiple dialects of assembler language (such as
|
|
different opcodes), define this macro as a C expression that gives the
|
|
numeric index of the assembler language dialect to use, with zero as the
|
|
first variant.
|
|
|
|
If this macro is defined, you may use constructs of the form
|
|
@smallexample
|
|
@samp{@{option0|option1|option2@dots{}@}}
|
|
@end smallexample
|
|
@noindent
|
|
in the output templates of patterns (@pxref{Output Template}) or in the
|
|
first argument of @code{asm_fprintf}. This construct outputs
|
|
@samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of
|
|
@code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters
|
|
within these strings retain their usual meaning. If there are fewer
|
|
alternatives within the braces than the value of
|
|
@code{ASSEMBLER_DIALECT}, the construct outputs nothing. If it's needed
|
|
to print curly braces or @samp{|} character in assembler output directly,
|
|
@samp{%@{}, @samp{%@}} and @samp{%|} can be used.
|
|
|
|
If you do not define this macro, the characters @samp{@{}, @samp{|} and
|
|
@samp{@}} do not have any special meaning when used in templates or
|
|
operands to @code{asm_fprintf}.
|
|
|
|
Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX},
|
|
@code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express
|
|
the variations in assembler language syntax with that mechanism. Define
|
|
@code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax
|
|
if the syntax variant are larger and involve such things as different
|
|
opcodes or operand order.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno})
|
|
A C expression to output to @var{stream} some assembler code
|
|
which will push hard register number @var{regno} onto the stack.
|
|
The code need not be optimal, since this macro is used only when
|
|
profiling.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno})
|
|
A C expression to output to @var{stream} some assembler code
|
|
which will pop hard register number @var{regno} off of the stack.
|
|
The code need not be optimal, since this macro is used only when
|
|
profiling.
|
|
@end defmac
|
|
|
|
@node Dispatch Tables
|
|
@subsection Output of Dispatch Tables
|
|
|
|
@c prevent bad page break with this line
|
|
This concerns dispatch tables.
|
|
|
|
@cindex dispatch table
|
|
@defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel})
|
|
A C statement to output to the stdio stream @var{stream} an assembler
|
|
pseudo-instruction to generate a difference between two labels.
|
|
@var{value} and @var{rel} are the numbers of two internal labels. The
|
|
definitions of these labels are output using
|
|
@code{(*targetm.asm_out.internal_label)}, and they must be printed in the same
|
|
way here. For example,
|
|
|
|
@smallexample
|
|
fprintf (@var{stream}, "\t.word L%d-L%d\n",
|
|
@var{value}, @var{rel})
|
|
@end smallexample
|
|
|
|
You must provide this macro on machines where the addresses in a
|
|
dispatch table are relative to the table's own address. If defined, GCC
|
|
will also use this macro on all machines when producing PIC@.
|
|
@var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the
|
|
mode and flags can be read.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value})
|
|
This macro should be provided on machines where the addresses
|
|
in a dispatch table are absolute.
|
|
|
|
The definition should be a C statement to output to the stdio stream
|
|
@var{stream} an assembler pseudo-instruction to generate a reference to
|
|
a label. @var{value} is the number of an internal label whose
|
|
definition is output using @code{(*targetm.asm_out.internal_label)}.
|
|
For example,
|
|
|
|
@smallexample
|
|
fprintf (@var{stream}, "\t.word L%d\n", @var{value})
|
|
@end smallexample
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table})
|
|
Define this if the label before a jump-table needs to be output
|
|
specially. The first three arguments are the same as for
|
|
@code{(*targetm.asm_out.internal_label)}; the fourth argument is the
|
|
jump-table which follows (a @code{jump_table_data} containing an
|
|
@code{addr_vec} or @code{addr_diff_vec}).
|
|
|
|
This feature is used on system V to output a @code{swbeg} statement
|
|
for the table.
|
|
|
|
If this macro is not defined, these labels are output with
|
|
@code{(*targetm.asm_out.internal_label)}.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table})
|
|
Define this if something special must be output at the end of a
|
|
jump-table. The definition should be a C statement to be executed
|
|
after the assembler code for the table is written. It should write
|
|
the appropriate code to stdio stream @var{stream}. The argument
|
|
@var{table} is the jump-table insn, and @var{num} is the label-number
|
|
of the preceding label.
|
|
|
|
If this macro is not defined, nothing special is output at the end of
|
|
the jump-table.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_POST_CFI_STARTPROC (FILE *@var{}, @var{tree})
|
|
This target hook is used to emit assembly strings required by the target
|
|
after the .cfi_startproc directive. The first argument is the file stream to
|
|
write the strings to and the second argument is the function's declaration. The
|
|
expected use is to add more .cfi_* directives.
|
|
|
|
The default is to not output any assembly strings.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_EMIT_UNWIND_LABEL (FILE *@var{stream}, tree @var{decl}, int @var{for_eh}, int @var{empty})
|
|
This target hook emits a label at the beginning of each FDE@. It
|
|
should be defined on targets where FDEs need special labels, and it
|
|
should write the appropriate label, for the FDE associated with the
|
|
function declaration @var{decl}, to the stdio stream @var{stream}.
|
|
The third argument, @var{for_eh}, is a boolean: true if this is for an
|
|
exception table. The fourth argument, @var{empty}, is a boolean:
|
|
true if this is a placeholder label for an omitted FDE@.
|
|
|
|
The default is that FDEs are not given nonlocal labels.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL (FILE *@var{stream})
|
|
This target hook emits a label at the beginning of the exception table.
|
|
It should be defined on targets where it is desirable for the table
|
|
to be broken up according to function.
|
|
|
|
The default is that no label is emitted.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_EMIT_EXCEPT_PERSONALITY (rtx @var{personality})
|
|
If the target implements @code{TARGET_ASM_UNWIND_EMIT}, this hook may be
|
|
used to emit a directive to install a personality hook into the unwind
|
|
info. This hook should not be used if dwarf2 unwind info is used.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_UNWIND_EMIT (FILE *@var{stream}, rtx_insn *@var{insn})
|
|
This target hook emits assembly directives required to unwind the
|
|
given instruction. This is only used when @code{TARGET_EXCEPT_UNWIND_INFO}
|
|
returns @code{UI_TARGET}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_ASM_MAKE_EH_SYMBOL_INDIRECT (rtx @var{origsymbol}, bool @var{pubvis})
|
|
If necessary, modify personality and LSDA references to handle indirection.
|
|
The original symbol is in @code{origsymbol} and if @code{pubvis} is true
|
|
the symbol is visible outside the TU.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_ASM_UNWIND_EMIT_BEFORE_INSN
|
|
True if the @code{TARGET_ASM_UNWIND_EMIT} hook should be called before
|
|
the assembly for @var{insn} has been emitted, false if the hook should
|
|
be called afterward.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ASM_SHOULD_RESTORE_CFA_STATE (void)
|
|
For DWARF-based unwind frames, two CFI instructions provide for save and
|
|
restore of register state. GCC maintains the current frame address (CFA)
|
|
separately from the register bank but the unwinder in libgcc preserves this
|
|
state along with the registers (and this is expected by the code that writes
|
|
the unwind frames). This hook allows the target to specify that the CFA data
|
|
is not saved/restored along with the registers by the target unwinder so that
|
|
suitable additional instructions should be emitted to restore it.
|
|
@end deftypefn
|
|
|
|
@node Exception Region Output
|
|
@subsection Assembler Commands for Exception Regions
|
|
|
|
@c prevent bad page break with this line
|
|
|
|
This describes commands marking the start and the end of an exception
|
|
region.
|
|
|
|
@defmac EH_FRAME_SECTION_NAME
|
|
If defined, a C string constant for the name of the section containing
|
|
exception handling frame unwind information. If not defined, GCC will
|
|
provide a default definition if the target supports named sections.
|
|
@file{crtstuff.c} uses this macro to switch to the appropriate section.
|
|
|
|
You should define this symbol if your target supports DWARF 2 frame
|
|
unwind information and the default definition does not work.
|
|
@end defmac
|
|
|
|
@defmac EH_FRAME_THROUGH_COLLECT2
|
|
If defined, DWARF 2 frame unwind information will identified by
|
|
specially named labels. The collect2 process will locate these
|
|
labels and generate code to register the frames.
|
|
|
|
This might be necessary, for instance, if the system linker will not
|
|
place the eh_frames in-between the sentinals from @file{crtstuff.c},
|
|
or if the system linker does garbage collection and sections cannot
|
|
be marked as not to be collected.
|
|
@end defmac
|
|
|
|
@defmac EH_TABLES_CAN_BE_READ_ONLY
|
|
Define this macro to 1 if your target is such that no frame unwind
|
|
information encoding used with non-PIC code will ever require a
|
|
runtime relocation, but the linker may not support merging read-only
|
|
and read-write sections into a single read-write section.
|
|
@end defmac
|
|
|
|
@defmac MASK_RETURN_ADDR
|
|
An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so
|
|
that it does not contain any extraneous set bits in it.
|
|
@end defmac
|
|
|
|
@defmac DWARF2_UNWIND_INFO
|
|
Define this macro to 0 if your target supports DWARF 2 frame unwind
|
|
information, but it does not yet work with exception handling.
|
|
Otherwise, if your target supports this information (if it defines
|
|
@code{INCOMING_RETURN_ADDR_RTX} and @code{OBJECT_FORMAT_ELF}),
|
|
GCC will provide a default definition of 1.
|
|
@end defmac
|
|
|
|
@deftypefn {Common Target Hook} {enum unwind_info_type} TARGET_EXCEPT_UNWIND_INFO (struct gcc_options *@var{opts})
|
|
This hook defines the mechanism that will be used for exception handling
|
|
by the target. If the target has ABI specified unwind tables, the hook
|
|
should return @code{UI_TARGET}. If the target is to use the
|
|
@code{setjmp}/@code{longjmp}-based exception handling scheme, the hook
|
|
should return @code{UI_SJLJ}. If the target supports DWARF 2 frame unwind
|
|
information, the hook should return @code{UI_DWARF2}.
|
|
|
|
A target may, if exceptions are disabled, choose to return @code{UI_NONE}.
|
|
This may end up simplifying other parts of target-specific code. The
|
|
default implementation of this hook never returns @code{UI_NONE}.
|
|
|
|
Note that the value returned by this hook should be constant. It should
|
|
not depend on anything except the command-line switches described by
|
|
@var{opts}. In particular, the
|
|
setting @code{UI_SJLJ} must be fixed at compiler start-up as C pre-processor
|
|
macros and builtin functions related to exception handling are set up
|
|
depending on this setting.
|
|
|
|
The default implementation of the hook first honors the
|
|
@option{--enable-sjlj-exceptions} configure option, then
|
|
@code{DWARF2_UNWIND_INFO}, and finally defaults to @code{UI_SJLJ}. If
|
|
@code{DWARF2_UNWIND_INFO} depends on command-line options, the target
|
|
must define this hook so that @var{opts} is used correctly.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Common Target Hook} bool TARGET_UNWIND_TABLES_DEFAULT
|
|
This variable should be set to @code{true} if the target ABI requires unwinding
|
|
tables even when exceptions are not used. It must not be modified by
|
|
command-line option processing.
|
|
@end deftypevr
|
|
|
|
@defmac DONT_USE_BUILTIN_SETJMP
|
|
Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme
|
|
should use the @code{setjmp}/@code{longjmp} functions from the C library
|
|
instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery.
|
|
@end defmac
|
|
|
|
@defmac JMP_BUF_SIZE
|
|
This macro has no effect unless @code{DONT_USE_BUILTIN_SETJMP} is also
|
|
defined. Define this macro if the default size of @code{jmp_buf} buffer
|
|
for the @code{setjmp}/@code{longjmp}-based exception handling mechanism
|
|
is not large enough, or if it is much too large.
|
|
The default size is @code{FIRST_PSEUDO_REGISTER * sizeof(void *)}.
|
|
@end defmac
|
|
|
|
@defmac DWARF_CIE_DATA_ALIGNMENT
|
|
This macro need only be defined if the target might save registers in the
|
|
function prologue at an offset to the stack pointer that is not aligned to
|
|
@code{UNITS_PER_WORD}. The definition should be the negative minimum
|
|
alignment if @code{STACK_GROWS_DOWNWARD} is true, and the positive
|
|
minimum alignment otherwise. @xref{DWARF}. Only applicable if
|
|
the target supports DWARF 2 frame unwind information.
|
|
@end defmac
|
|
|
|
@deftypevr {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO
|
|
Contains the value true if the target should add a zero word onto the
|
|
end of a Dwarf-2 frame info section when used for exception handling.
|
|
Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and
|
|
true otherwise.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_DWARF_REGISTER_SPAN (rtx @var{reg})
|
|
Given a register, this hook should return a parallel of registers to
|
|
represent where to find the register pieces. Define this hook if the
|
|
register and its mode are represented in Dwarf in non-contiguous
|
|
locations, or if the register should be represented in more than one
|
|
register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}.
|
|
If not defined, the default is to return @code{NULL_RTX}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} machine_mode TARGET_DWARF_FRAME_REG_MODE (int @var{regno})
|
|
Given a register, this hook should return the mode which the
|
|
corresponding Dwarf frame register should have. This is normally
|
|
used to return a smaller mode than the raw mode to prevent call
|
|
clobbered parts of a register altering the frame register size
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_INIT_DWARF_REG_SIZES_EXTRA (tree @var{address})
|
|
If some registers are represented in Dwarf-2 unwind information in
|
|
multiple pieces, define this hook to fill in information about the
|
|
sizes of those pieces in the table used by the unwinder at runtime.
|
|
It will be called by @code{expand_builtin_init_dwarf_reg_sizes} after
|
|
filling in a single size corresponding to each hard register;
|
|
@var{address} is the address of the table.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ASM_TTYPE (rtx @var{sym})
|
|
This hook is used to output a reference from a frame unwinding table to
|
|
the type_info object identified by @var{sym}. It should return @code{true}
|
|
if the reference was output. Returning @code{false} will cause the
|
|
reference to be output using the normal Dwarf2 routines.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_ARM_EABI_UNWINDER
|
|
This flag should be set to @code{true} on targets that use an ARM EABI
|
|
based unwinding library, and @code{false} on other targets. This effects
|
|
the format of unwinding tables, and how the unwinder in entered after
|
|
running a cleanup. The default is @code{false}.
|
|
@end deftypevr
|
|
|
|
@node Alignment Output
|
|
@subsection Assembler Commands for Alignment
|
|
|
|
@c prevent bad page break with this line
|
|
This describes commands for alignment.
|
|
|
|
@defmac JUMP_ALIGN (@var{label})
|
|
The alignment (log base 2) to put in front of @var{label}, which is
|
|
a common destination of jumps and has no fallthru incoming edge.
|
|
|
|
This macro need not be defined if you don't want any special alignment
|
|
to be done at such a time. Most machine descriptions do not currently
|
|
define the macro.
|
|
|
|
Unless it's necessary to inspect the @var{label} parameter, it is better
|
|
to set the variable @var{align_jumps} in the target's
|
|
@code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's
|
|
selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation.
|
|
@end defmac
|
|
|
|
@defmac LABEL_ALIGN_AFTER_BARRIER (@var{label})
|
|
The alignment (log base 2) to put in front of @var{label}, which follows
|
|
a @code{BARRIER}.
|
|
|
|
This macro need not be defined if you don't want any special alignment
|
|
to be done at such a time. Most machine descriptions do not currently
|
|
define the macro.
|
|
@end defmac
|
|
|
|
@defmac LOOP_ALIGN (@var{label})
|
|
The alignment (log base 2) to put in front of @var{label} that heads
|
|
a frequently executed basic block (usually the header of a loop).
|
|
|
|
This macro need not be defined if you don't want any special alignment
|
|
to be done at such a time. Most machine descriptions do not currently
|
|
define the macro.
|
|
|
|
Unless it's necessary to inspect the @var{label} parameter, it is better
|
|
to set the variable @code{align_loops} in the target's
|
|
@code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's
|
|
selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation.
|
|
@end defmac
|
|
|
|
@defmac LABEL_ALIGN (@var{label})
|
|
The alignment (log base 2) to put in front of @var{label}.
|
|
If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment,
|
|
the maximum of the specified values is used.
|
|
|
|
Unless it's necessary to inspect the @var{label} parameter, it is better
|
|
to set the variable @code{align_labels} in the target's
|
|
@code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's
|
|
selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes})
|
|
A C statement to output to the stdio stream @var{stream} an assembler
|
|
instruction to advance the location counter by @var{nbytes} bytes.
|
|
Those bytes should be zero when loaded. @var{nbytes} will be a C
|
|
expression of type @code{unsigned HOST_WIDE_INT}.
|
|
@end defmac
|
|
|
|
@defmac ASM_NO_SKIP_IN_TEXT
|
|
Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the
|
|
text section because it fails to put zeros in the bytes that are skipped.
|
|
This is true on many Unix systems, where the pseudo--op to skip bytes
|
|
produces no-op instructions rather than zeros when used in the text
|
|
section.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power})
|
|
A C statement to output to the stdio stream @var{stream} an assembler
|
|
command to advance the location counter to a multiple of 2 to the
|
|
@var{power} bytes. @var{power} will be a C expression of type @code{int}.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power})
|
|
Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used
|
|
for padding, if necessary.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip})
|
|
A C statement to output to the stdio stream @var{stream} an assembler
|
|
command to advance the location counter to a multiple of 2 to the
|
|
@var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to
|
|
satisfy the alignment request. @var{power} and @var{max_skip} will be
|
|
a C expression of type @code{int}.
|
|
@end defmac
|
|
|
|
@need 3000
|
|
@node Debugging Info
|
|
@section Controlling Debugging Information Format
|
|
|
|
@c prevent bad page break with this line
|
|
This describes how to specify debugging information.
|
|
|
|
@menu
|
|
* All Debuggers:: Macros that affect all debugging formats uniformly.
|
|
* DBX Options:: Macros enabling specific options in DBX format.
|
|
* DBX Hooks:: Hook macros for varying DBX format.
|
|
* File Names and DBX:: Macros controlling output of file names in DBX format.
|
|
* DWARF:: Macros for DWARF format.
|
|
* VMS Debug:: Macros for VMS debug format.
|
|
* CTF Debug:: Macros for CTF debug format.
|
|
* BTF Debug:: Macros for BTF debug format.
|
|
@end menu
|
|
|
|
@node All Debuggers
|
|
@subsection Macros Affecting All Debugging Formats
|
|
|
|
@c prevent bad page break with this line
|
|
These macros affect all debugging formats.
|
|
|
|
@defmac DBX_REGISTER_NUMBER (@var{regno})
|
|
A C expression that returns the DBX register number for the compiler
|
|
register number @var{regno}. In the default macro provided, the value
|
|
of this expression will be @var{regno} itself. But sometimes there are
|
|
some registers that the compiler knows about and DBX does not, or vice
|
|
versa. In such cases, some register may need to have one number in the
|
|
compiler and another for DBX@.
|
|
|
|
If two registers have consecutive numbers inside GCC, and they can be
|
|
used as a pair to hold a multiword value, then they @emph{must} have
|
|
consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}.
|
|
Otherwise, debuggers will be unable to access such a pair, because they
|
|
expect register pairs to be consecutive in their own numbering scheme.
|
|
|
|
If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that
|
|
does not preserve register pairs, then what you must do instead is
|
|
redefine the actual register numbering scheme.
|
|
@end defmac
|
|
|
|
@defmac DEBUGGER_AUTO_OFFSET (@var{x})
|
|
A C expression that returns the integer offset value for an automatic
|
|
variable having address @var{x} (an RTL expression). The default
|
|
computation assumes that @var{x} is based on the frame-pointer and
|
|
gives the offset from the frame-pointer. This is required for targets
|
|
that produce debugging output for DBX and allow the frame-pointer to be
|
|
eliminated when the @option{-g} option is used.
|
|
@end defmac
|
|
|
|
@defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x})
|
|
A C expression that returns the integer offset value for an argument
|
|
having address @var{x} (an RTL expression). The nominal offset is
|
|
@var{offset}.
|
|
@end defmac
|
|
|
|
@defmac PREFERRED_DEBUGGING_TYPE
|
|
A C expression that returns the type of debugging output GCC should
|
|
produce when the user specifies just @option{-g}. Define
|
|
this if you have arranged for GCC to support more than one format of
|
|
debugging output. Currently, the allowable values are @code{DBX_DEBUG},
|
|
@code{DWARF2_DEBUG}, @code{XCOFF_DEBUG}, @code{VMS_DEBUG},
|
|
and @code{VMS_AND_DWARF2_DEBUG}.
|
|
|
|
When the user specifies @option{-ggdb}, GCC normally also uses the
|
|
value of this macro to select the debugging output format, but with two
|
|
exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the
|
|
value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is
|
|
defined, GCC uses @code{DBX_DEBUG}.
|
|
|
|
The value of this macro only affects the default debugging output; the
|
|
user can always get a specific type of output by using @option{-gstabs},
|
|
@option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}.
|
|
@end defmac
|
|
|
|
@node DBX Options
|
|
@subsection Specific Options for DBX Output
|
|
|
|
@c prevent bad page break with this line
|
|
These are specific options for DBX output.
|
|
|
|
@defmac DBX_DEBUGGING_INFO
|
|
Define this macro if GCC should produce debugging output for DBX
|
|
in response to the @option{-g} option.
|
|
@end defmac
|
|
|
|
@defmac XCOFF_DEBUGGING_INFO
|
|
Define this macro if GCC should produce XCOFF format debugging output
|
|
in response to the @option{-g} option. This is a variant of DBX format.
|
|
@end defmac
|
|
|
|
@defmac DEFAULT_GDB_EXTENSIONS
|
|
Define this macro to control whether GCC should by default generate
|
|
GDB's extended version of DBX debugging information (assuming DBX-format
|
|
debugging information is enabled at all). If you don't define the
|
|
macro, the default is 1: always generate the extended information
|
|
if there is any occasion to.
|
|
@end defmac
|
|
|
|
@defmac DEBUG_SYMS_TEXT
|
|
Define this macro if all @code{.stabs} commands should be output while
|
|
in the text section.
|
|
@end defmac
|
|
|
|
@defmac ASM_STABS_OP
|
|
A C string constant, including spacing, naming the assembler pseudo op to
|
|
use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol.
|
|
If you don't define this macro, @code{"\t.stabs\t"} is used. This macro
|
|
applies only to DBX debugging information format.
|
|
@end defmac
|
|
|
|
@defmac ASM_STABD_OP
|
|
A C string constant, including spacing, naming the assembler pseudo op to
|
|
use instead of @code{"\t.stabd\t"} to define a debugging symbol whose
|
|
value is the current location. If you don't define this macro,
|
|
@code{"\t.stabd\t"} is used. This macro applies only to DBX debugging
|
|
information format.
|
|
@end defmac
|
|
|
|
@defmac ASM_STABN_OP
|
|
A C string constant, including spacing, naming the assembler pseudo op to
|
|
use instead of @code{"\t.stabn\t"} to define a debugging symbol with no
|
|
name. If you don't define this macro, @code{"\t.stabn\t"} is used. This
|
|
macro applies only to DBX debugging information format.
|
|
@end defmac
|
|
|
|
@defmac DBX_NO_XREFS
|
|
Define this macro if DBX on your system does not support the construct
|
|
@samp{xs@var{tagname}}. On some systems, this construct is used to
|
|
describe a forward reference to a structure named @var{tagname}.
|
|
On other systems, this construct is not supported at all.
|
|
@end defmac
|
|
|
|
@defmac DBX_CONTIN_LENGTH
|
|
A symbol name in DBX-format debugging information is normally
|
|
continued (split into two separate @code{.stabs} directives) when it
|
|
exceeds a certain length (by default, 80 characters). On some
|
|
operating systems, DBX requires this splitting; on others, splitting
|
|
must not be done. You can inhibit splitting by defining this macro
|
|
with the value zero. You can override the default splitting-length by
|
|
defining this macro as an expression for the length you desire.
|
|
@end defmac
|
|
|
|
@defmac DBX_CONTIN_CHAR
|
|
Normally continuation is indicated by adding a @samp{\} character to
|
|
the end of a @code{.stabs} string when a continuation follows. To use
|
|
a different character instead, define this macro as a character
|
|
constant for the character you want to use. Do not define this macro
|
|
if backslash is correct for your system.
|
|
@end defmac
|
|
|
|
@defmac DBX_STATIC_STAB_DATA_SECTION
|
|
Define this macro if it is necessary to go to the data section before
|
|
outputting the @samp{.stabs} pseudo-op for a non-global static
|
|
variable.
|
|
@end defmac
|
|
|
|
@defmac DBX_TYPE_DECL_STABS_CODE
|
|
The value to use in the ``code'' field of the @code{.stabs} directive
|
|
for a typedef. The default is @code{N_LSYM}.
|
|
@end defmac
|
|
|
|
@defmac DBX_STATIC_CONST_VAR_CODE
|
|
The value to use in the ``code'' field of the @code{.stabs} directive
|
|
for a static variable located in the text section. DBX format does not
|
|
provide any ``right'' way to do this. The default is @code{N_FUN}.
|
|
@end defmac
|
|
|
|
@defmac DBX_REGPARM_STABS_CODE
|
|
The value to use in the ``code'' field of the @code{.stabs} directive
|
|
for a parameter passed in registers. DBX format does not provide any
|
|
``right'' way to do this. The default is @code{N_RSYM}.
|
|
@end defmac
|
|
|
|
@defmac DBX_REGPARM_STABS_LETTER
|
|
The letter to use in DBX symbol data to identify a symbol as a parameter
|
|
passed in registers. DBX format does not customarily provide any way to
|
|
do this. The default is @code{'P'}.
|
|
@end defmac
|
|
|
|
@defmac DBX_FUNCTION_FIRST
|
|
Define this macro if the DBX information for a function and its
|
|
arguments should precede the assembler code for the function. Normally,
|
|
in DBX format, the debugging information entirely follows the assembler
|
|
code.
|
|
@end defmac
|
|
|
|
@defmac DBX_BLOCKS_FUNCTION_RELATIVE
|
|
Define this macro, with value 1, if the value of a symbol describing
|
|
the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be
|
|
relative to the start of the enclosing function. Normally, GCC uses
|
|
an absolute address.
|
|
@end defmac
|
|
|
|
@defmac DBX_LINES_FUNCTION_RELATIVE
|
|
Define this macro, with value 1, if the value of a symbol indicating
|
|
the current line number (@code{N_SLINE}) should be relative to the
|
|
start of the enclosing function. Normally, GCC uses an absolute address.
|
|
@end defmac
|
|
|
|
@defmac DBX_USE_BINCL
|
|
Define this macro if GCC should generate @code{N_BINCL} and
|
|
@code{N_EINCL} stabs for included header files, as on Sun systems. This
|
|
macro also directs GCC to output a type number as a pair of a file
|
|
number and a type number within the file. Normally, GCC does not
|
|
generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single
|
|
number for a type number.
|
|
@end defmac
|
|
|
|
@node DBX Hooks
|
|
@subsection Open-Ended Hooks for DBX Format
|
|
|
|
@c prevent bad page break with this line
|
|
These are hooks for DBX format.
|
|
|
|
@defmac DBX_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}, @var{counter})
|
|
A C statement to output DBX debugging information before code for line
|
|
number @var{line} of the current source file to the stdio stream
|
|
@var{stream}. @var{counter} is the number of time the macro was
|
|
invoked, including the current invocation; it is intended to generate
|
|
unique labels in the assembly output.
|
|
|
|
This macro should not be defined if the default output is correct, or
|
|
if it can be made correct by defining @code{DBX_LINES_FUNCTION_RELATIVE}.
|
|
@end defmac
|
|
|
|
@defmac NO_DBX_FUNCTION_END
|
|
Some stabs encapsulation formats (in particular ECOFF), cannot handle the
|
|
@code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct.
|
|
On those machines, define this macro to turn this feature off without
|
|
disturbing the rest of the gdb extensions.
|
|
@end defmac
|
|
|
|
@defmac NO_DBX_BNSYM_ENSYM
|
|
Some assemblers cannot handle the @code{.stabd BNSYM/ENSYM,0,0} gdb dbx
|
|
extension construct. On those machines, define this macro to turn this
|
|
feature off without disturbing the rest of the gdb extensions.
|
|
@end defmac
|
|
|
|
@node File Names and DBX
|
|
@subsection File Names in DBX Format
|
|
|
|
@c prevent bad page break with this line
|
|
This describes file names in DBX format.
|
|
|
|
@defmac DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name})
|
|
A C statement to output DBX debugging information to the stdio stream
|
|
@var{stream}, which indicates that file @var{name} is the main source
|
|
file---the file specified as the input file for compilation.
|
|
This macro is called only once, at the beginning of compilation.
|
|
|
|
This macro need not be defined if the standard form of output
|
|
for DBX debugging information is appropriate.
|
|
|
|
It may be necessary to refer to a label equal to the beginning of the
|
|
text section. You can use @samp{assemble_name (stream, ltext_label_name)}
|
|
to do so. If you do this, you must also set the variable
|
|
@var{used_ltext_label_name} to @code{true}.
|
|
@end defmac
|
|
|
|
@defmac NO_DBX_MAIN_SOURCE_DIRECTORY
|
|
Define this macro, with value 1, if GCC should not emit an indication
|
|
of the current directory for compilation and current source language at
|
|
the beginning of the file.
|
|
@end defmac
|
|
|
|
@defmac NO_DBX_GCC_MARKER
|
|
Define this macro, with value 1, if GCC should not emit an indication
|
|
that this object file was compiled by GCC@. The default is to emit
|
|
an @code{N_OPT} stab at the beginning of every source file, with
|
|
@samp{gcc2_compiled.} for the string and value 0.
|
|
@end defmac
|
|
|
|
@defmac DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name})
|
|
A C statement to output DBX debugging information at the end of
|
|
compilation of the main source file @var{name}. Output should be
|
|
written to the stdio stream @var{stream}.
|
|
|
|
If you don't define this macro, nothing special is output at the end
|
|
of compilation, which is correct for most machines.
|
|
@end defmac
|
|
|
|
@defmac DBX_OUTPUT_NULL_N_SO_AT_MAIN_SOURCE_FILE_END
|
|
Define this macro @emph{instead of} defining
|
|
@code{DBX_OUTPUT_MAIN_SOURCE_FILE_END}, if what needs to be output at
|
|
the end of compilation is an @code{N_SO} stab with an empty string,
|
|
whose value is the highest absolute text address in the file.
|
|
@end defmac
|
|
|
|
@need 2000
|
|
@node DWARF
|
|
@subsection Macros for DWARF Output
|
|
|
|
@c prevent bad page break with this line
|
|
Here are macros for DWARF output.
|
|
|
|
@defmac DWARF2_DEBUGGING_INFO
|
|
Define this macro if GCC should produce dwarf version 2 format
|
|
debugging output in response to the @option{-g} option.
|
|
|
|
@deftypefn {Target Hook} int TARGET_DWARF_CALLING_CONVENTION (const_tree @var{function})
|
|
Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to
|
|
be emitted for each function. Instead of an integer return the enum
|
|
value for the @code{DW_CC_} tag.
|
|
@end deftypefn
|
|
|
|
To support optional call frame debugging information, you must also
|
|
define @code{INCOMING_RETURN_ADDR_RTX} and either set
|
|
@code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the
|
|
prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save}
|
|
as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't.
|
|
@end defmac
|
|
|
|
@defmac DWARF2_FRAME_INFO
|
|
Define this macro to a nonzero value if GCC should always output
|
|
Dwarf 2 frame information. If @code{TARGET_EXCEPT_UNWIND_INFO}
|
|
(@pxref{Exception Region Output}) returns @code{UI_DWARF2}, and
|
|
exceptions are enabled, GCC will output this information not matter
|
|
how you define @code{DWARF2_FRAME_INFO}.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} {enum unwind_info_type} TARGET_DEBUG_UNWIND_INFO (void)
|
|
This hook defines the mechanism that will be used for describing frame
|
|
unwind information to the debugger. Normally the hook will return
|
|
@code{UI_DWARF2} if DWARF 2 debug information is enabled, and
|
|
return @code{UI_NONE} otherwise.
|
|
|
|
A target may return @code{UI_DWARF2} even when DWARF 2 debug information
|
|
is disabled in order to always output DWARF 2 frame information.
|
|
|
|
A target may return @code{UI_TARGET} if it has ABI specified unwind tables.
|
|
This will suppress generation of the normal debug frame unwind information.
|
|
@end deftypefn
|
|
|
|
@defmac DWARF2_ASM_LINE_DEBUG_INFO
|
|
Define this macro to be a nonzero value if the assembler can generate Dwarf 2
|
|
line debug info sections. This will result in much more compact line number
|
|
tables, and hence is desirable if it works.
|
|
@end defmac
|
|
|
|
@defmac DWARF2_ASM_VIEW_DEBUG_INFO
|
|
Define this macro to be a nonzero value if the assembler supports view
|
|
assignment and verification in @code{.loc}. If it does not, but the
|
|
user enables location views, the compiler may have to fallback to
|
|
internal line number tables.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} int TARGET_RESET_LOCATION_VIEW (rtx_insn *@var{})
|
|
This hook, if defined, enables -ginternal-reset-location-views, and
|
|
uses its result to override cases in which the estimated min insn
|
|
length might be nonzero even when a PC advance (i.e., a view reset)
|
|
cannot be taken for granted.
|
|
|
|
If the hook is defined, it must return a positive value to indicate
|
|
the insn definitely advances the PC, and so the view number can be
|
|
safely assumed to be reset; a negative value to mean the insn
|
|
definitely does not advance the PC, and os the view number must not
|
|
be reset; or zero to decide based on the estimated insn length.
|
|
|
|
If insn length is to be regarded as reliable, set the hook to
|
|
@code{hook_int_rtx_insn_0}.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_WANT_DEBUG_PUB_SECTIONS
|
|
True if the @code{.debug_pubtypes} and @code{.debug_pubnames} sections
|
|
should be emitted. These sections are not used on most platforms, and
|
|
in particular GDB does not use them.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} bool TARGET_DELAY_SCHED2
|
|
True if sched2 is not to be run at its normal place.
|
|
This usually means it will be run as part of machine-specific reorg.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} bool TARGET_DELAY_VARTRACK
|
|
True if vartrack is not to be run at its normal place.
|
|
This usually means it will be run as part of machine-specific reorg.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} bool TARGET_NO_REGISTER_ALLOCATION
|
|
True if register allocation and the passes
|
|
following it should not be run. Usually true only for virtual assembler
|
|
targets.
|
|
@end deftypevr
|
|
|
|
@defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
|
|
A C statement to issue assembly directives that create a difference
|
|
@var{lab1} minus @var{lab2}, using an integer of the given @var{size}.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_DWARF_VMS_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2})
|
|
A C statement to issue assembly directives that create a difference
|
|
between the two given labels in system defined units, e.g.@: instruction
|
|
slots on IA64 VMS, using an integer of the given size.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{offset}, @var{section})
|
|
A C statement to issue assembly directives that create a
|
|
section-relative reference to the given @var{label} plus @var{offset}, using
|
|
an integer of the given @var{size}. The label is known to be defined in the
|
|
given @var{section}.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label})
|
|
A C statement to issue assembly directives that create a self-relative
|
|
reference to the given @var{label}, using an integer of the given @var{size}.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_DWARF_DATAREL (@var{stream}, @var{size}, @var{label})
|
|
A C statement to issue assembly directives that create a reference to the
|
|
given @var{label} relative to the dbase, using an integer of the given @var{size}.
|
|
@end defmac
|
|
|
|
@defmac ASM_OUTPUT_DWARF_TABLE_REF (@var{label})
|
|
A C statement to issue assembly directives that create a reference to
|
|
the DWARF table identifier @var{label} from the current section. This
|
|
is used on some systems to avoid garbage collecting a DWARF table which
|
|
is referenced by a function.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_DWARF_DTPREL (FILE *@var{file}, int @var{size}, rtx @var{x})
|
|
If defined, this target hook is a function which outputs a DTP-relative
|
|
reference to the given TLS symbol of the specified size.
|
|
@end deftypefn
|
|
|
|
@need 2000
|
|
@node VMS Debug
|
|
@subsection Macros for VMS Debug Format
|
|
|
|
@c prevent bad page break with this line
|
|
Here are macros for VMS debug format.
|
|
|
|
@defmac VMS_DEBUGGING_INFO
|
|
Define this macro if GCC should produce debugging output for VMS
|
|
in response to the @option{-g} option. The default behavior for VMS
|
|
is to generate minimal debug info for a traceback in the absence of
|
|
@option{-g} unless explicitly overridden with @option{-g0}. This
|
|
behavior is controlled by @code{TARGET_OPTION_OPTIMIZATION} and
|
|
@code{TARGET_OPTION_OVERRIDE}.
|
|
@end defmac
|
|
|
|
@need 2000
|
|
@node CTF Debug
|
|
@subsection Macros for CTF Debug Format
|
|
|
|
@c prevent bad page break with this line
|
|
Here are macros for CTF debug format.
|
|
|
|
@defmac CTF_DEBUGGING_INFO
|
|
Define this macro if GCC should produce debugging output in CTF debug
|
|
format in response to the @option{-gctf} option.
|
|
@end defmac
|
|
|
|
@need 2000
|
|
@node BTF Debug
|
|
@subsection Macros for BTF Debug Format
|
|
|
|
@c prevent bad page break with this line
|
|
Here are macros for BTF debug format.
|
|
|
|
@defmac BTF_DEBUGGING_INFO
|
|
Define this macro if GCC should produce debugging output in BTF debug
|
|
format in response to the @option{-gbtf} option.
|
|
@end defmac
|
|
|
|
@node Floating Point
|
|
@section Cross Compilation and Floating Point
|
|
@cindex cross compilation and floating point
|
|
@cindex floating point and cross compilation
|
|
|
|
While all modern machines use twos-complement representation for integers,
|
|
there are a variety of representations for floating point numbers. This
|
|
means that in a cross-compiler the representation of floating point numbers
|
|
in the compiled program may be different from that used in the machine
|
|
doing the compilation.
|
|
|
|
Because different representation systems may offer different amounts of
|
|
range and precision, all floating point constants must be represented in
|
|
the target machine's format. Therefore, the cross compiler cannot
|
|
safely use the host machine's floating point arithmetic; it must emulate
|
|
the target's arithmetic. To ensure consistency, GCC always uses
|
|
emulation to work with floating point values, even when the host and
|
|
target floating point formats are identical.
|
|
|
|
The following macros are provided by @file{real.h} for the compiler to
|
|
use. All parts of the compiler which generate or optimize
|
|
floating-point calculations must use these macros. They may evaluate
|
|
their operands more than once, so operands must not have side effects.
|
|
|
|
@defmac REAL_VALUE_TYPE
|
|
The C data type to be used to hold a floating point value in the target
|
|
machine's format. Typically this is a @code{struct} containing an
|
|
array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque
|
|
quantity.
|
|
@end defmac
|
|
|
|
@deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x})
|
|
Truncates @var{x} to a signed integer, rounding toward zero.
|
|
@end deftypefn
|
|
|
|
@deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x})
|
|
Truncates @var{x} to an unsigned integer, rounding toward zero. If
|
|
@var{x} is negative, returns zero.
|
|
@end deftypefn
|
|
|
|
@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, machine_mode @var{mode})
|
|
Converts @var{string} into a floating point number in the target machine's
|
|
representation for mode @var{mode}. This routine can handle both
|
|
decimal and hexadecimal floating point constants, using the syntax
|
|
defined by the C language for both.
|
|
@end deftypefn
|
|
|
|
@deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x})
|
|
Returns 1 if @var{x} is negative (including negative zero), 0 otherwise.
|
|
@end deftypefn
|
|
|
|
@deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x})
|
|
Determines whether @var{x} represents infinity (positive or negative).
|
|
@end deftypefn
|
|
|
|
@deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x})
|
|
Determines whether @var{x} represents a ``NaN'' (not-a-number).
|
|
@end deftypefn
|
|
|
|
@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x})
|
|
Returns the negative of the floating point value @var{x}.
|
|
@end deftypefn
|
|
|
|
@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x})
|
|
Returns the absolute value of @var{x}.
|
|
@end deftypefn
|
|
|
|
@node Mode Switching
|
|
@section Mode Switching Instructions
|
|
@cindex mode switching
|
|
The following macros control mode switching optimizations:
|
|
|
|
@defmac OPTIMIZE_MODE_SWITCHING (@var{entity})
|
|
Define this macro if the port needs extra instructions inserted for mode
|
|
switching in an optimizing compilation.
|
|
|
|
For an example, the SH4 can perform both single and double precision
|
|
floating point operations, but to perform a single precision operation,
|
|
the FPSCR PR bit has to be cleared, while for a double precision
|
|
operation, this bit has to be set. Changing the PR bit requires a general
|
|
purpose register as a scratch register, hence these FPSCR sets have to
|
|
be inserted before reload, i.e.@: you cannot put this into instruction emitting
|
|
or @code{TARGET_MACHINE_DEPENDENT_REORG}.
|
|
|
|
You can have multiple entities that are mode-switched, and select at run time
|
|
which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should
|
|
return nonzero for any @var{entity} that needs mode-switching.
|
|
If you define this macro, you also have to define
|
|
@code{NUM_MODES_FOR_MODE_SWITCHING}, @code{TARGET_MODE_NEEDED},
|
|
@code{TARGET_MODE_PRIORITY} and @code{TARGET_MODE_EMIT}.
|
|
@code{TARGET_MODE_AFTER}, @code{TARGET_MODE_ENTRY}, and @code{TARGET_MODE_EXIT}
|
|
are optional.
|
|
@end defmac
|
|
|
|
@defmac NUM_MODES_FOR_MODE_SWITCHING
|
|
If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as
|
|
initializer for an array of integers. Each initializer element
|
|
N refers to an entity that needs mode switching, and specifies the number
|
|
of different modes that might need to be set for this entity.
|
|
The position of the initializer in the initializer---starting counting at
|
|
zero---determines the integer that is used to refer to the mode-switched
|
|
entity in question.
|
|
In macros that take mode arguments / yield a mode result, modes are
|
|
represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode
|
|
switch is needed / supplied.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_MODE_EMIT (int @var{entity}, int @var{mode}, int @var{prev_mode}, HARD_REG_SET @var{regs_live})
|
|
Generate one or more insns to set @var{entity} to @var{mode}.
|
|
@var{hard_reg_live} is the set of hard registers live at the point where
|
|
the insn(s) are to be inserted. @var{prev_moxde} indicates the mode
|
|
to switch from. Sets of a lower numbered entity will be emitted before
|
|
sets of a higher numbered entity to a mode of the same or lower priority.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_MODE_NEEDED (int @var{entity}, rtx_insn *@var{insn})
|
|
@var{entity} is an integer specifying a mode-switched entity.
|
|
If @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro
|
|
to return an integer value not larger than the corresponding element
|
|
in @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity}
|
|
must be switched into prior to the execution of @var{insn}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_MODE_AFTER (int @var{entity}, int @var{mode}, rtx_insn *@var{insn})
|
|
@var{entity} is an integer specifying a mode-switched entity.
|
|
If this macro is defined, it is evaluated for every @var{insn} during mode
|
|
switching. It determines the mode that an insn results
|
|
in (if different from the incoming mode).
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_MODE_ENTRY (int @var{entity})
|
|
If this macro is defined, it is evaluated for every @var{entity} that
|
|
needs mode switching. It should evaluate to an integer, which is a mode
|
|
that @var{entity} is assumed to be switched to at function entry.
|
|
If @code{TARGET_MODE_ENTRY} is defined then @code{TARGET_MODE_EXIT}
|
|
must be defined.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_MODE_EXIT (int @var{entity})
|
|
If this macro is defined, it is evaluated for every @var{entity} that
|
|
needs mode switching. It should evaluate to an integer, which is a mode
|
|
that @var{entity} is assumed to be switched to at function exit.
|
|
If @code{TARGET_MODE_EXIT} is defined then @code{TARGET_MODE_ENTRY}
|
|
must be defined.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_MODE_PRIORITY (int @var{entity}, int @var{n})
|
|
This macro specifies the order in which modes for @var{entity}
|
|
are processed. 0 is the highest priority,
|
|
@code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the lowest.
|
|
The value of the macro should be an integer designating a mode
|
|
for @var{entity}. For any fixed @var{entity}, @code{mode_priority}
|
|
(@var{entity}, @var{n}) shall be a bijection in 0 @dots{}
|
|
@code{num_modes_for_mode_switching[@var{entity}] - 1}.
|
|
@end deftypefn
|
|
|
|
@node Target Attributes
|
|
@section Defining target-specific uses of @code{__attribute__}
|
|
@cindex target attributes
|
|
@cindex machine attributes
|
|
@cindex attributes, target-specific
|
|
|
|
Target-specific attributes may be defined for functions, data and types.
|
|
These are described using the following target hooks; they also need to
|
|
be documented in @file{extend.texi}.
|
|
|
|
@deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE
|
|
If defined, this target hook points to an array of @samp{struct
|
|
attribute_spec} (defined in @file{tree-core.h}) specifying the machine
|
|
specific attributes for this target and some of the restrictions on the
|
|
entities to which these attributes are applied and the arguments they
|
|
take.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P (const_tree @var{name})
|
|
If defined, this target hook is a function which returns true if the
|
|
machine-specific attribute named @var{name} expects an identifier
|
|
given as its first argument to be passed on as a plain identifier, not
|
|
subjected to name lookup. If this is not defined, the default is
|
|
false for all machine-specific attributes.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (const_tree @var{type1}, const_tree @var{type2})
|
|
If defined, this target hook is a function which returns zero if the attributes on
|
|
@var{type1} and @var{type2} are incompatible, one if they are compatible,
|
|
and two if they are nearly compatible (which causes a warning to be
|
|
generated). If this is not defined, machine-specific attributes are
|
|
supposed always to be compatible.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type})
|
|
If defined, this target hook is a function which assigns default attributes to
|
|
the newly defined @var{type}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2})
|
|
Define this target hook if the merging of type attributes needs special
|
|
handling. If defined, the result is a list of the combined
|
|
@code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed
|
|
that @code{comptypes} has already been called and returned 1. This
|
|
function may call @code{merge_attributes} to handle machine-independent
|
|
merging.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl})
|
|
Define this target hook if the merging of decl attributes needs special
|
|
handling. If defined, the result is a list of the combined
|
|
@code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}.
|
|
@var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of
|
|
when this is needed are when one attribute overrides another, or when an
|
|
attribute is nullified by a subsequent definition. This function may
|
|
call @code{merge_attributes} to handle machine-independent merging.
|
|
|
|
@findex TARGET_DLLIMPORT_DECL_ATTRIBUTES
|
|
If the only target-specific handling you require is @samp{dllimport}
|
|
for Microsoft Windows targets, you should define the macro
|
|
@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}. The compiler
|
|
will then define a function called
|
|
@code{merge_dllimport_decl_attributes} which can then be defined as
|
|
the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. You can also
|
|
add @code{handle_dll_attribute} in the attribute table for your port
|
|
to perform initial processing of the @samp{dllimport} and
|
|
@samp{dllexport} attributes. This is done in @file{i386/cygwin.h} and
|
|
@file{i386/i386.cc}, for example.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_VALID_DLLIMPORT_ATTRIBUTE_P (const_tree @var{decl})
|
|
@var{decl} is a variable or function with @code{__attribute__((dllimport))}
|
|
specified. Use this hook if the target needs to add extra validation
|
|
checks to @code{handle_dll_attribute}.
|
|
@end deftypefn
|
|
|
|
@defmac TARGET_DECLSPEC
|
|
Define this macro to a nonzero value if you want to treat
|
|
@code{__declspec(X)} as equivalent to @code{__attribute((X))}. By
|
|
default, this behavior is enabled only for targets that define
|
|
@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation
|
|
of @code{__declspec} is via a built-in macro, but you should not rely
|
|
on this implementation detail.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr})
|
|
Define this target hook if you want to be able to add attributes to a decl
|
|
when it is being created. This is normally useful for back ends which
|
|
wish to implement a pragma by using the attributes which correspond to
|
|
the pragma's effect. The @var{node} argument is the decl which is being
|
|
created. The @var{attr_ptr} argument is a pointer to the attribute list
|
|
for this decl. The list itself should not be modified, since it may be
|
|
shared with other decls, but attributes may be chained on the head of
|
|
the list and @code{*@var{attr_ptr}} modified to point to the new
|
|
attributes, or a copy of the list may be made if further changes are
|
|
needed.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_HANDLE_GENERIC_ATTRIBUTE (tree *@var{node}, tree @var{name}, tree @var{args}, int @var{flags}, bool *@var{no_add_attrs})
|
|
Define this target hook if you want to be able to perform additional
|
|
target-specific processing of an attribute which is handled generically
|
|
by a front end. The arguments are the same as those which are passed to
|
|
attribute handlers. So far this only affects the @var{noinit} and
|
|
@var{section} attribute.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (const_tree @var{fndecl})
|
|
@cindex inlining
|
|
This target hook returns @code{true} if it is OK to inline @var{fndecl}
|
|
into the current function, despite its having target-specific
|
|
attributes, @code{false} otherwise. By default, if a function has a
|
|
target specific attribute attached to it, it will not be inlined.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_OPTION_VALID_ATTRIBUTE_P (tree @var{fndecl}, tree @var{name}, tree @var{args}, int @var{flags})
|
|
This hook is called to parse @code{attribute(target("..."))}, which
|
|
allows setting target-specific options on individual functions.
|
|
These function-specific options may differ
|
|
from the options specified on the command line. The hook should return
|
|
@code{true} if the options are valid.
|
|
|
|
The hook should set the @code{DECL_FUNCTION_SPECIFIC_TARGET} field in
|
|
the function declaration to hold a pointer to a target-specific
|
|
@code{struct cl_target_option} structure.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_OPTION_SAVE (struct cl_target_option *@var{ptr}, struct gcc_options *@var{opts}, struct gcc_options *@var{opts_set})
|
|
This hook is called to save any additional target-specific information
|
|
in the @code{struct cl_target_option} structure for function-specific
|
|
options from the @code{struct gcc_options} structure.
|
|
@xref{Option file format}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_OPTION_RESTORE (struct gcc_options *@var{opts}, struct gcc_options *@var{opts_set}, struct cl_target_option *@var{ptr})
|
|
This hook is called to restore any additional target-specific
|
|
information in the @code{struct cl_target_option} structure for
|
|
function-specific options to the @code{struct gcc_options} structure.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_OPTION_POST_STREAM_IN (struct cl_target_option *@var{ptr})
|
|
This hook is called to update target-specific information in the
|
|
@code{struct cl_target_option} structure after it is streamed in from
|
|
LTO bytecode.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_OPTION_PRINT (FILE *@var{file}, int @var{indent}, struct cl_target_option *@var{ptr})
|
|
This hook is called to print any additional target-specific
|
|
information in the @code{struct cl_target_option} structure for
|
|
function-specific options.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_OPTION_PRAGMA_PARSE (tree @var{args}, tree @var{pop_target})
|
|
This target hook parses the options for @code{#pragma GCC target}, which
|
|
sets the target-specific options for functions that occur later in the
|
|
input stream. The options accepted should be the same as those handled by the
|
|
@code{TARGET_OPTION_VALID_ATTRIBUTE_P} hook.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_OPTION_OVERRIDE (void)
|
|
Sometimes certain combinations of command options do not make sense on
|
|
a particular target machine. You can override the hook
|
|
@code{TARGET_OPTION_OVERRIDE} to take account of this. This hooks is called
|
|
once just after all the command options have been parsed.
|
|
|
|
Don't use this hook to turn on various extra optimizations for
|
|
@option{-O}. That is what @code{TARGET_OPTION_OPTIMIZATION} is for.
|
|
|
|
If you need to do something whenever the optimization level is
|
|
changed via the optimize attribute or pragma, see
|
|
@code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE}
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_OPTION_FUNCTION_VERSIONS (tree @var{decl1}, tree @var{decl2})
|
|
This target hook returns @code{true} if @var{DECL1} and @var{DECL2} are
|
|
versions of the same function. @var{DECL1} and @var{DECL2} are function
|
|
versions if and only if they have the same function signature and
|
|
different target specific attributes, that is, they are compiled for
|
|
different target machines.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CAN_INLINE_P (tree @var{caller}, tree @var{callee})
|
|
This target hook returns @code{false} if the @var{caller} function
|
|
cannot inline @var{callee}, based on target specific information. By
|
|
default, inlining is not allowed if the callee function has function
|
|
specific target options and the caller does not use the same options.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_UPDATE_IPA_FN_TARGET_INFO (unsigned int& @var{info}, const gimple* @var{stmt})
|
|
Allow target to analyze all gimple statements for the given function to
|
|
record and update some target specific information for inlining. A typical
|
|
example is that a caller with one isa feature disabled is normally not
|
|
allowed to inline a callee with that same isa feature enabled even which is
|
|
attributed by always_inline, but with the conservative analysis on all
|
|
statements of the callee if we are able to guarantee the callee does not
|
|
exploit any instructions from the mismatch isa feature, it would be safe to
|
|
allow the caller to inline the callee.
|
|
@var{info} is one @code{unsigned int} value to record information in which
|
|
one set bit indicates one corresponding feature is detected in the analysis,
|
|
@var{stmt} is the statement being analyzed. Return true if target still
|
|
need to analyze the subsequent statements, otherwise return false to stop
|
|
subsequent analysis.
|
|
The default version of this hook returns false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_NEED_IPA_FN_TARGET_INFO (const_tree @var{decl}, unsigned int& @var{info})
|
|
Allow target to check early whether it is necessary to analyze all gimple
|
|
statements in the given function to update target specific information for
|
|
inlining. See hook @code{update_ipa_fn_target_info} for usage example of
|
|
target specific information. This hook is expected to be invoked ahead of
|
|
the iterating with hook @code{update_ipa_fn_target_info}.
|
|
@var{decl} is the function being analyzed, @var{info} is the same as what
|
|
in hook @code{update_ipa_fn_target_info}, target can do one time update
|
|
into @var{info} without iterating for some case. Return true if target
|
|
decides to analyze all gimple statements to collect information, otherwise
|
|
return false.
|
|
The default version of this hook returns false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_RELAYOUT_FUNCTION (tree @var{fndecl})
|
|
This target hook fixes function @var{fndecl} after attributes are processed.
|
|
Default does nothing. On ARM, the default function's alignment is updated
|
|
with the attribute target.
|
|
@end deftypefn
|
|
|
|
@node Emulated TLS
|
|
@section Emulating TLS
|
|
@cindex Emulated TLS
|
|
|
|
For targets whose psABI does not provide Thread Local Storage via
|
|
specific relocations and instruction sequences, an emulation layer is
|
|
used. A set of target hooks allows this emulation layer to be
|
|
configured for the requirements of a particular target. For instance
|
|
the psABI may in fact specify TLS support in terms of an emulation
|
|
layer.
|
|
|
|
The emulation layer works by creating a control object for every TLS
|
|
object. To access the TLS object, a lookup function is provided
|
|
which, when given the address of the control object, will return the
|
|
address of the current thread's instance of the TLS object.
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_GET_ADDRESS
|
|
Contains the name of the helper function that uses a TLS control
|
|
object to locate a TLS instance. The default causes libgcc's
|
|
emulated TLS helper function to be used.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_REGISTER_COMMON
|
|
Contains the name of the helper function that should be used at
|
|
program startup to register TLS objects that are implicitly
|
|
initialized to zero. If this is @code{NULL}, all TLS objects will
|
|
have explicit initializers. The default causes libgcc's emulated TLS
|
|
registration function to be used.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_VAR_SECTION
|
|
Contains the name of the section in which TLS control variables should
|
|
be placed. The default of @code{NULL} allows these to be placed in
|
|
any section.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_TMPL_SECTION
|
|
Contains the name of the section in which TLS initializers should be
|
|
placed. The default of @code{NULL} allows these to be placed in any
|
|
section.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_VAR_PREFIX
|
|
Contains the prefix to be prepended to TLS control variable names.
|
|
The default of @code{NULL} uses a target-specific prefix.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_TMPL_PREFIX
|
|
Contains the prefix to be prepended to TLS initializer objects. The
|
|
default of @code{NULL} uses a target-specific prefix.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} tree TARGET_EMUTLS_VAR_FIELDS (tree @var{type}, tree *@var{name})
|
|
Specifies a function that generates the FIELD_DECLs for a TLS control
|
|
object type. @var{type} is the RECORD_TYPE the fields are for and
|
|
@var{name} should be filled with the structure tag, if the default of
|
|
@code{__emutls_object} is unsuitable. The default creates a type suitable
|
|
for libgcc's emulated TLS function.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_EMUTLS_VAR_INIT (tree @var{var}, tree @var{decl}, tree @var{tmpl_addr})
|
|
Specifies a function that generates the CONSTRUCTOR to initialize a
|
|
TLS control object. @var{var} is the TLS control object, @var{decl}
|
|
is the TLS object and @var{tmpl_addr} is the address of the
|
|
initializer. The default initializes libgcc's emulated TLS control object.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_EMUTLS_VAR_ALIGN_FIXED
|
|
Specifies whether the alignment of TLS control variable objects is
|
|
fixed and should not be increased as some backends may do to optimize
|
|
single objects. The default is false.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} bool TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS
|
|
Specifies whether a DWARF @code{DW_OP_form_tls_address} location descriptor
|
|
may be used to describe emulated TLS control objects.
|
|
@end deftypevr
|
|
|
|
@node MIPS Coprocessors
|
|
@section Defining coprocessor specifics for MIPS targets.
|
|
@cindex MIPS coprocessor-definition macros
|
|
|
|
The MIPS specification allows MIPS implementations to have as many as 4
|
|
coprocessors, each with as many as 32 private registers. GCC supports
|
|
accessing these registers and transferring values between the registers
|
|
and memory using asm-ized variables. For example:
|
|
|
|
@smallexample
|
|
register unsigned int cp0count asm ("c0r1");
|
|
unsigned int d;
|
|
|
|
d = cp0count + 3;
|
|
@end smallexample
|
|
|
|
(``c0r1'' is the default name of register 1 in coprocessor 0; alternate
|
|
names may be added as described below, or the default names may be
|
|
overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.)
|
|
|
|
Coprocessor registers are assumed to be epilogue-used; sets to them will
|
|
be preserved even if it does not appear that the register is used again
|
|
later in the function.
|
|
|
|
Another note: according to the MIPS spec, coprocessor 1 (if present) is
|
|
the FPU@. One accesses COP1 registers through standard mips
|
|
floating-point support; they are not included in this mechanism.
|
|
|
|
@node PCH Target
|
|
@section Parameters for Precompiled Header Validity Checking
|
|
@cindex parameters, precompiled headers
|
|
|
|
@deftypefn {Target Hook} {void *} TARGET_GET_PCH_VALIDITY (size_t *@var{sz})
|
|
This hook returns a pointer to the data needed by
|
|
@code{TARGET_PCH_VALID_P} and sets
|
|
@samp{*@var{sz}} to the size of the data in bytes.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_PCH_VALID_P (const void *@var{data}, size_t @var{sz})
|
|
This hook checks whether the options used to create a PCH file are
|
|
compatible with the current settings. It returns @code{NULL}
|
|
if so and a suitable error message if not. Error messages will
|
|
be presented to the user and must be localized using @samp{_(@var{msg})}.
|
|
|
|
@var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY}
|
|
when the PCH file was created and @var{sz} is the size of that data in bytes.
|
|
It's safe to assume that the data was created by the same version of the
|
|
compiler, so no format checking is needed.
|
|
|
|
The default definition of @code{default_pch_valid_p} should be
|
|
suitable for most targets.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_CHECK_PCH_TARGET_FLAGS (int @var{pch_flags})
|
|
If this hook is nonnull, the default implementation of
|
|
@code{TARGET_PCH_VALID_P} will use it to check for compatible values
|
|
of @code{target_flags}. @var{pch_flags} specifies the value that
|
|
@code{target_flags} had when the PCH file was created. The return
|
|
value is the same as for @code{TARGET_PCH_VALID_P}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_PREPARE_PCH_SAVE (void)
|
|
Called before writing out a PCH file. If the target has some
|
|
garbage-collected data that needs to be in a particular state on PCH loads,
|
|
it can use this hook to enforce that state. Very few targets need
|
|
to do anything here.
|
|
@end deftypefn
|
|
|
|
@node C++ ABI
|
|
@section C++ ABI parameters
|
|
@cindex parameters, c++ abi
|
|
|
|
@deftypefn {Target Hook} tree TARGET_CXX_GUARD_TYPE (void)
|
|
Define this hook to override the integer type used for guard variables.
|
|
These are used to implement one-time construction of static objects. The
|
|
default is long_long_integer_type_node.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CXX_GUARD_MASK_BIT (void)
|
|
This hook determines how guard variables are used. It should return
|
|
@code{false} (the default) if the first byte should be used. A return value of
|
|
@code{true} indicates that only the least significant bit should be used.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_CXX_GET_COOKIE_SIZE (tree @var{type})
|
|
This hook returns the size of the cookie to use when allocating an array
|
|
whose elements have the indicated @var{type}. Assumes that it is already
|
|
known that a cookie is needed. The default is
|
|
@code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the
|
|
IA64/Generic C++ ABI@.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CXX_COOKIE_HAS_SIZE (void)
|
|
This hook should return @code{true} if the element size should be stored in
|
|
array cookies. The default is to return @code{false}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_CXX_IMPORT_EXPORT_CLASS (tree @var{type}, int @var{import_export})
|
|
If defined by a backend this hook allows the decision made to export
|
|
class @var{type} to be overruled. Upon entry @var{import_export}
|
|
will contain 1 if the class is going to be exported, @minus{}1 if it is going
|
|
to be imported and 0 otherwise. This function should return the
|
|
modified value and perform any other actions necessary to support the
|
|
backend's targeted operating system.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CXX_CDTOR_RETURNS_THIS (void)
|
|
This hook should return @code{true} if constructors and destructors return
|
|
the address of the object created/destroyed. The default is to return
|
|
@code{false}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CXX_KEY_METHOD_MAY_BE_INLINE (void)
|
|
This hook returns true if the key method for a class (i.e., the method
|
|
which, if defined in the current translation unit, causes the virtual
|
|
table to be emitted) may be an inline function. Under the standard
|
|
Itanium C++ ABI the key method may be an inline function so long as
|
|
the function is not declared inline in the class definition. Under
|
|
some variants of the ABI, an inline function can never be the key
|
|
method. The default is to return @code{true}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY (tree @var{decl})
|
|
@var{decl} is a virtual table, virtual table table, typeinfo object,
|
|
or other similar implicit class data object that will be emitted with
|
|
external linkage in this translation unit. No ELF visibility has been
|
|
explicitly specified. If the target needs to specify a visibility
|
|
other than that of the containing class, use this hook to set
|
|
@code{DECL_VISIBILITY} and @code{DECL_VISIBILITY_SPECIFIED}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT (void)
|
|
This hook returns true (the default) if virtual tables and other
|
|
similar implicit class data objects are always COMDAT if they have
|
|
external linkage. If this hook returns false, then class data for
|
|
classes whose virtual table will be emitted in only one translation
|
|
unit will not be COMDAT.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CXX_LIBRARY_RTTI_COMDAT (void)
|
|
This hook returns true (the default) if the RTTI information for
|
|
the basic types which is defined in the C++ runtime should always
|
|
be COMDAT, false if it should not be COMDAT.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CXX_USE_AEABI_ATEXIT (void)
|
|
This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI)
|
|
should be used to register static destructors when @option{-fuse-cxa-atexit}
|
|
is in effect. The default is to return false to use @code{__cxa_atexit}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT (void)
|
|
This hook returns true if the target @code{atexit} function can be used
|
|
in the same manner as @code{__cxa_atexit} to register C++ static
|
|
destructors. This requires that @code{atexit}-registered functions in
|
|
shared libraries are run in the correct order when the libraries are
|
|
unloaded. The default is to return false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_CXX_ADJUST_CLASS_AT_DEFINITION (tree @var{type})
|
|
@var{type} is a C++ class (i.e., RECORD_TYPE or UNION_TYPE) that has just
|
|
been defined. Use this hook to make adjustments to the class (eg, tweak
|
|
visibility or perform any other required target modifications).
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_CXX_DECL_MANGLING_CONTEXT (const_tree @var{decl})
|
|
Return target-specific mangling context of @var{decl} or @code{NULL_TREE}.
|
|
@end deftypefn
|
|
|
|
@node D Language and ABI
|
|
@section D ABI parameters
|
|
@cindex parameters, d abi
|
|
|
|
@deftypefn {D Target Hook} void TARGET_D_CPU_VERSIONS (void)
|
|
Declare all environmental version identifiers relating to the target CPU
|
|
using the function @code{builtin_version}, which takes a string representing
|
|
the name of the version. Version identifiers predefined by this hook apply
|
|
to all modules that are being compiled and imported.
|
|
@end deftypefn
|
|
|
|
@deftypefn {D Target Hook} void TARGET_D_OS_VERSIONS (void)
|
|
Similarly to @code{TARGET_D_CPU_VERSIONS}, but is used for versions
|
|
relating to the target operating system.
|
|
@end deftypefn
|
|
|
|
@deftypefn {D Target Hook} void TARGET_D_REGISTER_CPU_TARGET_INFO (void)
|
|
Register all target information keys relating to the target CPU using the
|
|
function @code{d_add_target_info_handlers}, which takes a
|
|
@samp{struct d_target_info_spec} (defined in @file{d/d-target.h}). The keys
|
|
added by this hook are made available at compile time by the
|
|
@code{__traits(getTargetInfo)} extension, the result is an expression
|
|
describing the requested target information.
|
|
@end deftypefn
|
|
|
|
@deftypefn {D Target Hook} void TARGET_D_REGISTER_OS_TARGET_INFO (void)
|
|
Same as @code{TARGET_D_CPU_TARGET_INFO}, but is used for keys relating to
|
|
the target operating system.
|
|
@end deftypefn
|
|
|
|
@deftypevr {D Target Hook} {const char *} TARGET_D_MINFO_SECTION
|
|
Contains the name of the section in which module info references should be
|
|
placed. This section is expected to be bracketed by two symbols to indicate
|
|
the start and end address of the section, so that the runtime library can
|
|
collect all modules for each loaded shared library and executable. The
|
|
default value of @code{NULL} disables the use of sections altogether.
|
|
@end deftypevr
|
|
|
|
@deftypevr {D Target Hook} {const char *} TARGET_D_MINFO_START_NAME
|
|
If @code{TARGET_D_MINFO_SECTION} is defined, then this must also be defined
|
|
as the name of the symbol indicating the start address of the module info
|
|
section
|
|
@end deftypevr
|
|
|
|
@deftypevr {D Target Hook} {const char *} TARGET_D_MINFO_END_NAME
|
|
If @code{TARGET_D_MINFO_SECTION} is defined, then this must also be defined
|
|
as the name of the symbol indicating the end address of the module info
|
|
section
|
|
@end deftypevr
|
|
|
|
@deftypefn {D Target Hook} bool TARGET_D_HAS_STDCALL_CONVENTION (unsigned int *@var{link_system}, unsigned int *@var{link_windows})
|
|
Returns @code{true} if the target supports the stdcall calling convention.
|
|
The hook should also set @var{link_system} to @code{1} if the @code{stdcall}
|
|
attribute should be applied to functions with @code{extern(System)} linkage,
|
|
and @var{link_windows} to @code{1} to apply @code{stdcall} to functions with
|
|
@code{extern(Windows)} linkage.
|
|
@end deftypefn
|
|
|
|
@deftypevr {D Target Hook} bool TARGET_D_TEMPLATES_ALWAYS_COMDAT
|
|
This flag is true if instantiated functions and variables are always COMDAT
|
|
if they have external linkage. If this flag is false, then instantiated
|
|
decls will be emitted as weak symbols. The default is @code{false}.
|
|
@end deftypevr
|
|
|
|
@node Named Address Spaces
|
|
@section Adding support for named address spaces
|
|
@cindex named address spaces
|
|
|
|
The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275
|
|
standards committee, @cite{Programming Languages - C - Extensions to
|
|
support embedded processors}, specifies a syntax for embedded
|
|
processors to specify alternate address spaces. You can configure a
|
|
GCC port to support section 5.1 of the draft report to add support for
|
|
address spaces other than the default address space. These address
|
|
spaces are new keywords that are similar to the @code{volatile} and
|
|
@code{const} type attributes.
|
|
|
|
Pointers to named address spaces can have a different size than
|
|
pointers to the generic address space.
|
|
|
|
For example, the SPU port uses the @code{__ea} address space to refer
|
|
to memory in the host processor, rather than memory local to the SPU
|
|
processor. Access to memory in the @code{__ea} address space involves
|
|
issuing DMA operations to move data between the host processor and the
|
|
local processor memory address space. Pointers in the @code{__ea}
|
|
address space are either 32 bits or 64 bits based on the
|
|
@option{-mea32} or @option{-mea64} switches (native SPU pointers are
|
|
always 32 bits).
|
|
|
|
Internally, address spaces are represented as a small integer in the
|
|
range 0 to 15 with address space 0 being reserved for the generic
|
|
address space.
|
|
|
|
To register a named address space qualifier keyword with the C front end,
|
|
the target may call the @code{c_register_addr_space} routine. For example,
|
|
the SPU port uses the following to declare @code{__ea} as the keyword for
|
|
named address space #1:
|
|
@smallexample
|
|
#define ADDR_SPACE_EA 1
|
|
c_register_addr_space ("__ea", ADDR_SPACE_EA);
|
|
@end smallexample
|
|
|
|
@deftypefn {Target Hook} scalar_int_mode TARGET_ADDR_SPACE_POINTER_MODE (addr_space_t @var{address_space})
|
|
Define this to return the machine mode to use for pointers to
|
|
@var{address_space} if the target supports named address spaces.
|
|
The default version of this hook returns @code{ptr_mode}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} scalar_int_mode TARGET_ADDR_SPACE_ADDRESS_MODE (addr_space_t @var{address_space})
|
|
Define this to return the machine mode to use for addresses in
|
|
@var{address_space} if the target supports named address spaces.
|
|
The default version of this hook returns @code{Pmode}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ADDR_SPACE_VALID_POINTER_MODE (scalar_int_mode @var{mode}, addr_space_t @var{as})
|
|
Define this to return nonzero if the port can handle pointers
|
|
with machine mode @var{mode} to address space @var{as}. This target
|
|
hook is the same as the @code{TARGET_VALID_POINTER_MODE} target hook,
|
|
except that it includes explicit named address space support. The default
|
|
version of this hook returns true for the modes returned by either the
|
|
@code{TARGET_ADDR_SPACE_POINTER_MODE} or @code{TARGET_ADDR_SPACE_ADDRESS_MODE}
|
|
target hooks for the given address space.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P (machine_mode @var{mode}, rtx @var{exp}, bool @var{strict}, addr_space_t @var{as})
|
|
Define this to return true if @var{exp} is a valid address for mode
|
|
@var{mode} in the named address space @var{as}. The @var{strict}
|
|
parameter says whether strict addressing is in effect after reload has
|
|
finished. This target hook is the same as the
|
|
@code{TARGET_LEGITIMATE_ADDRESS_P} target hook, except that it includes
|
|
explicit named address space support.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS (rtx @var{x}, rtx @var{oldx}, machine_mode @var{mode}, addr_space_t @var{as})
|
|
Define this to modify an invalid address @var{x} to be a valid address
|
|
with mode @var{mode} in the named address space @var{as}. This target
|
|
hook is the same as the @code{TARGET_LEGITIMIZE_ADDRESS} target hook,
|
|
except that it includes explicit named address space support.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ADDR_SPACE_SUBSET_P (addr_space_t @var{subset}, addr_space_t @var{superset})
|
|
Define this to return whether the @var{subset} named address space is
|
|
contained within the @var{superset} named address space. Pointers to
|
|
a named address space that is a subset of another named address space
|
|
will be converted automatically without a cast if used together in
|
|
arithmetic operations. Pointers to a superset address space can be
|
|
converted to pointers to a subset address space via explicit casts.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID (addr_space_t @var{as})
|
|
Define this to modify the default handling of address 0 for the
|
|
address space. Return true if 0 should be considered a valid address.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_ADDR_SPACE_CONVERT (rtx @var{op}, tree @var{from_type}, tree @var{to_type})
|
|
Define this to convert the pointer expression represented by the RTL
|
|
@var{op} with type @var{from_type} that points to a named address
|
|
space to a new pointer expression with type @var{to_type} that points
|
|
to a different named address space. When this hook it called, it is
|
|
guaranteed that one of the two address spaces is a subset of the other,
|
|
as determined by the @code{TARGET_ADDR_SPACE_SUBSET_P} target hook.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_ADDR_SPACE_DEBUG (addr_space_t @var{as})
|
|
Define this to define how the address space is encoded in dwarf.
|
|
The result is the value to be used with @code{DW_AT_address_class}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ADDR_SPACE_DIAGNOSE_USAGE (addr_space_t @var{as}, location_t @var{loc})
|
|
Define this hook if the availability of an address space depends on
|
|
command line options and some diagnostics should be printed when the
|
|
address space is used. This hook is called during parsing and allows
|
|
to emit a better diagnostic compared to the case where the address space
|
|
was not registered with @code{c_register_addr_space}. @var{as} is
|
|
the address space as registered with @code{c_register_addr_space}.
|
|
@var{loc} is the location of the address space qualifier token.
|
|
The default implementation does nothing.
|
|
@end deftypefn
|
|
|
|
@node Misc
|
|
@section Miscellaneous Parameters
|
|
@cindex parameters, miscellaneous
|
|
|
|
@c prevent bad page break with this line
|
|
Here are several miscellaneous parameters.
|
|
|
|
@defmac HAS_LONG_COND_BRANCH
|
|
Define this boolean macro to indicate whether or not your architecture
|
|
has conditional branches that can span all of memory. It is used in
|
|
conjunction with an optimization that partitions hot and cold basic
|
|
blocks into separate sections of the executable. If this macro is
|
|
set to false, gcc will convert any conditional branches that attempt
|
|
to cross between sections into unconditional branches or indirect jumps.
|
|
@end defmac
|
|
|
|
@defmac HAS_LONG_UNCOND_BRANCH
|
|
Define this boolean macro to indicate whether or not your architecture
|
|
has unconditional branches that can span all of memory. It is used in
|
|
conjunction with an optimization that partitions hot and cold basic
|
|
blocks into separate sections of the executable. If this macro is
|
|
set to false, gcc will convert any unconditional branches that attempt
|
|
to cross between sections into indirect jumps.
|
|
@end defmac
|
|
|
|
@defmac CASE_VECTOR_MODE
|
|
An alias for a machine mode name. This is the machine mode that
|
|
elements of a jump-table should have.
|
|
@end defmac
|
|
|
|
@defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body})
|
|
Optional: return the preferred mode for an @code{addr_diff_vec}
|
|
when the minimum and maximum offset are known. If you define this,
|
|
it enables extra code in branch shortening to deal with @code{addr_diff_vec}.
|
|
To make this work, you also have to define @code{INSN_ALIGN} and
|
|
make the alignment for @code{addr_diff_vec} explicit.
|
|
The @var{body} argument is provided so that the offset_unsigned and scale
|
|
flags can be updated.
|
|
@end defmac
|
|
|
|
@defmac CASE_VECTOR_PC_RELATIVE
|
|
Define this macro to be a C expression to indicate when jump-tables
|
|
should contain relative addresses. You need not define this macro if
|
|
jump-tables never contain relative addresses, or jump-tables should
|
|
contain relative addresses only when @option{-fPIC} or @option{-fPIC}
|
|
is in effect.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_CASE_VALUES_THRESHOLD (void)
|
|
This function return the smallest number of different values for which it
|
|
is best to use a jump-table instead of a tree of conditional branches.
|
|
The default is four for machines with a @code{casesi} instruction and
|
|
five otherwise. This is best for most machines.
|
|
@end deftypefn
|
|
|
|
@defmac WORD_REGISTER_OPERATIONS
|
|
Define this macro to 1 if operations between registers with integral mode
|
|
smaller than a word are always performed on the entire register. To be
|
|
more explicit, if you start with a pair of @code{word_mode} registers with
|
|
known values and you do a subword, for example @code{QImode}, addition on
|
|
the low part of the registers, then the compiler may consider that the
|
|
result has a known value in @code{word_mode} too if the macro is defined
|
|
to 1. Most RISC machines have this property and most CISC machines do not.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_MIN_ARITHMETIC_PRECISION (void)
|
|
On some RISC architectures with 64-bit registers, the processor also
|
|
maintains 32-bit condition codes that make it possible to do real 32-bit
|
|
arithmetic, although the operations are performed on the full registers.
|
|
|
|
On such architectures, defining this hook to 32 tells the compiler to try
|
|
using 32-bit arithmetical operations setting the condition codes instead
|
|
of doing full 64-bit arithmetic.
|
|
|
|
More generally, define this hook on RISC architectures if you want the
|
|
compiler to try using arithmetical operations setting the condition codes
|
|
with a precision lower than the word precision.
|
|
|
|
You need not define this hook if @code{WORD_REGISTER_OPERATIONS} is not
|
|
defined to 1.
|
|
@end deftypefn
|
|
|
|
@defmac LOAD_EXTEND_OP (@var{mem_mode})
|
|
Define this macro to be a C expression indicating when insns that read
|
|
memory in @var{mem_mode}, an integral mode narrower than a word, set the
|
|
bits outside of @var{mem_mode} to be either the sign-extension or the
|
|
zero-extension of the data read. Return @code{SIGN_EXTEND} for values
|
|
of @var{mem_mode} for which the
|
|
insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and
|
|
@code{UNKNOWN} for other modes.
|
|
|
|
This macro is not called with @var{mem_mode} non-integral or with a width
|
|
greater than or equal to @code{BITS_PER_WORD}, so you may return any
|
|
value in this case. Do not define this macro if it would always return
|
|
@code{UNKNOWN}. On machines where this macro is defined, you will normally
|
|
define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}.
|
|
|
|
You may return a non-@code{UNKNOWN} value even if for some hard registers
|
|
the sign extension is not performed, if for the @code{REGNO_REG_CLASS}
|
|
of these hard registers @code{TARGET_CAN_CHANGE_MODE_CLASS} returns false
|
|
when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any
|
|
integral mode larger than this but not larger than @code{word_mode}.
|
|
|
|
You must return @code{UNKNOWN} if for some hard registers that allow this
|
|
mode, @code{TARGET_CAN_CHANGE_MODE_CLASS} says that they cannot change to
|
|
@code{word_mode}, but that they can change to another integral mode that
|
|
is larger then @var{mem_mode} but still smaller than @code{word_mode}.
|
|
@end defmac
|
|
|
|
@defmac SHORT_IMMEDIATES_SIGN_EXTEND
|
|
Define this macro to 1 if loading short immediate values into registers sign
|
|
extends.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_MIN_DIVISIONS_FOR_RECIP_MUL (machine_mode @var{mode})
|
|
When @option{-ffast-math} is in effect, GCC tries to optimize
|
|
divisions by the same divisor, by turning them into multiplications by
|
|
the reciprocal. This target hook specifies the minimum number of divisions
|
|
that should be there for GCC to perform the optimization for a variable
|
|
of mode @var{mode}. The default implementation returns 3 if the machine
|
|
has an instruction for the division, and 2 if it does not.
|
|
@end deftypefn
|
|
|
|
@defmac MOVE_MAX
|
|
The maximum number of bytes that a single instruction can move quickly
|
|
between memory and registers or between two memory locations.
|
|
@end defmac
|
|
|
|
@defmac MAX_MOVE_MAX
|
|
The maximum number of bytes that a single instruction can move quickly
|
|
between memory and registers or between two memory locations. If this
|
|
is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the
|
|
constant value that is the largest value that @code{MOVE_MAX} can have
|
|
at run-time.
|
|
@end defmac
|
|
|
|
@defmac SHIFT_COUNT_TRUNCATED
|
|
A C expression that is nonzero if on this machine the number of bits
|
|
actually used for the count of a shift operation is equal to the number
|
|
of bits needed to represent the size of the object being shifted. When
|
|
this macro is nonzero, the compiler will assume that it is safe to omit
|
|
a sign-extend, zero-extend, and certain bitwise `and' instructions that
|
|
truncates the count of a shift operation. On machines that have
|
|
instructions that act on bit-fields at variable positions, which may
|
|
include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED}
|
|
also enables deletion of truncations of the values that serve as
|
|
arguments to bit-field instructions.
|
|
|
|
If both types of instructions truncate the count (for shifts) and
|
|
position (for bit-field operations), or if no variable-position bit-field
|
|
instructions exist, you should define this macro.
|
|
|
|
However, on some machines, such as the 80386 and the 680x0, truncation
|
|
only applies to shift operations and not the (real or pretended)
|
|
bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on
|
|
such machines. Instead, add patterns to the @file{md} file that include
|
|
the implied truncation of the shift instructions.
|
|
|
|
You need not define this macro if it would always have the value of zero.
|
|
@end defmac
|
|
|
|
@anchor{TARGET_SHIFT_TRUNCATION_MASK}
|
|
@deftypefn {Target Hook} {unsigned HOST_WIDE_INT} TARGET_SHIFT_TRUNCATION_MASK (machine_mode @var{mode})
|
|
This function describes how the standard shift patterns for @var{mode}
|
|
deal with shifts by negative amounts or by more than the width of the mode.
|
|
@xref{shift patterns}.
|
|
|
|
On many machines, the shift patterns will apply a mask @var{m} to the
|
|
shift count, meaning that a fixed-width shift of @var{x} by @var{y} is
|
|
equivalent to an arbitrary-width shift of @var{x} by @var{y & m}. If
|
|
this is true for mode @var{mode}, the function should return @var{m},
|
|
otherwise it should return 0. A return value of 0 indicates that no
|
|
particular behavior is guaranteed.
|
|
|
|
Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does
|
|
@emph{not} apply to general shift rtxes; it applies only to instructions
|
|
that are generated by the named shift patterns.
|
|
|
|
The default implementation of this function returns
|
|
@code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED}
|
|
and 0 otherwise. This definition is always safe, but if
|
|
@code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns
|
|
nevertheless truncate the shift count, you may get better code
|
|
by overriding it.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_TRULY_NOOP_TRUNCATION (poly_uint64 @var{outprec}, poly_uint64 @var{inprec})
|
|
This hook returns true if it is safe to ``convert'' a value of
|
|
@var{inprec} bits to one of @var{outprec} bits (where @var{outprec} is
|
|
smaller than @var{inprec}) by merely operating on it as if it had only
|
|
@var{outprec} bits. The default returns true unconditionally, which
|
|
is correct for most machines. When @code{TARGET_TRULY_NOOP_TRUNCATION}
|
|
returns false, the machine description should provide a @code{trunc}
|
|
optab to specify the RTL that performs the required truncation.
|
|
|
|
If @code{TARGET_MODES_TIEABLE_P} returns false for a pair of modes,
|
|
suboptimal code can result if this hook returns true for the corresponding
|
|
mode sizes. Making this hook return false in such cases may improve things.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_MODE_REP_EXTENDED (scalar_int_mode @var{mode}, scalar_int_mode @var{rep_mode})
|
|
The representation of an integral mode can be such that the values
|
|
are always extended to a wider integral mode. Return
|
|
@code{SIGN_EXTEND} if values of @var{mode} are represented in
|
|
sign-extended form to @var{rep_mode}. Return @code{UNKNOWN}
|
|
otherwise. (Currently, none of the targets use zero-extended
|
|
representation this way so unlike @code{LOAD_EXTEND_OP},
|
|
@code{TARGET_MODE_REP_EXTENDED} is expected to return either
|
|
@code{SIGN_EXTEND} or @code{UNKNOWN}. Also no target extends
|
|
@var{mode} to @var{rep_mode} so that @var{rep_mode} is not the next
|
|
widest integral mode and currently we take advantage of this fact.)
|
|
|
|
Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN}
|
|
value even if the extension is not performed on certain hard registers
|
|
as long as for the @code{REGNO_REG_CLASS} of these hard registers
|
|
@code{TARGET_CAN_CHANGE_MODE_CLASS} returns false.
|
|
|
|
Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP}
|
|
describe two related properties. If you define
|
|
@code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want
|
|
to define @code{LOAD_EXTEND_OP (mode)} to return the same type of
|
|
extension.
|
|
|
|
In order to enforce the representation of @code{mode},
|
|
@code{TARGET_TRULY_NOOP_TRUNCATION} should return false when truncating to
|
|
@code{mode}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_SETJMP_PRESERVES_NONVOLATILE_REGS_P (void)
|
|
On some targets, it is assumed that the compiler will spill all pseudos
|
|
that are live across a call to @code{setjmp}, while other targets treat
|
|
@code{setjmp} calls as normal function calls.
|
|
|
|
This hook returns false if @code{setjmp} calls do not preserve all
|
|
non-volatile registers so that gcc that must spill all pseudos that are
|
|
live across @code{setjmp} calls. Define this to return true if the
|
|
target does not need to spill all pseudos live across @code{setjmp} calls.
|
|
The default implementation conservatively assumes all pseudos must be
|
|
spilled across @code{setjmp} calls.
|
|
@end deftypefn
|
|
|
|
@defmac STORE_FLAG_VALUE
|
|
A C expression describing the value returned by a comparison operator
|
|
with an integral mode and stored by a store-flag instruction
|
|
(@samp{cstore@var{mode}4}) when the condition is true. This description must
|
|
apply to @emph{all} the @samp{cstore@var{mode}4} patterns and all the
|
|
comparison operators whose results have a @code{MODE_INT} mode.
|
|
|
|
A value of 1 or @minus{}1 means that the instruction implementing the
|
|
comparison operator returns exactly 1 or @minus{}1 when the comparison is true
|
|
and 0 when the comparison is false. Otherwise, the value indicates
|
|
which bits of the result are guaranteed to be 1 when the comparison is
|
|
true. This value is interpreted in the mode of the comparison
|
|
operation, which is given by the mode of the first operand in the
|
|
@samp{cstore@var{mode}4} pattern. Either the low bit or the sign bit of
|
|
@code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by
|
|
the compiler.
|
|
|
|
If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will
|
|
generate code that depends only on the specified bits. It can also
|
|
replace comparison operators with equivalent operations if they cause
|
|
the required bits to be set, even if the remaining bits are undefined.
|
|
For example, on a machine whose comparison operators return an
|
|
@code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as
|
|
@samp{0x80000000}, saying that just the sign bit is relevant, the
|
|
expression
|
|
|
|
@smallexample
|
|
(ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0))
|
|
@end smallexample
|
|
|
|
@noindent
|
|
can be converted to
|
|
|
|
@smallexample
|
|
(ashift:SI @var{x} (const_int @var{n}))
|
|
@end smallexample
|
|
|
|
@noindent
|
|
where @var{n} is the appropriate shift count to move the bit being
|
|
tested into the sign bit.
|
|
|
|
There is no way to describe a machine that always sets the low-order bit
|
|
for a true value, but does not guarantee the value of any other bits,
|
|
but we do not know of any machine that has such an instruction. If you
|
|
are trying to port GCC to such a machine, include an instruction to
|
|
perform a logical-and of the result with 1 in the pattern for the
|
|
comparison operators and let us know at @email{gcc@@gcc.gnu.org}.
|
|
|
|
Often, a machine will have multiple instructions that obtain a value
|
|
from a comparison (or the condition codes). Here are rules to guide the
|
|
choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions
|
|
to be used:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
Use the shortest sequence that yields a valid definition for
|
|
@code{STORE_FLAG_VALUE}. It is more efficient for the compiler to
|
|
``normalize'' the value (convert it to, e.g., 1 or 0) than for the
|
|
comparison operators to do so because there may be opportunities to
|
|
combine the normalization with other operations.
|
|
|
|
@item
|
|
For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being
|
|
slightly preferred on machines with expensive jumps and 1 preferred on
|
|
other machines.
|
|
|
|
@item
|
|
As a second choice, choose a value of @samp{0x80000001} if instructions
|
|
exist that set both the sign and low-order bits but do not define the
|
|
others.
|
|
|
|
@item
|
|
Otherwise, use a value of @samp{0x80000000}.
|
|
@end itemize
|
|
|
|
Many machines can produce both the value chosen for
|
|
@code{STORE_FLAG_VALUE} and its negation in the same number of
|
|
instructions. On those machines, you should also define a pattern for
|
|
those cases, e.g., one matching
|
|
|
|
@smallexample
|
|
(set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C})))
|
|
@end smallexample
|
|
|
|
Some machines can also perform @code{and} or @code{plus} operations on
|
|
condition code values with less instructions than the corresponding
|
|
@samp{cstore@var{mode}4} insn followed by @code{and} or @code{plus}. On those
|
|
machines, define the appropriate patterns. Use the names @code{incscc}
|
|
and @code{decscc}, respectively, for the patterns which perform
|
|
@code{plus} or @code{minus} operations on condition code values. See
|
|
@file{rs6000.md} for some examples. The GNU Superoptimizer can be used to
|
|
find such instruction sequences on other machines.
|
|
|
|
If this macro is not defined, the default value, 1, is used. You need
|
|
not define @code{STORE_FLAG_VALUE} if the machine has no store-flag
|
|
instructions, or if the value generated by these instructions is 1.
|
|
@end defmac
|
|
|
|
@defmac FLOAT_STORE_FLAG_VALUE (@var{mode})
|
|
A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is
|
|
returned when comparison operators with floating-point results are true.
|
|
Define this macro on machines that have comparison operations that return
|
|
floating-point values. If there are no such operations, do not define
|
|
this macro.
|
|
@end defmac
|
|
|
|
@defmac VECTOR_STORE_FLAG_VALUE (@var{mode})
|
|
A C expression that gives an rtx representing the nonzero true element
|
|
for vector comparisons. The returned rtx should be valid for the inner
|
|
mode of @var{mode} which is guaranteed to be a vector mode. Define
|
|
this macro on machines that have vector comparison operations that
|
|
return a vector result. If there are no such operations, do not define
|
|
this macro. Typically, this macro is defined as @code{const1_rtx} or
|
|
@code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent
|
|
the compiler optimizing such vector comparison operations for the
|
|
given mode.
|
|
@end defmac
|
|
|
|
@defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
|
|
@defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value})
|
|
A C expression that indicates whether the architecture defines a value
|
|
for @code{clz} or @code{ctz} with a zero operand.
|
|
A result of @code{0} indicates the value is undefined.
|
|
If the value is defined for only the RTL expression, the macro should
|
|
evaluate to @code{1}; if the value applies also to the corresponding optab
|
|
entry (which is normally the case if it expands directly into
|
|
the corresponding RTL), then the macro should evaluate to @code{2}.
|
|
In the cases where the value is defined, @var{value} should be set to
|
|
this value.
|
|
|
|
If this macro is not defined, the value of @code{clz} or
|
|
@code{ctz} at zero is assumed to be undefined.
|
|
|
|
This macro must be defined if the target's expansion for @code{ffs}
|
|
relies on a particular value to get correct results. Otherwise it
|
|
is not necessary, though it may be used to optimize some corner cases, and
|
|
to provide a default expansion for the @code{ffs} optab.
|
|
|
|
Note that regardless of this macro the ``definedness'' of @code{clz}
|
|
and @code{ctz} at zero do @emph{not} extend to the builtin functions
|
|
visible to the user. Thus one may be free to adjust the value at will
|
|
to match the target expansion of these operations without fear of
|
|
breaking the API@.
|
|
@end defmac
|
|
|
|
@defmac Pmode
|
|
An alias for the machine mode for pointers. On most machines, define
|
|
this to be the integer mode corresponding to the width of a hardware
|
|
pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines.
|
|
On some machines you must define this to be one of the partial integer
|
|
modes, such as @code{PSImode}.
|
|
|
|
The width of @code{Pmode} must be at least as large as the value of
|
|
@code{POINTER_SIZE}. If it is not equal, you must define the macro
|
|
@code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended
|
|
to @code{Pmode}.
|
|
@end defmac
|
|
|
|
@defmac FUNCTION_MODE
|
|
An alias for the machine mode used for memory references to functions
|
|
being called, in @code{call} RTL expressions. On most CISC machines,
|
|
where an instruction can begin at any byte address, this should be
|
|
@code{QImode}. On most RISC machines, where all instructions have fixed
|
|
size and alignment, this should be a mode with the same size and alignment
|
|
as the machine instruction words - typically @code{SImode} or @code{HImode}.
|
|
@end defmac
|
|
|
|
@defmac STDC_0_IN_SYSTEM_HEADERS
|
|
In normal operation, the preprocessor expands @code{__STDC__} to the
|
|
constant 1, to signify that GCC conforms to ISO Standard C@. On some
|
|
hosts, like Solaris, the system compiler uses a different convention,
|
|
where @code{__STDC__} is normally 0, but is 1 if the user specifies
|
|
strict conformance to the C Standard.
|
|
|
|
Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host
|
|
convention when processing system header files, but when processing user
|
|
files @code{__STDC__} will always expand to 1.
|
|
@end defmac
|
|
|
|
@deftypefn {C Target Hook} {const char *} TARGET_C_PREINCLUDE (void)
|
|
Define this hook to return the name of a header file to be included at
|
|
the start of all compilations, as if it had been included with
|
|
@code{#include <@var{file}>}. If this hook returns @code{NULL}, or is
|
|
not defined, or the header is not found, or if the user specifies
|
|
@option{-ffreestanding} or @option{-nostdinc}, no header is included.
|
|
|
|
This hook can be used together with a header provided by the system C
|
|
library to implement ISO C requirements for certain macros to be
|
|
predefined that describe properties of the whole implementation rather
|
|
than just the compiler.
|
|
@end deftypefn
|
|
|
|
@deftypefn {C Target Hook} bool TARGET_CXX_IMPLICIT_EXTERN_C (const char*@var{})
|
|
Define this hook to add target-specific C++ implicit extern C functions.
|
|
If this function returns true for the name of a file-scope function, that
|
|
function implicitly gets extern "C" linkage rather than whatever language
|
|
linkage the declaration would normally have. An example of such function
|
|
is WinMain on Win32 targets.
|
|
@end deftypefn
|
|
|
|
@defmac SYSTEM_IMPLICIT_EXTERN_C
|
|
Define this macro if the system header files do not support C++@.
|
|
This macro handles system header files by pretending that system
|
|
header files are enclosed in @samp{extern "C" @{@dots{}@}}.
|
|
@end defmac
|
|
|
|
@findex #pragma
|
|
@findex pragma
|
|
@defmac REGISTER_TARGET_PRAGMAS ()
|
|
Define this macro if you want to implement any target-specific pragmas.
|
|
If defined, it is a C expression which makes a series of calls to
|
|
@code{c_register_pragma} or @code{c_register_pragma_with_expansion}
|
|
for each pragma. The macro may also do any
|
|
setup required for the pragmas.
|
|
|
|
The primary reason to define this macro is to provide compatibility with
|
|
other compilers for the same target. In general, we discourage
|
|
definition of target-specific pragmas for GCC@.
|
|
|
|
If the pragma can be implemented by attributes then you should consider
|
|
defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well.
|
|
|
|
Preprocessor macros that appear on pragma lines are not expanded. All
|
|
@samp{#pragma} directives that do not match any registered pragma are
|
|
silently ignored, unless the user specifies @option{-Wunknown-pragmas}.
|
|
@end defmac
|
|
|
|
@deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
|
|
@deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *))
|
|
|
|
Each call to @code{c_register_pragma} or
|
|
@code{c_register_pragma_with_expansion} establishes one pragma. The
|
|
@var{callback} routine will be called when the preprocessor encounters a
|
|
pragma of the form
|
|
|
|
@smallexample
|
|
#pragma [@var{space}] @var{name} @dots{}
|
|
@end smallexample
|
|
|
|
@var{space} is the case-sensitive namespace of the pragma, or
|
|
@code{NULL} to put the pragma in the global namespace. The callback
|
|
routine receives @var{pfile} as its first argument, which can be passed
|
|
on to cpplib's functions if necessary. You can lex tokens after the
|
|
@var{name} by calling @code{pragma_lex}. Tokens that are not read by the
|
|
callback will be silently ignored. The end of the line is indicated by
|
|
a token of type @code{CPP_EOF}. Macro expansion occurs on the
|
|
arguments of pragmas registered with
|
|
@code{c_register_pragma_with_expansion} but not on the arguments of
|
|
pragmas registered with @code{c_register_pragma}.
|
|
|
|
Note that the use of @code{pragma_lex} is specific to the C and C++
|
|
compilers. It will not work in the Java or Fortran compilers, or any
|
|
other language compilers for that matter. Thus if @code{pragma_lex} is going
|
|
to be called from target-specific code, it must only be done so when
|
|
building the C and C++ compilers. This can be done by defining the
|
|
variables @code{c_target_objs} and @code{cxx_target_objs} in the
|
|
target entry in the @file{config.gcc} file. These variables should name
|
|
the target-specific, language-specific object file which contains the
|
|
code that uses @code{pragma_lex}. Note it will also be necessary to add a
|
|
rule to the makefile fragment pointed to by @code{tmake_file} that shows
|
|
how to build this object file.
|
|
@end deftypefun
|
|
|
|
@defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION
|
|
Define this macro if macros should be expanded in the
|
|
arguments of @samp{#pragma pack}.
|
|
@end defmac
|
|
|
|
@defmac TARGET_DEFAULT_PACK_STRUCT
|
|
If your target requires a structure packing default other than 0 (meaning
|
|
the machine default), define this macro to the necessary value (in bytes).
|
|
This must be a value that would also be valid to use with
|
|
@samp{#pragma pack()} (that is, a small power of two).
|
|
@end defmac
|
|
|
|
@defmac DOLLARS_IN_IDENTIFIERS
|
|
Define this macro to control use of the character @samp{$} in
|
|
identifier names for the C family of languages. 0 means @samp{$} is
|
|
not allowed by default; 1 means it is allowed. 1 is the default;
|
|
there is no need to define this macro in that case.
|
|
@end defmac
|
|
|
|
@defmac INSN_SETS_ARE_DELAYED (@var{insn})
|
|
Define this macro as a C expression that is nonzero if it is safe for the
|
|
delay slot scheduler to place instructions in the delay slot of @var{insn},
|
|
even if they appear to use a resource set or clobbered in @var{insn}.
|
|
@var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that
|
|
every @code{call_insn} has this behavior. On machines where some @code{insn}
|
|
or @code{jump_insn} is really a function call and hence has this behavior,
|
|
you should define this macro.
|
|
|
|
You need not define this macro if it would always return zero.
|
|
@end defmac
|
|
|
|
@defmac INSN_REFERENCES_ARE_DELAYED (@var{insn})
|
|
Define this macro as a C expression that is nonzero if it is safe for the
|
|
delay slot scheduler to place instructions in the delay slot of @var{insn},
|
|
even if they appear to set or clobber a resource referenced in @var{insn}.
|
|
@var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where
|
|
some @code{insn} or @code{jump_insn} is really a function call and its operands
|
|
are registers whose use is actually in the subroutine it calls, you should
|
|
define this macro. Doing so allows the delay slot scheduler to move
|
|
instructions which copy arguments into the argument registers into the delay
|
|
slot of @var{insn}.
|
|
|
|
You need not define this macro if it would always return zero.
|
|
@end defmac
|
|
|
|
@defmac MULTIPLE_SYMBOL_SPACES
|
|
Define this macro as a C expression that is nonzero if, in some cases,
|
|
global symbols from one translation unit may not be bound to undefined
|
|
symbols in another translation unit without user intervention. For
|
|
instance, under Microsoft Windows symbols must be explicitly imported
|
|
from shared libraries (DLLs).
|
|
|
|
You need not define this macro if it would always evaluate to zero.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} {rtx_insn *} TARGET_MD_ASM_ADJUST (vec<rtx>& @var{outputs}, vec<rtx>& @var{inputs}, vec<machine_mode>& @var{input_modes}, vec<const char *>& @var{constraints}, vec<rtx>& @var{clobbers}, HARD_REG_SET& @var{clobbered_regs}, location_t @var{loc})
|
|
This target hook may add @dfn{clobbers} to @var{clobbers} and
|
|
@var{clobbered_regs} for any hard regs the port wishes to automatically
|
|
clobber for an asm. The @var{outputs} and @var{inputs} may be inspected
|
|
to avoid clobbering a register that is already used by the asm. @var{loc}
|
|
is the source location of the asm.
|
|
|
|
It may modify the @var{outputs}, @var{inputs}, @var{input_modes}, and
|
|
@var{constraints} as necessary for other pre-processing. In this case the
|
|
return value is a sequence of insns to emit after the asm. Note that
|
|
changes to @var{inputs} must be accompanied by the corresponding changes
|
|
to @var{input_modes}.
|
|
@end deftypefn
|
|
|
|
@defmac MATH_LIBRARY
|
|
Define this macro as a C string constant for the linker argument to link
|
|
in the system math library, minus the initial @samp{"-l"}, or
|
|
@samp{""} if the target does not have a
|
|
separate math library.
|
|
|
|
You need only define this macro if the default of @samp{"m"} is wrong.
|
|
@end defmac
|
|
|
|
@defmac LIBRARY_PATH_ENV
|
|
Define this macro as a C string constant for the environment variable that
|
|
specifies where the linker should look for libraries.
|
|
|
|
You need only define this macro if the default of @samp{"LIBRARY_PATH"}
|
|
is wrong.
|
|
@end defmac
|
|
|
|
@defmac TARGET_POSIX_IO
|
|
Define this macro if the target supports the following POSIX@ file
|
|
functions, access, mkdir and file locking with fcntl / F_SETLKW@.
|
|
Defining @code{TARGET_POSIX_IO} will enable the test coverage code
|
|
to use file locking when exiting a program, which avoids race conditions
|
|
if the program has forked. It will also create directories at run-time
|
|
for cross-profiling.
|
|
@end defmac
|
|
|
|
@defmac MAX_CONDITIONAL_EXECUTE
|
|
|
|
A C expression for the maximum number of instructions to execute via
|
|
conditional execution instructions instead of a branch. A value of
|
|
@code{BRANCH_COST}+1 is the default.
|
|
@end defmac
|
|
|
|
@defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr})
|
|
Used if the target needs to perform machine-dependent modifications on the
|
|
conditionals used for turning basic blocks into conditionally executed code.
|
|
@var{ce_info} points to a data structure, @code{struct ce_if_block}, which
|
|
contains information about the currently processed blocks. @var{true_expr}
|
|
and @var{false_expr} are the tests that are used for converting the
|
|
then-block and the else-block, respectively. Set either @var{true_expr} or
|
|
@var{false_expr} to a null pointer if the tests cannot be converted.
|
|
@end defmac
|
|
|
|
@defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr})
|
|
Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated
|
|
if-statements into conditions combined by @code{and} and @code{or} operations.
|
|
@var{bb} contains the basic block that contains the test that is currently
|
|
being processed and about to be turned into a condition.
|
|
@end defmac
|
|
|
|
@defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn})
|
|
A C expression to modify the @var{PATTERN} of an @var{INSN} that is to
|
|
be converted to conditional execution format. @var{ce_info} points to
|
|
a data structure, @code{struct ce_if_block}, which contains information
|
|
about the currently processed blocks.
|
|
@end defmac
|
|
|
|
@defmac IFCVT_MODIFY_FINAL (@var{ce_info})
|
|
A C expression to perform any final machine dependent modifications in
|
|
converting code to conditional execution. The involved basic blocks
|
|
can be found in the @code{struct ce_if_block} structure that is pointed
|
|
to by @var{ce_info}.
|
|
@end defmac
|
|
|
|
@defmac IFCVT_MODIFY_CANCEL (@var{ce_info})
|
|
A C expression to cancel any machine dependent modifications in
|
|
converting code to conditional execution. The involved basic blocks
|
|
can be found in the @code{struct ce_if_block} structure that is pointed
|
|
to by @var{ce_info}.
|
|
@end defmac
|
|
|
|
@defmac IFCVT_MACHDEP_INIT (@var{ce_info})
|
|
A C expression to initialize any machine specific data for if-conversion
|
|
of the if-block in the @code{struct ce_if_block} structure that is pointed
|
|
to by @var{ce_info}.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG (void)
|
|
If non-null, this hook performs a target-specific pass over the
|
|
instruction stream. The compiler will run it at all optimization levels,
|
|
just before the point at which it normally does delayed-branch scheduling.
|
|
|
|
The exact purpose of the hook varies from target to target. Some use
|
|
it to do transformations that are necessary for correctness, such as
|
|
laying out in-function constant pools or avoiding hardware hazards.
|
|
Others use it as an opportunity to do some machine-dependent optimizations.
|
|
|
|
You need not implement the hook if it has nothing to do. The default
|
|
definition is null.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_INIT_BUILTINS (void)
|
|
Define this hook if you have any machine-specific built-in functions
|
|
that need to be defined. It should be a function that performs the
|
|
necessary setup.
|
|
|
|
Machine specific built-in functions can be useful to expand special machine
|
|
instructions that would otherwise not normally be generated because
|
|
they have no equivalent in the source language (for example, SIMD vector
|
|
instructions or prefetch instructions).
|
|
|
|
To create a built-in function, call the function
|
|
@code{lang_hooks.builtin_function}
|
|
which is defined by the language front end. You can use any type nodes set
|
|
up by @code{build_common_tree_nodes};
|
|
only language front ends that use those two functions will call
|
|
@samp{TARGET_INIT_BUILTINS}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_BUILTIN_DECL (unsigned @var{code}, bool @var{initialize_p})
|
|
Define this hook if you have any machine-specific built-in functions
|
|
that need to be defined. It should be a function that returns the
|
|
builtin function declaration for the builtin function code @var{code}.
|
|
If there is no such builtin and it cannot be initialized at this time
|
|
if @var{initialize_p} is true the function should return @code{NULL_TREE}.
|
|
If @var{code} is out of range the function should return
|
|
@code{error_mark_node}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, machine_mode @var{mode}, int @var{ignore})
|
|
|
|
Expand a call to a machine specific built-in function that was set up by
|
|
@samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the
|
|
function call; the result should go to @var{target} if that is
|
|
convenient, and have mode @var{mode} if that is convenient.
|
|
@var{subtarget} may be used as the target for computing one of
|
|
@var{exp}'s operands. @var{ignore} is nonzero if the value is to be
|
|
ignored. This function should return the result of the call to the
|
|
built-in function.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_RESOLVE_OVERLOADED_BUILTIN (unsigned int @var{loc}, tree @var{fndecl}, void *@var{arglist})
|
|
Select a replacement for a machine specific built-in function that
|
|
was set up by @samp{TARGET_INIT_BUILTINS}. This is done
|
|
@emph{before} regular type checking, and so allows the target to
|
|
implement a crude form of function overloading. @var{fndecl} is the
|
|
declaration of the built-in function. @var{arglist} is the list of
|
|
arguments passed to the built-in function. The result is a
|
|
complete expression that implements the operation, usually
|
|
another @code{CALL_EXPR}.
|
|
@var{arglist} really has type @samp{VEC(tree,gc)*}
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CHECK_BUILTIN_CALL (location_t @var{loc}, vec<location_t> @var{arg_loc}, tree @var{fndecl}, tree @var{orig_fndecl}, unsigned int @var{nargs}, tree *@var{args})
|
|
Perform semantic checking on a call to a machine-specific built-in
|
|
function after its arguments have been constrained to the function
|
|
signature. Return true if the call is valid, otherwise report an error
|
|
and return false.
|
|
|
|
This hook is called after @code{TARGET_RESOLVE_OVERLOADED_BUILTIN}.
|
|
The call was originally to built-in function @var{orig_fndecl},
|
|
but after the optional @code{TARGET_RESOLVE_OVERLOADED_BUILTIN}
|
|
step is now to built-in function @var{fndecl}. @var{loc} is the
|
|
location of the call and @var{args} is an array of function arguments,
|
|
of which there are @var{nargs}. @var{arg_loc} specifies the location
|
|
of each argument.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_FOLD_BUILTIN (tree @var{fndecl}, int @var{n_args}, tree *@var{argp}, bool @var{ignore})
|
|
Fold a call to a machine specific built-in function that was set up by
|
|
@samp{TARGET_INIT_BUILTINS}. @var{fndecl} is the declaration of the
|
|
built-in function. @var{n_args} is the number of arguments passed to
|
|
the function; the arguments themselves are pointed to by @var{argp}.
|
|
The result is another tree, valid for both GIMPLE and GENERIC,
|
|
containing a simplified expression for the call's result. If
|
|
@var{ignore} is true the value will be ignored.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_GIMPLE_FOLD_BUILTIN (gimple_stmt_iterator *@var{gsi})
|
|
Fold a call to a machine specific built-in function that was set up
|
|
by @samp{TARGET_INIT_BUILTINS}. @var{gsi} points to the gimple
|
|
statement holding the function call. Returns true if any change
|
|
was made to the GIMPLE stream.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_COMPARE_VERSION_PRIORITY (tree @var{decl1}, tree @var{decl2})
|
|
This hook is used to compare the target attributes in two functions to
|
|
determine which function's features get higher priority. This is used
|
|
during function multi-versioning to figure out the order in which two
|
|
versions must be dispatched. A function version with a higher priority
|
|
is checked for dispatching earlier. @var{decl1} and @var{decl2} are
|
|
the two function decls that will be compared.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_GET_FUNCTION_VERSIONS_DISPATCHER (void *@var{decl})
|
|
This hook is used to get the dispatcher function for a set of function
|
|
versions. The dispatcher function is called to invoke the right function
|
|
version at run-time. @var{decl} is one version from a set of semantically
|
|
identical versions.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_GENERATE_VERSION_DISPATCHER_BODY (void *@var{arg})
|
|
This hook is used to generate the dispatcher logic to invoke the right
|
|
function version at run-time for a given set of function versions.
|
|
@var{arg} points to the callgraph node of the dispatcher function whose
|
|
body must be generated.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_PREDICT_DOLOOP_P (class loop *@var{loop})
|
|
Return true if we can predict it is possible to use a low-overhead loop
|
|
for a particular loop. The parameter @var{loop} is a pointer to the loop.
|
|
This target hook is required only when the target supports low-overhead
|
|
loops, and will help ivopts to make some decisions.
|
|
The default version of this hook returns false.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_HAVE_COUNT_REG_DECR_P
|
|
Return true if the target supports hardware count register for decrement
|
|
and branch.
|
|
The default value is false.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} int64_t TARGET_DOLOOP_COST_FOR_GENERIC
|
|
One IV candidate dedicated for doloop is introduced in IVOPTs, we can
|
|
calculate the computation cost of adopting it to any generic IV use by
|
|
function get_computation_cost as before. But for targets which have
|
|
hardware count register support for decrement and branch, it may have to
|
|
move IV value from hardware count register to general purpose register
|
|
while doloop IV candidate is used for generic IV uses. It probably takes
|
|
expensive penalty. This hook allows target owners to define the cost for
|
|
this especially for generic IV uses.
|
|
The default value is zero.
|
|
@end deftypevr
|
|
|
|
@deftypevr {Target Hook} int64_t TARGET_DOLOOP_COST_FOR_ADDRESS
|
|
One IV candidate dedicated for doloop is introduced in IVOPTs, we can
|
|
calculate the computation cost of adopting it to any address IV use by
|
|
function get_computation_cost as before. But for targets which have
|
|
hardware count register support for decrement and branch, it may have to
|
|
move IV value from hardware count register to general purpose register
|
|
while doloop IV candidate is used for address IV uses. It probably takes
|
|
expensive penalty. This hook allows target owners to define the cost for
|
|
this escpecially for address IV uses.
|
|
The default value is zero.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CAN_USE_DOLOOP_P (const widest_int @var{&iterations}, const widest_int @var{&iterations_max}, unsigned int @var{loop_depth}, bool @var{entered_at_top})
|
|
Return true if it is possible to use low-overhead loops (@code{doloop_end}
|
|
and @code{doloop_begin}) for a particular loop. @var{iterations} gives the
|
|
exact number of iterations, or 0 if not known. @var{iterations_max} gives
|
|
the maximum number of iterations, or 0 if not known. @var{loop_depth} is
|
|
the nesting depth of the loop, with 1 for innermost loops, 2 for loops that
|
|
contain innermost loops, and so on. @var{entered_at_top} is true if the
|
|
loop is only entered from the top.
|
|
|
|
This hook is only used if @code{doloop_end} is available. The default
|
|
implementation returns true. You can use @code{can_use_doloop_if_innermost}
|
|
if the loop must be the innermost, and if there are no other restrictions.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_INVALID_WITHIN_DOLOOP (const rtx_insn *@var{insn})
|
|
|
|
Take an instruction in @var{insn} and return NULL if it is valid within a
|
|
low-overhead loop, otherwise return a string explaining why doloop
|
|
could not be applied.
|
|
|
|
Many targets use special registers for low-overhead looping. For any
|
|
instruction that clobbers these this function should return a string indicating
|
|
the reason why the doloop could not be applied.
|
|
By default, the RTL loop optimizer does not use a present doloop pattern for
|
|
loops containing function calls or branch on table instructions.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} machine_mode TARGET_PREFERRED_DOLOOP_MODE (machine_mode @var{mode})
|
|
This hook takes a @var{mode} for a doloop IV, where @code{mode} is the
|
|
original mode for the operation. If the target prefers an alternate
|
|
@code{mode} for the operation, then this hook should return that mode;
|
|
otherwise the original @code{mode} should be returned. For example, on a
|
|
64-bit target, @code{DImode} might be preferred over @code{SImode}. Both the
|
|
original and the returned modes should be @code{MODE_INT}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_LEGITIMATE_COMBINED_INSN (rtx_insn *@var{insn})
|
|
Take an instruction in @var{insn} and return @code{false} if the instruction
|
|
is not appropriate as a combination of two or more instructions. The
|
|
default is to accept all instructions.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CAN_FOLLOW_JUMP (const rtx_insn *@var{follower}, const rtx_insn *@var{followee})
|
|
FOLLOWER and FOLLOWEE are JUMP_INSN instructions;
|
|
return true if FOLLOWER may be modified to follow FOLLOWEE;
|
|
false, if it can't.
|
|
For example, on some targets, certain kinds of branches can't be made to
|
|
follow through a hot/cold partitioning.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_COMMUTATIVE_P (const_rtx @var{x}, int @var{outer_code})
|
|
This target hook returns @code{true} if @var{x} is considered to be commutative.
|
|
Usually, this is just COMMUTATIVE_P (@var{x}), but the HP PA doesn't consider
|
|
PLUS to be commutative inside a MEM@. @var{outer_code} is the rtx code
|
|
of the enclosing rtl, if known, otherwise it is UNKNOWN.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_ALLOCATE_INITIAL_VALUE (rtx @var{hard_reg})
|
|
|
|
When the initial value of a hard register has been copied in a pseudo
|
|
register, it is often not necessary to actually allocate another register
|
|
to this pseudo register, because the original hard register or a stack slot
|
|
it has been saved into can be used. @code{TARGET_ALLOCATE_INITIAL_VALUE}
|
|
is called at the start of register allocation once for each hard register
|
|
that had its initial value copied by using
|
|
@code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}.
|
|
Possible values are @code{NULL_RTX}, if you don't want
|
|
to do any special allocation, a @code{REG} rtx---that would typically be
|
|
the hard register itself, if it is known not to be clobbered---or a
|
|
@code{MEM}.
|
|
If you are returning a @code{MEM}, this is only a hint for the allocator;
|
|
it might decide to use another register anyways.
|
|
You may use @code{current_function_is_leaf} or
|
|
@code{REG_N_SETS} in the hook to determine if the hard
|
|
register in question will not be clobbered.
|
|
The default value of this hook is @code{NULL}, which disables any special
|
|
allocation.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} int TARGET_UNSPEC_MAY_TRAP_P (const_rtx @var{x}, unsigned @var{flags})
|
|
This target hook returns nonzero if @var{x}, an @code{unspec} or
|
|
@code{unspec_volatile} operation, might cause a trap. Targets can use
|
|
this hook to enhance precision of analysis for @code{unspec} and
|
|
@code{unspec_volatile} operations. You may call @code{may_trap_p_1}
|
|
to analyze inner elements of @var{x} in which case @var{flags} should be
|
|
passed along.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_SET_CURRENT_FUNCTION (tree @var{decl})
|
|
The compiler invokes this hook whenever it changes its current function
|
|
context (@code{cfun}). You can define this function if
|
|
the back end needs to perform any initialization or reset actions on a
|
|
per-function basis. For example, it may be used to implement function
|
|
attributes that affect register usage or code generation patterns.
|
|
The argument @var{decl} is the declaration for the new function context,
|
|
and may be null to indicate that the compiler has left a function context
|
|
and is returning to processing at the top level.
|
|
The default hook function does nothing.
|
|
|
|
GCC sets @code{cfun} to a dummy function context during initialization of
|
|
some parts of the back end. The hook function is not invoked in this
|
|
situation; you need not worry about the hook being invoked recursively,
|
|
or when the back end is in a partially-initialized state.
|
|
@code{cfun} might be @code{NULL} to indicate processing at top level,
|
|
outside of any function scope.
|
|
@end deftypefn
|
|
|
|
@defmac TARGET_OBJECT_SUFFIX
|
|
Define this macro to be a C string representing the suffix for object
|
|
files on your target machine. If you do not define this macro, GCC will
|
|
use @samp{.o} as the suffix for object files.
|
|
@end defmac
|
|
|
|
@defmac TARGET_EXECUTABLE_SUFFIX
|
|
Define this macro to be a C string representing the suffix to be
|
|
automatically added to executable files on your target machine. If you
|
|
do not define this macro, GCC will use the null string as the suffix for
|
|
executable files.
|
|
@end defmac
|
|
|
|
@defmac COLLECT_EXPORT_LIST
|
|
If defined, @code{collect2} will scan the individual object files
|
|
specified on its command line and create an export list for the linker.
|
|
Define this macro for systems like AIX, where the linker discards
|
|
object files that are not referenced from @code{main} and uses export
|
|
lists.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void)
|
|
This target hook returns @code{true} past the point in which new jump
|
|
instructions could be created. On machines that require a register for
|
|
every jump such as the SHmedia ISA of SH5, this point would typically be
|
|
reload, so this target hook should be defined to a function such as:
|
|
|
|
@smallexample
|
|
static bool
|
|
cannot_modify_jumps_past_reload_p ()
|
|
@{
|
|
return (reload_completed || reload_in_progress);
|
|
@}
|
|
@end smallexample
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_HAVE_CONDITIONAL_EXECUTION (void)
|
|
This target hook returns true if the target supports conditional execution.
|
|
This target hook is required only when the target has several different
|
|
modes and they have different conditional execution capability, such as ARM.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_GEN_CCMP_FIRST (rtx_insn **@var{prep_seq}, rtx_insn **@var{gen_seq}, int @var{code}, tree @var{op0}, tree @var{op1})
|
|
This function prepares to emit a comparison insn for the first compare in a
|
|
sequence of conditional comparisions. It returns an appropriate comparison
|
|
with @code{CC} for passing to @code{gen_ccmp_next} or @code{cbranch_optab}.
|
|
The insns to prepare the compare are saved in @var{prep_seq} and the compare
|
|
insns are saved in @var{gen_seq}. They will be emitted when all the
|
|
compares in the conditional comparision are generated without error.
|
|
@var{code} is the @code{rtx_code} of the compare for @var{op0} and @var{op1}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_GEN_CCMP_NEXT (rtx_insn **@var{prep_seq}, rtx_insn **@var{gen_seq}, rtx @var{prev}, int @var{cmp_code}, tree @var{op0}, tree @var{op1}, int @var{bit_code})
|
|
This function prepares to emit a conditional comparison within a sequence
|
|
of conditional comparisons. It returns an appropriate comparison with
|
|
@code{CC} for passing to @code{gen_ccmp_next} or @code{cbranch_optab}.
|
|
The insns to prepare the compare are saved in @var{prep_seq} and the compare
|
|
insns are saved in @var{gen_seq}. They will be emitted when all the
|
|
compares in the conditional comparision are generated without error. The
|
|
@var{prev} expression is the result of a prior call to @code{gen_ccmp_first}
|
|
or @code{gen_ccmp_next}. It may return @code{NULL} if the combination of
|
|
@var{prev} and this comparison is not supported, otherwise the result must
|
|
be appropriate for passing to @code{gen_ccmp_next} or @code{cbranch_optab}.
|
|
@var{code} is the @code{rtx_code} of the compare for @var{op0} and @var{op1}.
|
|
@var{bit_code} is @code{AND} or @code{IOR}, which is the op on the compares.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_GEN_MEMSET_SCRATCH_RTX (machine_mode @var{mode})
|
|
This hook should return an rtx for a scratch register in @var{mode} to
|
|
be used when expanding memset calls. The backend can use a hard scratch
|
|
register to avoid stack realignment when expanding memset. The default
|
|
is @code{gen_reg_rtx}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} unsigned TARGET_LOOP_UNROLL_ADJUST (unsigned @var{nunroll}, class loop *@var{loop})
|
|
This target hook returns a new value for the number of times @var{loop}
|
|
should be unrolled. The parameter @var{nunroll} is the number of times
|
|
the loop is to be unrolled. The parameter @var{loop} is a pointer to
|
|
the loop, which is going to be checked for unrolling. This target hook
|
|
is required only when the target has special constraints like maximum
|
|
number of memory accesses.
|
|
@end deftypefn
|
|
|
|
@defmac POWI_MAX_MULTS
|
|
If defined, this macro is interpreted as a signed integer C expression
|
|
that specifies the maximum number of floating point multiplications
|
|
that should be emitted when expanding exponentiation by an integer
|
|
constant inline. When this value is defined, exponentiation requiring
|
|
more than this number of multiplications is implemented by calling the
|
|
system library's @code{pow}, @code{powf} or @code{powl} routines.
|
|
The default value places no upper bound on the multiplication count.
|
|
@end defmac
|
|
|
|
@deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
|
|
This target hook should register any extra include files for the
|
|
target. The parameter @var{stdinc} indicates if normal include files
|
|
are present. The parameter @var{sysroot} is the system root directory.
|
|
The parameter @var{iprefix} is the prefix for the gcc directory.
|
|
@end deftypefn
|
|
|
|
@deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc})
|
|
This target hook should register any extra include files for the
|
|
target before any standard headers. The parameter @var{stdinc}
|
|
indicates if normal include files are present. The parameter
|
|
@var{sysroot} is the system root directory. The parameter
|
|
@var{iprefix} is the prefix for the gcc directory.
|
|
@end deftypefn
|
|
|
|
@deftypefn Macro void TARGET_OPTF (char *@var{path})
|
|
This target hook should register special include paths for the target.
|
|
The parameter @var{path} is the include to register. On Darwin
|
|
systems, this is used for Framework includes, which have semantics
|
|
that are different from @option{-I}.
|
|
@end deftypefn
|
|
|
|
@defmac bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl})
|
|
This target macro returns @code{true} if it is safe to use a local alias
|
|
for a virtual function @var{fndecl} when constructing thunks,
|
|
@code{false} otherwise. By default, the macro returns @code{true} for all
|
|
functions, if a target supports aliases (i.e.@: defines
|
|
@code{ASM_OUTPUT_DEF}), @code{false} otherwise,
|
|
@end defmac
|
|
|
|
@defmac TARGET_FORMAT_TYPES
|
|
If defined, this macro is the name of a global variable containing
|
|
target-specific format checking information for the @option{-Wformat}
|
|
option. The default is to have no target-specific format checks.
|
|
@end defmac
|
|
|
|
@defmac TARGET_N_FORMAT_TYPES
|
|
If defined, this macro is the number of entries in
|
|
@code{TARGET_FORMAT_TYPES}.
|
|
@end defmac
|
|
|
|
@defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES
|
|
If defined, this macro is the name of a global variable containing
|
|
target-specific format overrides for the @option{-Wformat} option. The
|
|
default is to have no target-specific format overrides. If defined,
|
|
@code{TARGET_FORMAT_TYPES} must be defined, too.
|
|
@end defmac
|
|
|
|
@defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT
|
|
If defined, this macro specifies the number of entries in
|
|
@code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES}.
|
|
@end defmac
|
|
|
|
@defmac TARGET_OVERRIDES_FORMAT_INIT
|
|
If defined, this macro specifies the optional initialization
|
|
routine for target specific customizations of the system printf
|
|
and scanf formatter settings.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN (const_tree @var{typelist}, const_tree @var{funcdecl}, const_tree @var{val})
|
|
If defined, this macro returns the diagnostic message when it is
|
|
illegal to pass argument @var{val} to function @var{funcdecl}
|
|
with prototype @var{typelist}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_INVALID_CONVERSION (const_tree @var{fromtype}, const_tree @var{totype})
|
|
If defined, this macro returns the diagnostic message when it is
|
|
invalid to convert from @var{fromtype} to @var{totype}, or @code{NULL}
|
|
if validity should be determined by the front end.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_INVALID_UNARY_OP (int @var{op}, const_tree @var{type})
|
|
If defined, this macro returns the diagnostic message when it is
|
|
invalid to apply operation @var{op} (where unary plus is denoted by
|
|
@code{CONVERT_EXPR}) to an operand of type @var{type}, or @code{NULL}
|
|
if validity should be determined by the front end.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {const char *} TARGET_INVALID_BINARY_OP (int @var{op}, const_tree @var{type1}, const_tree @var{type2})
|
|
If defined, this macro returns the diagnostic message when it is
|
|
invalid to apply operation @var{op} to operands of types @var{type1}
|
|
and @var{type2}, or @code{NULL} if validity should be determined by
|
|
the front end.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_PROMOTED_TYPE (const_tree @var{type})
|
|
If defined, this target hook returns the type to which values of
|
|
@var{type} should be promoted when they appear in expressions,
|
|
analogous to the integer promotions, or @code{NULL_TREE} to use the
|
|
front end's normal promotion rules. This hook is useful when there are
|
|
target-specific types with special promotion rules.
|
|
This is currently used only by the C and C++ front ends.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} tree TARGET_CONVERT_TO_TYPE (tree @var{type}, tree @var{expr})
|
|
If defined, this hook returns the result of converting @var{expr} to
|
|
@var{type}. It should return the converted expression,
|
|
or @code{NULL_TREE} to apply the front end's normal conversion rules.
|
|
This hook is useful when there are target-specific types with special
|
|
conversion rules.
|
|
This is currently used only by the C and C++ front ends.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_VERIFY_TYPE_CONTEXT (location_t @var{loc}, type_context_kind @var{context}, const_tree @var{type}, bool @var{silent_p})
|
|
If defined, this hook returns false if there is a target-specific reason
|
|
why type @var{type} cannot be used in the source language context described
|
|
by @var{context}. When @var{silent_p} is false, the hook also reports an
|
|
error against @var{loc} for invalid uses of @var{type}.
|
|
|
|
Calls to this hook should be made through the global function
|
|
@code{verify_type_context}, which makes the @var{silent_p} parameter
|
|
default to false and also handles @code{error_mark_node}.
|
|
|
|
The default implementation always returns true.
|
|
@end deftypefn
|
|
|
|
@defmac OBJC_JBLEN
|
|
This macro determines the size of the objective C jump buffer for the
|
|
NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value.
|
|
@end defmac
|
|
|
|
@defmac LIBGCC2_UNWIND_ATTRIBUTE
|
|
Define this macro if any target-specific attributes need to be attached
|
|
to the functions in @file{libgcc} that provide low-level support for
|
|
call stack unwinding. It is used in declarations in @file{unwind-generic.h}
|
|
and the associated definitions of those functions.
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} void TARGET_UPDATE_STACK_BOUNDARY (void)
|
|
Define this macro to update the current function stack boundary if
|
|
necessary.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_GET_DRAP_RTX (void)
|
|
This hook should return an rtx for Dynamic Realign Argument Pointer (DRAP) if a
|
|
different argument pointer register is needed to access the function's
|
|
argument list due to stack realignment. Return @code{NULL} if no DRAP
|
|
is needed.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} HARD_REG_SET TARGET_ZERO_CALL_USED_REGS (HARD_REG_SET @var{selected_regs})
|
|
This target hook emits instructions to zero the subset of @var{selected_regs}
|
|
that could conceivably contain values that are useful to an attacker.
|
|
Return the set of registers that were actually cleared.
|
|
|
|
For most targets, the returned set of registers is a subset of
|
|
@var{selected_regs}, however, for some of the targets (for example MIPS),
|
|
clearing some registers that are in the @var{selected_regs} requires
|
|
clearing other call used registers that are not in the @var{selected_regs},
|
|
under such situation, the returned set of registers must be a subset of all
|
|
call used registers.
|
|
|
|
The default implementation uses normal move instructions to zero
|
|
all the registers in @var{selected_regs}. Define this hook if the
|
|
target has more efficient ways of zeroing certain registers,
|
|
or if you believe that certain registers would never contain
|
|
values that are useful to an attacker.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS (void)
|
|
When optimization is disabled, this hook indicates whether or not
|
|
arguments should be allocated to stack slots. Normally, GCC allocates
|
|
stacks slots for arguments when not optimizing in order to make
|
|
debugging easier. However, when a function is declared with
|
|
@code{__attribute__((naked))}, there is no stack frame, and the compiler
|
|
cannot safely move arguments from the registers in which they are passed
|
|
to the stack. Therefore, this hook should return true in general, but
|
|
false for naked functions. The default implementation always returns true.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} {unsigned HOST_WIDE_INT} TARGET_CONST_ANCHOR
|
|
On some architectures it can take multiple instructions to synthesize
|
|
a constant. If there is another constant already in a register that
|
|
is close enough in value then it is preferable that the new constant
|
|
is computed from this register using immediate addition or
|
|
subtraction. We accomplish this through CSE. Besides the value of
|
|
the constant we also add a lower and an upper constant anchor to the
|
|
available expressions. These are then queried when encountering new
|
|
constants. The anchors are computed by rounding the constant up and
|
|
down to a multiple of the value of @code{TARGET_CONST_ANCHOR}.
|
|
@code{TARGET_CONST_ANCHOR} should be the maximum positive value
|
|
accepted by immediate-add plus one. We currently assume that the
|
|
value of @code{TARGET_CONST_ANCHOR} is a power of 2. For example, on
|
|
MIPS, where add-immediate takes a 16-bit signed value,
|
|
@code{TARGET_CONST_ANCHOR} is set to @samp{0x8000}. The default value
|
|
is zero, which disables this optimization.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} {unsigned HOST_WIDE_INT} TARGET_ASAN_SHADOW_OFFSET (void)
|
|
Return the offset bitwise ored into shifted address to get corresponding
|
|
Address Sanitizer shadow memory address. NULL if Address Sanitizer is not
|
|
supported by the target. May return 0 if Address Sanitizer is not supported
|
|
by a subtarget.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {unsigned HOST_WIDE_INT} TARGET_MEMMODEL_CHECK (unsigned HOST_WIDE_INT @var{val})
|
|
Validate target specific memory model mask bits. When NULL no target specific
|
|
memory model bits are allowed.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} {unsigned char} TARGET_ATOMIC_TEST_AND_SET_TRUEVAL
|
|
This value should be set if the result written by
|
|
@code{atomic_test_and_set} is not exactly 1, i.e.@: the
|
|
@code{bool} @code{true}.
|
|
@end deftypevr
|
|
|
|
@deftypefn {Target Hook} bool TARGET_HAS_IFUNC_P (void)
|
|
It returns true if the target supports GNU indirect functions.
|
|
The support includes the assembler, linker and dynamic linker.
|
|
The default value of this hook is based on target's libc.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_IFUNC_REF_LOCAL_OK (void)
|
|
Return true if it is OK to reference indirect function resolvers
|
|
locally. The default is to return false.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {unsigned int} TARGET_ATOMIC_ALIGN_FOR_MODE (machine_mode @var{mode})
|
|
If defined, this function returns an appropriate alignment in bits for an
|
|
atomic object of machine_mode @var{mode}. If 0 is returned then the
|
|
default alignment for the specified mode is used.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_ATOMIC_ASSIGN_EXPAND_FENV (tree *@var{hold}, tree *@var{clear}, tree *@var{update})
|
|
ISO C11 requires atomic compound assignments that may raise floating-point
|
|
exceptions to raise exceptions corresponding to the arithmetic operation
|
|
whose result was successfully stored in a compare-and-exchange sequence.
|
|
This requires code equivalent to calls to @code{feholdexcept},
|
|
@code{feclearexcept} and @code{feupdateenv} to be generated at
|
|
appropriate points in the compare-and-exchange sequence. This hook should
|
|
set @code{*@var{hold}} to an expression equivalent to the call to
|
|
@code{feholdexcept}, @code{*@var{clear}} to an expression equivalent to
|
|
the call to @code{feclearexcept} and @code{*@var{update}} to an expression
|
|
equivalent to the call to @code{feupdateenv}. The three expressions are
|
|
@code{NULL_TREE} on entry to the hook and may be left as @code{NULL_TREE}
|
|
if no code is required in a particular place. The default implementation
|
|
leaves all three expressions as @code{NULL_TREE}. The
|
|
@code{__atomic_feraiseexcept} function from @code{libatomic} may be of use
|
|
as part of the code generated in @code{*@var{update}}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_RECORD_OFFLOAD_SYMBOL (tree)
|
|
Used when offloaded functions are seen in the compilation unit and no named
|
|
sections are available. It is called once for each symbol that must be
|
|
recorded in the offload function and variable table.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} {char *} TARGET_OFFLOAD_OPTIONS (void)
|
|
Used when writing out the list of options into an LTO file. It should
|
|
translate any relevant target-specific options (such as the ABI in use)
|
|
into one of the @option{-foffload} options that exist as a common interface
|
|
to express such options. It should return a string containing these options,
|
|
separated by spaces, which the caller will free.
|
|
|
|
@end deftypefn
|
|
|
|
@defmac TARGET_SUPPORTS_WIDE_INT
|
|
|
|
On older ports, large integers are stored in @code{CONST_DOUBLE} rtl
|
|
objects. Newer ports define @code{TARGET_SUPPORTS_WIDE_INT} to be nonzero
|
|
to indicate that large integers are stored in
|
|
@code{CONST_WIDE_INT} rtl objects. The @code{CONST_WIDE_INT} allows
|
|
very large integer constants to be represented. @code{CONST_DOUBLE}
|
|
is limited to twice the size of the host's @code{HOST_WIDE_INT}
|
|
representation.
|
|
|
|
Converting a port mostly requires looking for the places where
|
|
@code{CONST_DOUBLE}s are used with @code{VOIDmode} and replacing that
|
|
code with code that accesses @code{CONST_WIDE_INT}s. @samp{"grep -i
|
|
const_double"} at the port level gets you to 95% of the changes that
|
|
need to be made. There are a few places that require a deeper look.
|
|
|
|
@itemize @bullet
|
|
@item
|
|
There is no equivalent to @code{hval} and @code{lval} for
|
|
@code{CONST_WIDE_INT}s. This would be difficult to express in the md
|
|
language since there are a variable number of elements.
|
|
|
|
Most ports only check that @code{hval} is either 0 or -1 to see if the
|
|
value is small. As mentioned above, this will no longer be necessary
|
|
since small constants are always @code{CONST_INT}. Of course there
|
|
are still a few exceptions, the alpha's constraint used by the zap
|
|
instruction certainly requires careful examination by C code.
|
|
However, all the current code does is pass the hval and lval to C
|
|
code, so evolving the c code to look at the @code{CONST_WIDE_INT} is
|
|
not really a large change.
|
|
|
|
@item
|
|
Because there is no standard template that ports use to materialize
|
|
constants, there is likely to be some futzing that is unique to each
|
|
port in this code.
|
|
|
|
@item
|
|
The rtx costs may have to be adjusted to properly account for larger
|
|
constants that are represented as @code{CONST_WIDE_INT}.
|
|
@end itemize
|
|
|
|
All and all it does not take long to convert ports that the
|
|
maintainer is familiar with.
|
|
|
|
@end defmac
|
|
|
|
@deftypefn {Target Hook} bool TARGET_HAVE_SPECULATION_SAFE_VALUE (bool @var{active})
|
|
This hook is used to determine the level of target support for
|
|
@code{__builtin_speculation_safe_value}. If called with an argument
|
|
of false, it returns true if the target has been modified to support
|
|
this builtin. If called with an argument of true, it returns true
|
|
if the target requires active mitigation execution might be speculative.
|
|
|
|
The default implementation returns false if the target does not define
|
|
a pattern named @code{speculation_barrier}. Else it returns true
|
|
for the first case and whether the pattern is enabled for the current
|
|
compilation for the second case.
|
|
|
|
For targets that have no processors that can execute instructions
|
|
speculatively an alternative implemenation of this hook is available:
|
|
simply redefine this hook to @code{speculation_safe_value_not_needed}
|
|
along with your other target hooks.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_SPECULATION_SAFE_VALUE (machine_mode @var{mode}, rtx @var{result}, rtx @var{val}, rtx @var{failval})
|
|
This target hook can be used to generate a target-specific code
|
|
sequence that implements the @code{__builtin_speculation_safe_value}
|
|
built-in function. The function must always return @var{val} in
|
|
@var{result} in mode @var{mode} when the cpu is not executing
|
|
speculatively, but must never return that when speculating until it
|
|
is known that the speculation will not be unwound. The hook supports
|
|
two primary mechanisms for implementing the requirements. The first
|
|
is to emit a speculation barrier which forces the processor to wait
|
|
until all prior speculative operations have been resolved; the second
|
|
is to use a target-specific mechanism that can track the speculation
|
|
state and to return @var{failval} if it can determine that
|
|
speculation must be unwound at a later time.
|
|
|
|
The default implementation simply copies @var{val} to @var{result} and
|
|
emits a @code{speculation_barrier} instruction if that is defined.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} void TARGET_RUN_TARGET_SELFTESTS (void)
|
|
If selftests are enabled, run any selftests for this target.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} bool TARGET_MEMTAG_CAN_TAG_ADDRESSES ()
|
|
True if the backend architecture naturally supports ignoring some region
|
|
of pointers. This feature means that @option{-fsanitize=hwaddress} can
|
|
work.
|
|
|
|
At preset, this feature does not support address spaces. It also requires
|
|
@code{Pmode} to be the same as @code{ptr_mode}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} uint8_t TARGET_MEMTAG_TAG_SIZE ()
|
|
Return the size of a tag (in bits) for this platform.
|
|
|
|
The default returns 8.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} uint8_t TARGET_MEMTAG_GRANULE_SIZE ()
|
|
Return the size in real memory that each byte in shadow memory refers to.
|
|
I.e. if a variable is @var{X} bytes long in memory, then this hook should
|
|
return the value @var{Y} such that the tag in shadow memory spans
|
|
@var{X}/@var{Y} bytes.
|
|
|
|
Most variables will need to be aligned to this amount since two variables
|
|
that are neighbors in memory and share a tag granule would need to share
|
|
the same tag.
|
|
|
|
The default returns 16.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_MEMTAG_INSERT_RANDOM_TAG (rtx @var{untagged}, rtx @var{target})
|
|
Return an RTX representing the value of @var{untagged} but with a
|
|
(possibly) random tag in it.
|
|
Put that value into @var{target} if it is convenient to do so.
|
|
This function is used to generate a tagged base for the current stack frame.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_MEMTAG_ADD_TAG (rtx @var{base}, poly_int64 @var{addr_offset}, uint8_t @var{tag_offset})
|
|
Return an RTX that represents the result of adding @var{addr_offset} to
|
|
the address in pointer @var{base} and @var{tag_offset} to the tag in pointer
|
|
@var{base}.
|
|
The resulting RTX must either be a valid memory address or be able to get
|
|
put into an operand with @code{force_operand}.
|
|
|
|
Unlike other memtag hooks, this must return an expression and not emit any
|
|
RTL.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_MEMTAG_SET_TAG (rtx @var{untagged_base}, rtx @var{tag}, rtx @var{target})
|
|
Return an RTX representing @var{untagged_base} but with the tag @var{tag}.
|
|
Try and store this in @var{target} if convenient.
|
|
@var{untagged_base} is required to have a zero tag when this hook is called.
|
|
The default of this hook is to set the top byte of @var{untagged_base} to
|
|
@var{tag}.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_MEMTAG_EXTRACT_TAG (rtx @var{tagged_pointer}, rtx @var{target})
|
|
Return an RTX representing the tag stored in @var{tagged_pointer}.
|
|
Store the result in @var{target} if it is convenient.
|
|
The default represents the top byte of the original pointer.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} rtx TARGET_MEMTAG_UNTAGGED_POINTER (rtx @var{tagged_pointer}, rtx @var{target})
|
|
Return an RTX representing @var{tagged_pointer} with its tag set to zero.
|
|
Store the result in @var{target} if convenient.
|
|
The default clears the top byte of the original pointer.
|
|
@end deftypefn
|
|
|
|
@deftypefn {Target Hook} HOST_WIDE_INT TARGET_GCOV_TYPE_SIZE (void)
|
|
Returns the gcov type size in bits. This type is used for example for
|
|
counters incremented by profiling and code-coverage events. The default
|
|
value is 64, if the type size of long long is greater than 32, otherwise the
|
|
default value is 32. A 64-bit type is recommended to avoid overflows of the
|
|
counters. If the @option{-fprofile-update=atomic} is used, then the
|
|
counters are incremented using atomic operations. Targets not supporting
|
|
64-bit atomic operations may override the default value and request a 32-bit
|
|
type.
|
|
@end deftypefn
|
|
|
|
@deftypevr {Target Hook} bool TARGET_HAVE_SHADOW_CALL_STACK
|
|
This value is true if the target platform supports
|
|
@option{-fsanitize=shadow-call-stack}. The default value is false.
|
|
@end deftypevr
|