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invoke.texi (Optimization Options): Group together optional and experimental flags. 

* gcc/doc/invoke.texi (Optimization Options): Group together
	optional and experimental flags.  Move trapv and bounds-check
	out of this section.
	(Code Gen Options): Move trapv and bounds-check to here.

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Jerry Quinn 2003-01-27 18:06:39 +00:00 committed by Gerald Pfeifer
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@ -1,3 +1,10 @@
2003-01-25 Jerry Quinn <jlquinn@optonline.net>
* gcc/doc/invoke.texi (Optimization Options): Group together
optional and experimental flags. Move trapv and bounds-check
out of this section.
(Code Gen Options): Move trapv and bounds-check to here.
2003-01-27 Josef Zlomek <zlomekj@suse.cz>
* gcse.c (constprop_register): Check NEXT_INSN (insn) != NULL.

434
gcc/doc/invoke.texi
View File

@ -265,7 +265,6 @@ in the following sections.
@gccoptlist{
-falign-functions=@var{n} -falign-jumps=@var{n} @gol
-falign-labels=@var{n} -falign-loops=@var{n} @gol
-fbounds-check @gol
-fbranch-probabilities -fcaller-saves -fcprop-registers @gol
-fcse-follow-jumps -fcse-skip-blocks -fdata-sections @gol
-fdelayed-branch -fdelete-null-pointer-checks @gol
@ -291,7 +290,7 @@ in the following sections.
-fsched-spec-load-dangerous -fsignaling-nans @gol
-fsingle-precision-constant -fssa -fssa-ccp -fssa-dce @gol
-fstrength-reduce -fstrict-aliasing -ftracer -fthread-jumps @gol
-ftrapv -funroll-all-loops -funroll-loops @gol
-funroll-all-loops -funroll-loops @gol
--param @var{name}=@var{value}
-O -O0 -O1 -O2 -O3 -Os}
@ -712,7 +711,8 @@ in the following sections.
-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
-fargument-alias -fargument-noalias @gol
-fargument-noalias-global -fleading-underscore @gol
-ftls-model=@var{model}}
-ftls-model=@var{model} @gol
-ftrapv -fbounds-check}
@end table
@menu
@ -3527,21 +3527,6 @@ can use the following flags in the rare cases when ``fine-tuning'' of
optimizations to be performed is desired.
@table @gcctabopt
@item -ffloat-store
@opindex ffloat-store
Do not store floating point variables in registers, and inhibit other
options that might change whether a floating point value is taken from a
register or memory.
@cindex floating point precision
This option prevents undesirable excess precision on machines such as
the 68000 where the floating registers (of the 68881) keep more
precision than a @code{double} is supposed to have. Similarly for the
x86 architecture. For most programs, the excess precision does only
good, but a few programs rely on the precise definition of IEEE floating
point. Use @option{-ffloat-store} for such programs, after modifying
them to store all pertinent intermediate computations into variables.
@item -fno-default-inline
@opindex fno-default-inline
Do not make member functions inline by default merely because they are
@ -3598,11 +3583,6 @@ Optimize sibling and tail recursive calls.
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
@item -ftrapv
@opindex ftrapv
This option generates traps for signed overflow on addition, subtraction,
multiplication operations.
@item -fno-inline
@opindex fno-inline
Don't pay attention to the @code{inline} keyword. Normally this option
@ -3704,89 +3684,6 @@ performed when this option is not used.
The default is @option{-ffunction-cse}
@item -ffast-math
@opindex ffast-math
Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
@option{-fno-trapping-math}, @option{-ffinite-math-only} and @*
@option{-fno-signaling-nans}.
This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
@item -fno-math-errno
@opindex fno-math-errno
Do not set ERRNO after calling math functions that are executed
with a single instruction, e.g., sqrt. A program that relies on
IEEE exceptions for math error handling may want to use this flag
for speed while maintaining IEEE arithmetic compatibility.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
The default is @option{-fmath-errno}.
@item -funsafe-math-optimizations
@opindex funsafe-math-optimizations
Allow optimizations for floating-point arithmetic that (a) assume
that arguments and results are valid and (b) may violate IEEE or
ANSI standards. When used at link-time, it may include libraries
or startup files that change the default FPU control word or other
similar optimizations.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
The default is @option{-fno-unsafe-math-optimizations}.
@item -ffinite-math-only
@opindex ffinite-math-only
Allow optimizations for floating-point arithmetic that assume
that arguments and results are not NaNs or +-Infs.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications.
The default is @option{-fno-finite-math-only}.
@item -fno-trapping-math
@opindex fno-trapping-math
Compile code assuming that floating-point operations cannot generate
user-visible traps. These traps include division by zero, overflow,
underflow, inexact result and invalid operation. This option implies
@option{-fno-signaling-nans}. Setting this option may allow faster
code if one relies on ``non-stop'' IEEE arithmetic, for example.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
The default is @option{-ftrapping-math}.
@item -fsignaling-nans
@opindex fsignaling-nans
Compile code assuming that IEEE signaling NaNs may generate user-visible
traps during floating-point operations. Setting this option disables
optimizations that may change the number of exceptions visible with
signaling NaNs. This option implies @option{-ftrapping-math}.
This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
be defined.
The default is @option{-fno-signaling-nans}.
This option is experimental and does not currently guarantee to
disable all GCC optimizations that affect signaling NaN behavior.
@item -fno-zero-initialized-in-bss
@opindex fno-zero-initialized-in-bss
If the target supports a BSS section, GCC by default puts variables that
@ -3800,13 +3697,6 @@ assumptions based on that.
The default is @option{-fzero-initialized-in-bss}.
@item -fbounds-check
@opindex fbounds-check
For front-ends that support it, generate additional code to check that
indices used to access arrays are within the declared range. This is
currently only supported by the Java and Fortran 77 front-ends, where
this option defaults to true and false respectively.
@item -fstrength-reduce
@opindex fstrength-reduce
Perform the optimizations of loop strength reduction and
@ -4003,28 +3893,6 @@ Allow speculative motion of more load instructions. This only makes
sense when scheduling before register allocation, i.e.@: with
@option{-fschedule-insns} or at @option{-O2} or higher.
@item -ffunction-sections
@itemx -fdata-sections
@opindex ffunction-sections
@opindex fdata-sections
Place each function or data item into its own section in the output
file if the target supports arbitrary sections. The name of the
function or the name of the data item determines the section's name
in the output file.
Use these options on systems where the linker can perform optimizations
to improve locality of reference in the instruction space. HPPA
processors running HP-UX and SPARC processors running Solaris 2 have
linkers with such optimizations. Other systems using the ELF object format
as well as AIX may have these optimizations in the future.
Only use these options when there are significant benefits from doing
so. When you specify these options, the assembler and linker will
create larger object and executable files and will also be slower.
You will not be able to use @command{gprof} on all systems if you
specify this option and you may have problems with debugging if
you specify both this option and @option{-g}.
@item -fcaller-saves
@opindex fcaller-saves
Enable values to be allocated in registers that will be clobbered by
@ -4037,33 +3905,6 @@ those which have no call-preserved registers to use instead.
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
@item -ftracer
@opindex ftracer
Perform tail duplication to enlarge superblock size. This transformation
simplifies the control flow of the function allowing other optimizations to do
better job.
@item -funroll-loops
@opindex funroll-loops
Unroll loops whose number of iterations can be determined at compile
time or upon entry to the loop. @option{-funroll-loops} implies both
@option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
option makes code larger, and may or may not make it run faster.
@item -funroll-all-loops
@opindex funroll-all-loops
Unroll all loops, even if their number of iterations is uncertain when
the loop is entered. This usually makes programs run more slowly.
@option{-funroll-all-loops} implies the same options as
@option{-funroll-loops},
@item -fprefetch-loop-arrays
@opindex fprefetch-loop-arrays
If supported by the target machine, generate instructions to prefetch
memory to improve the performance of loops that access large arrays.
Disabled at level @option{-Os}.
@item -fmove-all-movables
@opindex fmove-all-movables
Forces all invariant computations in loops to be moved
@ -4103,27 +3944,6 @@ other, a few use both.
@option{-fpeephole} is enabled by default.
@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
@item -fbranch-probabilities
@opindex fbranch-probabilities
After running a program compiled with @option{-fprofile-arcs}
(@pxref{Debugging Options,, Options for Debugging Your Program or
@command{gcc}}), you can compile it a second time using
@option{-fbranch-probabilities}, to improve optimizations based on
the number of times each branch was taken. When the program
compiled with @option{-fprofile-arcs} exits it saves arc execution
counts to a file called @file{@var{sourcename}.da} for each source
file The information in this data file is very dependent on the
structure of the generated code, so you must use the same source code
and the same optimization options for both compilations.
With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT}
note on the first instruction of each basic block, and a
@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
These can be used to improve optimization. Currently, they are only
used in one place: in @file{reorg.c}, instead of guessing which path a
branch is mostly to take, the @samp{REG_BR_PROB} values are used to
exactly determine which path is taken more often.
@item -fno-guess-branch-probability
@opindex fno-guess-branch-probability
Do not guess branch probabilities using a randomized model.
@ -4270,28 +4090,6 @@ If @var{n} is not specified, use a machine-dependent default.
Enabled at levels @option{-O2}, @option{-O3}.
@item -fssa
@opindex fssa
Perform optimizations in static single assignment form. Each function's
flow graph is translated into SSA form, optimizations are performed, and
the flow graph is translated back from SSA form. Users should not
specify this option, since it is not yet ready for production use.
@item -fssa-ccp
@opindex fssa-ccp
Perform Sparse Conditional Constant Propagation in SSA form. Requires
@option{-fssa}. Like @option{-fssa}, this is an experimental feature.
@item -fssa-dce
@opindex fssa-dce
Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
Like @option{-fssa}, this is an experimental feature.
@item -fsingle-precision-constant
@opindex fsingle-precision-constant
Treat floating point constant as single precision constant instead of
implicitly converting it to double precision constant.
@item -frename-registers
@opindex frename-registers
Attempt to avoid false dependencies in scheduled code by making use
@ -4310,6 +4108,220 @@ and occasionally eliminate the copy.
Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
@end table
The following options control compiler behavior regarding floating
point arithmetic. These options trade off between speed and
correctness. All must be specifically enabled.
@table @gcctabopt
@item -ffloat-store
@opindex ffloat-store
Do not store floating point variables in registers, and inhibit other
options that might change whether a floating point value is taken from a
register or memory.
@cindex floating point precision
This option prevents undesirable excess precision on machines such as
the 68000 where the floating registers (of the 68881) keep more
precision than a @code{double} is supposed to have. Similarly for the
x86 architecture. For most programs, the excess precision does only
good, but a few programs rely on the precise definition of IEEE floating
point. Use @option{-ffloat-store} for such programs, after modifying
them to store all pertinent intermediate computations into variables.
@item -ffast-math
@opindex ffast-math
Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, @*
@option{-fno-trapping-math}, @option{-ffinite-math-only} and @*
@option{-fno-signaling-nans}.
This option causes the preprocessor macro @code{__FAST_MATH__} to be defined.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
@item -fno-math-errno
@opindex fno-math-errno
Do not set ERRNO after calling math functions that are executed
with a single instruction, e.g., sqrt. A program that relies on
IEEE exceptions for math error handling may want to use this flag
for speed while maintaining IEEE arithmetic compatibility.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
The default is @option{-fmath-errno}.
@item -funsafe-math-optimizations
@opindex funsafe-math-optimizations
Allow optimizations for floating-point arithmetic that (a) assume
that arguments and results are valid and (b) may violate IEEE or
ANSI standards. When used at link-time, it may include libraries
or startup files that change the default FPU control word or other
similar optimizations.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
The default is @option{-fno-unsafe-math-optimizations}.
@item -ffinite-math-only
@opindex ffinite-math-only
Allow optimizations for floating-point arithmetic that assume
that arguments and results are not NaNs or +-Infs.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications.
The default is @option{-fno-finite-math-only}.
@item -fno-trapping-math
@opindex fno-trapping-math
Compile code assuming that floating-point operations cannot generate
user-visible traps. These traps include division by zero, overflow,
underflow, inexact result and invalid operation. This option implies
@option{-fno-signaling-nans}. Setting this option may allow faster
code if one relies on ``non-stop'' IEEE arithmetic, for example.
This option should never be turned on by any @option{-O} option since
it can result in incorrect output for programs which depend on
an exact implementation of IEEE or ISO rules/specifications for
math functions.
The default is @option{-ftrapping-math}.
@item -fsignaling-nans
@opindex fsignaling-nans
Compile code assuming that IEEE signaling NaNs may generate user-visible
traps during floating-point operations. Setting this option disables
optimizations that may change the number of exceptions visible with
signaling NaNs. This option implies @option{-ftrapping-math}.
This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to
be defined.
The default is @option{-fno-signaling-nans}.
This option is experimental and does not currently guarantee to
disable all GCC optimizations that affect signaling NaN behavior.
@item -fsingle-precision-constant
@opindex fsingle-precision-constant
Treat floating point constant as single precision constant instead of
implicitly converting it to double precision constant.
@end table
The following options control optimizations that may improve
performance, but are not enabled by any @option{-O} options. This
section includes experimental options that may produce broken code.
@table @gcctabopt
@item -fbranch-probabilities
@opindex fbranch-probabilities
After running a program compiled with @option{-fprofile-arcs}
(@pxref{Debugging Options,, Options for Debugging Your Program or
@command{gcc}}), you can compile it a second time using
@option{-fbranch-probabilities}, to improve optimizations based on
the number of times each branch was taken. When the program
compiled with @option{-fprofile-arcs} exits it saves arc execution
counts to a file called @file{@var{sourcename}.da} for each source
file The information in this data file is very dependent on the
structure of the generated code, so you must use the same source code
and the same optimization options for both compilations.
With @option{-fbranch-probabilities}, GCC puts a @samp{REG_EXEC_COUNT}
note on the first instruction of each basic block, and a
@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}.
These can be used to improve optimization. Currently, they are only
used in one place: in @file{reorg.c}, instead of guessing which path a
branch is mostly to take, the @samp{REG_BR_PROB} values are used to
exactly determine which path is taken more often.
@item -fnew-ra
@opindex fnew-ra
Use a graph coloring register allocator. Currently this option is meant
for testing, so we are interested to hear about miscompilations with
@option{-fnew-ra}.
@item -ftracer
@opindex ftracer
Perform tail duplication to enlarge superblock size. This transformation
simplifies the control flow of the function allowing other optimizations to do
better job.
@item -funroll-loops
@opindex funroll-loops
Unroll loops whose number of iterations can be determined at compile
time or upon entry to the loop. @option{-funroll-loops} implies both
@option{-fstrength-reduce} and @option{-frerun-cse-after-loop}. This
option makes code larger, and may or may not make it run faster.
@item -funroll-all-loops
@opindex funroll-all-loops
Unroll all loops, even if their number of iterations is uncertain when
the loop is entered. This usually makes programs run more slowly.
@option{-funroll-all-loops} implies the same options as
@option{-funroll-loops},
@item -fprefetch-loop-arrays
@opindex fprefetch-loop-arrays
If supported by the target machine, generate instructions to prefetch
memory to improve the performance of loops that access large arrays.
Disabled at level @option{-Os}.
@item -ffunction-sections
@itemx -fdata-sections
@opindex ffunction-sections
@opindex fdata-sections
Place each function or data item into its own section in the output
file if the target supports arbitrary sections. The name of the
function or the name of the data item determines the section's name
in the output file.
Use these options on systems where the linker can perform optimizations
to improve locality of reference in the instruction space. HPPA
processors running HP-UX and SPARC processors running Solaris 2 have
linkers with such optimizations. Other systems using the ELF object format
as well as AIX may have these optimizations in the future.
Only use these options when there are significant benefits from doing
so. When you specify these options, the assembler and linker will
create larger object and executable files and will also be slower.
You will not be able to use @code{gprof} on all systems if you
specify this option and you may have problems with debugging if
you specify both this option and @option{-g}.
@item -fssa
@opindex fssa
Perform optimizations in static single assignment form. Each function's
flow graph is translated into SSA form, optimizations are performed, and
the flow graph is translated back from SSA form. Users should not
specify this option, since it is not yet ready for production use.
@item -fssa-ccp
@opindex fssa-ccp
Perform Sparse Conditional Constant Propagation in SSA form. Requires
@option{-fssa}. Like @option{-fssa}, this is an experimental feature.
@item -fssa-dce
@opindex fssa-dce
Perform aggressive dead-code elimination in SSA form. Requires @option{-fssa}.
Like @option{-fssa}, this is an experimental feature.
@item --param @var{name}=@var{value}
@opindex param
In some places, GCC uses various constants to control the amount of
@ -10578,6 +10590,18 @@ can figure out the other form by either removing @samp{no-} or adding
it.
@table @gcctabopt
@item -fbounds-check
@opindex fbounds-check
For front-ends that support it, generate additional code to check that
indices used to access arrays are within the declared range. This is
currently only supported by the Java and Fortran 77 front-ends, where
this option defaults to true and false respectively.
@item -ftrapv
@opindex ftrapv
This option generates traps for signed overflow on addition, subtraction,
multiplication operations.
@item -fexceptions
@opindex fexceptions
Enable exception handling. Generates extra code needed to propagate