@item Optimization Options
@xref{Optimize Options,,Options that Control Optimization}.
-@gccoptlist{-falign-functions=@var{n} -falign-jumps=@var{n} @gol
--falign-labels=@var{n} -falign-loops=@var{n} @gol
--fbounds-check -fmudflap -fmudflapth -fmudflapir @gol
--fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize @gol
+@gccoptlist{-falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol
+-falign-labels[=@var{n}] -falign-loops[=@var{n}] @gol
+-fmudflap -fmudflapth -fmudflapir @gol
+-fbranch-probabilities -fprofile-values -fvpt @gol
+-fbranch-target-load-optimize @gol
-fbranch-target-load-optimize2 -fbtr-bb-exclusive @gol
-fcaller-saves -fcprop-registers -fcse-follow-jumps @gol
-fcse-skip-blocks -fcx-limited-range -fdata-sections @gol
-fschedule-insns -fschedule-insns2 @gol
-fno-sched-interblock -fno-sched-spec -fsched-spec-load @gol
-fsched-spec-load-dangerous @gol
--fsched-stalled-insns=@var{n} -fsched-stalled-insns-dep=@var{n} @gol
+-fsched-stalled-insns[=@var{n}] -fsched-stalled-insns-dep[=@var{n}] @gol
-fsched2-use-superblocks @gol
-fsched2-use-traces -fsee -freschedule-modulo-scheduled-loops @gol
-fsection-anchors -fsignaling-nans -fsingle-precision-constant @gol
-ftree-dominator-opts -ftree-dse -ftree-copyrename -ftree-sink @gol
-ftree-ch -ftree-sra -ftree-ter -ftree-lrs -ftree-fre -ftree-vectorize @gol
-ftree-vect-loop-version -ftree-salias -fipa-pta -fweb @gol
--ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -fwhole-program @gol
+-ftree-copy-prop -ftree-store-ccp -ftree-store-copy-prop -ftree-vrp @gol
+-funit-at-a-time -fwhole-program @gol
--param @var{name}=@var{value}
-O -O0 -O1 -O2 -O3 -Os}
-fshort-double -fshort-wchar @gol
-fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol
-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol
--fargument-alias -fargument-noalias @gol
--fargument-noalias-global -fargument-noalias-anything
+-fno-stack-limit -fargument-alias -fargument-noalias @gol
+-fargument-noalias-global -fargument-noalias-anything @gol
-fleading-underscore -ftls-model=@var{model} @gol
-ftrapv -fwrapv -fbounds-check @gol
-fvisibility}
optimization is turned on, use the @option{-fno-keep-static-consts} option.
@item -fmerge-constants
+@opindex fmerge-constants
Attempt to merge identical constants (string constants and floating point
constants) across compilation units.
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
@item -fmerge-all-constants
+@opindex fmerge-all-constants
Attempt to merge identical constants and identical variables.
This option implies @option{-fmerge-constants}. In addition to
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 front-ends, where
-this option defaults to true and false respectively.
-
@item -fmudflap -fmudflapth -fmudflapir
@opindex fmudflap
@opindex fmudflapth
if it finds this kind of loop.
@item -fcrossjumping
-@opindex crossjumping
+@opindex fcrossjumping
Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The
resulting code may or may not perform better than without cross-jumping.
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
@item -fif-conversion
-@opindex if-conversion
+@opindex fif-conversion
Attempt to transform conditional jumps into branch-less equivalents. This
include use of conditional moves, min, max, set flags and abs instructions, and
some tricks doable by standard arithmetics. The use of conditional execution
Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
@item -fif-conversion2
-@opindex if-conversion2
+@opindex fif-conversion2
Use conditional execution (where available) to transform conditional jumps into
branch-less equivalents.
sense when scheduling before register allocation, i.e.@: with
@option{-fschedule-insns} or at @option{-O2} or higher.
-@item -fsched-stalled-insns=@var{n}
+@item -fsched-stalled-insns
+@itemx -fsched-stalled-insns=@var{n}
@opindex fsched-stalled-insns
Define how many insns (if any) can be moved prematurely from the queue
of stalled insns into the ready list, during the second scheduling pass.
+@option{-fno-fsched-stalled-insns} and @option{-fsched-stalled-insns=0}
+are equivalent and mean that no insns will be moved prematurely.
+If @var{n} is unspecified then there is no limit on how many queued
+insns can be moved prematurely.
-@item -fsched-stalled-insns-dep=@var{n}
+@item -fsched-stalled-insns-dep
+@itemx -fsched-stalled-insns-dep=@var{n}
@opindex fsched-stalled-insns-dep
Define how many insn groups (cycles) will be examined for a dependency
on a stalled insn that is candidate for premature removal from the queue
-of stalled insns. Has an effect only during the second scheduling pass,
+of stalled insns. This has an effect only during the second scheduling pass,
and only if @option{-fsched-stalled-insns} is used and its value is not zero.
+@option{-fno-sched-stalled-insns-dep} is equivalent to
+@option{-fsched-stalled-insns-dep=0}.
+@option{-fsched-stalled-insns-dep} without a value is equivalent to
+@option{-fsched-stalled-insns-dep=1}.
@item -fsched2-use-superblocks
@opindex fsched2-use-superblocks
ones to optimal placement using LCM.
@item -freschedule-modulo-scheduled-loops
-@opindex fscheduling-in-modulo-scheduled-loops
+@opindex freschedule-modulo-scheduled-loops
The modulo scheduling comes before the traditional scheduling, if a loop was modulo scheduled
we may want to prevent the later scheduling passes from changing its schedule, we use this
option to control that.
Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}.
@item -ftree-pre
+@opindex ftree-pre
Perform Partial Redundancy Elimination (PRE) on trees. This flag is
enabled by default at @option{-O2} and @option{-O3}.
This flag is enabled by default at @option{-O} and higher.
@item -ftree-copy-prop
+@opindex ftree-copy-prop
Perform copy propagation on trees. This pass eliminates unnecessary
copy operations. This flag is enabled by default at @option{-O} and
higher.
default at @option{-O2} and higher.
@item -ftree-salias
+@opindex ftree-salias
Perform structural alias analysis on trees. This flag
is enabled by default at @option{-O} and higher.
@item -fipa-pta
+@opindex fipa-pta
Perform interprocedural pointer analysis.
@item -ftree-sink
+@opindex ftree-sink
Perform forward store motion on trees. This flag is
enabled by default at @option{-O} and higher.
@item -ftree-ccp
+@opindex ftree-ccp
Perform sparse conditional constant propagation (CCP) on trees. This
pass only operates on local scalar variables and is enabled by default
at @option{-O} and higher.
@item -ftree-store-ccp
+@opindex ftree-store-ccp
Perform sparse conditional constant propagation (CCP) on trees. This
pass operates on both local scalar variables and memory stores and
loads (global variables, structures, arrays, etc). This flag is
enabled by default at @option{-O2} and higher.
@item -ftree-dce
+@opindex ftree-dce
Perform dead code elimination (DCE) on trees. This flag is enabled by
default at @option{-O} and higher.
@item -ftree-dominator-opts
+@opindex ftree-dominator-opts
Perform a variety of simple scalar cleanups (constant/copy
propagation, redundancy elimination, range propagation and expression
simplification) based on a dominator tree traversal. This also
enabled by default at @option{-O} and higher.
@item -ftree-ch
+@opindex ftree-ch
Perform loop header copying on trees. This is beneficial since it increases
effectiveness of code motion optimizations. It also saves one jump. This flag
is enabled by default at @option{-O} and higher. It is not enabled
for @option{-Os}, since it usually increases code size.
@item -ftree-loop-optimize
+@opindex ftree-loop-optimize
Perform loop optimizations on trees. This flag is enabled by default
at @option{-O} and higher.
@item -ftree-loop-linear
+@opindex ftree-loop-linear
Perform linear loop transformations on tree. This flag can improve cache
performance and allow further loop optimizations to take place.
@item -ftree-loop-im
+@opindex ftree-loop-im
Perform loop invariant motion on trees. This pass moves only invariants that
would be hard to handle at RTL level (function calls, operations that expand to
nontrivial sequences of insns). With @option{-funswitch-loops} it also moves
store motion.
@item -ftree-loop-ivcanon
+@opindex ftree-loop-ivcanon
Create a canonical counter for number of iterations in the loop for that
determining number of iterations requires complicated analysis. Later
optimizations then may determine the number easily. Useful especially
in connection with unrolling.
@item -fivopts
+@opindex fivopts
Perform induction variable optimizations (strength reduction, induction
variable merging and induction variable elimination) on trees.
@item -ftree-sra
+@opindex ftree-sra
Perform scalar replacement of aggregates. This pass replaces structure
references with scalars to prevent committing structures to memory too
early. This flag is enabled by default at @option{-O} and higher.
@item -ftree-copyrename
+@opindex ftree-copyrename
Perform copy renaming on trees. This pass attempts to rename compiler
temporaries to other variables at copy locations, usually resulting in
variable names which more closely resemble the original variables. This flag
is enabled by default at @option{-O} and higher.
@item -ftree-ter
+@opindex ftree-ter
Perform temporary expression replacement during the SSA->normal phase. Single
use/single def temporaries are replaced at their use location with their
defining expression. This results in non-GIMPLE code, but gives the expanders
enabled by default at @option{-O} and higher.
@item -ftree-lrs
+@opindex ftree-lrs
Perform live range splitting during the SSA->normal phase. Distinct live
ranges of a variable are split into unique variables, allowing for better
optimization later. This is enabled by default at @option{-O} and higher.
@item -ftree-vectorize
+@opindex ftree-vectorize
Perform loop vectorization on trees.
@item -ftree-vect-loop-version
except at level @option{-Os} where it is disabled.
@item -ftree-vrp
+@opindex ftree-vrp
Perform Value Range Propagation on trees. This is similar to the
constant propagation pass, but instead of values, ranges of values are
propagated. This allows the optimizers to remove unnecessary range
compilation unit, not for the single source file itself.
-@item -fno-cprop-registers
-@opindex fno-cprop-registers
+@item -fcprop-registers
+@opindex fcprop-registers
After register allocation and post-register allocation instruction splitting,
we perform a copy-propagation pass to try to reduce scheduling dependencies
and occasionally eliminate the copy.
-Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
+Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}.
@item -fprofile-generate
@opindex fprofile-generate
implicitly converting it to double precision constant.
@item -fcx-limited-range
-@itemx -fno-cx-limited-range
@opindex fcx-limited-range
-@opindex fno-cx-limited-range
When enabled, this option states that a range reduction step is not
needed when performing complex division. The default is
@option{-fno-cx-limited-range}, but is enabled by @option{-ffast-math}.
branch target registers in within any basic block.
@item -fstack-protector
+@opindex fstack-protector
Emit extra code to check for buffer overflows, such as stack smashing
attacks. This is done by adding a guard variable to functions with
vulnerable objects. This includes functions that call alloca, and
If a guard check fails, an error message is printed and the program exits.
@item -fstack-protector-all
+@opindex fstack-protector-all
Like @option{-fstack-protector} except that all functions are protected.
@item -fsection-anchors
Not all targets provide complete support for this switch.
@item -ftls-model=@var{model}
+@opindex ftls-model=@var{model}
Alter the thread-local storage model to be used (@pxref{Thread-Local}).
The @var{model} argument should be one of @code{global-dynamic},
@code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
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