aarch64-linux-gnu-4.9/share/doc/gcc/Optimize-Options.html - toolchains/linux-x86/gcc - Git at Google

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 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
 <a name="Optimize-Options"></a>
 <div class="header">
 <p>
 Next: <a href="Preprocessor-Options.html#Preprocessor-Options" accesskey="n" rel="next">Preprocessor Options</a>, Previous: <a href="Debugging-Options.html#Debugging-Options" accesskey="p" rel="prev">Debugging Options</a>, Up: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="u" rel="up">Invoking GCC</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Options-That-Control-Optimization"></a>
 <h3 class="section">3.10 Options That Control Optimization</h3>
 <a name="index-optimize-options"></a>
 <a name="index-options_002c-optimization"></a>

 <p>These options control various sorts of optimizations.
 </p>
 <p>Without any optimization option, the compiler&rsquo;s goal is to reduce the
 cost of compilation and to make debugging produce the expected
 results.  Statements are independent: if you stop the program with a
 breakpoint between statements, you can then assign a new value to any
 variable or change the program counter to any other statement in the
 function and get exactly the results you expect from the source
 code.
 </p>
 <p>Turning on optimization flags makes the compiler attempt to improve
 the performance and/or code size at the expense of compilation time
 and possibly the ability to debug the program.
 </p>
 <p>The compiler performs optimization based on the knowledge it has of the
 program.  Compiling multiple files at once to a single output file mode allows
 the compiler to use information gained from all of the files when compiling
 each of them.
 </p>
 <p>Not all optimizations are controlled directly by a flag.  Only
 optimizations that have a flag are listed in this section.
 </p>
 <p>Most optimizations are only enabled if an <samp>-O</samp> level is set on
 the command line.  Otherwise they are disabled, even if individual
 optimization flags are specified.
 </p>
 <p>Depending on the target and how GCC was configured, a slightly different
 set of optimizations may be enabled at each <samp>-O</samp> level than
 those listed here.  You can invoke GCC with <samp>-Q --help=optimizers</samp>
 to find out the exact set of optimizations that are enabled at each level.
 See <a href="Overall-Options.html#Overall-Options">Overall Options</a>, for examples.
 </p>
 <dl compact="compact">
 <dt><code>-O</code></dt>
 <dt><code>-O1</code></dt>
 <dd><a name="index-O"></a>
 <a name="index-O1"></a>
 <p>Optimize.  Optimizing compilation takes somewhat more time, and a lot
 more memory for a large function.
 </p>
 <p>With <samp>-O</samp>, the compiler tries to reduce code size and execution
 time, without performing any optimizations that take a great deal of
 compilation time.
 </p>
 <p><samp>-O</samp> turns on the following optimization flags:
 </p><div class="smallexample">
 <pre class="smallexample">-fauto-inc-dec
 -fcompare-elim
 -fcprop-registers
 -fdce
 -fdefer-pop
 -fdelayed-branch
 -fdse
 -fguess-branch-probability
 -fif-conversion2
 -fif-conversion
 -fipa-pure-const
 -fipa-profile
 -fipa-reference
 -fmerge-constants
 -fsplit-wide-types
 -ftree-bit-ccp
 -ftree-builtin-call-dce
 -ftree-ccp
 -ftree-ch
 -ftree-copyrename
 -ftree-dce
 -ftree-dominator-opts
 -ftree-dse
 -ftree-forwprop
 -ftree-fre
 -ftree-phiprop
 -ftree-slsr
 -ftree-sra
 -ftree-pta
 -ftree-ter
 -funit-at-a-time
 </pre></div>

 <p><samp>-O</samp> also turns on <samp>-fomit-frame-pointer</samp> on machines
 where doing so does not interfere with debugging.
 </p>
 </dd>
 <dt><code>-O2</code></dt>
 <dd><a name="index-O2"></a>
 <p>Optimize even more.  GCC performs nearly all supported optimizations
 that do not involve a space-speed tradeoff.
 As compared to <samp>-O</samp>, this option increases both compilation time
 and the performance of the generated code.
 </p>
 <p><samp>-O2</samp> turns on all optimization flags specified by <samp>-O</samp>.  It
 also turns on the following optimization flags:
 </p><div class="smallexample">
 <pre class="smallexample">-fthread-jumps
 -falign-functions  -falign-jumps
 -falign-loops  -falign-labels
 -fcaller-saves
 -fcrossjumping
 -fcse-follow-jumps  -fcse-skip-blocks
 -fdelete-null-pointer-checks
 -fdevirtualize -fdevirtualize-speculatively
 -fexpensive-optimizations
 -fgcse  -fgcse-lm
 -fhoist-adjacent-loads
 -finline-small-functions
 -findirect-inlining
 -fipa-sra
 -fisolate-erroneous-paths-dereference
 -foptimize-sibling-calls
 -fpartial-inlining
 -fpeephole2
 -freorder-blocks  -freorder-functions
 -frerun-cse-after-loop
 -fsched-interblock  -fsched-spec
 -fschedule-insns  -fschedule-insns2
 -fstrict-aliasing -fstrict-overflow
 -ftree-switch-conversion -ftree-tail-merge
 -ftree-pre
 -ftree-vrp
 </pre></div>

 <p>Please note the warning under <samp>-fgcse</samp> about
 invoking <samp>-O2</samp> on programs that use computed gotos.
 </p>
 </dd>
 <dt><code>-O3</code></dt>
 <dd><a name="index-O3"></a>
 <p>Optimize yet more.  <samp>-O3</samp> turns on all optimizations specified
 by <samp>-O2</samp> and also turns on the <samp>-finline-functions</samp>,
 <samp>-funswitch-loops</samp>, <samp>-fpredictive-commoning</samp>,
 <samp>-fgcse-after-reload</samp>, <samp>-ftree-loop-vectorize</samp>,
 <samp>-ftree-slp-vectorize</samp>, <samp>-fvect-cost-model</samp>,
 <samp>-ftree-partial-pre</samp> and <samp>-fipa-cp-clone</samp> options.
 </p>
 </dd>
 <dt><code>-O0</code></dt>
 <dd><a name="index-O0"></a>
 <p>Reduce compilation time and make debugging produce the expected
 results.  This is the default.
 </p>
 </dd>
 <dt><code>-Os</code></dt>
 <dd><a name="index-Os"></a>
 <p>Optimize for size.  <samp>-Os</samp> enables all <samp>-O2</samp> optimizations that
 do not typically increase code size.  It also performs further
 optimizations designed to reduce code size.
 </p>
 <p><samp>-Os</samp> disables the following optimization flags:
 </p><div class="smallexample">
 <pre class="smallexample">-falign-functions  -falign-jumps  -falign-loops
 -falign-labels  -freorder-blocks  -freorder-blocks-and-partition
 -fprefetch-loop-arrays
 </pre></div>

 </dd>
 <dt><code>-Ofast</code></dt>
 <dd><a name="index-Ofast"></a>
 <p>Disregard strict standards compliance.  <samp>-Ofast</samp> enables all
 <samp>-O3</samp> optimizations.  It also enables optimizations that are not
 valid for all standard-compliant programs.
 It turns on <samp>-ffast-math</samp> and the Fortran-specific
 <samp>-fno-protect-parens</samp> and <samp>-fstack-arrays</samp>.
 </p>
 </dd>
 <dt><code>-Og</code></dt>
 <dd><a name="index-Og"></a>
 <p>Optimize debugging experience.  <samp>-Og</samp> enables optimizations
 that do not interfere with debugging. It should be the optimization
 level of choice for the standard edit-compile-debug cycle, offering
 a reasonable level of optimization while maintaining fast compilation
 and a good debugging experience.
 </p>
 <p>If you use multiple <samp>-O</samp> options, with or without level numbers,
 the last such option is the one that is effective.
 </p></dd>
 </dl>

 <p>Options of the form <samp>-f<var>flag</var></samp> specify machine-independent
 flags.  Most flags have both positive and negative forms; the negative
 form of <samp>-ffoo</samp> is <samp>-fno-foo</samp>.  In the table
 below, only one of the forms is listed&mdash;the one you typically
 use.  You can figure out the other form by either removing &lsquo;<samp>no-</samp>&rsquo;
 or adding it.
 </p>
 <p>The following options control specific optimizations.  They are either
 activated by <samp>-O</samp> options or are related to ones that are.  You
 can use the following flags in the rare cases when &ldquo;fine-tuning&rdquo; of
 optimizations to be performed is desired.
 </p>
 <dl compact="compact">
 <dt><code>-fno-defer-pop</code></dt>
 <dd><a name="index-fno_002ddefer_002dpop"></a>
 <p>Always pop the arguments to each function call as soon as that function
 returns.  For machines that must pop arguments after a function call,
 the compiler normally lets arguments accumulate on the stack for several
 function calls and pops them all at once.
 </p>
 <p>Disabled at levels <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fforward-propagate</code></dt>
 <dd><a name="index-fforward_002dpropagate"></a>
 <p>Perform a forward propagation pass on RTL.  The pass tries to combine two
 instructions and checks if the result can be simplified.  If loop unrolling
 is active, two passes are performed and the second is scheduled after
 loop unrolling.
 </p>
 <p>This option is enabled by default at optimization levels <samp>-O</samp>,
 <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-ffp-contract=<var>style</var></code></dt>
 <dd><a name="index-ffp_002dcontract"></a>
 <p><samp>-ffp-contract=off</samp> disables floating-point expression contraction.
 <samp>-ffp-contract=fast</samp> enables floating-point expression contraction
 such as forming of fused multiply-add operations if the target has
 native support for them.
 <samp>-ffp-contract=on</samp> enables floating-point expression contraction
 if allowed by the language standard.  This is currently not implemented
 and treated equal to <samp>-ffp-contract=off</samp>.
 </p>
 <p>The default is <samp>-ffp-contract=fast</samp>.
 </p>
 </dd>
 <dt><code>-fomit-frame-pointer</code></dt>
 <dd><a name="index-fomit_002dframe_002dpointer"></a>
 <p>Don&rsquo;t keep the frame pointer in a register for functions that
 don&rsquo;t need one.  This avoids the instructions to save, set up and
 restore frame pointers; it also makes an extra register available
 in many functions.  <strong>It also makes debugging impossible on
 some machines.</strong>
 </p>
 <p>On some machines, such as the VAX, this flag has no effect, because
 the standard calling sequence automatically handles the frame pointer
 and nothing is saved by pretending it doesn&rsquo;t exist.  The
 machine-description macro <code>FRAME_POINTER_REQUIRED</code> controls
 whether a target machine supports this flag.  See <a href="http://gcc.gnu.org/onlinedocs/gccint/Registers.html#Registers">Register
 Usage</a> in <cite>GNU Compiler Collection (GCC) Internals</cite>.
 </p>
 <p>Starting with GCC version 4.6, the default setting (when not optimizing for
 size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets has been changed to
 <samp>-fomit-frame-pointer</samp>.  The default can be reverted to
 <samp>-fno-omit-frame-pointer</samp> by configuring GCC with the
 <samp>--enable-frame-pointer</samp> configure option.
 </p>
 <p>Enabled at levels <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-foptimize-sibling-calls</code></dt>
 <dd><a name="index-foptimize_002dsibling_002dcalls"></a>
 <p>Optimize sibling and tail recursive calls.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fno-inline</code></dt>
 <dd><a name="index-fno_002dinline"></a>
 <p>Do not expand any functions inline apart from those marked with
 the <code>always_inline</code> attribute.  This is the default when not
 optimizing.
 </p>
 <p>Single functions can be exempted from inlining by marking them
 with the <code>noinline</code> attribute.
 </p>
 </dd>
 <dt><code>-finline-small-functions</code></dt>
 <dd><a name="index-finline_002dsmall_002dfunctions"></a>
 <p>Integrate functions into their callers when their body is smaller than expected
 function call code (so overall size of program gets smaller).  The compiler
 heuristically decides which functions are simple enough to be worth integrating
 in this way.  This inlining applies to all functions, even those not declared
 inline.
 </p>
 <p>Enabled at level <samp>-O2</samp>.
 </p>
 </dd>
 <dt><code>-findirect-inlining</code></dt>
 <dd><a name="index-findirect_002dinlining"></a>
 <p>Inline also indirect calls that are discovered to be known at compile
 time thanks to previous inlining.  This option has any effect only
 when inlining itself is turned on by the <samp>-finline-functions</samp>
 or <samp>-finline-small-functions</samp> options.
 </p>
 <p>Enabled at level <samp>-O2</samp>.
 </p>
 </dd>
 <dt><code>-finline-functions</code></dt>
 <dd><a name="index-finline_002dfunctions"></a>
 <p>Consider all functions for inlining, even if they are not declared inline.
 The compiler heuristically decides which functions are worth integrating
 in this way.
 </p>
 <p>If all calls to a given function are integrated, and the function is
 declared <code>static</code>, then the function is normally not output as
 assembler code in its own right.
 </p>
 <p>Enabled at level <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-finline-functions-called-once</code></dt>
 <dd><a name="index-finline_002dfunctions_002dcalled_002donce"></a>
 <p>Consider all <code>static</code> functions called once for inlining into their
 caller even if they are not marked <code>inline</code>.  If a call to a given
 function is integrated, then the function is not output as assembler code
 in its own right.
 </p>
 <p>Enabled at levels <samp>-O1</samp>, <samp>-O2</samp>, <samp>-O3</samp> and <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fearly-inlining</code></dt>
 <dd><a name="index-fearly_002dinlining"></a>
 <p>Inline functions marked by <code>always_inline</code> and functions whose body seems
 smaller than the function call overhead early before doing
 <samp>-fprofile-generate</samp> instrumentation and real inlining pass.  Doing so
 makes profiling significantly cheaper and usually inlining faster on programs
 having large chains of nested wrapper functions.
 </p>
 <p>Enabled by default.
 </p>
 </dd>
 <dt><code>-fipa-sra</code></dt>
 <dd><a name="index-fipa_002dsra"></a>
 <p>Perform interprocedural scalar replacement of aggregates, removal of
 unused parameters and replacement of parameters passed by reference
 by parameters passed by value.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp> and <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-finline-limit=<var>n</var></code></dt>
 <dd><a name="index-finline_002dlimit"></a>
 <p>By default, GCC limits the size of functions that can be inlined.  This flag
 allows coarse control of this limit.  <var>n</var> is the size of functions that
 can be inlined in number of pseudo instructions.
 </p>
 <p>Inlining is actually controlled by a number of parameters, which may be
 specified individually by using <samp>--param <var>name</var>=<var>value</var></samp>.
 The <samp>-finline-limit=<var>n</var></samp> option sets some of these parameters
 as follows:
 </p>
 <dl compact="compact">
 <dt><code>max-inline-insns-single</code></dt>
 <dd><p>is set to <var>n</var>/2.
 </p></dd>
 <dt><code>max-inline-insns-auto</code></dt>
 <dd><p>is set to <var>n</var>/2.
 </p></dd>
 </dl>

 <p>See below for a documentation of the individual
 parameters controlling inlining and for the defaults of these parameters.
 </p>
 <p><em>Note:</em> there may be no value to <samp>-finline-limit</samp> that results
 in default behavior.
 </p>
 <p><em>Note:</em> pseudo instruction represents, in this particular context, an
 abstract measurement of function&rsquo;s size.  In no way does it represent a count
 of assembly instructions and as such its exact meaning might change from one
 release to an another.
 </p>
 </dd>
 <dt><code>-fno-keep-inline-dllexport</code></dt>
 <dd><a name="index-_002dfno_002dkeep_002dinline_002ddllexport"></a>
 <p>This is a more fine-grained version of <samp>-fkeep-inline-functions</samp>,
 which applies only to functions that are declared using the <code>dllexport</code>
 attribute or declspec (See <a href="Function-Attributes.html#Function-Attributes">Declaring Attributes of
 Functions</a>.)
 </p>
 </dd>
 <dt><code>-fkeep-inline-functions</code></dt>
 <dd><a name="index-fkeep_002dinline_002dfunctions"></a>
 <p>In C, emit <code>static</code> functions that are declared <code>inline</code>
 into the object file, even if the function has been inlined into all
 of its callers.  This switch does not affect functions using the
 <code>extern inline</code> extension in GNU C90.  In C++, emit any and all
 inline functions into the object file.
 </p>
 </dd>
 <dt><code>-fkeep-static-consts</code></dt>
 <dd><a name="index-fkeep_002dstatic_002dconsts"></a>
 <p>Emit variables declared <code>static const</code> when optimization isn&rsquo;t turned
 on, even if the variables aren&rsquo;t referenced.
 </p>
 <p>GCC enables this option by default.  If you want to force the compiler to
 check if a variable is referenced, regardless of whether or not
 optimization is turned on, use the <samp>-fno-keep-static-consts</samp> option.
 </p>
 </dd>
 <dt><code>-fmerge-constants</code></dt>
 <dd><a name="index-fmerge_002dconstants"></a>
 <p>Attempt to merge identical constants (string constants and floating-point
 constants) across compilation units.
 </p>
 <p>This option is the default for optimized compilation if the assembler and
 linker support it.  Use <samp>-fno-merge-constants</samp> to inhibit this
 behavior.
 </p>
 <p>Enabled at levels <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fmerge-all-constants</code></dt>
 <dd><a name="index-fmerge_002dall_002dconstants"></a>
 <p>Attempt to merge identical constants and identical variables.
 </p>
 <p>This option implies <samp>-fmerge-constants</samp>.  In addition to
 <samp>-fmerge-constants</samp> this considers e.g. even constant initialized
 arrays or initialized constant variables with integral or floating-point
 types.  Languages like C or C++ require each variable, including multiple
 instances of the same variable in recursive calls, to have distinct locations,
 so using this option results in non-conforming
 behavior.
 </p>
 </dd>
 <dt><code>-fmodulo-sched</code></dt>
 <dd><a name="index-fmodulo_002dsched"></a>
 <p>Perform swing modulo scheduling immediately before the first scheduling
 pass.  This pass looks at innermost loops and reorders their
 instructions by overlapping different iterations.
 </p>
 </dd>
 <dt><code>-fmodulo-sched-allow-regmoves</code></dt>
 <dd><a name="index-fmodulo_002dsched_002dallow_002dregmoves"></a>
 <p>Perform more aggressive SMS-based modulo scheduling with register moves
 allowed.  By setting this flag certain anti-dependences edges are
 deleted, which triggers the generation of reg-moves based on the
 life-range analysis.  This option is effective only with
 <samp>-fmodulo-sched</samp> enabled.
 </p>
 </dd>
 <dt><code>-fno-branch-count-reg</code></dt>
 <dd><a name="index-fno_002dbranch_002dcount_002dreg"></a>
 <p>Do not use &ldquo;decrement and branch&rdquo; instructions on a count register,
 but instead generate a sequence of instructions that decrement a
 register, compare it against zero, then branch based upon the result.
 This option is only meaningful on architectures that support such
 instructions, which include x86, PowerPC, IA-64 and S/390.
 </p>
 <p>The default is <samp>-fbranch-count-reg</samp>.
 </p>
 </dd>
 <dt><code>-fno-function-cse</code></dt>
 <dd><a name="index-fno_002dfunction_002dcse"></a>
 <p>Do not put function addresses in registers; make each instruction that
 calls a constant function contain the function&rsquo;s address explicitly.
 </p>
 <p>This option results in less efficient code, but some strange hacks
 that alter the assembler output may be confused by the optimizations
 performed when this option is not used.
 </p>
 <p>The default is <samp>-ffunction-cse</samp>
 </p>
 </dd>
 <dt><code>-fno-zero-initialized-in-bss</code></dt>
 <dd><a name="index-fno_002dzero_002dinitialized_002din_002dbss"></a>
 <p>If the target supports a BSS section, GCC by default puts variables that
 are initialized to zero into BSS.  This can save space in the resulting
 code.
 </p>
 <p>This option turns off this behavior because some programs explicitly
 rely on variables going to the data section&mdash;e.g., so that the
 resulting executable can find the beginning of that section and/or make
 assumptions based on that.
 </p>
 <p>The default is <samp>-fzero-initialized-in-bss</samp>.
 </p>
 </dd>
 <dt><code>-fthread-jumps</code></dt>
 <dd><a name="index-fthread_002djumps"></a>
 <p>Perform optimizations that check to see if a jump branches to a
 location where another comparison subsumed by the first is found.  If
 so, the first branch is redirected to either the destination of the
 second branch or a point immediately following it, depending on whether
 the condition is known to be true or false.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fsplit-wide-types</code></dt>
 <dd><a name="index-fsplit_002dwide_002dtypes"></a>
 <p>When using a type that occupies multiple registers, such as <code>long
 long</code> on a 32-bit system, split the registers apart and allocate them
 independently.  This normally generates better code for those types,
 but may make debugging more difficult.
 </p>
 <p>Enabled at levels <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>,
 <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fcse-follow-jumps</code></dt>
 <dd><a name="index-fcse_002dfollow_002djumps"></a>
 <p>In common subexpression elimination (CSE), scan through jump instructions
 when the target of the jump is not reached by any other path.  For
 example, when CSE encounters an <code>if</code> statement with an
 <code>else</code> clause, CSE follows the jump when the condition
 tested is false.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fcse-skip-blocks</code></dt>
 <dd><a name="index-fcse_002dskip_002dblocks"></a>
 <p>This is similar to <samp>-fcse-follow-jumps</samp>, but causes CSE to
 follow jumps that conditionally skip over blocks.  When CSE
 encounters a simple <code>if</code> statement with no else clause,
 <samp>-fcse-skip-blocks</samp> causes CSE to follow the jump around the
 body of the <code>if</code>.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-frerun-cse-after-loop</code></dt>
 <dd><a name="index-frerun_002dcse_002dafter_002dloop"></a>
 <p>Re-run common subexpression elimination after loop optimizations are
 performed.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fgcse</code></dt>
 <dd><a name="index-fgcse"></a>
 <p>Perform a global common subexpression elimination pass.
 This pass also performs global constant and copy propagation.
 </p>
 <p><em>Note:</em> When compiling a program using computed gotos, a GCC
 extension, you may get better run-time performance if you disable
 the global common subexpression elimination pass by adding
 <samp>-fno-gcse</samp> to the command line.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fgcse-lm</code></dt>
 <dd><a name="index-fgcse_002dlm"></a>
 <p>When <samp>-fgcse-lm</samp> is enabled, global common subexpression elimination
 attempts to move loads that are only killed by stores into themselves.  This
 allows a loop containing a load/store sequence to be changed to a load outside
 the loop, and a copy/store within the loop.
 </p>
 <p>Enabled by default when <samp>-fgcse</samp> is enabled.
 </p>
 </dd>
 <dt><code>-fgcse-sm</code></dt>
 <dd><a name="index-fgcse_002dsm"></a>
 <p>When <samp>-fgcse-sm</samp> is enabled, a store motion pass is run after
 global common subexpression elimination.  This pass attempts to move
 stores out of loops.  When used in conjunction with <samp>-fgcse-lm</samp>,
 loops containing a load/store sequence can be changed to a load before
 the loop and a store after the loop.
 </p>
 <p>Not enabled at any optimization level.
 </p>
 </dd>
 <dt><code>-fgcse-las</code></dt>
 <dd><a name="index-fgcse_002dlas"></a>
 <p>When <samp>-fgcse-las</samp> is enabled, the global common subexpression
 elimination pass eliminates redundant loads that come after stores to the
 same memory location (both partial and full redundancies).
 </p>
 <p>Not enabled at any optimization level.
 </p>
 </dd>
 <dt><code>-fgcse-after-reload</code></dt>
 <dd><a name="index-fgcse_002dafter_002dreload"></a>
 <p>When <samp>-fgcse-after-reload</samp> is enabled, a redundant load elimination
 pass is performed after reload.  The purpose of this pass is to clean up
 redundant spilling.
 </p>
 </dd>
 <dt><code>-faggressive-loop-optimizations</code></dt>
 <dd><a name="index-faggressive_002dloop_002doptimizations"></a>
 <p>This option tells the loop optimizer to use language constraints to
 derive bounds for the number of iterations of a loop.  This assumes that
 loop code does not invoke undefined behavior by for example causing signed
 integer overflows or out-of-bound array accesses.  The bounds for the
 number of iterations of a loop are used to guide loop unrolling and peeling
 and loop exit test optimizations.
 This option is enabled by default.
 </p>
 </dd>
 <dt><code>-funsafe-loop-optimizations</code></dt>
 <dd><a name="index-funsafe_002dloop_002doptimizations"></a>
 <p>This option tells the loop optimizer to assume that loop indices do not
 overflow, and that loops with nontrivial exit condition are not
 infinite.  This enables a wider range of loop optimizations even if
 the loop optimizer itself cannot prove that these assumptions are valid.
 If you use <samp>-Wunsafe-loop-optimizations</samp>, the compiler warns you
 if it finds this kind of loop.
 </p>
 </dd>
 <dt><code>-fcrossjumping</code></dt>
 <dd><a name="index-fcrossjumping"></a>
 <p>Perform cross-jumping transformation.
 This transformation unifies equivalent code and saves code size.  The
 resulting code may or may not perform better than without cross-jumping.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fauto-inc-dec</code></dt>
 <dd><a name="index-fauto_002dinc_002ddec"></a>
 <p>Combine increments or decrements of addresses with memory accesses.
 This pass is always skipped on architectures that do not have
 instructions to support this.  Enabled by default at <samp>-O</samp> and
 higher on architectures that support this.
 </p>
 </dd>
 <dt><code>-fdce</code></dt>
 <dd><a name="index-fdce"></a>
 <p>Perform dead code elimination (DCE) on RTL.
 Enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-fdse</code></dt>
 <dd><a name="index-fdse"></a>
 <p>Perform dead store elimination (DSE) on RTL.
 Enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-fif-conversion</code></dt>
 <dd><a name="index-fif_002dconversion"></a>
 <p>Attempt to transform conditional jumps into branch-less equivalents.  This
 includes use of conditional moves, min, max, set flags and abs instructions, and
 some tricks doable by standard arithmetics.  The use of conditional execution
 on chips where it is available is controlled by <code>if-conversion2</code>.
 </p>
 <p>Enabled at levels <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fif-conversion2</code></dt>
 <dd><a name="index-fif_002dconversion2"></a>
 <p>Use conditional execution (where available) to transform conditional jumps into
 branch-less equivalents.
 </p>
 <p>Enabled at levels <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fdeclone-ctor-dtor</code></dt>
 <dd><a name="index-fdeclone_002dctor_002ddtor"></a>
 <p>The C++ ABI requires multiple entry points for constructors and
 destructors: one for a base subobject, one for a complete object, and
 one for a virtual destructor that calls operator delete afterwards.
 For a hierarchy with virtual bases, the base and complete variants are
 clones, which means two copies of the function.  With this option, the
 base and complete variants are changed to be thunks that call a common
 implementation.
 </p>
 <p>Enabled by <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fdelete-null-pointer-checks</code></dt>
 <dd><a name="index-fdelete_002dnull_002dpointer_002dchecks"></a>
 <p>Assume that programs cannot safely dereference null pointers, and that
 no code or data element resides there.  This enables simple constant
 folding optimizations at all optimization levels.  In addition, other
 optimization passes in GCC use this flag to control global dataflow
 analyses that eliminate useless checks for null pointers; these assume
 that if a pointer is checked after it has already been dereferenced,
 it cannot be null.
 </p>
 <p>Note however that in some environments this assumption is not true.
 Use <samp>-fno-delete-null-pointer-checks</samp> to disable this optimization
 for programs that depend on that behavior.
 </p>
 <p>Some targets, especially embedded ones, disable this option at all levels.
 Otherwise it is enabled at all levels: <samp>-O0</samp>, <samp>-O1</samp>,
 <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.  Passes that use the information
 are enabled independently at different optimization levels.
 </p>
 </dd>
 <dt><code>-fdevirtualize</code></dt>
 <dd><a name="index-fdevirtualize"></a>
 <p>Attempt to convert calls to virtual functions to direct calls.  This
 is done both within a procedure and interprocedurally as part of
 indirect inlining (<code>-findirect-inlining</code>) and interprocedural constant
 propagation (<samp>-fipa-cp</samp>).
 Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fdevirtualize-speculatively</code></dt>
 <dd><a name="index-fdevirtualize_002dspeculatively"></a>
 <p>Attempt to convert calls to virtual functions to speculative direct calls.
 Based on the analysis of the type inheritance graph, determine for a given call
 the set of likely targets. If the set is small, preferably of size 1, change
 the call into an conditional deciding on direct and indirect call.  The
 speculative calls enable more optimizations, such as inlining.  When they seem
 useless after further optimization, they are converted back into original form.
 </p>
 </dd>
 <dt><code>-fexpensive-optimizations</code></dt>
 <dd><a name="index-fexpensive_002doptimizations"></a>
 <p>Perform a number of minor optimizations that are relatively expensive.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-free</code></dt>
 <dd><a name="index-free"></a>
 <p>Attempt to remove redundant extension instructions.  This is especially
 helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit
 registers after writing to their lower 32-bit half.
 </p>
 <p>Enabled for Alpha, AArch64 and x86 at levels <samp>-O2</samp>,
 <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fno-lifetime-dse</code></dt>
 <dd><a name="index-fno_002dlifetime_002ddse"></a>
 <p>In C++ the value of an object is only affected by changes within its
 lifetime: when the constructor begins, the object has an indeterminate
 value, and any changes during the lifetime of the object are dead when
 the object is destroyed.  Normally dead store elimination will take
 advantage of this; if your code relies on the value of the object
 storage persisting beyond the lifetime of the object, you can use this
 flag to disable this optimization.
 </p>
 </dd>
 <dt><code>-flive-range-shrinkage</code></dt>
 <dd><a name="index-flive_002drange_002dshrinkage"></a>
 <p>Attempt to decrease register pressure through register live range
 shrinkage.  This is helpful for fast processors with small or moderate
 size register sets.
 </p>
 </dd>
 <dt><code>-fira-algorithm=<var>algorithm</var></code></dt>
 <dd><p>Use the specified coloring algorithm for the integrated register
 allocator.  The <var>algorithm</var> argument can be &lsquo;<samp>priority</samp>&rsquo;, which
 specifies Chow&rsquo;s priority coloring, or &lsquo;<samp>CB</samp>&rsquo;, which specifies
 Chaitin-Briggs coloring.  Chaitin-Briggs coloring is not implemented
 for all architectures, but for those targets that do support it, it is
 the default because it generates better code.
 </p>
 </dd>
 <dt><code>-fira-region=<var>region</var></code></dt>
 <dd><p>Use specified regions for the integrated register allocator.  The
 <var>region</var> argument should be one of the following:
 </p>
 <dl compact="compact">
 <dt>&lsquo;<samp>all</samp>&rsquo;</dt>
 <dd><p>Use all loops as register allocation regions.
 This can give the best results for machines with a small and/or
 irregular register set.
 </p>
 </dd>
 <dt>&lsquo;<samp>mixed</samp>&rsquo;</dt>
 <dd><p>Use all loops except for loops with small register pressure
 as the regions.  This value usually gives
 the best results in most cases and for most architectures,
 and is enabled by default when compiling with optimization for speed
 (<samp>-O</samp>, <samp>-O2</samp>, &hellip;).
 </p>
 </dd>
 <dt>&lsquo;<samp>one</samp>&rsquo;</dt>
 <dd><p>Use all functions as a single region.
 This typically results in the smallest code size, and is enabled by default for
 <samp>-Os</samp> or <samp>-O0</samp>.
 </p>
 </dd>
 </dl>

 </dd>
 <dt><code>-fira-hoist-pressure</code></dt>
 <dd><a name="index-fira_002dhoist_002dpressure"></a>
 <p>Use IRA to evaluate register pressure in the code hoisting pass for
 decisions to hoist expressions.  This option usually results in smaller
 code, but it can slow the compiler down.
 </p>
 <p>This option is enabled at level <samp>-Os</samp> for all targets.
 </p>
 </dd>
 <dt><code>-fira-loop-pressure</code></dt>
 <dd><a name="index-fira_002dloop_002dpressure"></a>
 <p>Use IRA to evaluate register pressure in loops for decisions to move
 loop invariants.  This option usually results in generation
 of faster and smaller code on machines with large register files (&gt;= 32
 registers), but it can slow the compiler down.
 </p>
 <p>This option is enabled at level <samp>-O3</samp> for some targets.
 </p>
 </dd>
 <dt><code>-fno-ira-share-save-slots</code></dt>
 <dd><a name="index-fno_002dira_002dshare_002dsave_002dslots"></a>
 <p>Disable sharing of stack slots used for saving call-used hard
 registers living through a call.  Each hard register gets a
 separate stack slot, and as a result function stack frames are
 larger.
 </p>
 </dd>
 <dt><code>-fno-ira-share-spill-slots</code></dt>
 <dd><a name="index-fno_002dira_002dshare_002dspill_002dslots"></a>
 <p>Disable sharing of stack slots allocated for pseudo-registers.  Each
 pseudo-register that does not get a hard register gets a separate
 stack slot, and as a result function stack frames are larger.
 </p>
 </dd>
 <dt><code>-fira-verbose=<var>n</var></code></dt>
 <dd><a name="index-fira_002dverbose"></a>
 <p>Control the verbosity of the dump file for the integrated register allocator.
 The default value is 5.  If the value <var>n</var> is greater or equal to 10,
 the dump output is sent to stderr using the same format as <var>n</var> minus 10.
 </p>
 </dd>
 <dt><code>-fdelayed-branch</code></dt>
 <dd><a name="index-fdelayed_002dbranch"></a>
 <p>If supported for the target machine, attempt to reorder instructions
 to exploit instruction slots available after delayed branch
 instructions.
 </p>
 <p>Enabled at levels <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fschedule-insns</code></dt>
 <dd><a name="index-fschedule_002dinsns"></a>
 <p>If supported for the target machine, attempt to reorder instructions to
 eliminate execution stalls due to required data being unavailable.  This
 helps machines that have slow floating point or memory load instructions
 by allowing other instructions to be issued until the result of the load
 or floating-point instruction is required.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-fschedule-insns2</code></dt>
 <dd><a name="index-fschedule_002dinsns2"></a>
 <p>Similar to <samp>-fschedule-insns</samp>, but requests an additional pass of
 instruction scheduling after register allocation has been done.  This is
 especially useful on machines with a relatively small number of
 registers and where memory load instructions take more than one cycle.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fno-sched-interblock</code></dt>
 <dd><a name="index-fno_002dsched_002dinterblock"></a>
 <p>Don&rsquo;t schedule instructions across basic blocks.  This is normally
 enabled by default when scheduling before register allocation, i.e.
 with <samp>-fschedule-insns</samp> or at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fno-sched-spec</code></dt>
 <dd><a name="index-fno_002dsched_002dspec"></a>
 <p>Don&rsquo;t allow speculative motion of non-load instructions.  This is normally
 enabled by default when scheduling before register allocation, i.e.
 with <samp>-fschedule-insns</samp> or at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fsched-pressure</code></dt>
 <dd><a name="index-fsched_002dpressure"></a>
 <p>Enable register pressure sensitive insn scheduling before register
 allocation.  This only makes sense when scheduling before register
 allocation is enabled, i.e. with <samp>-fschedule-insns</samp> or at
 <samp>-O2</samp> or higher.  Usage of this option can improve the
 generated code and decrease its size by preventing register pressure
 increase above the number of available hard registers and subsequent
 spills in register allocation.
 </p>
 </dd>
 <dt><code>-fsched-spec-load</code></dt>
 <dd><a name="index-fsched_002dspec_002dload"></a>
 <p>Allow speculative motion of some load instructions.  This only makes
 sense when scheduling before register allocation, i.e. with
 <samp>-fschedule-insns</samp> or at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fsched-spec-load-dangerous</code></dt>
 <dd><a name="index-fsched_002dspec_002dload_002ddangerous"></a>
 <p>Allow speculative motion of more load instructions.  This only makes
 sense when scheduling before register allocation, i.e. with
 <samp>-fschedule-insns</samp> or at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fsched-stalled-insns</code></dt>
 <dt><code>-fsched-stalled-insns=<var>n</var></code></dt>
 <dd><a name="index-fsched_002dstalled_002dinsns"></a>
 <p>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.
 <samp>-fno-sched-stalled-insns</samp> means that no insns are moved
 prematurely, <samp>-fsched-stalled-insns=0</samp> means there is no limit
 on how many queued insns can be moved prematurely.
 <samp>-fsched-stalled-insns</samp> without a value is equivalent to
 <samp>-fsched-stalled-insns=1</samp>.
 </p>
 </dd>
 <dt><code>-fsched-stalled-insns-dep</code></dt>
 <dt><code>-fsched-stalled-insns-dep=<var>n</var></code></dt>
 <dd><a name="index-fsched_002dstalled_002dinsns_002ddep"></a>
 <p>Define how many insn groups (cycles) are examined for a dependency
 on a stalled insn that is a candidate for premature removal from the queue
 of stalled insns.  This has an effect only during the second scheduling pass,
 and only if <samp>-fsched-stalled-insns</samp> is used.
 <samp>-fno-sched-stalled-insns-dep</samp> is equivalent to
 <samp>-fsched-stalled-insns-dep=0</samp>.
 <samp>-fsched-stalled-insns-dep</samp> without a value is equivalent to
 <samp>-fsched-stalled-insns-dep=1</samp>.
 </p>
 </dd>
 <dt><code>-fsched2-use-superblocks</code></dt>
 <dd><a name="index-fsched2_002duse_002dsuperblocks"></a>
 <p>When scheduling after register allocation, use superblock scheduling.
 This allows motion across basic block boundaries,
 resulting in faster schedules.  This option is experimental, as not all machine
 descriptions used by GCC model the CPU closely enough to avoid unreliable
 results from the algorithm.
 </p>
 <p>This only makes sense when scheduling after register allocation, i.e. with
 <samp>-fschedule-insns2</samp> or at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fsched-group-heuristic</code></dt>
 <dd><a name="index-fsched_002dgroup_002dheuristic"></a>
 <p>Enable the group heuristic in the scheduler.  This heuristic favors
 the instruction that belongs to a schedule group.  This is enabled
 by default when scheduling is enabled, i.e. with <samp>-fschedule-insns</samp>
 or <samp>-fschedule-insns2</samp> or at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fsched-critical-path-heuristic</code></dt>
 <dd><a name="index-fsched_002dcritical_002dpath_002dheuristic"></a>
 <p>Enable the critical-path heuristic in the scheduler.  This heuristic favors
 instructions on the critical path.  This is enabled by default when
 scheduling is enabled, i.e. with <samp>-fschedule-insns</samp>
 or <samp>-fschedule-insns2</samp> or at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fsched-spec-insn-heuristic</code></dt>
 <dd><a name="index-fsched_002dspec_002dinsn_002dheuristic"></a>
 <p>Enable the speculative instruction heuristic in the scheduler.  This
 heuristic favors speculative instructions with greater dependency weakness.
 This is enabled by default when scheduling is enabled, i.e.
 with <samp>-fschedule-insns</samp> or <samp>-fschedule-insns2</samp>
 or at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fsched-rank-heuristic</code></dt>
 <dd><a name="index-fsched_002drank_002dheuristic"></a>
 <p>Enable the rank heuristic in the scheduler.  This heuristic favors
 the instruction belonging to a basic block with greater size or frequency.
 This is enabled by default when scheduling is enabled, i.e.
 with <samp>-fschedule-insns</samp> or <samp>-fschedule-insns2</samp> or
 at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fsched-last-insn-heuristic</code></dt>
 <dd><a name="index-fsched_002dlast_002dinsn_002dheuristic"></a>
 <p>Enable the last-instruction heuristic in the scheduler.  This heuristic
 favors the instruction that is less dependent on the last instruction
 scheduled.  This is enabled by default when scheduling is enabled,
 i.e. with <samp>-fschedule-insns</samp> or <samp>-fschedule-insns2</samp> or
 at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-fsched-dep-count-heuristic</code></dt>
 <dd><a name="index-fsched_002ddep_002dcount_002dheuristic"></a>
 <p>Enable the dependent-count heuristic in the scheduler.  This heuristic
 favors the instruction that has more instructions depending on it.
 This is enabled by default when scheduling is enabled, i.e.
 with <samp>-fschedule-insns</samp> or <samp>-fschedule-insns2</samp> or
 at <samp>-O2</samp> or higher.
 </p>
 </dd>
 <dt><code>-freschedule-modulo-scheduled-loops</code></dt>
 <dd><a name="index-freschedule_002dmodulo_002dscheduled_002dloops"></a>
 <p>Modulo scheduling is performed before traditional scheduling.  If a loop
 is modulo scheduled, later scheduling passes may change its schedule.
 Use this option to control that behavior.
 </p>
 </dd>
 <dt><code>-fselective-scheduling</code></dt>
 <dd><a name="index-fselective_002dscheduling"></a>
 <p>Schedule instructions using selective scheduling algorithm.  Selective
 scheduling runs instead of the first scheduler pass.
 </p>
 </dd>
 <dt><code>-fselective-scheduling2</code></dt>
 <dd><a name="index-fselective_002dscheduling2"></a>
 <p>Schedule instructions using selective scheduling algorithm.  Selective
 scheduling runs instead of the second scheduler pass.
 </p>
 </dd>
 <dt><code>-fsel-sched-pipelining</code></dt>
 <dd><a name="index-fsel_002dsched_002dpipelining"></a>
 <p>Enable software pipelining of innermost loops during selective scheduling.
 This option has no effect unless one of <samp>-fselective-scheduling</samp> or
 <samp>-fselective-scheduling2</samp> is turned on.
 </p>
 </dd>
 <dt><code>-fsel-sched-pipelining-outer-loops</code></dt>
 <dd><a name="index-fsel_002dsched_002dpipelining_002douter_002dloops"></a>
 <p>When pipelining loops during selective scheduling, also pipeline outer loops.
 This option has no effect unless <samp>-fsel-sched-pipelining</samp> is turned on.
 </p>
 </dd>
 <dt><code>-fshrink-wrap</code></dt>
 <dd><a name="index-fshrink_002dwrap"></a>
 <p>Emit function prologues only before parts of the function that need it,
 rather than at the top of the function.  This flag is enabled by default at
 <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-fcaller-saves</code></dt>
 <dd><a name="index-fcaller_002dsaves"></a>
 <p>Enable allocation of values to registers that are clobbered by
 function calls, by emitting extra instructions to save and restore the
 registers around such calls.  Such allocation is done only when it
 seems to result in better code.
 </p>
 <p>This option is always enabled by default on certain machines, usually
 those which have no call-preserved registers to use instead.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fcombine-stack-adjustments</code></dt>
 <dd><a name="index-fcombine_002dstack_002dadjustments"></a>
 <p>Tracks stack adjustments (pushes and pops) and stack memory references
 and then tries to find ways to combine them.
 </p>
 <p>Enabled by default at <samp>-O1</samp> and higher.
 </p>
 </dd>
 <dt><code>-fconserve-stack</code></dt>
 <dd><a name="index-fconserve_002dstack"></a>
 <p>Attempt to minimize stack usage.  The compiler attempts to use less
 stack space, even if that makes the program slower.  This option
 implies setting the <samp>large-stack-frame</samp> parameter to 100
 and the <samp>large-stack-frame-growth</samp> parameter to 400.
 </p>
 </dd>
 <dt><code>-ftree-reassoc</code></dt>
 <dd><a name="index-ftree_002dreassoc"></a>
 <p>Perform reassociation on trees.  This flag is enabled by default
 at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-pre</code></dt>
 <dd><a name="index-ftree_002dpre"></a>
 <p>Perform partial redundancy elimination (PRE) on trees.  This flag is
 enabled by default at <samp>-O2</samp> and <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-ftree-partial-pre</code></dt>
 <dd><a name="index-ftree_002dpartial_002dpre"></a>
 <p>Make partial redundancy elimination (PRE) more aggressive.  This flag is
 enabled by default at <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-ftree-forwprop</code></dt>
 <dd><a name="index-ftree_002dforwprop"></a>
 <p>Perform forward propagation on trees.  This flag is enabled by default
 at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-fre</code></dt>
 <dd><a name="index-ftree_002dfre"></a>
 <p>Perform full redundancy elimination (FRE) on trees.  The difference
 between FRE and PRE is that FRE only considers expressions
 that are computed on all paths leading to the redundant computation.
 This analysis is faster than PRE, though it exposes fewer redundancies.
 This flag is enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-phiprop</code></dt>
 <dd><a name="index-ftree_002dphiprop"></a>
 <p>Perform hoisting of loads from conditional pointers on trees.  This
 pass is enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-fhoist-adjacent-loads</code></dt>
 <dd><a name="index-hoist_002dadjacent_002dloads"></a>
 <p>Speculatively hoist loads from both branches of an if-then-else if the
 loads are from adjacent locations in the same structure and the target
 architecture has a conditional move instruction.  This flag is enabled
 by default at <samp>-O2</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-copy-prop</code></dt>
 <dd><a name="index-ftree_002dcopy_002dprop"></a>
 <p>Perform copy propagation on trees.  This pass eliminates unnecessary
 copy operations.  This flag is enabled by default at <samp>-O</samp> and
 higher.
 </p>
 </dd>
 <dt><code>-fipa-pure-const</code></dt>
 <dd><a name="index-fipa_002dpure_002dconst"></a>
 <p>Discover which functions are pure or constant.
 Enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-fipa-reference</code></dt>
 <dd><a name="index-fipa_002dreference"></a>
 <p>Discover which static variables do not escape the
 compilation unit.
 Enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-fipa-pta</code></dt>
 <dd><a name="index-fipa_002dpta"></a>
 <p>Perform interprocedural pointer analysis and interprocedural modification
 and reference analysis.  This option can cause excessive memory and
 compile-time usage on large compilation units.  It is not enabled by
 default at any optimization level.
 </p>
 </dd>
 <dt><code>-fipa-profile</code></dt>
 <dd><a name="index-fipa_002dprofile"></a>
 <p>Perform interprocedural profile propagation.  The functions called only from
 cold functions are marked as cold. Also functions executed once (such as
 <code>cold</code>, <code>noreturn</code>, static constructors or destructors) are identified. Cold
 functions and loop less parts of functions executed once are then optimized for
 size.
 Enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-fipa-cp</code></dt>
 <dd><a name="index-fipa_002dcp"></a>
 <p>Perform interprocedural constant propagation.
 This optimization analyzes the program to determine when values passed
 to functions are constants and then optimizes accordingly.
 This optimization can substantially increase performance
 if the application has constants passed to functions.
 This flag is enabled by default at <samp>-O2</samp>, <samp>-Os</samp> and <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-fipa-cp-clone</code></dt>
 <dd><a name="index-fipa_002dcp_002dclone"></a>
 <p>Perform function cloning to make interprocedural constant propagation stronger.
 When enabled, interprocedural constant propagation performs function cloning
 when externally visible function can be called with constant arguments.
 Because this optimization can create multiple copies of functions,
 it may significantly increase code size
 (see <samp>--param ipcp-unit-growth=<var>value</var></samp>).
 This flag is enabled by default at <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-fisolate-erroneous-paths-dereference</code></dt>
 <dd><p>Detect paths which trigger erroneous or undefined behaviour due to
 dereferencing a NULL pointer.  Isolate those paths from the main control
 flow and turn the statement with erroneous or undefined behaviour into a trap.
 </p>
 </dd>
 <dt><code>-fisolate-erroneous-paths-attribute</code></dt>
 <dd><p>Detect paths which trigger erroneous or undefined behaviour due a NULL value
 being used in a way which is forbidden by a <code>returns_nonnull</code> or <code>nonnull</code>
 attribute.  Isolate those paths from the main control flow and turn the
 statement with erroneous or undefined behaviour into a trap.  This is not
 currently enabled, but may be enabled by <code>-O2</code> in the future.
 </p>
 </dd>
 <dt><code>-ftree-sink</code></dt>
 <dd><a name="index-ftree_002dsink"></a>
 <p>Perform forward store motion  on trees.  This flag is
 enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-bit-ccp</code></dt>
 <dd><a name="index-ftree_002dbit_002dccp"></a>
 <p>Perform sparse conditional bit constant propagation on trees and propagate
 pointer alignment information.
 This pass only operates on local scalar variables and is enabled by default
 at <samp>-O</samp> and higher.  It requires that <samp>-ftree-ccp</samp> is enabled.
 </p>
 </dd>
 <dt><code>-ftree-ccp</code></dt>
 <dd><a name="index-ftree_002dccp"></a>
 <p>Perform sparse conditional constant propagation (CCP) on trees.  This
 pass only operates on local scalar variables and is enabled by default
 at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-switch-conversion</code></dt>
 <dd><p>Perform conversion of simple initializations in a switch to
 initializations from a scalar array.  This flag is enabled by default
 at <samp>-O2</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-tail-merge</code></dt>
 <dd><p>Look for identical code sequences.  When found, replace one with a jump to the
 other.  This optimization is known as tail merging or cross jumping.  This flag
 is enabled by default at <samp>-O2</samp> and higher.  The compilation time
 in this pass can
 be limited using <samp>max-tail-merge-comparisons</samp> parameter and
 <samp>max-tail-merge-iterations</samp> parameter.
 </p>
 </dd>
 <dt><code>-ftree-dce</code></dt>
 <dd><a name="index-ftree_002ddce"></a>
 <p>Perform dead code elimination (DCE) on trees.  This flag is enabled by
 default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-builtin-call-dce</code></dt>
 <dd><a name="index-ftree_002dbuiltin_002dcall_002ddce"></a>
 <p>Perform conditional dead code elimination (DCE) for calls to built-in functions
 that may set <code>errno</code> but are otherwise side-effect free.  This flag is
 enabled by default at <samp>-O2</samp> and higher if <samp>-Os</samp> is not also
 specified.
 </p>
 </dd>
 <dt><code>-ftree-dominator-opts</code></dt>
 <dd><a name="index-ftree_002ddominator_002dopts"></a>
 <p>Perform a variety of simple scalar cleanups (constant/copy
 propagation, redundancy elimination, range propagation and expression
 simplification) based on a dominator tree traversal.  This also
 performs jump threading (to reduce jumps to jumps). This flag is
 enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-dse</code></dt>
 <dd><a name="index-ftree_002ddse"></a>
 <p>Perform dead store elimination (DSE) on trees.  A dead store is a store into
 a memory location that is later overwritten by another store without
 any intervening loads.  In this case the earlier store can be deleted.  This
 flag is enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-ch</code></dt>
 <dd><a name="index-ftree_002dch"></a>
 <p>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 <samp>-O</samp> and higher.  It is not enabled
 for <samp>-Os</samp>, since it usually increases code size.
 </p>
 </dd>
 <dt><code>-ftree-loop-optimize</code></dt>
 <dd><a name="index-ftree_002dloop_002doptimize"></a>
 <p>Perform loop optimizations on trees.  This flag is enabled by default
 at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-loop-linear</code></dt>
 <dd><a name="index-ftree_002dloop_002dlinear"></a>
 <p>Perform loop interchange transformations on tree.  Same as
 <samp>-floop-interchange</samp>.  To use this code transformation, GCC has
 to be configured with <samp>--with-ppl</samp> and <samp>--with-cloog</samp> to
 enable the Graphite loop transformation infrastructure.
 </p>
 </dd>
 <dt><code>-floop-interchange</code></dt>
 <dd><a name="index-floop_002dinterchange"></a>
 <p>Perform loop interchange transformations on loops.  Interchanging two
 nested loops switches the inner and outer loops.  For example, given a
 loop like:
 </p><div class="smallexample">
 <pre class="smallexample">DO J = 1, M
   DO I = 1, N
     A(J, I) = A(J, I) * C
   ENDDO
 ENDDO
 </pre></div>
 <p>loop interchange transforms the loop as if it were written:
 </p><div class="smallexample">
 <pre class="smallexample">DO I = 1, N
   DO J = 1, M
     A(J, I) = A(J, I) * C
   ENDDO
 ENDDO
 </pre></div>
 <p>which can be beneficial when <code>N</code> is larger than the caches,
 because in Fortran, the elements of an array are stored in memory
 contiguously by column, and the original loop iterates over rows,
 potentially creating at each access a cache miss.  This optimization
 applies to all the languages supported by GCC and is not limited to
 Fortran.  To use this code transformation, GCC has to be configured
 with <samp>--with-ppl</samp> and <samp>--with-cloog</samp> to enable the
 Graphite loop transformation infrastructure.
 </p>
 </dd>
 <dt><code>-floop-strip-mine</code></dt>
 <dd><a name="index-floop_002dstrip_002dmine"></a>
 <p>Perform loop strip mining transformations on loops.  Strip mining
 splits a loop into two nested loops.  The outer loop has strides
 equal to the strip size and the inner loop has strides of the
 original loop within a strip.  The strip length can be changed
 using the <samp>loop-block-tile-size</samp> parameter.  For example,
 given a loop like:
 </p><div class="smallexample">
 <pre class="smallexample">DO I = 1, N
   A(I) = A(I) + C
 ENDDO
 </pre></div>
 <p>loop strip mining transforms the loop as if it were written:
 </p><div class="smallexample">
 <pre class="smallexample">DO II = 1, N, 51
   DO I = II, min (II + 50, N)
     A(I) = A(I) + C
   ENDDO
 ENDDO
 </pre></div>
 <p>This optimization applies to all the languages supported by GCC and is
 not limited to Fortran.  To use this code transformation, GCC has to
 be configured with <samp>--with-ppl</samp> and <samp>--with-cloog</samp> to
 enable the Graphite loop transformation infrastructure.
 </p>
 </dd>
 <dt><code>-floop-block</code></dt>
 <dd><a name="index-floop_002dblock"></a>
 <p>Perform loop blocking transformations on loops.  Blocking strip mines
 each loop in the loop nest such that the memory accesses of the
 element loops fit inside caches.  The strip length can be changed
 using the <samp>loop-block-tile-size</samp> parameter.  For example, given
 a loop like:
 </p><div class="smallexample">
 <pre class="smallexample">DO I = 1, N
   DO J = 1, M
     A(J, I) = B(I) + C(J)
   ENDDO
 ENDDO
 </pre></div>
 <p>loop blocking transforms the loop as if it were written:
 </p><div class="smallexample">
 <pre class="smallexample">DO II = 1, N, 51
   DO JJ = 1, M, 51
     DO I = II, min (II + 50, N)
       DO J = JJ, min (JJ + 50, M)
         A(J, I) = B(I) + C(J)
       ENDDO
     ENDDO
   ENDDO
 ENDDO
 </pre></div>
 <p>which can be beneficial when <code>M</code> is larger than the caches,
 because the innermost loop iterates over a smaller amount of data
 which can be kept in the caches.  This optimization applies to all the
 languages supported by GCC and is not limited to Fortran.  To use this
 code transformation, GCC has to be configured with <samp>--with-ppl</samp>
 and <samp>--with-cloog</samp> to enable the Graphite loop transformation
 infrastructure.
 </p>
 </dd>
 <dt><code>-fgraphite-identity</code></dt>
 <dd><a name="index-fgraphite_002didentity"></a>
 <p>Enable the identity transformation for graphite.  For every SCoP we generate
 the polyhedral representation and transform it back to gimple.  Using
 <samp>-fgraphite-identity</samp> we can check the costs or benefits of the
 GIMPLE -&gt; GRAPHITE -&gt; GIMPLE transformation.  Some minimal optimizations
 are also performed by the code generator CLooG, like index splitting and
 dead code elimination in loops.
 </p>
 </dd>
 <dt><code>-floop-nest-optimize</code></dt>
 <dd><a name="index-floop_002dnest_002doptimize"></a>
 <p>Enable the ISL based loop nest optimizer.  This is a generic loop nest
 optimizer based on the Pluto optimization algorithms.  It calculates a loop
 structure optimized for data-locality and parallelism.  This option
 is experimental.
 </p>
 </dd>
 <dt><code>-floop-parallelize-all</code></dt>
 <dd><a name="index-floop_002dparallelize_002dall"></a>
 <p>Use the Graphite data dependence analysis to identify loops that can
 be parallelized.  Parallelize all the loops that can be analyzed to
 not contain loop carried dependences without checking that it is
 profitable to parallelize the loops.
 </p>
 </dd>
 <dt><code>-fcheck-data-deps</code></dt>
 <dd><a name="index-fcheck_002ddata_002ddeps"></a>
 <p>Compare the results of several data dependence analyzers.  This option
 is used for debugging the data dependence analyzers.
 </p>
 </dd>
 <dt><code>-ftree-loop-if-convert</code></dt>
 <dd><p>Attempt to transform conditional jumps in the innermost loops to
 branch-less equivalents.  The intent is to remove control-flow from
 the innermost loops in order to improve the ability of the
 vectorization pass to handle these loops.  This is enabled by default
 if vectorization is enabled.
 </p>
 </dd>
 <dt><code>-ftree-loop-if-convert-stores</code></dt>
 <dd><p>Attempt to also if-convert conditional jumps containing memory writes.
 This transformation can be unsafe for multi-threaded programs as it
 transforms conditional memory writes into unconditional memory writes.
 For example,
 </p><div class="smallexample">
 <pre class="smallexample">for (i = 0; i &lt; N; i++)
   if (cond)
     A[i] = expr;
 </pre></div>
 <p>is transformed to
 </p><div class="smallexample">
 <pre class="smallexample">for (i = 0; i &lt; N; i++)
   A[i] = cond ? expr : A[i];
 </pre></div>
 <p>potentially producing data races.
 </p>
 </dd>
 <dt><code>-ftree-loop-distribution</code></dt>
 <dd><p>Perform loop distribution.  This flag can improve cache performance on
 big loop bodies and allow further loop optimizations, like
 parallelization or vectorization, to take place.  For example, the loop
 </p><div class="smallexample">
 <pre class="smallexample">DO I = 1, N
   A(I) = B(I) + C
   D(I) = E(I) * F
 ENDDO
 </pre></div>
 <p>is transformed to
 </p><div class="smallexample">
 <pre class="smallexample">DO I = 1, N
    A(I) = B(I) + C
 ENDDO
 DO I = 1, N
    D(I) = E(I) * F
 ENDDO
 </pre></div>

 </dd>
 <dt><code>-ftree-loop-distribute-patterns</code></dt>
 <dd><p>Perform loop distribution of patterns that can be code generated with
 calls to a library.  This flag is enabled by default at <samp>-O3</samp>.
 </p>
 <p>This pass distributes the initialization loops and generates a call to
 memset zero.  For example, the loop
 </p><div class="smallexample">
 <pre class="smallexample">DO I = 1, N
   A(I) = 0
   B(I) = A(I) + I
 ENDDO
 </pre></div>
 <p>is transformed to
 </p><div class="smallexample">
 <pre class="smallexample">DO I = 1, N
    A(I) = 0
 ENDDO
 DO I = 1, N
    B(I) = A(I) + I
 ENDDO
 </pre></div>
 <p>and the initialization loop is transformed into a call to memset zero.
 </p>
 </dd>
 <dt><code>-ftree-loop-im</code></dt>
 <dd><a name="index-ftree_002dloop_002dim"></a>
 <p>Perform loop invariant motion on trees.  This pass moves only invariants that
 are hard to handle at RTL level (function calls, operations that expand to
 nontrivial sequences of insns).  With <samp>-funswitch-loops</samp> it also moves
 operands of conditions that are invariant out of the loop, so that we can use
 just trivial invariantness analysis in loop unswitching.  The pass also includes
 store motion.
 </p>
 </dd>
 <dt><code>-ftree-loop-ivcanon</code></dt>
 <dd><a name="index-ftree_002dloop_002divcanon"></a>
 <p>Create a canonical counter for number of iterations in loops for which
 determining number of iterations requires complicated analysis.  Later
 optimizations then may determine the number easily.  Useful especially
 in connection with unrolling.
 </p>
 </dd>
 <dt><code>-fivopts</code></dt>
 <dd><a name="index-fivopts"></a>
 <p>Perform induction variable optimizations (strength reduction, induction
 variable merging and induction variable elimination) on trees.
 </p>
 </dd>
 <dt><code>-ftree-parallelize-loops=n</code></dt>
 <dd><a name="index-ftree_002dparallelize_002dloops"></a>
 <p>Parallelize loops, i.e., split their iteration space to run in n threads.
 This is only possible for loops whose iterations are independent
 and can be arbitrarily reordered.  The optimization is only
 profitable on multiprocessor machines, for loops that are CPU-intensive,
 rather than constrained e.g. by memory bandwidth.  This option
 implies <samp>-pthread</samp>, and thus is only supported on targets
 that have support for <samp>-pthread</samp>.
 </p>
 </dd>
 <dt><code>-ftree-pta</code></dt>
 <dd><a name="index-ftree_002dpta"></a>
 <p>Perform function-local points-to analysis on trees.  This flag is
 enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-sra</code></dt>
 <dd><a name="index-ftree_002dsra"></a>
 <p>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 <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-copyrename</code></dt>
 <dd><a name="index-ftree_002dcopyrename"></a>
 <p>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 <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-coalesce-inlined-vars</code></dt>
 <dd><a name="index-ftree_002dcoalesce_002dinlined_002dvars"></a>
 <p>Tell the copyrename pass (see <samp>-ftree-copyrename</samp>) to attempt to
 combine small user-defined variables too, but only if they were inlined
 from other functions.  It is a more limited form of
 <samp>-ftree-coalesce-vars</samp>.  This may harm debug information of such
 inlined variables, but it will keep variables of the inlined-into
 function apart from each other, such that they are more likely to
 contain the expected values in a debugging session.  This was the
 default in GCC versions older than 4.7.
 </p>
 </dd>
 <dt><code>-ftree-coalesce-vars</code></dt>
 <dd><a name="index-ftree_002dcoalesce_002dvars"></a>
 <p>Tell the copyrename pass (see <samp>-ftree-copyrename</samp>) to attempt to
 combine small user-defined variables too, instead of just compiler
 temporaries.  This may severely limit the ability to debug an optimized
 program compiled with <samp>-fno-var-tracking-assignments</samp>.  In the
 negated form, this flag prevents SSA coalescing of user variables,
 including inlined ones.  This option is enabled by default.
 </p>
 </dd>
 <dt><code>-ftree-ter</code></dt>
 <dd><a name="index-ftree_002dter"></a>
 <p>Perform temporary expression replacement during the SSA-&gt;normal phase.  Single
 use/single def temporaries are replaced at their use location with their
 defining expression.  This results in non-GIMPLE code, but gives the expanders
 much more complex trees to work on resulting in better RTL generation.  This is
 enabled by default at <samp>-O</samp> and higher.
 </p>
 </dd>
 <dt><code>-ftree-slsr</code></dt>
 <dd><a name="index-ftree_002dslsr"></a>
 <p>Perform straight-line strength reduction on trees.  This recognizes related
 expressions involving multiplications and replaces them by less expensive
 calculations when possible.  This is enabled by default at <samp>-O</samp> and
 higher.
 </p>
 </dd>
 <dt><code>-ftree-vectorize</code></dt>
 <dd><a name="index-ftree_002dvectorize"></a>
 <p>Perform vectorization on trees. This flag enables <samp>-ftree-loop-vectorize</samp>
 and <samp>-ftree-slp-vectorize</samp> if not explicitly specified.
 </p>
 </dd>
 <dt><code>-ftree-loop-vectorize</code></dt>
 <dd><a name="index-ftree_002dloop_002dvectorize"></a>
 <p>Perform loop vectorization on trees. This flag is enabled by default at
 <samp>-O3</samp> and when <samp>-ftree-vectorize</samp> is enabled.
 </p>
 </dd>
 <dt><code>-ftree-slp-vectorize</code></dt>
 <dd><a name="index-ftree_002dslp_002dvectorize"></a>
 <p>Perform basic block vectorization on trees. This flag is enabled by default at
 <samp>-O3</samp> and when <samp>-ftree-vectorize</samp> is enabled.
 </p>
 </dd>
 <dt><code>-fvect-cost-model=<var>model</var></code></dt>
 <dd><a name="index-fvect_002dcost_002dmodel"></a>
 <p>Alter the cost model used for vectorization.  The <var>model</var> argument
 should be one of <code>unlimited</code>, <code>dynamic</code> or <code>cheap</code>.
 With the <code>unlimited</code> model the vectorized code-path is assumed
 to be profitable while with the <code>dynamic</code> model a runtime check
 will guard the vectorized code-path to enable it only for iteration
 counts that will likely execute faster than when executing the original
 scalar loop.  The <code>cheap</code> model will disable vectorization of
 loops where doing so would be cost prohibitive for example due to
 required runtime checks for data dependence or alignment but otherwise
 is equal to the <code>dynamic</code> model.
 The default cost model depends on other optimization flags and is
 either <code>dynamic</code> or <code>cheap</code>.
 </p>
 </dd>
 <dt><code>-fsimd-cost-model=<var>model</var></code></dt>
 <dd><a name="index-fsimd_002dcost_002dmodel"></a>
 <p>Alter the cost model used for vectorization of loops marked with the OpenMP
 or Cilk Plus simd directive.  The <var>model</var> argument should be one of
 <code>unlimited</code>, <code>dynamic</code>, <code>cheap</code>.  All values of <var>model</var>
 have the same meaning as described in <samp>-fvect-cost-model</samp> and by
 default a cost model defined with <samp>-fvect-cost-model</samp> is used.
 </p>
 </dd>
 <dt><code>-ftree-vrp</code></dt>
 <dd><a name="index-ftree_002dvrp"></a>
 <p>Perform Value Range Propagation on trees.  This is similar to the
 constant propagation pass, but instead of values, ranges of values are
 propagated.  This allows the optimizers to remove unnecessary range
 checks like array bound checks and null pointer checks.  This is
 enabled by default at <samp>-O2</samp> and higher.  Null pointer check
 elimination is only done if <samp>-fdelete-null-pointer-checks</samp> is
 enabled.
 </p>
 </dd>
 <dt><code>-ftracer</code></dt>
 <dd><a name="index-ftracer"></a>
 <p>Perform tail duplication to enlarge superblock size.  This transformation
 simplifies the control flow of the function allowing other optimizations to do
 a better job.
 </p>
 </dd>
 <dt><code>-funroll-loops</code></dt>
 <dd><a name="index-funroll_002dloops"></a>
 <p>Unroll loops whose number of iterations can be determined at compile
 time or upon entry to the loop.  <samp>-funroll-loops</samp> implies
 <samp>-frerun-cse-after-loop</samp>.  This option makes code larger,
 and may or may not make it run faster.
 </p>
 </dd>
 <dt><code>-funroll-all-loops</code></dt>
 <dd><a name="index-funroll_002dall_002dloops"></a>
 <p>Unroll all loops, even if their number of iterations is uncertain when
 the loop is entered.  This usually makes programs run more slowly.
 <samp>-funroll-all-loops</samp> implies the same options as
 <samp>-funroll-loops</samp>,
 </p>
 </dd>
 <dt><code>-fsplit-ivs-in-unroller</code></dt>
 <dd><a name="index-fsplit_002divs_002din_002dunroller"></a>
 <p>Enables expression of values of induction variables in later iterations
 of the unrolled loop using the value in the first iteration.  This breaks
 long dependency chains, thus improving efficiency of the scheduling passes.
 </p>
 <p>A combination of <samp>-fweb</samp> and CSE is often sufficient to obtain the
 same effect.  However, that is not reliable in cases where the loop body
 is more complicated than a single basic block.  It also does not work at all
 on some architectures due to restrictions in the CSE pass.
 </p>
 <p>This optimization is enabled by default.
 </p>
 </dd>
 <dt><code>-fvariable-expansion-in-unroller</code></dt>
 <dd><a name="index-fvariable_002dexpansion_002din_002dunroller"></a>
 <p>With this option, the compiler creates multiple copies of some
 local variables when unrolling a loop, which can result in superior code.
 </p>
 </dd>
 <dt><code>-fpartial-inlining</code></dt>
 <dd><a name="index-fpartial_002dinlining"></a>
 <p>Inline parts of functions.  This option has any effect only
 when inlining itself is turned on by the <samp>-finline-functions</samp>
 or <samp>-finline-small-functions</samp> options.
 </p>
 <p>Enabled at level <samp>-O2</samp>.
 </p>
 </dd>
 <dt><code>-fpredictive-commoning</code></dt>
 <dd><a name="index-fpredictive_002dcommoning"></a>
 <p>Perform predictive commoning optimization, i.e., reusing computations
 (especially memory loads and stores) performed in previous
 iterations of loops.
 </p>
 <p>This option is enabled at level <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-fprefetch-loop-arrays</code></dt>
 <dd><a name="index-fprefetch_002dloop_002darrays"></a>
 <p>If supported by the target machine, generate instructions to prefetch
 memory to improve the performance of loops that access large arrays.
 </p>
 <p>This option may generate better or worse code; results are highly
 dependent on the structure of loops within the source code.
 </p>
 <p>Disabled at level <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fno-peephole</code></dt>
 <dt><code>-fno-peephole2</code></dt>
 <dd><a name="index-fno_002dpeephole"></a>
 <a name="index-fno_002dpeephole2"></a>
 <p>Disable any machine-specific peephole optimizations.  The difference
 between <samp>-fno-peephole</samp> and <samp>-fno-peephole2</samp> is in how they
 are implemented in the compiler; some targets use one, some use the
 other, a few use both.
 </p>
 <p><samp>-fpeephole</samp> is enabled by default.
 <samp>-fpeephole2</samp> enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fno-guess-branch-probability</code></dt>
 <dd><a name="index-fno_002dguess_002dbranch_002dprobability"></a>
 <p>Do not guess branch probabilities using heuristics.
 </p>
 <p>GCC uses heuristics to guess branch probabilities if they are
 not provided by profiling feedback (<samp>-fprofile-arcs</samp>).  These
 heuristics are based on the control flow graph.  If some branch probabilities
 are specified by &lsquo;<samp>__builtin_expect</samp>&rsquo;, then the heuristics are
 used to guess branch probabilities for the rest of the control flow graph,
 taking the &lsquo;<samp>__builtin_expect</samp>&rsquo; info into account.  The interactions
 between the heuristics and &lsquo;<samp>__builtin_expect</samp>&rsquo; can be complex, and in
 some cases, it may be useful to disable the heuristics so that the effects
 of &lsquo;<samp>__builtin_expect</samp>&rsquo; are easier to understand.
 </p>
 <p>The default is <samp>-fguess-branch-probability</samp> at levels
 <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-freorder-blocks</code></dt>
 <dd><a name="index-freorder_002dblocks"></a>
 <p>Reorder basic blocks in the compiled function in order to reduce number of
 taken branches and improve code locality.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-freorder-blocks-and-partition</code></dt>
 <dd><a name="index-freorder_002dblocks_002dand_002dpartition"></a>
 <p>In addition to reordering basic blocks in the compiled function, in order
 to reduce number of taken branches, partitions hot and cold basic blocks
 into separate sections of the assembly and .o files, to improve
 paging and cache locality performance.
 </p>
 <p>This optimization is automatically turned off in the presence of
 exception handling, for linkonce sections, for functions with a user-defined
 section attribute and on any architecture that does not support named
 sections.
 </p>
 <p>Enabled for x86 at levels <samp>-O2</samp>, <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-freorder-functions</code></dt>
 <dd><a name="index-freorder_002dfunctions"></a>
 <p>Reorder functions in the object file in order to
 improve code locality.  This is implemented by using special
 subsections <code>.text.hot</code> for most frequently executed functions and
 <code>.text.unlikely</code> for unlikely executed functions.  Reordering is done by
 the linker so object file format must support named sections and linker must
 place them in a reasonable way.
 </p>
 <p>Also profile feedback must be available to make this option effective.  See
 <samp>-fprofile-arcs</samp> for details.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fstrict-aliasing</code></dt>
 <dd><a name="index-fstrict_002daliasing"></a>
 <p>Allow the compiler to assume the strictest aliasing rules applicable to
 the language being compiled.  For C (and C++), this activates
 optimizations based on the type of expressions.  In particular, an
 object of one type is assumed never to reside at the same address as an
 object of a different type, unless the types are almost the same.  For
 example, an <code>unsigned int</code> can alias an <code>int</code>, but not a
 <code>void*</code> or a <code>double</code>.  A character type may alias any other
 type.
 </p>
 <a name="Type_002dpunning"></a><p>Pay special attention to code like this:
 </p><div class="smallexample">
 <pre class="smallexample">union a_union {
   int i;
   double d;
 };

 int f() {
   union a_union t;
   t.d = 3.0;
   return t.i;
 }
 </pre></div>
 <p>The practice of reading from a different union member than the one most
 recently written to (called &ldquo;type-punning&rdquo;) is common.  Even with
 <samp>-fstrict-aliasing</samp>, type-punning is allowed, provided the memory
 is accessed through the union type.  So, the code above works as
 expected.  See <a href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation">Structures unions enumerations and bit-fields implementation</a>.  However, this code might not:
 </p><div class="smallexample">
 <pre class="smallexample">int f() {
   union a_union t;
   int* ip;
   t.d = 3.0;
   ip = &amp;t.i;
   return *ip;
 }
 </pre></div>

 <p>Similarly, access by taking the address, casting the resulting pointer
 and dereferencing the result has undefined behavior, even if the cast
 uses a union type, e.g.:
 </p><div class="smallexample">
 <pre class="smallexample">int f() {
   double d = 3.0;
   return ((union a_union *) &amp;d)-&gt;i;
 }
 </pre></div>

 <p>The <samp>-fstrict-aliasing</samp> option is enabled at levels
 <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fstrict-overflow</code></dt>
 <dd><a name="index-fstrict_002doverflow"></a>
 <p>Allow the compiler to assume strict signed overflow rules, depending
 on the language being compiled.  For C (and C++) this means that
 overflow when doing arithmetic with signed numbers is undefined, which
 means that the compiler may assume that it does not happen.  This
 permits various optimizations.  For example, the compiler assumes
 that an expression like <code>i + 10 &gt; i</code> is always true for
 signed <code>i</code>.  This assumption is only valid if signed overflow is
 undefined, as the expression is false if <code>i + 10</code> overflows when
 using twos complement arithmetic.  When this option is in effect any
 attempt to determine whether an operation on signed numbers
 overflows must be written carefully to not actually involve overflow.
 </p>
 <p>This option also allows the compiler to assume strict pointer
 semantics: given a pointer to an object, if adding an offset to that
 pointer does not produce a pointer to the same object, the addition is
 undefined.  This permits the compiler to conclude that <code>p + u &gt;
 p</code> is always true for a pointer <code>p</code> and unsigned integer
 <code>u</code>.  This assumption is only valid because pointer wraparound is
 undefined, as the expression is false if <code>p + u</code> overflows using
 twos complement arithmetic.
 </p>
 <p>See also the <samp>-fwrapv</samp> option.  Using <samp>-fwrapv</samp> means
 that integer signed overflow is fully defined: it wraps.  When
 <samp>-fwrapv</samp> is used, there is no difference between
 <samp>-fstrict-overflow</samp> and <samp>-fno-strict-overflow</samp> for
 integers.  With <samp>-fwrapv</samp> certain types of overflow are
 permitted.  For example, if the compiler gets an overflow when doing
 arithmetic on constants, the overflowed value can still be used with
 <samp>-fwrapv</samp>, but not otherwise.
 </p>
 <p>The <samp>-fstrict-overflow</samp> option is enabled at levels
 <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-falign-functions</code></dt>
 <dt><code>-falign-functions=<var>n</var></code></dt>
 <dd><a name="index-falign_002dfunctions"></a>
 <p>Align the start of functions to the next power-of-two greater than
 <var>n</var>, skipping up to <var>n</var> bytes.  For instance,
 <samp>-falign-functions=32</samp> aligns functions to the next 32-byte
 boundary, but <samp>-falign-functions=24</samp> aligns to the next
 32-byte boundary only if this can be done by skipping 23 bytes or less.
 </p>
 <p><samp>-fno-align-functions</samp> and <samp>-falign-functions=1</samp> are
 equivalent and mean that functions are not aligned.
 </p>
 <p>Some assemblers only support this flag when <var>n</var> is a power of two;
 in that case, it is rounded up.
 </p>
 <p>If <var>n</var> is not specified or is zero, use a machine-dependent default.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-falign-labels</code></dt>
 <dt><code>-falign-labels=<var>n</var></code></dt>
 <dd><a name="index-falign_002dlabels"></a>
 <p>Align all branch targets to a power-of-two boundary, skipping up to
 <var>n</var> bytes like <samp>-falign-functions</samp>.  This option can easily
 make code slower, because it must insert dummy operations for when the
 branch target is reached in the usual flow of the code.
 </p>
 <p><samp>-fno-align-labels</samp> and <samp>-falign-labels=1</samp> are
 equivalent and mean that labels are not aligned.
 </p>
 <p>If <samp>-falign-loops</samp> or <samp>-falign-jumps</samp> are applicable and
 are greater than this value, then their values are used instead.
 </p>
 <p>If <var>n</var> is not specified or is zero, use a machine-dependent default
 which is very likely to be &lsquo;<samp>1</samp>&rsquo;, meaning no alignment.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-falign-loops</code></dt>
 <dt><code>-falign-loops=<var>n</var></code></dt>
 <dd><a name="index-falign_002dloops"></a>
 <p>Align loops to a power-of-two boundary, skipping up to <var>n</var> bytes
 like <samp>-falign-functions</samp>.  If the loops are
 executed many times, this makes up for any execution of the dummy
 operations.
 </p>
 <p><samp>-fno-align-loops</samp> and <samp>-falign-loops=1</samp> are
 equivalent and mean that loops are not aligned.
 </p>
 <p>If <var>n</var> is not specified or is zero, use a machine-dependent default.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-falign-jumps</code></dt>
 <dt><code>-falign-jumps=<var>n</var></code></dt>
 <dd><a name="index-falign_002djumps"></a>
 <p>Align branch targets to a power-of-two boundary, for branch targets
 where the targets can only be reached by jumping, skipping up to <var>n</var>
 bytes like <samp>-falign-functions</samp>.  In this case, no dummy operations
 need be executed.
 </p>
 <p><samp>-fno-align-jumps</samp> and <samp>-falign-jumps=1</samp> are
 equivalent and mean that loops are not aligned.
 </p>
 <p>If <var>n</var> is not specified or is zero, use a machine-dependent default.
 </p>
 <p>Enabled at levels <samp>-O2</samp>, <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>-funit-at-a-time</code></dt>
 <dd><a name="index-funit_002dat_002da_002dtime"></a>
 <p>This option is left for compatibility reasons. <samp>-funit-at-a-time</samp>
 has no effect, while <samp>-fno-unit-at-a-time</samp> implies
 <samp>-fno-toplevel-reorder</samp> and <samp>-fno-section-anchors</samp>.
 </p>
 <p>Enabled by default.
 </p>
 </dd>
 <dt><code>-fno-toplevel-reorder</code></dt>
 <dd><a name="index-fno_002dtoplevel_002dreorder"></a>
 <p>Do not reorder top-level functions, variables, and <code>asm</code>
 statements.  Output them in the same order that they appear in the
 input file.  When this option is used, unreferenced static variables
 are not removed.  This option is intended to support existing code
 that relies on a particular ordering.  For new code, it is better to
 use attributes when possible.
 </p>
 <p>Enabled at level <samp>-O0</samp>.  When disabled explicitly, it also implies
 <samp>-fno-section-anchors</samp>, which is otherwise enabled at <samp>-O0</samp> on some
 targets.
 </p>
 </dd>
 <dt><code>-fweb</code></dt>
 <dd><a name="index-fweb"></a>
 <p>Constructs webs as commonly used for register allocation purposes and assign
 each web individual pseudo register.  This allows the register allocation pass
 to operate on pseudos directly, but also strengthens several other optimization
 passes, such as CSE, loop optimizer and trivial dead code remover.  It can,
 however, make debugging impossible, since variables no longer stay in a
 &ldquo;home register&rdquo;.
 </p>
 <p>Enabled by default with <samp>-funroll-loops</samp>.
 </p>
 </dd>
 <dt><code>-fwhole-program</code></dt>
 <dd><a name="index-fwhole_002dprogram"></a>
 <p>Assume that the current compilation unit represents the whole program being
 compiled.  All public functions and variables with the exception of <code>main</code>
 and those merged by attribute <code>externally_visible</code> become static functions
 and in effect are optimized more aggressively by interprocedural optimizers.
 </p>
 <p>This option should not be used in combination with <code>-flto</code>.
 Instead relying on a linker plugin should provide safer and more precise
 information.
 </p>
 </dd>
 <dt><code>-flto[=<var>n</var>]</code></dt>
 <dd><a name="index-flto"></a>
 <p>This option runs the standard link-time optimizer.  When invoked
 with source code, it generates GIMPLE (one of GCC&rsquo;s internal
 representations) and writes it to special ELF sections in the object
 file.  When the object files are linked together, all the function
 bodies are read from these ELF sections and instantiated as if they
 had been part of the same translation unit.
 </p>
 <p>To use the link-time optimizer, <samp>-flto</samp> and optimization
 options should be specified at compile time and during the final link.
 For example:
 </p>
 <div class="smallexample">
 <pre class="smallexample">gcc -c -O2 -flto foo.c
 gcc -c -O2 -flto bar.c
 gcc -o myprog -flto -O2 foo.o bar.o
 </pre></div>

 <p>The first two invocations to GCC save a bytecode representation
 of GIMPLE into special ELF sections inside <samp>foo.o</samp> and
 <samp>bar.o</samp>.  The final invocation reads the GIMPLE bytecode from
 <samp>foo.o</samp> and <samp>bar.o</samp>, merges the two files into a single
 internal image, and compiles the result as usual.  Since both
 <samp>foo.o</samp> and <samp>bar.o</samp> are merged into a single image, this
 causes all the interprocedural analyses and optimizations in GCC to
 work across the two files as if they were a single one.  This means,
 for example, that the inliner is able to inline functions in
 <samp>bar.o</samp> into functions in <samp>foo.o</samp> and vice-versa.
 </p>
 <p>Another (simpler) way to enable link-time optimization is:
 </p>
 <div class="smallexample">
 <pre class="smallexample">gcc -o myprog -flto -O2 foo.c bar.c
 </pre></div>

 <p>The above generates bytecode for <samp>foo.c</samp> and <samp>bar.c</samp>,
 merges them together into a single GIMPLE representation and optimizes
 them as usual to produce <samp>myprog</samp>.
 </p>
 <p>The only important thing to keep in mind is that to enable link-time
 optimizations you need to use the GCC driver to perform the link-step.
 GCC then automatically performs link-time optimization if any of the
 objects involved were compiled with the <samp>-flto</samp>.  You generally
 should specify the optimization options to be used for link-time
 optimization though GCC will try to be clever at guessing an
 optimization level to use from the options used at compile-time
 if you fail to specify one at link-time.  You can always override
 the automatic decision to do link-time optimization at link-time
 by passing <samp>-fno-lto</samp> to the link command.
 </p>
 <p>To make whole program optimization effective, it is necessary to make
 certain whole program assumptions.  The compiler needs to know
 what functions and variables can be accessed by libraries and runtime
 outside of the link-time optimized unit.  When supported by the linker,
 the linker plugin (see <samp>-fuse-linker-plugin</samp>) passes information
 to the compiler about used and externally visible symbols.  When
 the linker plugin is not available, <samp>-fwhole-program</samp> should be
 used to allow the compiler to make these assumptions, which leads
 to more aggressive optimization decisions.
 </p>
 <p>When <samp>-fuse-linker-plugin</samp> is not enabled then, when a file is
 compiled with <samp>-flto</samp>, the generated object file is larger than
 a regular object file because it contains GIMPLE bytecodes and the usual
 final code (see <samp>-ffat-lto-objects</samp>.  This means that
 object files with LTO information can be linked as normal object
 files; if <samp>-fno-lto</samp> is passed to the linker, no
 interprocedural optimizations are applied.  Note that when
 <samp>-fno-fat-lto-objects</samp> is enabled the compile-stage is faster
 but you cannot perform a regular, non-LTO link on them.
 </p>
 <p>Additionally, the optimization flags used to compile individual files
 are not necessarily related to those used at link time.  For instance,
 </p>
 <div class="smallexample">
 <pre class="smallexample">gcc -c -O0 -ffat-lto-objects -flto foo.c
 gcc -c -O0 -ffat-lto-objects -flto bar.c
 gcc -o myprog -O3 foo.o bar.o
 </pre></div>

 <p>This produces individual object files with unoptimized assembler
 code, but the resulting binary <samp>myprog</samp> is optimized at
 <samp>-O3</samp>.  If, instead, the final binary is generated with
 <samp>-fno-lto</samp>, then <samp>myprog</samp> is not optimized.
 </p>
 <p>When producing the final binary, GCC only
 applies link-time optimizations to those files that contain bytecode.
 Therefore, you can mix and match object files and libraries with
 GIMPLE bytecodes and final object code.  GCC automatically selects
 which files to optimize in LTO mode and which files to link without
 further processing.
 </p>
 <p>There are some code generation flags preserved by GCC when
 generating bytecodes, as they need to be used during the final link
 stage.  Generally options specified at link-time override those
 specified at compile-time.
 </p>
 <p>If you do not specify an optimization level option <samp>-O</samp> at
 link-time then GCC will compute one based on the optimization levels
 used when compiling the object files.  The highest optimization
 level will win here.
 </p>
 <p>Currently, the following options and their setting are take from
 the first object file that explicitely specified it:
 <samp>-fPIC</samp>, <samp>-fpic</samp>, <samp>-fpie</samp>, <samp>-fcommon</samp>,
 <samp>-fexceptions</samp>, <samp>-fnon-call-exceptions</samp>, <samp>-fgnu-tm</samp>
 and all the <samp>-m</samp> target flags.
 </p>
 <p>Certain ABI changing flags are required to match in all compilation-units
 and trying to override this at link-time with a conflicting value
 is ignored.  This includes options such as <samp>-freg-struct-return</samp>
 and <samp>-fpcc-struct-return</samp>.
 </p>
 <p>Other options such as <samp>-ffp-contract</samp>, <samp>-fno-strict-overflow</samp>,
 <samp>-fwrapv</samp>, <samp>-fno-trapv</samp> or <samp>-fno-strict-aliasing</samp>
 are passed through to the link stage and merged conservatively for
 conflicting translation units.  Specifically
 <samp>-fno-strict-overflow</samp>, <samp>-fwrapv</samp> and <samp>-fno-trapv</samp> take
 precedence and for example <samp>-ffp-contract=off</samp> takes precedence
 over <samp>-ffp-contract=fast</samp>.  You can override them at linke-time.
 </p>
 <p>It is recommended that you compile all the files participating in the
 same link with the same options and also specify those options at
 link time.
 </p>
 <p>If LTO encounters objects with C linkage declared with incompatible
 types in separate translation units to be linked together (undefined
 behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be
 issued.  The behavior is still undefined at run time.  Similar
 diagnostics may be raised for other languages.
 </p>
 <p>Another feature of LTO is that it is possible to apply interprocedural
 optimizations on files written in different languages:
 </p>
 <div class="smallexample">
 <pre class="smallexample">gcc -c -flto foo.c
 g++ -c -flto bar.cc
 gfortran -c -flto baz.f90
 g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
 </pre></div>

 <p>Notice that the final link is done with <code>g++</code> to get the C++
 runtime libraries and <samp>-lgfortran</samp> is added to get the Fortran
 runtime libraries.  In general, when mixing languages in LTO mode, you
 should use the same link command options as when mixing languages in a
 regular (non-LTO) compilation.
 </p>
 <p>If object files containing GIMPLE bytecode are stored in a library archive, say
 <samp>libfoo.a</samp>, it is possible to extract and use them in an LTO link if you
 are using a linker with plugin support.  To create static libraries suitable
 for LTO, use <code>gcc-ar</code> and <code>gcc-ranlib</code> instead of <code>ar</code>
 and <code>ranlib</code>; to show the symbols of object files with GIMPLE bytecode, use
 <code>gcc-nm</code>.  Those commands require that <code>ar</code>, <code>ranlib</code>
 and <code>nm</code> have been compiled with plugin support.  At link time, use the the
 flag <samp>-fuse-linker-plugin</samp> to ensure that the library participates in
 the LTO optimization process:
 </p>
 <div class="smallexample">
 <pre class="smallexample">gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
 </pre></div>

 <p>With the linker plugin enabled, the linker extracts the needed
 GIMPLE files from <samp>libfoo.a</samp> and passes them on to the running GCC
 to make them part of the aggregated GIMPLE image to be optimized.
 </p>
 <p>If you are not using a linker with plugin support and/or do not
 enable the linker plugin, then the objects inside <samp>libfoo.a</samp>
 are extracted and linked as usual, but they do not participate
 in the LTO optimization process.  In order to make a static library suitable
 for both LTO optimization and usual linkage, compile its object files with
 <samp>-flto</samp> <code>-ffat-lto-objects</code>.
 </p>
 <p>Link-time optimizations do not require the presence of the whole program to
 operate.  If the program does not require any symbols to be exported, it is
 possible to combine <samp>-flto</samp> and <samp>-fwhole-program</samp> to allow
 the interprocedural optimizers to use more aggressive assumptions which may
 lead to improved optimization opportunities.
 Use of <samp>-fwhole-program</samp> is not needed when linker plugin is
 active (see <samp>-fuse-linker-plugin</samp>).
 </p>
 <p>The current implementation of LTO makes no
 attempt to generate bytecode that is portable between different
 types of hosts.  The bytecode files are versioned and there is a
 strict version check, so bytecode files generated in one version of
 GCC will not work with an older or newer version of GCC.
 </p>
 <p>Link-time optimization does not work well with generation of debugging
 information.  Combining <samp>-flto</samp> with
 <samp>-g</samp> is currently experimental and expected to produce unexpected
 results.
 </p>
 <p>If you specify the optional <var>n</var>, the optimization and code
 generation done at link time is executed in parallel using <var>n</var>
 parallel jobs by utilizing an installed <code>make</code> program.  The
 environment variable <code>MAKE</code> may be used to override the program
 used.  The default value for <var>n</var> is 1.
 </p>
 <p>You can also specify <samp>-flto=jobserver</samp> to use GNU make&rsquo;s
 job server mode to determine the number of parallel jobs. This
 is useful when the Makefile calling GCC is already executing in parallel.
 You must prepend a &lsquo;<samp>+</samp>&rsquo; to the command recipe in the parent Makefile
 for this to work.  This option likely only works if <code>MAKE</code> is
 GNU make.
 </p>
 </dd>
 <dt><code>-flto-partition=<var>alg</var></code></dt>
 <dd><a name="index-flto_002dpartition"></a>
 <p>Specify the partitioning algorithm used by the link-time optimizer.
 The value is either <code>1to1</code> to specify a partitioning mirroring
 the original source files or <code>balanced</code> to specify partitioning
 into equally sized chunks (whenever possible) or <code>max</code> to create
 new partition for every symbol where possible.  Specifying <code>none</code>
 as an algorithm disables partitioning and streaming completely.
 The default value is <code>balanced</code>. While <code>1to1</code> can be used
 as an workaround for various code ordering issues, the <code>max</code>
 partitioning is intended for internal testing only.
 </p>
 </dd>
 <dt><code>-flto-compression-level=<var>n</var></code></dt>
 <dd><p>This option specifies the level of compression used for intermediate
 language written to LTO object files, and is only meaningful in
 conjunction with LTO mode (<samp>-flto</samp>).  Valid
 values are 0 (no compression) to 9 (maximum compression).  Values
 outside this range are clamped to either 0 or 9.  If the option is not
 given, a default balanced compression setting is used.
 </p>
 </dd>
 <dt><code>-flto-report</code></dt>
 <dd><p>Prints a report with internal details on the workings of the link-time
 optimizer.  The contents of this report vary from version to version.
 It is meant to be useful to GCC developers when processing object
 files in LTO mode (via <samp>-flto</samp>).
 </p>
 <p>Disabled by default.
 </p>
 </dd>
 <dt><code>-flto-report-wpa</code></dt>
 <dd><p>Like <samp>-flto-report</samp>, but only print for the WPA phase of Link
 Time Optimization.
 </p>
 </dd>
 <dt><code>-fuse-linker-plugin</code></dt>
 <dd><p>Enables the use of a linker plugin during link-time optimization.  This
 option relies on plugin support in the linker, which is available in gold
 or in GNU ld 2.21 or newer.
 </p>
 <p>This option enables the extraction of object files with GIMPLE bytecode out
 of library archives. This improves the quality of optimization by exposing
 more code to the link-time optimizer.  This information specifies what
 symbols can be accessed externally (by non-LTO object or during dynamic
 linking).  Resulting code quality improvements on binaries (and shared
 libraries that use hidden visibility) are similar to <code>-fwhole-program</code>.
 See <samp>-flto</samp> for a description of the effect of this flag and how to
 use it.
 </p>
 <p>This option is enabled by default when LTO support in GCC is enabled
 and GCC was configured for use with
 a linker supporting plugins (GNU ld 2.21 or newer or gold).
 </p>
 </dd>
 <dt><code>-ffat-lto-objects</code></dt>
 <dd><a name="index-ffat_002dlto_002dobjects"></a>
 <p>Fat LTO objects are object files that contain both the intermediate language
 and the object code. This makes them usable for both LTO linking and normal
 linking. This option is effective only when compiling with <samp>-flto</samp>
 and is ignored at link time.
 </p>
 <p><samp>-fno-fat-lto-objects</samp> improves compilation time over plain LTO, but
 requires the complete toolchain to be aware of LTO. It requires a linker with
 linker plugin support for basic functionality.  Additionally,
 <code>nm</code>, <code>ar</code> and <code>ranlib</code>
 need to support linker plugins to allow a full-featured build environment
 (capable of building static libraries etc).  GCC provides the <code>gcc-ar</code>,
 <code>gcc-nm</code>, <code>gcc-ranlib</code> wrappers to pass the right options
 to these tools. With non fat LTO makefiles need to be modified to use them.
 </p>
 <p>The default is <samp>-fno-fat-lto-objects</samp> on targets with linker plugin
 support.
 </p>
 </dd>
 <dt><code>-fcompare-elim</code></dt>
 <dd><a name="index-fcompare_002delim"></a>
 <p>After register allocation and post-register allocation instruction splitting,
 identify arithmetic instructions that compute processor flags similar to a
 comparison operation based on that arithmetic.  If possible, eliminate the
 explicit comparison operation.
 </p>
 <p>This pass only applies to certain targets that cannot explicitly represent
 the comparison operation before register allocation is complete.
 </p>
 <p>Enabled at levels <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fuse-ld=bfd</code></dt>
 <dd><a name="index-fuse_002dld_003dbfd"></a>
 <p>Use the <code>bfd</code> linker instead of the default linker.
 </p>
 </dd>
 <dt><code>-fuse-ld=gold</code></dt>
 <dd><a name="index-fuse_002dld_003dgold"></a>
 <p>Use the <code>gold</code> linker instead of the default linker.
 </p>
 </dd>
 <dt><code>-fcprop-registers</code></dt>
 <dd><a name="index-fcprop_002dregisters"></a>
 <p>After register allocation and post-register allocation instruction splitting,
 perform a copy-propagation pass to try to reduce scheduling dependencies
 and occasionally eliminate the copy.
 </p>
 <p>Enabled at levels <samp>-O</samp>, <samp>-O2</samp>, <samp>-O3</samp>, <samp>-Os</samp>.
 </p>
 </dd>
 <dt><code>-fprofile-correction</code></dt>
 <dd><a name="index-fprofile_002dcorrection"></a>
 <p>Profiles collected using an instrumented binary for multi-threaded programs may
 be inconsistent due to missed counter updates. When this option is specified,
 GCC uses heuristics to correct or smooth out such inconsistencies. By
 default, GCC emits an error message when an inconsistent profile is detected.
 </p>
 </dd>
 <dt><code>-fprofile-dir=<var>path</var></code></dt>
 <dd><a name="index-fprofile_002ddir"></a>

 <p>Set the directory to search for the profile data files in to <var>path</var>.
 This option affects only the profile data generated by
 <samp>-fprofile-generate</samp>, <samp>-ftest-coverage</samp>, <samp>-fprofile-arcs</samp>
 and used by <samp>-fprofile-use</samp> and <samp>-fbranch-probabilities</samp>
 and its related options.  Both absolute and relative paths can be used.
 By default, GCC uses the current directory as <var>path</var>, thus the
 profile data file appears in the same directory as the object file.
 </p>
 </dd>
 <dt><code>-fprofile-generate</code></dt>
 <dt><code>-fprofile-generate=<var>path</var></code></dt>
 <dd><a name="index-fprofile_002dgenerate"></a>

 <p>Enable options usually used for instrumenting application to produce
 profile useful for later recompilation with profile feedback based
 optimization.  You must use <samp>-fprofile-generate</samp> both when
 compiling and when linking your program.
 </p>
 <p>The following options are enabled: <code>-fprofile-arcs</code>, <code>-fprofile-values</code>, <code>-fvpt</code>.
 </p>
 <p>If <var>path</var> is specified, GCC looks at the <var>path</var> to find
 the profile feedback data files. See <samp>-fprofile-dir</samp>.
 </p>
 </dd>
 <dt><code>-fprofile-use</code></dt>
 <dt><code>-fprofile-use=<var>path</var></code></dt>
 <dd><a name="index-fprofile_002duse"></a>
 <p>Enable profile feedback directed optimizations, and optimizations
 generally profitable only with profile feedback available.
 </p>
 <p>The following options are enabled: <code>-fbranch-probabilities</code>, <code>-fvpt</code>,
 <code>-funroll-loops</code>, <code>-fpeel-loops</code>, <code>-ftracer</code>, <code>-ftree-vectorize</code>,
 <code>ftree-loop-distribute-patterns</code>
 </p>
 <p>By default, GCC emits an error message if the feedback profiles do not
 match the source code.  This error can be turned into a warning by using
 <samp>-Wcoverage-mismatch</samp>.  Note this may result in poorly optimized
 code.
 </p>
 <p>If <var>path</var> is specified, GCC looks at the <var>path</var> to find
 the profile feedback data files. See <samp>-fprofile-dir</samp>.
 </p></dd>
 </dl>

 <p>The following options control compiler behavior regarding floating-point
 arithmetic.  These options trade off between speed and
 correctness.  All must be specifically enabled.
 </p>
 <dl compact="compact">
 <dt><code>-ffloat-store</code></dt>
 <dd><a name="index-ffloat_002dstore"></a>
 <p>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.
 </p>
 <a name="index-floating_002dpoint-precision"></a>
 <p>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</code> 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 <samp>-ffloat-store</samp> for such programs, after modifying
 them to store all pertinent intermediate computations into variables.
 </p>
 </dd>
 <dt><code>-fexcess-precision=<var>style</var></code></dt>
 <dd><a name="index-fexcess_002dprecision"></a>
 <p>This option allows further control over excess precision on machines
 where floating-point registers have more precision than the IEEE
 <code>float</code> and <code>double</code> types and the processor does not
 support operations rounding to those types.  By default,
 <samp>-fexcess-precision=fast</samp> is in effect; this means that
 operations are carried out in the precision of the registers and that
 it is unpredictable when rounding to the types specified in the source
 code takes place.  When compiling C, if
 <samp>-fexcess-precision=standard</samp> is specified then excess
 precision follows the rules specified in ISO C99; in particular,
 both casts and assignments cause values to be rounded to their
 semantic types (whereas <samp>-ffloat-store</samp> only affects
 assignments).  This option is enabled by default for C if a strict
 conformance option such as <samp>-std=c99</samp> is used.
 </p>
 <a name="index-mfpmath"></a>
 <p><samp>-fexcess-precision=standard</samp> is not implemented for languages
 other than C, and has no effect if
 <samp>-funsafe-math-optimizations</samp> or <samp>-ffast-math</samp> is
 specified.  On the x86, it also has no effect if <samp>-mfpmath=sse</samp>
 or <samp>-mfpmath=sse+387</samp> is specified; in the former case, IEEE
 semantics apply without excess precision, and in the latter, rounding
 is unpredictable.
 </p>
 </dd>
 <dt><code>-ffast-math</code></dt>
 <dd><a name="index-ffast_002dmath"></a>
 <p>Sets <samp>-fno-math-errno</samp>, <samp>-funsafe-math-optimizations</samp>,
 <samp>-ffinite-math-only</samp>, <samp>-fno-rounding-math</samp>,
 <samp>-fno-signaling-nans</samp> and <samp>-fcx-limited-range</samp>.
 </p>
 <p>This option causes the preprocessor macro <code>__FAST_MATH__</code> to be defined.
 </p>
 <p>This option is not turned on by any <samp>-O</samp> option besides
 <samp>-Ofast</samp> since it can result in incorrect output for programs
 that depend on an exact implementation of IEEE or ISO rules/specifications
 for math functions. It may, however, yield faster code for programs
 that do not require the guarantees of these specifications.
 </p>
 </dd>
 <dt><code>-fno-math-errno</code></dt>
 <dd><a name="index-fno_002dmath_002derrno"></a>
 <p>Do not set <code>errno</code> after calling math functions that are executed
 with a single instruction, e.g., <code>sqrt</code>.  A program that relies on
 IEEE exceptions for math error handling may want to use this flag
 for speed while maintaining IEEE arithmetic compatibility.
 </p>
 <p>This option is not turned on by any <samp>-O</samp> option since
 it can result in incorrect output for programs that depend on
 an exact implementation of IEEE or ISO rules/specifications for
 math functions. It may, however, yield faster code for programs
 that do not require the guarantees of these specifications.
 </p>
 <p>The default is <samp>-fmath-errno</samp>.
 </p>
 <p>On Darwin systems, the math library never sets <code>errno</code>.  There is
 therefore no reason for the compiler to consider the possibility that
 it might, and <samp>-fno-math-errno</samp> is the default.
 </p>
 </dd>
 <dt><code>-funsafe-math-optimizations</code></dt>
 <dd><a name="index-funsafe_002dmath_002doptimizations"></a>

 <p>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.
 </p>
 <p>This option is not turned on by any <samp>-O</samp> option since
 it can result in incorrect output for programs that depend on
 an exact implementation of IEEE or ISO rules/specifications for
 math functions. It may, however, yield faster code for programs
 that do not require the guarantees of these specifications.
 Enables <samp>-fno-signed-zeros</samp>, <samp>-fno-trapping-math</samp>,
 <samp>-fassociative-math</samp> and <samp>-freciprocal-math</samp>.
 </p>
 <p>The default is <samp>-fno-unsafe-math-optimizations</samp>.
 </p>
 </dd>
 <dt><code>-fassociative-math</code></dt>
 <dd><a name="index-fassociative_002dmath"></a>

 <p>Allow re-association of operands in series of floating-point operations.
 This violates the ISO C and C++ language standard by possibly changing
 computation result.  NOTE: re-ordering may change the sign of zero as
 well as ignore NaNs and inhibit or create underflow or overflow (and
 thus cannot be used on code that relies on rounding behavior like
 <code>(x + 2**52) - 2**52</code>.  May also reorder floating-point comparisons
 and thus may not be used when ordered comparisons are required.
 This option requires that both <samp>-fno-signed-zeros</samp> and
 <samp>-fno-trapping-math</samp> be in effect.  Moreover, it doesn&rsquo;t make
 much sense with <samp>-frounding-math</samp>. For Fortran the option
 is automatically enabled when both <samp>-fno-signed-zeros</samp> and
 <samp>-fno-trapping-math</samp> are in effect.
 </p>
 <p>The default is <samp>-fno-associative-math</samp>.
 </p>
 </dd>
 <dt><code>-freciprocal-math</code></dt>
 <dd><a name="index-freciprocal_002dmath"></a>

 <p>Allow the reciprocal of a value to be used instead of dividing by
 the value if this enables optimizations.  For example <code>x / y</code>
 can be replaced with <code>x * (1/y)</code>, which is useful if <code>(1/y)</code>
 is subject to common subexpression elimination.  Note that this loses
 precision and increases the number of flops operating on the value.
 </p>
 <p>The default is <samp>-fno-reciprocal-math</samp>.
 </p>
 </dd>
 <dt><code>-ffinite-math-only</code></dt>
 <dd><a name="index-ffinite_002dmath_002donly"></a>
 <p>Allow optimizations for floating-point arithmetic that assume
 that arguments and results are not NaNs or +-Infs.
 </p>
 <p>This option is not turned on by any <samp>-O</samp> option since
 it can result in incorrect output for programs that depend on
 an exact implementation of IEEE or ISO rules/specifications for
 math functions. It may, however, yield faster code for programs
 that do not require the guarantees of these specifications.
 </p>
 <p>The default is <samp>-fno-finite-math-only</samp>.
 </p>
 </dd>
 <dt><code>-fno-signed-zeros</code></dt>
 <dd><a name="index-fno_002dsigned_002dzeros"></a>
 <p>Allow optimizations for floating-point arithmetic that ignore the
 signedness of zero.  IEEE arithmetic specifies the behavior of
 distinct +0.0 and -0.0 values, which then prohibits simplification
 of expressions such as x+0.0 or 0.0*x (even with <samp>-ffinite-math-only</samp>).
 This option implies that the sign of a zero result isn&rsquo;t significant.
 </p>
 <p>The default is <samp>-fsigned-zeros</samp>.
 </p>
 </dd>
 <dt><code>-fno-trapping-math</code></dt>
 <dd><a name="index-fno_002dtrapping_002dmath"></a>
 <p>Compile code assuming that floating-point operations cannot generate
 user-visible traps.  These traps include division by zero, overflow,
 underflow, inexact result and invalid operation.  This option requires
 that <samp>-fno-signaling-nans</samp> be in effect.  Setting this option may
 allow faster code if one relies on &ldquo;non-stop&rdquo; IEEE arithmetic, for example.
 </p>
 <p>This option should never be turned on by any <samp>-O</samp> option since
 it can result in incorrect output for programs that depend on
 an exact implementation of IEEE or ISO rules/specifications for
 math functions.
 </p>
 <p>The default is <samp>-ftrapping-math</samp>.
 </p>
 </dd>
 <dt><code>-frounding-math</code></dt>
 <dd><a name="index-frounding_002dmath"></a>
 <p>Disable transformations and optimizations that assume default floating-point
 rounding behavior.  This is round-to-zero for all floating point
 to integer conversions, and round-to-nearest for all other arithmetic
 truncations.  This option should be specified for programs that change
 the FP rounding mode dynamically, or that may be executed with a
 non-default rounding mode.  This option disables constant folding of
 floating-point expressions at compile time (which may be affected by
 rounding mode) and arithmetic transformations that are unsafe in the
 presence of sign-dependent rounding modes.
 </p>
 <p>The default is <samp>-fno-rounding-math</samp>.
 </p>
 <p>This option is experimental and does not currently guarantee to
 disable all GCC optimizations that are affected by rounding mode.
 Future versions of GCC may provide finer control of this setting
 using C99&rsquo;s <code>FENV_ACCESS</code> pragma.  This command-line option
 will be used to specify the default state for <code>FENV_ACCESS</code>.
 </p>
 </dd>
 <dt><code>-fsignaling-nans</code></dt>
 <dd><a name="index-fsignaling_002dnans"></a>
 <p>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 <samp>-ftrapping-math</samp>.
 </p>
 <p>This option causes the preprocessor macro <code>__SUPPORT_SNAN__</code> to
 be defined.
 </p>
 <p>The default is <samp>-fno-signaling-nans</samp>.
 </p>
 <p>This option is experimental and does not currently guarantee to
 disable all GCC optimizations that affect signaling NaN behavior.
 </p>
 </dd>
 <dt><code>-fsingle-precision-constant</code></dt>
 <dd><a name="index-fsingle_002dprecision_002dconstant"></a>
 <p>Treat floating-point constants as single precision instead of
 implicitly converting them to double-precision constants.
 </p>
 </dd>
 <dt><code>-fcx-limited-range</code></dt>
 <dd><a name="index-fcx_002dlimited_002drange"></a>
 <p>When enabled, this option states that a range reduction step is not
 needed when performing complex division.  Also, there is no checking
 whether the result of a complex multiplication or division is <code>NaN
 + I*NaN</code>, with an attempt to rescue the situation in that case.  The
 default is <samp>-fno-cx-limited-range</samp>, but is enabled by
 <samp>-ffast-math</samp>.
 </p>
 <p>This option controls the default setting of the ISO C99
 <code>CX_LIMITED_RANGE</code> pragma.  Nevertheless, the option applies to
 all languages.
 </p>
 </dd>
 <dt><code>-fcx-fortran-rules</code></dt>
 <dd><a name="index-fcx_002dfortran_002drules"></a>
 <p>Complex multiplication and division follow Fortran rules.  Range
 reduction is done as part of complex division, but there is no checking
 whether the result of a complex multiplication or division is <code>NaN
 + I*NaN</code>, with an attempt to rescue the situation in that case.
 </p>
 <p>The default is <samp>-fno-cx-fortran-rules</samp>.
 </p>
 </dd>
 </dl>

 <p>The following options control optimizations that may improve
 performance, but are not enabled by any <samp>-O</samp> options.  This
 section includes experimental options that may produce broken code.
 </p>
 <dl compact="compact">
 <dt><code>-fbranch-probabilities</code></dt>
 <dd><a name="index-fbranch_002dprobabilities"></a>
 <p>After running a program compiled with <samp>-fprofile-arcs</samp>
 (see <a href="Debugging-Options.html#Debugging-Options">Options for Debugging Your Program or
 <code>gcc</code></a>), you can compile it a second time using
 <samp>-fbranch-probabilities</samp>, to improve optimizations based on
 the number of times each branch was taken.  When a program
 compiled with <samp>-fprofile-arcs</samp> exits, it saves arc execution
 counts to a file called <samp><var>sourcename</var>.gcda</samp> 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.
 </p>
 <p>With <samp>-fbranch-probabilities</samp>, GCC puts a
 &lsquo;<samp>REG_BR_PROB</samp>&rsquo; note on each &lsquo;<samp>JUMP_INSN</samp>&rsquo; and &lsquo;<samp>CALL_INSN</samp>&rsquo;.
 These can be used to improve optimization.  Currently, they are only
 used in one place: in <samp>reorg.c</samp>, instead of guessing which path a
 branch is most likely to take, the &lsquo;<samp>REG_BR_PROB</samp>&rsquo; values are used to
 exactly determine which path is taken more often.
 </p>
 </dd>
 <dt><code>-fprofile-values</code></dt>
 <dd><a name="index-fprofile_002dvalues"></a>
 <p>If combined with <samp>-fprofile-arcs</samp>, it adds code so that some
 data about values of expressions in the program is gathered.
 </p>
 <p>With <samp>-fbranch-probabilities</samp>, it reads back the data gathered
 from profiling values of expressions for usage in optimizations.
 </p>
 <p>Enabled with <samp>-fprofile-generate</samp> and <samp>-fprofile-use</samp>.
 </p>
 </dd>
 <dt><code>-fprofile-reorder-functions</code></dt>
 <dd><a name="index-fprofile_002dreorder_002dfunctions"></a>
 <p>Function reordering based on profile instrumentation collects
 first time of execution of a function and orders these functions
 in ascending order.
 </p>
 <p>Enabled with <samp>-fprofile-use</samp>.
 </p>
 </dd>
 <dt><code>-fvpt</code></dt>
 <dd><a name="index-fvpt"></a>
 <p>If combined with <samp>-fprofile-arcs</samp>, this option instructs the compiler
 to add code to gather information about values of expressions.
 </p>
 <p>With <samp>-fbranch-probabilities</samp>, it reads back the data gathered
 and actually performs the optimizations based on them.
 Currently the optimizations include specialization of division operations
 using the knowledge about the value of the denominator.
 </p>
 </dd>
 <dt><code>-frename-registers</code></dt>
 <dd><a name="index-frename_002dregisters"></a>
 <p>Attempt to avoid false dependencies in scheduled code by making use
 of registers left over after register allocation.  This optimization
 most benefits processors with lots of registers.  Depending on the
 debug information format adopted by the target, however, it can
 make debugging impossible, since variables no longer stay in
 a &ldquo;home register&rdquo;.
 </p>
 <p>Enabled by default with <samp>-funroll-loops</samp> and <samp>-fpeel-loops</samp>.
 </p>
 </dd>
 <dt><code>-ftracer</code></dt>
 <dd><a name="index-ftracer-1"></a>
 <p>Perform tail duplication to enlarge superblock size.  This transformation
 simplifies the control flow of the function allowing other optimizations to do
 a better job.
 </p>
 <p>Enabled with <samp>-fprofile-use</samp>.
 </p>
 </dd>
 <dt><code>-funroll-loops</code></dt>
 <dd><a name="index-funroll_002dloops-1"></a>
 <p>Unroll loops whose number of iterations can be determined at compile time or
 upon entry to the loop.  <samp>-funroll-loops</samp> implies
 <samp>-frerun-cse-after-loop</samp>, <samp>-fweb</samp> and <samp>-frename-registers</samp>.
 It also turns on complete loop peeling (i.e. complete removal of loops with
 a small constant number of iterations).  This option makes code larger, and may
 or may not make it run faster.
 </p>
 <p>Enabled with <samp>-fprofile-use</samp>.
 </p>
 </dd>
 <dt><code>-funroll-all-loops</code></dt>
 <dd><a name="index-funroll_002dall_002dloops-1"></a>
 <p>Unroll all loops, even if their number of iterations is uncertain when
 the loop is entered.  This usually makes programs run more slowly.
 <samp>-funroll-all-loops</samp> implies the same options as
 <samp>-funroll-loops</samp>.
 </p>
 </dd>
 <dt><code>-fpeel-loops</code></dt>
 <dd><a name="index-fpeel_002dloops"></a>
 <p>Peels loops for which there is enough information that they do not
 roll much (from profile feedback).  It also turns on complete loop peeling
 (i.e. complete removal of loops with small constant number of iterations).
 </p>
 <p>Enabled with <samp>-fprofile-use</samp>.
 </p>
 </dd>
 <dt><code>-fmove-loop-invariants</code></dt>
 <dd><a name="index-fmove_002dloop_002dinvariants"></a>
 <p>Enables the loop invariant motion pass in the RTL loop optimizer.  Enabled
 at level <samp>-O1</samp>
 </p>
 </dd>
 <dt><code>-funswitch-loops</code></dt>
 <dd><a name="index-funswitch_002dloops"></a>
 <p>Move branches with loop invariant conditions out of the loop, with duplicates
 of the loop on both branches (modified according to result of the condition).
 </p>
 </dd>
 <dt><code>-ffunction-sections</code></dt>
 <dt><code>-fdata-sections</code></dt>
 <dd><a name="index-ffunction_002dsections"></a>
 <a name="index-fdata_002dsections"></a>
 <p>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&rsquo;s name
 in the output file.
 </p>
 <p>Use these options on systems where the linker can perform optimizations
 to improve locality of reference in the instruction space.  Most systems
 using the ELF object format and SPARC processors running Solaris 2 have
 linkers with such optimizations.  AIX may have these optimizations in
 the future.
 </p>
 <p>Only use these options when there are significant benefits from doing
 so.  When you specify these options, the assembler and linker
 create larger object and executable files and are also slower.
 You cannot use <code>gprof</code> on all systems if you
 specify this option, and you may have problems with debugging if
 you specify both this option and <samp>-g</samp>.
 </p>
 </dd>
 <dt><code>-fbranch-target-load-optimize</code></dt>
 <dd><a name="index-fbranch_002dtarget_002dload_002doptimize"></a>
 <p>Perform branch target register load optimization before prologue / epilogue
 threading.
 The use of target registers can typically be exposed only during reload,
 thus hoisting loads out of loops and doing inter-block scheduling needs
 a separate optimization pass.
 </p>
 </dd>
 <dt><code>-fbranch-target-load-optimize2</code></dt>
 <dd><a name="index-fbranch_002dtarget_002dload_002doptimize2"></a>
 <p>Perform branch target register load optimization after prologue / epilogue
 threading.
 </p>
 </dd>
 <dt><code>-fbtr-bb-exclusive</code></dt>
 <dd><a name="index-fbtr_002dbb_002dexclusive"></a>
 <p>When performing branch target register load optimization, don&rsquo;t reuse
 branch target registers within any basic block.
 </p>
 </dd>
 <dt><code>-fstack-protector</code></dt>
 <dd><a name="index-fstack_002dprotector"></a>
 <p>Emit extra code to check for buffer overflows, such as stack smashing
 attacks.  This is done by adding a guard variable to functions with
 vulnerable objects.  This includes functions that call <code>alloca</code>, and
 functions with buffers larger than 8 bytes.  The guards are initialized
 when a function is entered and then checked when the function exits.
 If a guard check fails, an error message is printed and the program exits.
 </p>
 </dd>
 <dt><code>-fstack-protector-all</code></dt>
 <dd><a name="index-fstack_002dprotector_002dall"></a>
 <p>Like <samp>-fstack-protector</samp> except that all functions are protected.
 </p>
 </dd>
 <dt><code>-fstack-protector-strong</code></dt>
 <dd><a name="index-fstack_002dprotector_002dstrong"></a>
 <p>Like <samp>-fstack-protector</samp> but includes additional functions to
 be protected &mdash; those that have local array definitions, or have
 references to local frame addresses.
 </p>
 </dd>
 <dt><code>-fsection-anchors</code></dt>
 <dd><a name="index-fsection_002danchors"></a>
 <p>Try to reduce the number of symbolic address calculations by using
 shared &ldquo;anchor&rdquo; symbols to address nearby objects.  This transformation
 can help to reduce the number of GOT entries and GOT accesses on some
 targets.
 </p>
 <p>For example, the implementation of the following function <code>foo</code>:
 </p>
 <div class="smallexample">
 <pre class="smallexample">static int a, b, c;
 int foo (void) { return a + b + c; }
 </pre></div>

 <p>usually calculates the addresses of all three variables, but if you
 compile it with <samp>-fsection-anchors</samp>, it accesses the variables
 from a common anchor point instead.  The effect is similar to the
 following pseudocode (which isn&rsquo;t valid C):
 </p>
 <div class="smallexample">
 <pre class="smallexample">int foo (void)
 {
   register int *xr = &amp;x;
   return xr[&amp;a - &amp;x] + xr[&amp;b - &amp;x] + xr[&amp;c - &amp;x];
 }
 </pre></div>

 <p>Not all targets support this option.
 </p>
 </dd>
 <dt><code>--param <var>name</var>=<var>value</var></code></dt>
 <dd><a name="index-param"></a>
 <p>In some places, GCC uses various constants to control the amount of
 optimization that is done.  For example, GCC does not inline functions
 that contain more than a certain number of instructions.  You can
 control some of these constants on the command line using the
 <samp>--param</samp> option.
 </p>
 <p>The names of specific parameters, and the meaning of the values, are
 tied to the internals of the compiler, and are subject to change
 without notice in future releases.
 </p>
 <p>In each case, the <var>value</var> is an integer.  The allowable choices for
 <var>name</var> are:
 </p>
 <dl compact="compact">
 <dt><code>predictable-branch-outcome</code></dt>
 <dd><p>When branch is predicted to be taken with probability lower than this threshold
 (in percent), then it is considered well predictable. The default is 10.
 </p>
 </dd>
 <dt><code>max-crossjump-edges</code></dt>
 <dd><p>The maximum number of incoming edges to consider for cross-jumping.
 The algorithm used by <samp>-fcrossjumping</samp> is <em>O(N^2)</em> in
 the number of edges incoming to each block.  Increasing values mean
 more aggressive optimization, making the compilation time increase with
 probably small improvement in executable size.
 </p>
 </dd>
 <dt><code>min-crossjump-insns</code></dt>
 <dd><p>The minimum number of instructions that must be matched at the end
 of two blocks before cross-jumping is performed on them.  This
 value is ignored in the case where all instructions in the block being
 cross-jumped from are matched.  The default value is 5.
 </p>
 </dd>
 <dt><code>max-grow-copy-bb-insns</code></dt>
 <dd><p>The maximum code size expansion factor when copying basic blocks
 instead of jumping.  The expansion is relative to a jump instruction.
 The default value is 8.
 </p>
 </dd>
 <dt><code>max-goto-duplication-insns</code></dt>
 <dd><p>The maximum number of instructions to duplicate to a block that jumps
 to a computed goto.  To avoid <em>O(N^2)</em> behavior in a number of
 passes, GCC factors computed gotos early in the compilation process,
 and unfactors them as late as possible.  Only computed jumps at the
 end of a basic blocks with no more than max-goto-duplication-insns are
 unfactored.  The default value is 8.
 </p>
 </dd>
 <dt><code>max-delay-slot-insn-search</code></dt>
 <dd><p>The maximum number of instructions to consider when looking for an
 instruction to fill a delay slot.  If more than this arbitrary number of
 instructions are searched, the time savings from filling the delay slot
 are minimal, so stop searching.  Increasing values mean more
 aggressive optimization, making the compilation time increase with probably
 small improvement in execution time.
 </p>
 </dd>
 <dt><code>max-delay-slot-live-search</code></dt>
 <dd><p>When trying to fill delay slots, the maximum number of instructions to
 consider when searching for a block with valid live register
 information.  Increasing this arbitrarily chosen value means more
 aggressive optimization, increasing the compilation time.  This parameter
 should be removed when the delay slot code is rewritten to maintain the
 control-flow graph.
 </p>
 </dd>
 <dt><code>max-gcse-memory</code></dt>
 <dd><p>The approximate maximum amount of memory that can be allocated in
 order to perform the global common subexpression elimination
 optimization.  If more memory than specified is required, the
 optimization is not done.
 </p>
 </dd>
 <dt><code>max-gcse-insertion-ratio</code></dt>
 <dd><p>If the ratio of expression insertions to deletions is larger than this value
 for any expression, then RTL PRE inserts or removes the expression and thus
 leaves partially redundant computations in the instruction stream.  The default value is 20.
 </p>
 </dd>
 <dt><code>max-pending-list-length</code></dt>
 <dd><p>The maximum number of pending dependencies scheduling allows
 before flushing the current state and starting over.  Large functions
 with few branches or calls can create excessively large lists which
 needlessly consume memory and resources.
 </p>
 </dd>
 <dt><code>max-modulo-backtrack-attempts</code></dt>
 <dd><p>The maximum number of backtrack attempts the scheduler should make
 when modulo scheduling a loop.  Larger values can exponentially increase
 compilation time.
 </p>
 </dd>
 <dt><code>max-inline-insns-single</code></dt>
 <dd><p>Several parameters control the tree inliner used in GCC.
 This number sets the maximum number of instructions (counted in GCC&rsquo;s
 internal representation) in a single function that the tree inliner
 considers for inlining.  This only affects functions declared
 inline and methods implemented in a class declaration (C++).
 The default value is 400.
 </p>
 </dd>
 <dt><code>max-inline-insns-auto</code></dt>
 <dd><p>When you use <samp>-finline-functions</samp> (included in <samp>-O3</samp>),
 a lot of functions that would otherwise not be considered for inlining
 by the compiler are investigated.  To those functions, a different
 (more restrictive) limit compared to functions declared inline can
 be applied.
 The default value is 40.
 </p>
 </dd>
 <dt><code>inline-min-speedup</code></dt>
 <dd><p>When estimated performance improvement of caller + callee runtime exceeds this
 threshold (in precent), the function can be inlined regardless the limit on
 <samp>--param max-inline-insns-single</samp> and <samp>--param
 max-inline-insns-auto</samp>.
 </p>
 </dd>
 <dt><code>large-function-insns</code></dt>
 <dd><p>The limit specifying really large functions.  For functions larger than this
 limit after inlining, inlining is constrained by
 <samp>--param large-function-growth</samp>.  This parameter is useful primarily
 to avoid extreme compilation time caused by non-linear algorithms used by the
 back end.
 The default value is 2700.
 </p>
 </dd>
 <dt><code>large-function-growth</code></dt>
 <dd><p>Specifies maximal growth of large function caused by inlining in percents.
 The default value is 100 which limits large function growth to 2.0 times
 the original size.
 </p>
 </dd>
 <dt><code>large-unit-insns</code></dt>
 <dd><p>The limit specifying large translation unit.  Growth caused by inlining of
 units larger than this limit is limited by <samp>--param inline-unit-growth</samp>.
 For small units this might be too tight.
 For example, consider a unit consisting of function A
 that is inline and B that just calls A three times.  If B is small relative to
 A, the growth of unit is 300\% and yet such inlining is very sane.  For very
 large units consisting of small inlineable functions, however, the overall unit
 growth limit is needed to avoid exponential explosion of code size.  Thus for
 smaller units, the size is increased to <samp>--param large-unit-insns</samp>
 before applying <samp>--param inline-unit-growth</samp>.  The default is 10000.
 </p>
 </dd>
 <dt><code>inline-unit-growth</code></dt>
 <dd><p>Specifies maximal overall growth of the compilation unit caused by inlining.
 The default value is 30 which limits unit growth to 1.3 times the original
 size.
 </p>
 </dd>
 <dt><code>ipcp-unit-growth</code></dt>
 <dd><p>Specifies maximal overall growth of the compilation unit caused by
 interprocedural constant propagation.  The default value is 10 which limits
 unit growth to 1.1 times the original size.
 </p>
 </dd>
 <dt><code>large-stack-frame</code></dt>
 <dd><p>The limit specifying large stack frames.  While inlining the algorithm is trying
 to not grow past this limit too much.  The default value is 256 bytes.
 </p>
 </dd>
 <dt><code>large-stack-frame-growth</code></dt>
 <dd><p>Specifies maximal growth of large stack frames caused by inlining in percents.
 The default value is 1000 which limits large stack frame growth to 11 times
 the original size.
 </p>
 </dd>
 <dt><code>max-inline-insns-recursive</code></dt>
 <dt><code>max-inline-insns-recursive-auto</code></dt>
 <dd><p>Specifies the maximum number of instructions an out-of-line copy of a
 self-recursive inline
 function can grow into by performing recursive inlining.
 </p>
 <p>For functions declared inline, <samp>--param max-inline-insns-recursive</samp> is
 taken into account.  For functions not declared inline, recursive inlining
 happens only when <samp>-finline-functions</samp> (included in <samp>-O3</samp>) is
 enabled and <samp>--param max-inline-insns-recursive-auto</samp> is used.  The
 default value is 450.
 </p>
 </dd>
 <dt><code>max-inline-recursive-depth</code></dt>
 <dt><code>max-inline-recursive-depth-auto</code></dt>
 <dd><p>Specifies the maximum recursion depth used for recursive inlining.
 </p>
 <p>For functions declared inline, <samp>--param max-inline-recursive-depth</samp> is
 taken into account.  For functions not declared inline, recursive inlining
 happens only when <samp>-finline-functions</samp> (included in <samp>-O3</samp>) is
 enabled and <samp>--param max-inline-recursive-depth-auto</samp> is used.  The
 default value is 8.
 </p>
 </dd>
 <dt><code>min-inline-recursive-probability</code></dt>
 <dd><p>Recursive inlining is profitable only for function having deep recursion
 in average and can hurt for function having little recursion depth by
 increasing the prologue size or complexity of function body to other
 optimizers.
 </p>
 <p>When profile feedback is available (see <samp>-fprofile-generate</samp>) the actual
 recursion depth can be guessed from probability that function recurses via a
 given call expression.  This parameter limits inlining only to call expressions
 whose probability exceeds the given threshold (in percents).
 The default value is 10.
 </p>
 </dd>
 <dt><code>early-inlining-insns</code></dt>
 <dd><p>Specify growth that the early inliner can make.  In effect it increases
 the amount of inlining for code having a large abstraction penalty.
 The default value is 10.
 </p>
 </dd>
 <dt><code>max-early-inliner-iterations</code></dt>
 <dt><code>max-early-inliner-iterations</code></dt>
 <dd><p>Limit of iterations of the early inliner.  This basically bounds
 the number of nested indirect calls the early inliner can resolve.
 Deeper chains are still handled by late inlining.
 </p>
 </dd>
 <dt><code>comdat-sharing-probability</code></dt>
 <dt><code>comdat-sharing-probability</code></dt>
 <dd><p>Probability (in percent) that C++ inline function with comdat visibility
 are shared across multiple compilation units.  The default value is 20.
 </p>
 </dd>
 <dt><code>min-vect-loop-bound</code></dt>
 <dd><p>The minimum number of iterations under which loops are not vectorized
 when <samp>-ftree-vectorize</samp> is used.  The number of iterations after
 vectorization needs to be greater than the value specified by this option
 to allow vectorization.  The default value is 0.
 </p>
 </dd>
 <dt><code>gcse-cost-distance-ratio</code></dt>
 <dd><p>Scaling factor in calculation of maximum distance an expression
 can be moved by GCSE optimizations.  This is currently supported only in the
 code hoisting pass.  The bigger the ratio, the more aggressive code hoisting
 is with simple expressions, i.e., the expressions that have cost
 less than <samp>gcse-unrestricted-cost</samp>.  Specifying 0 disables
 hoisting of simple expressions.  The default value is 10.
 </p>
 </dd>
 <dt><code>gcse-unrestricted-cost</code></dt>
 <dd><p>Cost, roughly measured as the cost of a single typical machine
 instruction, at which GCSE optimizations do not constrain
 the distance an expression can travel.  This is currently
 supported only in the code hoisting pass.  The lesser the cost,
 the more aggressive code hoisting is.  Specifying 0
 allows all expressions to travel unrestricted distances.
 The default value is 3.
 </p>
 </dd>
 <dt><code>max-hoist-depth</code></dt>
 <dd><p>The depth of search in the dominator tree for expressions to hoist.
 This is used to avoid quadratic behavior in hoisting algorithm.
 The value of 0 does not limit on the search, but may slow down compilation
 of huge functions.  The default value is 30.
 </p>
 </dd>
 <dt><code>max-tail-merge-comparisons</code></dt>
 <dd><p>The maximum amount of similar bbs to compare a bb with.  This is used to
 avoid quadratic behavior in tree tail merging.  The default value is 10.
 </p>
 </dd>
 <dt><code>max-tail-merge-iterations</code></dt>
 <dd><p>The maximum amount of iterations of the pass over the function.  This is used to
 limit compilation time in tree tail merging.  The default value is 2.
 </p>
 </dd>
 <dt><code>max-unrolled-insns</code></dt>
 <dd><p>The maximum number of instructions that a loop may have to be unrolled.
 If a loop is unrolled, this parameter also determines how many times
 the loop code is unrolled.
 </p>
 </dd>
 <dt><code>max-average-unrolled-insns</code></dt>
 <dd><p>The maximum number of instructions biased by probabilities of their execution
 that a loop may have to be unrolled.  If a loop is unrolled,
 this parameter also determines how many times the loop code is unrolled.
 </p>
 </dd>
 <dt><code>max-unroll-times</code></dt>
 <dd><p>The maximum number of unrollings of a single loop.
 </p>
 </dd>
 <dt><code>max-peeled-insns</code></dt>
 <dd><p>The maximum number of instructions that a loop may have to be peeled.
 If a loop is peeled, this parameter also determines how many times
 the loop code is peeled.
 </p>
 </dd>
 <dt><code>max-peel-times</code></dt>
 <dd><p>The maximum number of peelings of a single loop.
 </p>
 </dd>
 <dt><code>max-peel-branches</code></dt>
 <dd><p>The maximum number of branches on the hot path through the peeled sequence.
 </p>
 </dd>
 <dt><code>max-completely-peeled-insns</code></dt>
 <dd><p>The maximum number of insns of a completely peeled loop.
 </p>
 </dd>
 <dt><code>max-completely-peel-times</code></dt>
 <dd><p>The maximum number of iterations of a loop to be suitable for complete peeling.
 </p>
 </dd>
 <dt><code>max-completely-peel-loop-nest-depth</code></dt>
 <dd><p>The maximum depth of a loop nest suitable for complete peeling.
 </p>
 </dd>
 <dt><code>max-unswitch-insns</code></dt>
 <dd><p>The maximum number of insns of an unswitched loop.
 </p>
 </dd>
 <dt><code>max-unswitch-level</code></dt>
 <dd><p>The maximum number of branches unswitched in a single loop.
 </p>
 </dd>
 <dt><code>lim-expensive</code></dt>
 <dd><p>The minimum cost of an expensive expression in the loop invariant motion.
 </p>
 </dd>
 <dt><code>iv-consider-all-candidates-bound</code></dt>
 <dd><p>Bound on number of candidates for induction variables, below which
 all candidates are considered for each use in induction variable
 optimizations.  If there are more candidates than this,
 only the most relevant ones are considered to avoid quadratic time complexity.
 </p>
 </dd>
 <dt><code>iv-max-considered-uses</code></dt>
 <dd><p>The induction variable optimizations give up on loops that contain more
 induction variable uses.
 </p>
 </dd>
 <dt><code>iv-always-prune-cand-set-bound</code></dt>
 <dd><p>If the number of candidates in the set is smaller than this value,
 always try to remove unnecessary ivs from the set
 when adding a new one.
 </p>
 </dd>
 <dt><code>scev-max-expr-size</code></dt>
 <dd><p>Bound on size of expressions used in the scalar evolutions analyzer.
 Large expressions slow the analyzer.
 </p>
 </dd>
 <dt><code>scev-max-expr-complexity</code></dt>
 <dd><p>Bound on the complexity of the expressions in the scalar evolutions analyzer.
 Complex expressions slow the analyzer.
 </p>
 </dd>
 <dt><code>omega-max-vars</code></dt>
 <dd><p>The maximum number of variables in an Omega constraint system.
 The default value is 128.
 </p>
 </dd>
 <dt><code>omega-max-geqs</code></dt>
 <dd><p>The maximum number of inequalities in an Omega constraint system.
 The default value is 256.
 </p>
 </dd>
 <dt><code>omega-max-eqs</code></dt>
 <dd><p>The maximum number of equalities in an Omega constraint system.
 The default value is 128.
 </p>
 </dd>
 <dt><code>omega-max-wild-cards</code></dt>
 <dd><p>The maximum number of wildcard variables that the Omega solver is
 able to insert.  The default value is 18.
 </p>
 </dd>
 <dt><code>omega-hash-table-size</code></dt>
 <dd><p>The size of the hash table in the Omega solver.  The default value is
 550.
 </p>
 </dd>
 <dt><code>omega-max-keys</code></dt>
 <dd><p>The maximal number of keys used by the Omega solver.  The default
 value is 500.
 </p>
 </dd>
 <dt><code>omega-eliminate-redundant-constraints</code></dt>
 <dd><p>When set to 1, use expensive methods to eliminate all redundant
 constraints.  The default value is 0.
 </p>
 </dd>
 <dt><code>vect-max-version-for-alignment-checks</code></dt>
 <dd><p>The maximum number of run-time checks that can be performed when
 doing loop versioning for alignment in the vectorizer.
 </p>
 </dd>
 <dt><code>vect-max-version-for-alias-checks</code></dt>
 <dd><p>The maximum number of run-time checks that can be performed when
 doing loop versioning for alias in the vectorizer.
 </p>
 </dd>
 <dt><code>vect-max-peeling-for-alignment</code></dt>
 <dd><p>The maximum number of loop peels to enhance access alignment
 for vectorizer. Value -1 means &rsquo;no limit&rsquo;.
 </p>
 </dd>
 <dt><code>max-iterations-to-track</code></dt>
 <dd><p>The maximum number of iterations of a loop the brute-force algorithm
 for analysis of the number of iterations of the loop tries to evaluate.
 </p>
 </dd>
 <dt><code>hot-bb-count-ws-permille</code></dt>
 <dd><p>A basic block profile count is considered hot if it contributes to
 the given permillage (i.e. 0...1000) of the entire profiled execution.
 </p>
 </dd>
 <dt><code>hot-bb-frequency-fraction</code></dt>
 <dd><p>Select fraction of the entry block frequency of executions of basic block in
 function given basic block needs to have to be considered hot.
 </p>
 </dd>
 <dt><code>max-predicted-iterations</code></dt>
 <dd><p>The maximum number of loop iterations we predict statically.  This is useful
 in cases where a function contains a single loop with known bound and
 another loop with unknown bound.
 The known number of iterations is predicted correctly, while
 the unknown number of iterations average to roughly 10.  This means that the
 loop without bounds appears artificially cold relative to the other one.
 </p>
 </dd>
 <dt><code>builtin-expect-probability</code></dt>
 <dd><p>Control the probability of the expression having the specified value. This
 parameter takes a percentage (i.e. 0 ... 100) as input.
 The default probability of 90 is obtained empirically.
 </p>
 </dd>
 <dt><code>align-threshold</code></dt>
 <dd>
 <p>Select fraction of the maximal frequency of executions of a basic block in
 a function to align the basic block.
 </p>
 </dd>
 <dt><code>align-loop-iterations</code></dt>
 <dd>
 <p>A loop expected to iterate at least the selected number of iterations is
 aligned.
 </p>
 </dd>
 <dt><code>tracer-dynamic-coverage</code></dt>
 <dt><code>tracer-dynamic-coverage-feedback</code></dt>
 <dd>
 <p>This value is used to limit superblock formation once the given percentage of
 executed instructions is covered.  This limits unnecessary code size
 expansion.
 </p>
 <p>The <samp>tracer-dynamic-coverage-feedback</samp> is used only when profile
 feedback is available.  The real profiles (as opposed to statically estimated
 ones) are much less balanced allowing the threshold to be larger value.
 </p>
 </dd>
 <dt><code>tracer-max-code-growth</code></dt>
 <dd><p>Stop tail duplication once code growth has reached given percentage.  This is
 a rather artificial limit, as most of the duplicates are eliminated later in
 cross jumping, so it may be set to much higher values than is the desired code
 growth.
 </p>
 </dd>
 <dt><code>tracer-min-branch-ratio</code></dt>
 <dd>
 <p>Stop reverse growth when the reverse probability of best edge is less than this
 threshold (in percent).
 </p>
 </dd>
 <dt><code>tracer-min-branch-ratio</code></dt>
 <dt><code>tracer-min-branch-ratio-feedback</code></dt>
 <dd>
 <p>Stop forward growth if the best edge has probability lower than this
 threshold.
 </p>
 <p>Similarly to <samp>tracer-dynamic-coverage</samp> two values are present, one for
 compilation for profile feedback and one for compilation without.  The value
 for compilation with profile feedback needs to be more conservative (higher) in
 order to make tracer effective.
 </p>
 </dd>
 <dt><code>max-cse-path-length</code></dt>
 <dd>
 <p>The maximum number of basic blocks on path that CSE considers.
 The default is 10.
 </p>
 </dd>
 <dt><code>max-cse-insns</code></dt>
 <dd><p>The maximum number of instructions CSE processes before flushing.
 The default is 1000.
 </p>
 </dd>
 <dt><code>ggc-min-expand</code></dt>
 <dd>
 <p>GCC uses a garbage collector to manage its own memory allocation.  This
 parameter specifies the minimum percentage by which the garbage
 collector&rsquo;s heap should be allowed to expand between collections.
 Tuning this may improve compilation speed; it has no effect on code
 generation.
 </p>
 <p>The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when
 RAM &gt;= 1GB.  If <code>getrlimit</code> is available, the notion of &ldquo;RAM&rdquo; is
 the smallest of actual RAM and <code>RLIMIT_DATA</code> or <code>RLIMIT_AS</code>.  If
 GCC is not able to calculate RAM on a particular platform, the lower
 bound of 30% is used.  Setting this parameter and
 <samp>ggc-min-heapsize</samp> to zero causes a full collection to occur at
 every opportunity.  This is extremely slow, but can be useful for
 debugging.
 </p>
 </dd>
 <dt><code>ggc-min-heapsize</code></dt>
 <dd>
 <p>Minimum size of the garbage collector&rsquo;s heap before it begins bothering
 to collect garbage.  The first collection occurs after the heap expands
 by <samp>ggc-min-expand</samp>% beyond <samp>ggc-min-heapsize</samp>.  Again,
 tuning this may improve compilation speed, and has no effect on code
 generation.
 </p>
 <p>The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that
 tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but
 with a lower bound of 4096 (four megabytes) and an upper bound of
 131072 (128 megabytes).  If GCC is not able to calculate RAM on a
 particular platform, the lower bound is used.  Setting this parameter
 very large effectively disables garbage collection.  Setting this
 parameter and <samp>ggc-min-expand</samp> to zero causes a full collection
 to occur at every opportunity.
 </p>
 </dd>
 <dt><code>max-reload-search-insns</code></dt>
 <dd><p>The maximum number of instruction reload should look backward for equivalent
 register.  Increasing values mean more aggressive optimization, making the
 compilation time increase with probably slightly better performance.
 The default value is 100.
 </p>
 </dd>
 <dt><code>max-cselib-memory-locations</code></dt>
 <dd><p>The maximum number of memory locations cselib should take into account.
 Increasing values mean more aggressive optimization, making the compilation time
 increase with probably slightly better performance.  The default value is 500.
 </p>
 </dd>
 <dt><code>reorder-blocks-duplicate</code></dt>
 <dt><code>reorder-blocks-duplicate-feedback</code></dt>
 <dd>
 <p>Used by the basic block reordering pass to decide whether to use unconditional
 branch or duplicate the code on its destination.  Code is duplicated when its
 estimated size is smaller than this value multiplied by the estimated size of
 unconditional jump in the hot spots of the program.
 </p>
 <p>The <samp>reorder-block-duplicate-feedback</samp> is used only when profile
 feedback is available.  It may be set to higher values than
 <samp>reorder-block-duplicate</samp> since information about the hot spots is more
 accurate.
 </p>
 </dd>
 <dt><code>max-sched-ready-insns</code></dt>
 <dd><p>The maximum number of instructions ready to be issued the scheduler should
 consider at any given time during the first scheduling pass.  Increasing
 values mean more thorough searches, making the compilation time increase
 with probably little benefit.  The default value is 100.
 </p>
 </dd>
 <dt><code>max-sched-region-blocks</code></dt>
 <dd><p>The maximum number of blocks in a region to be considered for
 interblock scheduling.  The default value is 10.
 </p>
 </dd>
 <dt><code>max-pipeline-region-blocks</code></dt>
 <dd><p>The maximum number of blocks in a region to be considered for
 pipelining in the selective scheduler.  The default value is 15.
 </p>
 </dd>
 <dt><code>max-sched-region-insns</code></dt>
 <dd><p>The maximum number of insns in a region to be considered for
 interblock scheduling.  The default value is 100.
 </p>
 </dd>
 <dt><code>max-pipeline-region-insns</code></dt>
 <dd><p>The maximum number of insns in a region to be considered for
 pipelining in the selective scheduler.  The default value is 200.
 </p>
 </dd>
 <dt><code>min-spec-prob</code></dt>
 <dd><p>The minimum probability (in percents) of reaching a source block
 for interblock speculative scheduling.  The default value is 40.
 </p>
 </dd>
 <dt><code>max-sched-extend-regions-iters</code></dt>
 <dd><p>The maximum number of iterations through CFG to extend regions.
 A value of 0 (the default) disables region extensions.
 </p>
 </dd>
 <dt><code>max-sched-insn-conflict-delay</code></dt>
 <dd><p>The maximum conflict delay for an insn to be considered for speculative motion.
 The default value is 3.
 </p>
 </dd>
 <dt><code>sched-spec-prob-cutoff</code></dt>
 <dd><p>The minimal probability of speculation success (in percents), so that
 speculative insns are scheduled.
 The default value is 40.
 </p>
 </dd>
 <dt><code>sched-spec-state-edge-prob-cutoff</code></dt>
 <dd><p>The minimum probability an edge must have for the scheduler to save its
 state across it.
 The default value is 10.
 </p>
 </dd>
 <dt><code>sched-mem-true-dep-cost</code></dt>
 <dd><p>Minimal distance (in CPU cycles) between store and load targeting same
 memory locations.  The default value is 1.
 </p>
 </dd>
 <dt><code>selsched-max-lookahead</code></dt>
 <dd><p>The maximum size of the lookahead window of selective scheduling.  It is a
 depth of search for available instructions.
 The default value is 50.
 </p>
 </dd>
 <dt><code>selsched-max-sched-times</code></dt>
 <dd><p>The maximum number of times that an instruction is scheduled during
 selective scheduling.  This is the limit on the number of iterations
 through which the instruction may be pipelined.  The default value is 2.
 </p>
 </dd>
 <dt><code>selsched-max-insns-to-rename</code></dt>
 <dd><p>The maximum number of best instructions in the ready list that are considered
 for renaming in the selective scheduler.  The default value is 2.
 </p>
 </dd>
 <dt><code>sms-min-sc</code></dt>
 <dd><p>The minimum value of stage count that swing modulo scheduler
 generates.  The default value is 2.
 </p>
 </dd>
 <dt><code>max-last-value-rtl</code></dt>
 <dd><p>The maximum size measured as number of RTLs that can be recorded in an expression
 in combiner for a pseudo register as last known value of that register.  The default
 is 10000.
 </p>
 </dd>
 <dt><code>integer-share-limit</code></dt>
 <dd><p>Small integer constants can use a shared data structure, reducing the
 compiler&rsquo;s memory usage and increasing its speed.  This sets the maximum
 value of a shared integer constant.  The default value is 256.
 </p>
 </dd>
 <dt><code>ssp-buffer-size</code></dt>
 <dd><p>The minimum size of buffers (i.e. arrays) that receive stack smashing
 protection when <samp>-fstack-protection</samp> is used.
 </p>
 </dd>
 <dt><code>min-size-for-stack-sharing</code></dt>
 <dd><p>The minimum size of variables taking part in stack slot sharing when not
 optimizing. The default value is 32.
 </p>
 </dd>
 <dt><code>max-jump-thread-duplication-stmts</code></dt>
 <dd><p>Maximum number of statements allowed in a block that needs to be
 duplicated when threading jumps.
 </p>
 </dd>
 <dt><code>max-fields-for-field-sensitive</code></dt>
 <dd><p>Maximum number of fields in a structure treated in
 a field sensitive manner during pointer analysis.  The default is zero
 for <samp>-O0</samp> and <samp>-O1</samp>,
 and 100 for <samp>-Os</samp>, <samp>-O2</samp>, and <samp>-O3</samp>.
 </p>
 </dd>
 <dt><code>prefetch-latency</code></dt>
 <dd><p>Estimate on average number of instructions that are executed before
 prefetch finishes.  The distance prefetched ahead is proportional
 to this constant.  Increasing this number may also lead to less
 streams being prefetched (see <samp>simultaneous-prefetches</samp>).
 </p>
 </dd>
 <dt><code>simultaneous-prefetches</code></dt>
 <dd><p>Maximum number of prefetches that can run at the same time.
 </p>
 </dd>
 <dt><code>l1-cache-line-size</code></dt>
 <dd><p>The size of cache line in L1 cache, in bytes.
 </p>
 </dd>
 <dt><code>l1-cache-size</code></dt>
 <dd><p>The size of L1 cache, in kilobytes.
 </p>
 </dd>
 <dt><code>l2-cache-size</code></dt>
 <dd><p>The size of L2 cache, in kilobytes.
 </p>
 </dd>
 <dt><code>min-insn-to-prefetch-ratio</code></dt>
 <dd><p>The minimum ratio between the number of instructions and the
 number of prefetches to enable prefetching in a loop.
 </p>
 </dd>
 <dt><code>prefetch-min-insn-to-mem-ratio</code></dt>
 <dd><p>The minimum ratio between the number of instructions and the
 number of memory references to enable prefetching in a loop.
 </p>
 </dd>
 <dt><code>use-canonical-types</code></dt>
 <dd><p>Whether the compiler should use the &ldquo;canonical&rdquo; type system.  By
 default, this should always be 1, which uses a more efficient internal
 mechanism for comparing types in C++ and Objective-C++.  However, if
 bugs in the canonical type system are causing compilation failures,
 set this value to 0 to disable canonical types.
 </p>
 </dd>
 <dt><code>switch-conversion-max-branch-ratio</code></dt>
 <dd><p>Switch initialization conversion refuses to create arrays that are
 bigger than <samp>switch-conversion-max-branch-ratio</samp> times the number of
 branches in the switch.
 </p>
 </dd>
 <dt><code>max-partial-antic-length</code></dt>
 <dd><p>Maximum length of the partial antic set computed during the tree
 partial redundancy elimination optimization (<samp>-ftree-pre</samp>) when
 optimizing at <samp>-O3</samp> and above.  For some sorts of source code
 the enhanced partial redundancy elimination optimization can run away,
 consuming all of the memory available on the host machine.  This
 parameter sets a limit on the length of the sets that are computed,
 which prevents the runaway behavior.  Setting a value of 0 for
 this parameter allows an unlimited set length.
 </p>
 </dd>
 <dt><code>sccvn-max-scc-size</code></dt>
 <dd><p>Maximum size of a strongly connected component (SCC) during SCCVN
 processing.  If this limit is hit, SCCVN processing for the whole
 function is not done and optimizations depending on it are
 disabled.  The default maximum SCC size is 10000.
 </p>
 </dd>
 <dt><code>sccvn-max-alias-queries-per-access</code></dt>
 <dd><p>Maximum number of alias-oracle queries we perform when looking for
 redundancies for loads and stores.  If this limit is hit the search
 is aborted and the load or store is not considered redundant.  The
 number of queries is algorithmically limited to the number of
 stores on all paths from the load to the function entry.
 The default maxmimum number of queries is 1000.
 </p>
 </dd>
 <dt><code>ira-max-loops-num</code></dt>
 <dd><p>IRA uses regional register allocation by default.  If a function
 contains more loops than the number given by this parameter, only at most
 the given number of the most frequently-executed loops form regions
 for regional register allocation.  The default value of the
 parameter is 100.
 </p>
 </dd>
 <dt><code>ira-max-conflict-table-size</code></dt>
 <dd><p>Although IRA uses a sophisticated algorithm to compress the conflict
 table, the table can still require excessive amounts of memory for
 huge functions.  If the conflict table for a function could be more
 than the size in MB given by this parameter, the register allocator
 instead uses a faster, simpler, and lower-quality
 algorithm that does not require building a pseudo-register conflict table.
 The default value of the parameter is 2000.
 </p>
 </dd>
 <dt><code>ira-loop-reserved-regs</code></dt>
 <dd><p>IRA can be used to evaluate more accurate register pressure in loops
 for decisions to move loop invariants (see <samp>-O3</samp>).  The number
 of available registers reserved for some other purposes is given
 by this parameter.  The default value of the parameter is 2, which is
 the minimal number of registers needed by typical instructions.
 This value is the best found from numerous experiments.
 </p>
 </dd>
 <dt><code>loop-invariant-max-bbs-in-loop</code></dt>
 <dd><p>Loop invariant motion can be very expensive, both in compilation time and
 in amount of needed compile-time memory, with very large loops.  Loops
 with more basic blocks than this parameter won&rsquo;t have loop invariant
 motion optimization performed on them.  The default value of the
 parameter is 1000 for <samp>-O1</samp> and 10000 for <samp>-O2</samp> and above.
 </p>
 </dd>
 <dt><code>loop-max-datarefs-for-datadeps</code></dt>
 <dd><p>Building data dapendencies is expensive for very large loops.  This
 parameter limits the number of data references in loops that are
 considered for data dependence analysis.  These large loops are no
 handled by the optimizations using loop data dependencies.
 The default value is 1000.
 </p>
 </dd>
 <dt><code>max-vartrack-size</code></dt>
 <dd><p>Sets a maximum number of hash table slots to use during variable
 tracking dataflow analysis of any function.  If this limit is exceeded
 with variable tracking at assignments enabled, analysis for that
 function is retried without it, after removing all debug insns from
 the function.  If the limit is exceeded even without debug insns, var
 tracking analysis is completely disabled for the function.  Setting
 the parameter to zero makes it unlimited.
 </p>
 </dd>
 <dt><code>max-vartrack-expr-depth</code></dt>
 <dd><p>Sets a maximum number of recursion levels when attempting to map
 variable names or debug temporaries to value expressions.  This trades
 compilation time for more complete debug information.  If this is set too
 low, value expressions that are available and could be represented in
 debug information may end up not being used; setting this higher may
 enable the compiler to find more complex debug expressions, but compile
 time and memory use may grow.  The default is 12.
 </p>
 </dd>
 <dt><code>min-nondebug-insn-uid</code></dt>
 <dd><p>Use uids starting at this parameter for nondebug insns.  The range below
 the parameter is reserved exclusively for debug insns created by
 <samp>-fvar-tracking-assignments</samp>, but debug insns may get
 (non-overlapping) uids above it if the reserved range is exhausted.
 </p>
 </dd>
 <dt><code>ipa-sra-ptr-growth-factor</code></dt>
 <dd><p>IPA-SRA replaces a pointer to an aggregate with one or more new
 parameters only when their cumulative size is less or equal to
 <samp>ipa-sra-ptr-growth-factor</samp> times the size of the original
 pointer parameter.
 </p>
 </dd>
 <dt><code>tm-max-aggregate-size</code></dt>
 <dd><p>When making copies of thread-local variables in a transaction, this
 parameter specifies the size in bytes after which variables are
 saved with the logging functions as opposed to save/restore code
 sequence pairs.  This option only applies when using
 <samp>-fgnu-tm</samp>.
 </p>
 </dd>
 <dt><code>graphite-max-nb-scop-params</code></dt>
 <dd><p>To avoid exponential effects in the Graphite loop transforms, the
 number of parameters in a Static Control Part (SCoP) is bounded.  The
 default value is 10 parameters.  A variable whose value is unknown at
 compilation time and defined outside a SCoP is a parameter of the SCoP.
 </p>
 </dd>
 <dt><code>graphite-max-bbs-per-function</code></dt>
 <dd><p>To avoid exponential effects in the detection of SCoPs, the size of
 the functions analyzed by Graphite is bounded.  The default value is
 100 basic blocks.
 </p>
 </dd>
 <dt><code>loop-block-tile-size</code></dt>
 <dd><p>Loop blocking or strip mining transforms, enabled with
 <samp>-floop-block</samp> or <samp>-floop-strip-mine</samp>, strip mine each
 loop in the loop nest by a given number of iterations.  The strip
 length can be changed using the <samp>loop-block-tile-size</samp>
 parameter.  The default value is 51 iterations.
 </p>
 </dd>
 <dt><code>ipa-cp-value-list-size</code></dt>
 <dd><p>IPA-CP attempts to track all possible values and types passed to a function&rsquo;s
 parameter in order to propagate them and perform devirtualization.
 <samp>ipa-cp-value-list-size</samp> is the maximum number of values and types it
 stores per one formal parameter of a function.
 </p>
 </dd>
 <dt><code>ipa-cp-eval-threshold</code></dt>
 <dd><p>IPA-CP calculates its own score of cloning profitability heuristics
 and performs those cloning opportunities with scores that exceed
 <samp>ipa-cp-eval-threshold</samp>.
 </p>
 </dd>
 <dt><code>ipa-max-agg-items</code></dt>
 <dd><p>IPA-CP is also capable to propagate a number of scalar values passed
 in an aggregate. <samp>ipa-max-agg-items</samp> controls the maximum
 number of such values per one parameter.
 </p>
 </dd>
 <dt><code>ipa-cp-loop-hint-bonus</code></dt>
 <dd><p>When IPA-CP determines that a cloning candidate would make the number
 of iterations of a loop known, it adds a bonus of
 <samp>ipa-cp-loop-hint-bonus</samp> bonus to the profitability score of
 the candidate.
 </p>
 </dd>
 <dt><code>ipa-cp-array-index-hint-bonus</code></dt>
 <dd><p>When IPA-CP determines that a cloning candidate would make the index of
 an array access known, it adds a bonus of
 <samp>ipa-cp-array-index-hint-bonus</samp> bonus to the profitability
 score of the candidate.
 </p>
 </dd>
 <dt><code>lto-partitions</code></dt>
 <dd><p>Specify desired number of partitions produced during WHOPR compilation.
 The number of partitions should exceed the number of CPUs used for compilation.
 The default value is 32.
 </p>
 </dd>
 <dt><code>lto-minpartition</code></dt>
 <dd><p>Size of minimal partition for WHOPR (in estimated instructions).
 This prevents expenses of splitting very small programs into too many
 partitions.
 </p>
 </dd>
 <dt><code>cxx-max-namespaces-for-diagnostic-help</code></dt>
 <dd><p>The maximum number of namespaces to consult for suggestions when C++
 name lookup fails for an identifier.  The default is 1000.
 </p>
 </dd>
 <dt><code>sink-frequency-threshold</code></dt>
 <dd><p>The maximum relative execution frequency (in percents) of the target block
 relative to a statement&rsquo;s original block to allow statement sinking of a
 statement.  Larger numbers result in more aggressive statement sinking.
 The default value is 75.  A small positive adjustment is applied for
 statements with memory operands as those are even more profitable so sink.
 </p>
 </dd>
 <dt><code>max-stores-to-sink</code></dt>
 <dd><p>The maximum number of conditional stores paires that can be sunk.  Set to 0
 if either vectorization (<samp>-ftree-vectorize</samp>) or if-conversion
 (<samp>-ftree-loop-if-convert</samp>) is disabled.  The default is 2.
 </p>
 </dd>
 <dt><code>allow-load-data-races</code></dt>
 <dd><p>Allow optimizers to introduce new data races on loads.
 Set to 1 to allow, otherwise to 0.  This option is enabled by default
 unless implicitly set by the <samp>-fmemory-model=</samp> option.
 </p>
 </dd>
 <dt><code>allow-store-data-races</code></dt>
 <dd><p>Allow optimizers to introduce new data races on stores.
 Set to 1 to allow, otherwise to 0.  This option is enabled by default
 unless implicitly set by the <samp>-fmemory-model=</samp> option.
 </p>
 </dd>
 <dt><code>allow-packed-load-data-races</code></dt>
 <dd><p>Allow optimizers to introduce new data races on packed data loads.
 Set to 1 to allow, otherwise to 0.  This option is enabled by default
 unless implicitly set by the <samp>-fmemory-model=</samp> option.
 </p>
 </dd>
 <dt><code>allow-packed-store-data-races</code></dt>
 <dd><p>Allow optimizers to introduce new data races on packed data stores.
 Set to 1 to allow, otherwise to 0.  This option is enabled by default
 unless implicitly set by the <samp>-fmemory-model=</samp> option.
 </p>
 </dd>
 <dt><code>case-values-threshold</code></dt>
 <dd><p>The smallest number of different values for which it is best to use a
 jump-table instead of a tree of conditional branches.  If the value is
 0, use the default for the machine.  The default is 0.
 </p>
 </dd>
 <dt><code>tree-reassoc-width</code></dt>
 <dd><p>Set the maximum number of instructions executed in parallel in
 reassociated tree. This parameter overrides target dependent
 heuristics used by default if has non zero value.
 </p>
 </dd>
 <dt><code>sched-pressure-algorithm</code></dt>
 <dd><p>Choose between the two available implementations of
 <samp>-fsched-pressure</samp>.  Algorithm 1 is the original implementation
 and is the more likely to prevent instructions from being reordered.
 Algorithm 2 was designed to be a compromise between the relatively
 conservative approach taken by algorithm 1 and the rather aggressive
 approach taken by the default scheduler.  It relies more heavily on
 having a regular register file and accurate register pressure classes.
 See <samp>haifa-sched.c</samp> in the GCC sources for more details.
 </p>
 <p>The default choice depends on the target.
 </p>
 </dd>
 <dt><code>max-slsr-cand-scan</code></dt>
 <dd><p>Set the maximum number of existing candidates that will be considered when
 seeking a basis for a new straight-line strength reduction candidate.
 </p>
 </dd>
 <dt><code>asan-globals</code></dt>
 <dd><p>Enable buffer overflow detection for global objects.  This kind
 of protection is enabled by default if you are using
 <samp>-fsanitize=address</samp> option.
 To disable global objects protection use <samp>--param asan-globals=0</samp>.
 </p>
 </dd>
 <dt><code>asan-stack</code></dt>
 <dd><p>Enable buffer overflow detection for stack objects.  This kind of
 protection is enabled by default when using<samp>-fsanitize=address</samp>.
 To disable stack protection use <samp>--param asan-stack=0</samp> option.
 </p>
 </dd>
 <dt><code>asan-instrument-reads</code></dt>
 <dd><p>Enable buffer overflow detection for memory reads.  This kind of
 protection is enabled by default when using <samp>-fsanitize=address</samp>.
 To disable memory reads protection use
 <samp>--param asan-instrument-reads=0</samp>.
 </p>
 </dd>
 <dt><code>asan-instrument-writes</code></dt>
 <dd><p>Enable buffer overflow detection for memory writes.  This kind of
 protection is enabled by default when using <samp>-fsanitize=address</samp>.
 To disable memory writes protection use
 <samp>--param asan-instrument-writes=0</samp> option.
 </p>
 </dd>
 <dt><code>asan-memintrin</code></dt>
 <dd><p>Enable detection for built-in functions.  This kind of protection
 is enabled by default when using <samp>-fsanitize=address</samp>.
 To disable built-in functions protection use
 <samp>--param asan-memintrin=0</samp>.
 </p>
 </dd>
 <dt><code>asan-use-after-return</code></dt>
 <dd><p>Enable detection of use-after-return.  This kind of protection
 is enabled by default when using <samp>-fsanitize=address</samp> option.
 To disable use-after-return detection use
 <samp>--param asan-use-after-return=0</samp>.
 </p>
 </dd>
 <dt><code>asan-instrumentation-with-call-threshold</code></dt>
 <dd><p>If number of memory accesses in function being instrumented
 is greater or equal to this number, use callbacks instead of inline checks.
 E.g. to disable inline code use
 <samp>--param asan-instrumentation-with-call-threshold=0</samp>.
 </p>
 </dd>
 <dt><code>max-fsm-thread-path-insns</code></dt>
 <dd><p>Maximum number of instructions to copy when duplicating blocks on a
 finite state automaton jump thread path.  The default is 100.
 </p>
 </dd>
 <dt><code>max-fsm-thread-length</code></dt>
 <dd><p>Maximum number of basic blocks on a finite state automaton jump thread
 path.  The default is 10.
 </p>
 </dd>
 <dt><code>max-fsm-thread-paths</code></dt>
 <dd><p>Maximum number of new jump thread paths to create for a finite state
 automaton.  The default is 50.
 </p>
 </dd>
 </dl>
 </dd>
 </dl>

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