neulab/tldr huggingface dataset:
-funroll-all-loops Unroll all loops, even if their number of iterations is uncertain when the loop is entered.  This usually makes programs run more slowly.  -funroll-all-loops implies the same options as -funroll-loops.
-fpeel-loops Peels loops for which there is enough information that they do not roll much (from profile feedback or static analysis).  It also turns on complete loop peeling (i.e. complete removal of loops with small constant number of iterations).
Enabled by -O3, -fprofile-use, and -fauto-profile.
-fmove-loop-invariants Enables the loop invariant motion pass in the RTL loop optimizer. Enabled at level -O1 and higher, except for -Og.
-fsplit-loops Split a loop into two if it contains a condition that's always true for one side of the iteration space and false for the other.
-funswitch-loops Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches (modified according to result of the condition).
-fversion-loops-for-strides If a loop iterates over an array with a variable stride, create another version of the loop that assumes the stride is always one. For example:
for (int i = 0; i < n; ++i) x[i * stride] = ...;
becomes:
if (stride == 1) for (int i = 0; i < n; ++i) x[i] = ...; else for (int i = 0; i < n; ++i) x[i * stride] = ...;
This is particularly useful for assumed-shape arrays in Fortran where (for example) it allows better vectorization assuming contiguous accesses.  This flag is enabled by default at -O3.  It is also enabled by -fprofile-use and -fauto-profile.
-ffunction-sections -fdata-sections Place each function or data item into its own section in the output file if the target supports arbitrary sections.  The name of the function or the name of the data item determines the section's name in the output file.
Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space.  Most systems using the ELF object format have linkers with such optimizations.  On AIX, the linker rearranges sections (CSECTs) based on the call graph.  The performance impact varies.
Together with a linker garbage collection (linker --gc-sections option) these options may lead to smaller statically-linked executables (after stripping).
On ELF/DWARF systems these options do not degenerate the quality of the debug information.  There could be issues with other object files/debug info formats.
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.  These options affect code generation.  They prevent optimizations by the compiler and assembler using relative locations inside a translation unit since the locations are unknown until link time.  An example of such an optimization is relaxing calls to short call instructions.
-fstdarg-opt Optimize the prologue of variadic argument functions with respect to usage of those arguments.
-fsection-anchors Try to reduce the number of symbolic address calculations by using shared "anchor" symbols to address nearby objects.  This transformation can help to reduce the number of GOT entries and GOT accesses on some targets.
For example, the implementation of the following function "foo":
static int a, b, c; int foo (void) { return a + b + c; }
usually calculates the addresses of all three variables, but if you compile it with -fsection-anchors, it accesses the variables from a common anchor point instead.  The effect is similar to the following pseudocode (which isn't valid C):
int foo (void) { register int *xr = &x; return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; }
Not all targets support this option.
-fzero-call-used-regs=choice Zero call-used registers at function return to increase program security by either mitigating Return-Oriented Programming (ROP) attacks or preventing information leakage through registers.
The possible values of choice are the same as for the "zero_call_used_regs" attribute.  The default is skip.
You can control this behavior for a specific function by using the function attribute "zero_call_used_regs".
--param name=value 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 --param option.
The names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases.
In order to get minimal, maximal and default value of a parameter, one can use --help=param -Q options.
In each case, the value is an integer.  The following choices of name are recognized for all targets:
predictable-branch-outcome When branch is predicted to be taken with probability lower than this threshold (in percent), then it is considered well predictable.
max-rtl-if-conversion-insns RTL if-conversion tries to remove conditional branches around a block and replace them with conditionally executed instructions. This parameter gives the maximum number of instructions in a block which should be considered for if-conversion.  The compiler will also use other heuristics to decide whether if-conversion is likely to be profitable.
max-rtl-if-conversion-predictable-cost RTL if-conversion will try to remove conditional branches around a block and replace them with conditionally executed instructions.  These parameters give the maximum permissible cost for the sequence that would be generated by if-conversion depending on whether the branch is statically determined to be predictable or not.  The units for this parameter are the same as those for the GCC internal seq_cost metric.  The compiler will try to provide a reasonable default for this parameter using the BRANCH_COST target macro.
max-crossjump-edges The maximum number of incoming edges to consider for cross- jumping.  The algorithm used by -fcrossjumping is O(N^2) in the number of edges incoming to each block.  Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in executable size.
min-crossjump-insns The minimum number of instructions that must be matched at the end of two blocks before cross-jumping is performed on them. This value is ignored in the case where all instructions in the block being cross-jumped from are matched.
max-grow-copy-bb-insns The maximum code size expansion factor when copying basic blocks instead of jumping.  The expansion is relative to a jump instruction.
max-goto-duplication-insns The maximum number of instructions to duplicate to a block that jumps to a computed goto.  To avoid O(N^2) behavior in a number of passes, GCC factors computed gotos early in the compilation process, and unfactors them as late as possible.  Only computed jumps at the end of a basic blocks with no more than max-goto- duplication-insns are unfactored.
max-delay-slot-insn-search The maximum number of instructions to consider when looking for an instruction to fill a delay slot.  If more than this arbitrary number of instructions are searched, the time savings from filling the delay slot are minimal, so stop searching. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in execution time.
max-delay-slot-live-search When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information.  Increasing this arbitrarily chosen value means more aggressive optimization, increasing the compilation time.  This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph.
max-gcse-memory The approximate maximum amount of memory in "kB" 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.
max-gcse-insertion-ratio If the ratio of expression insertions to deletions is larger than this value for any expression, then RTL PRE inserts or removes the expression and thus leaves partially redundant computations in the instruction stream.
max-pending-list-length The maximum number of pending dependencies scheduling allows before flushing the current state and starting over.  Large functions with few branches or calls can create excessively large lists which needlessly consume memory and resources.
max-modulo-backtrack-attempts The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop.  Larger values can exponentially increase compilation time.
max-inline-insns-single Several parameters control the tree inliner used in GCC.  This number sets the maximum number of instructions (counted in GCC's internal representation) in a single function that the tree inliner considers for inlining.  This only affects functions declared inline and methods implemented in a class declaration (C++).
max-inline-insns-auto When you use -finline-functions (included in -O3), a lot of functions that would otherwise not be considered for inlining by the compiler are investigated.  To those functions, a different (more restrictive) limit compared to functions declared inline can be applied (--param max-inline-insns-auto).
max-inline-insns-small This is bound applied to calls which are considered relevant with -finline-small-functions.
max-inline-insns-size This is bound applied to calls which are optimized for size. Small growth may be desirable to anticipate optimization oppurtunities exposed by inlining.
uninlined-function-insns Number of instructions accounted by inliner for function overhead such as function prologue and epilogue.
uninlined-function-time Extra time accounted by inliner for function overhead such as time needed to execute function prologue and epilogue
inline-heuristics-hint-percent The scale (in percents) applied to inline-insns-single, inline-insns-single-O2, inline-insns-auto when inline heuristics hints that inlining is very profitable (will enable later optimizations).
uninlined-thunk-insns uninlined-thunk-time Same as --param uninlined-function-insns and --param uninlined- function-time but applied to function thunks
inline-min-speedup When estimated performance improvement of caller + callee runtime exceeds this threshold (in percent), the function can be inlined regardless of the limit on --param max-inline-insns-single and --param max-inline-insns-auto.
large-function-insns The limit specifying really large functions.  For functions larger than this limit after inlining, inlining is constrained by --param large-function-growth.  This parameter is useful primarily to avoid extreme compilation time caused by non-linear algorithms used by the back end.
large-function-growth Specifies maximal growth of large function caused by inlining in percents.  For example, parameter value 100 limits large function growth to 2.0 times the original size.
large-unit-insns The limit specifying large translation unit.  Growth caused by inlining of units larger than this limit is limited by --param inline-unit-growth.  For small units this might be too tight. For example, consider a unit consisting of function A that is inline and B that just calls A three times.  If B is small relative to A, the growth of unit is 300\% and yet such inlining is very sane.  For very large units consisting of small inlineable functions, however, the overall unit growth limit is needed to avoid exponential explosion of code size.  Thus for smaller units, the size is increased to --param large-unit-insns before applying --param inline-unit-growth.
lazy-modules Maximum number of concurrently open C++ module files when lazy loading.
inline-unit-growth Specifies maximal overall growth of the compilation unit caused by inlining.  For example, parameter value 20 limits unit growth to 1.2 times the original size. Cold functions (either marked cold via an attribute or by profile feedback) are not accounted into the unit size.
ipa-cp-unit-growth Specifies maximal overall growth of the compilation unit caused by interprocedural constant propagation.  For example, parameter value 10 limits unit growth to 1.1 times the original size.
ipa-cp-large-unit-insns The size of translation unit that IPA-CP pass considers large.
large-stack-frame The limit specifying large stack frames.  While inlining the algorithm is trying to not grow past this limit too much.
large-stack-frame-growth Specifies maximal growth of large stack frames caused by inlining in percents.  For example, parameter value 1000 limits large stack frame growth to 11 times the original size.
max-inline-insns-recursive max-inline-insns-recursive-auto Specifies the maximum number of instructions an out-of-line copy of a self-recursive inline function can grow into by performing recursive inlining.
--param max-inline-insns-recursive applies to functions declared inline.  For functions not declared inline, recursive inlining happens only when -finline-functions (included in -O3) is enabled; --param max-inline-insns-recursive-auto applies instead.
max-inline-recursive-depth max-inline-recursive-depth-auto Specifies the maximum recursion depth used for recursive inlining.
--param max-inline-recursive-depth applies to functions declared inline.  For functions not declared inline, recursive inlining happens only when -finline-functions (included in -O3) is enabled; --param max-inline-recursive-depth-auto applies instead.
min-inline-recursive-probability Recursive inlining is profitable only for function having deep recursion in average and can hurt for function having little recursion depth by increasing the prologue size or complexity of function body to other optimizers.
When profile feedback is available (see -fprofile-generate) the actual recursion depth can be guessed from the probability that function recurses via a given call expression.  This parameter limits inlining only to call expressions whose probability exceeds the given threshold (in percents).
early-inlining-insns Specify growth that the early inliner can make.  In effect it increases the amount of inlining for code having a large abstraction penalty.
max-early-inliner-iterations Limit of iterations of the early inliner.  This basically bounds the number of nested indirect calls the early inliner can resolve.  Deeper chains are still handled by late inlining.
comdat-sharing-probability Probability (in percent) that C++ inline function with comdat visibility are shared across multiple compilation units.
modref-max-bases modref-max-refs modref-max-accesses Specifies the maximal number of base pointers, references and accesses stored for a single function by mod/ref analysis.
modref-max-tests Specifies the maxmal number of tests alias oracle can perform to disambiguate memory locations using the mod/ref information. This parameter ought to be bigger than --param modref-max-bases and --param modref-max-refs.
modref-max-depth Specifies the maximum depth of DFS walk used by modref escape analysis.  Setting to 0 disables the analysis completely.
modref-max-escape-points Specifies the maximum number of escape points tracked by modref per SSA-name.
profile-func-internal-id A parameter to control whether to use function internal id in profile database lookup. If the value is 0, the compiler uses an id that is based on function assembler name and filename, which makes old profile data more tolerant to source changes such as function reordering etc.
min-vect-loop-bound The minimum number of iterations under which loops are not vectorized when -ftree-vectorize is used.  The number of iterations after vectorization needs to be greater than the value specified by this option to allow vectorization.
gcse-cost-distance-ratio Scaling factor in calculation of maximum distance an expression can be moved by GCSE optimizations.  This is currently supported only in the code hoisting pass.  The bigger the ratio, the more aggressive code hoisting is with simple expressions, i.e., the expressions that have cost less than gcse-unrestricted-cost. Specifying 0 disables hoisting of simple expressions.
gcse-unrestricted-cost Cost, roughly measured as the cost of a single typical machine instruction, at which GCSE optimizations do not constrain the distance an expression can travel.  This is currently supported only in the code hoisting pass.  The lesser the cost, the more aggressive code hoisting is.  Specifying 0 allows all expressions to travel unrestricted distances.
max-hoist-depth The depth of search in the dominator tree for expressions to hoist.  This is used to avoid quadratic behavior in hoisting algorithm.  The value of 0 does not limit on the search, but may slow down compilation of huge functions.
max-tail-merge-comparisons The maximum amount of similar bbs to compare a bb with.  This is used to avoid quadratic behavior in tree tail merging.
max-tail-merge-iterations The maximum amount of iterations of the pass over the function. This is used to limit compilation time in tree tail merging.
store-merging-allow-unaligned Allow the store merging pass to introduce unaligned stores if it is legal to do so.
max-stores-to-merge The maximum number of stores to attempt to merge into wider stores in the store merging pass.
max-store-chains-to-track The maximum number of store chains to track at the same time in the attempt to merge them into wider stores in the store merging pass.
max-stores-to-track The maximum number of stores to track at the same time in the attemt to to merge them into wider stores in the store merging pass.
max-unrolled-insns The maximum number of instructions that a loop may have to be unrolled.  If a loop is unrolled, this parameter also determines how many times the loop code is unrolled.
max-average-unrolled-insns The maximum number of instructions biased by probabilities of their execution that a loop may have to be unrolled.  If a loop is unrolled, this parameter also determines how many times the loop code is unrolled.
max-unroll-times The maximum number of unrollings of a single loop.
max-peeled-insns The maximum number of instructions that a loop may have to be peeled.  If a loop is peeled, this parameter also determines how many times the loop code is peeled.
max-peel-times The maximum number of peelings of a single loop.
max-peel-branches The maximum number of branches on the hot path through the peeled sequence.
max-completely-peeled-insns The maximum number of insns of a completely peeled loop.
max-completely-peel-times The maximum number of iterations of a loop to be suitable for complete peeling.
max-completely-peel-loop-nest-depth The maximum depth of a loop nest suitable for complete peeling.
max-unswitch-insns The maximum number of insns of an unswitched loop.
max-unswitch-level The maximum number of branches unswitched in a single loop.
lim-expensive The minimum cost of an expensive expression in the loop invariant motion.
min-loop-cond-split-prob When FDO profile information is available, min-loop-cond-split- prob specifies minimum threshold for probability of semi- invariant condition statement to trigger loop split.
iv-consider-all-candidates-bound Bound on number of candidates for induction variables, below which all candidates are considered for each use in induction variable optimizations.  If there are more candidates than this, only the most relevant ones are considered to avoid quadratic time complexity.
iv-max-considered-uses The induction variable optimizations give up on loops that contain more induction variable uses.
iv-always-prune-cand-set-bound If the number of candidates in the set is smaller than this value, always try to remove unnecessary ivs from the set when adding a new one.
avg-loop-niter Average number of iterations of a loop.
dse-max-object-size Maximum size (in bytes) of objects tracked bytewise by dead store elimination.  Larger values may result in larger compilation times.
dse-max-alias-queries-per-store Maximum number of queries into the alias oracle per store. Larger values result in larger compilation times and may result in more removed dead stores.
scev-max-expr-size Bound on size of expressions used in the scalar evolutions analyzer.  Large expressions slow the analyzer.
scev-max-expr-complexity Bound on the complexity of the expressions in the scalar evolutions analyzer.  Complex expressions slow the analyzer.
max-tree-if-conversion-phi-args Maximum number of arguments in a PHI supported by TREE if conversion unless the loop is marked with simd pragma.
vect-max-version-for-alignment-checks The maximum number of run-time checks that can be performed when doing loop versioning for alignment in the vectorizer.
vect-max-version-for-alias-checks The maximum number of run-time checks that can be performed when doing loop versioning for alias in the vectorizer.
vect-max-peeling-for-alignment The maximum number of loop peels to enhance access alignment for vectorizer. Value -1 means no limit.
max-iterations-to-track The maximum number of iterations of a loop the brute-force algorithm for analysis of the number of iterations of the loop tries to evaluate.
hot-bb-count-fraction The denominator n of fraction 1/n of the maximal execution count of a basic block in the entire program that a basic block needs to at least have in order to be considered hot.  The default is 10000, which means that a basic block is considered hot if its execution count is greater than 1/10000 of the maximal execution count.  0 means that it is never considered hot.  Used in non-LTO mode.
hot-bb-count-ws-permille The number of most executed permilles, ranging from 0 to 1000, of the profiled execution of the entire program to which the execution count of a basic block must be part of in order to be considered hot.  The default is 990, which means that a basic block is considered hot if its execution count contributes to the upper 990 permilles, or 99.0%, of the profiled execution of the entire program.  0 means that it is never considered hot.  Used in LTO mode.
hot-bb-frequency-fraction The denominator n of fraction 1/n of the execution frequency of the entry block of a function that a basic block of this function needs to at least have in order to be considered hot.  The default is 1000, which means that a basic block is considered hot in a function if it is executed more frequently than 1/1000 of the frequency of the entry block of the function.  0 means that it is never considered hot.
unlikely-bb-count-fraction The denominator n of fraction 1/n of the number of profiled runs of the entire program below which the execution count of a basic block must be in order for the basic block to be considered unlikely executed.  The default is 20, which means that a basic block is considered unlikely executed if it is executed in fewer than 1/20, or 5%, of the runs of the program.  0 means that it is always considered unlikely executed.
max-predicted-iterations The maximum number of loop iterations we predict statically. This is useful in cases where a function contains a single loop with known bound and another loop with unknown bound.  The known number of iterations is predicted correctly, while the unknown number of iterations average to roughly 10.  This means that the loop without bounds appears artificially cold relative to the other one.
builtin-expect-probability Control the probability of the expression having the specified value. This parameter takes a percentage (i.e. 0 ... 100) as input.
builtin-string-cmp-inline-length The maximum length of a constant string for a builtin string cmp call eligible for inlining.
align-threshold Select fraction of the maximal frequency of executions of a basic block in a function to align the basic block.
align-loop-iterations A loop expected to iterate at least the selected number of iterations is aligned.
tracer-dynamic-coverage tracer-dynamic-coverage-feedback This value is used to limit superblock formation once the given percentage of executed instructions is covered.  This limits unnecessary code size expansion.
The tracer-dynamic-coverage-feedback parameter is used only when profile feedback is available.  The real profiles (as opposed to statically estimated ones) are much less balanced allowing the threshold to be larger value.
tracer-max-code-growth Stop tail duplication once code growth has reached given percentage.  This is a rather artificial limit, as most of the duplicates are eliminated later in cross jumping, so it may be set to much higher values than is the desired code growth.
tracer-min-branch-ratio Stop reverse growth when the reverse probability of best edge is less than this threshold (in percent).
tracer-min-branch-probability tracer-min-branch-probability-feedback Stop forward growth if the best edge has probability lower than this threshold.
Similarly to tracer-dynamic-coverage two parameters are provided. tracer-min-branch-probability-feedback is used for compilation with profile feedback and tracer-min-branch-probability compilation without.  The value for compilation with profile feedback needs to be more conservative (higher) in order to make tracer effective.
stack-clash-protection-guard-size Specify the size of the operating system provided stack guard as 2 raised to num bytes.  Higher values may reduce the number of explicit probes, but a value larger than the operating system provided guard will leave code vulnerable to stack clash style attacks.
stack-clash-protection-probe-interval Stack clash protection involves probing stack space as it is allocated.  This param controls the maximum distance between probes into the stack as 2 raised to num bytes.  Higher values may reduce the number of explicit probes, but a value larger than the operating system provided guard will leave code vulnerable to stack clash style attacks.
max-cse-path-length The maximum number of basic blocks on path that CSE considers.
max-cse-insns The maximum number of instructions CSE processes before flushing.
ggc-min-expand GCC uses a garbage collector to manage its own memory allocation. This parameter specifies the minimum percentage by which the garbage collector's heap should be allowed to expand between collections.  Tuning this may improve compilation speed; it has no effect on code generation.
The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when RAM >= 1GB.  If "getrlimit" is available, the notion of "RAM" is the smallest of actual RAM and "RLIMIT_DATA" or "RLIMIT_AS".  If GCC is not able to calculate RAM on a particular platform, the lower bound of 30% is used.  Setting this parameter and ggc-min-heapsize to zero causes a full collection to occur at every opportunity.  This is extremely slow, but can be useful for debugging.
ggc-min-heapsize Minimum size of the garbage collector's heap before it begins bothering to collect garbage.  The first collection occurs after the heap expands by ggc-min-expand% beyond ggc-min-heapsize. Again, tuning this may improve compilation speed, and has no effect on code generation.
The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but with a lower bound of 4096 (four megabytes) and an upper bound of 131072 (128 megabytes).  If GCC is not able to calculate RAM on a particular platform, the lower bound is used.  Setting this parameter very large effectively disables garbage collection.  Setting this parameter and ggc-min-expand to zero causes a full collection to occur at every opportunity.
max-reload-search-insns The maximum number of instruction reload should look backward for equivalent register.  Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance.
max-cselib-memory-locations The maximum number of memory locations cselib should take into account.  Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance.
max-sched-ready-insns The maximum number of instructions ready to be issued the scheduler should consider at any given time during the first scheduling pass.  Increasing values mean more thorough searches, making the compilation time increase with probably little benefit.
max-sched-region-blocks The maximum number of blocks in a region to be considered for interblock scheduling.
max-pipeline-region-blocks The maximum number of blocks in a region to be considered for pipelining in the selective scheduler.
max-sched-region-insns The maximum number of insns in a region to be considered for interblock scheduling.
max-pipeline-region-insns The maximum number of insns in a region to be considered for pipelining in the selective scheduler.
min-spec-prob The minimum probability (in percents) of reaching a source block for interblock speculative scheduling.
max-sched-extend-regions-iters The maximum number of iterations through CFG to extend regions. A value of 0 disables region extensions.
max-sched-insn-conflict-delay The maximum conflict delay for an insn to be considered for speculative motion.
sched-spec-prob-cutoff The minimal probability of speculation success (in percents), so that speculative insns are scheduled.
sched-state-edge-prob-cutoff The minimum probability an edge must have for the scheduler to save its state across it.
sched-mem-true-dep-cost Minimal distance (in CPU cycles) between store and load targeting same memory locations.
selsched-max-lookahead The maximum size of the lookahead window of selective scheduling. It is a depth of search for available instructions.
selsched-max-sched-times The maximum number of times that an instruction is scheduled during selective scheduling.  This is the limit on the number of iterations through which the instruction may be pipelined.
selsched-insns-to-rename The maximum number of best instructions in the ready list that are considered for renaming in the selective scheduler.
sms-min-sc The minimum value of stage count that swing modulo scheduler generates.
max-last-value-rtl The maximum size measured as number of RTLs that can be recorded in an expression in combiner for a pseudo register as last known value of that register.
max-combine-insns The maximum number of instructions the RTL combiner tries to combine.
integer-share-limit Small integer constants can use a shared data structure, reducing the compiler's memory usage and increasing its speed.  This sets the maximum value of a shared integer constant.
ssp-buffer-size The minimum size of buffers (i.e. arrays) that receive stack smashing protection when -fstack-protection is used.
min-size-for-stack-sharing The minimum size of variables taking part in stack slot sharing when not optimizing.
max-jump-thread-duplication-stmts Maximum number of statements allowed in a block that needs to be duplicated when threading jumps.
max-fields-for-field-sensitive Maximum number of fields in a structure treated in a field sensitive manner during pointer analysis.
prefetch-latency Estimate on average number of instructions that are executed before prefetch finishes.  The distance prefetched ahead is proportional to this constant.  Increasing this number may also lead to less streams being prefetched (see simultaneous- prefetches).
simultaneous-prefetches Maximum number of prefetches that can run at the same time.
l1-cache-line-size The size of cache line in L1 data cache, in bytes.
l1-cache-size The size of L1 data cache, in kilobytes.
l2-cache-size The size of L2 data cache, in kilobytes.
prefetch-dynamic-strides Whether the loop array prefetch pass should issue software prefetch hints for strides that are non-constant.  In some cases this may be beneficial, though the fact the stride is non- constant may make it hard to predict when there is clear benefit to issuing these hints.
Set to 1 if the prefetch hints should be issued for non-constant strides.  Set to 0 if prefetch hints should be issued only for strides that are known to be constant and below prefetch-minimum- stride.
prefetch-minimum-stride Minimum constant stride, in bytes, to start using prefetch hints for.  If the stride is less than this threshold, prefetch hints will not be issued.
This setting is useful for processors that have hardware prefetchers, in which case there may be conflicts between the hardware prefetchers and the software prefetchers.  If the hardware prefetchers have a maximum stride they can handle, it should be used here to improve the use of software prefetchers.
A value of -1 means we don't have a threshold and therefore prefetch hints can be issued for any constant stride.
This setting is only useful for strides that are known and constant.
loop-interchange-max-num-stmts The maximum number of stmts in a loop to be interchanged.
loop-interchange-stride-ratio The minimum ratio between stride of two loops for interchange to be profitable.
min-insn-to-prefetch-ratio The minimum ratio between the number of instructions and the number of prefetches to enable prefetching in a loop.
prefetch-min-insn-to-mem-ratio The minimum ratio between the number of instructions and the number of memory references to enable prefetching in a loop.
use-canonical-types Whether the compiler should use the "canonical" type system. 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.
switch-conversion-max-branch-ratio Switch initialization conversion refuses to create arrays that are bigger than switch-conversion-max-branch-ratio times the number of branches in the switch.
max-partial-antic-length Maximum length of the partial antic set computed during the tree partial redundancy elimination optimization (-ftree-pre) when optimizing at -O3 and above.  For some sorts of source code the enhanced partial redundancy elimination optimization can run away, consuming all of the memory available on the host machine. This parameter sets a limit on the length of the sets that are computed, which prevents the runaway behavior.  Setting a value of 0 for this parameter allows an unlimited set length.
rpo-vn-max-loop-depth Maximum loop depth that is value-numbered optimistically.  When the limit hits the innermost rpo-vn-max-loop-depth loops and the outermost loop in the loop nest are value-numbered optimistically and the remaining ones not.
sccvn-max-alias-queries-per-access Maximum number of alias-oracle queries we perform when looking for redundancies for loads and stores.  If this limit is hit the search is aborted and the load or store is not considered redundant.  The number of queries is algorithmically limited to the number of stores on all paths from the load to the function entry.
ira-max-loops-num IRA uses regional register allocation by default.  If a function contains more loops than the number given by this parameter, only at most the given number of the most frequently-executed loops form regions for regional register allocation.
ira-max-conflict-table-size Although IRA uses a sophisticated algorithm to compress the conflict table, the table can still require excessive amounts of memory for huge functions.  If the conflict table for a function could be more than the size in MB given by this parameter, the register allocator instead uses a faster, simpler, and lower- quality algorithm that does not require building a pseudo- register conflict table.
ira-loop-reserved-regs IRA can be used to evaluate more accurate register pressure in loops for decisions to move loop invariants (see -O3).  The number of available registers reserved for some other purposes is given by this parameter.  Default of the parameter is the best found from numerous experiments.
lra-inheritance-ebb-probability-cutoff LRA tries to reuse values reloaded in registers in subsequent insns.  This optimization is called inheritance.  EBB is used as a region to do this optimization.  The parameter defines a minimal fall-through edge probability in percentage used to add BB to inheritance EBB in LRA.  The default value was chosen from numerous runs of SPEC2000 on x86-64.
loop-invariant-max-bbs-in-loop Loop invariant motion can be very expensive, both in compilation time and in amount of needed compile-time memory, with very large loops.  Loops with more basic blocks than this parameter won't have loop invariant motion optimization performed on them.
loop-max-datarefs-for-datadeps Building data dependencies is expensive for very large loops. This parameter limits the number of data references in loops that are considered for data dependence analysis.  These large loops are no handled by the optimizations using loop data dependencies.
max-vartrack-size Sets a maximum number of hash table slots to use during variable tracking dataflow analysis of any function.  If this limit is exceeded with variable tracking at assignments enabled, analysis for that function is retried without it, after removing all debug insns from the function.  If the limit is exceeded even without debug insns, var tracking analysis is completely disabled for the function.  Setting the parameter to zero makes it unlimited.
max-vartrack-expr-depth Sets a maximum number of recursion levels when attempting to map variable names or debug temporaries to value expressions.  This trades compilation time for more complete debug information.  If this is set too low, value expressions that are available and could be represented in debug information may end up not being used; setting this higher may enable the compiler to find more complex debug expressions, but compile time and memory use may grow.
max-debug-marker-count Sets a threshold on the number of debug markers (e.g. begin stmt markers) to avoid complexity explosion at inlining or expanding to RTL.  If a function has more such gimple stmts than the set limit, such stmts will be dropped from the inlined copy of a function, and from its RTL expansion.
min-nondebug-insn-uid Use uids starting at this parameter for nondebug insns.  The range below the parameter is reserved exclusively for debug insns created by -fvar-tracking-assignments, but debug insns may get (non-overlapping) uids above it if the reserved range is exhausted.
ipa-sra-ptr-growth-factor IPA-SRA replaces a pointer to an aggregate with one or more new parameters only when their cumulative size is less or equal to ipa-sra-ptr-growth-factor times the size of the original pointer parameter.
ipa-sra-max-replacements Maximum pieces of an aggregate that IPA-SRA tracks.  As a consequence, it is also the maximum number of replacements of a formal parameter.
sra-max-scalarization-size-Ospeed sra-max-scalarization-size-Osize The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to replace scalar parts of aggregates with uses of independent scalar variables.  These parameters control the maximum size, in storage units, of aggregate which is considered for replacement when compiling for speed (sra-max-scalarization- size-Ospeed) or size (sra-max-scalarization-size-Osize) respectively.
sra-max-propagations The maximum number of artificial accesses that Scalar Replacement of Aggregates (SRA) will track, per one local variable, in order to facilitate copy propagation.
tm-max-aggregate-size When making copies of thread-local variables in a transaction, this parameter specifies the size in bytes after which variables are saved with the logging functions as opposed to save/restore code sequence pairs.  This option only applies when using -fgnu-tm.
graphite-max-nb-scop-params To avoid exponential effects in the Graphite loop transforms, the number of parameters in a Static Control Part (SCoP) is bounded. A value of zero can be used to lift the bound.  A variable whose value is unknown at compilation time and defined outside a SCoP is a parameter of the SCoP.
loop-block-tile-size Loop blocking or strip mining transforms, enabled with -floop-block or -floop-strip-mine, strip mine each loop in the loop nest by a given number of iterations.  The strip length can be changed using the loop-block-tile-size parameter.
ipa-jump-function-lookups Specifies number of statements visited during jump function offset discovery.
ipa-cp-value-list-size IPA-CP attempts to track all possible values and types passed to a function's parameter in order to propagate them and perform devirtualization.  ipa-cp-value-list-size is the maximum number of values and types it stores per one formal parameter of a function.
ipa-cp-eval-threshold IPA-CP calculates its own score of cloning profitability heuristics and performs those cloning opportunities with scores that exceed ipa-cp-eval-threshold.
ipa-cp-max-recursive-depth Maximum depth of recursive cloning for self-recursive function.
ipa-cp-min-recursive-probability Recursive cloning only when the probability of call being executed exceeds the parameter.
ipa-cp-recursion-penalty Percentage penalty the recursive functions will receive when they are evaluated for cloning.
ipa-cp-single-call-penalty Percentage penalty functions containing a single call to another function will receive when they are evaluated for cloning.
ipa-max-agg-items IPA-CP is also capable to propagate a number of scalar values passed in an aggregate. ipa-max-agg-items controls the maximum number of such values per one parameter.
ipa-cp-loop-hint-bonus When IPA-CP determines that a cloning candidate would make the number of iterations of a loop known, it adds a bonus of ipa-cp- loop-hint-bonus to the profitability score of the candidate.
ipa-max-loop-predicates The maximum number of different predicates IPA will use to describe when loops in a function have known properties.
ipa-max-aa-steps During its analysis of function bodies, IPA-CP employs alias analysis in order to track values pointed to by function parameters.  In order not spend too much time analyzing huge functions, it gives up and consider all memory clobbered after examining ipa-max-aa-steps statements modifying memory.
ipa-max-switch-predicate-bounds Maximal number of boundary endpoints of case ranges of switch statement.  For switch exceeding this limit, IPA-CP will not construct cloning cost predicate, which is used to estimate cloning benefit, for default case of the switch statement.
ipa-max-param-expr-ops IPA-CP will analyze conditional statement that references some function parameter to estimate benefit for cloning upon certain constant value.  But if number of operations in a parameter expression exceeds ipa-max-param-expr-ops, the expression is treated as complicated one, and is not handled by IPA analysis.
lto-partitions Specify desired number of partitions produced during WHOPR compilation.  The number of partitions should exceed the number of CPUs used for compilation.
lto-min-partition Size of minimal partition for WHOPR (in estimated instructions). This prevents expenses of splitting very small programs into too many partitions.
lto-max-partition Size of max partition for WHOPR (in estimated instructions).  to provide an upper bound for individual size of partition.  Meant to be used only with balanced partitioning.
lto-max-streaming-parallelism Maximal number of parallel processes used for LTO streaming.
cxx-max-namespaces-for-diagnostic-help The maximum number of namespaces to consult for suggestions when C++ name lookup fails for an identifier.
sink-frequency-threshold The maximum relative execution frequency (in percents) of the target block relative to a statement's original block to allow statement sinking of a statement.  Larger numbers result in more aggressive statement sinking.  A small positive adjustment is applied for statements with memory operands as those are even more profitable so sink.
max-stores-to-sink The maximum number of conditional store pairs that can be sunk. Set to 0 if either vectorization (-ftree-vectorize) or if- conversion (-ftree-loop-if-convert) is disabled.
case-values-threshold The smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches.  If the value is 0, use the default for the machine.
jump-table-max-growth-ratio-for-size The maximum code size growth ratio when expanding into a jump table (in percent).  The parameter is used when optimizing for size.
jump-table-max-growth-ratio-for-speed The maximum code size growth ratio when expanding into a jump table (in percent).  The parameter is used when optimizing for speed.
tree-reassoc-width Set the maximum number of instructions executed in parallel in reassociated tree. This parameter overrides target dependent heuristics used by default if has non zero value.
sched-pressure-algorithm Choose between the two available implementations of -fsched-pressure.  Algorithm 1 is the original implementation and is the more likely to prevent instructions from being reordered. Algorithm 2 was designed to be a compromise between the relatively conservative approach taken by algorithm 1 and the rather aggressive approach taken by the default scheduler.  It relies more heavily on having a regular register file and accurate register pressure classes.  See haifa-sched.c in the GCC sources for more details.
The default choice depends on the target.
max-slsr-cand-scan Set the maximum number of existing candidates that are considered when seeking a basis for a new straight-line strength reduction candidate.
asan-globals Enable buffer overflow detection for global objects.  This kind of protection is enabled by default if you are using -fsanitize=address option.  To disable global objects protection use --param asan-globals=0.
asan-stack Enable buffer overflow detection for stack objects.  This kind of protection is enabled by default when using -fsanitize=address. To disable stack protection use --param asan-stack=0 option.
asan-instrument-reads Enable buffer overflow detection for memory reads.  This kind of protection is enabled by default when using -fsanitize=address. To disable memory reads protection use --param asan-instrument-reads=0.
asan-instrument-writes Enable buffer overflow detection for memory writes.  This kind of protection is enabled by default when using -fsanitize=address. To disable memory writes protection use --param asan-instrument-writes=0 option.
asan-memintrin Enable detection for built-in functions.  This kind of protection is enabled by default when using -fsanitize=address.  To disable built-in functions protection use --param asan-memintrin=0.
asan-use-after-return Enable detection of use-after-return.  This kind of protection is enabled by default when using the -fsanitize=address option.  To disable it use --param asan-use-after-return=0.
Note: By default the check is disabled at run time.  To enable it, add "detect_stack_use_after_return=1" to the environment variable ASAN_OPTIONS.
asan-instrumentation-with-call-threshold If number of memory accesses in function being instrumented is greater or equal to this number, use callbacks instead of inline checks.  E.g. to disable inline code use --param asan-instrumentation-with-call-threshold=0.
hwasan-instrument-stack Enable hwasan instrumentation of statically sized stack-allocated variables.  This kind of instrumentation is enabled by default when using -fsanitize=hwaddress and disabled by default when using -fsanitize=kernel-hwaddress.  To disable stack instrumentation use --param hwasan-instrument-stack=0, and to enable it use --param hwasan-instrument-stack=1.
hwasan-random-frame-tag When using stack instrumentation, decide tags for stack variables using a deterministic sequence beginning at a random tag for each frame.  With this parameter unset tags are chosen using the same sequence but beginning from 1.  This is enabled by default for -fsanitize=hwaddress and unavailable for -fsanitize=kernel-hwaddress.  To disable it use --param hwasan-random-frame-tag=0.
hwasan-instrument-allocas Enable hwasan instrumentation of dynamically sized stack- allocated variables.  This kind of instrumentation is enabled by default when using -fsanitize=hwaddress and disabled by default when using -fsanitize=kernel-hwaddress.  To disable instrumentation of such variables use --param hwasan-instrument-allocas=0, and to enable it use --param hwasan-instrument-allocas=1.
hwasan-instrument-reads Enable hwasan checks on memory reads.  Instrumentation of reads is enabled by default for both -fsanitize=hwaddress and -fsanitize=kernel-hwaddress.  To disable checking memory reads use --param hwasan-instrument-reads=0.