This is enabled by default if vectorization is enabled. 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. Perform loop distribution of patterns that can be code generated with calls to a library. This flag is enabled by default at -O2 and higher, and by -fprofile-use and -fauto-profile.

This pass distributes the initialization loops and generates a call to memset zero. and the initialization loop is transformed into a call to memset zero. Perform loop interchange outside of graphite. This flag can improve cache performance on loop nest and allow further loop optimizations, like vectorization, to take place. Apply unroll and jam transformations on feasible loops.

In a loop nest this unrolls the outer loop by some factor and fuses the resulting multiple inner loops. 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 -funswitch-loops 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. 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. Perform final value replacement. If a variable is modified in a loop in such a way that its value when exiting the loop can be determined using only its initial value and the number of loop iterations, replace uses of the final value by such a computation, provided it is sufficiently cheap.

This reduces data dependencies and may allow further simplifications. Perform induction variable optimizations strength reduction, induction variable merging and induction variable elimination on trees. Parallelize loops, i. 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. by memory bandwidth. This option implies -pthread , and thus is only supported on targets that have support for -pthread. Perform function-local points-to analysis on trees. This flag is enabled by default at -O1 and higher, except for -Og. Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early.

Perform merging of narrow stores to consecutive memory addresses. This pass merges contiguous stores of immediate values narrower than a word into fewer wider stores to reduce the number of instructions.

This is enabled by default at -O2 and higher as well as -Os. 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 -O1 and higher. Perform straight-line strength reduction on trees. This recognizes related expressions involving multiplications and replaces them by less expensive calculations when possible.

Perform vectorization on trees. This flag enables -ftree-loop-vectorize and -ftree-slp-vectorize if not explicitly specified. Perform loop vectorization on trees. This flag is enabled by default at -O2 and by -ftree-vectorize , -fprofile-use , and -fauto-profile. Perform basic block vectorization on trees. Initialize automatic variables with either a pattern or with zeroes to increase the security and predictability of a program by preventing uninitialized memory disclosure and use.

With this option, GCC will also initialize any padding of automatic variables that have structure or union types to zeroes. However, the current implementation cannot initialize automatic variables that are declared between the controlling expression and the first case of a switch statement.

Using -Wtrivial-auto-var-init to report all such cases. You can control this behavior for a specific variable by using the variable attribute uninitialized see Variable Attributes. Alter the cost model used for vectorization. Alter the cost model used for vectorization of loops marked with the OpenMP simd directive. All values of model have the same meaning as described in -fvect-cost-model and by default a cost model defined with -fvect-cost-model is used.

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 -O2 and higher. Null pointer check elimination is only done if -fdelete-null-pointer-checks is enabled.

Split paths leading to loop backedges. This can improve dead code elimination and common subexpression elimination. This is enabled by default at -O3 and above. 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. A combination of -fweb 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. With this option, the compiler creates multiple copies of some local variables when unrolling a loop, which can result in superior code.

Inline parts of functions. Perform predictive commoning optimization, i. This option is enabled at level -O3. If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays. This option may generate better or worse code; results are highly dependent on the structure of loops within the source code. Do not substitute constants for known return value of formatted output functions such as sprintf , snprintf , vsprintf , and vsnprintf but not printf of fprintf.

This transformation allows GCC to optimize or even eliminate branches based on the known return value of these functions called with arguments that are either constant, or whose values are known to be in a range that makes determining the exact return value possible. For example, when -fprintf-return-value is in effect, both the branch and the body of the if statement but not the call to snprint can be optimized away when i is a bit or smaller integer because the return value is guaranteed to be at most 8.

The -fprintf-return-value option relies on other optimizations and yields best results with -O2 and above. It works in tandem with the -Wformat-overflow and -Wformat-truncation options. The -fprintf-return-value option is enabled by default.

Disable any machine-specific peephole optimizations. The difference between -fno-peephole and -fno-peephole2 is in how they are implemented in the compiler; some targets use one, some use the other, a few use both. GCC uses heuristics to guess branch probabilities if they are not provided by profiling feedback -fprofile-arcs. These heuristics are based on the control flow graph. The default is -fguess-branch-probability at levels -O , -O2 , -O3 , -Os. Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality.

Use the specified algorithm for basic block reordering. 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. When -fsplit-stack is used this option is not enabled by default to avoid linker errors , but may be enabled explicitly if using a working linker.

Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections. hot for most frequently executed functions and. unlikely 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.

Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. 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. A character type may alias any other type. Even with -fstrict-aliasing , type-punning is allowed, provided the memory is accessed through the union type. So, the code above works as expected. See Structures unions enumerations and bit-fields implementation.

However, this code might not:. 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. The -fstrict-aliasing option is enabled at levels -O2 , -O3 , -Os. Controls whether rules of -fstrict-aliasing are applied across function boundaries.

Note that if multiple functions gets inlined into a single function the memory accesses are no longer considered to be crossing a function boundary. The -fipa-strict-aliasing option is enabled by default and is effective only in combination with -fstrict-aliasing. Align the start of functions to the next power-of-two greater than or equal to n , skipping up to m -1 bytes. This ensures that at least the first m bytes of the function can be fetched by the CPU without crossing an n -byte alignment boundary.

If m2 is not specified, it defaults to n2. Some assemblers only support this flag when n is a power of two; in that case, it is rounded up. If n is not specified or is zero, use a machine-dependent default. The maximum allowed n option value is If this option is enabled, the compiler tries to avoid unnecessarily overaligning functions.

It attempts to instruct the assembler to align by the amount specified by -falign-functions , but not to skip more bytes than the size of the function. Parameters of this option are analogous to the -falign-functions option.

If -falign-loops or -falign-jumps are applicable and are greater than this value, then their values are used instead. Align loops to a power-of-two boundary. If the loops are executed many times, this makes up for any execution of the dummy padding instructions. Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping. In this case, no dummy operations need be executed.

Allow the compiler to perform optimizations that may introduce new data races on stores, without proving that the variable cannot be concurrently accessed by other threads. Does not affect optimization of local data. It is safe to use this option if it is known that global data will not be accessed by multiple threads. Examples of optimizations enabled by -fallow-store-data-races include hoisting or if-conversions that may cause a value that was already in memory to be re-written with that same value.

Such re-writing is safe in a single threaded context but may be unsafe in a multi-threaded context. Note that on some processors, if-conversions may be required in order to enable vectorization.

This option is left for compatibility reasons. Do not reorder top-level functions, variables, and asm 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. Additionally -fno-toplevel-reorder implies -fno-section-anchors.

This also affects any such calls implicitly generated by the compiler. 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.

Assume that the current compilation unit represents the whole program being compiled. This option should not be used in combination with -flto. Instead relying on a linker plugin should provide safer and more precise information. This option runs the standard link-time optimizer. 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. To use the link-time optimizer, -flto and optimization options should be specified at compile time and during the final link.

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. For example:. The first two invocations to GCC save a bytecode representation of GIMPLE into special ELF sections inside foo. o and bar. The final invocation reads the GIMPLE bytecode from foo. o , merges the two files into a single internal image, and compiles the result as usual. Since both foo. o 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 bar. o into functions in foo. o and vice-versa. The above generates bytecode for foo. c and bar. c , merges them together into a single GIMPLE representation and optimizes them as usual to produce myprog.

The 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 automatically performs link-time optimization if any of the objects involved were compiled with the -flto command-line option.

You can always override the automatic decision to do link-time optimization by passing -fno-lto to the link command. 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 -fuse-linker-plugin passes information to the compiler about used and externally visible symbols. When the linker plugin is not available, -fwhole-program should be used to allow the compiler to make these assumptions, which leads to more aggressive optimization decisions.

When a file is compiled with -flto without -fuse-linker-plugin , the generated object file is larger than a regular object file because it contains GIMPLE bytecodes and the usual final code see -ffat-lto-objects. This means that object files with LTO information can be linked as normal object files; if -fno-lto is passed to the linker, no interprocedural optimizations are applied.

Note that when -fno-fat-lto-objects is enabled the compile stage is faster but you cannot perform a regular, non-LTO link on them. 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.

Generally, options specified at link time override those specified at compile time, although in some cases GCC attempts to infer link-time options from the settings used to compile the input files. If you do not specify an optimization level option -O at link time, then GCC uses the highest optimization level used when compiling the object files.

Note that it is generally ineffective to specify an optimization level option only at link time and not at compile time, for two reasons. First, compiling without optimization suppresses compiler passes that gather information needed for effective optimization at link time. Second, some early optimization passes can be performed only at compile time and not at link time.

There are some code generation flags preserved by GCC when generating bytecodes, as they need to be used during the final link.

Currently, the following options and their settings are taken from the first object file that explicitly specifies them: -fcommon , -fexceptions , -fnon-call-exceptions , -fgnu-tm and all the -m target flags.

The following options -fPIC , -fpic , -fpie and -fPIE are combined based on the following scheme:. 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 -freg-struct-return and -fpcc-struct-return. Other options such as -ffp-contract , -fno-strict-overflow , -fwrapv , -fno-trapv or -fno-strict-aliasing are passed through to the link stage and merged conservatively for conflicting translation units. You can override them at link time. Diagnostic options such as -Wstringop-overflow are passed through to the link stage and their setting matches that of the compile-step at function granularity.

Note that this matters only for diagnostics emitted during optimization. Note that code transforms such as inlining can lead to warnings being enabled or disabled for regions if code not consistent with the setting at compile time.

When you need to pass options to the assembler via -Wa or -Xassembler make sure to either compile such translation units with -fno-lto or consistently use the same assembler options on all translation units. You can alternatively also specify assembler options at LTO link time. To enable debug info generation you need to supply -g at compile time. If any of the input files at link time were built with debug info generation enabled the link will enable debug info generation as well.

Any elaborate debug info settings like the dwarf level -gdwarf-5 need to be explicitly repeated at the linker command line and mixing different settings in different translation units is discouraged.

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. The behavior is still undefined at run time. Similar diagnostics may be raised for other languages. Another feature of LTO is that it is possible to apply interprocedural optimizations on files written in different languages:. 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.

If object files containing GIMPLE bytecode are stored in a library archive, say libfoo. a , 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 gcc-ar and gcc-ranlib instead of ar and ranlib ; to show the symbols of object files with GIMPLE bytecode, use gcc-nm.

Those commands require that ar , ranlib and nm have been compiled with plugin support. At link time, use the flag -fuse-linker-plugin to ensure that the library participates in the LTO optimization process:. With the linker plugin enabled, the linker extracts the needed GIMPLE files from libfoo. a and passes them on to the running GCC to make them part of the aggregated GIMPLE image to be optimized.

a 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 -flto -ffat-lto-objects. 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 -flto and -fwhole-program to allow the interprocedural optimizers to use more aggressive assumptions which may lead to improved optimization opportunities.

Use of -fwhole-program is not needed when linker plugin is active see -fuse-linker-plugin. 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 do not work with an older or newer version of GCC. Link-time optimization does not work well with generation of debugging information on systems other than those using a combination of ELF and DWARF.

If you specify the optional n , the optimization and code generation done at link time is executed in parallel using n parallel jobs by utilizing an installed make program. The environment variable MAKE may be used to override the program used. This is useful when the Makefile calling GCC is already executing in parallel. This option likely only works if MAKE is GNU make.

Specify the partitioning algorithm used by the link-time optimizer. 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 -flto.

GCC currently supports two LTO compression algorithms. For zstd, valid values are 0 no compression to 19 maximum compression , while zlib supports values from 0 to 9. Values outside this range are clamped to either minimum or maximum of the supported values. If the option is not given, a default balanced compression setting is used.

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. 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 -fwhole-program. See -flto for a description of the effect of this flag and how to use it.

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. 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 -flto and is ignored at link time. It requires a linker with linker plugin support for basic functionality. Additionally, nm , ar and ranlib need to support linker plugins to allow a full-featured build environment capable of building static libraries etc.

GCC provides the gcc-ar , gcc-nm , gcc-ranlib wrappers to pass the right options to these tools. With non fat LTO makefiles need to be modified to use them. Note that modern binutils provide plugin auto-load mechanism. 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. This pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete. 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.

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. With -fprofile-use all portions of programs not executed during train run are optimized agressively for size rather than speed. In some cases it is not practical to train all possible hot paths in the program.

For example, program may contain functions specific for a given hardware and trianing may not cover all hardware configurations program is run on. With -fprofile-partial-training profile feedback will be ignored for all functions not executed during the train run leading them to be optimized as if they were compiled without profile feedback. This leads to better performance when train run is not representative but also leads to significantly bigger code.

Enable profile feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available:.

Before you can use this option, you must first generate profiling information. See Instrumentation Options , for information about the -fprofile-generate option. By default, GCC emits an error message if the feedback profiles do not match the source code. Note this may result in poorly optimized code. Additionally, by default, GCC also emits a warning message if the feedback profiles do not exist see -Wmissing-profile. If path is specified, GCC looks at the path to find the profile feedback data files.

See -fprofile-dir. Enable sampling-based feedback-directed optimizations, and the following optimizations, many of which are generally profitable only with profile feedback available:.

path is the name of a file containing AutoFDO profile information. If omitted, it defaults to fbdata. afdo in the current directory. You must also supply the unstripped binary for your program to this tool.

The following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness.

All must be specifically enabled. 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. This option prevents undesirable excess precision on machines such as the where the floating registers of the keep more precision than a double is supposed to have.

Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point. Use -ffloat-store for such programs, after modifying them to store all pertinent intermediate computations into variables. This option allows further control over excess precision on machines where floating-point operations occur in a format with more precision or range than the IEEE standard and interchange floating-point types.

It may, however, yield faster code for programs that do not require the guarantees of these specifications. Do not set errno after calling math functions that are executed with a single instruction, e. A program that relies on IEEE exceptions for math error handling may want to use this flag for speed while maintaining IEEE arithmetic compatibility.

On Darwin systems, the math library never sets errno. There is therefore no reason for the compiler to consider the possibility that it might, and -fno-math-errno is the default. 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. Enables -fno-signed-zeros , -fno-trapping-math , -fassociative-math and -freciprocal-math. Allow re-association of operands in series of floating-point operations. May also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both -fno-signed-zeros and -fno-trapping-math be in effect.

For Fortran the option is automatically enabled when both -fno-signed-zeros and -fno-trapping-math are in effect. Allow the reciprocal of a value to be used instead of dividing by the value if this enables optimizations. Note that this loses precision and increases the number of flops operating on the value.

Allow optimizations for floating-point arithmetic that ignore the signedness of zero. 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 -fno-signaling-nans be in effect. 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. This option is experimental and does not currently guarantee to disable all GCC optimizations that are affected by rounding mode.

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 -ftrapping-math. This option is experimental and does not currently guarantee to disable all GCC optimizations that affect signaling NaN behavior. The default is -ffp-int-builtin-inexact , allowing the exception to be raised, unless C2X or a later C standard is selected.

This option does nothing unless -ftrapping-math is in effect. Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants.

When enabled, this option states that a range reduction step is not needed when performing complex division. The default is -fno-cx-limited-range , but is enabled by -ffast-math. Nevertheless, the option applies to all languages. Complex multiplication and division follow Fortran rules. The following options control optimizations that may improve performance, but are not enabled by any -O options. This section includes experimental options that may produce broken code.

After running a program compiled with -fprofile-arcs see Instrumentation Options , you can compile it a second time using -fbranch-probabilities , to improve optimizations based on the number of times each branch was taken. When a program compiled with -fprofile-arcs exits, it saves arc execution counts to a file called sourcename. gcda 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. See details about the file naming in -fprofile-arcs. These can be used to improve optimization. Currently, they are only used in one place: in reorg. If combined with -fprofile-arcs , it adds code so that some data about values of expressions in the program is gathered.

With -fbranch-probabilities , it reads back the data gathered from profiling values of expressions for usage in optimizations. Enabled by -fprofile-generate , -fprofile-use , and -fauto-profile.

Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions in ascending order. If combined with -fprofile-arcs , this option instructs the compiler to add code to gather information about values of expressions. With -fbranch-probabilities , 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.

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.

Performs a target dependent pass over the instruction stream to schedule instructions of same type together because target machine can execute them more efficiently if they are adjacent to each other in the instruction flow. Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better job.

Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. It also turns on complete loop peeling i. 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. Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. Peels loops for which there is enough information that they do not roll much from profile feedback or static analysis.

complete removal of loops with small constant number of iterations. Enables the loop invariant motion pass in the RTL loop optimizer. Enabled at level -O1 and higher, except for -Og.

Enables the loop store motion pass in the GIMPLE loop optimizer. This moves invariant stores to after the end of the loop in exchange for carrying the stored value in a register across the iteration.

Note for this option to have an effect -ftree-loop-im has to be enabled as well. 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. If a loop iterates over an array with a variable stride, create another version of the loop that assumes the stride is always one. This is particularly useful for assumed-shape arrays in Fortran where for example it allows better vectorization assuming contiguous accesses.

Place each function or data item into its own section in the output file if the target supports arbitrary sections. 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. 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.

This transformation can help to reduce the number of GOT entries and GOT accesses on some targets. 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. 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.

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 each case, the value is an integer. The following choices of name are recognized for all targets:.

When branch is predicted to be taken with probability lower than this threshold in percent , then it is considered well predictable. 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.

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 maximum number of incoming edges to consider for cross-jumping. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in executable size.

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 maximum code size expansion factor when copying basic blocks instead of jumping. The expansion is relative to a jump instruction. The maximum number of instructions to duplicate to a block that jumps to a computed goto. Only computed jumps at the end of a basic blocks with no more than max-goto-duplication-insns are unfactored. 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.

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. 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. 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 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. The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop. Larger values can exponentially increase compilation time. Maximal loop depth of a call considered by inline heuristics that tries to inline all functions called once. Several parameters control the tree inliner used in GCC.

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. This is bound applied to calls which are considered relevant with -finline-small-functions. This is bound applied to calls which are optimized for size.

Small growth may be desirable to anticipate optimization oppurtunities exposed by inlining. Number of instructions accounted by inliner for function overhead such as function prologue and epilogue. Extra time accounted by inliner for function overhead such as time needed to execute function prologue and epilogue. 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.

Same as --param uninlined-function-insns and --param uninlined-function-time but applied to function thunks. 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.

Specifies maximal growth of large function caused by inlining in percents. For example, parameter value limits large function growth to 2. 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. 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. Specifies maximal overall growth of the compilation unit caused by inlining. For example, parameter value 20 limits unit growth to 1. Cold functions either marked cold via an attribute or by profile feedback are not accounted into the unit size.

Specifies maximal overall growth of the compilation unit caused by interprocedural constant propagation. For example, parameter value 10 limits unit growth to 1. The limit specifying large stack frames. While inlining the algorithm is trying to not grow past this limit too much.

Specifies maximal growth of large stack frames caused by inlining in percents. For example, parameter value limits large stack frame growth to 11 times the original size. Specifies the maximum number of instructions an out-of-line copy of a self-recursive inline function can grow into by performing recursive inlining. 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.

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.

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. Specify growth that the early inliner can make. In effect it increases the amount of inlining for code having a large abstraction penalty. 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. This parameter ought to be bigger than --param modref-max-bases and --param modref-max-refs. Specifies the maximum depth of DFS walk used by modref escape analysis. Setting to 0 disables the analysis completely. 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.

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. 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.

Specifying 0 disables hoisting of simple expressions. 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.

The lesser the cost, the more aggressive code hoisting is. Specifying 0 allows all expressions to travel unrestricted distances. 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 maximum amount of similar bbs to compare a bb with. This is used to avoid quadratic behavior in tree tail merging. The maximum amount of iterations of the pass over the function. This is used to limit compilation time in tree tail merging. 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. 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.

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. The maximum number of instructions biased by probabilities of their execution that a loop may have to be unrolled. 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.

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. 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. 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.

Maximum size in bytes of objects tracked bytewise by dead store elimination. Larger values may result in larger compilation times. 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. Bound on size of expressions used in the scalar evolutions analyzer. Large expressions slow the analyzer. Bound on the complexity of the expressions in the scalar evolutions analyzer.

Complex expressions slow the analyzer. Maximum number of arguments in a PHI supported by TREE if conversion unless the loop is marked with simd pragma. The maximum number of possible vector layouts such as permutations to consider when optimizing to-be-vectorized code. The maximum number of run-time checks that can be performed when doing loop versioning for alignment in the vectorizer.

The maximum number of run-time checks that can be performed when doing loop versioning for alias in the vectorizer. The maximum number of loop peels to enhance access alignment for vectorizer. Value -1 means no limit. 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. Used in non-LTO mode. The number of most executed permilles, ranging from 0 to , 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 , which means that a basic block is considered hot if its execution count contributes to the upper permilles, or Used in LTO mode. 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 This means that the loop without bounds appears artificially cold relative to the other one.

Control the probability of the expression having the specified value. This parameter takes a percentage i. Select fraction of the maximal frequency of executions of a basic block in a function to align the basic block. 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. 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. Stop reverse growth when the reverse probability of best edge is less than this threshold in percent. 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.

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 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. GCC uses a garbage collector to manage its own memory allocation.

Not every stock will be available though, but generally you can choose from about 25 to popular stocks, such as Google and Apple. The asset lists are always listed clearly on every trading platform, and most brokers make their full asset lists available on their website. Trading cryptocurrency via binary trades is also booming. The volatile nature of cryptos makes them a popular binary asset.

Bitcoin and Ethereum remain the most traded, but you can find brokers that list 50 or more alt coins. The expiry time is the point at which a trade is closed and settled. The expiry for any given trade can range from 30 seconds, up to a year. While binaries initially started with very short expiries, demand has ensured there is now a broad range of expiry times available.

Some brokers even give traders the flexibility to set their own specific expiry time. While slow to react to binary options initially, regulators around the world are now starting to regulate the industry and make their presence felt.

The major regulators currently include:. There are also regulators operating in Malta, Japan and the Isle of Man. Many other authorities are now taking a keen a interest in binaries specifically, notably in Europe where domestic regulators are keen to bolster the CySec regulation.

Unregulated brokers still operate, and while some are trustworthy, a lack of regulation is a clear warning sign for potential new customers. Recently, ESMA European Securities and Markets Authority moved to ban the sale and marketing of binary options in the EU. The ban however, only applies to brokers regulated in the EU.

This leaves traders two choices to keep trading: Firstly, they can trade with an unregulated firm — this is extremely high risk and not advisable. Some unregulated firms are responsible and honest, but many are not. The second choice is to use a firm regulated by bodies outside of the EU. ASIC in Australia are a strong regulator — but they will not be implementing a ban. This means ASIC regulated firms can still accept EU traders.

See our broker lists for regulated or trusted brokers in your region. There is also a third option. A professional trader can continue trading at EU regulated brokers such as IQ Option.

To be classed as professional, an account holder must meet two of these three criteria:. We have a lot of detailed guides and strategy articles for both general education and specialized trading techniques. Below are a few to get you started if you want to learn the basic before you start trading. From Martingale to Rainbow, you can find plenty more on the strategy page.

For further reading on signals and reviews of different services go to the signals page. If you are totally new to the trading scene then watch this great video by Professor Shiller of Yale University who introduces the main ideas of options:.

The ability to trade the different types of binary options can be achieved by understanding certain concepts such as strike price or price barrier, settlement, and expiration date. All trades have dates at which they expire. In addition, the price targets are key levels that the trader sets as benchmarks to determine outcomes. We will see the application of price targets when we explain the different types. Expiry times can be as low as 5 minutes. How does it work? First, the trader sets two price targets to form a price range.

The best way to use the tunnel binaries is to use the pivot points of the asset. If you are familiar with pivot points in forex, then you should be able to trade this type. This type is predicated on the price action touching a price barrier or not. If the price action does not touch the price target the strike price before expiry, the trade will end up as a loss. Here you are betting on the price action of the underlying asset not touching the strike price before the expiration.

There are variations of this type where we have the Double Touch and Double No Touch. Here the trader can set two price targets and purchase a contract that bets on the price touching both targets before expiration Double Touch or not touching both targets before expiration Double No Touch. Normally you would only employ the Double Touch trade when there is intense market volatility and prices are expected to take out several price levels. Some brokers offer all three types, while others offer two, and there are those that offer only one variety.

In addition, some brokers also put restrictions on how expiration dates are set. In order to get the best of the different types, traders are advised to shop around for brokers who will give them maximum flexibility in terms of types and expiration times that can be set. Trading via your mobile has been made very easy as all major brokers provide fully developed mobile trading apps. Most trading platforms have been designed with mobile device users in mind. So the mobile version will be very similar, if not the same, as the full web version on the traditional websites.

Brokers will cater for both iOS and Android devices, and produce versions for each. Downloads are quick, and traders can sign up via the mobile site as well.

Our reviews contain more detail about each brokers mobile app, but most are fully aware that this is a growing area of trading. Traders want to react immediately to news events and market updates, so brokers provide the tools for clients to trade wherever they are. So, in short, they are a form of fixed return financial options. The steps above will be the same at every single broker. Call and Put are simply the terms given to buying or selling an option. If a trader thinks the underlying price will go up in value , they can open a call.

But where they expect the price to go down , they can place a put trade. Others drop the phrases put and call altogether. Almost every trading platform will make it absolutely clear which direction a trader is opening an option in.

As a financial investment tool binary options are not a scam, but there are brokers, trading robots and signal providers that are untrustworthy and dishonest.

The point is not to write off the concept of binary options, based solely on a handful of dishonest brokers. The image of these financial instruments has suffered as a result of these operators, but regulators are slowly starting to prosecute and fine the offenders and the industry is being cleaned up. Our forum is a great place to raise awareness of any wrongdoing. Binary trading strategies are unique to each trade. We have a binary options strategy section, and there are ideas that traders can experiment with.

Technical analysis is of use to some traders, combined with charts , indicators and price action research. Money management is essential to ensure risk management is applied to all trading. Different styles will suit different traders and strategies will also evolve and change. Traders need to ask questions of their investing aims and risk appetite and then learn what works for them. This will depend entirely on the habits of the trader. With no strategy or research, then any short term investment is going to win or lose based only on luck.

Conversely, a trader making a well researched trade will ensure they have done all they can to avoid relying on good fortune. Binary options can be used to gamble, but they can also be used to make trades based on value and expected profits. So the answer to the question will come down to the behavior of the individual trader.

Any investment or trade will be a gamble if done with no skill or knowledge. If you have traded forex or its more volatile cousins, crude oil or spot metals such as gold or silver, you will have probably learnt one thing: these markets carry a lot of risk and it is very easy to be blown off the market. Things like leverage and margin, news events, slippages and price re-quotes, etc can all affect a trade negatively. The situation is different in binary options trading. There is no leverage to contend with, and phenomena such as slippage and price re-quotes have no effect on binary option trade outcomes.

The binary options market allows traders to trade financial instruments spread across the currency and commodity markets as well as indices and bonds. This flexibility is unparalleled, and gives traders with the knowledge of how to trade these markets, a one-stop shop to trade all these instruments.

A binary trade outcome is based on just one parameter: direction. The trader is essentially betting on whether a financial asset will end up in a particular direction. In addition, the trader is at liberty to determine when the trade ends, by setting an expiry date. This gives a trade that initially started badly the opportunity to end well.

This is not the case with other markets. For example, control of losses can only be achieved using a stop loss. Otherwise, a trader has to endure a drawdown if a trade takes an adverse turn in order to give it room to turn profitable. The simple point being made here is that in binary options, the trader has less to worry about than if he were to trade other markets. Traders have better control of trades in binaries.

A footnote in Microsoft's submission opens in new tab to the UK's Competition and Markets Authority CMA has let slip the reason behind Call of Duty's absence from the Xbox Game Pass library: Sony and Activision Blizzard have a deal that restricts the games' presence on the service. The footnote appears in a section detailing the potential benefits to consumers from Microsoft's point of view of the Activision Blizzard catalogue coming to Game Pass.

What existing contractual obligations are those? Why, ones like the "agreement between Activision Blizzard and Sony," that places "restrictions on the ability of Activision Blizzard to place COD titles on Game Pass for a number of years". It was apparently these kinds of agreements that Xbox's Phil Spencer had in mind opens in new tab when he spoke to Sony bosses in January and confirmed Microsoft's "intent to honor all existing agreements upon acquisition of Activision Blizzard".

Unfortunately, the footnote ends there, so there's not much in the way of detail about what these restrictions are or how long they'd remain in effect in a potential post-acquisition world.

Given COD's continued non-appearance on Game Pass, you've got to imagine the restrictions are fairly significant if they're not an outright block on COD coming to the service.

Either way, the simple fact that Microsoft is apparently willing to maintain any restrictions on its own ability to put first-party games on Game Pass is rather remarkable, given that making Game Pass more appealing is one of the reasons for its acquisition spree. The irony of Sony making deals like this one while fretting about COD's future on PlayStation probably isn't lost on Microsoft's lawyers, which is no doubt part of why they brought it up to the CMA.

While it's absolutely reasonable to worry about a world in which more and more properties are concentrated in the hands of singular, giant megacorps, it does look a bit odd if you're complaining about losing access to games while stopping them from joining competing services. We'll find out if the CMA agrees when it completes its in-depth, "Phase 2" investigation opens in new tab into the Activision Blizzard acquisition, which is some way off yet.

For now, we'll have to content ourselves with poring over these kinds of corporate submissions for more interesting tidbits like this one. So far, we've already learned that Microsoft privately has a gloomy forecast for the future of cloud gaming opens in new tab , and that the company thinks Sony shouldn't worry so much since, hey, future COD games might be as underwhelming as Vanguard opens in new tab.

Who knows what we'll learn next? Sign up to get the best content of the week, and great gaming deals, as picked by the editors. One of Josh's first memories is of playing Quake 2 on the family computer when he was much too young to be doing that, and he's been irreparably game-brained ever since. His writing has been featured in Vice, Fanbyte, and the Financial Times. He'll play pretty much anything, and has written far too much on everything from visual novels to Assassin's Creed.

His most profound loves are for CRPGs, immersive sims, and any game whose ambition outstrips its budget. He thinks you're all far too mean about Deus Ex: Invisible War. Open menu Close menu PC Gamer PC Gamer THE GLOBAL AUTHORITY ON PC GAMES. opens in new tab opens in new tab opens in new tab opens in new tab opens in new tab opens in new tab. US Edition. News Reviews Hardware Best Of Magazine The Top Forum More PCGaming Show Podcasts Coupons Newsletter SignUp Community Guidelines Affiliate Links Meet the team About PC Gamer.

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This reduces data dependencies and may allow further simplifications. May also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. One of Josh's first memories is of playing Quake 2 on the family computer when he was much too young to be doing that, and he's been irreparably game-brained ever since. Mark Baldassare President and CEO Public Policy Institute of California. The maximum number of memory locations cselib should take into account. Perform loop interchange outside of graphite.

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