AMD Optimizing C/C++ Compiler Suite Version 5.0.0 Flag Descriptions

Set the optimization level to -O2.

If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.

Means "no optimization". This level compiles the fastest and generates the most debuggable code.

If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.

Somewhere between -O0 and -O2.

If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.

Moderate level of optimization which enables most optimizations. This is the default when no "-O" option is specified, or if no value is specified (i.e. "-O").

If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.

Like -O2, except that it enables optimizations that take longer to perform or that may generate larger code (in an attempt to make the program run faster).

If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.

Enables all the optimizations from -O3 along with other aggressive optimizations that may violate strict compliance with language standards. Refer to the AOCC options document for the language you're using for more detailed documentation of optimizations enabled under -Ofast.

This option enables a subset of scalar, vector and loop transformations including improved variants of loop invariant code motion, SLP and loop vectorizations, loop-fusion, loop-interchange, loop-unswitch, loop tiling and loop distribution.

Specify that Clang should generate code for a specific processor family member and later. For example, if you specify -march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but which may not exist on earlier products. -march=znver4 enables AVX 512 ISA for Genoa (znver4) processors.

Generate output files in LLVM formats suitable for link time optimization. When used with -S this generates LLVM intermediate language assembly files, otherwise this generates LLVM bitcode format object files (which may be passed to the linker depending on the stage selection options).

Generates code for a 32-bit environment. The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any i386 system. The compiler generates x86 or IA32 32-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target platform specified is 64-bit, otherwise the default is 32-bit.

Generates code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64, x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target platform specified is 64-bit, otherwise the default is 32-bit.

Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is ignored even if set by the system headers.

Enable handling of OpenMP directives and generate parallel code. The openmp library to be linked can be specified through -fopenmp=library option.

Instructs the compiler to link with system math libraries.

Instructs the compiler to link with AMD-supported optimized math library.

Instructs the linker to use the first definition encountered for a symbol, and ignore all others.

amdalloc is a AMD's memory allocator based on jemalloc library and is available as a part of AOCC binary package.

amdalloc-ext is a AMD's memory allocation library optimized for performance. You can link the library only on Linux platforms. This library provides optimized implementation of allocation routines malloc(), calloc(), realloc() and free(). It is C99 standard compliant. This library is not thread safe. It should not be used in multi threaded application.

Selects the C++ language dialect.

Instructs the compiler to link with the OpenMP runtime libraries.

Instructs the compiler to link with flang Fortran runtime libraries.

This option enables a subset of vector transformations including improved variants of SLP and loop vectorization.

This option enables a subset of scalar transformations including improved variants of various code movement optimizations like hosting and invariant code movement.

This option enables a subset of loop transformations including improved variants of loop-fusion, loop-interchange, loop blocking and distribution.

This option enables a subset of loop transformations including improved variants of loop unswitching, loop-tiling and versioning of loop invariant code motion.

Enables splitting of long live ranges of loop induction variables which span loop boundaries. This helps reduce register pressure and can help avoid needless spills to memory and reloads from memory.

This optimization enables generation of prefetch instructions for tightly coupled loops

Enables epilog vectorization of loops that require loop induction variables also to be vectorized.

Optimizes the cost model for strided accesses to memory.

This option enables an optimization that transforms the data layout of a single dimensional array to provide better cache locality by analysing the access patterns.

Enables dead virtual function elimination optimization. Requires -flto=full.

This option eliminates the array computations based on their usage. The computations on unused array elements and computations on zero valued array elements are eliminated with this optimization. -flto as whole program analysis is required to perform this optimization.

Possible values:

• 1: Eliminates the computations on unused array elements
• 2: Eliminates the computations on zero valued array elements
• 3: Eliminates the computations on unused and zero valued array elements

Block Reordering

Possible values:

• none: No block reorder
• simple: Simple block reorder
• complex: Do block reorder for more complex inputs such as inputs with exception handlers
• advanced: In addition to all cases handled by complex, this option handles more cases involving operations with side-effects

Analyzes the whole program to determine if the structures in the code can be peeled, if dead or redundant fields can be deleted, and if the pointer or integer fields in the structure can be compressed. If feasible, this optimization transforms the code to enable these improvements. This transformation is likely to improve cache utilization and memory bandwidth. It is expected to improve the scalability of programs executed on multiple cores. This is effective only under flto as the whole program analysis is required to perform this optimization. You can choose different levels of aggressiveness with which this optimization can be applied to your application; with 1 being the least aggressive and 7 being the most aggressive level.

Possible values:

• fstruct-layout=0: disables structure peeling (default).
• fstruct-layout=1: enables structure peeling.
• fstruct-layout=2: enables structure peeling and selectively compresses self-referential pointers in these structures to 32-bit pointers wherever safe.
• fstruct-layout=3: enables structure peeling and selectively compresses self-referential pointers in these structures to 16-bit pointers wherever safe.
• fstruct-layout=4: enables structure peeling, pointer compression as in level 2 and further enables compression of structure fields which are of 64-bit integer type to 32-bit integer type. This is performed under a strict safety check.
• fstruct-layout=5: enables structure peeling, pointer compression as in level 3 and further enables compression of structure fields which are of 64-bit integer type to 32-bit integer type. This is performed under a strict safety check.
• fstruct-layout=6: enables structure peeling, pointer compression as in level 2 and further enables compression of structure fields which are of type 64-bit integer type to 16-bit integer type. This is performed under a strict safety check.
• fstruct-layout=7: enables structure peeling, pointer compression as in level 3 and further enables compression of structure fields which are of type 64-bit integer type to 16-bit integer type. This is performed under a strict safety check.
• fstruct-layout=8: enables structure peeling, pointer compression, 64 bit integer type compression as in level 6 and creates optimal ordering of peeled structure fields which could improve runtime performance.
• fstruct-layout=9: enables structure peeling, pointer compression, 64 bit integer type compression as in level 7 and creates optimal ordering of peeled structure fields which could improve runtime performance.

fstruct-layout=4 and fstruct-layout=5 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added feature of safe compression of 64-bit integer fields to 32-bit integer fields in structures. Going from fstruct-layout=4 to fstruct-layout=5 may result in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.

fstruct-layout=6 and fstruct-layout=7 are derived from fstruct-layout=2 and fstructlayout=3 respectively, with the added feature of safe compression of 64 bit integer fields to 16 bit integer in structures. Going from fstruct-layout=6 to fstruct-layout=7 may result in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.

Turns on LLVM's instrumentation based profiling.

This option enables generation of gather instructions for cases where it is profitable.

Enables loop strip mining optimization. This optimization breaks a large loop into smaller segments or strips to improve temporal and spatial locality.

Uses the profiling files generated from a program compiled with -fprofile-instr-generate to guide optimization decisions.

In the 502/602.gcc benchmark description, "multiple definitions of symbols" is listed under the "Known Portability Issues" section, and this option is one of the suggested workarounds. This option causes Clang to revert to the same inlining behavior that GCC does when in pre-C99 mode.

Sets the compiler's inlining threshold level to the value passed as the argument. The inline threshold is used in the inliner heuristics to decide which functions should be inlined.

Enables inlining for recursive functions based on heuristics, with level 4 being most aggressive. Higher levels may lead to code bloat due to expansion of recursive functions at call sites.

Levels:

• 0 [DEFAULT]: Disables inlining for recursive functions.
• 1: Recursive functions are inlined up to depth 1. These recursive functions are chosen based on costing heuristics.
• 2: Same as level 1 but with more aggressive heuristics.
• 3: All recursive functions are inlined upto depth 1.
• 4: All recursive functions are inlined upto depth 10.

Enables loop strength reduction for nested loop structures. By default, the compiler performs loop strength reduction only for the innermost loop.

Enables loop distribution with scalar expansion for better vectorization.

Allocate local variables on the stack, thus allowing recursion. SAVEd, data-initialized, or namelist members are always allocated statically, regardless of the setting of this switch.

Disables generation of fma instructions when there is a chain of fma instructions and output of one fma instruction is used as input to other fma instruction.

Sets the limit at which loops will be unrolled. For example, if unroll threshold is set to 100 then only loops with 100 or fewer instructions will be unrolled.

Sets the limit at which loops will be unswitched. For example, if unswitch threshold is set to 100 then only loops with 100 or fewer instructions will be unswtched.

Enables aggressive heuristics to get loop unrolling.

This option instructs the compiler to unroll loops wherever possible.

Use the given vector functions library.

This option controls the vzeroupper instruction generation before a transfer of control flow. Not emitting the vzeroupper instruction can help minimize the AVX to SSE transition penalty.

Forces the alignment of all blocks that have no fall-through predecessors (i.e. don't add nops that are executed). In log2 format (e.g 4 means align on 16B boundaries).

Suppress error when linking multiple symbols of the same name.

Set the default symbol visibility for all global declarations.

Enable loop unrolling for loops with very short iteration counts where it is beneficial.

Toggle option for masked gather sequence generation.

Generate position independent executable. Usually this option will be used to compile code that will be linked using the -no-pie linker option.

Don’t produce a dynamically linked position independent executable(Linker option).

Schedule inlining optimization after few other optimizations.

libdl is a system library that has definitions for the functions for dynamic linking and loading.

This option enables use of RCPSS and RSQRTSS instructions with an additional Newton-Raphson step to increase precision instead of DIVSS and SQRTSS.

The binary datasets for some of the Fortran benchmarks in the SPEC CPU suites are stored in big-endian format. This option is necessary for those datasets to be read in correctly.

Specifies size of off_t data type.

This option instructs the compiler to treat char type as unsigned.

clang is a C compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking. Depending on which high-level mode setting is passed, Clang will stop before doing a full link.

clang++ C++ compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking. Depending on which high-level mode setting is passed, Clang will stop before doing a full link.

flang is a Fortran compiler which encompasses parsing, optimization, code generation, assembly, and linking. Depending on which high-level mode setting is passed, Flang will stop before doing a full link.

Do not warn about functions defined with a return type that defaults to "int" or which return something other than what they were declared to.

Do not warn about unused command line arguments.

This option controls warnings when a declaration does not specify a type.

Specifies a directory to search for libraries. Use -L to add directories to the search path for library files. Multiple -L options are valid. However, the position of multiple -L options is important relative to -l options supplied.

Specifies a directory to search for include files. Use -I to add directories to the search path for include files. Multiple -I options are valid.