OpenMP and OpenACC Options (Using the GNU Compiler Collection (GCC)) (original) (raw)

GCC supports OpenMP extensions to the C, C++, and Fortran languages with the -fopenmp option. Similarly, OpenACC extensions are supported in all three languages with -fopenacc. See OpenMP and OpenACC for an overview of these extensions.

-foffload=disable ¶

-foffload=default

-foffload=target-list

Specify for which OpenMP and OpenACC offload targets code should be generated. The default behavior, equivalent to -foffload=default, is to generate code for all supported offload targets. The -foffload=disable form generates code only for the host fallback, while-foffload=target-list generates code only for the specified comma-separated list of offload targets.

Offload targets are specified in GCC’s internal target-triplet format. You can run the compiler with -v to show the list of configured offload targets under OFFLOAD_TARGET_NAMES.

-foffload-options=options ¶

-foffload-options=target-triplet-list=options

With -foffload-options=options, GCC passes the specifiedoptions to the compilers for all enabled offloading targets. You can specify options that apply only to a specific target or targets by using the -foffload-options=target-list=options form. Thetarget-list is a comma-separated list in the same format as for the-foffload= option.

Typical command lines are

-foffload-options='-fno-math-errno -ffinite-math-only'
-foffload-options=nvptx-none=-latomic -foffload-options=amdgcn-amdhsa=-march=gfx906

-fopenacc ¶

Enable handling of OpenACC directives ‘#pragma acc’ in C/C++ and ‘!$acc’ in free-form Fortran and ‘!$acc’, ‘c$acc’ and ‘*$acc’ in fixed-form Fortran. This option implies -pthread, and thus is only supported on targets that have support for -pthread.

-fopenacc-dim=geom ¶

Specify default compute dimensions for parallel offload regions that do not explicitly specify them. The geom value is a triple of ‘:’-separated sizes, in order gang, worker, and vector. A size can be omitted, to use a target-specific default value.

-fopenmp ¶

Enable handling of OpenMP directives ‘#pragma omp’, ‘[[omp::directive(...)]]’, ‘[[omp::decl(...)]]’, and ‘[[omp::sequence(...)]]’ in C/C++. In Fortran, it enables ‘!$omp’ and the conditional compilation sentinel ‘!$’. In fixed source form Fortran, the sentinels can also start with ‘c’ or ‘*’.

This option implies -pthread, and thus is only supported on targets that have support for -pthread. -fopenmpimplies -fopenmp-simd.

-fopenmp-simd ¶

Enable handling of OpenMP’s simd, declare simd,declare reduction, assume, ordered, scanand loop directive, and of combined or composite directives withsimd as constituent with #pragma omp,[[omp::directive(...)]], [[omp::sequence(...)]] and[[omp::decl(...)]] in C/C++ and !$omp in Fortran. It additionally enables the conditional compilation sentinel ‘!$’ in Fortran. In fixed source form Fortran, the sentinels can also start with ‘c’ or ‘*’. Other OpenMP directives are ignored. Unless-fopenmp is additionally specified, the loop region binds to the current task region, independent of the specified bind clause.

-fopenmp-target-simd-clone ¶

-fopenmp-target-simd-clone=device-type

In addition to generating SIMD clones for functions marked with thedeclare simd directive, GCC also generates clones for functions marked with the OpenMP declare target directive that are suitable for vectorization when this option is in effect. Thedevice-type may be one of none, host, nohost, and any, which correspond to keywords for the device_typeclause of the declare target directive; clones are generated for the intersection of devices specified.-fopenmp-target-simd-clone is equivalent to-fopenmp-target-simd-clone=any and-fno-openmp-target-simd-clone is equivalent to-fopenmp-target-simd-clone=none.

At -O2 and higher (but not -Os or -Og) this optimization defaults to -fopenmp-target-simd-clone=nohost; otherwise it is disabled by default.