* Unnamed Fields:: Unnamed struct/union fields within structs/unions.
* Thread-Local:: Per-thread variables.
* Binary constants:: Binary constants using the @samp{0b} prefix.
+* OpenMP:: Multiprocessing extensions.
+* OpenACC:: Extensions for offloading code to accelerator devices.
@end menu
@node Statement Exprs
placement of @samp{[[]]} attributes within your code, as they differ
in some details from the rules for the GNU attribute syntax.
+With the @option{-fopenmp} option, GCC additionally recognizes OpenMP
+directives, with names prefixed with @samp{omp::}, using the standard
+@samp{[[]]} syntax. @xref{OpenMP}.
+
The remainder of this section describes the details of the GNU extension
@code{__attribute__} syntax,
and the constructs to which attribute specifiers bind, for the C
compiler pragmas documented here. Refer to the CPP manual for more
information.
+GCC additionally recognizes OpenMP pragmas when the @option{-fopenmp}
+option is specified, and OpenACC pragmas when the @option{-fopenacc}
+option is specified. @xref{OpenMP}, and @ref{OpenACC}.
+
@menu
* AArch64 Pragmas::
* ARM Pragmas::
hexadecimal integer constants, so suffixes like @samp{L} or @samp{UL}
can be applied.
+@node OpenMP
+@section OpenMP
+@cindex OpenMP extension support
+
+OpenMP (Open Multi-Processing) is an application programming
+interface (API) that supports multi-platform shared memory
+multiprocessing programming in C/C++ and Fortran on many
+architectures, including Unix and Microsoft Windows platforms.
+It consists of a set of compiler directives, library routines,
+and environment variables that influence run-time behavior.
+
+GCC implements all of the @uref{https://openmp.org/specifications/,
+OpenMP Application Program Interface v4.5}, and many features from later
+versions of the OpenMP specification.
+@xref{OpenMP Implementation Status,,,libgomp,
+GNU Offloading and Multi Processing Runtime Library},
+for more details about currently supported OpenMP features.
+
+To enable the processing of OpenMP directives @samp{#pragma omp},
+@samp{[[omp::directive(...)]]}, @samp{[[omp::decl(...)]]},
+and @samp{[[omp::sequence(...)]]} in C and C++,
+GCC needs to be invoked with the @option{-fopenmp} option.
+This option also arranges for automatic linking of the OpenMP
+runtime library.
+@xref{,,,libgomp,GNU Offloading and Multi Processing Runtime Library}.
+
+@xref{OpenMP and OpenACC Options}, for additional options useful with
+@option{-fopenmp}.
+
+@node OpenACC
+@section OpenACC
+@cindex OpenACC extension support
+
+OpenACC is an application programming interface (API) that supports
+offloading of code to accelerator devices. It consists of a set of
+compiler directives, library routines, and environment variables that
+influence run-time behavior.
+
+GCC strives to be compatible with the
+@uref{https://www.openacc.org/, OpenACC Application Programming
+Interface v2.6}.
+
+To enable the processing of OpenACC directives @samp{#pragma omp}
+in C and C++, GCC needs to be invoked with the @option{-fopenacc} option.
+This option also arranges for automatic linking of the OpenACC runtime
+library.
+@xref{,,,libgomp,GNU Offloading and Multi Processing Runtime Library}.
+
+@xref{OpenMP and OpenACC Options}, for additional options useful with
+@option{-fopenacc}.
+
@node C++ Extensions
@chapter Extensions to the C++ Language
@cindex extensions, C++ language
* C++ Dialect Options:: Variations on C++.
* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
and Objective-C++.
+* OpenMP and OpenACC Options:: Controlling multiprocessing and offloading.
* Diagnostic Message Formatting Options:: Controlling how diagnostics should
be formatted.
* Warning Options:: How picky should the compiler be?
-fno-builtin -fno-builtin-@var{function} -fcond-mismatch
-ffreestanding -fgimple -fgnu-tm -fgnu89-inline -fhosted
-flax-vector-conversions -fms-extensions
--foffload=@var{arg} -foffload-options=@var{arg}
--fopenacc -fopenacc-dim=@var{geom}
--fopenmp -fopenmp-simd -fopenmp-target-simd-clone@r{[}=@var{device-type}@r{]}
-fpermitted-flt-eval-methods=@var{standard}
-fplan9-extensions -fsigned-bitfields -funsigned-bitfields
-fsigned-char -funsigned-char -fstrict-flex-arrays[=@var{n}]
-Wstrict-selector-match
-Wundeclared-selector}
+@item OpenMP and OpenACC Options
+@xref{OpenMP and OpenACC Options,,Options Controlling OpenMP and OpenACC}.
+@gccoptlist{-foffload=@var{arg} -foffload-options=@var{arg}
+-fopenacc -fopenacc-dim=@var{geom}
+-fopenmp -fopenmp-simd -fopenmp-target-simd-clone@r{[}=@var{device-type}@r{]}}
+
@item Diagnostic Message Formatting Options
@xref{Diagnostic Message Formatting Options,,Options to Control Diagnostic Messages Formatting}.
@gccoptlist{-fmessage-length=@var{n}
Note that this option is off for all targets except for x86
targets using ms-abi.
-@opindex foffload
-@cindex Offloading targets
-@cindex OpenACC offloading targets
-@cindex OpenMP offloading targets
-@item -foffload=disable
-@itemx -foffload=default
-@itemx -foffload=@var{target-list}
-Specify for which OpenMP and OpenACC offload targets code should be generated.
-The default behavior, equivalent to @option{-foffload=default}, is to generate
-code for all supported offload targets. The @option{-foffload=disable} form
-generates code only for the host fallback, while
-@option{-foffload=@var{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 @option{-v} to show the list of configured offload targets
-under @code{OFFLOAD_TARGET_NAMES}.
-
-@opindex foffload-options
-@cindex Offloading options
-@cindex OpenACC offloading options
-@cindex OpenMP offloading options
-@item -foffload-options=@var{options}
-@itemx -foffload-options=@var{target-triplet-list}=@var{options}
-
-With @option{-foffload-options=@var{options}}, GCC passes the specified
-@var{options} to the compilers for all enabled offloading targets. You can
-specify options that apply only to a specific target or targets by using
-the @option{-foffload-options=@var{target-list}=@var{options}} form. The
-@var{target-list} is a comma-separated list in the same format as for the
-@option{-foffload=} option.
-
-Typical command lines are
-
-@smallexample
--foffload-options='-fno-math-errno -ffinite-math-only' -foffload-options=nvptx-none=-latomic
--foffload-options=amdgcn-amdhsa=-march=gfx906
-@end smallexample
-
-@opindex fopenacc
-@cindex OpenACC accelerator programming
-@item -fopenacc
-Enable handling of OpenACC directives @samp{#pragma acc} in C/C++ and
-@samp{!$acc} in free-form Fortran and @samp{!$acc}, @samp{c$acc} and
-@samp{*$acc} in fixed-form Fortran. When @option{-fopenacc} is specified,
-the compiler generates accelerated code according to the OpenACC Application
-Programming Interface v2.6 @w{@uref{https://www.openacc.org}}. This option
-implies @option{-pthread}, and thus is only supported on targets that
-have support for @option{-pthread}.
-
-@opindex fopenacc-dim
-@cindex OpenACC accelerator programming
-@item -fopenacc-dim=@var{geom}
-Specify default compute dimensions for parallel offload regions that do
-not explicitly specify. The @var{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.
-
-@opindex fopenmp
-@cindex OpenMP parallel
-@item -fopenmp
-Enable handling of OpenMP directives @samp{#pragma omp},
-@samp{[[omp::directive(...)]]}, @samp{[[omp::sequence(...)]]} and
-@samp{[[omp::decl(...)]]} in C/C++ and @samp{!$omp} in Fortran. It
-additionally enables the conditional compilation sentinel @samp{!$} in
-Fortran. In fixed source form Fortran, the sentinels can also start with
-@samp{c} or @samp{*}. When @option{-fopenmp} is specified, the
-compiler generates parallel code according to the OpenMP Application
-Program Interface v4.5 @w{@uref{https://www.openmp.org}}. This option
-implies @option{-pthread}, and thus is only supported on targets that
-have support for @option{-pthread}. @option{-fopenmp} implies
-@option{-fopenmp-simd}.
-
-@opindex fopenmp-simd
-@cindex OpenMP SIMD
-@cindex SIMD
-@item -fopenmp-simd
-Enable handling of OpenMP's @code{simd}, @code{declare simd},
-@code{declare reduction}, @code{assume}, @code{ordered}, @code{scan}
-and @code{loop} directive, and of combined or composite directives with
-@code{simd} as constituent with @code{#pragma omp},
-@code{[[omp::directive(...)]]}, @code{[[omp::sequence(...)]]} and
-@code{[[omp::decl(...)]]} in C/C++ and @code{!$omp} in Fortran. It
-additionally enables the conditional compilation sentinel @samp{!$} in
-Fortran. In fixed source form Fortran, the sentinels can also start with
-@samp{c} or @samp{*}. Other OpenMP directives are ignored. Unless
-@option{-fopenmp} is additionally specified, the @code{loop} region binds
-to the current task region, independent of the specified @code{bind} clause.
-
-@opindex fopenmp-target-simd-clone
-@cindex OpenMP target SIMD clone
-@item -fopenmp-target-simd-clone
-@item -fopenmp-target-simd-clone=@var{device-type}
-In addition to generating SIMD clones for functions marked with the
-@code{declare simd} directive, GCC also generates clones
-for functions marked with the OpenMP @code{declare target} directive
-that are suitable for vectorization when this option is in effect. The
-@var{device-type} may be one of @code{none}, @code{host}, @code{nohost},
-and @code{any}, which correspond to keywords for the @code{device_type}
-clause of the @code{declare target} directive; clones are generated for
-the intersection of devices specified.
-@option{-fopenmp-target-simd-clone} is equivalent to
-@option{-fopenmp-target-simd-clone=any} and
-@option{-fno-openmp-target-simd-clone} is equivalent to
-@option{-fopenmp-target-simd-clone=none}.
-
-At @option{-O2} and higher (but not @option{-Os} or @option{-Og}) this
-optimization defaults to @option{-fopenmp-target-simd-clone=nohost}; otherwise
-it is disabled by default.
-
@opindex fpermitted-flt-eval-methods
@opindex fpermitted-flt-eval-methods=c11
@opindex fpermitted-flt-eval-methods=ts-18661-3
@end table
+@node OpenMP and OpenACC Options
+@section Options Controlling OpenMP and OpenACC
+@cindex OpenMP options
+@cindex OpenACC options
+
+GCC supports OpenMP extensions to the C, C++, and Fortran languages
+with the @option{-fopenmp} option. Similarly, OpenACC extensions are
+supported in all three languages with @option{-fopenacc}.
+@xref{OpenMP} and @ref{OpenACC} for an overview of these extensions.
+
+@table @gcctabopt
+@opindex foffload
+@cindex Offloading targets
+@cindex OpenACC offloading targets
+@cindex OpenMP offloading targets
+@item -foffload=disable
+@itemx -foffload=default
+@itemx -foffload=@var{target-list}
+Specify for which OpenMP and OpenACC offload targets code should be generated.
+The default behavior, equivalent to @option{-foffload=default}, is to generate
+code for all supported offload targets. The @option{-foffload=disable} form
+generates code only for the host fallback, while
+@option{-foffload=@var{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 @option{-v} to show the list of configured offload targets
+under @code{OFFLOAD_TARGET_NAMES}.
+
+@opindex foffload-options
+@cindex Offloading options
+@cindex OpenACC offloading options
+@cindex OpenMP offloading options
+@item -foffload-options=@var{options}
+@itemx -foffload-options=@var{target-triplet-list}=@var{options}
+
+With @option{-foffload-options=@var{options}}, GCC passes the specified
+@var{options} to the compilers for all enabled offloading targets. You can
+specify options that apply only to a specific target or targets by using
+the @option{-foffload-options=@var{target-list}=@var{options}} form. The
+@var{target-list} is a comma-separated list in the same format as for the
+@option{-foffload=} option.
+
+Typical command lines are
+
+@smallexample
+-foffload-options='-fno-math-errno -ffinite-math-only' \
+ -foffload-options=nvptx-none=-latomic
+-foffload-options=amdgcn-amdhsa=-march=gfx906
+@end smallexample
+
+@opindex fopenacc
+@cindex OpenACC accelerator programming
+@item -fopenacc
+Enable handling of OpenACC directives @samp{#pragma acc} in C/C++ and
+@samp{!$acc} in free-form Fortran and @samp{!$acc}, @samp{c$acc} and
+@samp{*$acc} in fixed-form Fortran. This option
+implies @option{-pthread}, and thus is only supported on targets that
+have support for @option{-pthread}.
+
+@opindex fopenacc-dim
+@item -fopenacc-dim=@var{geom}
+Specify default compute dimensions for parallel offload regions that do
+not explicitly specify them. The @var{geom} value is a triple of
+@samp{:}-separated sizes, in order @var{gang}, @var{worker}, and @var{vector}.
+A size can be omitted, to use a target-specific default value.
+
+@opindex fopenmp
+@cindex OpenMP parallel
+@item -fopenmp
+Enable handling of OpenMP directives @samp{#pragma omp},
+@samp{[[omp::directive(...)]]}, @samp{[[omp::decl(...)]]},
+and @samp{[[omp::sequence(...)]]} in C/C++. In Fortran, it enables
+@samp{!$omp} and the conditional compilation sentinel @samp{!$}.
+In fixed source form Fortran, the sentinels can also start with
+@samp{c} or @samp{*}.
+
+This option implies @option{-pthread}, and thus is only supported on
+targets that have support for @option{-pthread}. @option{-fopenmp}
+implies @option{-fopenmp-simd}.
+
+@opindex fopenmp-simd
+@cindex OpenMP SIMD
+@cindex SIMD
+@item -fopenmp-simd
+Enable handling of OpenMP's @code{simd}, @code{declare simd},
+@code{declare reduction}, @code{assume}, @code{ordered}, @code{scan}
+and @code{loop} directive, and of combined or composite directives with
+@code{simd} as constituent with @code{#pragma omp},
+@code{[[omp::directive(...)]]}, @code{[[omp::sequence(...)]]} and
+@code{[[omp::decl(...)]]} in C/C++ and @code{!$omp} in Fortran. It
+additionally enables the conditional compilation sentinel @samp{!$} in
+Fortran. In fixed source form Fortran, the sentinels can also start with
+@samp{c} or @samp{*}. Other OpenMP directives are ignored. Unless
+@option{-fopenmp} is additionally specified, the @code{loop} region binds
+to the current task region, independent of the specified @code{bind} clause.
+
+@opindex fopenmp-target-simd-clone
+@cindex OpenMP target SIMD clone
+@item -fopenmp-target-simd-clone
+@item -fopenmp-target-simd-clone=@var{device-type}
+In addition to generating SIMD clones for functions marked with the
+@code{declare simd} directive, GCC also generates clones
+for functions marked with the OpenMP @code{declare target} directive
+that are suitable for vectorization when this option is in effect. The
+@var{device-type} may be one of @code{none}, @code{host}, @code{nohost},
+and @code{any}, which correspond to keywords for the @code{device_type}
+clause of the @code{declare target} directive; clones are generated for
+the intersection of devices specified.
+@option{-fopenmp-target-simd-clone} is equivalent to
+@option{-fopenmp-target-simd-clone=any} and
+@option{-fno-openmp-target-simd-clone} is equivalent to
+@option{-fopenmp-target-simd-clone=none}.
+
+At @option{-O2} and higher (but not @option{-Os} or @option{-Og}) this
+optimization defaults to @option{-fopenmp-target-simd-clone=nohost}; otherwise
+it is disabled by default.
+
+@end table
+
@node Diagnostic Message Formatting Options
@section Options to Control Diagnostic Messages Formatting
@cindex options to control diagnostics formatting
More details on support for these standards can be
found in the following sections of the documentation.
-Additionally, the GNU Fortran compilers supports the OpenMP specification
-(version 4.5 and partial support of the features of the 5.0 version,
-@url{https://openmp.org/@/specifications/}).
-There also is support for the OpenACC specification (targeting
-version 2.6, @uref{https://www.openacc.org/}). See
-@uref{https://gcc.gnu.org/wiki/OpenACC} for more information.
-
@node Fortran 95 status
@subsection Fortran 95 status
@cindex Varying length strings
It consists of a set of compiler directives, library routines,
and environment variables that influence run-time behavior.
-GNU Fortran strives to be compatible to the
-@uref{https://openmp.org/specifications/,
-OpenMP Application Program Interface v4.5}.
+GNU Fortran implements all of the @uref{https://openmp.org/specifications/,
+OpenMP Application Program Interface v4.5}, and many features from later
+versions of the OpenMP specification.
+@xref{OpenMP Implementation Status,,,libgomp,
+GNU Offloading and Multi Processing Runtime Library},
+for more details about currently supported OpenMP features.
To enable the processing of the OpenMP directive @code{!$omp} in
free-form source code; the @code{c$omp}, @code{*$omp} and @code{!$omp}
directives in fixed form; the @code{!$} conditional compilation sentinels
in free form; and the @code{c$}, @code{*$} and @code{!$} sentinels
in fixed form, @command{gfortran} needs to be invoked with the
-@option{-fopenmp}. This also arranges for automatic linking of the
-GNU Offloading and Multi Processing Runtime Library
-@ref{Top,,libgomp,libgomp,GNU Offloading and Multi Processing Runtime
-Library}.
+@option{-fopenmp} option. This option also arranges for automatic linking
+of the OpenMP runtime library.
+@xref{,,,libgomp,GNU Offloading and Multi Processing Runtime Library}.
The OpenMP Fortran runtime library routines are provided both in a
form of a Fortran 90 module named @code{omp_lib} and in a form of
END SUBROUTINE A1
@end smallexample
+@xref{OpenMP and OpenACC Options,,,gcc,
+Using the GNU Compiler Collection (GCC)}, for additional options useful with
+@option{-fopenmp}.
+
Please note:
@itemize
@item
@option{-fopenmp} implies @option{-frecursive}, i.e., all local arrays
-will be allocated on the stack. When porting existing code to OpenMP,
-this may lead to surprising results, especially to segmentation faults
-if the stacksize is limited.
+are allocated on the stack. When porting existing code to OpenMP,
+this may lead to surprising results, especially segmentation faults
+if the stack size is limited.
@item
-On glibc-based systems, OpenMP enabled applications cannot be statically
-linked due to limitations of the underlying pthreads-implementation. It
+On glibc-based systems, OpenMP-enabled applications cannot be statically
+linked due to limitations of the underlying pthreads implementation. It
might be possible to get a working solution if
@command{-Wl,--whole-archive -lpthread -Wl,--no-whole-archive} is added
-to the command line. However, this is not supported by @command{gcc} and
+to the command line. However, this is not supported by GCC and
thus not recommended.
@end itemize
compiler directives, library routines, and environment variables that
influence run-time behavior.
-GNU Fortran strives to be compatible to the
+GNU Fortran strives to be compatible with the
@uref{https://www.openacc.org/, OpenACC Application Programming
Interface v2.6}.
directives in fixed form; the @code{!$} conditional compilation
sentinels in free form; and the @code{c$}, @code{*$} and @code{!$}
sentinels in fixed form, @command{gfortran} needs to be invoked with
-the @option{-fopenacc}. This also arranges for automatic linking of
-the GNU Offloading and Multi Processing Runtime Library
-@ref{Top,,libgomp,libgomp,GNU Offloading and Multi Processing Runtime
-Library}.
+the @option{-fopenacc} option. This option also arranges for automatic
+linking of the OpenACC runtime library.
+@xref{,,,libgomp,GNU Offloading and Multi Processing Runtime Library}.
The OpenACC Fortran runtime library routines are provided both in a
form of a Fortran 90 module named @code{openacc} and in a form of a
Fortran @code{include} file named @file{openacc_lib.h}.
+@xref{OpenMP and OpenACC Options,,,gcc,
+Using the GNU Compiler Collection (GCC)}, for additional options useful with
+@option{-fopenacc}.
+
@node Argument list functions
@subsection Argument list functions @code{%VAL}, @code{%REF} and @code{%LOC}
@cindex argument list functions
projects / thirdparty / gcc.git / commitdiff
