@node ax_check_x86_features
@unnumberedsec ax_check_x86_features

@majorheading Synopsis

@smallexample
AX_CHECK_X86_FEATURES([ACTION-IF-FOUND],[ACTION-IF-NOT-FOUND])
@end smallexample

@majorheading Description

Checks if the host cpu supports various x86 instruction set, the
instructions that will get tested are "mmx, popcnt, sse, sse2, sse3,
sse4.1, sse4.2, sse4a, avx, avx2, avx512f, fma, fma4, bmi, bmi2". If the
instruction set is supported by the host cpu, the C preprocessor macro
HAVE_XXX_INSTRUCTIONS is set to 1. The XXX is up-cased instruction case
with dot replaced by underscore. For example, the test for "sse4.2"
would export HAVE_SSE4_2_INSTRUCTIONS=1. Also the compiler flag
"-msse4.2" would be added to X86_FEATURE_CFLAGS variable, that can be
obtained in Makefile.am using @@X86_FEATURE_CFLAGS@@.

If any of the test for the instruction set were succeeded, the configure
script would run ACTION-IF-FOUND if it is specified, or append
X86_FEATURE_CFLAGS to CFLAGS. If none of the instruction were found,
ACTION-IF-NOT-FOUND hook is triggered.

This macro requires gcc extended builtin function "__builtin_cpu_init"
and "__builtin_cpu_supports" to detect the cpu features. It will error
out if the compiler doesn't has these builtins.

See also AX_GCC_X86_CPU_SUPPORTS, which is the actual macro that perform
the checks for the instruction sets.

@majorheading Source Code

Download the
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=blob_plain;f=m4/ax_check_x86_features.m4,latest
version of @file{ax_check_x86_features.m4}} or browse
@uref{http://git.savannah.gnu.org/gitweb/?p=autoconf-archive.git;a=history;f=m4/ax_check_x86_features.m4,the
macro's revision history}.

@majorheading License

@w{Copyright @copyright{} 2016 Felix Chern @email{idryman@@gmail.com}}

This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
Public License for more details.

You should have received a copy of the GNU General Public License along
with this program. If not, see <https://www.gnu.org/licenses/>.

As a special exception, the respective Autoconf Macro's copyright owner
gives unlimited permission to copy, distribute and modify the configure
scripts that are the output of Autoconf when processing the Macro. You
need not follow the terms of the GNU General Public License when using
or distributing such scripts, even though portions of the text of the
Macro appear in them. The GNU General Public License (GPL) does govern
all other use of the material that constitutes the Autoconf Macro.

This special exception to the GPL applies to versions of the Autoconf
Macro released by the Autoconf Archive. When you make and distribute a
modified version of the Autoconf Macro, you may extend this special
exception to the GPL to apply to your modified version as well.