From a5139dd66d271c8600adcae834da00f578a50a36 Mon Sep 17 00:00:00 2001
From: Anthony Scemama <scemama@irsamc.ups-tlse.fr>
Date: Tue, 12 Sep 2023 11:22:27 +0200
Subject: [PATCH] Update ax_openmp.m4

---
 m4/ax_openmp.m4 | 43 ++++++++++++++++++++++++++++++++++---------
 1 file changed, 34 insertions(+), 9 deletions(-)

diff --git a/m4/ax_openmp.m4 b/m4/ax_openmp.m4
index 7ea794be..6a0830be 100644
--- a/m4/ax_openmp.m4
+++ b/m4/ax_openmp.m4
@@ -1,5 +1,5 @@
 # ===========================================================================
-#         http://www.gnu.org/software/autoconf-archive/ax_openmp.html
+#        https://www.gnu.org/software/autoconf-archive/ax_openmp.html
 # ===========================================================================
 #
 # SYNOPSIS
@@ -38,6 +38,8 @@
 # LICENSE
 #
 #   Copyright (c) 2008 Steven G. Johnson <stevenj@alum.mit.edu>
+#   Copyright (c) 2015 John W. Peterson <jwpeterson@gmail.com>
+#   Copyright (c) 2016 Nick R. Papior <nickpapior@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
@@ -50,7 +52,7 @@
 #   Public License for more details.
 #
 #   You should have received a copy of the GNU General Public License along
-#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#   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
@@ -65,16 +67,19 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 8
+#serial 14
 
 AC_DEFUN([AX_OPENMP], [
-AC_PREREQ(2.59) dnl for _AC_LANG_PREFIX
+AC_PREREQ([2.69]) dnl for _AC_LANG_PREFIX
 
 AC_CACHE_CHECK([for OpenMP flag of _AC_LANG compiler], ax_cv_[]_AC_LANG_ABBREV[]_openmp, [save[]_AC_LANG_PREFIX[]FLAGS=$[]_AC_LANG_PREFIX[]FLAGS
 ax_cv_[]_AC_LANG_ABBREV[]_openmp=unknown
-# Flags to try:  -fopenmp (gcc), -openmp (icc), -mp (SGI & PGI),
-#                -xopenmp (Sun), -omp (Tru64), -qsmp=omp (AIX), none
-ax_openmp_flags="-fopenmp -openmp -mp -xopenmp -omp -qsmp=omp none"
+# Flags to try:  -fopenmp (gcc), -mp (SGI & PGI),
+#                -qopenmp (icc>=15), -openmp (icc),
+#                -xopenmp (Sun), -omp (Tru64),
+#                -qsmp=omp (AIX),
+#                none
+ax_openmp_flags="-fopenmp -openmp -qopenmp -mp -xopenmp -omp -qsmp=omp none"
 if test "x$OPENMP_[]_AC_LANG_PREFIX[]FLAGS" != x; then
   ax_openmp_flags="$OPENMP_[]_AC_LANG_PREFIX[]FLAGS $ax_openmp_flags"
 fi
@@ -83,8 +88,27 @@ for ax_openmp_flag in $ax_openmp_flags; do
     none) []_AC_LANG_PREFIX[]FLAGS=$save[]_AC_LANG_PREFIX[] ;;
     *) []_AC_LANG_PREFIX[]FLAGS="$save[]_AC_LANG_PREFIX[]FLAGS $ax_openmp_flag" ;;
   esac
-  AC_TRY_LINK_FUNC(omp_set_num_threads,
-	[ax_cv_[]_AC_LANG_ABBREV[]_openmp=$ax_openmp_flag; break])
+  AC_LINK_IFELSE([AC_LANG_SOURCE([[
+@%:@include <omp.h>
+
+static void
+parallel_fill(int * data, int n)
+{
+  int i;
+@%:@pragma omp parallel for
+  for (i = 0; i < n; ++i)
+    data[i] = i;
+}
+
+int
+main(void)
+{
+  int arr[100000];
+  omp_set_num_threads(2);
+  parallel_fill(arr, 100000);
+  return 0;
+}
+]])],[ax_cv_[]_AC_LANG_ABBREV[]_openmp=$ax_openmp_flag; break],[])
 done
 []_AC_LANG_PREFIX[]FLAGS=$save[]_AC_LANG_PREFIX[]FLAGS
 ])
@@ -97,3 +121,4 @@ else
   m4_default([$1], [AC_DEFINE(HAVE_OPENMP,1,[Define if OpenMP is enabled])])
 fi
 ])dnl AX_OPENMP
+