Add ax_c_restrict

to check for broken gcc-5 and clang-6 implementations

1 files changed, 62 insertions, 0 deletions

diff --git a/m4/ax_c_restrict.m4 b/m4/ax_c_restrict.m4
new file mode 100644
index 0000000..1ca9e71
--- /dev/null
+++ b/m4/ax_c_restrict.m4
@@ -0,0 +1,62 @@
+# ===========================================================================
+#       https://www.gnu.org/software/autoconf-archive/ax_c_restrict.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_C_RESTRICT
+#
+# DESCRIPTION
+#
+#   This macro checks if the C99 restrict keyword is broken with the current
+#   compiler and optimizations settings. If broken, it undefines restrict to
+#   do no harm. As of 2019 gcc since 5.0 and clang since 6.0 (June 2017) are
+#   known to be broken and not yet fixed. See
+#   https://github.com/rust-lang/rust/issues/54878 with the links to the gcc
+#   and clang tickets.
+#
+# LICENSE
+#
+#   Copyright (c) 2019 Reini Urban <rurban@cpan.org>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved. This file is offered as-is, without any
+#   warranty.
+
+#serial 1
+
+AC_DEFUN([AX_C_RESTRICT],
+[AC_CACHE_CHECK([for restrict usability],
+  [ax_cv_c_restrict_usable],
+  [AC_RUN_IFELSE([AC_LANG_PROGRAM([],
+  [[
+    void copy (int * restrict to, int * restrict from) {
+    	*to = *from;
+    }
+    void test (int *a, int *b) {
+    	for (int i = 0; i < 4; i++) {
+    	    copy (&b[i & 1], &a[i & 1]);
+    	}
+    }
+    int main () {
+    	int ary[] = {0, 1, 2};
+    	test (&ary[1], &ary[0]);
+    	/* printf("%d %d %d\n", ary[0], ary[1], ary[2]);
+            2 2 2 is correct
+            1 2 2 wrong */
+    	return ary[0] == 2 ? 0 : 1;
+    }
+  ]])],
+  [ax_cv_c_restrict_usable=restrict],
+  [ax_cv_c_restrict_usable=],
+  [ax_cv_c_restrict_usable=])])
+
+if test -z $ax_cv_c_restrict_usable; then
+  AC_MSG_RESULT([no])
+  AC_DEFINE_UNQUOTED(restrict, $ax_cv_c_restrict_usable,
+    [If restrict is broken with this C compiler])
+else
+  AC_MSG_RESULT([yes])
+fi
+]) dnl AX_C_RESTRICT