asyncsafe-spin: Fix compilation error with GCC on 32-bit SPARC.

Reported by Paul Eggert in
<https://lists.gnu.org/archive/html/bug-gnulib/2020-11/msg00066.html>.

* m4/sparcv8+.m4: New file.
* modules/sparcv8+: New file.
* modules/asyncsafe-spin (Depends-on): Add sparcv8+.

4 files changed, 74 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 55053793bc..fa21e9cd28 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2020-11-28  Bruno Haible  <bruno@clisp.org>
 
+	asyncsafe-spin: Fix compilation error with GCC on 32-bit SPARC.
+	Reported by Paul Eggert in
+	<https://lists.gnu.org/archive/html/bug-gnulib/2020-11/msg00066.html>.
+	* m4/sparcv8+.m4: New file.
+	* modules/sparcv8+: New file.
+	* modules/asyncsafe-spin (Depends-on): Add sparcv8+.
+
+2020-11-28  Bruno Haible  <bruno@clisp.org>
+
 	asyncsafe-spin: Fix build error with GCC on 32-bit SPARC.
 	* lib/asyncsafe-spin.c: Don't use GCC >= 4.1 primitives on SPARC.
 
diff --git a/m4/sparcv8+.m4 b/m4/sparcv8+.m4
new file mode 100644
index 0000000000..2dbb8a90f4
--- /dev/null
+++ b/m4/sparcv8+.m4
@@ -0,0 +1,42 @@
+# sparcv8+.m4 serial 1
+dnl Copyright (C) 2020 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+dnl When compiling for SPARC in 32-bit mode, make sure that instructions for
+dnl SPARC v8+ are accepted.  This is necessary for multiprocessing (for
+dnl instructions like 'membar' or 'cas').  All SPARC CPUs made since 1993
+dnl support this instruction set.  But GCC in its default configuration, in
+dnl 32-bit mode (64-bit mode assumes SPARC v9 or newer), still defaults to
+dnl SPARC v7 instruction set: "By default (unless configured otherwise), GCC
+dnl generates code for the V7 variant of the SPARC architecture."  See
+dnl <https://gcc.gnu.org/onlinedocs/gcc-4.6.4/gcc/SPARC-Options.html>
+dnl <https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/SPARC-Options.html>
+
+AC_DEFUN([gl_SPARC_V8PLUS],
+[
+  AC_REQUIRE([AC_CANONICAL_HOST])
+
+  case "$host_cpu" in
+    sparc*)
+      if test -n "$GCC"; then
+        AC_CACHE_CHECK([whether SPARC v8+ instructions are supported],
+          [gl_cv_sparc_v8plus],
+          [AC_COMPILE_IFELSE(
+             [AC_LANG_PROGRAM(
+                [[]],
+                [[asm volatile ("membar 2");]])],
+             [gl_cv_sparc_v8plus=yes],
+             [gl_cv_sparc_v8plus=no])
+          ])
+        if test $gl_cv_sparc_v8plus = no; then
+          dnl Strangely enough, '-mv8plus' does not have the desired effect.
+          dnl But '-mcpu=v9' does.
+          CC="$CC -mcpu=v9"
+          CXX="$CXX -mcpu=v9"
+        fi
+      fi
+      ;;
+  esac
+])
diff --git a/modules/asyncsafe-spin b/modules/asyncsafe-spin
index fa27b087e1..fc734928db 100644
--- a/modules/asyncsafe-spin
+++ b/modules/asyncsafe-spin
@@ -10,6 +10,7 @@ signal-h
 stdbool
 sigprocmask
 windows-spin
+sparcv8+
 
 configure.ac:
 AC_REQUIRE([AC_C_INLINE])
diff --git a/modules/sparcv8+ b/modules/sparcv8+
new file mode 100644
index 0000000000..a4e38a8c4d
--- /dev/null
+++ b/modules/sparcv8+
@@ -0,0 +1,22 @@
+Description:
+When compiling for SPARC, assume SPARC v8+ or newer.
+
+Files:
+m4/sparcv8+.m4
+
+Depends-on:
+
+configure.ac-early:
+gl_SPARC_V8PLUS
+
+configure.ac:
+
+Makefile.am:
+
+Include:
+
+License:
+LGPLv2+
+
+Maintainer:
+all