Add pre pentium 4 compatibilty configure test

2 files changed, 51 insertions, 11 deletions

diff --git a/INSTALL.md b/INSTALL.md
index 2567b791e5..1061c5187a 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -277,7 +277,8 @@ Some of the available `configure` options are:
     x86 processors before pentium 4 (back to 486) in the ethread library. If
     not passed the ethread library (part of the runtime system) will use
     instructions that first appeared on the pentium 4 processor when building
-    for x86.
+    for x86. This option will be automatically enabled if required on the
+    build machine.
 *   `--with-libatomic_ops=PATH` - Use the `libatomic_ops` library for atomic
     memory accesses. If `configure` should inform you about no native atomic
     implementation available, you typically want to try using the
diff --git a/erts/aclocal.m4 b/erts/aclocal.m4
index 82014fe23d..3a951860e5 100644
--- a/erts/aclocal.m4
+++ b/erts/aclocal.m4
@@ -994,8 +994,8 @@ case "$THR_LIB_NAME" in
 
 	case "$host_cpu" in
 	  sun4u | sparc64 | sun4v)
-		ethr_have_native_atomics=yes;;
-	  i86pc | i386 | i486 | i586 | i686 | x86_64 | amd64)
+		ethr_have_native_atomics=yes;; 
+	  i86pc | i*86 | x86_64 | amd64)
 		ethr_have_native_atomics=yes;;
 	  macppc | ppc | "Power Macintosh")
 		ethr_have_native_atomics=yes;;
@@ -1099,21 +1099,60 @@ AC_ARG_ENABLE(prefer-gcc-native-ethr-impls,
 test $enable_prefer_gcc_native_ethr_impls = yes &&
   AC_DEFINE(ETHR_PREFER_GCC_NATIVE_IMPLS, 1, [Define if you prefer gcc native ethread implementations])
 
+AC_ARG_WITH(libatomic_ops,
+	    AS_HELP_STRING([--with-libatomic_ops=PATH],
+			   [use libatomic_ops with the ethread library]))
+
 AC_ARG_ENABLE(ethread-pre-pentium4-compatibility,
 	      AS_HELP_STRING([--enable-ethread-pre-pentium4-compatibility],
 			     [enable compatibility with x86 processors before pentium 4 (back to 486) in the ethread library]),
-[ case "$enableval" in
-    yes) enable_ethread_pre_pentium4_compatibility=yes ;;
-    *)  enable_ethread_pre_pentium4_compatibility=no ;;
-  esac ], enable_ethread_pre_pentium4_compatibility=no)
+[
+  case "$enable_ethread_pre_pentium4_compatibility" in
+    yes|no) ;;
+    *) enable_ethread_pre_pentium4_compatibility=check;;
+  esac
+],
+[enable_ethread_pre_pentium4_compatibility=check])
+
+test "$cross_compiling" != "yes" || enable_ethread_pre_pentium4_compatibility=no
+
+case "$enable_ethread_pre_pentium4_compatibility-$host_cpu" in
+  check-i86pc | check-i*86)
+    AC_MSG_CHECKING([whether pre pentium 4 compatibility should forced])
+    AC_RUN_IFELSE([
+#if defined(__GNUC__)
+#  if defined(ETHR_PREFER_LIBATOMIC_OPS_NATIVE_IMPLS)
+#    define CHECK_LIBATOMIC_OPS__
+#  else
+#    define CHECK_GCC_ASM__
+#  endif
+#elif defined(ETHR_HAVE_LIBATOMIC_OPS)
+#  define CHECK_LIBATOMIC_OPS__
+#endif
+#if defined(CHECK_LIBATOMIC_OPS__)
+#include "atomic_ops.h"
+#endif
+int main(void)
+{
+#if defined(CHECK_GCC_ASM__)
+    __asm__ __volatile__("mfence" : : : "memory");
+#elif defined(CHECK_LIBATOMIC_OPS__)
+    AO_nop_full();
+#endif
+    return 0;
+}
+	],
+	[enable_ethread_pre_pentium4_compatibility=no],
+	[enable_ethread_pre_pentium4_compatibility=yes],
+	[enable_ethread_pre_pentium4_compatibility=no])
+    AC_MSG_RESULT([$enable_ethread_pre_pentium4_compatibility]);;
+  *)
+    ;;
+esac
 
 test $enable_ethread_pre_pentium4_compatibility = yes &&
   AC_DEFINE(ETHR_PRE_PENTIUM4_COMPAT, 1, [Define if you want compatibilty with x86 processors before pentium4.])
 
-AC_ARG_WITH(libatomic_ops,
-	    AS_HELP_STRING([--with-libatomic_ops=PATH],
-			   [use libatomic_ops with the ethread library]))
-
 AC_DEFINE(ETHR_HAVE_ETHREAD_DEFINES, 1, \
 [Define if you have all ethread defines])