Use mutex hint bit in PPC LWARX instructions, where possible.

The hint bit makes for a small but measurable performance improvement
in access to contended spinlocks.

On the other hand, some PPC chips give an illegal-instruction failure.
There doesn't seem to be a completely bulletproof way to tell whether the
hint bit will cause an illegal-instruction failure other than by trying
it; but most if not all 64-bit PPC machines should accept it, so follow
the Linux kernel's lead and assume it's okay to use it in 64-bit builds.
Of course we must also check whether the assembler accepts the command,
since even with a recent CPU the toolchain could be old.

Patch by Manabu Ori, significantly modified by me.

1 files changed, 61 insertions, 1 deletions

diff --git a/configure b/configure
index baa1b970f8e..5cb3d9b14f0 100755
--- a/configure
+++ b/configure
@@ -1635,7 +1635,7 @@ Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
 This configure script is free software; the Free Software Foundation
 gives unlimited permission to copy, distribute and modify it.
 
-Copyright (c) 1996-2011, PostgreSQL Global Development Group
+Copyright (c) 1996-2012, PostgreSQL Global Development Group
 _ACEOF
   exit
 fi
@@ -18207,6 +18207,66 @@ rm -f core conftest.err conftest.$ac_objext conftest_ipa8_conftest.oo \
       conftest$ac_exeext conftest.$ac_ext
 fi
 
+# On PPC, check if assembler supports LWARX instruction's mutex hint bit
+case $host_cpu in
+  ppc*|powerpc*)
+    { $as_echo "$as_me:$LINENO: checking whether assembler supports lwarx hint bit" >&5
+$as_echo_n "checking whether assembler supports lwarx hint bit... " >&6; }
+    cat >conftest.$ac_ext <<_ACEOF
+/* confdefs.h.  */
+_ACEOF
+cat confdefs.h >>conftest.$ac_ext
+cat >>conftest.$ac_ext <<_ACEOF
+/* end confdefs.h.  */
+
+int
+main ()
+{
+int a = 0; int *p = &a; int r;
+	 __asm__ __volatile__ (" lwarx %0,0,%1,1\n" : "=&r"(r) : "r"(p));
+  ;
+  return 0;
+}
+_ACEOF
+rm -f conftest.$ac_objext
+if { (ac_try="$ac_compile"
+case "(($ac_try" in
+  *\"* | *\`* | *\\*) ac_try_echo=\$ac_try;;
+  *) ac_try_echo=$ac_try;;
+esac
+eval ac_try_echo="\"\$as_me:$LINENO: $ac_try_echo\""
+$as_echo "$ac_try_echo") >&5
+  (eval "$ac_compile") 2>conftest.er1
+  ac_status=$?
+  grep -v '^ *+' conftest.er1 >conftest.err
+  rm -f conftest.er1
+  cat conftest.err >&5
+  $as_echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); } && {
+	 test -z "$ac_c_werror_flag" ||
+	 test ! -s conftest.err
+       } && test -s conftest.$ac_objext; then
+  pgac_cv_have_ppc_mutex_hint=yes
+else
+  $as_echo "$as_me: failed program was:" >&5
+sed 's/^/| /' conftest.$ac_ext >&5
+
+	pgac_cv_have_ppc_mutex_hint=no
+fi
+
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+    { $as_echo "$as_me:$LINENO: result: $pgac_cv_have_ppc_mutex_hint" >&5
+$as_echo "$pgac_cv_have_ppc_mutex_hint" >&6; }
+    if test x"$pgac_cv_have_ppc_mutex_hint" = xyes ; then
+
+cat >>confdefs.h <<\_ACEOF
+#define HAVE_PPC_LWARX_MUTEX_HINT 1
+_ACEOF
+
+    fi
+  ;;
+esac
+
 # Check largefile support.  You might think this is a system service not a
 # compiler characteristic, but you'd be wrong.  We must check this before
 # probing existence of related functions such as fseeko, since the largefile