* As promised to George and per #93, add macros for hinting to the compiler

whether an if statement is likely to be taken and for prefetching memory.
  Current macros:

    OPAL_LIKELY(expression)
    OPAL_UNLIKELY(expression)
    OPAL_PREFETC(address)

This commit was SVN r10278.

config/ompi_setup_cc.m4

@@ -8,7 +8,7 @@ dnl                         of Tennessee Research Foundation.  All rights
 dnl                         reserved.
 dnl Copyright (c) 2004-2006 High Performance Computing Center Stuttgart, 
 dnl                         University of Stuttgart.  All rights reserved.
-dnl Copyright (c) 2004-2005 The Regents of the University of California.
+dnl Copyright (c) 2004-2006 The Regents of the University of California.
 dnl                         All rights reserved.
 dnl $COPYRIGHT$
 dnl 
@@ -153,6 +153,38 @@ AC_DEFUN([OMPI_SETUP_CC],[
         unset add
     fi
 
+    # see if the C compiler supports __builtin_expect
+    AC_CACHE_CHECK([if $CC supports __builtin_expect],
+        [ompi_cv_cc_supports___builtin_expect],
+        [AC_TRY_COMPILE([],
+          [void *ptr = (void*) 0;
+           if (__builtin_expect (ptr != NULL, 1)) return 0;],
+          [ompi_cv_cc_supports___builtin_expect="yes"],
+          [ompi_cv_cc_supports___builtin_expect="no"])])
+    if test "$ompi_cv_cc_supports___builtin_expect" = "yes" ; then
+        have_builtin_expect=1
+    else
+        have_builtin_expect=0
+    fi
+    AC_DEFINE_UNQUOTED([OMPI_C_HAVE_BUILTIN_EXPECT], [$have_builtin_expect],
+          [Whether C compiler supports __builtin_expect])
+
+    # see if the C compiler supports __builtin_prefetch
+    AC_CACHE_CHECK([if $CC supports __builtin_prefetch],
+        [ompi_cv_cc_supports___builtin_prefetch],
+        [AC_TRY_COMPILE([],
+          [int ptr;
+           __builtin_prefetch(&ptr);],
+          [ompi_cv_cc_supports___builtin_prefetch="yes"],
+          [ompi_cv_cc_supports___builtin_prefetch="no"])])
+    if test "$ompi_cv_cc_supports___builtin_prefetch" = "yes" ; then
+        have_builtin_prefetch=1
+    else
+        have_builtin_prefetch=0
+    fi
+    AC_DEFINE_UNQUOTED([OMPI_C_HAVE_BUILTIN_PREFETCH], [$have_builtin_prefetch],
+          [Whether C compiler supports __builtin_prefetch])
+
     # Preload the optflags for the case where the user didn't specify
     # any.  If we're using GNU compilers, use -O3 (since it GNU
     # doesn't require all compilation units to be compiled with the

config/ompi_setup_cxx.m4

@@ -8,7 +8,7 @@ dnl                         of Tennessee Research Foundation.  All rights
 dnl                         reserved.
 dnl Copyright (c) 2004-2005 High Performance Computing Center Stuttgart, 
 dnl                         University of Stuttgart.  All rights reserved.
-dnl Copyright (c) 2004-2005 The Regents of the University of California.
+dnl Copyright (c) 2004-2006 The Regents of the University of California.
 dnl                         All rights reserved.
 dnl $COPYRIGHT$
 dnl 
@@ -135,6 +135,42 @@ AC_DEFUN([OMPI_SETUP_CXX],[
     # config/cxx_find_template_parameters.m4
     OMPI_CXX_FIND_TEMPLATE_PARAMETERS
 
+    # see if the C++ compiler supports __builtin_expect
+    AC_LANG_PUSH(C++)
+    AC_CACHE_CHECK([if $CXX supports __builtin_expect],
+        [ompi_cv_cxx_supports___builtin_expect],
+        [AC_TRY_COMPILE([],
+          [void *ptr = (void*) 0;
+           if (__builtin_expect (ptr != NULL, 1)) return 0;],
+          [ompi_cv_cxx_supports___builtin_expect="yes"],
+          [ompi_cv_cxx_supports___builtin_expect="no"])])
+    if test "$ompi_cv_cxx_supports___builtin_expect" = "yes" ; then
+        have_builtin_expect=1
+    else
+        have_builtin_expect=0
+    fi
+    AC_DEFINE_UNQUOTED([OMPI_CXX_HAVE_BUILTIN_EXPECT], [$have_builtin_expect],
+          [Whether C++ compiler supports __builtin_expect])
+    AC_LANG_POP(C++)
+
+    # see if the C compiler supports __builtin_prefetch
+    AC_LANG_PUSH(C++)
+    AC_CACHE_CHECK([if $CXX supports __builtin_prefetch],
+        [ompi_cv_cxx_supports___builtin_prefetch],
+        [AC_TRY_COMPILE([],
+          [int ptr;
+           __builtin_prefetch(&ptr);],
+          [ompi_cv_cxx_supports___builtin_prefetch="yes"],
+          [ompi_cv_cxx_supports___builtin_prefetch="no"])])
+    if test "$ompi_cv_cxx_supports___builtin_prefetch" = "yes" ; then
+        have_builtin_prefetch=1
+    else
+        have_builtin_prefetch=0
+    fi
+    AC_DEFINE_UNQUOTED([OMPI_CXX_HAVE_BUILTIN_PREFETCH], [$have_builtin_prefetch],
+          [Whether C++ compiler supports __builtin_prefetch])
+    AC_LANG_POP(C++)
+
     # If we are on HP-UX, ensure that we're using aCC
     case "$host" in
     *hpux*)

opal/include/opal/prefetch.h

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2004-2006 The Regents of the University of California.
+ *                         All rights reserved.
+ * $COPYRIGHT$
+ * 
+ * Additional copyrights may follow
+ * 
+ * $HEADER$
+ */
+
+/** @file
+ *
+ * Compiler-specific prefetch functions
+ *
+ * A small set of prefetch / prediction interfaces for using compiler
+ * directives to improve memory prefetching and branch prediction
+ */
+
+#ifndef OPAL_PREFETCH_H
+#define OPAL_PREFETCH_H
+
+#if defined(c_plusplus) || defined(__cplusplus)
+/* C++ code */
+
+#if OMPI_CXX_HAVE_BUILTIN_EXPECT
+#define OPAL_LIKELY(expression) __builtin_expect(!!(expression), 1)
+#define OPAL_UNLIKELY(expression) __builtin_expect(!!(expression), 0)
+#else
+#define OPAL_LIKELY(expression) (expression)
+#define OPAL_UNLIKELY(expression) (expression)
+#endif
+
+#if OMPI_CXX_HAVE_BUILTIN_PREFETCH
+#define OPAL_PREFETCH(address) __builtin_prefetch(address)
+#else
+#define OPAL_PREFETCH(address)
+#endif
+
+#else
+/* C code */
+
+#if OMPI_C_HAVE_BUILTIN_EXPECT
+#define OPAL_LIKELY(expression) __builtin_expect(!!(expression), 1)
+#define OPAL_UNLIKELY(expression) __builtin_expect(!!(expression), 0)
+#else
+#define OPAL_LIKELY(expression) (expression)
+#define OPAL_UNLIKELY(expression) (expression)
+#endif
+
+#if OMPI_C_HAVE_BUILTIN_PREFETCH
+#define OPAL_PREFETCH(address) __builtin_prefetch(address)
+#else
+#define OPAL_PREFETCH(address)
+#endif
+
+#endif
+
+#endif