Check for __attribute__ to support advanced flags on the functions and structures.

They can be used to give additional knowledge to the compiler about the behaviour of a
function so it can optimize further. In the begining we just need it for the alias weak
a better way to create function aliases.

The problem was that the intel compiler version 8 to 9 support pragma weak but do not include
the function in the .o file if it's not used at least once in the same .c file. With the
alias weak this problem is solved as even intel support it correctly.

This commit was SVN r7330.

config/ompi_check_attributes.m4

@@ -0,0 +1,105 @@
+# -*- shell-script -*-
+#
+# Copyright (c) 2004-2005 The Trustees of Indiana University.
+#                         All rights reserved.
+# Copyright (c) 2004-2005 The Trustees of the University of Tennessee.
+#                         All rights reserved.
+# Copyright (c) 2004-2005 High Performance Computing Center Stuttgart,
+#                         University of Stuttgart.  All rights reserved.
+# Copyright (c) 2004-2005 The Regents of the University of California.
+#                         All rights reserved.
+# $COPYRIGHT$
+#
+# Additional copyrights may follow
+#
+# $HEADER$
+#
+
+AC_DEFUN([OMPI_CHECK____ATTRIBUTE__], [
+  AC_MSG_CHECKING(for __attribute__)
+  AC_CACHE_VAL(ac_cv___attribute__, [
+    AC_TRY_COMPILE(
+      [#include <stdlib.h>],
+      [static void foo(void) __attribute__ ((unused));
+       static void foo(void) { exit(1); }],
+      [ac_cv___attribute__=1 ac_cv___attribute__msg=yes],
+      [ac_cv___attribute__=0 ac_cv___attribute__msg=no],
+    )])
+  AC_DEFINE_UNQUOTED( HAVE___ATTRIBUTE__, [$ac_cv___attribute__],
+                      [define if your compiler has __attribute__] )
+  AC_MSG_RESULT($ac_cv___attribute__msg)
+
+#
+# Now that we know the compiler support __attribute__ let's check which kind of
+# attributed are supported.
+#
+  if test "$ac_cv___attribute__msg" = "yes"; then
+    AC_MSG_CHECKING("for __attribute__ ((alias))" )
+    AC_CACHE_VAL(ac_cv___attribute__alias, [
+      AC_TRY_COMPILE(
+        [#include <stdlib.h>
+         int foo(int arg) { return arg + 3; }
+         int foo2(int) __attribute__ ((weak, alias ("foo")));],
+        [],
+        [ac_cv___attribute__alias=1 ac_cv___attribute__alias_msg=yes],
+        [ac_cv___attribute__alias=0 ac_cv___attribute__alias_msg=no]
+      )])
+    AC_DEFINE_UNQUOTED( HAVE___ATTRIBUTE__WEAK_ALIAS, [$ac_cv___attribute__alias],
+                        [define if your compiler has __attribute__ alias weak] )
+    AC_MSG_RESULT($ac_cv___attribute__alias_msg)
+    
+
+    AC_MSG_CHECKING("for __attribute__ ((const))" )
+    AC_CACHE_VAL(ac_cv___attribute__const, [
+      AC_TRY_COMPILE(
+        [#include <stdlib.h>
+         int foo(int arg1, int arg2) __attribute__ ((const)) { return arg1 * arg2 + arg1; }],
+        [],
+        [ac_cv___attribute__const=1 ac_cv___attribute__const_msg=yes],
+        [ac_cv___attribute__const=0 ac_cv___attribute__const_msg=no]
+      )])
+    AC_DEFINE_UNQUOTED( HAVE___ATTRIBUTE__CONST, [$ac_cv___attribute__const],
+                        [define if your compiler has __attribute__ const] )
+    AC_MSG_RESULT($ac_cv___attribute__const_msg)
+
+    AC_MSG_CHECKING("for __attribute__ ((malloc))" )
+    AC_CACHE_VAL(ac_cv___attribute__malloc, [
+      AC_TRY_COMPILE(
+        [#include <stdlib.h>
+         int foo(int arg1) __attribute__ ((malloc)) { return malloc(arg1); }],
+        [],
+        [ac_cv___attribute__malloc=1 ac_cv___attribute__malloc_msg=yes],
+        [ac_cv___attribute__malloc=0 ac_cv___attribute__malloc_msg=no]
+      )])
+    AC_DEFINE_UNQUOTED( HAVE___ATTRIBUTE__MALLOC, [$ac_cv___attribute__malloc],
+                        [define if your compiler has __attribute__ malloc] )
+    AC_MSG_RESULT($ac_cv___attribute__malloc_msg)
+
+    AC_MSG_CHECKING("for __attribute__ ((noreturn))" )
+    AC_CACHE_VAL(ac_cv___attribute__noreturn, [
+      AC_TRY_COMPILE(
+        [#include <stdlib.h>
+         int fatal(int arg1) __attribute__ ((noreturn)) { exit(arg1); }],
+        [],
+        [ac_cv___attribute__noreturn=1 ac_cv___attribute__noreturn_msg=yes],
+        [ac_cv___attribute__noreturn=0 ac_cv___attribute__noreturn_msg=no]
+      )])
+    AC_DEFINE_UNQUOTED( HAVE___ATTRIBUTE__NORETURN, [$ac_cv___attribute__noreturn],
+                        [define if your compiler has __attribute__ noreturn] )
+    AC_MSG_RESULT($ac_cv___attribute__noreturn_msg)
+
+    AC_MSG_CHECKING("for __attribute__ ((pure))" )
+    AC_CACHE_VAL(ac_cv___attribute__pure, [
+      AC_TRY_COMPILE(
+        [#include <stdlib.h>
+         int square(int arg) __attribute__ ((pure)) { return arg * arg; }],
+        [],
+        [ac_cv___attribute__pure=1 ac_cv___attribute__pure_msg=yes],
+        [ac_cv___attribute__pure=0 ac_cv___attribute__pure_msg=no]
+      )])
+    AC_DEFINE_UNQUOTED( HAVE___ATTRIBUTE__PURE, [$ac_cv___attribute__PURE],
+                        [define if your compiler has __attribute__ PURE] )
+    AC_MSG_RESULT($ac_cv___attribute__pure_msg)
+
+  fi
+])