re PR middle-end/21595 (__builtin_constant_p(&"Hello"[0]) is true for C but not for C++)

2005-05-17  Richard Guenther  <rguenth@gcc.gnu.org>

	PR middle-end/21595
	* builtins.c (fold_builtin_constant_p): Handle
	&"string cst"[0] as constant.

	* g++.dg/tree-ssa/builtin1.C: New testcase.

From-SVN: r99825

gcc/ChangeLog

+2005-05-17  Richard Guenther  <rguenth@gcc.gnu.org>
+
+	PR middle-end/21595
+	* builtins.c (fold_builtin_constant_p): Handle
+	&"string cst"[0] as constant.
+
 2005-05-17  Richard Henderson  <rth@redhat.com>
 
 	* config/i386/sse.md (mulv16qi3, mulv2di3): New.

gcc/builtins.c

@@ -6338,10 +6338,17 @@ fold_builtin_constant_p (tree arglist)
   /* If we know this is a constant, emit the constant of one.  */
   if (CONSTANT_CLASS_P (arglist)
       || (TREE_CODE (arglist) == CONSTRUCTOR
-	  && TREE_CONSTANT (arglist))
-      || (TREE_CODE (arglist) == ADDR_EXPR
-	  && TREE_CODE (TREE_OPERAND (arglist, 0)) == STRING_CST))
+	  && TREE_CONSTANT (arglist)))
     return integer_one_node;
+  if (TREE_CODE (arglist) == ADDR_EXPR)
+    {
+       tree op = TREE_OPERAND (arglist, 0);
+       if (TREE_CODE (op) == STRING_CST
+	   || (TREE_CODE (op) == ARRAY_REF
+	       && integer_zerop (TREE_OPERAND (op, 1))
+	       && TREE_CODE (TREE_OPERAND (op, 0)) == STRING_CST))
+	 return integer_one_node;
+    }
 
   /* If this expression has side effects, show we don't know it to be a
      constant.  Likewise if it's a pointer or aggregate type since in

gcc/testsuite/ChangeLog

+2005-05-17  Richard Guenther  <rguenth@gcc.gnu.org>
+
+	PR middle-end/21595
+	* g++.dg/tree-ssa/builtin1.C: New testcase.
+
 2005-05-17  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/21454

gcc/testsuite/g++.dg/tree-ssa/builtin1.C

+// { dg-do link }
+
+extern void link_error();
+
+int main()
+{
+	if (! __builtin_constant_p (&"Hello"[0]))
+		link_error();
+	return 0;
+}