re PR c++/56998 (ICE in value_dependent_expression_p, at cp/pt.c:19598)

	PR c++/56998
	* call.c (null_ptr_cst_p): An expression with side-effects can't
	be a C++03 null pointer constant.

From-SVN: r198845

gcc/cp/ChangeLog

 2013-05-13  Jason Merrill  <jason@redhat.com>
 
+	PR c++/56998
+	* call.c (null_ptr_cst_p): An expression with side-effects can't
+	be a C++03 null pointer constant.
+
 	PR c++/57041
 	* decl.c (reshape_init_class): Handle error_mark_node.
 

gcc/cp/call.c

@@ -554,7 +554,7 @@ null_ptr_cst_p (tree t)
   if (CP_INTEGRAL_TYPE_P (TREE_TYPE (t)))
     {
       /* Core issue 903 says only literal 0 is a null pointer constant.  */
-      if (cxx_dialect < cxx0x)
+      if (cxx_dialect < cxx0x && !TREE_SIDE_EFFECTS (t))
 	t = maybe_constant_value (fold_non_dependent_expr_sfinae (t, tf_none));
       STRIP_NOPS (t);
       if (integer_zerop (t) && !TREE_OVERFLOW (t))

gcc/testsuite/g++.dg/template/overload13.C

+// PR c++/56998
+
+class Secret;
+char IsNullLiteralHelper(Secret* p);
+char (&IsNullLiteralHelper(...))[2];
+
+struct C
+{
+  int val() { return 42; }
+};
+
+template <typename T>
+unsigned f()
+{
+  return sizeof(IsNullLiteralHelper(C().val()));
+}