re PR c++/58814 (ICE with volatile and attribute vector_size)

	PR c++/58814
	* typeck.c (cp_build_modify_expr): Make the RHS an rvalue before
	stabilizing.

From-SVN: r207163

gcc/cp/ChangeLog

 2014-01-27  Jason Merrill  <jason@redhat.com>
 
+	PR c++/58814
+	* typeck.c (cp_build_modify_expr): Make the RHS an rvalue before
+	stabilizing.
+
 	PR c++/58837
 	* typeck.c (cp_truthvalue_conversion): Use explicit comparison for
 	FUNCTION_DECL.

gcc/cp/typeck.c

@@ -7399,8 +7399,7 @@ cp_build_modify_expr (tree lhs, enum tree_code modifycode, tree rhs,
 	     side effect associated with any single compound assignment
 	     operator. -- end note ]  */
 	  lhs = stabilize_reference (lhs);
-	  if (TREE_SIDE_EFFECTS (rhs))
-	    rhs = mark_rvalue_use (rhs);
+	  rhs = rvalue (rhs);
 	  rhs = stabilize_expr (rhs, &init);
 	  newrhs = cp_build_binary_op (input_location,
 				       modifycode, lhs, rhs,

gcc/testsuite/g++.dg/ext/vector25.C

+volatile int i __attribute__((vector_size(8)));
+
+void foo()
+{
+  i += i;
+}