re PR c++/51406 ([c++0x] Incorrect result of static_cast to rvalue reference to base class.)

	PR c++/51406

	* typeck.c (build_static_cast_1): Avoid folding back to lvalue.

From-SVN: r233946

gcc/cp/ChangeLog

 2016-03-03  Jason Merrill  <jason@redhat.com>
 
+	PR c++/51406
+	* typeck.c (build_static_cast_1): Avoid folding back to lvalue.
+
 	PR c++/67364
 	* constexpr.c (cxx_eval_component_reference): Just return an empty
 	CONSTRUCTOR for an empty class.

gcc/cp/typeck.c

@@ -6704,11 +6704,7 @@ build_static_cast_1 (tree type, tree expr, bool c_cast_p,
 	  tree lref = cp_build_reference_type (TREE_TYPE (type), false);
 	  result = (perform_direct_initialization_if_possible
 		    (lref, expr, c_cast_p, complain));
-	  result = cp_fold_convert (type, result);
-	  /* Make sure we don't fold back down to a named rvalue reference,
-	     because that would be an lvalue.  */
-	  if (DECL_P (result))
-	    result = build1 (NON_LVALUE_EXPR, type, result);
+	  result = build1 (NON_LVALUE_EXPR, type, result);
 	  return convert_from_reference (result);
 	}
       else

gcc/testsuite/g++.dg/cpp0x/rv-cast5.C

+// { dg-do compile { target c++11 } }
+
+template <typename T>
+struct hold {
+  T value;
+  constexpr T&& operator()() && { return static_cast<T&&>(value); }
+};
+
+int main()
+{
+  hold<bool&&>{42}();
+}