re PR c++/67364 ("accessing uninitialized member" error in constexpr context)

	PR c++/67364
	* constexpr.c (cxx_eval_component_reference): Don't complain about
	unevaluated empty classes.

From-SVN: r233716

gcc/cp/ChangeLog

 2016-02-25  Jason Merrill  <jason@redhat.com>
 
+	PR c++/67364
+	* constexpr.c (cxx_eval_component_reference): Don't complain about
+	unevaluated empty classes.
+
 	PR c++/68049
 	* tree.c (strip_typedefs): Use DECL_ORIGINAL_TYPE.
 

gcc/cp/constexpr.c

@@ -1983,7 +1983,8 @@ cxx_eval_component_reference (const constexpr_ctx *ctx, tree t,
       return t;
     }
 
-  if (CONSTRUCTOR_NO_IMPLICIT_ZERO (whole))
+  if (CONSTRUCTOR_NO_IMPLICIT_ZERO (whole)
+      && !is_empty_class (TREE_TYPE (part)))
     {
       /* 'whole' is part of the aggregate initializer we're currently
 	 building; if there's no initializer for this member yet, that's an

gcc/testsuite/g++.dg/cpp0x/constexpr-empty10.C

+// PR c++/67364
+// { dg-do compile { target c++11 } }
+
+template <typename Xn>
+struct element : Xn {
+  constexpr element() : Xn() { }
+};
+
+template <typename Xn>
+struct closure {
+  element<Xn> member;
+  constexpr closure() { }
+};
+
+struct empty { };
+constexpr closure<empty> tup{};
+constexpr empty first = tup.member;