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

	PR c++/67364

	* constexpr.c (cxx_eval_component_reference): Just return an empty
	CONSTRUCTOR for an empty class.

From-SVN: r233945

gcc/cp/ChangeLog

+2016-03-03  Jason Merrill  <jason@redhat.com>
+
+	PR c++/67364
+	* constexpr.c (cxx_eval_component_reference): Just return an empty
+	CONSTRUCTOR for an empty class.
+
 2016-03-01  Jason Merrill  <jason@redhat.com>
 
 	PR c++/70036

gcc/cp/constexpr.c

@@ -1988,11 +1988,12 @@ cxx_eval_component_reference (const constexpr_ctx *ctx, tree t,
     }
 
   if (CONSTRUCTOR_NO_IMPLICIT_ZERO (whole)
-      && !is_empty_class (TREE_TYPE (part)))
+      && !is_really_empty_class (TREE_TYPE (t)))
     {
       /* 'whole' is part of the aggregate initializer we're currently
 	 building; if there's no initializer for this member yet, that's an
-	 error. */
+	 error.  But expand_aggr_init_1 doesn't bother to initialize really
+	 empty classes, so ignore them here, too.  */
       if (!ctx->quiet)
 	error ("accessing uninitialized member %qD", part);
       *non_constant_p = true;

gcc/testsuite/g++.dg/cpp0x/constexpr-empty11.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 { struct {} s; };
+constexpr closure<empty> tup{};
+constexpr empty first = tup.member;