re PR c++/87934 (struct with NSDMI of enum makes initialization a non-constant expression)

	PR c++/87934
	* constexpr.c (cxx_eval_constant_expression) <case CONSTRUCTOR>: Do
	re-process TREE_CONSTANT CONSTRUCTORs if they aren't reduced constant
	expressions.

	* g++.dg/cpp0x/constexpr-87934.C: New test.

From-SVN: r267253

gcc/cp/ChangeLog

+2018-12-19  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/87934
+	* constexpr.c (cxx_eval_constant_expression) <case CONSTRUCTOR>: Do
+	re-process TREE_CONSTANT CONSTRUCTORs if they aren't reduced constant
+	expressions.
+
 2018-12-19  Alexandre Oliva <aoliva@redhat.com>
 
 	PR c++/87012

gcc/cp/constexpr.c

@@ -4681,7 +4681,7 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
       break;
 
     case CONSTRUCTOR:
-      if (TREE_CONSTANT (t))
+      if (TREE_CONSTANT (t) && reduced_constant_expression_p (t))
 	{
 	  /* Don't re-process a constant CONSTRUCTOR, but do fold it to
 	     VECTOR_CST if applicable.  */

gcc/testsuite/ChangeLog

+2018-12-19  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/87934
+	* g++.dg/cpp0x/constexpr-87934.C: New test.
+
 2018-12-19  Alexandre Oliva <aoliva@redhat.com>
 
 	PR testsuite/86153

gcc/testsuite/g++.dg/cpp0x/constexpr-87934.C

+// PR c++/87934
+// { dg-do compile { target c++11 } }
+
+struct Foo
+{
+  enum { BAR } bar = BAR;
+};
+
+constexpr Foo foo{};