re PR c++/84927 (ICE with NSDMI and reference)

	PR c++/84927
	* constexpr.c (cxx_eval_bare_aggregate): Update constructor's flags
	as we evaluate the elements.
	(cxx_eval_constant_expression): Verify constructor's flags
	unconditionally.

	* g++.dg/cpp1y/nsdmi-aggr9.C: New test.

From-SVN: r258691

gcc/cp/ChangeLog

+2018-03-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/84978, ICE with NRVO.
+	* constexpr.c (cxx_eval_constant_expression): Handle the case when
+	a RESULT_DECL isn't in the hash map.
+
 2018-03-20  Jason Merrill  <jason@redhat.com>
 
 	PR c++/84978, ICE with NRVO.

gcc/cp/constexpr.c

@@ -4111,7 +4111,15 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
       /* We ask for an rvalue for the RESULT_DECL when indirecting
 	 through an invisible reference, or in named return value
 	 optimization.  */
-      return (*ctx->values->get (t));
+      if (tree *p = ctx->values->get (t))
+	return *p;
+      else
+	{
+	  if (!ctx->quiet)
+	    error ("%qE is not a constant expression", t);
+	  *non_constant_p = true;
+	}
+      break;
 
     case VAR_DECL:
       if (DECL_HAS_VALUE_EXPR_P (t))

gcc/testsuite/ChangeLog

+2018-03-20  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/84978, ICE with NRVO.
+	* g++.dg/opt/nrv19.C: New test.
+
 2018-03-20  Nathan Sidwell  <nathan@acm.org>
 
 	PR c++/84962

gcc/testsuite/g++.dg/opt/nrv19.C

+// PR c++/84978
+// { dg-do compile }
+
+struct S {
+  void (*fn)();
+  int a[10];
+};
+
+S
+foo ()
+{
+  S s;
+  s.fn ();
+  return s;
+}