Fix PR c++/70347 (default member initializer not picked up by union)

gcc/cp/ChangeLog:

	PR c++/70347
	* typeck.c (process_init_constructor_union): If the initializer
	is empty, use the union's NSDMI if it has one.

gcc/testsuite/ChangeLog:

	PR c++/70347
	* g++.dg/cpp1y/nsdmi-union1.C: New test.

From-SVN: r234443

gcc/cp/ChangeLog

 2016-03-23  Patrick Palka  <ppalka@gcc.gnu.org>
 
+	PR c++/70347
+	* typeck.c (process_init_constructor_union): If the initializer
+	is empty, use the union's NSDMI if it has one.
+
+2016-03-23  Patrick Palka  <ppalka@gcc.gnu.org>
+
 	PR c++/70332
 	* pt.c (tsubst_copy) [PARM_DECL]: Handle the use of 'this' in an
 	NSDMI that's part of an aggregrate initialization.

gcc/cp/typeck2.c

@@ -1499,9 +1499,24 @@ process_init_constructor_union (tree type, tree init,
   constructor_elt *ce;
   int len;
 
-  /* If the initializer was empty, use default zero initialization.  */
+  /* If the initializer was empty, use the union's NSDMI if it has one.
+     Otherwise use default zero initialization.  */
   if (vec_safe_is_empty (CONSTRUCTOR_ELTS (init)))
-    return 0;
+    {
+      for (tree field = TYPE_FIELDS (type); field; field = TREE_CHAIN (field))
+	{
+	  if (DECL_INITIAL (field))
+	    {
+	      CONSTRUCTOR_APPEND_ELT (CONSTRUCTOR_ELTS (init),
+				      field,
+				      get_nsdmi (field, /*in_ctor=*/false));
+	      break;
+	    }
+	}
+
+      if (vec_safe_is_empty (CONSTRUCTOR_ELTS (init)))
+	return 0;
+    }
 
   len = CONSTRUCTOR_ELTS (init)->length ();
   if (len > 1)

gcc/testsuite/ChangeLog

 2016-03-23  Patrick Palka  <ppalka@gcc.gnu.org>
 
+	PR c++/70347
+	* g++.dg/cpp1y/nsdmi-union1.C: New test.
+
+2016-03-23  Patrick Palka  <ppalka@gcc.gnu.org>
+
 	PR c++/70332
 	* g++.dg/cpp1y/nsdmi-aggr5.C: New test.
 

gcc/testsuite/g++.dg/cpp1y/nsdmi-union1.C

+// PR c++/70347
+// { dg-do run { target c++14 } }
+
+union A {
+  char a;
+  long b = -42;
+};
+
+struct B {
+  union {
+    char a = 10;
+    long b;
+  };
+};
+
+A c1{};
+A c2{4};
+B c3{};
+B c4{{9}};
+
+int main() {
+  if (c1.b != -42)
+    __builtin_abort ();
+
+  if (c2.a != 4)
+    __builtin_abort ();
+
+  if (c3.a != 10)
+    __builtin_abort ();
+
+  if (c4.a != 9)
+    __builtin_abort ();
+}