Avoid duplicate visibility warning.

	* decl2.c (constrain_class_visibility): Don't warn about artificial
	fields.

From-SVN: r254973

gcc/cp/ChangeLog

+2017-11-20  Jason Merrill  <jason@redhat.com>
+
+	* decl2.c (constrain_class_visibility): Don't warn about artificial
+	fields.
+
 2017-11-20  Jakub Jelinek  <jakub@redhat.com>
 
 	P0329R4: Designated Initialization

gcc/cp/decl2.c

@@ -2553,7 +2553,8 @@ constrain_class_visibility (tree type)
     vis = VISIBILITY_INTERNAL;
 
   for (t = TYPE_FIELDS (type); t; t = DECL_CHAIN (t))
-    if (TREE_CODE (t) == FIELD_DECL && TREE_TYPE (t) != error_mark_node)
+    if (TREE_CODE (t) == FIELD_DECL && TREE_TYPE (t) != error_mark_node
+	&& !DECL_ARTIFICIAL (t))
       {
 	tree ftype = strip_pointer_or_array_types (TREE_TYPE (t));
 	int subvis = type_visibility (ftype);

gcc/testsuite/g++.dg/ext/visibility/warn6.C

+struct __attribute ((visibility ("hidden"))) A { int i; };
+struct B: A { }; // { dg-warning "base" }