PR c++/79393 DR 1658 workaround

	PR c++/79393 DR 1658 workaround
	* method.c (synthesized_method_base_walk): Inihibit abstract class
	virtual base access check here.
	(synthesized_method_walk): Not here.

From-SVN: r246126

gcc/cp/ChangeLog

+2017-03-14  Nathan Sidwell  <nathan@acm.org>
+
+	PR c++/79393 DR 1658 workaround
+	* method.c (synthesized_method_base_walk): Inihibit abstract class
+	virtual base access check here.
+	(synthesized_method_walk): Not here.
+
 2017-03-13  Nathan Sidwell  <nathan@acm.org>
 
 	PR c++/79393 DR 1658 workaround

gcc/cp/method.c

@@ -1420,10 +1420,10 @@ walk_field_subobs (tree fields, tree fnname, special_function_kind sfk,
     }
 }
 
-// Base walker helper for synthesized_method_walk.  Inspect a direct
-// or virtual base.  BINFO is the parent type's binfo.  BASE_BINFO is
-// the base binfo of interests.  All other parms are as for
-// synthesized_method_walk, or its local vars.
+/* Base walker helper for synthesized_method_walk.  Inspect a direct
+   or virtual base.  BINFO is the parent type's binfo.  BASE_BINFO is
+   the base binfo of interests.  All other parms are as for
+   synthesized_method_walk, or its local vars.  */
 
 static tree
 synthesized_method_base_walk (tree binfo, tree base_binfo, 
@@ -1436,7 +1436,8 @@ synthesized_method_base_walk (tree binfo, tree base_binfo,
 {
   bool inherited_binfo = false;
   tree argtype = NULL_TREE;
-  
+  deferring_kind defer = dk_no_deferred;
+
   if (copy_arg_p)
     argtype = build_stub_type (BINFO_TYPE (base_binfo), quals, move_p);
   else if ((inherited_binfo
@@ -1445,11 +1446,21 @@ synthesized_method_base_walk (tree binfo, tree base_binfo,
       argtype = inherited_parms;
       /* Don't check access on the inherited constructor.  */
       if (flag_new_inheriting_ctors)
-	push_deferring_access_checks (dk_deferred);
+	defer = dk_deferred;
     }
+  /* To be conservative, ignore access to the base dtor that
+     DR1658 instructs us to ignore.  See the comment in
+     synthesized_method_walk.  */
+  else if (cxx_dialect >= cxx14 && fnname == complete_dtor_identifier
+	   && BINFO_VIRTUAL_P (base_binfo)
+	   && ABSTRACT_CLASS_TYPE_P (BINFO_TYPE (binfo)))
+    defer = dk_no_check;
+
+  if (defer != dk_no_deferred)
+    push_deferring_access_checks (defer);
   tree rval = locate_fn_flags (base_binfo, fnname, argtype, flags,
 			       diag ? tf_warning_or_error : tf_none);
-  if (inherited_binfo && flag_new_inheriting_ctors)
+  if (defer != dk_no_deferred)
     pop_deferring_access_checks ();
 
   process_subob_fn (rval, spec_p, trivial_p, deleted_p,
@@ -1677,13 +1688,6 @@ synthesized_method_walk (tree ctype, special_function_kind sfk, bool const_p,
       if (constexpr_p)
 	*constexpr_p = false;
 
-      /* To be conservative, ignore access to the base dtor that
-	 DR1658 instructs us to ignore.  */
-      bool no_access_check = (cxx_dialect >= cxx14
-			      && ABSTRACT_CLASS_TYPE_P (ctype));
-
-      if (no_access_check)
-	push_deferring_access_checks (dk_no_check);
       FOR_EACH_VEC_ELT (*vbases, i, base_binfo)
 	synthesized_method_base_walk (binfo, base_binfo, quals,
 				      copy_arg_p, move_p, ctor_p,
@@ -1691,8 +1695,6 @@ synthesized_method_walk (tree ctype, special_function_kind sfk, bool const_p,
 				      fnname, flags, diag,
 				      spec_p, trivial_p,
 				      deleted_p, constexpr_p);
-      if (no_access_check)
-	pop_deferring_access_checks ();
     }
 
   /* Now handle the non-static data members.  */

gcc/testsuite/g++.dg/cpp1y/pr79393-2.C

+// { dg-do compile { target c++14 } }
+
+// DR 1658, inaccessible dtor of virtual base doesn't affect an
+// abstract class.  But we should stil check access to non-virtual bases.
+
+class C;
+
+struct A {
+private:
+  ~A (){  }
+  friend class C;
+};
+
+struct B : A { // { dg-error "is private" }
+  virtual bool Ok () = 0; // abstract
+};
+
+struct C : B {
+  ~C () 
+  { }  // { dg-error "use of deleted" }
+  virtual bool Ok ();
+};