PR c++/79960 - alias templates and partial ordering

* pt.c (comp_template_args): Add partial_order parm.
	(template_args_equal): Likewise.
	(comp_template_args_porder): New.
	(get_partial_spec_bindings): Use it.

From-SVN: r246042

gcc/cp/ChangeLog

@@ -1,3 +1,11 @@
+2017-03-10  Jason Merrill  <jason@redhat.com>
+
+	PR c++/79960 - alias templates and partial ordering
+	* pt.c (comp_template_args): Add partial_order parm.
+	(template_args_equal): Likewise.
+	(comp_template_args_porder): New.
+	(get_partial_spec_bindings): Use it.
+
 2017-03-10  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/79967

gcc/cp/cp-tree.h

@@ -6208,8 +6208,8 @@ extern int is_specialization_of			(tree, tree);
 extern bool is_specialization_of_friend		(tree, tree);
 extern tree get_pattern_parm			(tree, tree);
 extern int comp_template_args			(tree, tree, tree * = NULL,
-						 tree * = NULL);
+						 tree * = NULL, bool = false);
-extern int template_args_equal                  (tree, tree);
+extern int template_args_equal                  (tree, tree, bool = false);
 extern tree maybe_process_partial_specialization (tree);
 extern tree most_specialized_instantiation	(tree);
 extern void print_candidates			(tree);

gcc/cp/pt.c

@@ -8240,7 +8240,7 @@ coerce_innermost_template_parms (tree parms,
 /* Returns 1 if template args OT and NT are equivalent.  */
 
 int
-template_args_equal (tree ot, tree nt)
+template_args_equal (tree ot, tree nt, bool partial_order /* = false */)
 {
   if (nt == ot)
     return 1;
@@ -8288,8 +8288,13 @@ template_args_equal (tree ot, tree nt)
 	 template argument; we need them to be distinct so that we
 	 substitute into the specialization arguments at instantiation
 	 time.  And aliases can't be equivalent without being ==, so
-	 we don't need to look any deeper.  */
+	 we don't need to look any deeper.
-      if (TYPE_ALIAS_P (nt) || TYPE_ALIAS_P (ot))
+
+         During partial ordering, however, we need to treat them normally so
+         that we can order uses of the same alias with different
+         cv-qualification (79960).  */
+      if (!partial_order
+	  && (TYPE_ALIAS_P (nt) || TYPE_ALIAS_P (ot)))
 	return false;
       else
 	return same_type_p (ot, nt);
@@ -8321,7 +8326,8 @@ template_args_equal (tree ot, tree nt)
 
 int
 comp_template_args (tree oldargs, tree newargs,
-		    tree *oldarg_ptr, tree *newarg_ptr)
+		    tree *oldarg_ptr, tree *newarg_ptr,
+		    bool partial_order)
 {
   int i;
 
@@ -8339,7 +8345,7 @@ comp_template_args (tree oldargs, tree newargs,
       tree nt = TREE_VEC_ELT (newargs, i);
       tree ot = TREE_VEC_ELT (oldargs, i);
 
-      if (! template_args_equal (ot, nt))
+      if (! template_args_equal (ot, nt, partial_order))
 	{
 	  if (oldarg_ptr != NULL)
 	    *oldarg_ptr = ot;
@@ -8351,6 +8357,12 @@ comp_template_args (tree oldargs, tree newargs,
   return 1;
 }
 
+inline bool
+comp_template_args_porder (tree oargs, tree nargs)
+{
+  return comp_template_args (oargs, nargs, NULL, NULL, true);
+}
+
 static void
 add_pending_template (tree d)
 {
@@ -21584,8 +21596,8 @@ get_partial_spec_bindings (tree tmpl, tree spec_tmpl, tree args)
   if (spec_args == error_mark_node
       /* We only need to check the innermost arguments; the other
 	 arguments will always agree.  */
-      || !comp_template_args (INNERMOST_TEMPLATE_ARGS (spec_args),
+      || !comp_template_args_porder (INNERMOST_TEMPLATE_ARGS (spec_args),
-			      INNERMOST_TEMPLATE_ARGS (args)))
+				     INNERMOST_TEMPLATE_ARGS (args)))
     return NULL_TREE;
 
   /* Now that we have bindings for all of the template arguments,

gcc/testsuite/g++.dg/cpp0x/alias-decl-57.C

@@ -0,0 +1,30 @@
+// PR c++/79960
+// { dg-do compile { target c++11 } }
+
+using size_t = decltype(sizeof(0));
+
+template<typename T> struct tuple_size;
+
+template<typename T, size_t U = tuple_size<T>::value>
+  using __has_tuple_size = T;
+
+template<typename T> struct tuple_size<const __has_tuple_size<T>> {
+  static constexpr size_t value = tuple_size<T>::value;
+};
+
+template<typename T> struct tuple_size<volatile __has_tuple_size<T>> {
+  static constexpr size_t value = tuple_size<T>::value;
+};
+
+template<typename T> struct tuple_size<const __has_tuple_size<volatile T>> {
+  static constexpr size_t value = tuple_size<T>::value;
+};
+
+template<typename... T> struct tuple { };
+template<typename... T> struct tuple_size<tuple<T...>> {
+  static constexpr size_t value = sizeof...(T);
+};
+
+static_assert( tuple_size<const tuple<>>::value == 0, "" );  // OK
+static_assert( tuple_size<volatile tuple<>>::value == 0, "" ); // OK
+static_assert( tuple_size<const volatile tuple<>>::value == 0, "" ); // FAIL