re PR c++/68683 ([concepts] function satisfy_argument_deduction_constraint…

re PR c++/68683 ([concepts] function satisfy_argument_deduction_constraint modifies a type tree node but leaves TYPE_CANONICAL unchanged)

	PR c++/68683
	* constraint.cc (satisfy_argument_deduction_constraint): Set
	TYPE_CANONICAL to NULL_TREE if PLACEHOLDER_TYPE_CONSTRAINTS are
	changed.

From-SVN: r231385

gcc/cp/ChangeLog

+2015-12-07  Ryan Burn  <contact@rnburn.com>
+
+	PR c++/68683
+	* constraint.cc (satisfy_argument_deduction_constraint): Set
+	TYPE_CANONICAL to NULL_TREE if PLACEHOLDER_TYPE_CONSTRAINTS are
+	changed.
+
 2015-12-07  Jason Merrill  <jason@redhat.com>
 
 	PR c++/68464

gcc/cp/constraint.cc

@@ -1871,11 +1871,14 @@ satisfy_argument_deduction_constraint (tree t, tree args,
   tree pattern = DEDUCT_CONSTR_PATTERN (t);
   tree placeholder = DEDUCT_CONSTR_PLACEHOLDER (t);
   tree constr = PLACEHOLDER_TYPE_CONSTRAINTS (placeholder);
+  tree type_canonical = TYPE_CANONICAL (placeholder);
   PLACEHOLDER_TYPE_CONSTRAINTS (placeholder)
     = tsubst_constraint (constr, args, complain|tf_partial, in_decl);
+  TYPE_CANONICAL (placeholder) = NULL_TREE;
   tree type = do_auto_deduction (pattern, init, placeholder,
                                  complain, adc_requirement);
   PLACEHOLDER_TYPE_CONSTRAINTS (placeholder) = constr;
+  TYPE_CANONICAL (placeholder) = type_canonical;
   if (type == error_mark_node)
     return boolean_false_node;
 

gcc/testsuite/g++.dg/concepts/pr68683.C

+// { dg-options "-std=c++1z" }
+
+template <typename, typename>
+struct is_same {
+  static constexpr bool value = true;
+};
+
+template <typename T, typename U>
+concept bool Same = is_same<T, U>::value;
+
+template <typename T>
+concept bool Integral = requires {
+  { T () } -> Same<typename T::value_type>;
+};
+
+struct A {
+  using value_type = bool;
+};
+
+int main () {
+  Integral<A>;
+  Integral<A>;
+  return 0;
+}