PR c++/79549 - C++17 ICE with non-type auto template parameter pack

	* pt.c (convert_template_argument): Just return an auto arg pack.
	(tsubst_template_args): Don't tsubst an auto pack type.

From-SVN: r245544

gcc/cp/ChangeLog

 2017-02-17  Jason Merrill  <jason@redhat.com>
 
+	PR c++/79549 - C++17 ICE with non-type auto template parameter pack
+	* pt.c (convert_template_argument): Just return an auto arg pack.
+	(tsubst_template_args): Don't tsubst an auto pack type.
+
 	PR c++/79556 - C++17 ICE with non-type auto
 	* pt.c (do_auto_deduction): Don't try to deduce from null type.
 

gcc/cp/pt.c

@@ -7612,6 +7612,10 @@ convert_template_argument (tree parm,
 
       if (tree a = type_uses_auto (t))
 	{
+	  if (ARGUMENT_PACK_P (orig_arg))
+	    /* There's nothing to check for an auto argument pack.  */
+	    return orig_arg;
+
 	  t = do_auto_deduction (t, arg, a, complain, adc_unify, args);
 	  if (t == error_mark_node)
 	    return error_mark_node;
@@ -11649,8 +11653,11 @@ tsubst_template_args (tree t, tree args, tsubst_flags_t complain, tree in_decl)
             new_arg = error_mark_node;
 
           if (TREE_CODE (new_arg) == NONTYPE_ARGUMENT_PACK) {
-            TREE_TYPE (new_arg) = tsubst (TREE_TYPE (orig_arg), args,
-                                          complain, in_decl);
+	    if (type_uses_auto (TREE_TYPE (orig_arg)))
+	      TREE_TYPE (new_arg) = TREE_TYPE (orig_arg);
+	    else
+	      TREE_TYPE (new_arg) = tsubst (TREE_TYPE (orig_arg), args,
+					    complain, in_decl);
             TREE_CONSTANT (new_arg) = TREE_CONSTANT (orig_arg);
 
             if (TREE_TYPE (new_arg) == error_mark_node)

gcc/testsuite/g++.dg/cpp1z/nontype-auto8.C

+// PR c++/79549
+// { dg-options -std=c++1z }
+
+template <auto...>
+struct meow;
+
+template <auto C>
+struct meow<C> { };
+
+meow<1> m;