PR c++/79556 - C++17 ICE with non-type auto

	* pt.c (do_auto_deduction): Don't try to deduce from null type.

From-SVN: r245543

gcc/cp/ChangeLog

 2017-02-17  Jason Merrill  <jason@redhat.com>
 
+	PR c++/79556 - C++17 ICE with non-type auto
+	* pt.c (do_auto_deduction): Don't try to deduce from null type.
+
 	PR c++/79533 - C++17 ICE with temporary cast to reference
 	* call.c (build_over_call): Conversion to a reference prevents copy
 	elision.

gcc/cp/pt.c

@@ -25191,6 +25191,10 @@ do_auto_deduction (tree type, tree init, tree auto_node,
     /* C++17 class template argument deduction.  */
     return do_class_deduction (type, tmpl, init, flags, complain);
 
+  if (TREE_TYPE (init) == NULL_TREE)
+    /* Nothing we can do with this, even in deduction context.  */
+    return type;
+
   /* [dcl.spec.auto]: Obtain P from T by replacing the occurrences of auto
      with either a new invented type template parameter U or, if the
      initializer is a braced-init-list (8.5.4), with

gcc/testsuite/g++.dg/cpp1z/nontype-auto9.C

+// PR c++/79556
+// { dg-options -std=c++1z }
+
+template <auto> struct A;
+template <auto...> struct B;
+template <int N, auto Dim, auto... Dims> struct B<N, Dim, Dims...> {
+  static auto a = A<B<Dims...>::value>::value;
+};