PR c++/83947 - ICE with auto declarations.

	* pt.c (do_auto_deduction): Don't deduce from an auto decl.
	* decl.c (undeduced_auto_decl): Limit to vars and fns.

From-SVN: r257000

gcc/cp/ChangeLog

+2018-01-23  Jason Merrill  <jason@redhat.com>
+
+	PR c++/83947 - ICE with auto declarations.
+	* pt.c (do_auto_deduction): Don't deduce from an auto decl.
+	* decl.c (undeduced_auto_decl): Limit to vars and fns.
+
 2018-01-23  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c++/83974

gcc/cp/decl.c

@@ -16195,15 +16195,17 @@ fndecl_declared_return_type (tree fn)
   return TREE_TYPE (TREE_TYPE (fn));
 }
 
-/* Returns true iff DECL was declared with an auto type and it has
-   not yet been deduced to a real type.  */
+/* Returns true iff DECL is a variable or function declared with an auto type
+   that has not yet been deduced to a real type.  */
 
 bool
 undeduced_auto_decl (tree decl)
 {
   if (cxx_dialect < cxx11)
     return false;
-  return type_uses_auto (TREE_TYPE (decl));
+  return ((VAR_OR_FUNCTION_DECL_P (decl)
+	   || TREE_CODE (decl) == TEMPLATE_DECL)
+	  && type_uses_auto (TREE_TYPE (decl)));
 }
 
 /* Complain if DECL has an undeduced return type.  */

gcc/cp/pt.c

@@ -25884,6 +25884,10 @@ do_auto_deduction (tree type, tree init, tree auto_node,
        from ahead of time isn't worth the trouble.  */
     return type;
 
+  /* Similarly, we can't deduce from another undeduced decl.  */
+  if (init && undeduced_auto_decl (init))
+    return type;
+
   if (tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node))
     /* C++17 class template argument deduction.  */
     return do_class_deduction (type, tmpl, init, flags, complain);

gcc/testsuite/g++.dg/cpp1y/auto-fn46.C

+// PR c++/83947
+// { dg-do compile { target c++14 } }
+
+auto f ();
+template < int > auto g (f);	// { dg-error "before deduction" }
+auto h = g < 0 > ();