CWG 1847 - Clarifying compatibility during partial ordering

	* pt.c (more_specialized_fn): No order between two non-deducible
	parameters.

From-SVN: r247856

gcc/cp/ChangeLog

 2017-05-10  Jason Merrill  <jason@redhat.com>
 
+	CWG 1847 - Clarifying compatibility during partial ordering
+	* pt.c (more_specialized_fn): No order between two non-deducible
+	parameters.
+
 	* pt.c (dependent_type_p): Make sure we aren't called with
 	global_type_node.
 

gcc/cp/pt.c

@@ -21182,6 +21182,13 @@ more_specialized_fn (tree pat1, tree pat2, int len)
           len = 0;
         }
 
+      /* DR 1847: If a particular P contains no template-parameters that
+	 participate in template argument deduction, that P is not used to
+	 determine the ordering.  */
+      if (!uses_deducible_template_parms (arg1)
+	  && !uses_deducible_template_parms (arg2))
+	goto next;
+
       if (TREE_CODE (arg1) == REFERENCE_TYPE)
 	{
 	  ref1 = TYPE_REF_IS_RVALUE (arg1) + 1;
@@ -21303,6 +21310,8 @@ more_specialized_fn (tree pat1, tree pat2, int len)
 	   These must be unordered.  */
 	break;
 
+    next:
+
       if (TREE_CODE (arg1) == TYPE_PACK_EXPANSION
           || TREE_CODE (arg2) == TYPE_PACK_EXPANSION)
         /* We have already processed all of the arguments in our

gcc/testsuite/g++.dg/template/partial-order1.C

+// { dg-do compile { target c++11 } }
+
+using size_t = decltype(sizeof(0));
+template <class T> struct A
+{
+  using size_type = size_t;
+};
+
+template <class T>
+void f(size_t, T);
+
+template <class T>
+void f(typename A<T>::size_type, T);
+
+int main()
+{
+  f(1,2);			// { dg-error "ambiguous" }
+}