Avoid ICE on pmf{} in template.

Now that we return the original CONSTRUCTOR from finish_compound_literal,
the call to null_member_pointer_value_p in tsubst_copy_and_build was getting
confused because the CONSTRUCTOR was still empty rather than a valid PMF
value.

	* call.c (null_member_pointer_value_p): Handle an empty CONSTRUCTOR
	of PMF type.

From-SVN: r270324

gcc/cp/ChangeLog

+2019-04-12  Jason Merrill  <jason@redhat.com>
+
+	* call.c (null_member_pointer_value_p): Handle an empty CONSTRUCTOR
+	of PMF type.
+
 2019-04-12  Marek Polacek  <polacek@redhat.com>
 
 	* except.c (build_noexcept_spec): Use build_converted_constant_bool_expr

gcc/cp/call.c

@@ -569,6 +569,7 @@ null_member_pointer_value_p (tree t)
     return false;
   else if (TYPE_PTRMEMFUNC_P (type))
     return (TREE_CODE (t) == CONSTRUCTOR
+	    && CONSTRUCTOR_NELTS (t)
 	    && integer_zerop (CONSTRUCTOR_ELT (t, 0)->value));
   else if (TYPE_PTRDATAMEM_P (type))
     return integer_all_onesp (t);

gcc/testsuite/g++.dg/cpp0x/initlist-pmf1.C

+// { dg-do compile { target c++11 } }
+
+struct A
+{
+  void f();
+};
+
+using ftype = decltype(&A::f);
+
+template <class T>
+bool f()
+{
+  ftype p = ftype{};
+  return p;
+}
+
+int main()
+{
+  f<int>();
+}