C++ PATCH for c++/80639, ICE with invalid PMF initialization

[Jason Merrill]

In this testcase, instantiate_type resolves the overload, but the
result is a pointer to the wrong class; we need to then try to convert
it to the desired type in order to get the diagnostic we want.

Tested x86_64-pc-linux-gnu, applying to trunk and 7.

commit 9248f1e42712d3edfc5447e6df371b1458bc4f5e
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Jun 15 18:17:19 2017 -0400

            PR c++/80639 - ICE with invalid PMF initialization.
    
            PR c++/80043 - ICE with -fpermissive
            * typeck.c (convert_for_assignment): Recurse when instantiate_type
            returns without an error.

diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index 05b4fbb..0f22e64 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -8590,9 +8590,10 @@ convert_for_assignment (tree type, tree rhs,
              if (rhstype == unknown_type_node)
                {
                  tree r = instantiate_type (type, rhs, tf_warning_or_error);
-                 /* -fpermissive might allow this.  */
+                 /* -fpermissive might allow this; recurse.  */
                  if (!seen_error ())
-                   return r;
+                   return convert_for_assignment (type, r, errtype, fndecl,
+                                                  parmnum, complain, flags);
                }
              else if (fndecl)
                error ("cannot convert %qH to %qI for argument %qP to %qD",
diff --git a/gcc/testsuite/g++.dg/template/ptrmem31.C 
b/gcc/testsuite/g++.dg/template/ptrmem31.C
new file mode 100644
index 0000000..5c66b72
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ptrmem31.C
@@ -0,0 +1,23 @@
+// PR c++/80639
+// { dg-do compile { target c++14 } }
+
+template < typename > struct A;
+
+struct B
+{ 
+  template < int > void m ();
+  template < int > struct K { static void n (); };
+  void p () { K < 0 >::n (); }
+};
+
+template <> struct A < B >
+{ 
+  using T = void (A::*)();
+  template < int u > static constexpr T h = &B::m < u >; // { dg-error "cannot 
convert" }
+};
+
+template < int v > void B::K < v >::n ()
+{ 
+  using S = A < B >;
+  S::h < 0 >;
+}