c++: DEPENDENT_OPERATOR_TYPE as type of NTTP [PR104074]

We're incorrectly rejecting the below testcase during template argument
coercion because invalid_nontype_parm_type_p returns true for
DEPENDENT_OPERATOR_TYPE in C++17 mode.

This patch fixes this by partially rewriting invalid_nontype_parm_type_p
in terms of WILDCARD_TYPE_P, for which DEPENDENT_OPERATOR_TYPE is true,
so that the predicate handles wildcard types consistently.

	PR c++/104074

gcc/cp/ChangeLog:

	* pt.cc (invalid_nontype_parm_type_p): Use WILDCARD_TYPE_P so
	that we return false for DEPENDENT_OPERATOR_TYPE too.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/nontype-auto20.C: New test.

1 files changed, 6 insertions, 8 deletions

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 4a2b33e..586ad1c 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -26931,16 +26931,14 @@ invalid_nontype_parm_type_p (tree type, tsubst_flags_t complain)
 	}
       return false;
     }
-  else if (TREE_CODE (type) == TYPENAME_TYPE)
-    return false;
-  else if (TREE_CODE (type) == DECLTYPE_TYPE)
-    return false;
   else if (TREE_CODE (type) == NULLPTR_TYPE)
     return false;
-  /* A bound template template parm could later be instantiated to have a valid
-     nontype parm type via an alias template.  */
-  else if (cxx_dialect >= cxx11
-	   && TREE_CODE (type) == BOUND_TEMPLATE_TEMPLATE_PARM)
+  else if (TREE_CODE (type) == BOUND_TEMPLATE_TEMPLATE_PARM
+	   && cxx_dialect < cxx11)
+    /* Fall through; before C++11 alias templates, a bound ttp
+       always instantiates into a class type.  */;
+  else if (WILDCARD_TYPE_P (type))
+    /* Any other wildcard type not already handled above is allowed.  */
     return false;
   else if (TREE_CODE (type) == COMPLEX_TYPE)
     /* Fall through.  */;