C++ PATCH to add test for c++/90236

[Marek Polacek]

This valid test started to be accepted with r265789, which removed the
following checks.  I wonder if we want to remove them in gcc 8, or
just leave them in place.  For trunk I'm going to add the new test.

@@ -6985,27 +7071,10 @@ convert_nontype_argument (tree type, tree expr, 
tsubst_flags_t complain)
       itself value-dependent, since what we want here is its address.  */;
       else
    {
-     if (!DECL_P (expr))
-       {
-         if (complain & tf_error)
-       error ("%qE is not a valid template argument for type %qT "
-              "because it is not an object with linkage",
-              expr, type);
-         return NULL_TREE;
-       }
-
-     /* DR 1155 allows internal linkage in C++11 and up.  */
-     linkage_kind linkage = decl_linkage (expr);
-     if (linkage < (cxx_dialect >= cxx11 ? lk_internal : lk_external))
-       {
-         if (complain & tf_error)
-       error ("%qE is not a valid template argument for type %qT "
-              "because object %qD does not have linkage",
-              expr, type, expr);
-         return NULL_TREE;
-       }
-
      expr = build_address (expr);
+
+     if (invalid_tparm_referent_p (type, expr, complain))
+       return NULL_TREE;
    }

       if (!same_type_p (type, TREE_TYPE (expr)))

Tested on x86_64-linux, applying to trunk.

2019-04-24  Marek Polacek  <pola...@redhat.com>

        PR c++/90236
        * g++.dg/cpp1z/nontype-auto16.C: New test.

diff --git gcc/testsuite/g++.dg/cpp1z/nontype-auto16.C 
gcc/testsuite/g++.dg/cpp1z/nontype-auto16.C
new file mode 100644
index 00000000000..695bb11d780
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp1z/nontype-auto16.C
@@ -0,0 +1,13 @@
+// PR c++/90236
+// { dg-do compile { target c++17 } }
+
+struct foo { };
+
+template <const auto &> void fnc() { } 
+
+void
+test()
+{
+  static constexpr foo a;
+  fnc<a>();
+}