[PATCH] c++: unifying equal NONTYPE_ARGUMENT_PACKs [PR102547]

[Patrick Palka <ppalka@redhat.com>]

Here during partial ordering of the two partial specializations we end
up in unify with parm=arg=NONTYPE_ARGUMENT_PACK<V0, V1>, and crash shortly
thereafter because uses_template_parms calls potential_constant_expression
which doesn't handle NONTYPE_ARGUMENT_PACK.

This patch fixes this by checking dependent_template_arg_p instead of
uses_template_parms when parm==arg, which does handle NONTYPE_ARGUMENT_PACK.
We could also perhaps fix uses_template_parms / inst_dep_expr_p to better
handle NONTYPE_ARGUMENT_PACK, but interestingly none of our existing tests
exercise calling those functions on NONTYPE_ARGUMENT_PACK, so such a fix
would be seemingly moot.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/11?

	PR c++/102547

gcc/cp/ChangeLog:

	* pt.c (unify): Check dependent_template_arg_p instead of
	uses_template_parms when parm==arg.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/variadic-partial2.C: New test.
---
 gcc/cp/pt.c                                   |  2 +-
 .../g++.dg/cpp0x/variadic-partial2.C          | 16 ++++++++++++++
 .../g++.dg/cpp0x/variadic-partial2a.C         | 22 +++++++++++++++++++
 3 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/variadic-partial2.C
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/variadic-partial2a.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 1dcdffe322a..59c00c77a30 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -23587,7 +23587,7 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
      even if ARG == PARM, since we won't record unifications for the
      template parameters.  We might need them if we're trying to
      figure out which of two things is more specialized.  */
-  if (arg == parm && !uses_template_parms (parm))
+  if (arg == parm && !dependent_template_arg_p (parm))
     return unify_success (explain_p);
 
   /* Handle init lists early, so the rest of the function can assume
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic-partial2.C b/gcc/testsuite/g++.dg/cpp0x/variadic-partial2.C
new file mode 100644
index 00000000000..df61f26a3c1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic-partial2.C
@@ -0,0 +1,16 @@
+// PR c++/102547
+// { dg-do compile { target c++11 } }
+
+template<int... Vs>
+struct vals { };
+
+template<class V, class T>
+struct vals_client { };
+
+template<int V0, int V1, class T>
+struct vals_client<vals<V0, V1>, T> { };
+
+template<int V0, int V1>
+struct vals_client<vals<V0, V1>, void> { };
+
+template struct vals_client<vals<1, 2>, void>; //- "sorry, unimplemented..., ICE"
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic-partial2a.C b/gcc/testsuite/g++.dg/cpp0x/variadic-partial2a.C
new file mode 100644
index 00000000000..cc0ea488ad3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic-partial2a.C
@@ -0,0 +1,22 @@
+// PR c++/102547
+// { dg-do compile { target c++11 } }
+// A version of variadic-partial2.C where the partial ordering is performed
+// on function templates instead of class templates.
+
+template<int... Vs>
+struct vals { };
+
+template<class V, class T>
+void f(V, T) { };
+
+template<int V0, int V1, class T>
+void f(vals<V0, V1>, T) { };
+
+template<int V0, int V1>
+void f(vals<V0, V1>, char) { };
+
+template void f(vals<1, 2>, char); //- "sorry, unimplemented..., ICE"
+
+int main() {
+  f(vals<1, 3>{}, 'a'); //- "sorry, unimplemented..., ICE"
+}
-- 
2.33.0.610.gcefe983a32