From d4c470c376b4cb82c9a0b7e8a4b88c44d5e4289d Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Tue, 5 Oct 2021 15:35:21 -0400
Subject: [PATCH] c++: unifying equal NONTYPE_ARGUMENT_PACKs [PR102547]

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(parms) calls potential_const_expr
which doesn't handle NONTYPE_ARGUMENT_PACK.

This patch fixes this by extending potential_constant_expression to handle
NONTYPE_ARGUMENT_PACK appropriately.

	PR c++/102547

gcc/cp/ChangeLog:

	* constexpr.c (potential_constant_expression_1): Handle
	NONTYPE_ARGUMENT_PACK.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/variadic-partial2.C: New test.
	* g++.dg/cpp0x/variadic-partial2a.C: New test.
---
 gcc/cp/constexpr.c                            | 10 +++++++++
 .../g++.dg/cpp0x/variadic-partial2.C          | 16 ++++++++++++++
 .../g++.dg/cpp0x/variadic-partial2a.C         | 22 +++++++++++++++++++
 3 files changed, 48 insertions(+)
 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/constexpr.c b/gcc/cp/constexpr.c
index 18d9d117a48b..e95ff00774fc 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -9043,6 +9043,16 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
     case CO_RETURN_EXPR:
       return false;
 
+    case NONTYPE_ARGUMENT_PACK:
+      {
+	tree args = ARGUMENT_PACK_ARGS (t);
+	int len = TREE_VEC_LENGTH (args);
+	for (int i = 0; i < len; ++i)
+	  if (!RECUR (TREE_VEC_ELT (args, i), any))
+	    return false;
+	return true;
+      }
+
     default:
       if (objc_non_constant_expr_p (t))
 	return false;
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 000000000000..df61f26a3c16
--- /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 000000000000..e98bdbbc07bf
--- /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 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"
+}
-- 
2.47.2