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

[Patrick Palka]

On Fri, 1 Oct 2021, Jason Merrill wrote:

> On 10/1/21 09:46, Patrick Palka wrote:
> > 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,
> 
> Please.

Sounds good, like the following then?  Passes light testing, bootstrap
and regtest on progress.

-- >8 --

	PR c++/102547

gcc/cp/ChangeLog:

	* pt.c (instantiation_dependent_expression_p): Sidestep checking
	potential_constant_expression on NONTYPE_ARGUMENT_PACK.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/variadic-partial2.C: New test.
	* g++.dg/cpp0x/variadic-partial2a.C: New test.
---
 gcc/cp/pt.c                                   |  4 +++-
 .../g++.dg/cpp0x/variadic-partial2.C          | 16 ++++++++++++++
 .../g++.dg/cpp0x/variadic-partial2a.C         | 22 +++++++++++++++++++
 3 files changed, 41 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..643204103c5 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -27705,7 +27705,9 @@ instantiation_dependent_expression_p (tree expression)
 {
   return (instantiation_dependent_uneval_expression_p (expression)
 	  || (processing_template_decl
-	      && potential_constant_expression (expression)
+	      && expression != NULL_TREE
+	      && (TREE_CODE (expression) == NONTYPE_ARGUMENT_PACK
+		  || potential_constant_expression (expression))
 	      && value_dependent_expression_p (expression)));
 }
 
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