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

[Patrick Palka <ppalka@redhat.com>]

On Fri, 1 Oct 2021, Jason Merrill wrote:

> On 10/1/21 10:26, Patrick Palka wrote:
> > 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))
> 
> I'd prefer to loop over the elements of the pack, either here or (probably
> better) in potential_constant_expression.

Ah, makes sense.  Like so?  Bootstrapped and regtested on
x86_64-pc-linux-gnu.

-- >8 --

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.

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

	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 18d9d117a48..e95ff00774f 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 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..e98bdbbc07b
--- /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"
+}
-- 
2.33.0.610.gcefe983a32