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

[Patrick Palka <ppalka@redhat.com>]

On Fri, Oct 1, 2021 at 1:29 PM Patrick Palka <ppalka@redhat.com> wrote:
>
> 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.

On second thought given that a NONTYPE_ARGUMENT_PACK is by
construction a sequence of non-type template arguments, is looping
over its elements in potential_const_expr necessary?  Maybe we should
just return true unconditionally.

>
> -- >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
>