Re: [PATCH] c++: redundant targ coercion for var/alias tmpls

[Patrick Palka <ppalka@redhat.com>]

On Wed, Jun 28, 2023 at 11:50 AM Jason Merrill <jason@redhat.com> wrote:
>
> On 6/23/23 12:23, Patrick Palka wrote:
> > On Fri, 23 Jun 2023, Jason Merrill wrote:
> >
> >> On 6/21/23 13:19, Patrick Palka wrote:
> >>> When stepping through the variable/alias template specialization code
> >>> paths, I noticed we perform template argument coercion twice: first from
> >>> instantiate_alias_template / finish_template_variable and again from
> >>> tsubst_decl (during instantiate_template).  It should suffice to perform
> >>> coercion once.
> >>>
> >>> To that end patch elides this second coercion from tsubst_decl when
> >>> possible.  We can't get rid of it completely because we don't always
> >>> specialize a variable template from finish_template_variable: we could
> >>> also be doing so directly from instantiate_template during variable
> >>> template partial specialization selection, in which case the coercion
> >>> from tsubst_decl would be the first and only coercion.
> >>
> >> Perhaps we should be coercing in lookup_template_variable rather than
> >> finish_template_variable?
> >
> > Ah yes, there's a patch for that at
> > https://gcc.gnu.org/pipermail/gcc-patches/2023-May/617377.html :)
>
> So after that patch, can we get rid of the second coercion completely?

On second thought it should be possible to get rid of it, if we
rearrange things to always pass the primary arguments to tsubst_decl,
and perform partial specialization selection from there instead of
instantiate_template.  Let me try...

>
> Jason
>