Re: c++/modules: Emit definitions of ODR-used static members imported from modules [PR112899]

[Nathaniel Shead <nathanieloshead@gmail.com>]

On Thu, Jan 04, 2024 at 03:31:50PM -0500, Jason Merrill wrote:
> On 1/2/24 17:40, Nathaniel Shead wrote:
> > Static data members marked 'inline' should be emitted in TUs where they
> > are ODR-used.  We need to make sure that statics imported from modules
> > are correctly added to the 'pending_statics' map so that they get
> > emitted if needed, otherwise the attached testcase fails to link.
> 
> Hmm, this seems wrong to me; I'd think that static data members marked
> inline should be emitted in the module, and not in importers.
> 
> Jason
> 

That's what I'd initially thought too, but this is at least consistent
with non-class inlines (variables and functions), which similarly only
get emitted in TUs that they're ODR-used rather than always (and only)
being emitted within the module.

I guess an alternative would be to change it around so that all
exported definitions are marked as needed in the module interface file
(and emitted there), and then setting some flag so that they're never
emitted in importers. I'm not entirely sure what flag that would be
though, I still haven't quite wrapped my head what controls what with
regards to this, and I'm not convinced it wouldn't break template
instantiations.

I wonder if this might also be related to the issue Nathan noted with
regards to block-scope class methods, which I haven't completely worked
out how to solve yet otherwise (see
https://gcc.gnu.org/pipermail/gcc-patches/2023-November/638223.html).

Nathaniel