On 5/1/24 11:27 AM, Jason Merrill wrote:
On 5/1/24 07:11, Patrick Palka wrote:
On Wed, 1 May 2024, Nathaniel Shead wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
-- >8 --
When calling instantiate_pending_templates at end of parsing, any new
functions that are instantiated from this point have their module
purview set based on the current value of module_kind.
This is unideal, however, as the modules code will then treat these
instantiations as reachable and cause large swathes of the GMF to be
emitted into the module CMI, despite no code in the actual module
purview referencing it.
This patch fixes this by also remembering the value of module_kind when
the instantiation was deferred, and restoring it when doing this
deferred instantiation. That way newly instantiated declarations
appropriately get a DECL_MODULE_PURVIEW_P appropriate for where the
instantiation was required, meaning that GMF entities won't be counted
as reachable unless referenced by an actually reachable entity.
Note that purviewness and attachment etc. is generally only determined
by the base template: this is purely for determining whether a
specialisation was declared in the module purview and hence whether it
should be streamed out. See the comment on 'set_instantiating_module'.
PR c++/114630
PR c++/114795
gcc/cp/ChangeLog:
* cp-tree.h (struct tinst_level): Add field for tracking
module_kind.
* pt.cc (push_tinst_level_loc): Cache module_kind in new_level.
(reopen_tinst_level): Restore module_kind from level.
(instantiate_pending_templates): Save and restore module_kind so
it isn't affected by reopen_tinst_level.
LGTM. Another approach is to instantiate all so-far deferred
instantiations and vtables once we reach the start of the module
purview, but your approach is much cleaner.
Hmm, I actually think I like the approach of instantiating at that point
better, so that instantiations in the GMF can't depend on things in
module purview.
And probably do the same again when switching to the private module
fragment, when that's implemented.
Patrick mentioned these patches again today; I still think this is the
right approach, particularly for the private module fragment.
That said, could we just clear module_kind at EOF? As you say, only the
purviewness of the template matters for implicit instantiations. It is
seeming to me like "set_instantiating_module" should only apply for
explicit instantiations, at the point of the explicit instantiation
declaration.
Jason
