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.
Note that deferred instantiation can induce more deferred instantiation,
but your approach will do the right thing here (module_kind will be
inherited from the point of instantiation).
What if an instantiation is needed from both the GMF and the module
purview? Then IIUC it'll be instantiated as if from the GMF, which
seems right to me.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/modules/gmf-3.C: New test.
>
> Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
> ---
> gcc/cp/cp-tree.h | 3 +++
> gcc/cp/pt.cc | 4 ++++
> gcc/testsuite/g++.dg/modules/gmf-3.C | 13 +++++++++++++
> 3 files changed, 20 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/modules/gmf-3.C
>
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index 1938ada0268..0e619120ccc 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -6626,6 +6626,9 @@ struct GTY((chain_next ("%h.next"))) tinst_level {
> /* The location where the template is instantiated. */
> location_t locus;
>
> + /* The module kind where the template is instantiated. */
> + unsigned module_kind;
> +
> /* errorcount + sorrycount when we pushed this level. */
> unsigned short errors;
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 1c3eef60c06..401aa92bc3e 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -11277,6 +11277,7 @@ push_tinst_level_loc (tree tldcl, tree targs,
> location_t loc)
> new_level->tldcl = tldcl;
> new_level->targs = targs;
> new_level->locus = loc;
> + new_level->module_kind = module_kind;
> new_level->errors = errorcount + sorrycount;
> new_level->next = NULL;
> new_level->refcount = 0;
> @@ -11345,6 +11346,7 @@ reopen_tinst_level (struct tinst_level *level)
> for (t = level; t; t = t->next)
> ++tinst_depth;
>
> + module_kind = level->module_kind;
> set_refcount_ptr (current_tinst_level, level);
> pop_tinst_level ();
> if (current_tinst_level)
> @@ -27442,6 +27444,7 @@ instantiate_pending_templates (int retries)
> {
> int reconsider;
> location_t saved_loc = input_location;
> + unsigned saved_module_kind = module_kind;
>
> /* Instantiating templates may trigger vtable generation. This in turn
> may require further template instantiations. We place a limit here
> @@ -27532,6 +27535,7 @@ instantiate_pending_templates (int retries)
> while (reconsider);
>
> input_location = saved_loc;
> + module_kind = saved_module_kind;
> }
>
> /* Substitute ARGVEC into T, which is a list of initializers for
> diff --git a/gcc/testsuite/g++.dg/modules/gmf-3.C
> b/gcc/testsuite/g++.dg/modules/gmf-3.C
> new file mode 100644
> index 00000000000..e52ae904ea9
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/gmf-3.C
> @@ -0,0 +1,13 @@
> +// PR c++/114630
> +// { dg-additional-options "-fmodules-ts -Wno-global-module
> -fdump-lang-module" }
> +// { dg-module-cmi M }
> +
> +module;
> +template <typename> struct allocator {
> + allocator() {}
> +};
> +template class allocator<wchar_t>;
> +export module M;
> +
> +// The whole GMF should be discarded here
> +// { dg-final { scan-lang-dump "Wrote 0 clusters" module } }
> --
> 2.43.2
>
>
