On Tue, 4 Oct 2022, Patrick Palka wrote:
> Here when lazily loading the binding for f at parse time from the
> template g, processing_template_decl is set and thus the call to
> note_vague_linkage_fn from module_state::read_cluster has no effect,
> and we never push f onto deferred_fns and end up never emitting its
> definition.
>
> ISTM the behavior of the lazy loading machinery shouldn't be sensitive
> to whether we're inside a template, and therefore we should probably be
> clearing processing_template_decl somewhere e.g in lazy_load_binding.
> This is sufficient to fix the testcase.
>
> But it also seems the processing_template_decl test in
> note_vague_linkage_fn, added by r8-7539-g977bc3ee11383e for PR84973, is
> perhaps too strong: if the intent is to avoid deferring output for
> uninstantiated templates, we should make sure that DECL in question is
> an uninstantiated template by checking e.g. value_dependent_expression_p.
> This too is sufficient to fix the testcase (since f isn't a template)
> and survives bootstrap and regtest.
>
> Does one or the other approach look like the correct fix for this PR?
>
> PR c++/99377
>
> gcc/cp/ChangeLog:
>
> * decl2.cc (note_vague_linkage_fn): Relax processing_template_decl
> test to value_dependent_expression_p.
> * module.cc (lazy_load_binding): Clear processing_template_decl.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/modules/pr99377-2_a.C: New test.
> * g++.dg/modules/pr99377-2_b.C: New test.
> ---
> gcc/cp/decl2.cc | 2 +-
> gcc/cp/module.cc | 2 ++
> gcc/testsuite/g++.dg/modules/pr99377-2_a.C | 5 +++++
> gcc/testsuite/g++.dg/modules/pr99377-2_b.C | 6 ++++++
> 4 files changed, 14 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/modules/pr99377-2_a.C
> create mode 100644 gcc/testsuite/g++.dg/modules/pr99377-2_b.C
>
> diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
> index 9f18466192f..5af4d17ee3b 100644
> --- a/gcc/cp/decl2.cc
> +++ b/gcc/cp/decl2.cc
> @@ -876,7 +876,7 @@ check_classfn (tree ctype, tree function, tree
> template_parms)
> void
> note_vague_linkage_fn (tree decl)
> {
> - if (processing_template_decl)
> + if (value_dependent_expression_p (decl))
> return;
>
> DECL_DEFER_OUTPUT (decl) = 1;
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index 500ac06563a..79cbb346ffa 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -19074,6 +19074,8 @@ lazy_load_binding (unsigned mod, tree ns, tree id,
> binding_slot *mslot)
>
> timevar_start (TV_MODULE_IMPORT);
>
> + processing_template_decl_sentinel ptds;
> +
> /* Stop GC happening, even in outermost loads (because our caller
> could well be building up a lookup set). */
> function_depth++;
> diff --git a/gcc/testsuite/g++.dg/modules/pr99377-2_a.C
> b/gcc/testsuite/g++.dg/modules/pr99377-2_a.C
> new file mode 100644
> index 00000000000..26e2bccbbbe
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/pr99377-2_a.C
> @@ -0,0 +1,5 @@
> +// PR c++/99377
> +// { dg-additional-options -fmodules-ts }
> +// { dg-module-cmi pr99377 }
> +export module pr99377;
> +export inline void f() { }
> diff --git a/gcc/testsuite/g++.dg/modules/pr99377-2_b.C
> b/gcc/testsuite/g++.dg/modules/pr99377-2_b.C
> new file mode 100644
> index 00000000000..69571952c8a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/pr99377-2_b.C
> @@ -0,0 +1,6 @@
> +// PR c++/99377
> +// { dg-additional-options -fmodules-ts }
> +// { dg-do link }
> +import pr99377;
> +template<class> void g() { f(); }
> +int main() { g<int>(); }
This test can be simplified to:
import pr99377;
template<class> void g() { f(); }
int main() { f(); }
which probably illustrates the bug better: we lazily load f at the
point of its first use, which in this case is in the (uninstantiated)
template g with processing_template_decl != 0. Thus during lazy loading
the call to note_vague_linkage_fn has no effect and we never emit the
definition of f.
