On Fri, Mar 01, 2024 at 08:18:09AM -0500, Jason Merrill wrote:
> On 2/29/24 20:08, Nathaniel Shead wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
> >
> > -- >8 --
> >
> > An implicit instantiation has an initializer depending on whether
> > DECL_INITIALIZED_P is set (like normal VAR_DECLs) which needs to be
> > written to ensure that consumers of header modules properly emit
> > definitions for these instantiations. This patch ensures that we
> > correctly fallback to checking this flag when DECL_INITIAL is not set
> > for a template instantiation.
>
> Can you say more about how and why DECL_INITIAL and DECL_INITIALIZED_P are
> inconsistent here?
For variables with non-trivial dynamic initialization, DECL_INITIAL can
be empty after 'split_nonconstant_init' but DECL_INITIALIZED_P is still
set; we need to check the latter to determine if we need to go looking
for a definition to emit (often in 'static_aggregates' here). This is
the case in the linked testcase.
However, for template specialisations (not instantiations?) we primarily
care about DECL_INITIAL; if the variable has initialization depending on
a template parameter then we'll need to emit that definition even though
it doesn't yet have DECL_INITIALIZED_P set; this is the case in e.g.
template <int N> int value = N;
> > As a drive-by fix, also ensures that the count of initializers matches
> > the actual number of initializers written. This doesn't seem to be
> > necessary for correctness in the current testsuite, but feels wrong and
> > makes debugging harder when initializers aren't properly written for
> > other reasons.
> >
> > PR c++/114170
> >
> > gcc/cp/ChangeLog:
> >
> > * module.cc (has_definition): Fall back to DECL_INITIALIZED_P
> > when DECL_INITIAL is not set on a template.
> > (module_state::write_inits): Only increment count when
> > initializers are actually written.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/modules/var-tpl-2_a.H: New test.
> > * g++.dg/modules/var-tpl-2_b.C: New test.
> >
> > Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>
> > ---
> > gcc/cp/module.cc | 8 +++++---
> > gcc/testsuite/g++.dg/modules/var-tpl-2_a.H | 10 ++++++++++
> > gcc/testsuite/g++.dg/modules/var-tpl-2_b.C | 10 ++++++++++
> > 3 files changed, 25 insertions(+), 3 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/modules/var-tpl-2_a.H
> > create mode 100644 gcc/testsuite/g++.dg/modules/var-tpl-2_b.C
> >
> > diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> > index 1b2ba2e0fa8..09578de41ec 100644
> > --- a/gcc/cp/module.cc
> > +++ b/gcc/cp/module.cc
> > @@ -11586,8 +11586,9 @@ has_definition (tree decl)
> > case VAR_DECL:
> > if (DECL_LANG_SPECIFIC (decl)
> > - && DECL_TEMPLATE_INFO (decl))
> > - return DECL_INITIAL (decl);
> > + && DECL_TEMPLATE_INFO (decl)
> > + && DECL_INITIAL (decl))
> > + return true;
> > else
> > {
> > if (!DECL_INITIALIZED_P (decl))
> > @@ -17528,13 +17529,14 @@ module_state::write_inits (elf_out *to,
> > depset::hash &table, unsigned *crc_ptr)
> > tree list = static_aggregates;
> > for (int passes = 0; passes != 2; passes++)
> > {
> > - for (tree init = list; init; init = TREE_CHAIN (init), count++)
> > + for (tree init = list; init; init = TREE_CHAIN (init))
> > if (TREE_LANG_FLAG_0 (init))
> > {
> > tree decl = TREE_VALUE (init);
> > dump ("Initializer:%u for %N", count, decl);
> > sec.tree_node (decl);
> > + ++count;
> > }
> > list = tls_aggregates;
> > diff --git a/gcc/testsuite/g++.dg/modules/var-tpl-2_a.H
> > b/gcc/testsuite/g++.dg/modules/var-tpl-2_a.H
> > new file mode 100644
> > index 00000000000..607fc0b808e
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/modules/var-tpl-2_a.H
> > @@ -0,0 +1,10 @@
> > +// PR c++/114170
> > +// { dg-additional-options "-fmodule-header" }
> > +// { dg-module-cmi {} }
> > +
> > +inline int f() { return 42; }
> > +
> > +template<class>
> > +inline int v = f();
> > +
> > +inline int g() { return v<int>; }
> > diff --git a/gcc/testsuite/g++.dg/modules/var-tpl-2_b.C
> > b/gcc/testsuite/g++.dg/modules/var-tpl-2_b.C
> > new file mode 100644
> > index 00000000000..6d2ef4004e6
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/modules/var-tpl-2_b.C
> > @@ -0,0 +1,10 @@
> > +// PR c++/114170
> > +// { dg-module-do run }
> > +// { dg-additional-options "-fmodules-ts" }
> > +
> > +import "var-tpl-2_a.H";
> > +
> > +int main() {
> > + if (v<int> != 42)
> > + __builtin_abort();
> > +}
>
