Re: [PATCH v4] c++/modules: Emit definitions of ODR-used static members imported from modules [PR112899]

[Jason Merrill <jason@redhat.com>]

On 1/25/24 21:28, Nathaniel Shead wrote:
> On Wed, Jan 24, 2024 at 03:24:42PM -0500, Jason Merrill wrote:
>> On 1/20/24 05:45, Nathaniel Shead wrote:
>>> I also included
>>> your change to only add class variable templates to 'pending_statics'
>>> (and the normal 'static_decl's for non-class otherwise) as otherwise I
>>> could imagine that they would cause issues with this later too.
>>
>> That seems wrong; the 'static_decls' vec is just for checking that
>> static/inline variables got defined.
>>
>> pending_statics has been used for template instantiations for a long time,
>> for non-module code; let's not mess with that in a modules patch.
>>
> 
> OK, makes sense.
> 
>>> I know that there's been discussion about the correct ABI for inline
>>> declarations, but personally I'd like to have this fixed for normal uses
>>> in GCC14 at least, and we can revisit the specific cases where various
>>> kinds of declarations are emitted in stage 1.
>>
>> Makes sense.
>>
>>> P.S.  As I go to send this, I wonder if maybe something like
>>> 'note_static_member_variable' would be a clearer choice of name than
>>> 'note_static_storage_variable'?
>>
>> Let's call it note_vague_linkage_variable, to go with _fn just above.
>>
> 
> Sounds good.
> 
>>> -- >8 --
>>>
>>> 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.
>>
>> What about non-member variables marked inline, and non-member variable
>> template instantiations?
>>
>> Jason
>>
> 
> Non-member variables marked inline are already handled by 'static_decls'
> via 'add_module_namespace_decl' and 'add_decl_to_level' during
> stream-in, and then are later emitted from 'wrapup_namespace_globals'.
> 
> I'd assumed that non-member variable template instantiations would also
> be handled by here, but that turns out not to be the case, since the
> instantiations themselves are not (of course) namespace-scope decls.
> I've added a case to the tests for this.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?

OK.

> -- >8 --
> 
> Static data members marked 'inline' should be emitted in TUs where they
> are ODR-used.  We need to make sure that inlines 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.
> 
> 	PR c++/112899
> 
> gcc/cp/ChangeLog:
> 
> 	* cp-tree.h (note_variable_template_instantiation): Rename to...
> 	(note_vague_linkage_variable): ...this.
> 	* decl2.cc (note_variable_template_instantiation): Rename to...
> 	(note_vague_linkage_variable): ...this.
> 	* pt.cc (instantiate_decl): Rename usage of above function.
> 	* module.cc (trees_in::read_var_def): Remember pending statics
> 	that we stream in.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/modules/init-4_a.C: New test.
> 	* g++.dg/modules/init-4_b.C: New test.
> 	* g++.dg/modules/init-6_a.H: New test.
> 	* g++.dg/modules/init-6_b.C: New test.
> 
> Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
> Reviewed-by: Patrick Palka <ppalka@redhat.com>
> Reviewed-by: Jason Merrill <jason@redhat.com
> ---
>   gcc/cp/cp-tree.h                        |  2 +-
>   gcc/cp/decl2.cc                         |  4 ++--
>   gcc/cp/module.cc                        |  5 +++++
>   gcc/cp/pt.cc                            |  2 +-
>   gcc/testsuite/g++.dg/modules/init-4_a.C |  9 +++++++++
>   gcc/testsuite/g++.dg/modules/init-4_b.C | 11 +++++++++++
>   gcc/testsuite/g++.dg/modules/init-6_a.H | 20 ++++++++++++++++++++
>   gcc/testsuite/g++.dg/modules/init-6_b.C |  9 +++++++++
>   8 files changed, 58 insertions(+), 4 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/modules/init-4_a.C
>   create mode 100644 gcc/testsuite/g++.dg/modules/init-4_b.C
>   create mode 100644 gcc/testsuite/g++.dg/modules/init-6_a.H
>   create mode 100644 gcc/testsuite/g++.dg/modules/init-6_b.C
> 
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index 60e6dafc549..f46b448ce0d 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -7151,7 +7151,7 @@ extern tree maybe_get_tls_wrapper_call		(tree);
>   extern void mark_needed				(tree);
>   extern bool decl_needed_p			(tree);
>   extern void note_vague_linkage_fn		(tree);
> -extern void note_variable_template_instantiation (tree);
> +extern void note_vague_linkage_variable		(tree);
>   extern tree build_artificial_parm		(tree, tree, tree);
>   extern bool possibly_inlined_p			(tree);
>   extern int parm_index                           (tree);
> diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
> index 91d4e2e5ea4..f569d4045ec 100644
> --- a/gcc/cp/decl2.cc
> +++ b/gcc/cp/decl2.cc
> @@ -947,10 +947,10 @@ note_vague_linkage_fn (tree decl)
>     vec_safe_push (deferred_fns, decl);
>   }
>   
> -/* As above, but for variable template instantiations.  */
> +/* As above, but for variables.  */
>   
>   void
> -note_variable_template_instantiation (tree decl)
> +note_vague_linkage_variable (tree decl)
>   {
>     vec_safe_push (pending_statics, decl);
>   }
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index f26b2265bce..6176801b7a7 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -11789,6 +11789,11 @@ trees_in::read_var_def (tree decl, tree maybe_template)
>   	  DECL_INITIALIZED_P (decl) = true;
>   	  if (maybe_dup && DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (maybe_dup))
>   	    DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (decl) = true;
> +	  if (DECL_IMPLICIT_INSTANTIATION (decl)
> +	      || (DECL_CLASS_SCOPE_P (decl)
> +		  && !DECL_VTABLE_OR_VTT_P (decl)
> +		  && !DECL_TEMPLATE_INFO (decl)))
> +	    note_vague_linkage_variable (decl);
>   	}
>         DECL_INITIAL (decl) = init;
>         if (!dyn_init)
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 74013533b0f..f5bf159a879 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -27300,7 +27300,7 @@ instantiate_decl (tree d, bool defer_ok, bool expl_inst_class_mem_p)
>       {
>         set_instantiating_module (d);
>         if (variable_template_p (gen_tmpl))
> -	note_variable_template_instantiation (d);
> +	note_vague_linkage_variable (d);
>         instantiate_body (td, args, d, false);
>       }
>   
> diff --git a/gcc/testsuite/g++.dg/modules/init-4_a.C b/gcc/testsuite/g++.dg/modules/init-4_a.C
> new file mode 100644
> index 00000000000..e0eb97b474e
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/init-4_a.C
> @@ -0,0 +1,9 @@
> +// PR c++/112899
> +// { dg-additional-options "-fmodules-ts" }
> +// { dg-module-cmi M }
> +
> +export module M;
> +
> +export struct A {
> +  static constexpr int x = -1;
> +};
> diff --git a/gcc/testsuite/g++.dg/modules/init-4_b.C b/gcc/testsuite/g++.dg/modules/init-4_b.C
> new file mode 100644
> index 00000000000..d28017a1d14
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/init-4_b.C
> @@ -0,0 +1,11 @@
> +// PR c++/112899
> +// { dg-module-do run }
> +// { dg-additional-options "-fmodules-ts" }
> +
> +import M;
> +
> +int main() {
> +  const int& x = A::x;
> +  if (x != -1)
> +    __builtin_abort();
> +}
> diff --git a/gcc/testsuite/g++.dg/modules/init-6_a.H b/gcc/testsuite/g++.dg/modules/init-6_a.H
> new file mode 100644
> index 00000000000..1c3fe4535d4
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/init-6_a.H
> @@ -0,0 +1,20 @@
> +// { dg-additional-options "-fmodule-header" }
> +// { dg-module-cmi {} }
> +
> +template <bool _DecOnly>
> +struct __from_chars_alnum_to_val_table {
> +  static inline int value = 42;
> +};
> +
> +inline unsigned char
> +__from_chars_alnum_to_val() {
> +  return __from_chars_alnum_to_val_table<false>::value;
> +}
> +
> +template <bool Foo>
> +static inline int nonclass_value = 42;
> +
> +inline unsigned char
> +get_nonclass_val() {
> +  return nonclass_value<false>;
> +}
> diff --git a/gcc/testsuite/g++.dg/modules/init-6_b.C b/gcc/testsuite/g++.dg/modules/init-6_b.C
> new file mode 100644
> index 00000000000..d704968ec37
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/modules/init-6_b.C
> @@ -0,0 +1,9 @@
> +// { dg-module-do link }
> +// { dg-additional-options "-fmodules-ts" }
> +
> +import "init-6_a.H";
> +
> +int main() {
> +  __from_chars_alnum_to_val();
> +  get_nonclass_val();
> +}