Re: [PATCH] c++/modules: Stream unmergeable temporaries by value again [PR114856]

[Jason Merrill <jason@redhat.com>]

On 5/2/24 10:40, Patrick Palka wrote:
> On Thu, 2 May 2024, Nathaniel Shead wrote:
> 
>> Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk/14.2?
>>
>> Another alternative would be to stream such !DECL_NAME temporaries with
>> a merge key of MK_unique rather than attempting to find the matching
>> (nonexistant) field of the class context.
> 
> Both approaches sound good to me, hard to say which one is preferable..
> 
> The handling of function-scope vs class-scope temporaries seems to start
> diverging in:
> 
> @@ -8861,28 +8861,6 @@ trees_out::decl_node (tree decl, walk_kind ref)
>         return false;
>       }
>   
> !  tree ctx = CP_DECL_CONTEXT (decl);
> !  depset *dep = NULL;
> !  if (streaming_p ())
> !    dep = dep_hash->find_dependency (decl);
> !  else if (TREE_CODE (ctx) != FUNCTION_DECL
> !	   || TREE_CODE (decl) == TEMPLATE_DECL
> !	   || DECL_IMPLICIT_TYPEDEF_P (decl)
> !	   || (DECL_LANG_SPECIFIC (decl)
> !	       && DECL_MODULE_IMPORT_P (decl)))
> !    {
> !      auto kind = (TREE_CODE (decl) == NAMESPACE_DECL
> !		   && !DECL_NAMESPACE_ALIAS (decl)
> !		   ? depset::EK_NAMESPACE : depset::EK_DECL);
> !      dep = dep_hash->add_dependency (decl, kind);
> !    }
> !
> !  if (!dep)
> !    {
> !      /* Some internal entity of context.  Do by value.  */
> !      decl_value (decl, NULL);
> !      return false;
> !    }
>   
>     if (dep->get_entity_kind () == depset::EK_REDIRECT)
>       {
> 
> where for a class-scope temporary we add a dependency for it, stream
> it by reference, and then stream it by value separately, which seems
> unnecessary.
> 
> So if we decide to keep the create_temporary_var change, we probably
> would want to unify this code path's handling of temporaries (i.e.
> don't add_dependency a temporary regardless of its context).
> 
> If we decide your partially revert the create_temporary_var change,
> your patch LGTM.

Streaming by value sounds right, but as noted an important difference 
between reference temps and others is DECL_NAME.  Perhaps the code 
Patrick quotes could look at that as well as the context?

Jason