Re: [PATCH] c++ modules: ICE with class NTTP argument [PR100616]

[Nathan Sidwell <nathan@acm.org>]

On 9/26/22 10:08, Nathan Sidwell wrote:
> On 9/23/22 09:32, Patrick Palka wrote:
> 
>> Judging by the two commits that introduced/modified this part of
>> maybe_register_incomplete_var, r196852 and r214333, ISTM the code
>> is really only concerned with constexpr static data members (whose
>> initializer may contain a pointer-to-member for a currently open class).
>> So maybe we ought to restrict the branch like so, which effectively
>> disables this part of maybe_register_incomplete_var during stream-in, and
>> guarantees that outermost_open_class doesn't return NULL if the branch is
>> taken?
> 
> I think the problem is that we're streaming these VAR_DECLs as regular 
> VAR_DECLS, when we should be handling them as a new kind of object 
> fished out from the template they're instantiating. (I'm guessing 
> that'll just be a new tag, a type and an initializer?)
> 
> Then on stream-in we can handle them in the same way as a non-modules 
> compilation handles such redeclarations.  I.e. how does:
> 
> template<auto> struct C { };
> struct A { };
> C<A{}> c1; // #1
> C<A{}> c2; // #2
> 
> work.  Presumably at some point #2's A{} gets unified such that we find 
> the instantation that occurred at #1?
> 
> I notice the template arg for C<A{}> is a var decl mangled as 
> _ZTAXtl1AEE, which is a 'template paramete object for A{}'.  I see 
> that's a special mangler 'mangle_template_parm_object', called from 
> get_template_parm_object.  Perhaps these VAR_DECLs need an additional 
> in-tree flag that the streamer can check for?

I wonder if we're setting the module attachment for these variables 
sanely? They should be attached to the global module.  My guess is the 
pushdecl_top_level_and_finish call in get_templatE_parm_object is not 
doing what is needed (as well as the other issues).


-- 
Nathan Sidwell