Re: MPS experiment successful

[Gerd Möllmann]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Gerd Möllmann <gerd.moellmann@gmail.com>
>> Cc: emacs-devel@gnu.org
>> Date: Wed, 17 Apr 2024 18:29:53 +0200
>> 
>> As far as Emacs is is concerned, I don't have a clear picture what all
>> is currently supported in which combinations. For example, wasn't there
>> something that made Lisp_Object twice as large as a word? Not sure, but
>> I think that would make things more difficult.
>
> You mean --with-wide-int?

Yes, I think that's it. With 64 bit words, this makes Lisp_Object 128
bits, right? If that's the case, MPS won't work because if demands that
references are of word/pointer size, AFAIU.

OTOH, hm, pointers will still be of word size, so maybe one could come
up with something clever. Don't know what ATM, though, especially when
you say you are using !USE_LSB_TAG. Maybe one could make use of the GC
header somehow, if all objects have one. Or maybe one doesn't need the
tag bits at all... Except that symbols are a special case again.
Whatever... I think the least one can say is that this will not be easy.

>> I'm also currently supporting USE_LSB_TAG only. Could maybe be
>> supported, but unless someone tries...
>
> That and the previous item is a huge turn-off for me personally, FWIW,
> because I use exactly these two features.

If you want !USE_LSB_TAG, someone (tm) could implement that :-). But
it's not there now, because I didn't want to get lost in the lisp.h
macro jungle while still learning MPS. Keep it simple, and so on...