Subject: Re: bug#66117: 30.0.50; `find-buffer-visiting' is slow when opening large number of buffers

From: Ihor Radchenko <[email-masked]>
Date: Thu, 14 Dec 2023 19:02:13 +0000

Stefan Monnier <[email-masked]> writes:

>>>> It won't be buffer-local-if-changed, so binding it will not be costly.
>>> As mentioned elsewhere in this bug-report we can make `case-fold-search`
>>> into a `DEFVAR_LISP`: it would have no visible impact to ELisp and would
>>> avoid the costly let-bindings.
>> Wouldn't DEFVAR_LISP break major modes that do (setq case-fold-search ...)?
>
> No, it makes no difference to Lisp.  It only changes the implementation
> strategy: DEFVAR_LISP stores the value in a global C variable (which
> thus requires more processing when the var is buffer-local, more
> specifically updating the C var when we `set-buffer`), whereas
> DEFVAR_PER_BUFFER stores the value inside the buffer object (which
> thus requires more processing when the var is *not* buffer-local since
> the global value is duplicated in all the buffers where it's not made
> buffer-local).

Do I understand correctly that what is needed to implement your
suggestion is

1. Remove case_fold_search_ slot from buffer objects
2. Use DEFVAR_LISP for case-fold-search
3. Declare case-fold-search buffer-local
4. Replace BVAR(...) references in C with Vcase_fold_search

?

-- 
Ihor Radchenko // yantar92,
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