bug#64735: 29.0.92; find invocations are ~15x slower because of ignores

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: dmitry@gutov.dev, sbaugh@janestreet.com, 64735@debbugs.gnu.org
> Date: Thu, 20 Jul 2023 18:29:43 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> No. It uses less excessive regexp matching Emacs is trying to do in
> >> file-name-handler-alist.
> >
> > Where do you see regexp matching in the profiles you provided?
> 
> I did the analysis earlier for `directory-files-recursively'. See
> https://yhetil.org/emacs-devel/87cz0p2xlc.fsf@localhost/
> 
> Just to be sure, here is perf data for
> (ignore (let ((gc-cons-threshold most-positive-fixnum)) (benchmark-progn 
> (find-lisp-find-files "/home/yantar92/.data" ""))))
> 
>     54.89%  emacs    emacs                            [.] re_match_2_internal
>     10.19%  emacs    emacs                            [.] re_search_2
>      3.35%  emacs    emacs                            [.] unbind_to
>      3.02%  emacs    emacs                            [.] compile_pattern
>      3.02%  emacs    emacs                            [.] execute_charset
>      3.00%  emacs    emacs                            [.] process_mark_stack
>      1.59%  emacs    emacs                            [.] plist_get
>      1.26%  emacs    emacs                            [.] 
> RE_SETUP_SYNTAX_TABLE_FOR_OBJECT
>      1.17%  emacs    emacs                            [.] update_syntax_table
>      1.02%  emacs    emacs                            [.] Fexpand_file_name
> 
> Disabling `file-name-handler-alist' cuts the time more than 2x.

Disabling file-handlers is inconceivable in Emacs.  And I suspect that
find-file-name-handler is mostly called not from directory-files, but
from expand-file-name -- another call that cannot possibly be bypassed
in Emacs, since Emacs behaves as if CWD were different for each
buffer.  And expand-file-name also conses file names.  And then we
have encoding and decoding file names, something that with Find we do
much less.  Etc. etc.