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

[Ihor Radchenko]

Eli Zaretskii <eliz@gnu.org> writes:

>> Disabling `file-name-handler-alist' cuts the time more than 2x.
>
> Disabling file-handlers is inconceivable in Emacs.

Indeed. But we are talking about Emacs find vs. GNU find here.
In the scenarios where GNU find can be used, it is also safe to disable
file handlers, AFAIU.

> ... 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.

expand-file-name indeed calls Ffind_file_name_handler multiple times.
And what is worse: (1) `find-lisp-find-files-internal' calls
`expand-file-name' on every file in lisp, even when it is already
expanded (which it is, for every sub-directory); (2) `directory-files'
calls Fexpand_file_name again, on already expanded directory name;
(3) `directory-files' calls Ffind_file_name_handler yet again on top of
what was already done by Fexpand_file_name; (4) `directory-files' calls
`directory_files_internal' that calls `Fdirectory_file_name' that
searches `Ffind_file_name_handler' yet one more time.

There is a huge amount of repetitive calls to Ffind_file_name_handler
going on. They could at least be cached or re-used.

I do not see much of encoding and consing present in perf stats.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>