bug#60953: The :match predicate with large regexp in tree-sitter font-lock seems inefficient

[Yuan Fu]

> On Jan 25, 2023, at 10:50 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> Date: Thu, 26 Jan 2023 01:21:08 +0200
>> Cc: casouri@gmail.com, 60953@debbugs.gnu.org
>> From: Dmitry Gutov <dgutov@yandex.ru>
>> 
>> Thank you. Unfortunately, the performance improvement from this patch is 
>> still fairly negligible.
> 
> This is quite strange, since all of the approaches basically use the
> same primitives under the hood.  Perhaps the reason for the slowness
> is that the code which computes the text span of a node is slow?
> Otherwise, I must be missing something here, since the rest of the
> code on the C level is basically the same, give or take some wrappers
> that should not change the overall picture.
> 
> Yuan, do you have some insights here?

Sadly, no.

> 
>> Switching to using :pred with function (like I did in commit 
>> d94dc606a0934) which still uses buffer-substring inside is significantly 
>> faster.
> 
> If the performance issue is fixed, then the only aspect that we should
> perhaps try to improve is consing.  Consing a string each time you
> need to fontify increases the GC pressure, so if there's a good way of
> avoiding that without performance degradation, we should take it.  Is
> it possible to use your :pred technique in a way that doesn't need to
> produce strings from buffer text?

Why is :pred more performant though? They just use string-match-p. If anything, 
the :pred predicates should be more expensive, since they execute lisp 
functions and conses tree-sitter nodes into lisp objects.

Yuan