bug#56682: Fix the long lines font locking related slowdowns

[Eli Zaretskii]

> Date: Thu, 04 Aug 2022 19:26:03 +0000
> From: Gregory Heytings <gregory@heytings.org>
> cc: gerd.moellmann@gmail.com, 56682@debbugs.gnu.org, 
> monnier@iro.umontreal.ca, 
>     dgutov@yandex.ru
> 
> Alas, it becomes much more sluggish if with a larger frame (160 columns 
> instead of 80), and/or with only Arabic characters.  Emacs takes ~10 
> seconds to open a file with only 6000 characters on a single line, and 
> motion commands are slow.

It doesn't surprise me.  If you disable font-lock and show-paren-mode,
does it become significantly faster?  And how does disabling font-lock
that measure vs disabling auto-composition-mode with that file?

Can you post that file?  I'd like to try some ideas I might have with
it.

> >> You didn't tell me whether it's okay to merge the branch with the 
> >> latest changes?
> >
> > I think you can merge.
> 
> Done.

Thanks.