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

[Eli Zaretskii]

> Date: Sun, 14 Aug 2022 12:41:33 +0300
> Cc: 56682@debbugs.gnu.org, gregory@heytings.org, monnier@iro.umontreal.ca
> From: Dmitry Gutov <dgutov@yandex.ru>
> 
> > Stuttering in redisplay (and I think you actually mean stuttering in
> > cursor motion commands, but let's ignore that difference for now) is a
> > known issue, but it is NOT the goal of this effort.  The goal of this
> > effort is to avoid making Emacs_completely_unusable_  due to the need
> > to wait for many seconds for commands to complete and their results to
> > be shown on display.  Stuttering, while somewhat annoying, doesn't
> > make Emacs unusable.
> > 
> > So if you are talking about the cases of stuttering, you are focused
> > on cases that are of no particular interest to us here.  Of course,
> > any improvement in those other cases will also be welcome, but it is
> > not directly related to what we are trying to do here, and may or may
> > not solve the cases that are of interest to us.
> 
> They *are* solved by Gregory's work.

Not in all cases and not on all systems.  I still see stuttering in
some cases, at least with my unoptimized builds, and I don't consider
that a problem.