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

[Dmitry Gutov]

On 24.07.2022 08:50, Gerd Möllmann wrote:
> Eli Zaretskii<eliz@gnu.org>  writes:
>
> > > My bet is indeed on the mere presence of text properties, plus the
> > > fact that we need to merge faces.  But I could well be wrong.
> Can't say something about face merging, but "frequent" changes of faces
> certainly have an effect on iterator performance.  It stops, looks up
> properties again to determine the next stop pos, does what has to be
> done for current properties...

But the problem is contingent on having long lines, isn't it?

There must be some interplay between those circumstances. Not just 
having to look up faces (relatively) a lot.