bug#57245: 29.0.50; M-> in a large XML file (without long lines) is slow

[Dmitry Gutov]

On 17.08.2022 14:36, Eli Zaretskii wrote:
> > Date: Wed, 17 Aug 2022 01:20:38 +0300
> > Cc: Eli Zaretskii <eliz@gnu.org>, 57245@debbugs.gnu.org
> > From: Dmitry Gutov <dgutov@yandex.ru>
> >
> > Otherwise, syntax-wholeline-max seems to be doing its job fine: if I
> > comment out the narrowing code in handle_fontified_prop (or switch to
> > the branch I posted previously), two XML files -- one with long lines
> > and one without (the files differ only by addition of newlines) -- show
> > approximately the same delay on M->.
>
> Doesn't syntax-wholeline-max only affect long lines?  Because I don't
> think I see its effect in the XML file where lines were broken by
> newlines, and then the file was duplicated 100 times.

Its purpose is to handle the slowdown which occurred specifically on 
long lines because of 
font-lock-extend-region-functions/syntax-propertize-extend-region-functions. 
Now that it works -- I don't see any particular slowdowns on long lines, 
even with narrowing disabled.

And the performance of M-> depends solely on the size of a file. In my 
XML test files, at least.