bug#35453: 26.1; Poor performance of vertical-motion in large org buffer

[Eli Zaretskii <eliz@gnu.org>]

> From: Ihor Radchenko <yantar92@gmail.com>
> Cc: 35453@debbugs.gnu.org
> Date: Sun, 05 May 2019 09:05:46 +0800
> 
>   > Of course, if someone comes up with ideas how to speed up
>   > vertical-motion without changing what Org does with overlays and/or
>   > how overlays are implemented, such ideas will be most welcome.
> 
>   Rather dumb idea.
>   Currently, vertical-motion just loops over all the intervals in the
>   buffer. What if we optimise next-single-char-property-change and use it
>   in vertical-motion? Say, the interval data structure can extended. In
>   addition to the currently available pointers to next and previous
>   intervals, each (or just 'invisible') property of the interval might
>   also contain a pointer to next/previous interval with different property
>   value. Then, by increasing the structure size a bit, we can
>   significantly speed up the buffer motion commands.

There are no intervals in this story.  The way overlays are
implemented, they don't use intervals (if by that you mean the
facilities in intervals.c).  Someone was working on making overlays
more efficient by changing the low-level implementation details, but
that work is yet unfinished.