bug#21028: Performance regression in revision af1a69f4d17a482c359d98c00ef86fac835b5fac (Apr 2014).

[Eli Zaretskii]

> Cc: dmantipov@yandex.ru, 21028@debbugs.gnu.org
> From: Clément Pit--Claudel <clement.pitclaudel@live.com>
> Date: Wed, 20 Jul 2016 17:26:02 -0400
> 
> I've made more progress towards making this reproducible, too. My current 
> repro requires XITS Math 
> (https://github.com/khaledhosny/xits-math/blob/master/xits-mathbold.otf), and 
> Segoe UI Emoji.  Do you have a machine with that font? If so, could you try 
> the following?
> 
>     emacs-24.5 -Q -mm -l 21028.el 21028 -f prettify-symbols-mode
> 
> I've attached 21028.el and 21028. When I run this command, each full 
> redisplay takes about 5 seconds; same for pointer motion.

Thanks.  I think the evidence and the profiling data you presented
quite clearly indicate where the problem is.  So I think the efforts
should now be directed towards reproducing bug#17125 and then solving
it in some other way that doesn't suffer from performance problems.