Subject: bug#43631: 28.0.50; CC Mode multiline strings grinds performance to a halt

From: Theodor Thornhill <[email-masked]>
Date: Sat, 26 Sep 2020 14:40:36 +0200

Eli Zaretskii <[email-masked]> writes:

> All the profiles posted there end prematurely, thus making it
> impossible to make independent conclusions regarding the possible
> culprits.  Would it be possible to post here a full profile,
> completely expanded, obtained after loading all the relevant *.el
> files as *.el (NOT *.elc!), so that the profile is detailed enough to
> show the relevant parts?  It would make the discussion much more
> focused.
>
> Bonus points for posting another profile, where the feature you think
> is the main culprit is disabled.
>
> TIA

Attached is two reports, one which is super slow, and one that is fast.

Recipe:
 - git clone https://github.com/unhammer/csharp-mode/
 - git checkout 164-repro
 - eval csharp-mode.el
 - open superslow.cs and write some text
 - rinse, repeat, but with
   
(c-lang-defconst c-multiline-string-start-char
  csharp ?@)

commented out.

One is unbearably slow, the other is super fast.

Hope this helps a little!

All the best,
Theodor Thornhill