bug#58558: 29.0.50; re-search-forward is slow in some buffers

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@posteo.net>
> Cc: larsi@gnus.org, monnier@iro.umontreal.ca, 58558@debbugs.gnu.org
> Date: Tue, 13 Dec 2022 17:43:36 +0000
> 
> > If no other idea to find this out comes up, maybe run this with a
> > breakpoint in make-marker, look at the backtrace to see the callers.
> 
> I tried gdb now with break Fmake_marker.
> 
> The benchmark itself does not trigger the breakpoint.
> However, a huge number (hundreds) of breakpoint hits is generated upon
> finishing the benchmark execution.
> 
> bt:
> 
> #0  Fmake_marker () at alloc.c:3736
> #1  0x00005555557bb750 in Fmatch_data (integers=0x0, reuse=0x0, reseat=0x0) 
> at search.c:2903

Ha-ha, shooting ourselves in the foot!

Great sleuthing job.  Now we need to think what to do with this.
Hmm...

> If I read the backtrace correctly, something in my custom mode-line is
> triggering Fmatch_data that creates markers.

Yes, you have sone :eval form in the mode line, it seems?

Calling xbacktrace will show a Lisp backtrace, which could be
educational here.

> But that code has not changes for years from git log.
> 
> One suspicious thing is that my code gets called that much frequently
> (100s of times) by redisplay. Not sure if it is normal.

You cannot predict when redisplay decides to redraw the mode line.