bug#36566: 27.0.50; debug is sometimes horribly slow

[Michael Heerdegen <michael_heerdegen@web.de>]

Hi,

sometimes it takes 10 or 20 seconds until the debugger pops up.  I
debugged code using widgets (who are complicated long lists).  But both
the number of frames and the length of the printed lists were not
exorbitant - a quite normal situation.

When I revert

e09120d68694272ea5efbe13b16936b4382389d8
Add backtrace-mode and use it in the debugger, ERT and Edebug

the debugger becomes fast again and pops up in a reasonable time.  With
the commit, the debugger is quite unusable in some cases: stepping
(`debugger-step-through') takes ten seconds per hit etc.  Not good.

FWIW, I think I very much appreciate the cited commit - I didn't yet
make use of the added features but it seems to be cool.  I hope we can
find a solution here.  At least there should be a way to get a faster
behavior.  BTW, I used the profiler and found that most of the time is
spent while garbage collecting.  My first thought was that cl-print may
be the culprit but that doesn't seem to be the case.

TIA,

Michael.