bug#51734: 29.0.50; got slow

[Katsumi Yamaoka]

Hi,

I'm sorry for my ambiguous report, but the redisplay or the cursor
movement on an Emacs screen got awkward and slow recently.  This
happens on Emacs git master built on 64-bit Cygwin.
For instance, the cursor moves not smoothly while repeating `C-n's,
`C-s' takes a couple of seconds for the text searched to appear, etc.
It should have happened after my build on Thu 4 Nov 22:00 UTC
through the previous build on Mon 8 Nov 22:00 UTC.

Thanks.

In GNU Emacs 29.0.50 (build 1, x86_64-pc-cygwin, GTK+ Version 3.22.28, cairo 
version 1.17.4)
 of 2021-11-10 built on localhost
Windowing system distributor 'The Cygwin/X Project', version 11.0.12012000
Configured using:
 'configure 'CFLAGS=-O0 -g3' --verbose --with-x-toolkit=gtk3
 --with-imagemagick'