Undo deleting a large chunk of text takes very long time

[suzuyu1729]

I'm trying to use vim+ultisnips (+vimtex) as the daily LaTeX editing environment.
It's probably not so rare to have over 3000 lines in a LaTeX source file.
When I deleted a large chunk of (~3000 lines of) LaTeX source and undo it,
vim took very long time and almost looked like freezing.

Therefore, I made the following experiment (without vimtex):
Steps to reproduce

minimal.vim (I'm using vim-plug):

set nocompatible
call plug#begin()
Plug 'SirVer/ultisnips'
call plug#end()
let g:UltiSnipsSnippetDirectories=[$HOME.'/.vim/UltiSnips']

~/.vim/UltiSnips/all.snippets:

snippet (
($1)
endsnippet

Procedure of the experiment:

1. Make a test file with 3000 repetition of

AAAAA<CR>

and save it as test.
2. Launch vim by vim -u minimal.vim test.
3. Delete all lines by <Shift>-VGx.
4. Insert (, tab-complete it and back to the normal mode by i(<Tab><Esc>.
5. Undo the above 4, 3 by uuu.

Expected behavior:
The buffer for test immediately back to the original situation, i.e. 3000 repetition of AAAAA<CR>
(This is true if we manually insert () without tab completion in Step 4.)

Actual behavior:
It takes roughly 2 mins to do the last undo of uuu in Step 5. Is this the expected amount of slowdown?

---

• Operating System: MacOS Ventura 13.1
• Vim Version (both of vim and macvim produce the issue):
  VIM - Vi IMproved 9.0 (2022 Jun 28, compiled Sep 15 2022 19:27:32)
  macOS version - x86_64
  Included patches: 1-472
• UltiSnips Version: e99fdf1
• Python inside Vim: Python 3.10.9 (main, Dec 15 2022, 18:25:35) [Clang 14.0.0 (clang-1400.0.29.202)]
• Docker repo/vimrc:
  Sorry, I am not familiar with Docker and so skipped it, but if the issue can't be reproduced easily, I will try it.