bug#39598: 26.3; Emacs is extremely unresponsive on a trivial python file

[Eli Zaretskii]

> From: Ivan Oreshnikov <oreshnikov.ivan@gmail.com>
> Date: Fri, 14 Feb 2020 11:48:43 +0100
> 
> 1. Open an empty python buffer.
> 2. Insert a string "this is a test string" (including quotes) on the
>    first line of buffer. 
> 3. Copy it and insert it 10 times.
> 4. Copy all the lines in the buffer and insert them 10 times more. This
>    should give you 100 lines of python strings.
> 5. By the fifth paste command you can see 1 or 2 second delays before the
>    buffer is updated.
> 6. After that navigating to the beginning or the end of buffer will
>    trigger a couple of seconds of hangup. Page scrolls can randomly
>    hangup. Iserting a blank line somewhere in the middle of the buffer can
>    cause a random 1 or 2 second delay as well.
> 
> Those are some excerpts from the profiler report:
> 
> - command-execute                                               48141  87%
>  - call-interactively                                           48137  87%
>   - funcall-interactively                                       48064  87%
>    - end-of-buffer                                              46719  84%
>     - recenter                                                  46713  84%
>      - jit-lock-function                                        46713  84%
>       - jit-lock-fontify-now                                    46713  84%
>        - jit-lock--run-functions                                46713  84%
>         - run-hook-wrapped                                      46713  84%
>          + #<compiled 0xf8aa91>                                 46713  84%
> 
> ...
> 
> - redisplay_internal (C function)                                4935   8%
>  - jit-lock-function                                             4899   8%
>   - jit-lock-fontify-now                                         4897   8%
>    - jit-lock--run-functions                                     4894   8%
>     - run-hook-wrapped                                           4894   8%
>      + #<compiled 0xf8aa91>                                      4894   8%

Please show the entire expanded profile.

Thanks.