bug#64391: 30.0.50; buffer narrowing slowdown regression in emacs 29

[Eli Zaretskii]

> From: Andrew Cohen <acohen@ust.hk>
> Cc: 64391@debbugs.gnu.org,  gregory@heytings.org
> Date: Sat, 01 Jul 2023 15:31:53 +0800
> 
> >>>>> "EZ" == Eli Zaretskii <eliz@gnu.org> writes:
> 
>     EZ> Can you show a profile of the processing that takes a long time?
> 
> Not exactly sure how to answer this. The test case just goes through the
> buffer narrowing and widening (without modifying the buffer).  This
> takes very little time. Then the following takes a very  long time:
> 
>       (goto-char (point-min))
>       (while (not (eobp))
>         (delete-char 1)
>         (forward-line))

I asked for the profile produce by "M-x profiler-start RET RET" for
this very long processing.  is it feasible to produce such a profile?