bug#32523: 27.0.50; Emacs hangs when killing rectangle

[Joseph Mingrone <jrm@ftfl.ca>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Joseph Mingrone <jrm@ftfl.ca>
>> Date: Fri, 24 Aug 2018 21:59:48 -0300

>> Here is a recipe to make Emacs (nearly) hang indefinitely.

>> 1. emacs -Q

>> 2. Visit the file found https://ftfl.ca/misc/big_file_hangs_emacs.txt

>> 3. M-x toggle-truncate-lines

>> 4. Use rectangle-mark-mode (C-x SPC) to mark the rectangle that starts
>>    at the top left of the file (point 1), and includes the leading white
>>    space, the line numbers, and the space after the line numbers (point
>>    468848).

>> 5. Kill the rectangle with C-x r k.

>> For me, the Emacs process will continue to use 100% CPU and Emacs is
>> almost completely unresponsive and has to be killed.  Some actions such
>> as saving the file may complete, but only after a few minutes.

> It doesn't hang, it just takes very long to finish that operation (3
> min on my machine with an unoptimized build; should be something like
> 1 to 1.5 min in an optimized build).

> This belongs to the "Emacs is very slow with long lines" class of
> problems: the file has 2900-character lines.  If this file will never
> include any text, I suggest to visit it with
> "M-x find-file-literally", then the problem of slowness will go away.

Thanks for the `find-file-literally' tip.

The rectangle does eventually get cut for me as well.  Ignoring speed,
the problem is that Emacs is unusable afterwards.  For example, if I go
away for an hour or so, then return, the Emacs process will still be
using something close to 100% CPU and trying to doing something simple,
like moving the point forward, may take minutes.

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