bug#50599: [PATCH] Don't recommend against "\[...]" substitutions for performance

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Wed, 15 Sep 2021 08:27:55 +0200
> 
> (progn (require 'ibuffer)
>        (let ((times 100))
>          (/ (car (benchmark-run
>                      times (documentation 'ibuffer-mode)))
>             times)))
> 
>     => 0.00499586008
> 
> When I increase the number of substitutions in that docstring to around 1000 (by
> duplicating the docstring 10 times), I get:
> 
>     => 0.05029239337
> 
> This is 10 times slower, but still fast enough that it does not matter much.
> It also suggests that this is O(N) in time.
> 
> My conclusion is that the above recommendation in `(elisp) Documentation Tips'
> is irrelevant these days, and I suggest to remove it.
> 
> Please see the attached patch.

Thanks for the research, but the removal you propose is too radical.
The text already says "very many times".  You are saying that on your
system (which has what CPU, btw?) "very many" is a very large number,
but even for you 1000 references takes 50 msec, which begins to be
significant.

So I'm okay with somehow modifying the text to provide a better idea
of what "very many" means nowadays, but I think the advice is still
valid and shouldn't be removed.  We cannot guarantee that arbitrarily
large number of such references will not slow down help display.