bug#73484: 31.0.50; Abolishing etags-regen-file-extensions

[Eli Zaretskii <eliz@gnu.org>]

> From: Francesco Potortì <pot@gnu.org>
> Date: Thu, 10 Oct 2024 10:27:57 +0200
> Cc: spwhitton@spwhitton.name,
> 	73484@debbugs.gnu.org,
> 	dmitry@gutov.dev
> 
> >That's not what I see in the code.  But it should be easy to count the
> >number of loop iterations in the use case we are talking about
> >(running etags on the geck-dev tree), so we don't need to argue about
> >facts.
> 
> Yes.  If finding a bottleneck is the objective, you should maybe instrument the string comparison functions so that you can count how many times they are called from different places.
> 
> I had a quick look at the whole code and in fact the only place I can find where ou have O^2 behaviour seems to be file name comparison, and it still looks so strange to me that this can in facrt cause significant delay.

We are using etags on a huge tree: about 375K files.  I think that's
the reason, because non-linear behaviors are like that: they are
insignificant with small sets, but huge with larger ones...

Profiles don't lie...