bug#57245: 29.0.50; M-> in a large XML file (without long lines) is slow

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Dmitry Gutov <dgutov@yandex.ru>,  57245@debbugs.gnu.org
> Date: Tue, 16 Aug 2022 14:40:33 -0400
> 
> > What the above profile doesn't show is that this code creates
> > tons of garbage, so GC is called a lot, and adds its share of
> > slowdown.
> 
> Hmm... I wonder where this might come from.

Run the recipe with a watchpoint on consing_until_gc, and you will
see.