bug#12463: 24.2; pos-visible-in-window-p gets slower over time

[Eli Zaretskii]

> From: Chong Yidong <cyd@gnu.org>
> Cc: jwalt@garni.ch (Jörg Walter),  12463@debbugs.gnu.org
> Date: Tue, 18 Sep 2012 23:17:53 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Can anyone else reproduce this?
> 
> I can reproduce this.  On bisecting, the problem first shows up with
> 
>   revno: 104186
>   fixes bug: http://debbugs.gnu.org/8640
>   committer: Juanma Barranquero <lekktu@gmail.com>
>   branch nick: trunk
>   timestamp: Tue 2011-05-10 12:31:33 +0200
>   message:
>   src/image.c (Finit_image_library): Return t for built-in image types.
> 
> A quick glance at the diff of this revision does not reveal immediately
> why it causes the problem, though.

Can you see what happened in revision 104105?  That was before the
previous image-handling code was modified into its present form, which
originally made pbm images unavailable (that was fixed in 104186).
The question is, was the recipe in this bug slow or fast then.
Knowing that will probably give a hint in the right direction.