Re: Redisplay slower in Emacs 28 than Emacs 27

[Gregory Heytings]

> > With equal_lists 18.7s, with !equal_lists 16.1s.
> >
> > This difference is not due to an obscure compiler bug, the timings 
> > above are with GCC 10, but the timings with Clang 9 are similar: with 
> > equal_lists 19.0s, with !equal_lists 16.6s.
>
> Very interesting.  Using the image cache for small images slows Emacs 
> down?  Or is there a bug in equal_lists?
>
> Just to make 100% sure -- could you re-run the benchmark with something 
> like the following as the function:
>
> static struct image *
> search_image_cache (struct frame *f, Lisp_Object spec, EMACS_UINT hash,
>                    unsigned long foreground, unsigned long background,
>                    bool ignore_colors)
> {
>  return NULL;
> }

Sure.  As I just wrote to Alan, I changed "if (!c) return NULL;" into 
"return NULL;", and the result is: 18.6s, similar to the equal_lists case. 
As always, it's the average of ten runs.