Re: Redisplay slower in Emacs 28 than Emacs 27

[Gregory Heytings via "Emacs development discussions." <emacs-devel@gnu.org>]

>>> 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;
>> }
>
> I already tried that and it absolutely killed Emacs when the toolbar was 
> displayed.
>

Not on my computer.  I changed "if (!c) return NULL;" into "return NULL;" 
and it worked.