Re: Redisplay slower in Emacs 28 than Emacs 27

[Lars Ingebrigtsen]

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

> Following the "The Emacs master is much slower than the emacs-27
> branch." thread, I tested Alan's benchmark on the master branch.  The
> platform I used is a 64-bit GNU/Linux computer, with GCC 10.2.
>
> It turns out that the 10-15% slowdown of redisplay in Emacs 28,
> compared to Emacs 27, is due to a single character change, namely the
> "!" character removed in commit 165fd028.

That sounds rather odd, because the code in question is this:

  for (img = c->buckets[i]; img; img = img->next)
    if (img->hash == hash
        && equal_lists (img->spec, spec)

And the ! removed was in front of the equal_list (which was reversed
logically).

In comparison, the code looks like this in Emacs 27:

  for (img = c->buckets[i]; img; img = img->next)
    if (img->hash == hash
        && !NILP (Fequal (img->spec, spec))


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