Re: The Emacs master is much slower than the emacs-27 branch.

[Eli Zaretskii]

> Date: Sat, 05 Dec 2020 08:14:24 +0000
> From: Gregory Heytings <ghe@sdf.org>
> cc: acm@muc.de, stephen.berman@gmx.net, emacs-devel@gnu.org
> 
> >> Sorry, I meant: it only improves compilation with -Og _and -O0_.  I 
> >> don't know if -O0 is important.
> >
> > Given my measurements (see upthread), the effect on -O0 build is 
> > negligible.  And yes, -O0 _is_ important.
> >
> 
> I don't know what happens on your computer (what is your 
> platform/compiler?) but on mine (Debian GNU/Linux with the latest Linux 
> kernel and the latest GCC) the effect on -O0 is almost the same as on -Og 
> for this particular benchmark.  I just tried again on the emacs-27 branch:
> 
> -Og: ~67s
> -O0: ~63s
> -O1: ~26s
> -O2: ~18s
> -O3: ~17s

Well, this could be due to the fact that my builds are with
"--enable-checking=yes,glyphs" and --with-wide-int.  I wouldn't expect
any of these to have such a profound effect on the difference between
the two branches, though.

To answer your question: this is GCC 9.2.0 on MS-Windows.

In any case, this is not a bug, and doesn't affect the production
code, so making that change on emacs-27 is out of the question.