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

[Gregory Heytings]

> > 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
>
> So when I want to compare Emacs 27 and Emacs 28 benchmarks, -Og builds 
> are off limits.  Now can I use O0 builds or do I have to use O1-O3 
> builds exclusively?

The emacs-27 branch since commit 365dad197bac5deec9244fd9c189d23c46c99b31 
(Sep 4 2019) is about three times slower (at least on this benchmark, with 
GCC 10.2, on a 64-bit GNU/Linux) than the master branch since commit 
b9b32074cecb0e0d20cf527eadacbb0b7f5cced9 (Apr 7 2020) with -Og and -O0. 
With -O[1-3] it is not.

I'd guess that Eli will merge b9b32074cecb0e0d20cf527eadacbb0b7f5cced9 
into emacs-27 very soon after the Emacs 27.2 release, and this slowdown 
will disappear.