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

[Gregory Heytings]

> > 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