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

[Eli Zaretskii]

> From: Óscar Fuentes <ofv@wanadoo.es>
> Date: Sat, 05 Dec 2020 15:47:32 +0100
> 
> -Og is the recommended setting for the edit/build/debug cycle [1],
> because it *improves* debug info accuracy over -O0 *and* also runs
> faster, which is a significant bonus. So IMHO it is a good thing to not
> regress -Og too much. -O0, on the other hand, shouldn't be a concern.

Actually, my experience is that during development one should use -O0,
since even -Og sometimes messes up the code and backtrace so much that
GDB is unable to show variables or produce a reasonably accurate
backtrace.

But of course -O2 is of the main concern when slowdown is reported.

FWIW, I think the "original sin" here is the preference of inline
functions to C macros.  We would never have such problems if we
continued to use old and time-proven macros instead of converting a
large portion of them to inline functions, which caused us portability
problems and this issue, among others.