Re: Faster compilation speed

[Stan Shebs <shebs at apple dot com>]

Geoff Keating wrote:

> Stan Shebs <shebs@apple.com> writes:
>
> > Mike Stump wrote:
> >
> > > The first realization I came to is that the only existing control
> > > for such things is -O[123], and having thought about it, I think it
> > > would be best to retain and use those flags.  For minimal user
> > > impact, I think it would be good to not perturb existing users of
> > > -O[0123] too much, or at leaast, not at first.  If we wanted to
> > > change them, I think -O0 should be the `fast' version, -O1 should be
> > > what -O0 does now with some additions around the edges, and -O2 and
> > > -O3 also slide over (at least one).  What do you think, slide them
> > > all over one or more, or just make -O0 do less, or...?  Maybe we
> > > have a -O0.0 to mean compile very quickly?
> > I think it suffices to have -O0 mean "go as fast as possible".
> Note that that's different to what it means now, which is "I want the
> debugger to not surprise me."
There's been a little bit of a drift over the years - -O0 used to be
"no opts at all", -O1 was "not too surprising for the debugger", and
-O2 was all-out.  I remember some pressure from Cygnus customers to
make -O0 do more optimization, sometimes out of stupidity, but in the
legitimate cases because the -O0 code was too slow and/or large to
fit on the target embedded system, even for debugging.

So what *should* we do with -O0 optimizations that measurably
slow down the compiler?

Stan