optimization levels for 6-STABLE build{kernel,world}

[Ruslan Ermilov]

On Wed, Sep 13, 2006 at 03:08:23AM -0700, Pete Slagle wrote:
> Oliver Fromme wrote:
> 
> > Marc G. Fournier <freebsd at hub.org> wrote:
> >  > What are ppl currently using for CFLAGS/COPTFLAGS in /etc/make.conf for 
> >  > building kernel/world?  I know awhile back it wasn't recommended to go 
> >  > above -O2, for instance, but suspect that has changed ... ?
> > 
> > The best optimization is probably to not override the
> > defaults at all, because they're already pretty optimal.
> > In fact, by overriding the defaults there's a good chance
> > to make things worse.  :-)
> > 
> > The default CFLAGS are "-O2 -pipe -fno-strict-aliasing".
> > Anything above -O2 isn't supported, and using -O2 without
> > -fno-strict-aliasing also isn't supported (and will create
> > broken code for some programs).  A common mistake is to
> > specify CFLAGS="-O2 -pipe" and omit -fno-strict-aliasing.
> > That'll shot you in the foot sooner or later.
> 
> /etc/make.conf on most of my 6.1 machines contains (in part) this:
> 
>    CFLAGS=    -O2 -pipe -fno-strict-aliasing
>    COPTFLAGS= -O2 -pipe
> 
> I no longer remember exactly why, but at some point I must have
> understood or assumed that to be the recommendation.
> 
> Just to be completely clear, are you saying that this
> 
>    CFLAGS=    -O2 -pipe -fno-strict-aliasing
>    COPTFLAGS= -O2 -pipe -fno-strict-aliasing
> 
> would be better in the general case?
> 
Doesn't matter; kern.pre.mk will automatically add -fno-strict-aliasing
to COPTFLAGS if needed:

: . if !empty(COPTFLAGS:M-O[23s]) && empty(COPTFLAGS:M-fno-strict-aliasing)
: COPTFLAGS+= -fno-strict-aliasing
: . endif


Cheers,
-- 
Ruslan Ermilov
ru at FreeBSD.org
FreeBSD committer
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