Date: Wed, 13 Sep 2006 16:49:34 -0700
From: Gary Kline <kline@sage.thought.org>
To: Stefan Lambrev <stefan.lambrev@sun-fish.com>
Cc: freebsd-stable@freebsd.org
Subject: Re: optimization levels for 6-STABLE build{kernel,world}
Message-ID: <20060913234934.GA92067@thought.org>
In-Reply-To: <4507CC9B.60704@sun-fish.com>
References: <200609130905.k8D95idk062789@lurza.secnetix.de> <4507CC9B.60704@sun-fish.com>
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On Wed, Sep 13, 2006 at 12:17:15PM +0300, Stefan Lambrev wrote: > Hello, > > Oliver Fromme wrote: > >Marc G. Fournier <freebsd@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. > > > >Best regards > > Oliver > > > > > May be default flags have to be set here: > /usr/src/share/examples/etc/make.conf ? > I'm asking because in this file I read: > > # CFLAGS controls the compiler settings used when compiling C code. > # Note that optimization settings other than -O and -O2 are not recommended > # or supported for compiling the world or the kernel - please revert any > # nonstandard optimization settings to "-O" or -O2 before submitting bug > # reports without patches to the developers. > # > #CFLAGS= -O -pipe > > May be "-fno-strict-aliasing" have to be added here then ? > A couple of things. Will having gcc unroll loops have any negative consequences? (I can't imagine how:: but better informed than to have something crash inexplicability.) With 6.X safe at -O2 and with -funroll-loops, that should be a slight gain, right? (It also will make an upgrade from 5.5 to 6.[12] that much more rational.) [Dumb] questions:: first, what does the compiler do with "-fno-strict-aliasing"? And is there any guess, any SWAG even, on when FreeBSD will safe with -O3?? thanks, people, gary > -- > Best Wishes, > Stefan Lambrev > ICQ# 24134177 > > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" -- Gary Kline kline@thought.org www.thought.org Public service Unix
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