Date: Tue, 4 Nov 2003 08:57:14 +0000 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: Zhang Weiwu <weiwuzhang@hotmail.com> Cc: freebsd-questions@freebsd.org Subject: Re: optimize with -O2 or -O? Message-ID: <20031104085714.GC31448@happy-idiot-talk.infracaninophile.co.uk> In-Reply-To: <3FA76159.6010807@hotmail.com> References: <3FA76159.6010807@hotmail.com>
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--lCAWRPmW1mITcIfM Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Nov 04, 2003 at 04:20:41PM +0800, Zhang Weiwu wrote: > Hello. I'm running 5.1-RELEASE. >=20 > I read the gcc man page. It is not clear what -O implys. Is -O equal to= =20 > -O1 or -O2? If I wish to optimize making does it make sense to add=20 > CFLAGS=3D-O2 in the make.conf(5)? -O is the same as -O1 Ah -- the shibboleth of cranking up the optimisation level to make things run *really fast*. First of all, for general purpose code, -O gets you most of the available optimisation benefits without causing any problems. You can try CFLAGS=3D-O2 in /etc/make.conf if you like, and most things will work OK but by no means all: some code will not compile correctly under high optimization levels. The immediate response if you report this sort of thing as a bug will be to see if the problem is repeatable using a lower optimisation level. Secondly, you will achieve a much greater performance improvement by setting the CPUTYPE variable appropriately. Cheers, Matthew --=20 Dr Matthew J Seaman MA, D.Phil. 26 The Paddocks Savill Way PGP: http://www.infracaninophile.co.uk/pgpkey Marlow Tel: +44 1628 476614 Bucks., SL7 1TH UK --lCAWRPmW1mITcIfM Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.3 (FreeBSD) iD8DBQE/p2nqdtESqEQa7a0RAhBdAJ99+gkfnIMGgpIHI+jhVeua2KprCwCZAZ9Y GKXC2U2QFO+bykq5iaLtQbQ= =GSDE -----END PGP SIGNATURE----- --lCAWRPmW1mITcIfM--
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