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Date: Tue, 4 Nov 2003 09:59:07 +0100
From: Simon Barner <barner@in.tum.de>
To: Zhang Weiwu <weiwuzhang@hotmail.com>
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cc: freebsd-questions@freebsd.org
Subject: Re: optimize with -O2 or -O?
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> 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)?

Hi,

-O =3D=3D -O1 (see `info gcc' -> Invoking GCC -> Optimize Options)

It is recommended not to use anything higher than -O since GCC is known to
procduce broken code on higher optimization levels.

Depending on what gcc version you are using, also specifing CPUTYPE=3D...
in /etc/make.conf might bring you troubles (for certain CPUs, e.g.=20
athlon IIRC).

Post the output of `gcc --version' and people will be able to tell you.

What you could try is to use -O2 for some selected ports, but the question
is whether you will see a measurable performance gain.

Some ports that are known to build alright at -O2 (e.g. mplayer) have
WITH_OPTIMIZED_CFLAGS knob.

Regards,
 Simon

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