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Date: Tue, 19 Jul 2005 17:26:09 +0200 (CEST)
From: "Olexandr Konovalenko" <kono@kth.se>
To: freebsd-amd64@freebsd.org
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Subject: Re: better optimization flags for opteron (amd64)// -ffast-math 
 and -O3 are not friends
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hi!

I found that on my system combination of -ffast-math AND -O3 is slower than
-O0 on AMD64 (interestingly it is true for Xeon EM64 as well), how can it be?
though just -O3 gives fastest double precision floating point computations.
On  32bit platform this effect is not observed.

please look here: http://daemon.nanophys.kth.se/~kono/testfcpu

the compiler I use:
Using built-in specs.
Configured with: FreeBSD/amd64 system compiler
Thread model: posix
gcc version 3.4.2 [FreeBSD] 20040728

my platform:
uname -a
FreeBSD daemon.nanophys.kth.se 5.4-STABLE FreeBSD 5.4-STABLE #0: Tue Apr 19
20:26:31 CEST 2005
root@daemon.nanophys.kth.se:/usr/obj/usr/src/sys/DAEMON64  amd64

-- Alexander Konovalenko