Date: Tue, 19 Jul 2005 17:26:09 +0200 (CEST) From: "Olexandr Konovalenko" <kono@kth.se> To: freebsd-amd64@freebsd.org Subject: Re: better optimization flags for opteron (amd64)// -ffast-math and -O3 are not friends Message-ID: <49213.130.237.35.96.1121786769.squirrel@webmail.sys.kth.se>
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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
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