Date: Thu, 27 Feb 2003 01:04:11 +0100 From: Jens Rehsack <rehsack@liwing.de> To: Andre Guibert de Bruet <andy@siliconlandmark.com> Cc: Nuno Teixeira <nunotex@aeiou.pt>, current@FreeBSD.ORG Subject: Re: -O2 considered harmful Message-ID: <3E5D55FB.3010605@liwing.de> References: <xzpy943xnhx.fsf@flood.ping.uio.no> <20030226113815.W5357@znfgre.tberna.bet> <20030226200635.GA1368@torment.storming.org> <20030226215547.GA5510@gw.tex.bogus> <20030226184315.F91528@alpha.siliconlandmark.com>
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Andre Guibert de Bruet wrote:
> On Wed, 26 Feb 2003, Nuno Teixeira wrote:
>
>
>>Does -march=k6-2 implies -m3dnow? Or -march=pentiumpro implies -mmmx?
>>
>>I always thought that when I use -march it will enable other
>>porcessor specific optimizations like mmx and 3dnow (if available).
>
>
> IIRC, 166 and 180 Mhz PPros don't support MMX.
Neither do PPro's 200:
CPU: Pentium Pro (199.43-MHz 686-class CPU)
Origin = "GenuineIntel" Id = 0x619 Stepping = 9
Features=0xf9ff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,SEP,MTRR,PGE,MCA,CMOV>
> I'm seeing differences in compiled code between simple -march=athlon-xp
> and -march=athlon-xp -mmmx -m3dnow -msse.
The documentation says the same: those options have to be enabled to use
extended instruction sets. -march/-mcpu just optmizes boundaries of jump
labels, variables, etc... - and sometimes the kind of instructions to
use, eg. 'loop label' or 'dec bcx, jne label', but that's all, AFAIK.
So long,
Jens
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