From owner-freebsd-current Thu Feb 27 20:56:11 2003 Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id C267237B401 for ; Thu, 27 Feb 2003 20:56:09 -0800 (PST) Received: from web40306.mail.yahoo.com (web40306.mail.yahoo.com [66.218.78.85]) by mx1.FreeBSD.org (Postfix) with SMTP id 3303E43FA3 for ; Thu, 27 Feb 2003 20:56:09 -0800 (PST) (envelope-from victorysoldier@yahoo.com) Message-ID: <20030228045609.95808.qmail@web40306.mail.yahoo.com> Received: from [194.44.215.101] by web40306.mail.yahoo.com via HTTP; Thu, 27 Feb 2003 20:56:09 PST Date: Thu, 27 Feb 2003 20:56:09 -0800 (PST) From: Rhett Monteg Hollander Reply-To: alasir@supereva.it Subject: Re: -O2 considered harmful To: current@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG Bruce Cran wrote: > I'm afraid you're wrong - the V2SI datatype and MMX functions > automatically become available after -march=pentium2, while > with other processor types you've got to explicitly add -mmmx. > -msse is presumed with -march=pentium3 and up. I'm afraid I'm not; I was talking strictly about -march=pentiumpro, not -march=pentium2 et cetera. > ... I've seen code which runs 40x faster when compiled for > athlon-xp than for i386, and I would guess that a lot of that > is because of clever use of sse and mmx. That wasn't an > audio/video program, it was the libgmp arbitrary precision maths > package. MMX won't help you even a bit in precise mathematical calculations, unlike SSE. Also, if you're familiar with the way how MMX works, you won't enable it when compiling any application that requires heavy floating-point computations, because constant switching between MMX unit and FPU results in significant latency. > Also, I'm sure most people wouldn't say no to 50% more processing > speed for free! I didn't mean to stop using MMX at all; I only intended to note that there is no need to enable it for _all_ applications. > So, if you've got a pentium, k6 or pentiumpro which supports MMX, > you _do_ need to explicitly add -mmmx, but for other processors > it's implied. You didn't pay enough attention to my original post; PPro doesn't support MMX. Though, you can specify -mmmx anyway, if you feel comfortable with SIGILLs. --- Regards, Rhett __________________________________________________ Do you Yahoo!? Yahoo! Tax Center - forms, calculators, tips, more http://taxes.yahoo.com/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message