Date: Sat, 24 Feb 2001 23:26:39 -0800 From: Kris Kennaway <kris@obsecurity.org> To: Bruce Evans <bde@zeta.org.au> Cc: Alexander Leidinger <Alexander@Leidinger.net>, arch@FreeBSD.ORG Subject: Re: cvs commit: src/share/mk sys.mk Message-ID: <20010224232638.A6907@mollari.cthul.hu> In-Reply-To: <Pine.BSF.4.21.0102241315540.25623-100000@besplex.bde.org>; from bde@zeta.org.au on Sat, Feb 24, 2001 at 01:33:14PM %2B1100 References: <20010223010514.A41551@mollari.cthul.hu> <Pine.BSF.4.21.0102241315540.25623-100000@besplex.bde.org>
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On Sat, Feb 24, 2001 at 01:33:14PM +1100, Bruce Evans wrote:
> > Okay, I've built several binaries and libraries with -march=pentiumpro
> > and -march=pentiumpro -mcpu=pentiumpro, and verified with diff -b that
> > the output in both cases is indeed identical. It looks like the docs
> > are correct.
>
> ITYM "incorrect".
>
> This just shows that your tests didn't test the small areas where
> -march makes a difference (other than implying -mcpu). Examination
> of gcc.295/config/i386/i386.{md,h} shows that it it only mainly (only?)
> affects areas related to the i686 fcmov instruction. The following
> program uses these areas, so compiling it with -march=pentiumpro and
> -mcpu=pentiumpro gives different results:
I never disputed that - what I said above was that -march implies
-mcpu for i386 code (as documented), therefore for "optimal
optimization" we only need -march. The docs say that -mcpu alone does
different things to -march, as your test also demonstrates.
Kris
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