Date: Thu, 4 Jun 1998 01:31:26 +0000 (GMT) From: Donn Miller <dmm125@bellatlantic.net> To: "John S. Dyson" <dyson@FreeBSD.ORG> Cc: Mike Smith <mike@smith.net.au>, hackers@FreeBSD.ORG Subject: Re: Recompiling sources with "-O2 -m486 -pipe" Message-ID: <Pine.NEB.3.96.980604011707.720A-100000@myname.my.domain> In-Reply-To: <199806040447.XAA00815@dyson.iquest.net>
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On Wed, 3 Jun 1998, John S. Dyson wrote:
> Mike Smith said:
> > >
> > > About the -m486 option -- I use -m486 -O3 -pipe all the time; does it slow
> > > down the execution somewhat? I noticed the Mozilla sources defined
> > > -mno-486. Do you know if compiling with -mno-486 gives better results
> > > than -m486 as far as speed, etc.? I figured that -m486 generated 486
> > > instructions, which would make a pentium run faster.
> >
> > There are no 486 instructions to generate, and anything over -O runs
> > the risk of exposing bugs in the gcc optimiser it seems.
> >
> -m486 expands the code somewhat, with larger alignment boundaries. Netscape
> is already very big :-).
Some postings in DejaNews claim that the -mno-486 runs faster on a Pentium
(than -m486). Other postings say just the opposite.
The -m486 option, from what I understand, benefits the 486 more than a Pentium.
I thought that the Pentium architecture was a ``superset'' more or less
of the 486, so I figured whatever makes a 486 run faster will make a
Pentium run faster.
I figure that:
use: CFLAGS -m486 -O3 for small to medium-sized code.
use: CFLAGS -mno-486 -O3 for large code (ex. - Mozilla, compiling
entire XFree86 dist. from source).
--Donn
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