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Re: march question on pentium4
- From: Joe Buck <Joe dot Buck at synopsys dot com>
- To: tprince at computer dot org
- Cc: martin dot kahlert at infineon dot com, gcc at gcc dot gnu dot org
- Date: Fri, 30 Aug 2002 12:08:28 -0700 (PDT)
- Subject: Re: march question on pentium4
On Thursday 29 August 2002 23:04, Martin Kahlert wrote:
> > Hi!
> > I use gcc-3.2 release on a FreeBSD system running on a Pentium 4 machine.
> > My (integer based, no floating point at all) code shows a strange
> > behaviour: It is faster when compiled with -march=pentium3 than
> > with -march=pentium4. Is this a known issue or a problem that should be
> > investigated further?
Tim Prince writes:
> If I am to speculate without an example, the pentium4 costs for shift
> and multiply are set so high that the compiler will always use the
> alternative of add sequences...
It would be better, I think, to look at the actual example and determine
if there are any outright errors in costs for the P4 or P3.