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Gmane
From: H. J. Lu <hjl <at> lucon.org>
Subject: Re: -m{arch,tune}=native and Core Duo
Newsgroups: gmane.comp.gcc.devel
Date: Friday 1st December 2006 14:43:46 UTC (over 10 years ago)
On Fri, Dec 01, 2006 at 03:36:59AM -0600, Ryan Hill wrote:
> Currently, the way the native CPU detection code in driver-i386.c
> is set up, using -m{arch,tune}=native with an Intel Core Duo (*not
> Core 2 Duo*) processor will result in -m{arch,tune}=prescott.  Is this
> the correct setting for this chip?  There seems to be a lot of confusion
> across the net as to whether a Core Duo (aka Yonah, aka Centrino Duo)
> should be using -march=prescott or -march=pentium-m.  Some argue
> that because Core chips share a lot more in common with with the P6
> microarchitecture than with Netburst, -march=pentium-m should be the
> correct choice.  Others (myself included) point out that just because
> the design is based on the Pentium M doesn't make it a Pentium M.  One
> major argument supporting -march=prescott is that using
> -march=pentium-m will greatly prefer using x87 over SSE scalar code,
> since the Pentium M sucked at SSE (~30% slower than x87 according to
> Intel's Optimization Manual).  Since then, things like improved
> decoding and micro-op fusion have made SSE a definite win on Netburst
> and Core CPUs.  Some have come to the conclusion that
> -march=pentium-m -mfpmath=sse -msse3 is the best solution.
> 
> So anyways, should -m{arch,tune}=native be setting pentium-m for Core
> CPU's, or is prescott really the better choice in the end?

It should be -march=prescott -mtune=generic. I will look into it.


H.J.
 
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