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Subject: Re: crafty faster on AMD however

Author: Robert Hyatt

Date: 19:43:58 10/01/02

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On October 01, 2002 at 09:43:00, Vincent Diepeveen wrote:

>On September 30, 2002 at 12:13:44, Robert Hyatt wrote:
>
>>On September 30, 2002 at 00:09:28, Jeremiah Penery wrote:
>>
>>>On September 29, 2002 at 23:31:36, Robert Hyatt wrote:
>>>
>>>>I don't know what this means.  I have several dozen programs (Crafty
>>>>is only one) that we have run using intel's compiler and gcc, and in
>>>>_every_ case, Intel's compiler is faster.  On P2's, on P3's and on
>>>>P4's...  Of course I wouldn't use intel's compiler for an AMD chip,
>>>>why would they want to optimize for a competitor's chip???
>>>
>>>They don't have to optimize specifically for the competitor's chip, as Intel
>>>compiler still produces probably the fastest binaries for AMD machines.  Any
>>>general optimizations (P2, P3, and even P4 optimizations (excluding SSE2 stuff
>>>or whatever)) are just as helpful for AMD processors as they are for Intel ones.
>>
>>
>>Maybe or maybe not.  AMD's pipeline is different, and there are subtle
>>differences in instruction choices, that can make a difference in speed.  I
>>don't see why the Intel compiler guys would bother studying AMD at all...
>
>I bet 50% of their time goes into studying what is faster for P4 than for K7 :)


I'd bet they don't.  Optimizing for a specific processor family is tough.

Trying to optimize for one while producing code that does worse on another
processor is a _real_ can of worms.  I don't think anyone would waste that
kind of time.



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