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Subject: Re: crafty faster on AMD however

Author: Vincent Diepeveen

Date: 06:21:35 10/01/02

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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.

Oh well very old intel c++ compilers i already found out i couldn't
use P4 optimizations. I never would *assume* in fact that P4 optimizations
are downwards compatible.

So i never went further than P3 optimizations for all other hardware than
P4.

And it's definitely *not* the case that optimizations that work for P3
also are fast for AMD. A good example is doing 2 vector instructions
after each other at the AMD, which is very bad for it. There are of course
thousands of other combinations which hurt AMD more than P3 or P2.

I hope you realize a chip is a very complex thing. It's millions of
transistors, so there is plenty of combinations to execute instructions
which are getting some kind of penalty on cpu A and not on cpu I.
In short there is plenty of room to make your own cpu look better
than a competing cpu.

Best regards,
Vincent



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