Message-ID: <3EF33B12.7070901@inet.com>
Date: Fri, 20 Jun 2003 11:49:22 -0500
From: Eli Carter <eli.carter@inet.com>
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To: John Bradford <john@grabjohn.com>
CC: nuno.silva@vgertech.com, torvalds@transmeta.com,
       linux-kernel@vger.kernel.org, samphan@thai.com, vojtech@suse.cz
Subject: Re: Crusoe's persistent translation on linux?
References: <200306201040.h5KAerPK000431@81-2-122-30.bradfords.org.uk>
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John Bradford wrote:
>>The translations are usually _better_ than statically compiled native 
>>code (because the whole CPU is designed for speculation, and the static 
>>compilers don't know how to do that), and thus going to native mode is not 
>>necessarily a performance improvement.
> 
> 
> Would it be possible, (with relevant documentation), to tune the code
> morphing software for optimum performance of code generated by a
> specific compiler, though?
> 
> If a particular version of GCC favours certain constructs and uses
> particular sets of registers for a given piece of code, couldn't we
> optimise for those cases, at the expense of others?  Maybe a
> particular compiler doesn't use certain X86 instructions at all, and
> these could be eliminated altogether?
> 
> It's not unlikely that an entirely open source system could have all
> code compiled with the same compiler, and so maybe we can use this to
> avoid implementing expensive corner cases in the CPU, because we're
> never going to trigger them.

Hmm... basically you want to trim the x86 instruction set to get closer 
to RISC mentality.  Interesting.  gcc may already do that to some extent 
by not using the really complex instructions.  If that is the case, 
dropping those instructions might give some room for testing some of its 
possible benefits.  I doubt restricting the registers used by some 
instructions would help... I've heard comments that the x86 is 
register-starved enough already.

Have fun,

Eli
--------------------. "If it ain't broke now,
Eli Carter           \                  it will be soon." -- crypto-gram
eli.carter(a)inet.com `-------------------------------------------------

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