linux-kernel - Re: [patch 5/8] Immediate Values

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Message-ID: <473A4909.1020609@zytor.com>
Date:	Tue, 13 Nov 2007 17:02:01 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@....de>, Chuck Ebbert <cebbert@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [patch 5/8] Immediate Values - x86 Optimization (update)

Mathieu Desnoyers wrote:
> 
> Ok, so the most flexible solution that I see, that should fit for both
> i386 and x86_64 would be :
> 
> 
> 1 byte  : "=Q" : Any register accessible as rh: a, b, c, and d.
> 2, 4 bytes : "=R" : Legacy register—the eight integer registers available
>                  on all i386 processors (a, b, c, d, si, di, bp, sp). 
> 8 bytes : (only for x86_64)
>           "=r" : A register operand is allowed provided that it is in a
>                  general register.
> 
> That should make sure x86_64 won't try to use REX prefixed opcodes for
> 1, 2 and 4 bytes values.
> 
> Does it make sense ?
> 

That's probably the best bet.

	-hpa
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