linux-kernel - Re: [RFC] x86: bitops asm constraint fixes

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Message-ID: <47E112C7.8020406@zytor.com>
Date:	Wed, 19 Mar 2008 06:19:03 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jan Beulich <jbeulich@...ell.com>
CC:	Chuck Ebbert <cebbert@...hat.com>, mingo@...e.hu,
	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [RFC] x86: bitops asm constraint fixes

Jan Beulich wrote:
> 
> That's not very desirable: For one part, because there are uses of
> bitops on arrays of ints (and casting these up isn't fully correct on
> x86-64 because of the same reason that using the bitops on char
> arrays isn't correct (see the other response I sent to Jeremy's reply),
> but also because operating on longs requires REX prefixes n x86-64,
> hence making the code bigger for no good reason.
> 

It might be worthwhile to find out if 64-bit bitops are faster.

Bitops are normally defined only on longs, but since x86 is a 
littleendian architecture we sometimes fudge that in arch-specific code.

	-hpa
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