linux-kernel - Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm__ __volatile_

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Message-ID: <46A4F360.2000905@goop.org>
Date:	Mon, 23 Jul 2007 11:28:48 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Satyam Sharma <ssatyam@....iitk.ac.in>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm__ __volatile__

Satyam Sharma wrote:
> The (3) as I had originally written / meant was that multiple
> instructions in a volatile asm would not get _individually_
> interspersed with the rest of the code i.e. be emitted out
> _consecutively_. I don't think we need any such guarantees for
> the non-atomic variants of those operations, so it's good to
> let the compiler have a free hand with what it wants to do,
> and optimize/combine multiple bitops as necessary / possible,
> which was the original intention.
>   

No, a single asm statement is always emitted in one piece.  Gcc doesn't
parse the string other than to do %-substitution to insert arguments, so
it has no way to meaningfully split it up.

    J
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