linux-kernel - Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints

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Message-ID: <46A4F5EF.8010402@zytor.com>
Date:	Mon, 23 Jul 2007 11:39:43 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Satyam Sharma <ssatyam@....iitk.ac.in>,
	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>
Subject: Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints

Linus Torvalds wrote:
> 
> On Mon, 23 Jul 2007, Satyam Sharma wrote:
>> * The "I" constraint modifier is applicable only to immediate-value operands,
>>   and combining it with "r" is bogus.
> 
> This is wrong too.
> 
> The whole point of a "Ir" modifier is to say that the instruction takes 
> *either* an "I" or an "r".
> 
> Andrew - the ones I've looked at were all wrong. Please don't take this 
> series.
> 

Incidentally, I just noticed the x86-64 bitops have "dIr" as their
constraint set.  "d" would normally be redundant with "r", and as far as
I know, gcc doesn't prefer one over the other without having "?" or "!"
as part of the constraint, so is is "d" a stray or is there some meaning
behind it?

	-hpa
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