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Message-ID: <alpine.LFD.0.999.0708120251570.30176@woody.linux-foundation.org>
Date: Sun, 12 Aug 2007 02:54:16 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Martin Schwidefsky <schwidefsky@...ibm.com>
cc: Segher Boessenkool <segher@...nel.crashing.org>,
wjiang@...ilience.com, wensong@...ux-vs.org,
heiko.carstens@...ibm.com, linux-kernel@...r.kernel.org,
ak@...e.de, cfriesen@...tel.com, netdev@...r.kernel.org,
horms@...ge.net.au, akpm@...ux-foundation.org,
Chuck Ebbert <cebbert@...hat.com>, davem@...emloft.net,
zlynx@....org, Chris Snook <csnook@...hat.com>
Subject: Re: [PATCH] make atomic_t volatile on all architectures
On Sun, 12 Aug 2007, Martin Schwidefsky wrote:
>
> The duplication "=m" and "m" with the same constraint is rather
> annoying.
It's not only annoying, it causes gcc to generate bad code too. At least
certain versions of gcc will generate the address *twice*, even if there
is obviously only one address used.
If you have problems with "+m", you are often actually better off using
just "m" and then adding a memory clobber. But that has other code
generation downsides.
Linus
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