linux-kernel - Re: [PATCH]: x86_64: Remove unnecessary cast in prefetch()

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Message-ID: <87ejgziq8t.fsf@depni.sinp.msu.ru>
Date:	Sun, 16 Sep 2007 01:16:18 +0400
From:	Serge Belyshev <belyshev@...ni.sinp.msu.ru>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andi Kleen <ak@...e.de>, patches@...-64.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH]: x86_64: Remove unnecessary cast in prefetch()

Andi Kleen <andi@...stfloor.org> writes:

...
>> to make kernel work with GCC 4.3 and above.  (Also note that gcc 4.2 already
>> smart enough to break that code, but kernel is just lucky currently).
>
> How would it break the code exactly?  It more sounded like an optimization
> to me. Would it generate incorrect code without it?

See http://gcc.gnu.org/PR33294 for testcase which fails if compiled with gcc 4.2
and above.  Yes, incorrect code can be generated without the patch as demonstrated by
testcase, but i didn't analyze why kernel appears to work with 4.2 currently.
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