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

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Date:	Fri, 7 Sep 2007 08:18:03 +0100
From:	Andi Kleen <ak@...e.de>
To:	Serge Belyshev <belyshev@...ni.sinp.msu.ru>
Cc:	patches@...-64.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH]: x86_64: Remove unnecessary cast in prefetch()

On Thursday 06 September 2007 22:27, Serge Belyshev wrote:
> It is ok to call prefetch() function with NULL argument, as specifically
> commented in include/linux/prefetch.h.  But in standard C, it is invalid to
> dereference NULL pointer (see C99 standard 6.5.3.2 paragraph 4 and note
> #84). Newer gcc versions (4.3 and above) will use that to conclude that "x"
> argument is non-null and thus wreaking havok everywhere prefetch() was
> inlined. Fixed by removing cast and changing asm constraint.
>
> This can be fixed better by using gcc's __builtin_prefetch().

I changed it to just use that. Thanks.

It seems like gcc 3.1/3.2 already supported it and that's the earliest gcc
still supported so it can be used unconditionally.

-Andi
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