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Date: Wed, 27 Oct 2021 14:34:29 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Paul =?iso-8859-1?Q?Heidekr=FCger?= <paul.heidekrueger@in.tum.de>
Cc: paulmck@kernel.org, will@kernel.org, boqun.feng@gmail.com,
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	pramod.bhatotia@in.tum.de
Subject: Re: Potentially Broken Address Dependency via test_bit() When
 Compiling With Clang
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On Wed, Oct 27, 2021 at 02:17:48PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 27, 2021 at 12:19:48PM +0200, Paul Heidekrüger wrote:
> I would personally not consider this a dependend load. The result
> depends on two loads, but there is no actual ordering between them.
> 
>   r1 = *x
>   r2 = *y
>   b = 1 & (r1 >> r2);
> 
> (more or less)

melver pointed out on IRC that I missed the whole BIT_WORD(nr) thing.
And with that restored this should indeed be an address dependency.

Still, I wasn't actually expecting test_bit() to be one. Nice find.