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Subject: Re: [PATCH] mips: bug: add unlikely() to BUG_ON()
To:     Paul Burton <paul.burton@mips.com>
Cc:     David Daney <ddaney@caviumnetworks.com>,
        Igor Stoppa <igor.stoppa@huawei.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        James Hogan <jhogan@kernel.org>, linux-mips@linux-mips.org,
        linux-kernel@vger.kernel.org
References: <20180907180302.656-1-igor.stoppa@huawei.com>
 <20180907220208.nqucxycxsxmyxt4m@pburton-laptop>
From:   Igor Stoppa <igor.stoppa@gmail.com>
Message-ID: <d702acea-0aac-abc3-c48e-21f0e44d5870@gmail.com>
Date:   Mon, 10 Sep 2018 12:45:03 +0300
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Hi Paul,

On 08/09/18 01:02, Paul Burton wrote:

> I'm not sure this will actually do anything.
> 
> __BUG_ON() doesn't use the value of its condition argument for regular
> control flow unless it's compile-time constant anyway, in which case
> unlikely() should be redundant because the compiler knows the value
> already.
> 
> If the condition isn't compile-time constant then we just emit a tne
> (trap-if-not-equal) instruction using inline asm. That will generate an
> exception if the value is non-zero at runtime. I don't see how adding
> unlikely() is going to help the compiler do anything differently with
> that.

Thank you for the explanation. Please discard this patch.

--
igor