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Subject: Re: [PATCH] scripts: coccinelle: check for !(un)?likely usage
To:     Julia Lawall <julia.lawall@lip6.fr>,
        Denis Efremov <efremov@linux.com>
Cc:     Joe Perches <joe@perches.com>, cocci@systeme.lip6.fr,
        linux-kernel@vger.kernel.org,
        Gilles Muller <Gilles.Muller@lip6.fr>,
        Nicolas Palix <nicolas.palix@imag.fr>,
        Michal Marek <michal.lkml@markovi.net>
References: <20190825130536.14683-1-efremov@linux.com>
 <b5bae2981e27d133b61d99b08ee60244bf7aabe3.camel@perches.com>
 <88f6e48e-1230-9488-a973-397f4e6dfbb5@linux.com>
 <4E9DDF9E-C883-44F0-A3F4-CD49284DB60D@lip6.fr>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
Message-ID: <95c32d19-eb4d-a214-6332-038610ec3dbd@rasmusvillemoes.dk>
Date:   Wed, 28 Aug 2019 13:33:31 +0200
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On 25/08/2019 21.19, Julia Lawall wrote:
> 
> 
>> On 26 Aug 2019, at 02:59, Denis Efremov <efremov@linux.com> wrote:
>>
>>
>>
>>> On 25.08.2019 19:37, Joe Perches wrote:
>>>> On Sun, 2019-08-25 at 16:05 +0300, Denis Efremov wrote:
>>>> This patch adds coccinelle script for detecting !likely and !unlikely
>>>> usage. It's better to use unlikely instead of !likely and vice versa.
>>>
>>> Please explain _why_ is it better in the changelog.
>>>
>>
>> In my naive understanding the negation (!) before the likely/unlikely
>> could confuse the compiler
> 
> As a human I am confused. Is !likely(x) equivalent to x or !x?

#undef likely
#undef unlikely
#define likely(x) (x)
#define unlikely(x) (x)

should be a semantic no-op. So changing !likely(x) to unlikely(x) is
completely wrong. If anything, !likely(x) can be transformed to
unlikely(!x).

Rasmus