linux-kernel - Re: [PATCH v2] scripts: coccinelle: check for !(un)?likely usage

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Date:   Fri, 6 Sep 2019 23:55:39 +0300
From:   Denis Efremov <efremov@...ux.com>
To:     Julia Lawall <julia.lawall@...6.fr>
Cc:     linux-kernel@...r.kernel.org, cocci@...teme.lip6.fr,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Michal Marek <michal.lkml@...kovi.net>,
        Markus Elfring <Markus.Elfring@....de>,
        Joe Perches <joe@...ches.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v2] scripts: coccinelle: check for !(un)?likely usage

Hi,

On 06.09.2019 23:19, Julia Lawall wrote:
> 
> 
> On Thu, 29 Aug 2019, Denis Efremov wrote:
> 
>> This patch adds coccinelle script for detecting !likely and
>> !unlikely usage. These notations are confusing. It's better
>> to replace !likely(x) with unlikely(!x) and !unlikely(x) with
>> likely(!x) for readability.
>>
>> The rule transforms !likely(x) to unlikely(!x) based on this logic:
>>   !likely(x) iff
>>   !__builtin_expect(!!(x), 1) iff
>>    __builtin_expect(!!!(x), 0) iff
>>   unlikely(!x)
>>
>> For !unlikely(x) to likely(!x):
>>   !unlikely(x) iff
>>   !__builtin_expect(!!(x), 0) iff
>>   __builtin_expect(!!!(x), 1) iff
>>   likely(!x)
>>
>> Signed-off-by: Denis Efremov <efremov@...ux.com>
>> Cc: Julia Lawall <Julia.Lawall@...6.fr>
>> Cc: Gilles Muller <Gilles.Muller@...6.fr>
>> Cc: Nicolas Palix <nicolas.palix@...g.fr>
>> Cc: Michal Marek <michal.lkml@...kovi.net>
>> Cc: Markus Elfring <Markus.Elfring@....de>
>> Cc: Joe Perches <joe@...ches.com>
>> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
> 
> Acked-by: Julia Lawall <julia.lawall@...6.fr>
> 
> A small improvement though would be to improve the explicit dependency of
> the last four python rules on r1 and r2.  Those rules won't execute unless
> the inherited metavariable has a value, which makes the same dependency.
> 
> julia

I think I will resend this patch as a part of patchset with all warnings fixed
in a couple of days. Hope this will help to create a discussion point with other
developers about readability of "!likely" and "!unlikely".

Thanks,
Denis