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

[Rasmus Villemoes]

On 25/08/2019 21.19, Julia Lawall wrote:
> 
> 
>> On 26 Aug 2019, at 02:59, Denis Efremov <efremov@xxxxxxxxx> 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