Re: [Xen-devel] [PATCH v3 01/11] checkpatch: check for nested (un)?likely() calls

[Denis Efremov <efremov@xxxxxxxxx>]

On 31.08.2019 19:45, Markus Elfring wrote:
>>>> +# nested likely/unlikely calls
>>>> +        if ($line =~ 
>>>> /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
>>>> +            WARN("LIKELY_MISUSE",
>>>
>>> How do you think about to use the specification 
>>> “(?:IS_ERR(?:_(?:OR_NULL|VALUE))?|WARN)”
>>> in this regular expression?
> …
>>    IS_ERR
>>    (?:_ <- Another atomic group just to show that '_' is a common prefix?
> 
> Yes. - I hope that this specification detail can help a bit.

I'm not sure that another pair of brackets for a single char worth it.

>>            Usually, Perl interpreter is very good at optimizing such things.

The interpreter optimizes it internally:
echo 'IS_ERR_OR_NULL' | perl -Mre=debug -ne '/IS_ERR(?:_OR_NULL|_VALUE)?/ && 
print'
Compiling REx "IS_ERR(?:_OR_NULL|_VALUE)?"
Final program:
   1: EXACT <IS_ERR> (4)
   4: CURLYX[0]{0,1} (16)
   6:   EXACT <_> (8)      <-- common prefix
   8:   TRIE-EXACT[OV] (15)
        <OR_NULL> 
        <VALUE>
...
> 
> Would you like to help this software component by omitting a pair of
> non-capturing parentheses at the beginning?
> 
> \b(?:un)?likely\s*

This pair of brackets is required to match "unlikely" and it's
optional in order to match "likely".

Regards,
Denis

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