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Subject: Re: [PATCH v3 01/11] checkpatch: check for nested (un)?likely() calls
To:     Markus Elfring <Markus.Elfring@web.de>,
        Joe Perches <joe@perches.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Anton Altaparmakov <anton@tuxera.com>,
        Andy Whitcroft <apw@canonical.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Boris Pismenny <borisp@mellanox.com>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        "David S. Miller" <davem@davemloft.net>,
        Dennis Dalessandro <dennis.dalessandro@intel.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        dri-devel@lists.freedesktop.org,
        Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>,
        =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>,
        Leon Romanovsky <leon@kernel.org>,
        linux-arm-msm@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-ntfs-dev@lists.sourceforge.net, linux-rdma@vger.kernel.org,
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        Mike Marciniszyn <mike.marciniszyn@intel.com>,
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        =?UTF-8?Q?Pali_Roh=c3=a1r?= <pali.rohar@gmail.com>,
        Rob Clark <robdclark@gmail.com>,
        Saeed Mahameed <saeedm@mellanox.com>,
        Sean Paul <sean@poorly.run>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        xen-devel@lists.xenproject.org, Enrico Weigelt <lkml@metux.net>
References: <20190829165025.15750-1-efremov@linux.com>
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 <689c8baf-2298-f086-3461-5cd1cdd191c6@linux.com>
 <493a7377-2de9-1d44-cd8f-c658793d15db@web.de>
From:   Denis Efremov <efremov@linux.com>
Message-ID: <c5e4479d-2fb3-b5a5-00c3-b06e5177d869@linux.com>
Date:   Sat, 31 Aug 2019 20:07:34 +0300
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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