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Date: Fri, 14 Nov 2014 07:06:14 +0100 (CET)
From: Julia Lawall <julia.lawall@lip6.fr>
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To: Joe Perches <joe@perches.com>
cc: cocci <cocci@systeme.lip6.fr>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [Cocci] spatch for trivial pointer comparison style?
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On Thu, 13 Nov 2014, Joe Perches wrote:

> I added a checkpatch entry for this.
> Maybe some cocci test like this would be useful?
> 
> @@
> type t;
> t *p;
> @@
> -	p == NULL
> +	!p
> 
> @@
> type t;
> t *p;
> @@
> -	p != NULL
> +	p
> 
> @@
> type t;
> t *p;
> @@
> -	NULL == p
> +	!p
> 
> @@
> type t;
> t *p;
> @@
> -	NULL != p
> +	p

This was discussed many years ago.  I don't think that the change is 
desirable in all cases.  There are functions like kmalloc where NULL means 
failure and !p seems like the reasonable choice.  But there maybe other 
cases where NULL is somehow a meaningful value.  

Here is a link to the part of the discussion:

https://lkml.org/lkml/2007/7/27/103

julia