linux-kernel - Re: [PATCH] media: atomisp: silence "dubious: !x

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Message-ID: <20210420102747.GB1981@kadam>
Date:   Tue, 20 Apr 2021 13:27:47 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     "'Mauro Carvalho Chehab'" <mchehab@...nel.org>,
        Ashish Kalra <eashishkalra@...il.com>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [PATCH] media: atomisp: silence "dubious: !x | !y" warning

On Sat, Apr 17, 2021 at 09:31:32PM +0000, David Laight wrote:
> From: Mauro Carvalho Chehab
> > Sent: 17 April 2021 19:56
> > 
> > Em Sat, 17 Apr 2021 21:06:27 +0530
> > Ashish Kalra <eashishkalra@...il.com> escreveu:
> > 
> > > Upon running sparse, "warning: dubious: !x | !y" is brought to notice
> > > for this file.  Logical and bitwise OR are basically the same in this
> > > context so it doesn't cause a runtime bug.  But let's change it to
> > > logical OR to make it cleaner and silence the Sparse warning.
> 
> The old code is very likely to by slightly more efficient.
> 
> It may not matter here, but it might in a really hot path.
> 
> Since !x | !y and !x || !y always have the same value
> why is sparse complaining at all.
> 

Smatch doesn't warn about | vs || if both sides are true/false.  But
I've occasionally asked people if they were trying to do a fast path
optimization but it's always just a typo.

regards,
dan carpenter