From: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
To: David Laight <David.Laight@aculab.com>
Cc: 'Mauro Carvalho Chehab' <mchehab@kernel.org>,
Ashish Kalra <eashishkalra@gmail.com>,
Sakari Ailus <sakari.ailus@linux.intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
"devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] media: atomisp: silence "dubious: !x | !y" warning
Date: Sun, 18 Apr 2021 23:59:31 +0200 [thread overview]
Message-ID: <20210418215931.kbgme42kgnpqbwn4@mail> (raw)
In-Reply-To: <509f019decae433cab6cb367cdfa6fa9@AcuMS.aculab.com>
On Sat, Apr 17, 2021 at 09:31:32PM +0000, David Laight wrote:
> > > 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.
They both will have the same value here and any half-decent
compiler know that and thus generate the same code, so no
worries about efficiency.
Sparse complains because the programmer's intention is not clear.
Was a boolean context or a bitwise context that was meant?
Maybe '||' was meant and the RHS had to be short cut?
Maybe what was meant was '~x | ~y'?
-- Luc
WARNING: multiple messages have this Message-ID (diff)
From: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
To: David Laight <David.Laight@aculab.com>
Cc: "devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
Ashish Kalra <eashishkalra@gmail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Sakari Ailus <sakari.ailus@linux.intel.com>,
'Mauro Carvalho Chehab' <mchehab@kernel.org>,
"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>
Subject: Re: [PATCH] media: atomisp: silence "dubious: !x | !y" warning
Date: Sun, 18 Apr 2021 23:59:31 +0200 [thread overview]
Message-ID: <20210418215931.kbgme42kgnpqbwn4@mail> (raw)
In-Reply-To: <509f019decae433cab6cb367cdfa6fa9@AcuMS.aculab.com>
On Sat, Apr 17, 2021 at 09:31:32PM +0000, David Laight wrote:
> > > 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.
They both will have the same value here and any half-decent
compiler know that and thus generate the same code, so no
worries about efficiency.
Sparse complains because the programmer's intention is not clear.
Was a boolean context or a bitwise context that was meant?
Maybe '||' was meant and the RHS had to be short cut?
Maybe what was meant was '~x | ~y'?
-- Luc
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next prev parent reply other threads:[~2021-04-18 21:59 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-17 15:36 [PATCH] media: atomisp: silence "dubious: !x | !y" warning Ashish Kalra
2021-04-17 15:36 ` Ashish Kalra
2021-04-17 18:56 ` Mauro Carvalho Chehab
2021-04-17 18:56 ` Mauro Carvalho Chehab
2021-04-17 21:31 ` David Laight
2021-04-17 21:31 ` David Laight
2021-04-18 1:15 ` Ashish Kalra
2021-04-18 1:15 ` Ashish Kalra
2021-04-18 21:59 ` Luc Van Oostenryck [this message]
2021-04-18 21:59 ` Luc Van Oostenryck
2021-04-20 10:27 ` Dan Carpenter
2021-04-20 10:27 ` Dan Carpenter
2021-04-20 10:36 ` David Laight
2021-04-20 10:36 ` David Laight
2021-04-18 1:26 ` Ashish Kalra
2021-04-18 1:26 ` Ashish Kalra
2021-04-20 12:04 ` Hans Verkuil
2021-04-20 12:04 ` Hans Verkuil
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