linux-kernel - Re: [PATCH] staging: wlan-ng: Avoid bitwise vs logical OR warning in hfa384x_usb

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Date:   Mon, 18 Oct 2021 13:23:45 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] staging: wlan-ng: Avoid bitwise vs logical OR warning in hfa384x_usb_throttlefn()

On Fri, Oct 15, 2021 at 2:44 AM Dan Carpenter <dan.carpenter@...cle.com> wrote:
>
> On Thu, Oct 14, 2021 at 02:57:03PM -0700, Nathan Chancellor wrote:
> > A new warning in clang points out a place in this file where a bitwise
> > OR is being used with boolean expressions:
> >
> > In file included from drivers/staging/wlan-ng/prism2usb.c:2:
> > drivers/staging/wlan-ng/hfa384x_usb.c:3787:7: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
> >             ((test_and_clear_bit(THROTTLE_RX, &hw->usb_flags) &&
> >             ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > drivers/staging/wlan-ng/hfa384x_usb.c:3787:7: note: cast one or both operands to int to silence this warning
> > 1 warning generated.
>
> Both sides of this bitwise OR are bool, so | and || are equivalent
> logically.  Clang should not warn about it.

Not when the LHS AND RHS of the the binary operator have side effects,
which is the only condition under which this warning is emitted.  RHS
potentially sets a bit, and potentially would not be executed if `|`
was replaced with `||`.
-- 
Thanks,
~Nick Desaulniers