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From:   Valentin Schneider <vschneid@redhat.com>
To:     Dan Carpenter <dan.carpenter@linaro.org>,
        Steven Rostedt <rostedt@goodmis.org>
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Subject: Re: [RFC PATCH v2 06/20] tracing/filters: Optimise scalar vs
 cpumask filtering when the user mask is a single CPU
In-Reply-To: <b7cf996a-f443-402c-8e13-c5f25a964184@kadam.mountain>
References: <20230720163056.2564824-1-vschneid@redhat.com>
 <20230720163056.2564824-7-vschneid@redhat.com>
 <20230729155547.35719a1f@rorschach.local.home>
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 <20230731115453.395d20c6@gandalf.local.home>
 <b7cf996a-f443-402c-8e13-c5f25a964184@kadam.mountain>
Date:   Mon, 31 Jul 2023 18:20:49 +0100
Message-ID: <xhsmhy1iwq9ou.mognet@vschneid.remote.csb>
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On 31/07/23 19:03, Dan Carpenter wrote:
> On Mon, Jul 31, 2023 at 11:54:53AM -0400, Steven Rostedt wrote:
>> On Mon, 31 Jul 2023 15:07:52 +0300
>> Dan Carpenter <dan.carpenter@linaro.org> wrote:
>>
>> > On Sat, Jul 29, 2023 at 03:55:47PM -0400, Steven Rostedt wrote:
>> > > > @@ -1761,6 +1761,11 @@ static int parse_pred(const char *str, void=
 *data,
>> > > >                                FILTER_PRED_FN_CPUMASK;
>> > > >                } else if (field->filter_type =3D=3D FILTER_CPU) {
>> > > >                        pred->fn_num =3D FILTER_PRED_FN_CPU_CPUMASK;
>> > > > +		} else if (single) {
>> > > > +			pred->op =3D pred->op =3D=3D OP_BAND ? OP_EQ : pred->op;
>> > >
>> > > Nit, the above can be written as:
>> > >
>> > >                  pred->op =3D pret->op !=3D OP_BAND ? : OP_EQ;
>> > >
>> >
>> > Heh.  Those are not equivalent.  The right way to write this is:
>>
>> You mean because of my typo?
>
> No, I hadn't seen the s/pred/pret/ typo.  Your code does:
>
>       if (pred->op !=3D OP_BAND)
>               pred->op =3D true;
>       else
>               pred->op OP_EQ;
>
> Realy we should probably trigger a static checker warning any time
> someone does a compare operations as part of a "x =3D comparison ?: bar;
> Years ago, someone asked me to do that with regards to error codes like:
>
>       return ret < 0 ?: -EINVAL;
>
> but I don't remember the results.
>

FWIW this is caught by GCC:

     error: the omitted middle operand in ?: will always be =E2=80=98true=
=E2=80=99, suggest explicit middle operand [-Werror=3Dparentheses]
     pred->op =3D pred->op !=3D OP_BAND ? : OP_EQ;


> regards,
> dan carpenter