linux-kernel - Re: [PATCH] usb: remove redundant conditions

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Date:	Thu, 10 Dec 2015 12:29:51 -0300
From:	"Geyslan G. Bem" <geyslan@...il.com>
To:	David Laight <David.Laight@...lab.com>
Cc:	Felipe Balbi <balbi@...com>,
	"peter.senna@...il.com" <peter.senna@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Johan Hovold <johan@...nel.org>,
	Robert Baldyga <r.baldyga@...sung.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: remove redundant conditions

2015-12-10 12:17 GMT-03:00 David Laight <David.Laight@...lab.com>:
> From: Felipe Balbi
>> Sent: 10 December 2015 15:14
>> "Geyslan G. Bem" <geyslan@...il.com> writes:
>>
>> > This patch removes redundant conditions.
>> >
>> >  - (!A || (A && B)) is the same as (!A || B).
>> >  - (length && length > 5) can be reduced to a single evaluation.
>> >
>> > Caught by: cppcheck
>> >
>> > Signed-off-by: Geyslan G. Bem <geyslan@...il.com>
>> > ---
>>
>> I guess you didn't get previous comment in time; let's split this per
>> driver so different maintainers can pick their parts.
>
> I also suspect that gcc will optimise out the redundant checks as well.
Yes, David. it will.

Let's see.

void f(int f, int s)
{
        if (!f || (f && s))
                printf("branch\n");
}

Generates without optimization three comparisons:

        cmpl    $0, -4(%rbp)
        je      .L2
        cmpl    $0, -4(%rbp)
        je      .L4
        cmpl    $0, -8(%rbp)
        je      .L4

But with -O2 it generates only two:

        testl   %edi, %edi
        je      .L2
        testl   %esi, %esi
        je      .L1

Despite that, I think that the patches are welcome since they silence
checkpatch and make code clearer. Don't you think?

>
>         David
>



-- 
Regards,

Geyslan G. Bem
hackingbits.com
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