linux-kernel - Re: [PATCH] scsi: FlashPoint: Replace arithmetic addition by bitwise OR

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Message-ID: <9a78cdd254d5d962450242d2e01c3a0f702a63a0.camel@linux.ibm.com>
Date:   Tue, 07 Feb 2023 15:26:48 +0300
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Deepak R Varma <drv@...lo.com>,
        Khalid Aziz <khalid@...ehiking.org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>
Subject: Re: [PATCH] scsi: FlashPoint: Replace arithmetic addition by
 bitwise OR

On Tue, 2023-02-07 at 16:51 +0530, Deepak R Varma wrote:
> When adding two bit-field mask values, an OR operation offers higher
> performance over an arithmetic operation. So, convert such additions
> to an OR based expressions. Issue identified using orplus.cocci
> semantic patch script.

No it doesn't, at least not for constants, which is the entirety of
this patch: the compiler can find the value at compile time, so the
whole lot becomes a load immediate of a single value.  Whether the
compiler sees OR or + is immaterial to the compile time computation. 
Perhaps Coccinelle should be fixed not to complain about this case?

James