netdev - Re: [PATCH] igb: Convert a series of if statements to switch case

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Date:   Thu, 12 May 2022 21:31:58 +0800
From:   Linkui Xiao <xiaolinkui@...il.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "pmenzel@...gen.mpg.de" <pmenzel@...gen.mpg.de>,
        "jesse.brandeburg@...el.com" <jesse.brandeburg@...el.com>,
        "anthony.l.nguyen@...el.com" <anthony.l.nguyen@...el.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Linkui Xiao <xiaolinkui@...inos.cn>
Subject: Re: [PATCH] igb: Convert a series of if statements to switch case

Dear David,

Thanks for your reply

Logically the two versions are equivalent, hw->mac.type is defined as 
follows:

enum e1000_mac_type {
         e1000_undefined = 0,
         e1000_82575,
         e1000_82576,
         e1000_82580,
         e1000_i350,
         e1000_i354,
         e1000_i210,
         e1000_i211,
         e1000_num_macs  /* List is 1-based, so subtract 1 for true 
count. */
};
Therefore, hw->mac.type < e1000_82576 has only two cases: 
e1000_undefined or e1000_82575.

On 5/12/22 21:14, David Laight wrote:
>> From: Linkui Xiao <xiaolinkui@...inos.cn>
>>
>> Convert a series of if statements that handle different events to a switch
>> case statement to simplify the code.
>>
>> V2: fix patch description and email format.
>>
>> Signed-off-by: Linkui Xiao <xiaolinkui@...inos.cn>
>> ---
>>   drivers/net/ethernet/intel/igb/igb_main.c | 12 ++++++++----
>>   1 file changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
>> index 34b33b21e0dc..4ce0718eeff6 100644
>> --- a/drivers/net/ethernet/intel/igb/igb_main.c
>> +++ b/drivers/net/ethernet/intel/igb/igb_main.c
>> @@ -4588,13 +4588,17 @@ static inline void igb_set_vf_vlan_strip(struct igb_adapter *adapter,
>>        struct e1000_hw *hw = &adapter->hw;
>>        u32 val, reg;
>>
>> -     if (hw->mac.type < e1000_82576)
>> +     switch (hw->mac.type) {
>> +     case e1000_undefined:
>> +     case e1000_82575:
>>                return;
>> -
>> -     if (hw->mac.type == e1000_i350)
>> +     case e1000_i350:
>>                reg = E1000_DVMOLR(vfn);
>> -     else
>> +             break;
>> +     default:
>>                reg = E1000_VMOLR(vfn);
>> +             break;
>> +     }
>>
>>        val = rd32(reg);
>>        if (enable)
>> --
>> 2.17.1
> Are you sure that generates reasonable code?
> The compiler could generate something completely different
> for the two versions.
>
> It isn't even obvious they are equivalent.
>
> 	David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>