Re: [dpdk-dev] [PATCH 0/5] remove usage of register keyword in C

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 8/1/2018 10:03 PM, Stephen Hemminger wrote:
> On Wed, 1 Aug 2018 18:03:04 +0000
> Yongseok Koh <yskoh@mellanox.com> wrote:
> 
>>> On Jul 31, 2018, at 11:07 AM, Stephen Hemminger <stephen@networkplumber.org> wrote:
>>>
>>> On Tue, 31 Jul 2018 18:48:40 +0200
>>> Adrien Mazarguil <adrien.mazarguil@6wind.com> wrote:
>>>   
>>>> On Tue, Jul 31, 2018 at 09:30:54AM -0700, Stephen Hemminger wrote:  
>>>>> Declaring variables as register in C is a leftover from an earlier
>>>>> era (like cassette tape decks in cars).    
>>>>
>>>> I don't agree here. It's a hint for compilers and developers that the
>>>> address of such variables won't be needed (and cannot be taken) to enable
>>>> whatever optimizations are possible knowing this.
>>>>
>>>> Somewhat like inline functions, it's not a forced optimization, just a
>>>> useful hint that shouldn't hurt if used wisely.
>>>>
>>>> Besides, cassette decks are not dead yet :)  
>>>
>>> If you look at the code, that is not how register is being used (ie. don't take
>>> address of this). It seems like an attempt at optimization.  
>>
>> I know compilers are smart enough and the occurrences in mlx4/5 were made from
>> my old fashioned habit. But, I don't see any urgency to push this patch in RC
>> stage even though I'm 99% sure that it is harmless. And in general I don't even
>> understand why we can't live with that if it isn't harmful (or a violation) but
>> informative. I mean no badness but at least one goodness :-)
>>
>> Thanks,
>> Yongseok
>>
> 
> Sure, this is intended for next release not rc stage.
> Just trying to clean up code base where I see it.

I agree with Yongseok, at worst they show the intention of the developer, I
don't see motivation to remove them unless they are doing something wrong, which
seems not the reason of this patch.

And although I found some information that says "register" ignored completely
for gcc, I can see it differs when optimization disabled.
I am not saying practically it differs, since we enable optimization expect from
debugging, most probably there is no practical difference between having the
keyword or not, but what I am trying to say is it not completely ignored either.