linux-kernel - Re: warning from gcc version 4.6.0 20100416

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Message-ID: <4C1641D7.3070802@tmr.com>
Date:	Mon, 14 Jun 2010 10:51:03 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	"Justin P. Mattock" <justinmattock@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: warning from gcc version 4.6.0 20100416

Andi Kleen wrote:
> On Sun, Jun 13, 2010 at 09:17:41PM -0400, Bill Davidsen wrote:
>   
>> Justin P. Mattock wrote:
>>     
>>> o.k. andi,
>>>
>>> here is the rest of the warnings that
>>> I see when compiling the kernel
>>>
>>> I can try and create some patches for
>>> this(hopefully!!)
>>>
>>>       
>> There is no great solution to this, in a fair number of cases the fix would 
>> slow the code or make it harder to read, so some of these probably don't 
>>     
>
> Sorry that's wrong: the optimizer will generate the same
> code anyways as if the unused variable was not  there
> because it eliminates unused variables.
>
>   
If one puts an 'if' around the variable set (I've seen it) the test may 
well take longer than the assign, assuming that there's a case where the 
assign is done.
> So fixing this cannot make code slower.
>
> I also don't see how unused variables make the code easier 
> to read.
>
>   
No, my point was that putting a bunch of ifdef statements in to avoid 
the warning will make the code harder to read.

> The only difficult case sometimes is with #ifdef code,
> that has to be handled case by case. One elegant solution
> is to replace the ifdef code with an inline.
>
>   
>> want a fix. Of course some clearly are errors, so you are doing something 
>>     
>
> All warnings should be fixed, I only left those in that 
> are real code bugs if I couldn't fix the code.
>
> Kernel builds are expected to be relatively warning free
> so that you can easily spot new warnings.
>
> But eventually someone who knows the code better has to
> fix that bug.
>
> --Andi
>
>   


-- 
Bill Davidsen <davidsen@....com>
  "We can't solve today's problems by using the same thinking we
   used in creating them." - Einstein

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