[patch] Add a new warning flag -Wself-assign

[Le-Chun Wu]

Dave,

On Fri, May 28, 2010 at 5:24 PM, Dave Korn <dave.korn.cygwin@gmail.com> wrote:
> On 29/05/2010 00:47, Le-Chun Wu wrote:
>
>  Hello,
>
>> This patch adds a new warnings flag "-Wself-assign" that warns about
>> self-assignment (including self-initialization). This warning is
>> intended for detecting accidental self-assignment due to typos, and
>> therefore does not warn on a statement that is semantically a
>> self-assignment after constant folding. Here is an example of what
>> will trigger a self-assign warning and what will not:
>>
>>           void func()
>>           {
>>              int i = 2;
>>              int x = x;   /* warn */
>>              float f = 5.0;
>>              double a[3];
>>
>>              i = i + 0;   /* not warn */
>>              f = f / 1;   /* not warn */
>>              a[1] = a[1]; /* warn */
>>              i += 0;      /* not warn */
>>           }
>
>  It is a very common idiom to write:
>
>> <returntype> f (<type> x)
>> {
>>   x = x;
>>   [ ... do other stuff ... ]
>>   return [some value or none]
>> }
>
> ... in order try and avoid parameter-unused warnings in a portable fashion;
> how does your patch react to this technique?
>

Our recommendation is to use `(void) x' or `static_cast<void>(x)'
instead, which should also be portable. (I actually added this
recommendation in the documentation of -Wunused flag in my patch.)

Thanks,

Le-chun