On 09/21/2015 03:42 PM, David Howells wrote:
> Andrzej Hajda <a.hajda-sze3o3uu22jbdgjk7y7...@public.gmane.org> wrote:
>
>> Semantic patch finds comparisons of types:
>> unsigned < 0
>> unsigned >= 0
>> The former is always false, the latter is always true.
>> Such comparisons are useless, so theoretically they could be
>> safely removed, but their presence quite often indicates bugs.
>
> Or someone has left them in because they don't matter and there's the
> possibility that the type being tested might be or become signed under some
> circumstances. If the comparison is useless, I'd expect the compiler to just
> discard it - for such cases your patch is pointless.
>
> If I have, for example:
>
> unsigned x;
>
> if (x == 0 || x > 27)
> give_a_range_error();
>
> I will write this as:
>
> unsigned x;
>
> if (x <= 0 || x > 27)
> give_a_range_error();
>
> because it that gives a way to handle x being changed to signed at some point
> in the future for no cost. In which case, your changing the <= to an ==
> "because the < part of the case is useless" is arguably wrong.
This is why I have not checked for such cases - I have skipped checks of type
unsigned <= 0
exactly for the reasons above.
However I have left two other checks as they seems to me more suspicious - they
are always true or false. But as Dmitry and Andrew pointed out Linus have quite
strong opinion against removing range checks in such cases as he finds it
clearer. I think it applies to patches 29-36. I am not sure about patches
26-28,37.
Regards
Andrzej
>
> David
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