From: Murali Karicheri
> Sent: 31 July 2015 16:04
> On 07/31/2015 04:38 AM, Viresh Kumar wrote:
> > IS_ERR(_OR_NULL) already contain an 'unlikely' compiler flag and there
> > is no need to do that again from its callers. Drop it.
> >
>
> IS_ERR_OR_NULL() is defined as
>
> static inline bool __must_check IS_ERR_OR_NULL(__force const void *ptr)
> {
> return !ptr || IS_ERR_VALUE((unsigned long)ptr);
> }
>
> So the unlikely() applies only to second part. Wouldn't that be a
> problem for optimization?
Ugg...
The unlikely() in IS_ERR_VALUE() is likely to stop the compiler
doing a single 'window' comparison for the range [-MAX_ERROR .. 0].
So you are likely to end up with 2 comparisons.
I suspect that:
return IS_ERR_VALUE((unsigned long)ptr - 1);
would be a much better test.
(Ignoring the off-by-one for the highest error.)
David
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