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