From: Murali Karicheri

Sent: 31 July 2015 16:04
On 07/31/2015 04:38 AM, Viresh Kumar wrote:

quoted

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