* - likely(expr) - branch predicition optimization - is more likely
* that expr value will be 1 so optimize for this
* case.
* Example: if (likely(p!=NULL)) {... }
* - unlikely(expr) - branch prediction optimization - is unlikely that
* expr will be true, so optimize for this case
* - prefetch(addr) - will prefetch addr. for reading
* - prefetch_w(addr) - will prefetch addr. for writing
* - prefetch_loc_r(addr, loc) - prefetch for reading, data at addr has
* no temporal locality (loc==0), a short
* degree of temporal locality (loc==1),
* moderate (loc==2) or high (loc==3).
* prefetch(addr) is equiv. to
* prefetch_loc_r(addr, 3).
* prefetch_loc_w(addr, loc) - like above but for writing.
