[cygnus.project.sid] branch probability hinting

[Tom Tromey]

>> Also please everyone note that the compiler already knows that
>> if (p == NULL)
>> is unlikely

Hans> Presumably it will take a hint that it's likely, e.g. when
Hans> scanning a sparse chained hash table?

I don't know.

Hans> How do you tell gcc that the branch probability is around 50-50
Hans> if it already believes otherwise?  (E.g. half the child pointers
Hans> in a binary tree are NULL.)

I don't think there is a way.  Maybe this should be reported as a gcc
bug.  Maybe you ought to be able to tell __builtin_expect the
probability that the branch is taken.

Tom