[cygnus.project.sid] branch probability hinting

Mon Mar 5 20:58:00 GMT 2001

On 5 Mar 2001, Tom Tromey wrote:
> 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.

If I understand right, GCC takes branch probabilities into account
during a basic block reordering pass. 50-50 cannot be expressed by
simple reordering.
Out of curiosity, are there any targets that can make use of a 50-50
branch probability? IA-64 perhaps?
Jeff