The hardware itself is already very good at predicting the direction. I think the point about PGO here is that you need it to find infrequently-occuring biased-

The hardware itself is already very good at predicting the direction. I think the point about PGO here is that you need it to find infrequently-occuring biased-taken branches. When you encounter a biased-taken branch that isn't currently being tracked by the machine, you're always condemned to pay the cost of a misprediction because the default prediction is "not-taken". The hinting here is supposed to indicate "when encountering this branch, don't predict not-taken by default."