>It looks like there's no penalty on this processor, though I would be surprised if it does not have a branch predictor / return stack tracking at all One pote

>It looks like there's no penalty on this processor, though I would be surprised if it does not have a branch predictor / return stack tracking at all One potential explanation is that a lot of processors have "meta" predictors. That is, they have multiple distinct predictors that they then use a second level predictor to decide when and how they use it. This is really useful because some predictors perform very well in certain cases but very poorly in others. Therefore, what may be happening is that the RAS is getting overridden by another structure since the predictor detects that the RAS is frequently wrong but another predictor is frequently right.