Misprediction recovery is an important area of optimization. Mispredictions tend to flush and begin refetching ASAP, so rather than wait until retire, they will

Misprediction recovery is an important area of optimization. Mispredictions tend to flush and begin refetching ASAP, so rather than wait until retire, they will do that when they execute, including out of order (a newer branch could flush before an older one is resolved, and later itself could be flushed by that older one). There are also several levels of predictor and mistakes in the low latency but less accurate ones can cause recovery events if they are overridden a few cycles later by slower predictors. Flush / recovery is made as light weight as possible, only flushing instructions after the branch, and only the parts of the pipeline that the oldest one has reached. There is some literature on controlling speculation if you are not confident. Say if you have a really poorly predicted indirect branch target where a mispredict is not 50/50 but 99/1, and it depends on a very slow source, then you might not want to speculate 500 instructions ahead of that but say okay let's just wait for it to resolve. Or, if you have a 50/50 hard to predict branch, you might kick off some prefetching down the other path when you see it so recovery is faster (but this will cost more power). I don't know if anybody does anything with these "hard to predict branches" today. Apparently it's actually quite difficult to predict whether a branch is hard to predict, and the resources to make that prediction can be put to better use just trying to predict them instead of predicting that you can't predict them :) Although that might change. Point is al kinds of misprediction optimization are actively being pursued.