Mill Computing, Inc. › Forums › The Mill › Architecture › Can branch predictors perfectly predict counting loops? › Reply To: Can branch predictors perfectly predict counting loops?
One is the time required to reset the fetch. If the target is not in the I0 microcache then reset would take roughly as long as mispredict recovery, i.e. five cycles in our test configs. Even an I0 hit would likely need three cycles to reset.
It is hard to believe that reset on such early stage of instruction execution (no registry/belt/memory operations) is something different than stall of subsequent “correct” stages. So there should be no lower limit on its duration when the information is available earlier. Just issue correct instruction and wait for its “execution front”.