Tutorial 11, Final Review - ECSE 425 – Computer Organization and ...

Speculative Tomasulo●●●Branching can limit the ILP exploitable by Tomasulo's algorithmSpeculate on branch outcome and start executing the instructionsthat follow the branchDangerous: can modify the processor state irreversibly or raiseunwanted exceptions●●●●●●●Keep track of speculative execution and undo thoseExecute o-o-o but commit in-orderUse re-order buffer to hold uncommitted resultsRegister file updated only when instructions commitRS buffer instructions between issue and execution, but renaming done byROBMispredicted branches flush the later ROB entries and restart executionROB can provide precise exceptions since it commits in order