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Unformatted text preview: discard the results that have been computed beyond the branch point. It will also signal to the Branch Unit that the prediction was incorrect and indicate the correct branch destination. In this case the Branch Unit begins fetching at the new location. Such a misprediction incurs a signiﬁcant cost in performance. It takes a while before the new instructions can be fetched, decoded, and sent to the execution units. We explore this further in Section 5.12. Within the ICU, the Retirement Unit keeps track of the ongoing processing and makes sure that it obeys the sequential semantics of the machine-level program. Our ﬁgure shows a Register File, containing the integer and ﬂoating-point registers, as part of the Retirement Unit, because this unit controls the updating of these registers. As an instruction is decoded, information about it is placed in a ﬁrst-in, ﬁrst-out queue. This information remains in the queue until one of two outcomes occurs. First, once the operations for the instruction have completed and any branch points leading to this instruction are conﬁrmed as having been correctly pre...
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This note was uploaded on 09/02/2010 for the course ELECTRICAL 360 taught by Professor Schultz during the Spring '10 term at BYU.
- Spring '10
- The American