Efforts to reduce power consumption of processors have gained much attention recently. Dynamic branch predictor, including BTB, is exercised in every instruction cycle, yet branch instructions only constitute a small percentage of instructions during program execution. This study proposes a novel method to collect the next branch distances of the recent branch instructions at runtime, in order to eliminate unnecessary branch predictor lookups. Simulation results show that the proposed design reduces the energy consumption in the dynamic branch predictor by an average of 56.95% without performance degradation. The proposed method is fully compatible with BPP and SEPAS, and saves more energy than PPD, Lazy BTB, and EIB does.

Keywords: branch prediction, BTB, lookup filtering, low power, pipelined processor

Retrieve PDF document (200807_08.pdf)

Received September 12, 2006; revised January 25 & June 25 & October 19, 2007; accepted November 22, 2007.
Communicated by Tei-Wei Kuo.
^*This paper was partially supported by the National Science Council of Taiwan, R.O.C. under grant No. NSC 95-2221-E-009-065-MY3.