Understanding branches and designing branch predictors for high-performance microprocessors

Branch prediction is important in high-performance processors and its importance continues to grow. In the drive for higher execution frequencies, pipelines are lengthened and memory latencies are increased. This increases the cost of branch mispredictions. In this paper we describe some behavior patterns of branches. We believe that understanding the behavior of branches is helpful when designing fetch mechanisms for high-performance microprocessors. We also examine several current branch predictors and discuss how they work. Finally, we look at some of the challenges that we are faced with when designing fetch mechanisms and predictors for future microprocessors and discuss some of the possible solutions.