Branch history table prediction of moving target branches due to subroutine returns

Abstract

A Branch History Table (BHT) stores past action and target for branches, and predicts that future behavior will repeat. Although past action is a good indicator of future action, the subroutine CALL/RETURN paradigm makes correct prediction of the branch target difficult. The authors propose a new stack mechanism for reducing this type of misprediction. Using traces of the SPEC benchmark suite running on an RS/6000, they provide an analysis of the performance enhancements possible using a BHT. It is shown that the proposed mechanism can reduce the number of branch wrong guesses by 18.2% on average.