Apparatus and Method for Bias-Free Branch Prediction

摘要

Aspects of the present invention provide an apparatus and method for filtering biased conditional branches in a branch predictor in favor of non-biased conditional branches. Biased conditional branches, which are consistently skewed toward one direction or outcome, are filtered such that an increased number of non-biased conditional branches which resolve in both directions may be considered. As a result, more useful branches may be captured over larger distances, thereby providing correlations deeper in a global history to provide greater prediction accuracy. In addition, by tracking only the latest occurrences of non-biased conditional branches using a recency stack structure, even more distant branch correlations may be made.

主权项

1. An apparatus for branch prediction comprising:
a branch history buffer for capturing a plurality of conditional branches provided by an instruction stream; a biased branch filter for distinguishing between biased conditional branches and non-biased conditional branches and permitting only the non-biased conditional branches to be included in the branch history buffer, wherein non-biased conditional branches follow a first branch direction in a first instance during execution of the instruction stream and follow a second branch direction in a second instance during execution of the instruction stream; and a correlation element for correlating between non-biased conditional branches captured in the branch history buffer to predict a direction for a pending conditional branch.