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Open Access Publications from the University of California

A systematic approach to branch speculation


A general theoretical framework is developed for the study of branch speculation. The framework yields a systematic way to select the schedule in a given set that, for any (estimated) bias of the branch, minimizes the expected execution time. Among other things, it is shown that in some cases the optimal schedule is neither of those resulting from aggressively speculating on any given outcome of the conditional. Our results can be useful in either static or dynamic approaches. We propose a simple run-time estimator for the bias and discuss how to combine it with schedule selection. A number of examples motivate and illustrate the techniques, and show that our approach yields better performance in the case of highly unpredictable branches.

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