Boolean Formula-based Branch Prediction for Future Technologies
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We present a new method for branch prediction that encodes in the branch instruction a formula, chosen by profiling, that is used to perform history-based prediction. By using a special class of Boolean formulas, our encoding is extremely concise. By replacing the large tables found in current predictors with a small, fast circuit, our scheme is ideally suited to future technologies that will have large wire delays. In a projected 70 nm technology and an aggressive clock rate of about 5 GHz, an implementation of our method that uses an 8-bit formula encoding has a misprediction rate of 6.0%, 42% lower than that of the best gshare predictor implementable in that same technology. In today's technology, a 16-bit version of our predictor can replace bias bits in an 8K-entry agree predictor to achieve a 2.86% misprediction rate, which is slightly lower than the 2.93% misprediction rate of the Alpha 21264 hybrid predictor, even though the Alpha predictor has almost twice the hardware budget. Our predictor also consumes much less power than table-based predictors. This paper describes our predictor, explains our profiling algorithm, and presents experimental results using the SPEC 2000 integer benchmarks.
author list (cited authors)
Jimenez, D. A., Hanson, H. L., & Lint, C.