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Wormhole branch prediction using multi-dimensional histories

Analyzing the competition traces, we observe two important facts: 1) branches that require large local histories are typically enclosed within nested loops, and 2) many of these branches exhibit correlations with previous iterations of not only the inner loops but also the outer loops. In this work, we present the wormhole branch predictor, a mechanism that is able to predict and exploit these types of patterns by using multidimensional local histories. Our proposal is integrated on top of a base ISLTAGE predictor. The designs submitted to the 4KB, 32KB and unlimited tracks of the 4th Branch Prediction Championship achieve 3.995, 2.498, and 2.014 MPKI, respectively.