Novel O-GEHL Based Hyperblock Predictor for EDGE Architectures

Abstract

Control flow speculation plays a pushing role to the performance of block-atomic EDGE architectures. Hyperblock predictors, which leverage the style of "Exit + Target" to predict the next hyperblock address, enable high efficient hyperblock-level control flow speculation for EDGE architectures. Recently, a series of binary prediction techniques have been studied and modified to adapt for the exit predictor in hyperblock predictors, including the O-GEHL prediction technique, which was first presented at 1st Championship Branch Prediction Competition. Our paper investigated different mispredict sources in O-GEHL based exit predictor in hyperblock predictors, and proposed two improved strategies: the O-GEHL based exit predictor without chooser and the O-GEHL based exit predictor employing binary O-GEHL prediction. Performance evaluation results showed that: the proposal without chooser outperformed previously published one by 0.7% with the hardware resource ranging from 16KB to 1MB; the proposal employing 8 binary O-GEHL predictor improved the performance by 3% with the largest hardware resource in this paper (1MB); the proposal employing 4 binary O-GEHL predictor for the first 4 exits averagely improved the performance by 2% with the hardware resource ranging from 16KB to 1MB.