On the Interactions Between Value Prediction and Compiler Optimizations in the Context of EOLE

Abstract

Increasing instruction-level parallelism is regaining attractiveness within the microprocessor industry. The {Early | Out-of-order | Late} Execution (EOLE) microarchitecture and Differential Value TAgged GEometric (D-VTAGE) value predictor were recently introduced to solve practical issues of Value Prediction (VP). In particular, they remove the most significant difficulties that forbade an effective VP hardware. In this study, we present a detailed evaluation of the potential of VP in the context of EOLE/D-VTAGE and different compiler options. Our study shows that if no single general rule always applies—more optimization might sometimes lead to more performance—unoptimized codes often get a large benefit from the prediction of redundant loads.