Analysing value substitution and confidence estimation for value prediction

Value Prediction is one of the newest techniques used to break down ILP lim its. Despite being under continuous study during the last few years, a few aspects related to this emerging technique remain unanalysed in depth. Exha ustively investigated in the context of control speculation, confidence est imation has usually played a secondary role on value prediction and specula tion. Closely linked to confidence estimation, value substitution also repr esents a relegated subject of research. This paper is focussed on analysing , in an isolated way, the respective impact on predictor performance of bot h confidence estimation and value substitution mechanisms. By using detaile d pipeline-level simulations, we prove that improvements in these mechanism s are as important as reducing the predictor aliasing or even improving the prediction model. (C) 2001 Elsevier Science B.V. All rights reserved.