Improving Branch Prediction and Predicated Execution in Out-of-Order Processors

If-conversion is a compiler technique that reduces the misprediction penalties caused by hard-to-predict branches, transforming control dependencies into data dependencies. Although it is globally beneficial, it has a negative side-effect because the removal of branches eliminates useful correlation information necessary for conventional branch predictors. The remaining branches may become harder to predict. However, in predicated ISAs with a compare-branch model, the correlation information not only resides in branches, but also in compare instructions that compute their guarding predicates. When a branch is removed, its correlation information is still available in its compare instruction. We propose a branch prediction scheme based on predicate prediction. It has three advantages: First, since the prediction is not done on a branch basis but on a predicate define basis, branch removal after if-conversion does not lose any correlation information, so accuracy is not degraded. Second...

• Type: Conference
• Year: 2007
• Where: HPCA
• Authors: Eduardo Quiñones, Joan-Manuel Parcerisa, Antonio González
• Keywords: Branch Predicate, Branch Prediction Scheme, Computer Architecture, HPCA 2007, Selective Predicate Prediction