Methods and apparatus for predicting unaligned memory access

Abstract

In an instruction execution pipeline, the misalignment of memory access instructions is predicted. Based on the prediction, an additional micro-operation is generated in the pipeline prior to the effective address generation of the memory access instruction. The additional micro-operation accesses the memory falling across a predetermined address boundary. Predicting the misalignment and generating a micro-operation early in the pipeline ensures that sufficient pipeline control resources are available to generate and track the additional micro-operation, avoiding a pipeline flush if the resources are not available at the time of effective address generation. The misalignment prediction may employ known conditional branch prediction techniques, such as a flag, a bimodal counter, a local predictor, a global predictor, and combined predictors. A misalignment predictor may be enabled or biased by a memory access instruction flag or misaligned instruction type.