The accuracy of initial prediction in two-phase dynamic binary translators

Dynamic binary translators use a two-phase approach to identify and optimize frequently executed code dynamically. In the first step (profiling phase), blocks of code are interpreted or quickly translated to collect execution frequency information for the blocks. In the second phase (optimization phase), frequently executed blocks are grouped into regions and advanced optimizations are applied on them. This approach implicitly assumes that the initial profile of each block is representative of the block throughout its lifetime. We investigate the ability of the initial profile to predict the average program behavior. We compare the predicted behavior of varying lengths of the initial execution with the average program behavior for the whole program execution, and use the prediction from the training input as the reference. Our result indicates that, for the SPEC2000 benchmarks, even very short initial profiles have comparable prediction accuracy to the traditional profile-guided optimizations using the training input, although the initial profile is inadequate for predicting loop trip count information for some integer programs and several benchmarks can benefit from phase-awareness during dynamic binary translation.