A compiler scheme for reusing intermediate computation results

Recent research has shown that programs often exhibit value locality. Such locality occurs when a code segment, although executed repeatedly in the program, takes only a small number of different values as input and, naturally, generates a small number of different outputs. It is potentially beneficial to replace such a code segment by a table, which records the computation results for the previous inputs. When the program execution re-enters the code segment with a repeated input, its computation can be simplified to a table look-up. We discuss a compiler scheme to identify code segments, which are good candidates for computation reuse. We discuss the conditions under which the table look-up costs less than repeating the execution, and we perform profiling to identify candidates, which have many repeated inputs at run time. Compared to previous work, this scheme requires no special hardware support and is therefore particularly useful for resource constrained systems such as handheld computing devices. We implement our scheme and its supporting analyses in GCC. We experiment with several multimedia benchmarks and the GNU Go game by executing them on a handheld computing device. The results show the scheme to improve the performance and to reduce the energy consumption quite substantially for these programs.