Donald Bren School of Information and Computer Sciences

Memory intensive applications require considerable arithmetic for the computation and selection of the different memory access pointers. These memory address calculations often involve complex (non)linear arithmetic expressions which have to be calculated during program execution under tight timing constraints, thus becoming a crucial bottleneck in the overall system performance. This paper explores applicability and effectiveness of sourcelevel optimisations (as opposed to instruction-level) for address computations in the context of multimedia. We propose and evaluate two processor-target independent source-level optimisation techniques, namely, global scope operation cost minimisation complemented with loop-invariant code hoisting, and non-linear operator strength reduction. The transformations attempt to achieve minimal code execution within loops and reduced operator strengths. The effectiveness of the transformations is demonstrated with two real-life multimedia application kernels by comparing the improvements in the nu~ber of execution cycles, before and after applying the systematic source-level optimisations, using state-of-the-art C compilers on several popular RISC platforms.