Analysis of high-level address code transformations for programmable processors

Memory intensive applications require considerable arithmetic for the computation and selection of the different memory access pointers. These memory address calculations of-ten 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 source-level optimisations (as opposed to instruction-level) for address computations in the context of multimedia. We propose and evaluate two processor-target independent source-level op-timisation 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 number of execution cycles, before and after ap-plying the systematic source-level optimisations, using state-of-the-art C compilers on several popular RISC platforms.