Improving Offset Assignment for Embedded Processors

Embedded systems consisting of the application program ROM, RAM, the embedded processor core, and any custom hardware on a single wafer are becoming increasingly common in application domains such as signal processing. Given the rapid deployment of these systems, programming on such systems has shifted from assembly language to high-level languages such as C, C++, and Java. The processors used in such systems are usually targeted toward specific application domains, e.g., digital signal processing (DSP). As a result, these embedded processors include application-specific instruction sets, complex and irregular data paths, etc., thereby rendering code generation for these processors difficult. In this paper, we present new code optimization techniques for embedded fixed point DSP processors which have limited on-chip program ROM and include indirect addressing modes using post-increment and decrement operations. We present a heuristic to reduce code size by taking advantage of these addressing modes. Our solution aims at improving the offset assignment produced by Liao et al.'s solution. It finds a layout of variables in RAM, so that it is possible to subsume explicit address register manipulation instructions into other instructions as a post-increment or post-decrement operation. Experimental results show the effectiveness of our solution.