Compressed Instruction Set Coding (CISC) for Performance Optimization of Hand Held Devices

Compressing repeated instructions of the application program for mobile devices can significantly improve the performance and reduce the code size. The present work focuses on grouping of instructions based on data flow dependencies and repetition of operation code (Opcode). The compression is carried out by identifying the repeated sequences of instructions from the grouped Instruction Set (IS) and a new IS is generated which will result in performance improvement in terms of speed and memory usage. The repeated sequence of instructions are identified and then compressed to reduce the code size. The extra overhead incurred in decompressing the IS is compensated by eliminating the opcode translation look up time for the repeated instructions. A case study has been conducted by considering the ARM instructions for compression. For optimizing the instruction set of the application program, a novel method has been employed. Two approaches - one static and one dynamic are used for storing the opcodes and operands. The implementation of the proposed scheme shows that in comparison to existing method, an average reduction of 36% of code-size is possible and further improvement can be achieved by changing the instruction length of the given architecture.