Evaluation of extended dictionary-based static code compression schemes

• Authors: Martin Thuresson;Per Stenstrom
• Venue: Proceedings of the 2nd conference on Computing frontiers
• Year: 2005

This paper evaluates how much extended dictionary-based code compression techniques can reduce the static code size. In their simplest form, such methods statically identify identical instruction sequences in the code and replace them by a codeword if they yield a smaller code size based on a heuristic. At run-time, the codeword is replaced by a dictionary entry storing the corresponding instruction sequence.Two previously proposed schemes are evaluated. The first scheme, as used in DISE, provides operand parameters to catch a larger number of identical instruction sequences. The second scheme replaces different instruction sequences with the same dictionary entry if they can be derived from it using a bit mask that can cancel out individual instructions. Additionally, this paper offers a third scheme, namely, to combine the two previously proposed schemes along with an off-line algorithm to compress the program. Our data shows that all schemes in isolation improve the compressibility. However, the most important finding is that the number of operand parameters has a significant effect on the compressibility. In addition, our proposed combined scheme can reduce the size of the dictionary and the number of codewords significantly which can enable efficient implementations of extended dictionary-based code compression techniques