Hard-coding Bottom-up Code Generation Tables to Save Time and Space

Code generators based on bottom-up rewrite systems (BURS) are automatically generated from machinedescription grammars. They produce locally optimal code for expression trees, but their tables are large and require compile-time interpretation. This paper describes a program that compiles BURS tables into a combination of hard code and data. Hard-coding exposed important opportunities for compression that were previously hidden in the tables, so the hard-coded code generators are not just faster but also significantly smaller than their predecessors. A VAX code generator takes 21.4Kbytes and identifies optimal assembly code in about 50 VAX instructions per node.