Bruce W. Leverett

Code generation in a machine-independent compiler

This paper presents some code generation issues in the context of the PQCC Production-Quality Compiler-Compiler project [8]. The approach taken is unusual in several ways. The machine-dependent information for selection of code sequences, register assignments, etc., has been separated throughout, in tabular form, from the machine-independent algorithms. This not only greatly simplifies the development of code generators for new machines or languages, but paves the way for automatic generation of these tables from formal machine descriptions such as ISP [1]. A parse-tree-like internal program representation is used, facilitating the use of context and data dependency information about expressions. The code generation process has been broken into several phases. This leads to simplification and better understanding of the code generation process, and also allows important improvements in the quality of generated code. The algorithms for preliminary determination of addressing modes, allocation of registers and other locations, and the code selection case analysis are discussed. The algorithms described in the paper are being implemented and used in the PQCC compiler.

Chaining Span-Dependent Jump Instructions

The assembled length of a span-dependent jump instruction depends on the distance between the instruction and its target. Such instructions are found on many computers and typically have two forms, long and short. We consider the problem of minimizing object program length for such machines by chaining together jumps with the same target. Although the problem is NP-complete in its most general form, several mildly restricted forms of the problem exist that are of practical importance and have efficient solutions.

An adaptive system for dynamic storage allocation

We describe a technique (the adaptive creation of free lists) for dynamic storage allocation that is particularly suited to situations in which the distribution of sizes of blocks requested has one or more sharp peaks. We describe a particular dynamic storage allocation system and the environment in which it runs, and give the results of some experiments to determine the usefulness of the technique in this system. Our experiments also tested the efficacy of a technique suggested by Knuth for improving the performance of similar systems.