Efficient Programming

Abstract

In this chapter we give an overview of common program optimisation techniques. In each case the aim is to retain the program semantics but improve the “quality” somehow. For example, one might re-write the program so it executes more quickly or so that it uses less memory. These techniques are notoriously ad-hoc: our aim is to present a reasoned description, making the implications of each case clear when describing what they achieve. Many of the presented techniques can be achieved by hand or by using some level of automation in the compiler. In the former case it is important to understand the technique so it can be applied; in the latter case the understanding is important so one can reason about what the compiler is doing and why. The overall aim is that a given program gets the most from the underlying hardware: even efficient processors are only as efficient as the programs they execute !