Optimising Compilers

Lecturer: Dr A. Mycroft (am@cl.cam.ac.uk)

No. of lectures: 16

Prerequisite course: Compiler Construction

Aims

The aims of this course are to introduce the principles of program optimisation and related issues in decompilation. The course will cover optimisations of programs at the abstract syntax, flowgraph and target-code level. It will also examine how related techniques can be used in the process of decompilation.

Lectures

• Introduction and motivation. Outline of an optimising compiler. Optimisation partitioned: analysis shows a property holds which enables a transformation. Phase-order problem.

• Kinds of optimisation. Local optimisation, peephole optimisation, code selection, instruction scheduling. Global optimisation, common sub-expressions, code motion, strength reduction. Interprocedural optimisation. The call graph.

• Classical dataflow analysis. Graph algorithms, live and avail sets. Register allocation by register colouring. Common sub-expression elimination. Spilling to memory; treatment of CSE-introduced temporaries. Data flow anomalies.

• Functional program analysis. Abstract interpretation. Strictness analysis. Control flow analysis for lambda-calculus. Rule-based inference of program properties. Types and effect systems.

• Target-dependent optimisations. Instruction selection. Instruction scheduling. Scheduling may require additional registers.

• De-compilation. Legal/ethical issues. Some basic ideas, type discovery and inference.

Objectives

At the end of the course students should

• be able to explain program analyses as dataflow equations on a flowgraph

• know various techniques for high-level optimisation of programs at the abstract syntax level

• understand how code may be re-scheduled to improve execution speed

• know the basic ideas of decompilation

Recommended books

Aho, A.V., Sethi, R. & Ullman, J.D. (1986). Compilers: Principles, Techniques and Tools. Addison-Wesley.
Hankin, C.L., Nielson, F. & Nielson, H.R. (1999). Principles of Program Analysis. Springer.