Techniques for increasing the throughput of a peephole optimizer for intermediate code are presented. An analysis of the optimations to be performed enables an efficient matching and replacement algorithm to be found which minimizes rescanning after a successful replacement. The optimizer uses procedural interfaces; both for the input from the front end phase of the compiler and for the output to the back end. The result is a library module which may optionally be loaded with various other phases of the compiler to provide a flexible range of options regarding compiler size, quality of generated code and compilation speed.