Optimizing Smalltalk by selector code indexing can be practical

Abstract

Selector code indexing is a simple and effective way of optimizing method lookups. However, it has not been considered practically applicable in Smalltalk, because the space overhead is prohibitive. We propose a new technique called “dispatch caches indexed by selector codes” (CISCO), which maintains a small number of dispatch tables indexed by a small number of selector codes. The space overhead is thus a small constant, however many classes and selectors there are in a system, while it almost maintains the runtime efficiency of selector code indexing. The simulation results show that, when carefully applied, optimization by CISCO is very promising, with cache miss ratios of less than 1.0% in real programs.