Optimizing Dynamic Dispatches through Type Invariant Region Analysis

Abstract

Object oriented languages lead to dynamic dispatches of most method calls due to limitations on static analysis which have significant run-time overheads. In this work, we propose a new optimization to cut this overhead which is based on the following key observation: run-time type testing of a method at every call-site is extraneous. The technique makes use of an important observation: most of the times a polymorphic object, although statically unknown in type, is fixed at run-time and never mutates. In such cases, run-time type testing for its methods is only needed when an object is instantiated. The type check is hoisted at the entry point of a region and its results are shared over all dispatches that lie within the region. We implemented this optimization in Vortex, an optimizing object-oriented compiler back-end, and with our framework, we observed an average speed-up of 9.22%. We avoided 91% of the dynamic dispatches with a speed-up of 17.9% in the best case.

This research is partially supported by NSF under grant # CCR 9696129