Type Test Elimination using Typeflow Analysis

. Programs written in languages of the Oberon family usually contain runtime tests on the dynamic type of variables. In some cases it may be desirable to reduce the number of such tests. Typeflow analysis is a static method of determining bounds on the types that objects may possess at runtime. We show that this analysis is able to reduce the number of tests in certain plausible circumstances. Furthermore, the same analysis is able to detect certain program errors at compile time, which would normally only be detected at program execution. This paper introduces the concepts of typeflow analysis and details its use in the reduction of runtime overhead in Oberon-2 . 1 Introduction Implementations of object-oriented languages based on type extension[1] such as Oberon[2] and Oberon-2 [3] must perform tests on the dynamic type of objects. These type tests are comparable in runtime cost to the index bounds checks of Pascal-like languages[4]. Just as it is possible to eliminate much of the ..