Effective Flow Analysis for Avoiding Run-Time Checks

This paper describes a general purpose program analysis that computes global control-ow and data-ow information for higher-order, call-by-value programs. This information can be used to drive global program optimizations such as inlining and run-time check elimination, as well as optimizations like constant folding and loop invariant code motion that are typically based on special-purpose local analyses. The analysis employs a novel approximation technique called poly-morphic splitting that uses let-expressions as syntactic clues to gain precision. Polymorphic splitting borrows ideas from Hindley-Milner poly-morphic type inference systems to create an analog to polymorphism for ow analysis. Experimental results derived from an implementation of the analysis for Scheme indicate that the analysis is extremely precise and has reasonable cost. In particular, it eliminates signiicantly more run-time checks than simple ow analyses (i.e. 0CFA) or analyses based on type inference.