Fast strictness analysis based on demand propagation

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Strictness analysis is a well-known technique used in compilers for optimization of sequential and parallel evaluation of lazy functional programming languages. Ever since Mycroft's pioneering research in strictness analysis, there have been substantial research efforts in advancing the basic technique in several directions such as higher-order functions, nonflat domains, etc. While almost all of these methods define strictness based on denotational semantics, in 1990 we proposed an operational method called ee-analysis. Operational methods directly address the primary aspect of the strictness analysis problem, namely nontermination of evaluation, and can yield simplicity both in formulation and computational algorithms. Moreover, the use of operational approach has led us to a simple and natural treatment of polymorphism. While ee-analysis reasoned about normal-form evaluation herein we extend its power substantially so as to deal with other degrees of evaluation that are intermediate between normal and head-normal form. An interesting aspect of our approach is our formulation of a strictness property as a constraint that relates the demand placed on the output of a function to the demands placed on its arguments. Strictness properties are then computed using symbolic constraint-solving techniques. An important advantage of constraint-driven analysis is that it captures interargument dependencies accurately. Moreover, the analysis performance is relatively insensitive to domain size. Based on our implementation of this method, we show that our analysis techniques are efficient, as well as effective.