Loop Quasi-Invariance Code Motion

摘要

Loop optimization plays an important role in compiler optimization and program transformation. Many so- phisticated techniques such as loop-invariance code motion, loop restructuring and loop fusion have been developed. This paper introduces a novel technique called loop quasi-invariance code motion. It is a generalization of standard loop-invariance code motion, but based on loop quasi-invariance analysis. Loop quasi- invariance is similar to standard loop-invariance but allows for a finite number of iterations before computations in a loop be- come invariant. In this paper we define the notion of loop quasi- invariance, present an algorithm for statically computing the op- timal unfolding length in While-programs and give a transforma- tion method. Our method can increase the accuracy of program analyses and improve the efficiency of programs by making loops smaller and faster. Our technique is well-suited as supporting transformation in compilers, partial evaluators, and other pro- gram transformers.