A Loop Optimization Technique Based on Quasi- Invariance

Loop optimization plays an important role in compiler optimization and program transformation. Many sophisticated techniques such as loopinvariance 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 loopinvariance code motion, but based on loop quasiinvariance analysis. Loop quasi-invariance is similar to standard loop-invariance but allows for a finite number of iterations before computations in a loop become invariant. In this paper we define the notion of loop quasi-invariance, present an algorithm for statically computing the optimal unfolding length in While-programs and give a transformation 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 program transformers.