The effect of unrolling and inlining for Python bytecode optimizations

Abstract

In this study, we consider bytecode optimizations for Python, a programming language which combines object-oriented concepts with features of scripting languages, such as dynamic dictionaries. Due to its design nature, Python is relatively slow compared to other languages. It operates through compiling the code into powerful bytecode instructions that are executed by an interpreter. Python's speed is limited due to its interpreter design, and thus there is a significant need to optimize the language. In this paper, we discuss one possible approach and limitations in optimizing Python based on bytecode transformations. In the first stage of the proposed optimizer, the bytecode is expanded using function inline and loop unrolling. The second stage of transformations simplifies the bytecode by applying a complete set of data-flow optimizations, including constant propagation, algebraic simplifications, dead code elimination, copy propagation, common sub expressions elimination, loop invariant code motion and strength reduction. While these optimizations are known and their implementation mechanism (data flow analysis) is well developed, they have not been successfully implemented in Python due to its dynamic features which prevent their use. In this work we attempt to understand the dynamic features of Python and how these features affect and limit the implementation of these optimizations. In particular, we consider the significant effects of first unrolling and then inlining on the ability to apply the remaining optimizations. The results of our experiments indicate that these optimizations can indeed be implemented and dramatically improve execution times.