Towards Diverse Program Transformations for Program Simplification

By reducing the number of lines of code, program simplification reduces code complexity, improving software maintainability and code comprehension. While several existing techniques can be used for automatic program simplification, there is no consensus on the effectiveness of these approaches. We present the first study on how real-world developers simplify programs in open-source software projects. By analyzing 382 pull requests from 296 projects, we summarize the types of program transformations used, the motivations behind simplifications, and the set of program transformations that have not been covered by existing refactoring types. As a result of our study, we submitted eight bug reports to a widely used refactoring detection tool, RefactoringMiner, where seven were fixed. Our study also identifies gaps in applying existing approaches for automating program simplification and outlines the criteria for designing automatic program simplification techniques. In light of these observations, we propose SimpT5, a tool to automatically produce simplified programs that are semantically equivalent programs with reduced lines of code. SimpT5 is trained on our collected dataset of 92,485 simplified programs with two heuristics: (1) modified line localization that encodes lines changed in simplified programs, and (2) checkers that measure the quality of generated programs. Experimental results show that SimpT5 outperforms prior approaches in automating developer-induced program simplification.