Program reduction is a widely used technique in testing and debugging language processors. Given a program that triggers a bug in a language processor, program reduction searches for a canonicalized and minimized program that triggers the same bug, thereby facilitating bug deduplication and simplifying the debugging process. To improve reduction performance without sacrificing generality, prior research has leveraged the formal syntax of the programming language as guidance. Two key syntax-guided transformations—Compatible Substructure Hoisting and Quantified Node Reduction—were introduced to enhance this process. While these transformations have proven effective to some extent, their application excessively prunes the search space, preventing the discovery of many smaller results. Consequently, there remains significant potential for further improvement in overall reduction performance. To this end, we propose a novel syntax-guided transformation named Structure Form Conversion (SFC) to complement the aforementioned two transformations. Building on SFC, we introduce three reduction methods: Smaller Structure Replacement, Identifier Elimination, and Structure Canonicalization, designed to effectively and efficiently leverage SFC for program reduction. By integrating these reduction methods to previous language-agnostic program reducers, Perses and Vulcan, we implement two prototypes named SFC Perses and SFC Vulcan . Extensive evaluations show that SFC Perses and SFC Vulcan significantly outperforms Perses and Vulcan in both minimization and canonicalization. Specifically, compared to Perses, SFC Perses produces programs that are 36.82%, 18.71%, and 41.05% smaller on average on the C, Rust, and SMT-LIBv2 benchmarks at the cost of 3.65×, 16.99×, and 1.42× the time of Perses, respectively. Similarly, SFC Vulcan generates programs that are 14.51%, 7.65%, and 7.66% smaller than those produced by Vulcan at the cost of 1.56×, 2.35×, and 1.42× the execution time of Vulcan. Furthermore, in an experiment with a benchmark suite containing 3,796 C programs that trigger 46 unique bugs, SFC Perses and SFC Vulcan reduce 442 and 435 more duplicates (programs that trigger the same bug) to identical programs than Perses and Vulcan, respectively.

@article{paperbot2890,
  title = {Boosting Program Reduction with the Missing Piece of Syntax-Guided Transformations},
  author = {Zhenyang Xu and Yongqiang Tian and Mengxiao Zhang and Chengnian Sun},
  journal = {Proceedings of the ACM on Programming Languages},
  volume = {9},
  number = {OOPSLA2},
  year = {2025},
  doi = {10.1145/3763053}
}