Debugging Functionality-Twisting Translations by LLMs via Differential Testing with Bayesian Prior

Code translation, as a challenging and fundamental task, is increasingly relying on large language models (LLMs). However, LLMs often give seemingly plausible but fallacious translations, misleading and even deceptive to debugging developers. We propose tHinter, an automated approach that frames translation error localization as a differential testing task. By fuzzing and a novel Bayesian-inspired algorithm that integrates developer heuristics into SBFL, tHinter thoroughly exposes translation errors and effectively pinpoints functionality-twisting errors. We evaluate tHinter in a Python to C++ scenario, a representative and challenging task for migrating high-level logic to performance-critical systems. Experiments show that tHinter achieves the highest F1 in localizing translation errors, outperforming all baselines. When debugging LLM-translated code with human efforts, it averagely reduces 71% lines developers need to review. Furthermore, we provide a comprehensive evaluation reference beyond traditional fault localization metrics. We integrate mixed-factorial user studies, expert validation, and SWOT-based strategic analysis to assess the perceived helpfulness and resilience within the rapidly evolving LLM landscape, offering a methodologically rigorous example for researchers in the context of AI-augmented software engineering.