[2603.29109] SemLoc: Structured Grounding of Free-Form LLM Reasoning for Fault Localization

Computer Science > Software Engineering arXiv:2603.29109 (cs) [Submitted on 31 Mar 2026] Title:SemLoc: Structured Grounding of Free-Form LLM Reasoning for Fault Localization Authors:Zhaorui Yang, Haichao Zhu, Qian Zhang, Rajiv Gupta, Ashish Kundu View a PDF of the paper titled SemLoc: Structured Grounding of Free-Form LLM Reasoning for Fault Localization, by Zhaorui Yang and 4 other authors View PDF HTML (experimental) Abstract:Fault localization identifies program locations responsible for observed failures. Existing techniques rank suspicious code using syntactic spectra--signals derived from execution structure such as statement coverage, control-flow divergence, or dependency reachability. These signals collapse for semantic bugs, where failing and passing executions follow identical code paths and differ only in whether semantic intent is satisfied. Recent LLM-based approaches introduce semantic reasoning but produce stochastic, unverifiable outputs that cannot be systematically cross-referenced across tests or distinguish root causes from cascading effects. We present SemLoc, a fault localization framework based on structured semantic grounding. SemLoc converts free-form LLM reasoning into a closed intermediate representation that binds each inferred property to a typed program anchor, enabling runtime checking and attribution to program structure. It executes instrumented programs to construct a semantic violation spectrum--a constraint-by-test matrix--from which su...