INFCODE-C++: Autonomous C++ Issue Resolution

• INFCODE-C++ is an autonomous, C++-aware multi-agent framework that resolves complex issues in large repositories by combining semantic retrieval and AST queries.
• It leverages a dual-retrieval architecture with intent-guided semantic matching and structured AST querying to effectively localize bugs in intricate C++ codebases.
• Empirical evaluations on the MultiSWE-bench-CPP benchmark show state-of-the-art performance, more than doubling resolution rates of prior systems.

INFCODE-C++ is an autonomous, C++-aware multi-agent framework designed for end-to-end issue resolution in large, statically typed C++ repositories. Addressing the limitations of lexical-retrieval and shallow code navigation techniques—commonplace in Python-oriented LLM agents—INFCODE-C++ integrates intent-guided semantic retrieval and deterministic abstract syntax tree (AST) queries. This dual-retrieval architecture targets the semantic and structural complexity characteristic of C++ projects, such as overloaded identifiers, nested namespaces, and deep template instantiations, which significantly hinder traditional LLM-driven agents. Evaluated on the MultiSWE-bench-CPP benchmark, INFCODE-C++ achieves state-of-the-art results, more than doubling resolution rates of prior systems (Dong et al., 20 Nov 2025).

1. System Architecture and Workflow

INFCODE-C++ is structured as a multi-agent pipeline interacting through four principal stages:

1. Repository Parsing: Full-project code artifacts are indexed and embedded.
2. Issue Reproduction (Reproducer Agent): Given a natural-language issue description, the agent synthesizes a reproducible test $t_D$.
3. Patch Generation (Patch Agent): Employs semantic intent retrieval and AST-structured search to localize defects and synthesize candidate patches $\{p_1,...,p_n\}$.
4. Patch Selection (Selector Agent): Prunes, behaviorally tests, and votes on patches to select $p_{\text{final}}$.

Textual Collaboration Flow:

$p_{\text{final}}$7 The Patch Agent’s two-stage narrowing process first reduces the codebase to a succinct set of candidate modules via semantic retrieval, followed by precise localization within these modules using deterministic AST queries.

2. Semantic Code-Intent Retrieval

Intent Representation and Embedding:

All files, classes, and functions are embedded into a dense vector space using a pretrained C++-specific encoder $E(\cdot)$ during repository parsing. For an issue description $D$, the derived query $q$ is embedded as $v_q = E(q)$. An intent index,

$$\mathcal{I}_\mathrm{intent}: \{v_{A_i}\} \mapsto A_i,\quad A_i \in \{\text{files, classes, functions}\}$$

maps these code artifacts.

Similarity Scoring and Retrieval:

Artifacts are ranked by cosine similarity:

$$\mathrm{score}(q, A) = \frac{v_q \cdot v_A}{\|v_q\|\;\|v_A\|}$$

An approximate nearest-neighbor index (e.g., FAISS) enables retrieval of the top-$k$ relevant artifacts $\{p_1,...,p_n\}$0. By design, $\{p_1,...,p_n\}$1, sharply narrowing the context for downstream processing.

3. AST-Structured Querying

Global C++ AST Representation:

The codebase is parsed into $\{p_1,...,p_n\}$2, where $\{p_1,...,p_n\}$3 denotes syntactic constructs (e.g., NamespaceDecl, ClassDecl, TemplateInstantiation), and $\{p_1,...,p_n\}$4 captures relations such as containment, inheritance, overload sets, and function calls.

Deterministic Querying:

Within the semantic subset $\{p_1,...,p_n\}$5, the agent performs graph traversals and pattern matches to precisely locate defects, issuing queries such as:

• FindClass("Search")
• FindFunction({scope:"UI", name:"update", params:["int"]})
• GetInheritanceChain("DerivedClass")
• GetFunctionCalls("Database","insert")

Pseudocode Example:

$p_{\text{final}}$8 Each query returns concrete AST nodes with associated source location spans.

4. Context Construction and Localization

Integration Process:

The candidate modules $\{p_1,...,p_n\}$6 from semantic retrieval are refined by AST queries to yield $\{p_1,...,p_n\}$7, a subgraph implicated in the reported defect. Source locations $\{p_1,...,p_n\}$8 are determined by:

$\{p_1,...,p_n\}$9

Full source text for $p_{\text{final}}$0 is extracted and concatenated, forming an input window for LLM-based patch synthesis.

Localization Strategy:

By limiting semantic retrieval to top-5 artifacts and restricting AST spans to a narrow window ($p_{\text{final}}$1 lines), the approach avoids both context over-approximation and under-approximation, maximizing the token budget efficiency for downstream synthesis.

5. Empirical Evaluation and Benchmark Results

Benchmark and Evaluation Protocol:

INFCODE-C++ is evaluated on 129 C++ issues from five major GitHub repositories (MultiSWE-bench-CPP), each accompanied by an issue description $p_{\text{final}}$2 and regression test suite $p_{\text{final}}$3. A solution is valid if:

• The regression test $p_{\text{final}}$4 passes for the candidate patch $p_{\text{final}}$5.
• $p_{\text{final}}$6 (no behavioral regressions).

Resolution Rates:

System	Resolution Rate (%)
INFCODE-C++ + GPT-5	25.58
MOpenHands + Claude-3.7 Sonnet	14.73
MSWE-agent + Claude-3.7 Sonnet	11.63
MAgentless + Claude-3.7 Sonnet	3.88

INFCODE-C++ exceeds the best prior system by 10.85 percentage points and more than doubles the performance of MSWE-agent. Stratified results (easy/medium/hard) show robust improvement in all categories (e.g., 50.00% on easy vs. 32.14% for next-best). The size of the improvement on 129 items indicates high statistical significance by binomial confidence interval analysis (Dong et al., 20 Nov 2025).

6. Ablation and Behavioral Analysis

Ablation Study:

Each major system component was removed in isolation. The following results quantify their marginal contributions:

Configuration	Resolution Rate (%)	Δ vs. Full
Full system (GPT-5)	25.58	—
w/o semantic code-intent retrieval	19.37	-6.21
w/o AST-structured querying	17.05	-8.53
w/o Reproducer Agent	20.16	-5.42
w/o Selector Agent	22.48	-3.10

The largest performance drop occurs when AST querying is removed, confirming its criticality for defect localization and patch synthesis in C++. Semantic retrieval also provides a substantial boost. Removal of either retrieval step increases LLM reasoning turns (from 28.1 to 35.3 or 45.3), indicating both efficiency and accuracy improvements.

Behavioral Breakdown:

• Reproduction success: 28.81%
• File-level localization: 55.10%
• Function-level localization: 42.10%
• End-to-end resolution: 25.58%

Majority of failures are attributable to reproduction and localization, affirming the necessity of combined semantic and structural retrieval.

7. Significance and Implications

INFCODE-C++ represents the first system to combine semantic code-intent embeddings with explicit AST-structured querying for C++ repair. Its two-pronged retrieval pipeline overcomes challenges unique to C++—such as deeply nested templates, type overloading, and intricate scoping—that degrade the effectiveness of approaches tuned for dynamically typed languages. The architecture demonstrates that language-aware retrieval and structural analysis are prerequisites for effective LLM-driven repair of complex, statically typed ecosystems.

Results on MultiSWE-bench-CPP set a new benchmark for autonomous C++ issue resolution, and ablation studies isolate the specific technical advances underlying this improvement (Dong et al., 20 Nov 2025). A plausible implication is that future work in multi-language LLM agents for code repair should adopt similar retrieval and defect localization strategies to extend state-of-the-art performance across statically typed domains.