REVIEW 3 major objections 6 minor 38 references
hdl2v: A Code Translation Dataset for Enhanced LLM Verilog Generation
T0 review · 3 major / 6 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read Fine-tuning a 32-billion-parameter open-weight LLM on 46,549 VHDL-, Chisel-, and PyMTL3-to-Verilog pairs improves VerilogEvalV2 scores by up to 13% at pass@1 and 23% at pass@10.
desk verdict A solid dataset paper with a contamination question that must be answered before the headline numbers are trusted; otherwise the work is a clean contribution. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is hdl2v itself: a dataset of 46,549 prompt-response pairs in which the prompt is a hardware description in VHDL, Chisel, or PyMTL3 and the response is the corresponding Verilog module, obtained respectively by a VHDL-to-Verilog translator, by compiling Chisel designs from an SoC generator framework, and by compiling PyMTL3 designs through its Verilog translation pass. The mechanism is supervised fine-tuning on these pairs, which teaches the model to map HDL constructs and design intent onto Verilog syntax that it may not have seen during pretraining. The paper also uses perplexity, type-token ratio, and n-gram diversity of the Verilog responses to characterize what makes a translation dataset useful, and it performs ablations that remove comments or obfuscate variable names to isolate what the model actually learns.
What would settle it
Run a contamination check that matches hdl2v prompts and their source repositories against VerilogEvalV2 problem statements and reference solutions, then recompute pass@1 and pass@10 after excluding all overlapping or near-duplicate designs; if the gains largely disappear, the central claim is refuted.
Extended reading notes
Core claim
The central claim is that existing non-Verilog HDL code can be turned into novel Verilog training data by translation or compilation, and that this data materially improves LLM Verilog generation. Concretely, the paper constructs 8,626 VHDL-to-Verilog pairs via an open-source translator, 18,939 Chisel-to-Verilog pairs by compiling SoC configurations, and 18,636 PyMTL3-to-Verilog pairs by compiling PyMTL3 code, for 46,549 total. Fine-tuning a 32-billion-parameter open-weight coder LLM on combinations of these pairs raises VerilogEvalV2 pass@10 from 58.8% to 72.2% and pass@1 to 50.2%, which the paper attributes to the diversity and pre-training-novelty of the translated Verilog rather than to augmentation or knowledge distillation. It also establishes that, holding designs constant, VHDL-translated data outperforms C-translated data, and that removing comments barely hurts while obfuscating variable names sharply degrades performance, which it interprets as evidence the model learns from code structure, not natural language.
Load-bearing premise
The fine-tuning data is assumed to be essentially disjoint from the VerilogEvalV2 evaluation problems, so the measured gains reflect better Verilog generation rather than memorization; the paper performs no contamination check, and the PyMTL3 subset is drawn from a benchmark with designs similar to VerilogEval.
Editorial extensions
If this is right
- VerilogEvalV2 pass@10 for a 32-billion-parameter open-weight model rises from 58.8% to 72.2% after fine-tuning on combined hdl2v data, so translation pairs alone are a practical fine-tuning signal.
- Adding hdl2v VHDL and Chisel data to an augmented-Verilog training set lifts the fine-tuning gain from 3.8 to 6.6 percentage points, so the dataset strengthens, rather than duplicates, data augmentation.
- When designs are held constant, VHDL-to-Verilog pairs outperform C-to-Verilog pairs on VerilogEvalV2, indicating that domain-close HDL translation is more useful than translation through a software language.
- Removing comments from the VHDL dataset barely changes pass@10, while obfuscating variable names drops it from 59.8% to 39.1%, indicating that the model transfers code structure and meaningful identifiers, not natural-language comment content.
Reading between the lines
- Because the paper does not run a contamination check and the PyMTL3 subset is built from a benchmark whose designs are similar to VerilogEval, a reader should treat the PyMTL3-specific gains and part of the combined gains as provisional until overlap with VerilogEvalV2 is measured.
- The same translate-and-fine-tune recipe could be applied to other HDLs such as MyHDL, Amaranth, or SpinalHDL, and the VHDL-versus-C result predicts that languages with RTL semantics close to Verilog will transfer better than general-purpose software languages.
- Dataset-size and entry-length differences are not controlled in the combination experiments; an alternative design that balances token volume and sampling order across languages could separate the effect of language choice from the effect of sheer training-data volume.
- The comment-removal result suggests that adding natural-language descriptions to translation pairs may contribute less than preserving meaningful identifiers and code structure, which is a testable prediction for future dataset-construction work.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents hdl2v, a dataset of 46,549 pairs in which VHDL entities, Chisel modules, and PyMTL3 components are translated or compiled to Verilog. The authors fine-tune Qwen2.5-Coder-32B-Instruct on individual and combined subsets and report VerilogEvalV2 spec-to-rtl improvements of up to 13% for pass@1 and 23% for pass@10 (Section V-B, Figure 5), and a case study with Qwen2.5-Coder-7B-Instruct in which adding VHDL and Chisel augmented data to gpt-4o-augmented Verilog data increases the fine-tuning delta over the base model by 63% (Section V-C, Figure 6). The paper also reports dataset statistics and ablations that isolate C versus VHDL translation and the effect of comments and variable names on learning.
Significance. If the reported gains are not confounded by training/evaluation overlap, hdl2v is a useful and reasonably large open resource: it is, to the authors' knowledge, the first dataset to translate non-Verilog HDLs to Verilog for LLM fine-tuning, and the positive results are consistent in direction across two model sizes and several ablations. The datasets are publicly released, which enables direct external verification and reuse. The main uncertainties are contamination and variance, so the contribution's value is clear but the exact magnitude of the headline numbers is not yet established.
major comments (3)
- [Sections V-A and III-B3; Figure 4] The paper does not report a contamination analysis between any hdl2v training subset and the 156 VerilogEvalV2 evaluation problems. This is load-bearing because Section V-A states that the PyMTL3 subset targets 'a benchmark set of designs similar to VerilogEval' and Section III-B3 constructs that subset from PyHDL-Eval artifacts. If PyMTL3 examples reproduce the same designs or natural-language specifications as evaluation problems, the individual PyMTL3 result (49.4 vs. 44.6 pass@1 and 69.3 vs. 58.8 pass@10 in Figure 4) and part of the combined gains could reflect memorization rather than improved generation. The authors should perform an exact and near-duplicate overlap check per subset (VHDL, Chisel, and PyMTL3), remove overlapping entries, and re-report the main results.
- [Section V-C and Figure 6] The 63% augmentation-boost claim is based on inconsistent baseline numbers. The text says 'Compared to the baseline of 54.8%,' but Figure 6 labels the base model pass@10 as 54.4%. With 54.4, the augmented-Verilog delta is 4.2 points and the best hdl2v-augmented delta is 6.6 points, which is a 57% increase; with 54.8, the deltas are 3.8 and 6.2 points, which is a 63% increase. The text, table, and figure must be reconciled and the percentage increase recomputed from the reported values.
- [Sections V and VI, Figures 4-8] All fine-tuning results appear to be single-seed runs with no error bars, confidence intervals, or significance tests. Several conclusions depend on differences of a few percentage points, such as the claim in Section V-B that combining C and Verilog data yields no significant improvement and the C-versus-VHDL comparison in Figure 7. The authors should report multiple seeds or a variance estimate for the main comparisons, or explicitly qualify the ordering claims as preliminary.
minor comments (6)
- [Section II-A] The phrase 'Prior work has seeked' should be 'Prior work has sought.'
- [Section VI-A] The perplexity-to-accuracy formula is written as '1/perplexity × 100'; it should be '100/perplexity' or '1/perplexity × 100%.'
- [Section III-B2] The sentence 'which contain a single Verilog module' should be 'which contains a single Verilog module.'
- [Abstract and Sections I, III-B3] The abstract describes hdl2v as 'human-written Verilog data,' but the PyMTL3 subset is derived from LLM-generated PyMTL3 code from PyHDL-Eval and then compiled to Verilog; this qualification should be stated explicitly wherever the dataset is characterized as human-written.
- [Section III-B3] The statement that PyHDL-Eval contains 'about 50,000' examples is imprecise; the exact number of examples obtained from the artifact should be reported.
- [Reference [1]] Reference [1] is listed only as a URL; include the repository name and access date for completeness.
Circularity Check
No circularity: the headline gains rest on independently sourced VHDL and Chisel data, and the acknowledged PyMTL3/VerilogEval similarity is a contamination risk rather than a definitional reduction.
full rationale
The paper's central claims are empirical: translating VHDL, Chisel, and PyMTL3 to Verilog and fine-tuning Qwen2.5-Coder yields gains on the external VerilogEvalV2 benchmark. No equation defines the evaluand in terms of its input; no fitted parameter is renamed as a prediction; no load-bearing result is justified by a self-citation. The headline gains (up to 13% pass@1 and 23% pass@10) come from Chisel+VHDL combinations shown in Figure 5, with VHDL sourced from GitHub and Chisel from Chipyard, both independent of the evaluation benchmark. The VHDL-versus-C comparison in Section VI-B is controlled by using the same source designs for both translations. The only overlap-sensitive passage is Section V-A, which acknowledges that PyHDL-Eval 'generated code for a benchmark set of designs similar to VerilogEval', and the PyMTL3 subset is built from that artifact; this is a potential train/eval contamination risk for the individual PyMTL3 result, but it is not a circular definition or a fitted-input-as-prediction. Since the central result does not reduce to that subset and no derivation chain is self-referential, there is no circularity.
Assumptions & free parameters
assumptions (3)
- domain assumption VerilogEvalV2 is a valid proxy for Verilog generation ability
- domain assumption Translation tools (vhd2vl, v2c, Chipyard, PyMTL3 VerilogTranslationPass) produce correct Verilog that is useful for fine-tuning
- domain assumption hdl2v train data does not overlap with VerilogEvalV2 test problems
Cite this review
Pith. "Pith review of hdl2v: A Code Translation Dataset for Enhanced LLM Verilog Generation." pith.science (2026). https://pith.science/paper/ER2RRTEP
@misc{pith2026250604544,
author = {Pith},
title = {Pith review of: hdl2v: A Code Translation Dataset for Enhanced LLM Verilog Generation},
year = {2026},
howpublished = {\url{https://pith.science/paper/ER2RRTEP}},
note = {Machine review of arXiv:2506.04544}
}
read the original abstract
Large language models (LLMs) are playing an increasingly large role in domains such as code generation, including hardware code generation, where Verilog is the key language. However, the amount of publicly available Verilog code pales in comparison to the amount of code available for software languages like Python. In this work, we present hdl2v ("HDL-to-Verilog"), a dataset which seeks to increase the amount of available human-written Verilog data by translating or compiling three other hardware description languages - VHDL, Chisel, and PyMTL3 - to Verilog. Furthermore, we demonstrate the value of hdl2v in enhancing LLM Verilog generation by improving performance of a 32 billion-parameter open-weight model by up to 23% (pass@10) in VerilogEvalV2, without utilizing any data augmentation or knowledge distillation from larger models. We also show hdl2v's ability to boost the performance of a data augmentation-based fine-tuning approach by 63%. Finally, we characterize and analyze our dataset to better understand which characteristics of HDL-to-Verilog datasets can be expanded upon in future work for even better performance.
Figures
Figures from the paper (5 more)
Reference graph
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Reviewed August 7, 2026 · model on record in the stance chip above.
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