Finding Miscompiles for Fun, Not Profit
A developer spent over $10,000 on AI agents to find bugs in the LLVM compiler. Initially, they found five bugs in LLVM's instcombine but later discovered 80 miscompiles in NVIDIA's ptxas compiler. The project highlights the effectiveness of using AI for bug detection in compilers.
- ▪The developer has experience working on compilers for machine learning at major tech companies.
- ▪They initially found five bugs in LLVM before shifting focus to NVIDIA's ptxas compiler.
- ▪In just three days, they identified 40 miscompiles in ptxas, which increased to 80 within a week.
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| Original publisher | Hacker News (Newest) |
| Canonical URL | https://newsletter.semianalysis.com/p/finding-miscompiles-for-fun-not-profit |
| Publication time | Thu, 28 May 2026 01:10:39 +0000 |
| Retrieval time | 2026-05-28T01:28:05.981Z |
| Last seen | 2026-05-28T01:28:05.981Z |
| Headline source | Publisher (no WeSearch rewrite) |
| Excerpt source | publisher body |
| Excerpt method | First ~120 words (~800 chars) of extracted publisher body, fair-use limited. |
| Summary | WeSearch · cerebras-chat (WeSearch summarizer) |
| Summary source text | contentText |
| Citation coverage | Summary is a WeSearch-generated derivative; primary citation is the original publisher URL. |
| Cluster | GJClAdrm17j4 |
| Cluster logic | Grouped by semantic title/content similarity across sources within a rolling window. Same-publisher template collisions are excluded from coverage comparison. |
| Ranking reason | Story pages are not engagement-ranked. Hub feeds use recency, with optional source-diversified chronological ordering (cap consecutive stories per source). No personalized ranking. |
| Publisher visit | Yes — open original |
| Substitutes article? | No — link-out required for full text |
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| Indexing | May the item be indexed (stored, ranked, made findable)? | Allowed |
| Snippet | May a short excerpt of the publisher's text be shown? | Allowed |
| AI summary | May WeSearch generate its own short summary of the article? | Limited |
| Retrieval / RAG | May the content be exposed for third-party retrieval-augmented generation? | Not asserted |
| Model training | May the content be used to train AI models? | Not asserted |
| Commercial reuse | May the content be reused commercially? | Not permitted |
Basis: Derived from the published RSS/Atom feed. Contact: [email protected]. Reviewed: 2026-07-24.
Opening excerpt (first ~120 words) tap to expand
Finding Miscompiles for Fun, Not ProfitOr: You don’t need access to Claude Mythos to spend $10,000 in an afternoon.Justin LebarMay 28, 2026∙ Paid1261ShareI’ve worked on compilers for ML for the last decade across Google, Waymo, and OpenAI. This includes CUDA support in clang, XLA:GPU, Triton, and OpenAI’s custom hardware. I’ve seen stuff. But over the past week or so I had one of the unsettling experiences of my career: In one afternoon, I spent more than $10,000 running AI agents over compiler code, finding hundreds of plausible bugs in LLVM, including many miscompiles and at least one that’s Quite Serious.
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Excerpt limited to ~120 words for fair-use compliance. The full article is at Hacker News (Newest).
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