GPT and Opus via Copilot CLI uncover 180 JIT bugs in .NET, 49% already fixed
lucasmeijer · x · 2026-10-13
Developer EgorBo used a GPT + Opus (via Copilot CLI) "AI bug hunting" script to uncover 180 bugs in the .NET JIT compiler, each with a minimal safe-code-only Crepro (no unsafe/UB) — most had been hiding for many releases.
In tracking issue #134482 on dotnet/runtime, 89 (49%) are already fixed. The bugs span assertion propagation, wrongly eliminated bounds checks (e.g. treating a decreasing recurrence as monotonically increasing), signed underflow, and exponential compile-time blowups, all catalogued by category with repros and fix status.
Lucas Meijer amplified it: yes there's slop, but there's also this — a landmark case of AI systematically hunting compiler-level bugs.
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