alive2

Undefined behavior does not violate correctness. Undefined behavior is just wiggle room for compiler engineers to not have to worry so much about certain edge cases. "Correctness" must always be considered with respect to something else. If we take e.g. the C specification, then yes, there are plenty of compilers that are in almost all ways people will encounter correct according to that spec, UB and all. Yes, there are bugs but they are bugs and they can be fixed. The LLVM project has a very neat tool called Alive2 [1] that can verify optimization passes for correctness. I think there's a very big gap between the kind of reliability we can expect from a deterministic, verified compiler and the approximating behavior of a probabilistic LLM. [1]: https://github.com/AliveToolkit/alive2

But we do! For llvm there's https://github.com/AliveToolkit/alive2 There are papers like https://people.cs.rutgers.edu/~sn349/papers/cgo19-casmverify... There's https://github.com/google/souper There's https://cr.yp.to/papers/symexemu-20250505.pdf And probably other things I'm not aware of. If you're limiting the scope to a few blocks at a time, symbolic execution will do fine.