> Is this understandable, or does this tell us something bad about llvm?
LLVM is a large project that's mostly written in pre-modern C++, and "noalias" is a highly non-trivial feature that affects many parts of the compiler in 'cross-cutting' ways. It would be surprising if it did not turn up some initial bugs.
TBF the internal API could be designed more pessimistically, as in llvm could drop noalias annotations unless they’re explicitly maintained (/ converted).
This means optimisation phases would need to explicitly opt-in and aliasing optimisations would commonly be missed by default, but it would avoid miscompilations.
This is understandable. Rust really uses restrict semantics in anger compared to any other language I know of. Have you seen restrict used in a c codebase? The LLVM support for restrict just doesn't get exercised much outside of Rust.
I use it in c++ on most signal processing stuff. I think eigen will use it if you don't let it use intrinsics for simd. I also use g++ so I wouldn't have encountered it anyway.
