Not sure if that bug explicitly, but the fact that clang in noalias mode assumes that two pointers to different variants of the same union are not aliased (if it can't see from the immediate context that they are pointers to the same union variable) can very much affect Rust - if you call one function with a &mut to one field, than another function with a &mut to another field, and the optimizer inlines both functions in a broader context and loses the union information, you may well see reordering issues even in pure safe Rust.

Anyway, Rust has found plenty of noalias bugs in clang, which is why it still doesn't compile with noalias optimizations turned on.