Yeah, enabling noalias optimizations is on our todo-list. I think that’s one of the most interesting performance features of Rust. It could be the thing that makes Rust faster than C, ultimately.
TBF it wasn't just LLVM: in https://github.com/rust-lang/rust/issues/54878 "nikic" and "comex" provided C test cases which failed in both clang[0] and gcc[1]. Though GCC has since fixed the issue while it remains open on LLVM.
Too bad it‘s so broken in LLVM :(