I’d be interested to see a more thorough analysis, but there is a simple way to gauge this - rip out all the parts of the compiler where aliasing information is propagated to LLVM, and see what happens to performance.
I found a claim that noalias contributes about 5% performance improvement in terms of runtimes[0], though the data is obviously very old.
https://github.com/rust-lang/rust/issues/54878#issuecomment-...