Ah, right; missed that part of what you were saying. If you switch the compiler version on my godbolt link to beta, the &mut i32 and &mut UnsafeCell<i32> both

Ah, right; missed that part of what you were saying. If you switch the compiler version on my godbolt link to beta, the &mut i32 and &mut UnsafeCell<i32> both have the noalias attribute, so looks like it's on track. :)