Although Rust doesn't have this rule it isn't nearly as relevant due to the way immutable (shared) references work. While `a: &Foo` and `b: &Bar` may alias it d

Although Rust doesn't have this rule it isn't nearly as relevant due to the way immutable (shared) references work. While `a: &Foo` and `b: &Bar` may alias it doesn't matter much because Rust knows that nothing can write to them so it can do basically all of the optimization it needs. Rust also knows that `c: &mut T` doesn't alias with anything so in this case it can make loads of assumptions. One chink in this rule is interior mutability. This is why it is better to think of `&T` as a shared reference than an immutable reference. For example in the following code Rust can't assume that `a.get() == 5`. (Even if the second argument is changed to i8) pub fn test(a: &std::cell::Cell<u8>, b: &std::cell::Cell<u8>) -> u8 { a.set(5); b.set(7); a.get() } https://rust.godbolt.org/z/e1c6Kx4eb https://rust.godbolt.org/z/e1c6Kx4eb Commenting out the write to b does allow Rust to hardcode the return value as 5.