These are now supported enough that this example code hits the
limitations of the register allocator:

fn add(a: u32, b: u32) void {
    const c = a + b; // 7
    const d = a + c; // 10
    const e = d + b; // 14
    assert(e == 14);
}
// error: TODO implement copyToNewRegister

So now the next step is to implement register allocation as planned.