//# run
main() {
    let x: u64;
    let x_ref: &mut u64;
    let imm_ref: &u64;
label b0:
    x = 5;
    x_ref = &mut x;
    imm_ref = freeze(move(x_ref));
    // cannot write to an imm ref, even if it is a frozen mut ref
    *move(imm_ref) = 0;
    return;
}