As it stands, the move intrinsic does not carry any special side effects. I don't think we want to give it special side effects either. That's contrary to the intent of "just express what we intended the optimizer to do without otherwise inhibiting optimization". So I can't think of a language rule that prevents the transformation above. But I agree that it's harmful optimization behavior and should hopefully never happen in practice. The compiler does have a conservative understanding of where uniqueness checks may be performed. It would be pretty bad to hoist a uniqueness check above deinitialization of a potentially aliasing reference.