rvalue references. When do they extend the lifetime of temporaries?

I'm playing with prvalues, xvalues, etc... in this snippet.

#include<iostream>

class A
{
public:
    A() : i(1) {}
    int i;
};

A prvalue() { return A(); }
A&& xvalue() { return std::move(A()); }

int main()
{
    A&& a1 = prvalue(); // Ok
    A&& a2 = xvalue();  // UB
    A&& a3 = std::move(A());  // Does it extend the lifetime of the temporary?
    A&& a4 = A(); // I believe this extends the lifetime of the temporary
    a1.i = 2;
    a2.i = 2; // UB
    a3.i = 2; // Is this UB?
    a4.i = 2;

    std::cout << a1.i << '\n';
    std::cout << a2.i << '\n';
    std::cout << a3.i << '\n';
    std::cout << a4.i << '\n';
}

I can understand that A&& a2 = xvalue(); shows undefined behavior, because the temporary is destructed before the functionxvalue() returns. But what about the assignment A&& a3 = std::move(A());and A&& a4 = A();, do they extend the lifetime of the temporariesinvolved?

Apparently it's possible to call std::move() with a prvalue as argument. Is this correct?

See the output for the code here.

Edit:

There shouldn't be a problem with 

A&& a4 = A();

as this is equivalent to the first assignment.