MPQ3367 input schottky diode question

I have purchased an MPQ3367 EVB, and I have two questions that I would like to ask. The first question is, what is the function of the D3 Schottky diode with a 40V rating? Why is it placed between the M1 MOSFET and the L1 inductor?

The second question is, pin 22, VCC, is an LDO output.
Why is it necessary to add R1 and D4?