Back when I did IBM 370 BAL Assembly Language, we did the same thing to clear a register to zero.

  XR   15,15         XOR REGISTER 15 WITH REGISTER 15

vs

  L    15,=F'0'      LOAD REGISTER 15 WITH 0

This was alleged to be faster on the 370 because because XR operated entirely within the CPU registers, and L (Load) fetched data from memory (i.e.., the constant came from program memory).