Robin Abbott of Forest Electronic Developments says:

This might be of use to someone. Recently I had a project where a subroutine took a value in W and saved to a software stack:

movwf Temp
movfw sp        ; Stack pointer
movwf FSR    ; Point to it
movfw Temp
movwf 0

Trouble is it uses a temporary variable which I didn't have (it is in an interrupt). This alternative which makes use of XOR uses no temporary variable at the expense of 1 extra word:

  movwf FSR
  movfw sp
  xorwf FSR
  xorwf FSR,w
  xorwf FSR
  movwf 0

You can also use this to swap two variables (say x and y) without a temporary variable leaving X (or Y if order is reversed) in W.

    movfw x       ; Get X
    xorwf y         ; Y is now X^Y
    xorwf y,w     ; W is now (X^y)^X==Y  (say OldY)
    movwf x       ; Now X is OldY
    xorwf y         ; finally Y is (OldX^Y)^Y==OldX

I think this may be an old technique - I have vague memories of something similar from the pre-history of programming, but only found a use for

  .