gcc optimizations on AVR-CAN example source code

[banoso]

I recently purchased the Olimex AVR-CAN development board and an ATMEL AVRDRAGON for JTAG programming and debugging.  So far so good. I'm curious about the gcc optimization assembly language code included in the examples under the function "WDT_OFF(Void)". The comments indicate that the code does not meet the datasheet specifications unless these optimizations are included. The function messes with the CPU Z register. What is it doing?
Thanks,
El Chapo