Apart from the replies to your question here, there was another interesting sub-thread on HN on this topic recently:

"Also, I like how returning 0 is "xor eax, eax"."

https://news.ycombinator.com/item?id=13052503

That led to multiple replies on it.

Traditionally yes. On the latest CPUs - who knows.

Probably yes, because Intel knows this is the code every compiler outputs for zeroing a register.

Also, the reason it is "faster" is that the encoding is 1 byte, vs. 9 bytes (in 64 bit) for "mov rbp, 0" - roughly, 1 for "mov rbp,", 8 more for a 64 bit "0".

Technically you could get by with 5 bytes for "mov ebp, 0".

Another reason why it was faster was that the processor recognized it and avoided partial flags stalls after an "inc". But in 64-bit code you rarely have "inc" at all, so it matters less. On the other hand, a few years ago XOR had a false dependency on the register you're clearing; I'm not sure it is still that way on more recent processors.

I tip my hat to you, your analysis is far more interesting than mine.

Wrong too, it's partial register stalls not partial flags stalls.