> It's not only xor that does this, but most 32-bit operations zero-extend the result of the 64-bit register. AMD did this for backward compatibility.
It's not just that, zero-extending or sign-extending the result is also better for out-of-order implementations. If parts of the output register are preserved, the instruction needs an extra dependency on the original value.
It's not just that, zero-extending or sign-extending the result is also better for out-of-order implementations. If parts of the output register are preserved, the instruction needs an extra dependency on the original value.