The second example makes sense: rdi stores the first subroutine argument in amd64 calling conventions and rax stores the return value. I imagine it's easy for t

The second example makes sense: rdi stores the first subroutine argument in amd64 calling conventions and rax stores the return value. I imagine it's easy for the compiler to infer that the loop is just counting 1 bits, which popcnt does. I imagine if you called functions or initialized local variables in the loop, it would be much more messy