As says Charles Fiterman on comp.compilers about
human vs computer-generated assembly code:
The human should always win and here is why.
First the human writes the whole thing in a high level language.
Second he profiles it to find the hot spots where it spends its time.
Third he has the compiler produce assembly for those small sections of code.
Fourth he hand tunes them looking for tiny improvements over the machine generated code.
The human wins because he can use the machine.