[pechay]

1. MOV AL, BYTE PTR [RDI]

MOV EBX, EAX // partial register stall

2. MOVZX EAX, BYTE PTR [RDI]

AND EAX, 0xFFFFFF00

MOV EBX, EAX // no partial register

These don't do the same thing

[vardump]

Yeah. Second one would be shorter as XOR EBX, EBX, because EAX is always zero after that AND.