>Pretty much the only use of "reversed subtraction" instruction on a 3-operand machine is to implement NEG and NOT
I would argue that if you have sign-extended immediates, "imm - reg" is more useful to have than "reg - imm", as second form almost entirely overlaps with "reg + -imm".
I would argue that if you have sign-extended immediates, "imm - reg" is more useful to have than "reg - imm", as second form almost entirely overlaps with "reg + -imm".