It depends on the regime you're operating in. In a processor that's superscalar but in order the higher cost of decoding two x86 instructions versus decoding t

It depends on the regime you're operating in. In a processor that's superscalar but in order the higher cost of decoding two x86 instructions versus decoding two ARM instructions is actually significant. But if you're reading instructions in at one or two bytes per clock tick x86's more complicated instructions make a lot of sense since they save on instruction stream size. And if you're dealing with a modern wide issue out of order machine the decoding costs are just lost in the noise. EDIT: Oh, and load-op-store instructions make the level below superscalar a bit harder to design at least. And x86's strong versus ARM's weak memory ordering guarantee have effects even in OoO-land though which one is better is a very complicated issue I'm not going to try venturing an opinion on.