The base+index encoding is a significant code size reduction though, and as the element size is a restricted set of powers of two, the scaling is cheaper than a

The base+index encoding is a significant code size reduction though, and as the element size is a restricted set of powers of two, the scaling is cheaper than a generic shift. So base+index uses less memory (less icache specifically), less instruction dispatch overhead, and is able to perform the needed math more efficiently. I assume in modern chips most of these costs aren't really an issue, but that wasn't the case back when the ISA was created.