switch inst.Op {
		// TODO(rsc): Perhaps this instruction class should be derived from the CSV.
		case ADD, ADC, AND, BTC, BTR, BTS, CMPXCHG, CMPXCHG8B, CMPXCHG16B, DEC, INC, NEG, NOT, OR, SBB, SUB, XOR, XADD, XCHG:
			if isMem(inst.Args[0]) {
				hasLock = true
				break
			}
			fallthrough
		default:
			inst.Prefix[lockIndex] |= PrefixInvalid
		}
	}