if isMem(inst.Args[0]) {
			unmarkImplicit(&inst, PrefixDataSize)
		}

	case SYSEXIT:
		unmarkImplicit(&inst, PrefixDataSize)
	}

	if isCondJmp[inst.Op] || isLoop[inst.Op] || inst.Op == JCXZ || inst.Op == JECXZ || inst.Op == JRCXZ {
		if countPrefix(&inst, PrefixCS) > 0 && countPrefix(&inst, PrefixDS) > 0 {
			for i, p := range inst.Prefix {
				switch p & 0xFFF {
				case PrefixPN, PrefixPT:

	// so we'll follow along.
	// TODO(rsc): Perhaps this instruction class should be derived from the CSV.
	if isCondJmp[inst.Op] || isLoop[inst.Op] || inst.Op == JCXZ || inst.Op == JECXZ || inst.Op == JRCXZ {
	PredictLoop:
		for i := nprefix - 1; i >= 0; i-- {
			p := inst.Prefix[i]
			switch p & 0xFF {
			case PrefixCS:
				inst.Prefix[i] = PrefixPN
				break PredictLoop