p.errorf("invalid vtype: %v", err)
			}
			prog.AddRestSourceArgs([]obj.Addr{a[1], a[2], a[3], a[4]})
			prog.To = a[5]
			break
		}
		fallthrough
	default:
		p.errorf("can't handle %s instruction with %d operands", op, len(a))
		return
	}

	p.append(prog, cond, true)
}

	r := rand.New(rand.NewSource(99))
	for i := range x {
		switch r.Intn(10) {
		case 0:
			x[i] = ' '
		case 1:
			if i > 0 && x[i-1] == 'x' {
				copy(x[i-1:], "χ")
				break
			}
			fallthrough
		default:
			x[i] = 'x'
		}
	}
	return x
}

var makeFieldsInputASCII = func() []byte {
	x := make([]byte, 1<<20)
	// Input is ~10% space, rest ASCII non-space.