if x == nil {
		return UnaryOp(op, y, 0)
	}

	switch op {
	case token.EQL, token.NEQ, token.LSS, token.LEQ, token.GTR, token.GEQ:
		return MakeBool(Compare(x, op, y))
	case token.SHL, token.SHR:
		s, _ := Int64Val(y)
		return Shift(x, op, uint(s))
	default:
		return BinaryOp(x, op, y)
	}
}

// ----------------------------------------------------------------------------
// Other tests

	return op
}

func tracecmpArg(n ir.Node, t *types.Type, init *ir.Nodes) ir.Node {
	// Ugly hack to avoid "constant -1 overflows uintptr" errors, etc.
	if n.Op() == ir.OLITERAL && n.Type().IsSigned() && ir.Int64Val(n) < 0 {
		n = copyExpr(n, n.Type(), init)
	}

	return typecheck.Conv(n, t)

		}
		return -1
	}

	if isUntyped(x.typ) || isInteger(x.typ) {
		if val := constant.ToInt(x.val); val.Kind() == constant.Int {
			if representableConst(val, check, Typ[Int], nil) {
				if n, ok := constant.Int64Val(val); ok && n >= 0 {
					return n
				}
			}
		}
	}

	var msg string
	if isInteger(x.typ) {
		msg = "invalid array length %s"
	} else {
		msg = "array length %s must be integer"
	}

		}
		return -1
	}

	if isUntyped(x.typ) || isInteger(x.typ) {
		if val := constant.ToInt(x.val); val.Kind() == constant.Int {
			if representableConst(val, check, Typ[Int], nil) {
				if n, ok := constant.Int64Val(val); ok && n >= 0 {
					return n
				}
			}
		}
	}

	var msg string
	if isInteger(x.typ) {
		msg = "invalid array length %s"
	} else {
		msg = "array length %s must be integer"
	}

	// and string values, so only create Go values for these
	// types.
	switch val.Kind() {
	case constant.Int:
		if x, ok := constant.Int64Val(val); ok {
			return x
		}
		if x, ok := constant.Uint64Val(val); ok {
			return x
		}
	case constant.Float:
		if x, ok := constant.Float64Val(val); ok {
			return x
		}
	case constant.String:
		return constant.StringVal(val)

	// and string values, so only create Go values for these
	// types.
	switch val.Kind() {
	case constant.Int:
		if x, ok := constant.Int64Val(val); ok {
			return x
		}
		if x, ok := constant.Uint64Val(val); ok {
			return x
		}
	case constant.Float:
		if x, ok := constant.Float64Val(val); ok {
			return x
		}
	case constant.String:
		return constant.StringVal(val)

			ir.OSTR2BYTES,
			ir.OSTR2RUNES:
			return true
		}
		return false
	}
	return !ir.Any(n, bad)
}

func getlit(lit ir.Node) int {
	if ir.IsSmallIntConst(lit) {
		return int(ir.Int64Val(lit))
	}
	return -1
}

func isvaluelit(n ir.Node) bool {
	return n.Op() == ir.OARRAYLIT || n.Op() == ir.OSTRUCTLIT
}

func subst(n ir.Node, m map[*ir.Name]ir.Node) (ir.Node, bool) {

		if i.Kind() != constant.Int {
			v, _ := constant.Float64Val(x)
			return v
		}
		x = i
		fallthrough
	case constant.Int:
		if v, ok := constant.Int64Val(x); ok {
			return v
		}
		if v, ok := constant.Uint64Val(x); ok {
			return v
		}
	case constant.String:
		return constant.StringVal(x)
	case constant.Bool:
		return constant.BoolVal(x)
	}
	return x
}

		// we'll need idx-min anyway as the control value for the jump table.
		var min, max uint64
		if unsigned {
			min, _ = constant.Uint64Val(n.Cases[0])
			max, _ = constant.Uint64Val(n.Cases[len(n.Cases)-1])
		} else {
			mn, _ := constant.Int64Val(n.Cases[0])
			mx, _ := constant.Int64Val(n.Cases[len(n.Cases)-1])
			min = uint64(mn)
			max = uint64(mx)
		}

pkg go/constant, func Denom(Value) Value
pkg go/constant, func Float32Val(Value) (float32, bool)
pkg go/constant, func Float64Val(Value) (float64, bool)
pkg go/constant, func Imag(Value) Value
pkg go/constant, func Int64Val(Value) (int64, bool)
pkg go/constant, func MakeBool(bool) Value
pkg go/constant, func MakeFloat64(float64) Value
pkg go/constant, func MakeFromBytes([]uint8) Value