func (check *Checker) isTerminating(s syntax.Stmt, label string) bool {
	switch s := s.(type) {
	default:
		panic("unreachable")

	case *syntax.DeclStmt, *syntax.EmptyStmt, *syntax.SendStmt,
		*syntax.AssignStmt, *syntax.CallStmt:
		// no chance

	case *syntax.LabeledStmt:
		return check.isTerminating(s.Stmt, s.Label.Value)

	case *syntax.ExprStmt:
		// calling the predeclared (possibly parenthesized) panic() function is terminating

		// case *LabeledStmt:
		// case *BlockStmt:
		// case *ExprStmt:
		case *SendStmt:
			m = n.Chan
		// case *DeclStmt:
		case *AssignStmt:
			m = n.Lhs
		// case *BranchStmt:
		// case *CallStmt:
		// case *ReturnStmt:
		// case *IfStmt:
		// case *ForStmt:
		// case *SwitchStmt:
		// case *SelectStmt:

		// helper nodes
		case *RangeClause:
			if n.Lhs != nil {
				m = n.Lhs
				continue

	// empty line comment to exclude it from .String
	tokenCount //
)

const (
	// for BranchStmt
	Break       = _Break
	Continue    = _Continue
	Fallthrough = _Fallthrough
	Goto        = _Goto

	// for CallStmt
	Go    = _Go
	Defer = _Defer
)

// Make sure we have at most 64 tokens so we can use them in a set.
const _ uint64 = 1 << (tokenCount - 1)

// contains reports whether tok is in tokset.

	{"BranchStmt", `@break`},
	{"BranchStmt", `@break L`},
	{"BranchStmt", `@continue`},
	{"BranchStmt", `@continue L`},
	{"BranchStmt", `@fallthrough`},
	{"BranchStmt", `@goto L`},

	{"CallStmt", `@defer f()`},
	{"CallStmt", `@go f()`},

	{"ReturnStmt", `@return`},
	{"ReturnStmt", `@return x`},
	{"ReturnStmt", `@return a, b, a + b*f(1, 2, 3)`},

	{"IfStmt", `@if cond {}`},

		w.node(n.Lhs)
		if n.Rhs != nil {
			w.node(n.Rhs)
		}

	case *BranchStmt:
		if n.Label != nil {
			w.node(n.Label)
		}
		// Target points to nodes elsewhere in the syntax tree

	case *CallStmt:
		w.node(n.Call)

	case *ReturnStmt:
		if n.Results != nil {
			w.node(n.Results)
		}

	case *IfStmt:
		if n.Init != nil {
			w.node(n.Init)
		}
		w.node(n.Cond)
		w.node(n.Then)

		// or *ForStmt for breaks and continues, depending on the context of
		// the branch. Target is not set for fallthroughs.
		Target Stmt
		stmt
	}

	CallStmt struct {
		Tok     token // Go or Defer
		Call    Expr
		DeferAt Expr // argument to runtime.deferprocat
		stmt
	}

	ReturnStmt struct {
		Results Expr // nil means no explicit return values
		stmt