Filename    string
	StartLineno uint
	Lines       []string
}

// ByTopo sorts topologically: target function is on top,
// followed by inlined functions sorted by filename and line numbers.
type ByTopo []*FuncLines

func (x ByTopo) Len() int      { return len(x) }
func (x ByTopo) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
func (x ByTopo) Less(i, j int) bool {
	a := x[i]
	b := x[j]
	if a.Filename == b.Filename {