//	varkill: killed variables (set in block)
	uevar   bitvec.BitVec
	varkill bitvec.BitVec

	// Computed during Liveness.solve using control flow information:
	//
	//	livein: variables live at block entry
	//	liveout: variables live at block exit
	livein  bitvec.BitVec
	liveout bitvec.BitVec
}

// A collection of global state used by liveness analysis.
type liveness struct {
	fn         *ir.Func
	f          *ssa.Func

//  2. parse the nocallback and noescape directives.
func (f *File) ProcessCgoDirectives() {
	linesIn := strings.Split(f.Preamble, "\n")
	linesOut := make([]string, 0, len(linesIn))
	f.NoCallbacks = make(map[string]bool)
	f.NoEscapes = make(map[string]bool)
	for _, line := range linesIn {
		l := strings.TrimSpace(line)
		if len(l) < 5 || l[:4] != "#cgo" || !unicode.IsSpace(rune(l[4])) {

// Active spinning for sync.Mutex.
//
// sync_runtime_canSpin should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/livekit/protocol
//   - github.com/sagernet/gvisor
//   - gvisor.dev/gvisor
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:linkname sync_runtime_canSpin sync.runtime_canSpin