if nextIdx >= len(f.Blocks) { // reached end of function (maybe impossible?)
				break
			}
			nextb := f.Blocks[nextIdx]
			if nextb == p { // original loop predecessor is next
				break
			}
			if loopnest.b2l[nextb.ID] == loop {
				after[p.ID] = append(after[p.ID], nextb)
			}
			b = nextb
		}
		// Swap b and p so that we'll handle p before b when moving blocks.
		f.Blocks[idToIdx[loop.header.ID]] = p

	if id == "" {
		p.corner = true // goldmark accepts {#}
		return "", s
	}
	return s[i+2 : j], s[:i]
}

func newSetextHeading(p *parseState, s line) (line, bool) {
	var n int
	peek := s
	if p.nextB() == p.para() && peek.trimSetext(&n) {
		p.closeBlock()
		para, ok := p.last().(*Paragraph)
		if !ok {
			return s, false
		}
		p.deleteLast()

	for i := 0; i < 3 && tt.trimSpace(1, 1, false); i++ {
		m++
	}
	if !tt.trimSpace(1, 1, true) {
		n += m
		t = tt
	}

	// point of no return

	var list *listBuilder
	if c, ok := p.nextB().(*listBuilder); ok {
		list = c
	}
	if list == nil || list.bullet != rune(bullet) {
		// “When the first list item in a list interrupts a paragraph—that is,
		// when it starts on a line that would otherwise count as

	}

	return ps.root, ps.corner
}

func (p *parseState) curB() blockBuilder {
	if p.lineDepth < len(p.stack) {
		return p.stack[p.lineDepth].builder
	}
	return nil
}

func (p *parseState) nextB() blockBuilder {
	if p.lineDepth+1 < len(p.stack) {
		return p.stack[p.lineDepth+1].builder
	}
	return nil
}
func (p *parseState) trimStack(depth int) {
	if len(p.stack) < depth {
		panic("trimStack")

	type X struct {
		c     chan error
		nextx *X
	}
	type Y struct {
		X
		nexty *Y
		p     *int
	}
	var head *Y
	for i := 0; i < 10; i++ {
		p := &Y{}
		p.c = make(chan error)
		if head != nil {
			p.nextx = &head.X
		}
		p.nexty = head
		p.p = new(int)
		*p.p = 42
		head = p
		runtime.GC()
	}
	for p := head; p != nil; p = p.nexty {
		if *p.p != 42 {

	CMP	IN_LEN, $8
	BLT	next4
	MOVD	0(MASK_PTR), R14
	MOVD	0(BLK_INP), R15
	XOR	R14, R15, R14
	MOVD	R14, 0(BLK_OUT)
	ADD	$8, R16
	ADD	$-8, IN_LEN
next4:
	CMP	IN_LEN, $4
	BLT	next2
	MOVWZ	(BLK_INP)(R16), R15
	MOVWZ	(MASK_PTR)(R16), R14
	XOR	R14, R15, R14
	MOVW	R14, (R16)(BLK_OUT)
	ADD	$4, R16
	ADD	$-4, IN_LEN
next2:
	CMP	IN_LEN, $2
	BLT	next1

	// now reduce the tail

	CMP	$0,R7
	BEQ	next1

	LVX	(R4),V16
	LVX	(R3),V17
	VPMSUMW	V16,V17,V16
	VXOR	V0,V16,V0
	BC	18,0,next1

	LVX	(R4+off16),V16
	LVX	(R3+off16),V17
	VPMSUMW	V16,V17,V16
	VXOR	V0,V16,V0
	BC	18,0,next1

	LVX	(R4+off32),V16
	LVX	(R3+off32),V17
	VPMSUMW	V16,V17,V16
	VXOR	V0,V16,V0
	BC	18,0,next1

	LVX	(R4+off48),V16
	LVX	(R3+off48),V17

	ready := new(uint32)
	for i := 0; i < iters; i++ {
		*ready = 0
		next0 := (i & 1) == 0
		next1 := (i & 2) == 0
		runqput(p, &gs[0], next0)
		go func() {
			for atomic.Xadd(ready, 1); atomic.Load(ready) != 2; {
			}
			if runqempty(p) {
				println("next:", next0, next1)
				throw("queue is empty")
			}
			done <- true
		}()

// is simultaneously being destroyed.
func (tl traceLocker) GoSwitch(nextg *g, destroy bool) {
	// Emit a GoWaiting status if necessary for the unblocked goroutine.
	w := tl.eventWriter(traceGoRunning, traceProcRunning)
	// Careful: don't use the event writer. We never want status or in-progress events
	// to trigger more in-progress events.
	w.w = emitUnblockStatus(w.w, nextg, tl.gen)
	ev := traceEvGoSwitch
	if destroy {

	x := sgp.prev
	y := sgp.next
	if x != nil {
		if y != nil {
			// middle of queue
			x.next = y
			y.prev = x
			sgp.next = nil
			sgp.prev = nil
			return
		}
		// end of queue
		x.next = nil
		q.last = x
		sgp.prev = nil
		return
	}
	if y != nil {
		// start of queue
		y.prev = nil
		q.first = y
		sgp.next = nil
		return
	}