s0 := b.Succs[0].b
	i0 := b.Succs[0].i
	if s0.Kind != BlockPlain || !isEmpty(s0) {
		s0, ss0 = b, s0
	} else {
		ss0 = s0.Succs[0].b
		i0 = s0.Succs[0].i
	}
	s1 := b.Succs[1].b
	i1 := b.Succs[1].i
	if s1.Kind != BlockPlain || !isEmpty(s1) {
		s1, ss1 = b, s1
	} else {
		ss1 = s1.Succs[0].b
		i1 = s1.Succs[0].i
	}
	if ss0 != ss1 {
		if s0.Kind == BlockPlain && isEmpty(s0) && s1.Kind == BlockPlain && isEmpty(s1) {

					// the new blocks to be re-examined.
					d = f.NewBlock(BlockPlain)
					d.Pos = p.Pos
					blocks[argID] = d
					if f.pass.debug > 0 {
						f.Warnl(p.Pos, "split critical edge")
					}
				} else {
					reusedBlock = true
				}
			} else {
				// no existing block, so allocate a new block
				// to place on the edge
				d = f.NewBlock(BlockPlain)
				d.Pos = p.Pos
				if f.pass.debug > 0 {

// subject to the following criteria:
//   - it should not be the first block.
//   - it should be BlockPlain.
//   - it should not loop back to itself.
//   - it either is the single predecessor of the successor block or
//     contains no actual instructions.
func trimmableBlock(b *Block) bool {
	if b.Kind != BlockPlain || b == b.Func.Entry {
		return false
	}
	s := b.Succs[0].b

	// Check each loop header and decide if we want to move it.
	for _, loop := range loopnest.loops {
		b := loop.header
		var p *Block // b's in-loop predecessor
		for _, e := range b.Preds {
			if e.b.Kind != BlockPlain {
				continue
			}
			if loopnest.b2l[e.b.ID] != loop {
				continue
			}
			p = e.b
		}
		if p == nil {
			continue
		}
		p.Hotness |= HotInitial
		if f.IsPgoHot {
			p.Hotness |= HotPgo

		v.AddArg(pc)
		v.AddArg(bc)

		// Set the combined control value as the control value for b.
		b.SetControl(v)

		// Modify p so that it jumps directly to b.
		p.removeEdge(i)
		p.Kind = BlockPlain
		p.Likely = BranchUnknown
		p.ResetControls()

		return true
	}

	// TODO: could negate condition(s) to merge controls.
	return false
}

	}

	// Get rid of dead edges from live code.
	for _, b := range f.Blocks {
		if !reachable[b.ID] {
			continue
		}
		if b.Kind != BlockFirst {
			continue
		}
		b.removeEdge(1)
		b.Kind = BlockPlain
		b.Likely = BranchUnknown
	}

	// Splice out any copies introduced during dead block removal.
	copyelim(f)

	// Find live values.
	live, order := liveValues(f, reachable)