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 {

		Bloc("then",
			Goto("exit")),
		Bloc("else",
			Goto("exit")),
		Bloc("exit",
			Exit("mem")))

	CheckFunc(fun.f)
	Opt(fun.f)
	Deadcode(fun.f)
	CheckFunc(fun.f)

	if fun.blocks["entry"].Kind != BlockPlain {
		t.Errorf("if(false) not simplified")
	}
	for _, b := range fun.f.Blocks {
		if b == fun.blocks["then"] {
			t.Errorf("then block still present")
		}
		for _, v := range b.Values {

				s.Fatalf("atomic load not available")
			}
			merge = s.f.NewBlock(ssa.BlockPlain)
			cacheHit := s.f.NewBlock(ssa.BlockPlain)
			cacheMiss := s.f.NewBlock(ssa.BlockPlain)
			loopHead := s.f.NewBlock(ssa.BlockPlain)
			loopBody := s.f.NewBlock(ssa.BlockPlain)

			// Pick right size ops.
			var mul, and, add, zext ssa.Op
			if s.config.PtrSize == 4 {

// 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

	// Trash 'post' and 'simple'
	clobberBlock(post)
	clobberBlock(simple)

	f.invalidateCFG()
	return true
}

// is this a BlockPlain with one predecessor?
func isLeafPlain(b *Block) bool {
	return b.Kind == BlockPlain && len(b.Preds) == 1
}

func clobberBlock(b *Block) {
	b.Values = nil
	b.Preds = nil
	b.Succs = nil
	b.Aux = nil
	b.ResetControls()

		break
	case BlockDefer:
		// we know nothing about control flow, add all branch destinations
		t.edges = append(t.edges, block.Succs...)
	case BlockFirst:
		fallthrough // always takes the first branch
	case BlockPlain:
		t.edges = append(t.edges, block.Succs[0])
	case BlockIf, BlockJumpTable:
		cond := block.ControlValues()[0]
		condLattice := t.getLatticeCell(cond)
		if condLattice.tag == bottom {

		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
}

	return valu{name, op, t, auxint, aux, args}
}

// Goto specifies that this is a BlockPlain and names the single successor.
// TODO(matloob): choose a better name.
func Goto(succ string) ctrl {
	return ctrl{BlockPlain, "", []string{succ}}
}

// If specifies a BlockIf.
func If(cond, sub, alt string) ctrl {
	return ctrl{BlockIf, cond, []string{sub, alt}}
}