// approximate x dying with:
	//  1) target is x's only use.
	//  2) target is not in a deeper loop than x.
	if x.Uses != 1 {
		return false
	}
	loopnest := x.Block.Func.loopnest()
	loopnest.calculateDepths()
	if loopnest.depth(target.Block.ID) > loopnest.depth(x.Block.ID) {
		return false
	}
	return canMergeLoad(target, load)
}

// canMergeLoad reports whether the load can be merged into target without

	// components as single blocks, duplicated calculated liveness information
	// out to all of them.
	po := f.postorder()
	s.loopnest = f.loopnest()
	s.loopnest.calculateDepths()
	for {
		changed := false

		for _, b := range po {
			// Start with known live values at the end of the block.
			// Add len(b.Values) to adjust from end-of-block distance