}
	}
	t.numberBlock(f.Entry, 1)
	return t
}

// newSparseOrderedTree creates a SparseTree from a block-to-parent map (array indexed by Block.ID)
// children will appear in the reverse of their order in reverseOrder
// in particular, if reverseOrder is a dfs-reversePostOrder, then the root-to-children
// walk of the tree will yield a pre-order.
func newSparseOrderedTree(f *Func, parentOf, reverseOrder []*Block) SparseTree {

	// The ordering in the dominator tree matters; it's important that
	// the walk of the dominator tree also be a preorder (i.e., a node is
	// visited only after all its non-backedge predecessors have been visited).
	sdom := newSparseOrderedTree(f, idom, po)

	if f.pass.debug > 1 {
		fmt.Printf("before %s = %s\n", f.Name, sdom.treestructure(f.Entry))
	}

	tofixBackedges := []edgeMem{}