• Back edge*:* A back-edge is an edge a → b; whose head b dominates its tail a. (the naming is opposite here head is tail and tail is head)
• A natural loop has the following properties
  • It has a single-entry node called header that dominates all the nodes in the loop
  • There must be a back edge to the loop header
  • Given a back edge n → d, the natural loop of edge consists of node d and all the nodes that can reach n without going through d.
  • reverse the cfg for finding natural loop