• Introduce two special nodes entry and exit
• Control always enters through the entry node
• Control always leaves through the exit node

Loops in Flow Graphs

A loop has a single entry point and the components of a loop are strongly connected in a CFG.

Dominators

A node d dominates a node n if every path from entry to n passes through d. Every node dominates itself.
Dominance is a reflexive partial order.

• Reflexive: A dom a ∀ a
• Antisymmetry: A dom b and b dom a ⇒ a=b
• Transitive: A dom b and b dom c ⇒ a dom c