1. A node ‘d’ of a flow graph dominates node ‘n’, if every path from the initial node to ‘n’ goes through ‘d’.
2. The dominators[head] containing the tail node in a flow graph detects the presence of a back edge.
3. A pre-header is a basic block introduced during the loop optimisation to hold the quads that are moved from within the loop.
4. A ud-chain obtained from reaching definitions analysis is used for performing the loop invariant code motion optimisation in the loops