In structure flow graph condition and control statements like, if else, do while comes.
An useful property of structured flow graph such as for do-while statements is:
- There is a single beginning point at which control enters and a single endpoint that control leaves from when execution of the statement is over.
To do data flow analysis of structured flow graph, we define a portion of a flow graph called a region to be a set of nodes (N) that includes a header.
This header determine all other nodes in the region. All edges between nodes (N) are in the region, except for some that enter the header.
The portion of flow graph corresponding to a statement S is a region that obeys the further restriction that control can flow just once outside block when it leaves the region.