Flow graphs

. add control flow information to basic blocks

. nodes are the basic blocks

. there is a directed edge from B₁ to B₂ if B ₂can follow B₁ in some execution sequence

- there is a jump from the last statement of B₁ to the first statement of B₂

- B₂ follows B ₁ in natural order of execution

. initial node: block with first statement as leader

We can add flow control information to the set of basic blocks making up a program by constructing a directed graph called a flow graph. The nodes of a flow graph are the basic nodes. One node is distinguished as initial; it is the block whose leader is the first statement. There is a directed edge from block B₁ to block B₂ if B₂ can immediately follow B₁ in some execution sequence; that is, if

. There is conditional or unconditional jump from the last statement of B₁ to the first statement of B₂ , or

. B₂ immediately follows B₁ in the order of the program, and B₁ does not end in an unconditional jump. We say that B₁ is the predecessor of B ₂ , and B ₂ is a successor of B ₁ .