Exercise 1.

Consider the following three-address code fragment.

	a := 1
	b := 2
L2	c := a + b
	d := c - a
	if d = b goto L5
L3	d := b * d
	if d = b goto L5
	d := a + b
	e := e + 1
	goto L3
L5	b := a + b
	e := c - a
	if d = b goto L2
	a := b + d
	b := a - d

1. Give the flow graph of this program.
2. Identify the back edges and the loops.

Note that the results of these computations do not matter. We are only interested here in the relations between the basic blocks.

Answer 1  

Figure 1: The control flow graph.