Exercise 10.

Consider the following three-address code program fragment where t3 <> 0 is true if and only if t3 is not zero.

L0:	s:=0
	i:=0
	n:=10
L1:	t1 := a-b
	if t1 = 0 goto L3
L2:	t2 := i*4
	s := s+t2
	goto L4
L3:	s := s+i
L4:	i := i+1
	t3 := n-i
	if t3 <> 0 goto L1
L5:	t4 := a-b

1. Give the control-flow graph of this program.
2. Identify the back edges and the loops.
3. Which optimization (among copy propagation, dead-code elimination, common sub-expression elimination, invariant code motion) can be applied to this program? Show the intermediate transformations of the program. Computing the data-flow sets is not required. A brief justification of each transformation will be sufficient.

Answer 10