Analysis of Loops
- This CFG is for a loop. At the statement Y := 0, the value of X can not be determined. As value of predecessors X := 3 and A : 2*X is needed but see that A := 2*x can only be defined when Y := 0 can get some output.
To solve this initially bottom is given to that variable for that predecessor. In this case X would have value bottom for the loop edge and then all the values are updated.
See the video for example.