Purpose Use-define chain

notice x assigned value @ 3 points (marked a, b, , c). however, @ point marked 1 , use-def chain x should indicate current value must have come line b (and value @ line b must have come line a). contrariwise, @ point marked 2 , use-def chain x indicates current value must have come line c. since value of x in block 2 not depend on definitions in block 1 or earlier, x might different variable there; practically speaking, different variable — call x2.

the process of splitting x 2 separate variables called live range splitting. see static single assignment form.