This snippet fails:

 func foo(x: Int) {
 var z: Int
 while (x > 0) {
 z = 5
 if (x == 1)
 z = z+1
 x = x - 1
 }
 }

While this is okay

 func foo(x: Int) {
 var z = 0
 while (x > 0) {
 z = 5
 if (x == 1)
 z = z+1
 x = x - 1
 }
 }

The problem seems to be in 2nd block of search() where we look for instructions of form v = x op y. The declaration alone does not generate such an instruction.

Potential solution may be that declaration of a var generates a var instruction that defines the var.