Derive conditions for each variable assignment from pseudocode

I have some pseudocode that is in the form:

patch a:
  if b == "foo1"
  then
    a = "No"
    if c == "foo2"
    then
      if d == "foo3" || d == "foo4" || d == "foo5" || d == "foo6"
      then
        a = "Yes"
      else
        a = "No"
    else
      if c == "foo7"
      then
        if d == "foo8" || d == "foo9"
        then
          a = "Yes"
        else
          a = "No"
      else
        if c == "foo10"
        then
          if d == "foo11" || d == "foo12"
          then
            a = "Yes"
          else
            a = "No"
        else
          if c == "foo13"
          then
            if d != "foo11" && d != "foo12" && d != "foo8" && d != "foo9"
            then
              a = "Yes"
            else
              a = "No"
          else
            a = "Yes"

I have an ANTLR file that I am using to parse this pseudocode. I would like to be able to derive a single condition that satisfies each variable assignment I encounter as I parse the pseudocode. For the example above a single condition for a = "yes" would look like:

  (b == "foo1" AND c == "foo7" AND (d == "foo8" OR d == "foo9")) OR
  (b == "foo1" AND c == "foo10" AND (d == "foo11" OR d == "foo12")) OR
  (b == "foo1" AND c == "foo13" AND d != "foo11" AND d != "foo12" AND d != "foo8" AND d != "foo9")

and the single condition for a = "no" would look like:

(b == "foo1" AND c == "foo2" AND d != "foo3" AND d != "foo4" AND d != "foo5" AND d != "foo6") OR
  (b == "foo1" AND c == "foo7" AND d != "foo8" AND d != "foo9") OR
  (b == "foo1" AND c == "foo10" AND d != "foo11" AND d != "foo12") OR
  (b == "foo1" AND c == "foo13" AND (d == "foo11" OR d == "foo12" OR d == "foo8" OR d == "foo9"))

I am using a stack to maintain my conditions. Everytime, I enter an if block I push my condition to the stack and pop it when I leave the if block. When I enter a then block I push an AND to the stack and when I enter an else block I push an OR to stack. This works fine for simple patches but I am struggling to figure how to accommodate for line 4 in the example patch.

With the my current solution I am getting something like a = "No" when b == "foo1" OR ... this causing problems since it possible for a == "Yes" if a couple of more conditions are met. How do I account for this situation?

Update 1 Instead of trying to do this entirely in pass I decided to build an AST out of ANTLR's parse tree. It has a couple of node types which just store some data, like conditionNode storing if statements, assignmentNode storing assignments and the main ASTNode which captures scope and has things reference to parent, thenBranch, elseBranch and a root node which can be an assignmentNode or conditionNode. Using this structure it was easy to build out the conditions for leaf node assignments. Still would like help trying to figure out nonleaf node assignments.