Python ESSA: Fix performance of PythonSsaSourceVariable.hasRefinementEdge()

Author: markshannon

python/ql/src/semmle/python/dataflow/SsaDefinitions.qll

@@ -79,24 +79,12 @@ abstract class PythonSsaSourceVariable extends SsaSourceVariable {
     }
 
     override predicate hasRefinementEdge(ControlFlowNode use, BasicBlock pred, BasicBlock succ) {
+        test_contains(pred.getLastNode(), use) and
         use.(NameNode).uses(this) and
-        exists(ControlFlowNode test |
-            test.getAChild*() = use and
-            test.isBranch() and
-            test = pred.getLastNode()
-        ) and
-        (pred.getAFalseSuccessor() = succ or pred.getATrueSuccessor() = succ)
-        and
+        (pred.getAFalseSuccessor() = succ or pred.getATrueSuccessor() = succ) and
         /* There is a store to this variable -- We don't want to refine builtins */
-        exists(this.(Variable).getAStore()) and
-        /* There is at least one use or definition of the variable that is reachable by the test */
-        exists(ControlFlowNode n |
-            n = this.getAUse() or
-            this.hasDefiningNode(n) |
-            pred.(ConditionBlock).strictlyReaches(n.getBasicBlock())
-        )
+        exists(this.(Variable).getAStore())
     }
-
     override ControlFlowNode getASourceUse() {
         result.(NameNode).uses(this)
         or