C++: Remove flow through ssa phi back-edges.

Author: MathiasVP

cpp/ql/src/experimental/Likely Bugs/OverrunWriteProductFlow.ql

@@ -111,6 +111,10 @@ module StringSizeConfig implements ProductFlow::StateConfigSig {
 
   predicate isBarrier2(DataFlow::Node node, FlowState2 state) { none() }
 
+  predicate isBarrierOut2(DataFlow::Node node) {
+    node = any(DataFlow::SsaPhiNode phi).getAnInput(true)
+  }
+
   predicate isAdditionalFlowStep1(
     DataFlow::Node node1, FlowState1 state1, DataFlow::Node node2, FlowState1 state2
   ) {