C++: Flow out of phi inputs to the phi node.

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll

@@ -2232,6 +2232,9 @@ private module Cached {
       // Def-use/Use-use flow
       Ssa::ssaFlow(nodeFrom, nodeTo)
       or
+      // Phi input -> Phi
+      nodeFrom.(SsaPhiInputNode).getPhiNode() = nodeTo.(SsaPhiNode).getPhiNode()
+      or
       IteratorFlow::localFlowStep(nodeFrom, nodeTo)
       or
       // Operand -> Instruction flow