@Nullable
  public static ReadWriteVariableInstruction findRWInstruction(final GrReferenceExpression refExpr, final Instruction[] flow) {
    for (Instruction instruction : flow) {
      if (instruction instanceof ReadWriteVariableInstruction && instruction.getElement() == refExpr) {
        return (ReadWriteVariableInstruction)instruction;
      }
    }
    return null;
  }
@Nullable
  public static ReadWriteVariableInstruction findRWInstruction(final GrReferenceExpression refExpr, final Instruction[] flow)