[cpp] Check whether path between function A and function B exists

Hi! I'm trying to write a query that checks whether function A can call (directly or transitively) function B. I've implemented it with recursive predicate that uses `Function.calls`. It works, but is slow. I suspect DataFlow API can be handy but couldn't produce working query yet. I'm dealing with fairly simple cpp code that doesn't use virtual functions, doesn't use pointer arithmetic, so DataFlow might be a bit too excessive for my task. I wonder what is the most efficient way to solve this problem. Thanks!