CPP：Some questions about Control flow analyse and query time

I just start learning Codeql, and I want to analyze Data flow and Control flow of a program. Now I learn **_getASuccessor_** and Global DataFlow analyze. And I have some questions:

1. Is there any way （api）to do global control flow analysis? I find that **_getASuccessor_** can only get reachability within A function. How to know if a node in a function can reach node in some other functions?
2. I write a function to do global control flow analysis, but the query takes a long long time to run.... It's a function that recursively calls getASuccessor, I wonder why it's taking so long.....getASuccessor？or recursive?Is there any way to do this faster？
Part of the code：