[PATCH] D54498: AbstractCallSite -- A unified interface for (in)direct and callback calls

[Siddharth via Phabricator via llvm-commits]

bollu added a comment.

Thanks for the answer! That clears up a lot.

So, I believe the main difference between the `pthread` example and the one that I have is that of mutual recursion: I will often have mutual recursion between the `trampoline` and the `f_i`, which usually complicates inter-procedural analysis (as far as I understand?)

An extreme example of such messy code could be something like this:

  // computes if 9 is odd by calling two mutually recursive functions is_odd and is_even,
  // which in turn recurse through the trampoline
  entrypoint:
     push_int(9);
     push_call(IS_ODD);
     trampoline();
  
  // is_odd :: Int -> Int
  is_odd:
    i = pop_int();
    if (i == 0) { push_int(0); trampoline(); }
    if (i == 1) { push_int(1); trampoline(); }
  
    push_int(i - 1);
    push_call(IS_EVEN_LABEL);
    trampoline();
  
  // is_even Int -> Int
  is_even:
     i = pop_int();
     if (i == 0) { push_int(1); trampoline(); }
     if (i == 1) { push_int(0); trampoline(); }
     
     push_int(i - 1);
     push_call(IS_ODD_LABEL);
     trampoline();
  
  trampoline:
    tag = pop_call();
    switch (tag) {
       case IS_EVEN_LABEL:
           is_even();
       case IS_ODD_LABEL:
           is_odd();
       case ENTRYPOINT:
          entrypoint();
    }
   


Repository:
  rL LLVM

https://reviews.llvm.org/D54498