What part of the detection is giving you trouble? Detecting whether a call is recursive, or whether it is a tail call that can be optimized? The first part is r

What part of the detection is giving you trouble? Detecting whether a call is recursive, or whether it is a tail call that can be optimized? The first part is relatively easy, you typically have some sort of data structure representing calls and their targets, and you know what function you're currently compiling. If the function you're compiling is the same as a call's target, you have recursion. LLVM's code is at https://llvm.org/doxygen/TailRecursionElimination_8cpp_source.html https://llvm.org/doxygen/TailRecursionElimination_8cpp_sourc... The core of this detection is in findTRECandidate. It iterates backwards over a basic block, looking for call instructions whose call target is the current function F: CallInst *CI = nullptr; BasicBlock::iterator BBI(TI); while (true) { CI = dyn_cast<CallInst>(BBI); if (CI && CI->getCalledFunction() == &F) break; if (BBI == BB->begin()) return nullptr; // Didn't find a potential tail call. --BBI; } The harder part is detecting whether calls are in fact tail calls that you can replace by jumps. There are all sorts of special cases, like whether alloca() might be called by the function.