You may be better off building up the LLVM IR as text, vs. using the FFI builder. (If you want/need type safety as opposed to just waiting for the LLVM verifier to tell you what went wrong, you could write the builder in Lua.)

Here's a link with a Python example (along with a justification for this approach): http://eli.thegreenplace.net/2015/building-and-using-llvmlit...