When you are confused about this, it is a good idea to print it out as follows

  llvm::raw_fd_ostream outfile("output.ll", EC, llvm::sys::fs::OF_Text);
  legacy::PassManager pm;
  pm.add(createPrintModulePass(outfile));
  pm.run(*module); // this module is the one you generated
  // and the same to the function

then you can see the problems in your module or function:)