'Create function body and return LLVM IR'

def _create_function(self, expr):

    bb_entry = self.fn.append_basic_block('entry')
    builder = ll.IRBuilder(bb_entry)
    lj = LLVMJitPrinter(self.module, builder, self.fn, func_arg_map=self.param_dict)
    ret = self._convert_expr(lj, expr)
    lj.builder.ret(self._wrap_return(lj, ret))
    strmod = str(self.module)
    return strmod
