HowToUseLLJIT.cpp

//===------- HowToUseLLJIT.cpp - An example use of ORC-based LLJIT --------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  This small program provides an example of how to quickly build a small
//  module with a 'add1' function and use of IRBuilder to create add & return
//  instructions.
//
// Goal:
//  The goal of this snippet is to create in the memory
//  the LLVM module consisting of a function as follow:
//
// int add1(int x) {
//   return x+1;
// }
//  add1(42);
//
// then compile the module via LLJIT, then execute the 'add1'
// function and return result to a driver, i.e. to a "host program".
//
//===----------------------------------------------------------------------===//

#include "llvm/ExecutionEngine/Orc/LLJIT.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/InitLLVM.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;
using namespace llvm::orc;

ExitOnError ExitOnErr;

ThreadSafeModule createDemoModule() {
  auto Context = std::make_unique<LLVMContext>();
  auto M = std::make_unique<Module>("test", *Context);

  // Create the add1 function entry and insert this entry into module M.  The
  // function will have a return type of "int" and take an argument of "int".
  Function *Add1F =
      Function::Create(FunctionType::get(Type::getInt32Ty(*Context),
                                         {Type::getInt32Ty(*Context)}, false),
                       Function::ExternalLinkage, "add1", M.get());

  // Add a basic block to the function. As before, it automatically inserts
  // because of the last argument.
  BasicBlock *BB = BasicBlock::Create(*Context, "EntryBlock", Add1F);

  // Create a basic block builder with default parameters.  The builder will
  // automatically append instructions to the basic block `BB'.
  IRBuilder<> builder(BB);

  // Get pointers to the constant `1'.
  Value *One = builder.getInt32(1);

  // Get pointers to the integer argument of the add1 function...
  assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
  Argument *ArgX = &*Add1F->arg_begin();          // Get the arg
  ArgX->setName("AnArg"); // Give it a nice symbolic name for fun.

  // Create the add instruction, inserting it into the end of BB.
  Value *Add = builder.CreateAdd(One, ArgX);

  // Create the return instruction and add it to the basic block
  builder.CreateRet(Add);

  return ThreadSafeModule(std::move(M), std::move(Context));
}

int main(int argc, char *argv[]) {
  // Initialize LLVM.
  InitLLVM X(argc, argv);

  InitializeNativeTarget();
  InitializeNativeTargetAsmPrinter();

  cl::ParseCommandLineOptions(argc, argv, "HowToUseLLJIT");
  ExitOnErr.setBanner(std::string(argv[0]) + ": ");

  // Create an LLJIT instance.
  auto J = ExitOnErr(LLJITBuilder().create());
  auto M = createDemoModule();

  ExitOnErr(J->addIRModule(std::move(M)));

  // Look up the JIT'd function, cast it to a function pointer, then call it.
  auto Add1Sym = ExitOnErr(J->lookup("add1"));
  int (*Add1)(int) = (int (*)(int))Add1Sym.getAddress();

  int Result = Add1(42);
  outs() << "add1(42) = " << Result << "\n";

  return 0;
}