1//===-- examples/HowToUseJIT/HowToUseJIT.cpp - An example use of the JIT --===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10//  This small program provides an example of how to quickly build a small
11//  module with two functions and execute it with the JIT.
12//
13// Goal:
14//  The goal of this snippet is to create in the memory
15//  the LLVM module consisting of two functions as follow:
16//
17// int add1(int x) {
18//   return x+1;
19// }
20//
21// int foo() {
22//   return add1(10);
23// }
24//
25// then compile the module via JIT, then execute the `foo'
26// function and return result to a driver, i.e. to a "host program".
27//
28// Some remarks and questions:
29//
30// - could we invoke some code using noname functions too?
31//   e.g. evaluate "foo()+foo()" without fears to introduce
32//   conflict of temporary function name with some real
33//   existing function name?
34//
35//===----------------------------------------------------------------------===//
36
37#include "llvm/ADT/STLExtras.h"
38#include "llvm/ExecutionEngine/ExecutionEngine.h"
39#include "llvm/ExecutionEngine/GenericValue.h"
40#include "llvm/IR/Argument.h"
41#include "llvm/IR/BasicBlock.h"
42#include "llvm/IR/Constants.h"
43#include "llvm/IR/DerivedTypes.h"
44#include "llvm/IR/Function.h"
45#include "llvm/IR/IRBuilder.h"
46#include "llvm/IR/Instructions.h"
47#include "llvm/IR/LLVMContext.h"
48#include "llvm/IR/Module.h"
49#include "llvm/IR/Type.h"
50#include "llvm/Support/Casting.h"
51#include "llvm/Support/ManagedStatic.h"
52#include "llvm/Support/TargetSelect.h"
53#include "llvm/Support/raw_ostream.h"
54#include <algorithm>
55#include <cassert>
56#include <memory>
57#include <vector>
58
59using namespace llvm;
60
61int main() {
62  InitializeNativeTarget();
63
64  LLVMContext Context;
65
66  // Create some module to put our function into it.
67  std::unique_ptr<Module> Owner = make_unique<Module>("test", Context);
68  Module *M = Owner.get();
69
70  // Create the add1 function entry and insert this entry into module M.  The
71  // function will have a return type of "int" and take an argument of "int".
72  // The '0' terminates the list of argument types.
73  Function *Add1F =
74    cast<Function>(M->getOrInsertFunction("add1", Type::getInt32Ty(Context),
75                                          Type::getInt32Ty(Context),
76                                          nullptr));
77
78  // Add a basic block to the function. As before, it automatically inserts
79  // because of the last argument.
80  BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F);
81
82  // Create a basic block builder with default parameters.  The builder will
83  // automatically append instructions to the basic block `BB'.
84  IRBuilder<> builder(BB);
85
86  // Get pointers to the constant `1'.
87  Value *One = builder.getInt32(1);
88
89  // Get pointers to the integer argument of the add1 function...
90  assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
91  Argument *ArgX = &*Add1F->arg_begin();          // Get the arg
92  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
93
94  // Create the add instruction, inserting it into the end of BB.
95  Value *Add = builder.CreateAdd(One, ArgX);
96
97  // Create the return instruction and add it to the basic block
98  builder.CreateRet(Add);
99
100  // Now, function add1 is ready.
101
102  // Now we're going to create function `foo', which returns an int and takes no
103  // arguments.
104  Function *FooF =
105    cast<Function>(M->getOrInsertFunction("foo", Type::getInt32Ty(Context),
106                                          nullptr));
107
108  // Add a basic block to the FooF function.
109  BB = BasicBlock::Create(Context, "EntryBlock", FooF);
110
111  // Tell the basic block builder to attach itself to the new basic block
112  builder.SetInsertPoint(BB);
113
114  // Get pointer to the constant `10'.
115  Value *Ten = builder.getInt32(10);
116
117  // Pass Ten to the call to Add1F
118  CallInst *Add1CallRes = builder.CreateCall(Add1F, Ten);
119  Add1CallRes->setTailCall(true);
120
121  // Create the return instruction and add it to the basic block.
122  builder.CreateRet(Add1CallRes);
123
124  // Now we create the JIT.
125  ExecutionEngine* EE = EngineBuilder(std::move(Owner)).create();
126
127  outs() << "We just constructed this LLVM module:\n\n" << *M;
128  outs() << "\n\nRunning foo: ";
129  outs().flush();
130
131  // Call the `foo' function with no arguments:
132  std::vector<GenericValue> noargs;
133  GenericValue gv = EE->runFunction(FooF, noargs);
134
135  // Import result of execution:
136  outs() << "Result: " << gv.IntVal << "\n";
137  delete EE;
138  llvm_shutdown();
139  return 0;
140}
141