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/LLVMContext.h"
38#include "llvm/Module.h"
39#include "llvm/Constants.h"
40#include "llvm/DerivedTypes.h"
41#include "llvm/Instructions.h"
42#include "llvm/ExecutionEngine/JIT.h"
43#include "llvm/ExecutionEngine/Interpreter.h"
44#include "llvm/ExecutionEngine/GenericValue.h"
45#include "llvm/Support/TargetSelect.h"
46#include "llvm/Support/ManagedStatic.h"
47#include "llvm/Support/raw_ostream.h"
48#include "llvm/Support/IRBuilder.h"
49
50using namespace llvm;
51
52int main() {
53
54  InitializeNativeTarget();
55
56  LLVMContext Context;
57
58  // Create some module to put our function into it.
59  Module *M = new Module("test", Context);
60
61  // Create the add1 function entry and insert this entry into module M.  The
62  // function will have a return type of "int" and take an argument of "int".
63  // The '0' terminates the list of argument types.
64  Function *Add1F =
65    cast<Function>(M->getOrInsertFunction("add1", Type::getInt32Ty(Context),
66                                          Type::getInt32Ty(Context),
67                                          (Type *)0));
68
69  // Add a basic block to the function. As before, it automatically inserts
70  // because of the last argument.
71  BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F);
72
73  // Create a basic block builder with default parameters.  The builder will
74  // automatically append instructions to the basic block `BB'.
75  IRBuilder<> builder(BB);
76
77  // Get pointers to the constant `1'.
78  Value *One = builder.getInt32(1);
79
80  // Get pointers to the integer argument of the add1 function...
81  assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
82  Argument *ArgX = Add1F->arg_begin();  // Get the arg
83  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
84
85  // Create the add instruction, inserting it into the end of BB.
86  Value *Add = builder.CreateAdd(One, ArgX);
87
88  // Create the return instruction and add it to the basic block
89  builder.CreateRet(Add);
90
91  // Now, function add1 is ready.
92
93
94  // Now we're going to create function `foo', which returns an int and takes no
95  // arguments.
96  Function *FooF =
97    cast<Function>(M->getOrInsertFunction("foo", Type::getInt32Ty(Context),
98                                          (Type *)0));
99
100  // Add a basic block to the FooF function.
101  BB = BasicBlock::Create(Context, "EntryBlock", FooF);
102
103  // Tell the basic block builder to attach itself to the new basic block
104  builder.SetInsertPoint(BB);
105
106  // Get pointer to the constant `10'.
107  Value *Ten = builder.getInt32(10);
108
109  // Pass Ten to the call to Add1F
110  CallInst *Add1CallRes = builder.CreateCall(Add1F, Ten);
111  Add1CallRes->setTailCall(true);
112
113  // Create the return instruction and add it to the basic block.
114  builder.CreateRet(Add1CallRes);
115
116  // Now we create the JIT.
117  ExecutionEngine* EE = EngineBuilder(M).create();
118
119  outs() << "We just constructed this LLVM module:\n\n" << *M;
120  outs() << "\n\nRunning foo: ";
121  outs().flush();
122
123  // Call the `foo' function with no arguments:
124  std::vector<GenericValue> noargs;
125  GenericValue gv = EE->runFunction(FooF, noargs);
126
127  // Import result of execution:
128  outs() << "Result: " << gv.IntVal << "\n";
129  EE->freeMachineCodeForFunction(FooF);
130  delete EE;
131  llvm_shutdown();
132  return 0;
133}
134