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/GenericValue.h"
39 #include "llvm/ExecutionEngine/Interpreter.h"
40 #include "llvm/IR/Constants.h"
41 #include "llvm/IR/DerivedTypes.h"
42 #include "llvm/IR/IRBuilder.h"
43 #include "llvm/IR/Instructions.h"
44 #include "llvm/IR/LLVMContext.h"
45 #include "llvm/IR/Module.h"
46 #include "llvm/Support/ManagedStatic.h"
47 #include "llvm/Support/TargetSelect.h"
48 #include "llvm/Support/raw_ostream.h"
49
50 using namespace llvm;
51
main()52 int main() {
53
54 InitializeNativeTarget();
55
56 LLVMContext Context;
57
58 // Create some module to put our function into it.
59 std::unique_ptr<Module> Owner = make_unique<Module>("test", Context);
60 Module *M = Owner.get();
61
62 // Create the add1 function entry and insert this entry into module M. The
63 // function will have a return type of "int" and take an argument of "int".
64 // The '0' terminates the list of argument types.
65 Function *Add1F =
66 cast<Function>(M->getOrInsertFunction("add1", Type::getInt32Ty(Context),
67 Type::getInt32Ty(Context),
68 nullptr));
69
70 // Add a basic block to the function. As before, it automatically inserts
71 // because of the last argument.
72 BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F);
73
74 // Create a basic block builder with default parameters. The builder will
75 // automatically append instructions to the basic block `BB'.
76 IRBuilder<> builder(BB);
77
78 // Get pointers to the constant `1'.
79 Value *One = builder.getInt32(1);
80
81 // Get pointers to the integer argument of the add1 function...
82 assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg
83 Argument *ArgX = &*Add1F->arg_begin(); // Get the arg
84 ArgX->setName("AnArg"); // Give it a nice symbolic name for fun.
85
86 // Create the add instruction, inserting it into the end of BB.
87 Value *Add = builder.CreateAdd(One, ArgX);
88
89 // Create the return instruction and add it to the basic block
90 builder.CreateRet(Add);
91
92 // Now, function add1 is ready.
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 nullptr));
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(std::move(Owner)).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 delete EE;
130 llvm_shutdown();
131 return 0;
132 }
133