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
59 using namespace llvm;
60
main()61 int 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