1 //===-- examples/HowToUseJIT/HowToUseJIT.cpp - An example use of the JIT --===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This small program provides an example of how to quickly build a small
10 // module with two functions and execute it with the JIT.
11 //
12 // Goal:
13 // The goal of this snippet is to create in the memory
14 // the LLVM module consisting of two functions as follow:
15 //
16 // int add1(int x) {
17 // return x+1;
18 // }
19 //
20 // int foo() {
21 // return add1(10);
22 // }
23 //
24 // then compile the module via JIT, then execute the `foo'
25 // function and return result to a driver, i.e. to a "host program".
26 //
27 // Some remarks and questions:
28 //
29 // - could we invoke some code using noname functions too?
30 // e.g. evaluate "foo()+foo()" without fears to introduce
31 // conflict of temporary function name with some real
32 // existing function name?
33 //
34 //===----------------------------------------------------------------------===//
35
36 #include "llvm/ADT/STLExtras.h"
37 #include "llvm/ExecutionEngine/ExecutionEngine.h"
38 #include "llvm/ExecutionEngine/GenericValue.h"
39 #include "llvm/ExecutionEngine/MCJIT.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 LLVMInitializeNativeAsmPrinter();
64
65 LLVMContext Context;
66
67 // Create some module to put our function into it.
68 std::unique_ptr<Module> Owner = std::make_unique<Module>("test", Context);
69 Module *M = Owner.get();
70
71 // Create the add1 function entry and insert this entry into module M. The
72 // function will have a return type of "int" and take an argument of "int".
73 Function *Add1F =
74 Function::Create(FunctionType::get(Type::getInt32Ty(Context),
75 {Type::getInt32Ty(Context)}, false),
76 Function::ExternalLinkage, "add1", M);
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 Function::Create(FunctionType::get(Type::getInt32Ty(Context), {}, false),
106 Function::ExternalLinkage, "foo", M);
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