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 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
