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