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/Constants.h" 38 #include "llvm/DerivedTypes.h" 39 #include "llvm/IRBuilder.h" 40 #include "llvm/Instructions.h" 41 #include "llvm/LLVMContext.h" 42 #include "llvm/Module.h" 43 #include "llvm/ExecutionEngine/JIT.h" 44 #include "llvm/ExecutionEngine/Interpreter.h" 45 #include "llvm/ExecutionEngine/GenericValue.h" 46 #include "llvm/Support/TargetSelect.h" 47 #include "llvm/Support/ManagedStatic.h" 48 #include "llvm/Support/raw_ostream.h" 49 50 using namespace llvm; 51 52 int main() { 53 54 InitializeNativeTarget(); 55 56 LLVMContext Context; 57 58 // Create some module to put our function into it. 59 Module *M = new Module("test", Context); 60 61 // Create the add1 function entry and insert this entry into module M. The 62 // function will have a return type of "int" and take an argument of "int". 63 // The '0' terminates the list of argument types. 64 Function *Add1F = 65 cast<Function>(M->getOrInsertFunction("add1", Type::getInt32Ty(Context), 66 Type::getInt32Ty(Context), 67 (Type *)0)); 68 69 // Add a basic block to the function. As before, it automatically inserts 70 // because of the last argument. 71 BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", Add1F); 72 73 // Create a basic block builder with default parameters. The builder will 74 // automatically append instructions to the basic block `BB'. 75 IRBuilder<> builder(BB); 76 77 // Get pointers to the constant `1'. 78 Value *One = builder.getInt32(1); 79 80 // Get pointers to the integer argument of the add1 function... 81 assert(Add1F->arg_begin() != Add1F->arg_end()); // Make sure there's an arg 82 Argument *ArgX = Add1F->arg_begin(); // Get the arg 83 ArgX->setName("AnArg"); // Give it a nice symbolic name for fun. 84 85 // Create the add instruction, inserting it into the end of BB. 86 Value *Add = builder.CreateAdd(One, ArgX); 87 88 // Create the return instruction and add it to the basic block 89 builder.CreateRet(Add); 90 91 // Now, function add1 is ready. 92 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 (Type *)0)); 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(M).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 EE->freeMachineCodeForFunction(FooF); 130 delete EE; 131 llvm_shutdown(); 132 return 0; 133 } 134
