1 //===--- examples/Fibonacci/fibonacci.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 build quickly a small module 11 // with function Fibonacci and execute it with the JIT. 12 // 13 // The goal of this snippet is to create in the memory the LLVM module 14 // consisting of one function as follow: 15 // 16 // int fib(int x) { 17 // if(x<=2) return 1; 18 // return fib(x-1)+fib(x-2); 19 // } 20 // 21 // Once we have this, we compile the module via JIT, then execute the `fib' 22 // function and return result to a driver, i.e. to a "host program". 23 // 24 //===----------------------------------------------------------------------===// 25 26 #include "llvm/LLVMContext.h" 27 #include "llvm/Module.h" 28 #include "llvm/DerivedTypes.h" 29 #include "llvm/Constants.h" 30 #include "llvm/Instructions.h" 31 #include "llvm/Analysis/Verifier.h" 32 #include "llvm/ExecutionEngine/JIT.h" 33 #include "llvm/ExecutionEngine/Interpreter.h" 34 #include "llvm/ExecutionEngine/GenericValue.h" 35 #include "llvm/Support/raw_ostream.h" 36 #include "llvm/Support/TargetSelect.h" 37 using namespace llvm; 38 39 static Function *CreateFibFunction(Module *M, LLVMContext &Context) { 40 // Create the fib function and insert it into module M. This function is said 41 // to return an int and take an int parameter. 42 Function *FibF = 43 cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context), 44 Type::getInt32Ty(Context), 45 (Type *)0)); 46 47 // Add a basic block to the function. 48 BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF); 49 50 // Get pointers to the constants. 51 Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1); 52 Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2); 53 54 // Get pointer to the integer argument of the add1 function... 55 Argument *ArgX = FibF->arg_begin(); // Get the arg. 56 ArgX->setName("AnArg"); // Give it a nice symbolic name for fun. 57 58 // Create the true_block. 59 BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF); 60 // Create an exit block. 61 BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF); 62 63 // Create the "if (arg <= 2) goto exitbb" 64 Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond"); 65 BranchInst::Create(RetBB, RecurseBB, CondInst, BB); 66 67 // Create: ret int 1 68 ReturnInst::Create(Context, One, RetBB); 69 70 // create fib(x-1) 71 Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB); 72 CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB); 73 CallFibX1->setTailCall(); 74 75 // create fib(x-2) 76 Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB); 77 CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB); 78 CallFibX2->setTailCall(); 79 80 81 // fib(x-1)+fib(x-2) 82 Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2, 83 "addresult", RecurseBB); 84 85 // Create the return instruction and add it to the basic block 86 ReturnInst::Create(Context, Sum, RecurseBB); 87 88 return FibF; 89 } 90 91 92 int main(int argc, char **argv) { 93 int n = argc > 1 ? atol(argv[1]) : 24; 94 95 InitializeNativeTarget(); 96 LLVMContext Context; 97 98 // Create some module to put our function into it. 99 OwningPtr<Module> M(new Module("test", Context)); 100 101 // We are about to create the "fib" function: 102 Function *FibF = CreateFibFunction(M.get(), Context); 103 104 // Now we going to create JIT 105 std::string errStr; 106 ExecutionEngine *EE = 107 EngineBuilder(M.get()) 108 .setErrorStr(&errStr) 109 .setEngineKind(EngineKind::JIT) 110 .create(); 111 112 if (!EE) { 113 errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr 114 << "\n"; 115 return 1; 116 } 117 118 errs() << "verifying... "; 119 if (verifyModule(*M)) { 120 errs() << argv[0] << ": Error constructing function!\n"; 121 return 1; 122 } 123 124 errs() << "OK\n"; 125 errs() << "We just constructed this LLVM module:\n\n---------\n" << *M; 126 errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n"; 127 128 // Call the Fibonacci function with argument n: 129 std::vector<GenericValue> Args(1); 130 Args[0].IntVal = APInt(32, n); 131 GenericValue GV = EE->runFunction(FibF, Args); 132 133 // import result of execution 134 outs() << "Result: " << GV.IntVal << "\n"; 135 136 return 0; 137 } 138
