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/ADT/APInt.h" 27 #include "llvm/IR/Verifier.h" 28 #include "llvm/ExecutionEngine/ExecutionEngine.h" 29 #include "llvm/ExecutionEngine/GenericValue.h" 30 #include "llvm/ExecutionEngine/MCJIT.h" 31 #include "llvm/IR/Argument.h" 32 #include "llvm/IR/BasicBlock.h" 33 #include "llvm/IR/Constants.h" 34 #include "llvm/IR/DerivedTypes.h" 35 #include "llvm/IR/Function.h" 36 #include "llvm/IR/InstrTypes.h" 37 #include "llvm/IR/Instructions.h" 38 #include "llvm/IR/LLVMContext.h" 39 #include "llvm/IR/Module.h" 40 #include "llvm/IR/Type.h" 41 #include "llvm/Support/Casting.h" 42 #include "llvm/Support/TargetSelect.h" 43 #include "llvm/Support/raw_ostream.h" 44 #include <algorithm> 45 #include <cstdlib> 46 #include <memory> 47 #include <string> 48 #include <vector> 49 50 using namespace llvm; 51 52 static Function *CreateFibFunction(Module *M, LLVMContext &Context) { 53 // Create the fib function and insert it into module M. This function is said 54 // to return an int and take an int parameter. 55 Function *FibF = 56 cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context), 57 Type::getInt32Ty(Context), 58 nullptr)); 59 60 // Add a basic block to the function. 61 BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF); 62 63 // Get pointers to the constants. 64 Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1); 65 Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2); 66 67 // Get pointer to the integer argument of the add1 function... 68 Argument *ArgX = &*FibF->arg_begin(); // Get the arg. 69 ArgX->setName("AnArg"); // Give it a nice symbolic name for fun. 70 71 // Create the true_block. 72 BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF); 73 // Create an exit block. 74 BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF); 75 76 // Create the "if (arg <= 2) goto exitbb" 77 Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond"); 78 BranchInst::Create(RetBB, RecurseBB, CondInst, BB); 79 80 // Create: ret int 1 81 ReturnInst::Create(Context, One, RetBB); 82 83 // create fib(x-1) 84 Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB); 85 CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB); 86 CallFibX1->setTailCall(); 87 88 // create fib(x-2) 89 Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB); 90 CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB); 91 CallFibX2->setTailCall(); 92 93 // fib(x-1)+fib(x-2) 94 Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2, 95 "addresult", RecurseBB); 96 97 // Create the return instruction and add it to the basic block 98 ReturnInst::Create(Context, Sum, RecurseBB); 99 100 return FibF; 101 } 102 103 int main(int argc, char **argv) { 104 int n = argc > 1 ? atol(argv[1]) : 24; 105 106 InitializeNativeTarget(); 107 InitializeNativeTargetAsmPrinter(); 108 LLVMContext Context; 109 110 // Create some module to put our function into it. 111 std::unique_ptr<Module> Owner(new Module("test", Context)); 112 Module *M = Owner.get(); 113 114 // We are about to create the "fib" function: 115 Function *FibF = CreateFibFunction(M, Context); 116 117 // Now we going to create JIT 118 std::string errStr; 119 ExecutionEngine *EE = 120 EngineBuilder(std::move(Owner)) 121 .setErrorStr(&errStr) 122 .create(); 123 124 if (!EE) { 125 errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr 126 << "\n"; 127 return 1; 128 } 129 130 errs() << "verifying... "; 131 if (verifyModule(*M)) { 132 errs() << argv[0] << ": Error constructing function!\n"; 133 return 1; 134 } 135 136 errs() << "OK\n"; 137 errs() << "We just constructed this LLVM module:\n\n---------\n" << *M; 138 errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n"; 139 140 // Call the Fibonacci function with argument n: 141 std::vector<GenericValue> Args(1); 142 Args[0].IntVal = APInt(32, n); 143 GenericValue GV = EE->runFunction(FibF, Args); 144 145 // import result of execution 146 outs() << "Result: " << GV.IntVal << "\n"; 147 148 return 0; 149 } 150
