1 //===--- examples/Fibonacci/fibonacci.cpp - An example use of the JIT -----===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This small program provides an example of how to build quickly a small module 10 // with function Fibonacci and execute it with the JIT. 11 // 12 // The goal of this snippet is to create in the memory the LLVM module 13 // consisting of one function as follow: 14 // 15 // int fib(int x) { 16 // if(x<=2) return 1; 17 // return fib(x-1)+fib(x-2); 18 // } 19 // 20 // Once we have this, we compile the module via JIT, then execute the `fib' 21 // function and return result to a driver, i.e. to a "host program". 22 // 23 //===----------------------------------------------------------------------===// 24 25 #include "llvm/ADT/APInt.h" 26 #include "llvm/IR/Verifier.h" 27 #include "llvm/ExecutionEngine/ExecutionEngine.h" 28 #include "llvm/ExecutionEngine/GenericValue.h" 29 #include "llvm/ExecutionEngine/MCJIT.h" 30 #include "llvm/IR/Argument.h" 31 #include "llvm/IR/BasicBlock.h" 32 #include "llvm/IR/Constants.h" 33 #include "llvm/IR/DerivedTypes.h" 34 #include "llvm/IR/Function.h" 35 #include "llvm/IR/InstrTypes.h" 36 #include "llvm/IR/Instructions.h" 37 #include "llvm/IR/LLVMContext.h" 38 #include "llvm/IR/Module.h" 39 #include "llvm/IR/Type.h" 40 #include "llvm/Support/Casting.h" 41 #include "llvm/Support/TargetSelect.h" 42 #include "llvm/Support/raw_ostream.h" 43 #include <algorithm> 44 #include <cstdlib> 45 #include <memory> 46 #include <string> 47 #include <vector> 48 49 using namespace llvm; 50 51 static Function *CreateFibFunction(Module *M, LLVMContext &Context) { 52 // Create the fib function and insert it into module M. This function is said 53 // to return an int and take an int parameter. 54 Function *FibF = 55 cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context), 56 Type::getInt32Ty(Context))); 57 58 // Add a basic block to the function. 59 BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF); 60 61 // Get pointers to the constants. 62 Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1); 63 Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2); 64 65 // Get pointer to the integer argument of the add1 function... 66 Argument *ArgX = &*FibF->arg_begin(); // Get the arg. 67 ArgX->setName("AnArg"); // Give it a nice symbolic name for fun. 68 69 // Create the true_block. 70 BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF); 71 // Create an exit block. 72 BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF); 73 74 // Create the "if (arg <= 2) goto exitbb" 75 Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond"); 76 BranchInst::Create(RetBB, RecurseBB, CondInst, BB); 77 78 // Create: ret int 1 79 ReturnInst::Create(Context, One, RetBB); 80 81 // create fib(x-1) 82 Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB); 83 CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB); 84 CallFibX1->setTailCall(); 85 86 // create fib(x-2) 87 Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB); 88 CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB); 89 CallFibX2->setTailCall(); 90 91 // fib(x-1)+fib(x-2) 92 Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2, 93 "addresult", RecurseBB); 94 95 // Create the return instruction and add it to the basic block 96 ReturnInst::Create(Context, Sum, RecurseBB); 97 98 return FibF; 99 } 100 101 int main(int argc, char **argv) { 102 int n = argc > 1 ? atol(argv[1]) : 24; 103 104 InitializeNativeTarget(); 105 InitializeNativeTargetAsmPrinter(); 106 LLVMContext Context; 107 108 // Create some module to put our function into it. 109 std::unique_ptr<Module> Owner(new Module("test", Context)); 110 Module *M = Owner.get(); 111 112 // We are about to create the "fib" function: 113 Function *FibF = CreateFibFunction(M, Context); 114 115 // Now we going to create JIT 116 std::string errStr; 117 ExecutionEngine *EE = 118 EngineBuilder(std::move(Owner)) 119 .setErrorStr(&errStr) 120 .create(); 121 122 if (!EE) { 123 errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr 124 << "\n"; 125 return 1; 126 } 127 128 errs() << "verifying... "; 129 if (verifyModule(*M)) { 130 errs() << argv[0] << ": Error constructing function!\n"; 131 return 1; 132 } 133 134 errs() << "OK\n"; 135 errs() << "We just constructed this LLVM module:\n\n---------\n" << *M; 136 errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n"; 137 138 // Call the Fibonacci function with argument n: 139 std::vector<GenericValue> Args(1); 140 Args[0].IntVal = APInt(32, n); 141 GenericValue GV = EE->runFunction(FibF, Args); 142 143 // import result of execution 144 outs() << "Result: " << GV.IntVal << "\n"; 145 146 return 0; 147 } 148