149 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// This small program provides an example of how to build quickly a small module10// with function Fibonacci and execute it with the JIT.11//12// The goal of this snippet is to create in the memory the LLVM module13// 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 49using namespace llvm;50 51static Function *CreateFibFunction(Module *M, LLVMContext &Context) {52 // Create the fib function and insert it into module M. This function is said53 // to return an int and take an int parameter.54 FunctionType *FibFTy = FunctionType::get(Type::getInt32Ty(Context),55 {Type::getInt32Ty(Context)}, false);56 Function *FibF =57 Function::Create(FibFTy, Function::ExternalLinkage, "fib", M);58 59 // Add a basic block to the function.60 BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);61 62 // Get pointers to the constants.63 Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);64 Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);65 66 // Get pointer to the integer argument of the add1 function...67 Argument *ArgX = &*FibF->arg_begin(); // Get the arg.68 ArgX->setName("AnArg"); // Give it a nice symbolic name for fun.69 70 // Create the true_block.71 BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);72 // Create an exit block.73 BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);74 75 // Create the "if (arg <= 2) goto exitbb"76 Value *CondInst = new ICmpInst(BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");77 BranchInst::Create(RetBB, RecurseBB, CondInst, BB);78 79 // Create: ret int 180 ReturnInst::Create(Context, One, RetBB);81 82 // create fib(x-1)83 Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);84 CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);85 CallFibX1->setTailCall();86 87 // create fib(x-2)88 Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);89 CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);90 CallFibX2->setTailCall();91 92 // fib(x-1)+fib(x-2)93 Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,94 "addresult", RecurseBB);95 96 // Create the return instruction and add it to the basic block97 ReturnInst::Create(Context, Sum, RecurseBB);98 99 return FibF;100}101 102int main(int argc, char **argv) {103 int n = argc > 1 ? atol(argv[1]) : 24;104 105 InitializeNativeTarget();106 InitializeNativeTargetAsmPrinter();107 LLVMContext Context;108 109 // Create some module to put our function into it.110 std::unique_ptr<Module> Owner(new Module("test", Context));111 Module *M = Owner.get();112 113 // We are about to create the "fib" function:114 Function *FibF = CreateFibFunction(M, Context);115 116 // Now we going to create JIT117 std::string errStr;118 ExecutionEngine *EE =119 EngineBuilder(std::move(Owner))120 .setErrorStr(&errStr)121 .create();122 123 if (!EE) {124 errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr125 << "\n";126 return 1;127 }128 129 errs() << "verifying... ";130 if (verifyModule(*M)) {131 errs() << argv[0] << ": Error constructing function!\n";132 return 1;133 }134 135 errs() << "OK\n";136 errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;137 errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";138 139 // Call the Fibonacci function with argument n:140 std::vector<GenericValue> Args(1);141 Args[0].IntVal = APInt(32, n);142 GenericValue GV = EE->runFunction(FibF, Args);143 144 // import result of execution145 outs() << "Result: " << GV.IntVal << "\n";146 147 return 0;148}149