blob: 12393a414d0746813fb0d0104823d42639cccf84 [file] [log] [blame]
//===--- examples/Fibonacci/fibonacci.cpp - An example use of the JIT -----===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This small program provides an example of how to build quickly a small module
// with function Fibonacci and execute it with the JIT.
// The goal of this snippet is to create in the memory the LLVM module
// consisting of one function as follow:
// int fib(int x) {
// if(x<=2) return 1;
// return fib(x-1)+fib(x-2);
// }
// Once we have this, we compile the module via JIT, then execute the `fib'
// function and return result to a driver, i.e. to a "host program".
#include "llvm/ADT/APInt.h"
#include "llvm/IR/Verifier.h"
#include "llvm/ExecutionEngine/ExecutionEngine.h"
#include "llvm/ExecutionEngine/GenericValue.h"
#include "llvm/ExecutionEngine/MCJIT.h"
#include "llvm/IR/Argument.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cstdlib>
#include <memory>
#include <string>
#include <vector>
using namespace llvm;
static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
// Create the fib function and insert it into module M. This function is said
// to return an int and take an int parameter.
FunctionType *FibFTy = FunctionType::get(Type::getInt32Ty(Context),
{Type::getInt32Ty(Context)}, false);
Function *FibF =
Function::Create(FibFTy, Function::ExternalLinkage, "fib", M);
// Add a basic block to the function.
BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
// Get pointers to the constants.
Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);
// Get pointer to the integer argument of the add1 function...
Argument *ArgX = &*FibF->arg_begin(); // Get the arg.
ArgX->setName("AnArg"); // Give it a nice symbolic name for fun.
// Create the true_block.
BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);
// Create an exit block.
BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
// Create the "if (arg <= 2) goto exitbb"
Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
// Create: ret int 1
ReturnInst::Create(Context, One, RetBB);
// create fib(x-1)
Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);
CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);
// create fib(x-2)
Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);
CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);
// fib(x-1)+fib(x-2)
Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,
"addresult", RecurseBB);
// Create the return instruction and add it to the basic block
ReturnInst::Create(Context, Sum, RecurseBB);
return FibF;
int main(int argc, char **argv) {
int n = argc > 1 ? atol(argv[1]) : 24;
LLVMContext Context;
// Create some module to put our function into it.
std::unique_ptr<Module> Owner(new Module("test", Context));
Module *M = Owner.get();
// We are about to create the "fib" function:
Function *FibF = CreateFibFunction(M, Context);
// Now we going to create JIT
std::string errStr;
ExecutionEngine *EE =
if (!EE) {
errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr
<< "\n";
return 1;
errs() << "verifying... ";
if (verifyModule(*M)) {
errs() << argv[0] << ": Error constructing function!\n";
return 1;
errs() << "OK\n";
errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
// Call the Fibonacci function with argument n:
std::vector<GenericValue> Args(1);
Args[0].IntVal = APInt(32, n);
GenericValue GV = EE->runFunction(FibF, Args);
// import result of execution
outs() << "Result: " << GV.IntVal << "\n";
return 0;