//===--- examples/Fibonacci/fibonacci.cpp - An example use of the JIT -----===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // 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/Analysis/Verifier.h" #include "llvm/ExecutionEngine/GenericValue.h" #include "llvm/ExecutionEngine/Interpreter.h" #include "llvm/ExecutionEngine/JIT.h" #include "llvm/IR/Constants.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/LLVMContext.h" #include "llvm/IR/Module.h" #include "llvm/Support/TargetSelect.h" #include "llvm/Support/raw_ostream.h" 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. Function *FibF = cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context), Type::getInt32Ty(Context), (Type *)0)); // 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); CallFibX1->setTailCall(); // create fib(x-2) Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB); CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB); CallFibX2->setTailCall(); // 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; InitializeNativeTarget(); LLVMContext Context; // Create some module to put our function into it. OwningPtr<Module> M(new Module("test", Context)); // We are about to create the "fib" function: Function *FibF = CreateFibFunction(M.get(), Context); // Now we going to create JIT std::string errStr; ExecutionEngine *EE = EngineBuilder(M.get()) .setErrorStr(&errStr) .setEngineKind(EngineKind::JIT) .create(); 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; }