examples/Fibonacci/fibonacci.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-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   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 1
  80   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 block
  97   ReturnInst::Create(Context, Sum, RecurseBB);
  98
  99   return FibF;
 100 }
 101
 102 int 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 JIT
 117   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: " << errStr
 125            << "\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 execution
 145   outs() << "Result: " << GV.IntVal << "\n";
 146
 147   return 0;
 148 }