fibonacci.cpp revision 37ed9c199ca639565f6ce88105f9e39e898d82d0 
1//===--- examples/Fibonacci/fibonacci.cpp - An example use of the JIT -----===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This small program provides an example of how to build quickly a small module
11// with function Fibonacci and execute it with the JIT.
12//
13// The goal of this snippet is to create in the memory the LLVM module
14// consisting of one function as follow:
15//
16//   int fib(int x) {
17//     if(x<=2) return 1;
18//     return fib(x-1)+fib(x-2);
19//   }
20//
21// Once we have this, we compile the module via JIT, then execute the `fib'
22// function and return result to a driver, i.e. to a "host program".
23//
24//===----------------------------------------------------------------------===//
25
26#include "llvm/IR/Verifier.h"
27#include "llvm/ExecutionEngine/GenericValue.h"
28#include "llvm/ExecutionEngine/Interpreter.h"
29#include "llvm/IR/Constants.h"
30#include "llvm/IR/DerivedTypes.h"
31#include "llvm/IR/Instructions.h"
32#include "llvm/IR/LLVMContext.h"
33#include "llvm/IR/Module.h"
34#include "llvm/Support/TargetSelect.h"
35#include "llvm/Support/raw_ostream.h"
36using namespace llvm;
37
38static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
39  // Create the fib function and insert it into module M. This function is said
40  // to return an int and take an int parameter.
41  Function *FibF =
42    cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context),
43                                          Type::getInt32Ty(Context),
44                                          (Type *)0));
45
46  // Add a basic block to the function.
47  BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
48
49  // Get pointers to the constants.
50  Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
51  Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);
52
53  // Get pointer to the integer argument of the add1 function...
54  Argument *ArgX = FibF->arg_begin();   // Get the arg.
55  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
56
57  // Create the true_block.
58  BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);
59  // Create an exit block.
60  BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
61
62  // Create the "if (arg <= 2) goto exitbb"
63  Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
64  BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
65
66  // Create: ret int 1
67  ReturnInst::Create(Context, One, RetBB);
68
69  // create fib(x-1)
70  Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);
71  CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);
72  CallFibX1->setTailCall();
73
74  // create fib(x-2)
75  Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);
76  CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);
77  CallFibX2->setTailCall();
78
79
80  // fib(x-1)+fib(x-2)
81  Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,
82                                         "addresult", RecurseBB);
83
84  // Create the return instruction and add it to the basic block
85  ReturnInst::Create(Context, Sum, RecurseBB);
86
87  return FibF;
88}
89
90
91int main(int argc, char **argv) {
92  int n = argc > 1 ? atol(argv[1]) : 24;
93
94  InitializeNativeTarget();
95  LLVMContext Context;
96
97  // Create some module to put our function into it.
98  std::unique_ptr<Module> Owner(new Module("test", Context));
99  Module *M = Owner.get();
100
101  // We are about to create the "fib" function:
102  Function *FibF = CreateFibFunction(M, Context);
103
104  // Now we going to create JIT
105  std::string errStr;
106  ExecutionEngine *EE =
107    EngineBuilder(std::move(Owner))
108    .setErrorStr(&errStr)
109    .setEngineKind(EngineKind::JIT)
110    .create();
111
112  if (!EE) {
113    errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr
114           << "\n";
115    return 1;
116  }
117
118  errs() << "verifying... ";
119  if (verifyModule(*M)) {
120    errs() << argv[0] << ": Error constructing function!\n";
121    return 1;
122  }
123
124  errs() << "OK\n";
125  errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
126  errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
127
128  // Call the Fibonacci function with argument n:
129  std::vector<GenericValue> Args(1);
130  Args[0].IntVal = APInt(32, n);
131  GenericValue GV = EE->runFunction(FibF, Args);
132
133  // import result of execution
134  outs() << "Result: " << GV.IntVal << "\n";
135
136  return 0;
137}
138