fibonacci.cpp revision 7cf540bba0b262681a14058d01ad41a87ac870df 
1//===--- examples/Fibonacci/fibonacci.cpp - An example use of the JIT -----===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by Valery A. Khamenya and is distributed under the
6// University of Illinois Open Source 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/Module.h"
27#include "llvm/DerivedTypes.h"
28#include "llvm/Constants.h"
29#include "llvm/Instructions.h"
30#include "llvm/ModuleProvider.h"
31#include "llvm/Analysis/Verifier.h"
32#include "llvm/ExecutionEngine/ExecutionEngine.h"
33#include "llvm/ExecutionEngine/GenericValue.h"
34#include <iostream>
35using namespace llvm;
36
37static Function *CreateFibFunction(Module *M) {
38  // Create the fib function and insert it into module M.  This function is said
39  // to return an int and take an int parameter.
40  Function *FibF = M->getOrInsertFunction("fib", Type::IntTy, Type::IntTy, 0);
41
42  // Add a basic block to the function.
43  BasicBlock *BB = new BasicBlock("EntryBlock", FibF);
44
45  // Get pointers to the constants.
46  Value *One = ConstantSInt::get(Type::IntTy, 1);
47  Value *Two = ConstantSInt::get(Type::IntTy, 2);
48
49  // Get pointer to the integer argument of the add1 function...
50  Argument *ArgX = FibF->abegin();   // Get the arg.
51  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
52
53  // Create the true_block.
54  BasicBlock *RetBB = new BasicBlock("return", FibF);
55  // Create an exit block.
56  BasicBlock* RecurseBB = new BasicBlock("recurse", FibF);
57
58  // Create the "if (arg < 2) goto exitbb"
59  Value *CondInst = BinaryOperator::createSetLE(ArgX, Two, "cond", BB);
60  new BranchInst(RetBB, RecurseBB, CondInst, BB);
61
62  // Create: ret int 1
63  new ReturnInst(One, RetBB);
64
65  // create fib(x-1)
66  Value *Sub = BinaryOperator::createSub(ArgX, One, "arg", RecurseBB);
67  Value *CallFibX1 = new CallInst(FibF, Sub, "fibx1", RecurseBB);
68
69  // create fib(x-2)
70  Sub = BinaryOperator::createSub(ArgX, Two, "arg", RecurseBB);
71  Value *CallFibX2 = new CallInst(FibF, Sub, "fibx2", RecurseBB);
72
73  // fib(x-1)+fib(x-2)
74  Value *Sum = BinaryOperator::createAdd(CallFibX1, CallFibX2,
75                                         "addresult", RecurseBB);
76
77  // Create the return instruction and add it to the basic block
78  new ReturnInst(Sum, RecurseBB);
79
80  return FibF;
81}
82
83
84int main(int argc, char **argv) {
85  int n = argc > 1 ? atol(argv[1]) : 24;
86
87  // Create some module to put our function into it.
88  Module *M = new Module("test");
89
90  // We are about to create the "fib" function:
91  Function *FibF = CreateFibFunction(M);
92
93  // Now we going to create JIT
94  ExistingModuleProvider *MP = new ExistingModuleProvider(M);
95  ExecutionEngine *EE = ExecutionEngine::create(MP, false);
96
97  std::cerr << "verifying... ";
98  if (verifyModule(*M)) {
99    std::cerr << argv[0] << ": Error constructing function!\n";
100    return 1;
101  }
102
103  std::cerr << "OK\n";
104  std::cerr << "We just constructed this LLVM module:\n\n---------\n" << *M;
105  std::cerr << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
106
107  // Call the Fibonacci function with argument n:
108  std::vector<GenericValue> Args(1);
109  Args[0].IntVal = n;
110  GenericValue GV = EE->runFunction(FibF, Args);
111
112  // import result of execution
113  std::cout << "Result: " << GV.IntVal << "\n";
114  return 0;
115}
116