fibonacci.cpp revision 3c7d7ee76136bf0041693fc939e155f34a197b2b 
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
54  // Create the true_block.
55  BasicBlock *RetBB = new BasicBlock("return", FibF);
56  // Create an exit block.
57  BasicBlock* RecurseBB = new BasicBlock("recurse", FibF);
58
59  // Create the "if (arg < 2) goto exitbb"
60  Value *CondInst = BinaryOperator::createSetLE(ArgX, Two, "cond", BB);
61  new BranchInst(RetBB, RecurseBB, CondInst, BB);
62
63  // Create: ret int 1
64  new ReturnInst(One, RetBB);
65
66  // create fib(x-1)
67  Value *Sub = BinaryOperator::createSub(ArgX, One, "arg", RecurseBB);
68  Value *CallFibX1 = new CallInst(FibF, Sub, "fibx1", RecurseBB);
69
70  // create fib(x-2)
71  Sub = BinaryOperator::createSub(ArgX, Two, "arg", RecurseBB);
72  Value *CallFibX2 = new CallInst(FibF, Sub, "fibx2", RecurseBB);
73
74  // fib(x-1)+fib(x-2)
75  Value *Sum = BinaryOperator::createAdd(CallFibX1, CallFibX2,
76                                         "addresult", RecurseBB);
77
78  // Create the return instruction and add it to the basic block
79  new ReturnInst(Sum, RecurseBB);
80
81  return FibF;
82}
83
84
85int main(int argc, char **argv) {
86  int n = argc > 1 ? atol(argv[1]) : 24;
87
88  // Create some module to put our function into it.
89  Module *M = new Module("test");
90
91  // We are about to create the "fib" function:
92  Function *FibF = CreateFibFunction(M);
93
94  // Now we going to create JIT
95  ExistingModuleProvider *MP = new ExistingModuleProvider(M);
96  ExecutionEngine *EE = ExecutionEngine::create(MP, false);
97
98  std::cerr << "verifying... ";
99  if (verifyModule(*M)) {
100    std::cerr << argv[0] << ": Error constructing function!\n";
101    return 1;
102  }
103
104  std::cerr << "OK\n";
105  std::cerr << "We just constructed this LLVM module:\n\n---------\n" << *M;
106  std::cerr << "---------\nstarting fibonacci("
107	    << n << ") with JIT...\n";
108
109  // Call the `foo' function with argument n:
110  std::vector<GenericValue> Args(1);
111  Args[0].IntVal = n;
112  GenericValue GV = EE->runFunction(FibF, Args);
113
114  // import result of execution
115  std::cout << "Result: " << GV.IntVal << "\n";
116  return 0;
117}
118