fibonacci.cpp revision b83eb6447ba155342598f0fabe1f08f5baa9164a 
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/JIT.h"
33#include "llvm/ExecutionEngine/Interpreter.h"
34#include "llvm/ExecutionEngine/GenericValue.h"
35#include <iostream>
36using namespace llvm;
37
38static Function *CreateFibFunction(Module *M) {
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 = M->getOrInsertFunction("fib", Type::IntTy, Type::IntTy,
42                                          (Type *)0);
43
44  // Add a basic block to the function.
45  BasicBlock *BB = new BasicBlock("EntryBlock", FibF);
46
47  // Get pointers to the constants.
48  Value *One = ConstantInt::get(Type::IntTy, 1);
49  Value *Two = ConstantInt::get(Type::IntTy, 2);
50
51  // Get pointer to the integer argument of the add1 function...
52  Argument *ArgX = FibF->arg_begin();   // Get the arg.
53  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
54
55  // Create the true_block.
56  BasicBlock *RetBB = new BasicBlock("return", FibF);
57  // Create an exit block.
58  BasicBlock* RecurseBB = new BasicBlock("recurse", FibF);
59
60  // Create the "if (arg < 2) goto exitbb"
61  Value *CondInst = BinaryOperator::createSetLE(ArgX, Two, "cond", BB);
62  new BranchInst(RetBB, RecurseBB, CondInst, BB);
63
64  // Create: ret int 1
65  new ReturnInst(One, RetBB);
66
67  // create fib(x-1)
68  Value *Sub = BinaryOperator::createSub(ArgX, One, "arg", RecurseBB);
69  CallInst *CallFibX1 = new CallInst(FibF, Sub, "fibx1", RecurseBB);
70  CallFibX1->setTailCall();
71
72  // create fib(x-2)
73  Sub = BinaryOperator::createSub(ArgX, Two, "arg", RecurseBB);
74  CallInst *CallFibX2 = new CallInst(FibF, Sub, "fibx2", RecurseBB);
75  CallFibX2->setTailCall();
76
77
78  // fib(x-1)+fib(x-2)
79  Value *Sum = BinaryOperator::createAdd(CallFibX1, CallFibX2,
80                                         "addresult", RecurseBB);
81
82  // Create the return instruction and add it to the basic block
83  new ReturnInst(Sum, RecurseBB);
84
85  return FibF;
86}
87
88
89int main(int argc, char **argv) {
90  int n = argc > 1 ? atol(argv[1]) : 24;
91
92  // Create some module to put our function into it.
93  Module *M = new Module("test");
94
95  // We are about to create the "fib" function:
96  Function *FibF = CreateFibFunction(M);
97
98  // Now we going to create JIT
99  ExistingModuleProvider *MP = new ExistingModuleProvider(M);
100  ExecutionEngine *EE = ExecutionEngine::create(MP, false);
101
102  std::cerr << "verifying... ";
103  if (verifyModule(*M)) {
104    std::cerr << argv[0] << ": Error constructing function!\n";
105    return 1;
106  }
107
108  std::cerr << "OK\n";
109  std::cerr << "We just constructed this LLVM module:\n\n---------\n" << *M;
110  std::cerr << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
111
112  // Call the Fibonacci function with argument n:
113  std::vector<GenericValue> Args(1);
114  Args[0].IntVal = n;
115  GenericValue GV = EE->runFunction(FibF, Args);
116
117  // import result of execution
118  std::cout << "Result: " << GV.IntVal << "\n";
119  return 0;
120}
121