fibonacci.cpp revision 6a98754ebbc211958297b0d20a77e8c3261c3708 
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 =
42    cast<Function>(M->getOrInsertFunction("fib", Type::Int32Ty, Type::Int32Ty,
43                                          (Type *)0));
44
45  // Add a basic block to the function.
46  BasicBlock *BB = new BasicBlock("EntryBlock", FibF);
47
48  // Get pointers to the constants.
49  Value *One = ConstantInt::get(Type::Int32Ty, 1);
50  Value *Two = ConstantInt::get(Type::Int32Ty, 2);
51
52  // Get pointer to the integer argument of the add1 function...
53  Argument *ArgX = FibF->arg_begin();   // Get the arg.
54  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
55
56  // Create the true_block.
57  BasicBlock *RetBB = new BasicBlock("return", FibF);
58  // Create an exit block.
59  BasicBlock* RecurseBB = new BasicBlock("recurse", FibF);
60
61  // Create the "if (arg < 2) goto exitbb"
62  Value *CondInst = new ICmpInst(ICmpInst::ICMP_SLE, ArgX, Two, "cond", BB);
63  new BranchInst(RetBB, RecurseBB, CondInst, BB);
64
65  // Create: ret int 1
66  new ReturnInst(One, RetBB);
67
68  // create fib(x-1)
69  Value *Sub = BinaryOperator::createSub(ArgX, One, "arg", RecurseBB);
70  CallInst *CallFibX1 = new CallInst(FibF, Sub, "fibx1", RecurseBB);
71  CallFibX1->setTailCall();
72
73  // create fib(x-2)
74  Sub = BinaryOperator::createSub(ArgX, Two, "arg", RecurseBB);
75  CallInst *CallFibX2 = new CallInst(FibF, Sub, "fibx2", RecurseBB);
76  CallFibX2->setTailCall();
77
78
79  // fib(x-1)+fib(x-2)
80  Value *Sum = BinaryOperator::createAdd(CallFibX1, CallFibX2,
81                                         "addresult", RecurseBB);
82
83  // Create the return instruction and add it to the basic block
84  new ReturnInst(Sum, RecurseBB);
85
86  return FibF;
87}
88
89
90int main(int argc, char **argv) {
91  int n = argc > 1 ? atol(argv[1]) : 24;
92
93  // Create some module to put our function into it.
94  Module *M = new Module("test");
95
96  // We are about to create the "fib" function:
97  Function *FibF = CreateFibFunction(M);
98
99  // Now we going to create JIT
100  ExistingModuleProvider *MP = new ExistingModuleProvider(M);
101  ExecutionEngine *EE = ExecutionEngine::create(MP, false);
102
103  std::cerr << "verifying... ";
104  if (verifyModule(*M)) {
105    std::cerr << argv[0] << ": Error constructing function!\n";
106    return 1;
107  }
108
109  std::cerr << "OK\n";
110  std::cerr << "We just constructed this LLVM module:\n\n---------\n" << *M;
111  std::cerr << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
112
113  // Call the Fibonacci function with argument n:
114  std::vector<GenericValue> Args(1);
115  Args[0].Int32Val = n;
116  GenericValue GV = EE->runFunction(FibF, Args);
117
118  // import result of execution
119  std::cout << "Result: " << GV.Int32Val << "\n";
120  return 0;
121}
122