fibonacci.cpp revision 1d0be15f89cb5056e20e2d24faa8d6afb1573bca 
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/LLVMContext.h"
27#include "llvm/Module.h"
28#include "llvm/DerivedTypes.h"
29#include "llvm/Constants.h"
30#include "llvm/Instructions.h"
31#include "llvm/ModuleProvider.h"
32#include "llvm/Analysis/Verifier.h"
33#include "llvm/ExecutionEngine/JIT.h"
34#include "llvm/ExecutionEngine/Interpreter.h"
35#include "llvm/ExecutionEngine/GenericValue.h"
36#include "llvm/Support/raw_ostream.h"
37using namespace llvm;
38
39static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
40  // Create the fib function and insert it into module M.  This function is said
41  // to return an int and take an int parameter.
42  Function *FibF =
43    cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context),
44                                          Type::getInt32Ty(Context),
45                                          (Type *)0));
46
47  // Add a basic block to the function.
48  BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
49
50  // Get pointers to the constants.
51  Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
52  Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);
53
54  // Get pointer to the integer argument of the add1 function...
55  Argument *ArgX = FibF->arg_begin();   // Get the arg.
56  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
57
58  // Create the true_block.
59  BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);
60  // Create an exit block.
61  BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
62
63  // Create the "if (arg <= 2) goto exitbb"
64  Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
65  BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
66
67  // Create: ret int 1
68  ReturnInst::Create(Context, One, RetBB);
69
70  // create fib(x-1)
71  Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);
72  CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);
73  CallFibX1->setTailCall();
74
75  // create fib(x-2)
76  Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);
77  CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);
78  CallFibX2->setTailCall();
79
80
81  // fib(x-1)+fib(x-2)
82  Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,
83                                         "addresult", RecurseBB);
84
85  // Create the return instruction and add it to the basic block
86  ReturnInst::Create(Context, Sum, RecurseBB);
87
88  return FibF;
89}
90
91
92int main(int argc, char **argv) {
93  int n = argc > 1 ? atol(argv[1]) : 24;
94
95  LLVMContext Context;
96
97  // Create some module to put our function into it.
98  Module *M = new Module("test", Context);
99
100  // We are about to create the "fib" function:
101  Function *FibF = CreateFibFunction(M, Context);
102
103  // Now we going to create JIT
104  ExecutionEngine *EE = EngineBuilder(M).create();
105
106  errs() << "verifying... ";
107  if (verifyModule(*M)) {
108    errs() << argv[0] << ": Error constructing function!\n";
109    return 1;
110  }
111
112  errs() << "OK\n";
113  errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
114  errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
115
116  // Call the Fibonacci function with argument n:
117  std::vector<GenericValue> Args(1);
118  Args[0].IntVal = APInt(32, n);
119  GenericValue GV = EE->runFunction(FibF, Args);
120
121  // import result of execution
122  outs() << "Result: " << GV.IntVal << "\n";
123  return 0;
124}
125