fibonacci.cpp revision 18f0c677faaca54974333f2e7e353e94280628ab 
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"
37#include "llvm/Target/TargetSelect.h"
38using namespace llvm;
39
40static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
41  // Create the fib function and insert it into module M.  This function is said
42  // to return an int and take an int parameter.
43  Function *FibF =
44    cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context),
45                                          Type::getInt32Ty(Context),
46                                          (Type *)0));
47
48  // Add a basic block to the function.
49  BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
50
51  // Get pointers to the constants.
52  Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
53  Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);
54
55  // Get pointer to the integer argument of the add1 function...
56  Argument *ArgX = FibF->arg_begin();   // Get the arg.
57  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
58
59  // Create the true_block.
60  BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);
61  // Create an exit block.
62  BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
63
64  // Create the "if (arg <= 2) goto exitbb"
65  Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
66  BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
67
68  // Create: ret int 1
69  ReturnInst::Create(Context, One, RetBB);
70
71  // create fib(x-1)
72  Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);
73  CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);
74  CallFibX1->setTailCall();
75
76  // create fib(x-2)
77  Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);
78  CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);
79  CallFibX2->setTailCall();
80
81
82  // fib(x-1)+fib(x-2)
83  Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,
84                                         "addresult", RecurseBB);
85
86  // Create the return instruction and add it to the basic block
87  ReturnInst::Create(Context, Sum, RecurseBB);
88
89  return FibF;
90}
91
92
93int main(int argc, char **argv) {
94  int n = argc > 1 ? atol(argv[1]) : 24;
95
96  InitializeNativeTarget();
97  LLVMContext Context;
98
99  // Create some module to put our function into it.
100  Module *M = new Module("test", Context);
101
102  // We are about to create the "fib" function:
103  Function *FibF = CreateFibFunction(M, Context);
104
105  // Now we going to create JIT
106  std::string errStr;
107  ExecutionEngine *EE = EngineBuilder(M).setErrorStr(&errStr).setEngineKind(EngineKind::JIT).create();
108
109  if (!EE) {
110    errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr << "\n";
111    return 1;
112  }
113
114  errs() << "verifying... ";
115  if (verifyModule(*M)) {
116    errs() << argv[0] << ": Error constructing function!\n";
117    return 1;
118  }
119
120  errs() << "OK\n";
121  errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
122  errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
123
124  // Call the Fibonacci function with argument n:
125  std::vector<GenericValue> Args(1);
126  Args[0].IntVal = APInt(32, n);
127  GenericValue GV = EE->runFunction(FibF, Args);
128
129  // import result of execution
130  outs() << "Result: " << GV.IntVal << "\n";
131  return 0;
132}
133