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/ADT/APInt.h"
27 #include "llvm/IR/Verifier.h"
28 #include "llvm/ExecutionEngine/ExecutionEngine.h"
29 #include "llvm/ExecutionEngine/GenericValue.h"
30 #include "llvm/IR/Argument.h"
31 #include "llvm/IR/BasicBlock.h"
32 #include "llvm/IR/Constants.h"
33 #include "llvm/IR/DerivedTypes.h"
34 #include "llvm/IR/Function.h"
35 #include "llvm/IR/InstrTypes.h"
36 #include "llvm/IR/Instructions.h"
37 #include "llvm/IR/LLVMContext.h"
38 #include "llvm/IR/Module.h"
39 #include "llvm/IR/Type.h"
40 #include "llvm/Support/Casting.h"
41 #include "llvm/Support/TargetSelect.h"
42 #include "llvm/Support/raw_ostream.h"
43 #include <algorithm>
44 #include <cstdlib>
45 #include <memory>
46 #include <string>
47 #include <vector>
48 
49 using namespace llvm;
50 
51 static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
52   // Create the fib function and insert it into module M. This function is said
53   // to return an int and take an int parameter.
54   Function *FibF =
55     cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context),
56                                           Type::getInt32Ty(Context),
57                                           nullptr));
58 
59   // Add a basic block to the function.
60   BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
61 
62   // Get pointers to the constants.
63   Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
64   Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);
65 
66   // Get pointer to the integer argument of the add1 function...
67   Argument *ArgX = &*FibF->arg_begin(); // Get the arg.
68   ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
69 
70   // Create the true_block.
71   BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);
72   // Create an exit block.
73   BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
74 
75   // Create the "if (arg <= 2) goto exitbb"
76   Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
77   BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
78 
79   // Create: ret int 1
80   ReturnInst::Create(Context, One, RetBB);
81 
82   // create fib(x-1)
83   Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);
84   CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);
85   CallFibX1->setTailCall();
86 
87   // create fib(x-2)
88   Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);
89   CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);
90   CallFibX2->setTailCall();
91 
92   // fib(x-1)+fib(x-2)
93   Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,
94                                          "addresult", RecurseBB);
95 
96   // Create the return instruction and add it to the basic block
97   ReturnInst::Create(Context, Sum, RecurseBB);
98 
99   return FibF;
100 }
101 
102 int main(int argc, char **argv) {
103   int n = argc > 1 ? atol(argv[1]) : 24;
104 
105   InitializeNativeTarget();
106   LLVMContext Context;
107 
108   // Create some module to put our function into it.
109   std::unique_ptr<Module> Owner(new Module("test", Context));
110   Module *M = Owner.get();
111 
112   // We are about to create the "fib" function:
113   Function *FibF = CreateFibFunction(M, Context);
114 
115   // Now we going to create JIT
116   std::string errStr;
117   ExecutionEngine *EE =
118     EngineBuilder(std::move(Owner))
119     .setErrorStr(&errStr)
120     .create();
121 
122   if (!EE) {
123     errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr
124            << "\n";
125     return 1;
126   }
127 
128   errs() << "verifying... ";
129   if (verifyModule(*M)) {
130     errs() << argv[0] << ": Error constructing function!\n";
131     return 1;
132   }
133 
134   errs() << "OK\n";
135   errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
136   errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
137 
138   // Call the Fibonacci function with argument n:
139   std::vector<GenericValue> Args(1);
140   Args[0].IntVal = APInt(32, n);
141   GenericValue GV = EE->runFunction(FibF, Args);
142 
143   // import result of execution
144   outs() << "Result: " << GV.IntVal << "\n";
145 
146   return 0;
147 }
148