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