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/ExecutionEngine/MCJIT.h"
31 #include "llvm/IR/Argument.h"
32 #include "llvm/IR/BasicBlock.h"
33 #include "llvm/IR/Constants.h"
34 #include "llvm/IR/DerivedTypes.h"
35 #include "llvm/IR/Function.h"
36 #include "llvm/IR/InstrTypes.h"
37 #include "llvm/IR/Instructions.h"
38 #include "llvm/IR/LLVMContext.h"
39 #include "llvm/IR/Module.h"
40 #include "llvm/IR/Type.h"
41 #include "llvm/Support/Casting.h"
42 #include "llvm/Support/TargetSelect.h"
43 #include "llvm/Support/raw_ostream.h"
44 #include <algorithm>
45 #include <cstdlib>
46 #include <memory>
47 #include <string>
48 #include <vector>
49
50 using namespace llvm;
51
CreateFibFunction(Module * M,LLVMContext & Context)52 static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
53 // Create the fib function and insert it into module M. This function is said
54 // to return an int and take an int parameter.
55 Function *FibF =
56 cast<Function>(M->getOrInsertFunction("fib", Type::getInt32Ty(Context),
57 Type::getInt32Ty(Context),
58 nullptr));
59
60 // Add a basic block to the function.
61 BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
62
63 // Get pointers to the constants.
64 Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
65 Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);
66
67 // Get pointer to the integer argument of the add1 function...
68 Argument *ArgX = &*FibF->arg_begin(); // Get the arg.
69 ArgX->setName("AnArg"); // Give it a nice symbolic name for fun.
70
71 // Create the true_block.
72 BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);
73 // Create an exit block.
74 BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
75
76 // Create the "if (arg <= 2) goto exitbb"
77 Value *CondInst = new ICmpInst(*BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
78 BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
79
80 // Create: ret int 1
81 ReturnInst::Create(Context, One, RetBB);
82
83 // create fib(x-1)
84 Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);
85 CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);
86 CallFibX1->setTailCall();
87
88 // create fib(x-2)
89 Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);
90 CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);
91 CallFibX2->setTailCall();
92
93 // fib(x-1)+fib(x-2)
94 Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,
95 "addresult", RecurseBB);
96
97 // Create the return instruction and add it to the basic block
98 ReturnInst::Create(Context, Sum, RecurseBB);
99
100 return FibF;
101 }
102
main(int argc,char ** argv)103 int main(int argc, char **argv) {
104 int n = argc > 1 ? atol(argv[1]) : 24;
105
106 InitializeNativeTarget();
107 InitializeNativeTargetAsmPrinter();
108 LLVMContext Context;
109
110 // Create some module to put our function into it.
111 std::unique_ptr<Module> Owner(new Module("test", Context));
112 Module *M = Owner.get();
113
114 // We are about to create the "fib" function:
115 Function *FibF = CreateFibFunction(M, Context);
116
117 // Now we going to create JIT
118 std::string errStr;
119 ExecutionEngine *EE =
120 EngineBuilder(std::move(Owner))
121 .setErrorStr(&errStr)
122 .create();
123
124 if (!EE) {
125 errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr
126 << "\n";
127 return 1;
128 }
129
130 errs() << "verifying... ";
131 if (verifyModule(*M)) {
132 errs() << argv[0] << ": Error constructing function!\n";
133 return 1;
134 }
135
136 errs() << "OK\n";
137 errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
138 errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
139
140 // Call the Fibonacci function with argument n:
141 std::vector<GenericValue> Args(1);
142 Args[0].IntVal = APInt(32, n);
143 GenericValue GV = EE->runFunction(FibF, Args);
144
145 // import result of execution
146 outs() << "Result: " << GV.IntVal << "\n";
147
148 return 0;
149 }
150