1 //===--- examples/Fibonacci/fibonacci.cpp - An example use of the JIT -----===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This small program provides an example of how to build quickly a small module
10 // with function Fibonacci and execute it with the JIT.
11 //
12 // The goal of this snippet is to create in the memory the LLVM module
13 // consisting of one function as follow:
14 //
15 // int fib(int x) {
16 // if(x<=2) return 1;
17 // return fib(x-1)+fib(x-2);
18 // }
19 //
20 // Once we have this, we compile the module via JIT, then execute the `fib'
21 // function and return result to a driver, i.e. to a "host program".
22 //
23 //===----------------------------------------------------------------------===//
24
25 #include "llvm/ADT/APInt.h"
26 #include "llvm/IR/Verifier.h"
27 #include "llvm/ExecutionEngine/ExecutionEngine.h"
28 #include "llvm/ExecutionEngine/GenericValue.h"
29 #include "llvm/ExecutionEngine/MCJIT.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
CreateFibFunction(Module * M,LLVMContext & Context)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 FunctionType *FibFTy = FunctionType::get(Type::getInt32Ty(Context),
55 {Type::getInt32Ty(Context)}, false);
56 Function *FibF =
57 Function::Create(FibFTy, Function::ExternalLinkage, "fib", M);
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
main(int argc,char ** argv)102 int main(int argc, char **argv) {
103 int n = argc > 1 ? atol(argv[1]) : 24;
104
105 InitializeNativeTarget();
106 InitializeNativeTargetAsmPrinter();
107 LLVMContext Context;
108
109 // Create some module to put our function into it.
110 std::unique_ptr<Module> Owner(new Module("test", Context));
111 Module *M = Owner.get();
112
113 // We are about to create the "fib" function:
114 Function *FibF = CreateFibFunction(M, Context);
115
116 // Now we going to create JIT
117 std::string errStr;
118 ExecutionEngine *EE =
119 EngineBuilder(std::move(Owner))
120 .setErrorStr(&errStr)
121 .create();
122
123 if (!EE) {
124 errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr
125 << "\n";
126 return 1;
127 }
128
129 errs() << "verifying... ";
130 if (verifyModule(*M)) {
131 errs() << argv[0] << ": Error constructing function!\n";
132 return 1;
133 }
134
135 errs() << "OK\n";
136 errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
137 errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
138
139 // Call the Fibonacci function with argument n:
140 std::vector<GenericValue> Args(1);
141 Args[0].IntVal = APInt(32, n);
142 GenericValue GV = EE->runFunction(FibF, Args);
143
144 // import result of execution
145 outs() << "Result: " << GV.IntVal << "\n";
146
147 return 0;
148 }
149