1 //===-- RandomIRBuilder.cpp -----------------------------------------------===//
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 #include "llvm/FuzzMutate/RandomIRBuilder.h"
10 #include "llvm/ADT/STLExtras.h"
11 #include "llvm/FuzzMutate/Random.h"
12 #include "llvm/IR/BasicBlock.h"
13 #include "llvm/IR/Constants.h"
14 #include "llvm/IR/Function.h"
15 #include "llvm/IR/Instructions.h"
16 #include "llvm/IR/IntrinsicInst.h"
17
18 using namespace llvm;
19 using namespace fuzzerop;
20
findOrCreateSource(BasicBlock & BB,ArrayRef<Instruction * > Insts)21 Value *RandomIRBuilder::findOrCreateSource(BasicBlock &BB,
22 ArrayRef<Instruction *> Insts) {
23 return findOrCreateSource(BB, Insts, {}, anyType());
24 }
25
findOrCreateSource(BasicBlock & BB,ArrayRef<Instruction * > Insts,ArrayRef<Value * > Srcs,SourcePred Pred)26 Value *RandomIRBuilder::findOrCreateSource(BasicBlock &BB,
27 ArrayRef<Instruction *> Insts,
28 ArrayRef<Value *> Srcs,
29 SourcePred Pred) {
30 auto MatchesPred = [&Srcs, &Pred](Instruction *Inst) {
31 return Pred.matches(Srcs, Inst);
32 };
33 auto RS = makeSampler(Rand, make_filter_range(Insts, MatchesPred));
34 // Also consider choosing no source, meaning we want a new one.
35 RS.sample(nullptr, /*Weight=*/1);
36 if (Instruction *Src = RS.getSelection())
37 return Src;
38 return newSource(BB, Insts, Srcs, Pred);
39 }
40
newSource(BasicBlock & BB,ArrayRef<Instruction * > Insts,ArrayRef<Value * > Srcs,SourcePred Pred)41 Value *RandomIRBuilder::newSource(BasicBlock &BB, ArrayRef<Instruction *> Insts,
42 ArrayRef<Value *> Srcs, SourcePred Pred) {
43 // Generate some constants to choose from.
44 auto RS = makeSampler<Value *>(Rand);
45 RS.sample(Pred.generate(Srcs, KnownTypes));
46
47 // If we can find a pointer to load from, use it half the time.
48 Value *Ptr = findPointer(BB, Insts, Srcs, Pred);
49 if (Ptr) {
50 // Create load from the chosen pointer
51 auto IP = BB.getFirstInsertionPt();
52 if (auto *I = dyn_cast<Instruction>(Ptr)) {
53 IP = ++I->getIterator();
54 assert(IP != BB.end() && "guaranteed by the findPointer");
55 }
56 auto *NewLoad = new LoadInst(
57 cast<PointerType>(Ptr->getType())->getElementType(), Ptr, "L", &*IP);
58
59 // Only sample this load if it really matches the descriptor
60 if (Pred.matches(Srcs, NewLoad))
61 RS.sample(NewLoad, RS.totalWeight());
62 else
63 NewLoad->eraseFromParent();
64 }
65
66 assert(!RS.isEmpty() && "Failed to generate sources");
67 return RS.getSelection();
68 }
69
isCompatibleReplacement(const Instruction * I,const Use & Operand,const Value * Replacement)70 static bool isCompatibleReplacement(const Instruction *I, const Use &Operand,
71 const Value *Replacement) {
72 if (Operand->getType() != Replacement->getType())
73 return false;
74 switch (I->getOpcode()) {
75 case Instruction::GetElementPtr:
76 case Instruction::ExtractElement:
77 case Instruction::ExtractValue:
78 // TODO: We could potentially validate these, but for now just leave indices
79 // alone.
80 if (Operand.getOperandNo() >= 1)
81 return false;
82 break;
83 case Instruction::InsertValue:
84 case Instruction::InsertElement:
85 case Instruction::ShuffleVector:
86 if (Operand.getOperandNo() >= 2)
87 return false;
88 break;
89 default:
90 break;
91 }
92 return true;
93 }
94
connectToSink(BasicBlock & BB,ArrayRef<Instruction * > Insts,Value * V)95 void RandomIRBuilder::connectToSink(BasicBlock &BB,
96 ArrayRef<Instruction *> Insts, Value *V) {
97 auto RS = makeSampler<Use *>(Rand);
98 for (auto &I : Insts) {
99 if (isa<IntrinsicInst>(I))
100 // TODO: Replacing operands of intrinsics would be interesting, but
101 // there's no easy way to verify that a given replacement is valid given
102 // that intrinsics can impose arbitrary constraints.
103 continue;
104 for (Use &U : I->operands())
105 if (isCompatibleReplacement(I, U, V))
106 RS.sample(&U, 1);
107 }
108 // Also consider choosing no sink, meaning we want a new one.
109 RS.sample(nullptr, /*Weight=*/1);
110
111 if (Use *Sink = RS.getSelection()) {
112 User *U = Sink->getUser();
113 unsigned OpNo = Sink->getOperandNo();
114 U->setOperand(OpNo, V);
115 return;
116 }
117 newSink(BB, Insts, V);
118 }
119
newSink(BasicBlock & BB,ArrayRef<Instruction * > Insts,Value * V)120 void RandomIRBuilder::newSink(BasicBlock &BB, ArrayRef<Instruction *> Insts,
121 Value *V) {
122 Value *Ptr = findPointer(BB, Insts, {V}, matchFirstType());
123 if (!Ptr) {
124 if (uniform(Rand, 0, 1))
125 Ptr = new AllocaInst(V->getType(), 0, "A", &*BB.getFirstInsertionPt());
126 else
127 Ptr = UndefValue::get(PointerType::get(V->getType(), 0));
128 }
129
130 new StoreInst(V, Ptr, Insts.back());
131 }
132
findPointer(BasicBlock & BB,ArrayRef<Instruction * > Insts,ArrayRef<Value * > Srcs,SourcePred Pred)133 Value *RandomIRBuilder::findPointer(BasicBlock &BB,
134 ArrayRef<Instruction *> Insts,
135 ArrayRef<Value *> Srcs, SourcePred Pred) {
136 auto IsMatchingPtr = [&Srcs, &Pred](Instruction *Inst) {
137 // Invoke instructions sometimes produce valid pointers but currently
138 // we can't insert loads or stores from them
139 if (Inst->isTerminator())
140 return false;
141
142 if (auto PtrTy = dyn_cast<PointerType>(Inst->getType())) {
143 // We can never generate loads from non first class or non sized types
144 if (!PtrTy->getElementType()->isSized() ||
145 !PtrTy->getElementType()->isFirstClassType())
146 return false;
147
148 // TODO: Check if this is horribly expensive.
149 return Pred.matches(Srcs, UndefValue::get(PtrTy->getElementType()));
150 }
151 return false;
152 };
153 if (auto RS = makeSampler(Rand, make_filter_range(Insts, IsMatchingPtr)))
154 return RS.getSelection();
155 return nullptr;
156 }
157