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/OpDescriptor.h"
12 #include "llvm/FuzzMutate/Random.h"
13 #include "llvm/IR/BasicBlock.h"
14 #include "llvm/IR/Constants.h"
15 #include "llvm/IR/Instructions.h"
16 #include "llvm/IR/IntrinsicInst.h"
17 
18 using namespace llvm;
19 using namespace fuzzerop;
20 
21 Value *RandomIRBuilder::findOrCreateSource(BasicBlock &BB,
22                                            ArrayRef<Instruction *> Insts) {
23   return findOrCreateSource(BB, Insts, {}, anyType());
24 }
25 
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 
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     // For opaque pointers, pick the type independently.
57     Type *AccessTy = Ptr->getType()->isOpaquePointerTy()
58                          ? RS.getSelection()->getType()
59                          : Ptr->getType()->getNonOpaquePointerElementType();
60     auto *NewLoad = new LoadInst(AccessTy, Ptr, "L", &*IP);
61 
62     // Only sample this load if it really matches the descriptor
63     if (Pred.matches(Srcs, NewLoad))
64       RS.sample(NewLoad, RS.totalWeight());
65     else
66       NewLoad->eraseFromParent();
67   }
68 
69   assert(!RS.isEmpty() && "Failed to generate sources");
70   return RS.getSelection();
71 }
72 
73 static bool isCompatibleReplacement(const Instruction *I, const Use &Operand,
74                                     const Value *Replacement) {
75   if (Operand->getType() != Replacement->getType())
76     return false;
77   switch (I->getOpcode()) {
78   case Instruction::GetElementPtr:
79   case Instruction::ExtractElement:
80   case Instruction::ExtractValue:
81     // TODO: We could potentially validate these, but for now just leave indices
82     // alone.
83     if (Operand.getOperandNo() >= 1)
84       return false;
85     break;
86   case Instruction::InsertValue:
87   case Instruction::InsertElement:
88   case Instruction::ShuffleVector:
89     if (Operand.getOperandNo() >= 2)
90       return false;
91     break;
92   default:
93     break;
94   }
95   return true;
96 }
97 
98 void RandomIRBuilder::connectToSink(BasicBlock &BB,
99                                     ArrayRef<Instruction *> Insts, Value *V) {
100   auto RS = makeSampler<Use *>(Rand);
101   for (auto &I : Insts) {
102     if (isa<IntrinsicInst>(I))
103       // TODO: Replacing operands of intrinsics would be interesting, but
104       // there's no easy way to verify that a given replacement is valid given
105       // that intrinsics can impose arbitrary constraints.
106       continue;
107     for (Use &U : I->operands())
108       if (isCompatibleReplacement(I, U, V))
109         RS.sample(&U, 1);
110   }
111   // Also consider choosing no sink, meaning we want a new one.
112   RS.sample(nullptr, /*Weight=*/1);
113 
114   if (Use *Sink = RS.getSelection()) {
115     User *U = Sink->getUser();
116     unsigned OpNo = Sink->getOperandNo();
117     U->setOperand(OpNo, V);
118     return;
119   }
120   newSink(BB, Insts, V);
121 }
122 
123 void RandomIRBuilder::newSink(BasicBlock &BB, ArrayRef<Instruction *> Insts,
124                               Value *V) {
125   Value *Ptr = findPointer(BB, Insts, {V}, matchFirstType());
126   if (!Ptr) {
127     if (uniform(Rand, 0, 1))
128       Ptr = new AllocaInst(V->getType(), 0, "A", &*BB.getFirstInsertionPt());
129     else
130       Ptr = UndefValue::get(PointerType::get(V->getType(), 0));
131   }
132 
133   new StoreInst(V, Ptr, Insts.back());
134 }
135 
136 Value *RandomIRBuilder::findPointer(BasicBlock &BB,
137                                     ArrayRef<Instruction *> Insts,
138                                     ArrayRef<Value *> Srcs, SourcePred Pred) {
139   auto IsMatchingPtr = [&Srcs, &Pred](Instruction *Inst) {
140     // Invoke instructions sometimes produce valid pointers but currently
141     // we can't insert loads or stores from them
142     if (Inst->isTerminator())
143       return false;
144 
145     if (auto *PtrTy = dyn_cast<PointerType>(Inst->getType())) {
146       if (PtrTy->isOpaque())
147         return true;
148 
149       // We can never generate loads from non first class or non sized types
150       Type *ElemTy = PtrTy->getNonOpaquePointerElementType();
151       if (!ElemTy->isSized() || !ElemTy->isFirstClassType())
152         return false;
153 
154       // TODO: Check if this is horribly expensive.
155       return Pred.matches(Srcs, UndefValue::get(ElemTy));
156     }
157     return false;
158   };
159   if (auto RS = makeSampler(Rand, make_filter_range(Insts, IsMatchingPtr)))
160     return RS.getSelection();
161   return nullptr;
162 }
163