1 //===-- RandomIRBuilder.cpp -----------------------------------------------===//
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 #include "llvm/FuzzMutate/RandomIRBuilder.h"
11 #include "llvm/ADT/STLExtras.h"
12 #include "llvm/FuzzMutate/Random.h"
13 #include "llvm/IR/BasicBlock.h"
14 #include "llvm/IR/Constants.h"
15 #include "llvm/IR/Function.h"
16 #include "llvm/IR/Instructions.h"
17 #include "llvm/IR/IntrinsicInst.h"
18 #include "llvm/IR/Module.h"
19 
20 using namespace llvm;
21 using namespace fuzzerop;
22 
23 Value *RandomIRBuilder::findOrCreateSource(BasicBlock &BB,
24                                            ArrayRef<Instruction *> Insts) {
25   return findOrCreateSource(BB, Insts, {}, anyType());
26 }
27 
28 Value *RandomIRBuilder::findOrCreateSource(BasicBlock &BB,
29                                            ArrayRef<Instruction *> Insts,
30                                            ArrayRef<Value *> Srcs,
31                                            SourcePred Pred) {
32   auto MatchesPred = [&Srcs, &Pred](Instruction *Inst) {
33     return Pred.matches(Srcs, Inst);
34   };
35   auto RS = makeSampler(Rand, make_filter_range(Insts, MatchesPred));
36   // Also consider choosing no source, meaning we want a new one.
37   RS.sample(nullptr, /*Weight=*/1);
38   if (Instruction *Src = RS.getSelection())
39     return Src;
40   return newSource(BB, Insts, Srcs, Pred);
41 }
42 
43 Value *RandomIRBuilder::newSource(BasicBlock &BB, ArrayRef<Instruction *> Insts,
44                                   ArrayRef<Value *> Srcs, SourcePred Pred) {
45   // Generate some constants to choose from.
46   auto RS = makeSampler<Value *>(Rand);
47   RS.sample(Pred.generate(Srcs, KnownTypes));
48 
49   // If we can find a pointer to load from, use it half the time.
50   Value *Ptr = findPointer(BB, Insts, Srcs, Pred);
51   if (Ptr) {
52     // Create load from the chosen pointer
53     auto IP = BB.getFirstInsertionPt();
54     if (auto *I = dyn_cast<Instruction>(Ptr))
55       IP = ++I->getIterator();
56     auto *NewLoad = new LoadInst(Ptr, "L", &*IP);
57 
58     // Only sample this load if it really matches the descriptor
59     if (Pred.matches(Srcs, NewLoad))
60       RS.sample(NewLoad, RS.totalWeight());
61     else
62       NewLoad->eraseFromParent();
63   }
64 
65   assert(!RS.isEmpty() && "Failed to generate sources");
66   return RS.getSelection();
67 }
68 
69 static bool isCompatibleReplacement(const Instruction *I, const Use &Operand,
70                                     const Value *Replacement) {
71   if (Operand->getType() != Replacement->getType())
72     return false;
73   switch (I->getOpcode()) {
74   case Instruction::GetElementPtr:
75   case Instruction::ExtractElement:
76   case Instruction::ExtractValue:
77     // TODO: We could potentially validate these, but for now just leave indices
78     // alone.
79     if (Operand.getOperandNo() > 1)
80       return false;
81     break;
82   case Instruction::InsertValue:
83   case Instruction::InsertElement:
84     if (Operand.getOperandNo() > 2)
85       return false;
86     break;
87   default:
88     break;
89   }
90   return true;
91 }
92 
93 void RandomIRBuilder::connectToSink(BasicBlock &BB,
94                                     ArrayRef<Instruction *> Insts, Value *V) {
95   auto RS = makeSampler<Use *>(Rand);
96   for (auto &I : Insts) {
97     if (isa<IntrinsicInst>(I))
98       // TODO: Replacing operands of intrinsics would be interesting, but
99       // there's no easy way to verify that a given replacement is valid given
100       // that intrinsics can impose arbitrary constraints.
101       continue;
102     for (Use &U : I->operands())
103       if (isCompatibleReplacement(I, U, V))
104         RS.sample(&U, 1);
105   }
106   // Also consider choosing no sink, meaning we want a new one.
107   RS.sample(nullptr, /*Weight=*/1);
108 
109   if (Use *Sink = RS.getSelection()) {
110     User *U = Sink->getUser();
111     unsigned OpNo = Sink->getOperandNo();
112     U->setOperand(OpNo, V);
113     return;
114   }
115   newSink(BB, Insts, V);
116 }
117 
118 void RandomIRBuilder::newSink(BasicBlock &BB, ArrayRef<Instruction *> Insts,
119                               Value *V) {
120   Value *Ptr = findPointer(BB, Insts, {V}, matchFirstType());
121   if (!Ptr) {
122     if (uniform(Rand, 0, 1))
123       Ptr = new AllocaInst(V->getType(), 0, "A", &*BB.getFirstInsertionPt());
124     else
125       Ptr = UndefValue::get(PointerType::get(V->getType(), 0));
126   }
127 
128   new StoreInst(V, Ptr, Insts.back());
129 }
130 
131 Value *RandomIRBuilder::findPointer(BasicBlock &BB,
132                                     ArrayRef<Instruction *> Insts,
133                                     ArrayRef<Value *> Srcs, SourcePred Pred) {
134   auto IsMatchingPtr = [&Srcs, &Pred](Instruction *Inst) {
135     if (auto PtrTy = dyn_cast<PointerType>(Inst->getType()))
136       // TODO: Check if this is horribly expensive.
137       return Pred.matches(Srcs, UndefValue::get(PtrTy->getElementType()));
138     return false;
139   };
140   if (auto RS = makeSampler(Rand, make_filter_range(Insts, IsMatchingPtr)))
141     return RS.getSelection();
142   return nullptr;
143 }
144