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   assert(!RS.isEmpty() && "Failed to generate sources");
49 
50   // If we can find a pointer to load from, use it half the time.
51   Value *Ptr = findPointer(BB, Insts, Srcs, Pred);
52   if (Ptr)
53     RS.sample(Ptr, RS.totalWeight());
54 
55   Value *Result = RS.getSelection();
56   if (Result != Ptr)
57     return Result;
58 
59   // If we choose the pointer, we need to create a load.
60   auto IP = BB.getFirstInsertionPt();
61   if (auto *I = dyn_cast<Instruction>(Ptr))
62     IP = ++I->getIterator();
63   return new LoadInst(Ptr, "L", &*IP);
64 }
65 
66 static bool isCompatibleReplacement(const Instruction *I, const Use &Operand,
67                                     const Value *Replacement) {
68   if (Operand->getType() != Replacement->getType())
69     return false;
70   switch (I->getOpcode()) {
71   case Instruction::GetElementPtr:
72   case Instruction::ExtractElement:
73   case Instruction::ExtractValue:
74     // TODO: We could potentially validate these, but for now just leave indices
75     // alone.
76     if (Operand.getOperandNo() > 1)
77       return false;
78     break;
79   case Instruction::InsertValue:
80   case Instruction::InsertElement:
81     if (Operand.getOperandNo() > 2)
82       return false;
83     break;
84   default:
85     break;
86   }
87   return true;
88 }
89 
90 void RandomIRBuilder::connectToSink(BasicBlock &BB,
91                                     ArrayRef<Instruction *> Insts, Value *V) {
92   auto RS = makeSampler<Use *>(Rand);
93   for (auto &I : Insts) {
94     if (isa<IntrinsicInst>(I))
95       // TODO: Replacing operands of intrinsics would be interesting, but
96       // there's no easy way to verify that a given replacement is valid given
97       // that intrinsics can impose arbitrary constraints.
98       continue;
99     for (Use &U : I->operands())
100       if (isCompatibleReplacement(I, U, V))
101         RS.sample(&U, 1);
102   }
103   // Also consider choosing no sink, meaning we want a new one.
104   RS.sample(nullptr, /*Weight=*/1);
105 
106   if (Use *Sink = RS.getSelection()) {
107     User *U = Sink->getUser();
108     unsigned OpNo = Sink->getOperandNo();
109     U->setOperand(OpNo, V);
110     return;
111   }
112   newSink(BB, Insts, V);
113 }
114 
115 void RandomIRBuilder::newSink(BasicBlock &BB, ArrayRef<Instruction *> Insts,
116                               Value *V) {
117   Value *Ptr = findPointer(BB, Insts, {V}, matchFirstType());
118   if (!Ptr) {
119     if (uniform(Rand, 0, 1))
120       Ptr = new AllocaInst(V->getType(), 0, "A", &*BB.getFirstInsertionPt());
121     else
122       Ptr = UndefValue::get(PointerType::get(V->getType(), 0));
123   }
124 
125   new StoreInst(V, Ptr, Insts.back());
126 }
127 
128 Value *RandomIRBuilder::findPointer(BasicBlock &BB,
129                                     ArrayRef<Instruction *> Insts,
130                                     ArrayRef<Value *> Srcs, SourcePred Pred) {
131   auto IsMatchingPtr = [&Srcs, &Pred](Instruction *Inst) {
132     if (auto PtrTy = dyn_cast<PointerType>(Inst->getType()))
133       // TODO: Check if this is horribly expensive.
134       return Pred.matches(Srcs, UndefValue::get(PtrTy->getElementType()));
135     return false;
136   };
137   if (auto RS = makeSampler(Rand, make_filter_range(Insts, IsMatchingPtr)))
138     return RS.getSelection();
139   return nullptr;
140 }
141