1 //===- PointerTracking.cpp - Pointer Bounds Tracking ------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements tracking of pointer bounds.
12 //===----------------------------------------------------------------------===//
13 #include "llvm/Analysis/ConstantFolding.h"
14 #include "llvm/Analysis/Dominators.h"
15 #include "llvm/Analysis/LoopInfo.h"
16 #include "llvm/Analysis/PointerTracking.h"
17 #include "llvm/Analysis/ScalarEvolution.h"
18 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
19 #include "llvm/Constants.h"
20 #include "llvm/Module.h"
21 #include "llvm/Value.h"
22 #include "llvm/Support/CallSite.h"
23 #include "llvm/Support/InstIterator.h"
24 #include "llvm/Support/raw_ostream.h"
25 #include "llvm/Target/TargetData.h"
28 char PointerTracking::ID=0;
29 PointerTracking::PointerTracking() : FunctionPass(&ID) {}
31 bool PointerTracking::runOnFunction(Function &F) {
33 assert(analyzing.empty());
35 TD = getAnalysisIfAvailable<TargetData>();
36 SE = &getAnalysis<ScalarEvolution>();
37 LI = &getAnalysis<LoopInfo>();
38 DT = &getAnalysis<DominatorTree>();
42 void PointerTracking::getAnalysisUsage(AnalysisUsage &AU) const {
43 AU.addRequiredTransitive<DominatorTree>();
44 AU.addRequiredTransitive<LoopInfo>();
45 AU.addRequiredTransitive<ScalarEvolution>();
49 bool PointerTracking::doInitialization(Module &M) {
50 const Type *PTy = PointerType::getUnqual(Type::getInt8Ty(M.getContext()));
52 // Find calloc(i64, i64) or calloc(i32, i32).
53 callocFunc = M.getFunction("calloc");
55 const FunctionType *Ty = callocFunc->getFunctionType();
57 std::vector<const Type*> args, args2;
58 args.push_back(Type::getInt64Ty(M.getContext()));
59 args.push_back(Type::getInt64Ty(M.getContext()));
60 args2.push_back(Type::getInt32Ty(M.getContext()));
61 args2.push_back(Type::getInt32Ty(M.getContext()));
62 const FunctionType *Calloc1Type =
63 FunctionType::get(PTy, args, false);
64 const FunctionType *Calloc2Type =
65 FunctionType::get(PTy, args2, false);
66 if (Ty != Calloc1Type && Ty != Calloc2Type)
67 callocFunc = 0; // Give up
70 // Find realloc(i8*, i64) or realloc(i8*, i32).
71 reallocFunc = M.getFunction("realloc");
73 const FunctionType *Ty = reallocFunc->getFunctionType();
74 std::vector<const Type*> args, args2;
76 args.push_back(Type::getInt64Ty(M.getContext()));
78 args2.push_back(Type::getInt32Ty(M.getContext()));
80 const FunctionType *Realloc1Type =
81 FunctionType::get(PTy, args, false);
82 const FunctionType *Realloc2Type =
83 FunctionType::get(PTy, args2, false);
84 if (Ty != Realloc1Type && Ty != Realloc2Type)
85 reallocFunc = 0; // Give up
90 // Calculates the number of elements allocated for pointer P,
91 // the type of the element is stored in Ty.
92 const SCEV *PointerTracking::computeAllocationCount(Value *P,
93 const Type *&Ty) const {
94 Value *V = P->stripPointerCasts();
95 if (AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
96 Value *arraySize = AI->getArraySize();
97 Ty = AI->getAllocatedType();
98 // arraySize elements of type Ty.
99 return SE->getSCEV(arraySize);
102 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
103 if (GV->hasDefinitiveInitializer()) {
104 Constant *C = GV->getInitializer();
105 if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
106 Ty = ATy->getElementType();
107 return SE->getConstant(Type::getInt32Ty(Ty->getContext()),
108 ATy->getNumElements());
112 return SE->getConstant(Type::getInt32Ty(Ty->getContext()), 1);
113 //TODO: implement more tracking for globals
116 if (CallInst *CI = dyn_cast<CallInst>(V)) {
118 Function *F = dyn_cast<Function>(CS.getCalledValue()->stripPointerCasts());
119 const Loop *L = LI->getLoopFor(CI->getParent());
120 if (F == callocFunc) {
121 Ty = Type::getInt8Ty(Ty->getContext());
122 // calloc allocates arg0*arg1 bytes.
123 return SE->getSCEVAtScope(SE->getMulExpr(SE->getSCEV(CS.getArgument(0)),
124 SE->getSCEV(CS.getArgument(1))),
126 } else if (F == reallocFunc) {
127 Ty = Type::getInt8Ty(Ty->getContext());
128 // realloc allocates arg1 bytes.
129 return SE->getSCEVAtScope(CS.getArgument(1), L);
133 return SE->getCouldNotCompute();
136 // Calculates the number of elements of type Ty allocated for P.
137 const SCEV *PointerTracking::computeAllocationCountForType(Value *P,
140 const Type *elementTy;
141 const SCEV *Count = computeAllocationCount(P, elementTy);
142 if (isa<SCEVCouldNotCompute>(Count))
147 if (!TD) // need TargetData from this point forward
148 return SE->getCouldNotCompute();
150 uint64_t elementSize = TD->getTypeAllocSize(elementTy);
151 uint64_t wantSize = TD->getTypeAllocSize(Ty);
152 if (elementSize == wantSize)
154 if (elementSize % wantSize) //fractional counts not possible
155 return SE->getCouldNotCompute();
156 return SE->getMulExpr(Count, SE->getConstant(Count->getType(),
157 elementSize/wantSize));
160 const SCEV *PointerTracking::getAllocationElementCount(Value *V) const {
161 // We only deal with pointers.
162 const PointerType *PTy = cast<PointerType>(V->getType());
163 return computeAllocationCountForType(V, PTy->getElementType());
166 const SCEV *PointerTracking::getAllocationSizeInBytes(Value *V) const {
167 return computeAllocationCountForType(V, Type::getInt8Ty(V->getContext()));
170 // Helper for isLoopGuardedBy that checks the swapped and inverted predicate too
171 enum SolverResult PointerTracking::isLoopGuardedBy(const Loop *L,
174 const SCEV *B) const {
175 if (SE->isLoopGuardedByCond(L, Pred, A, B))
177 Pred = ICmpInst::getSwappedPredicate(Pred);
178 if (SE->isLoopGuardedByCond(L, Pred, B, A))
181 Pred = ICmpInst::getInversePredicate(Pred);
182 if (SE->isLoopGuardedByCond(L, Pred, B, A))
184 Pred = ICmpInst::getSwappedPredicate(Pred);
185 if (SE->isLoopGuardedByCond(L, Pred, A, B))
190 enum SolverResult PointerTracking::checkLimits(const SCEV *Offset,
194 //FIXME: merge implementation
198 void PointerTracking::getPointerOffset(Value *Pointer, Value *&Base,
200 const SCEV *&Offset) const
202 Pointer = Pointer->stripPointerCasts();
203 Base = Pointer->getUnderlyingObject();
204 Limit = getAllocationSizeInBytes(Base);
205 if (isa<SCEVCouldNotCompute>(Limit)) {
211 Offset = SE->getMinusSCEV(SE->getSCEV(Pointer), SE->getSCEV(Base));
212 if (isa<SCEVCouldNotCompute>(Offset)) {
218 void PointerTracking::print(raw_ostream &OS, const Module* M) const {
219 // Calling some PT methods may cause caches to be updated, however
220 // this should be safe for the same reason its safe for SCEV.
221 PointerTracking &PT = *const_cast<PointerTracking*>(this);
222 for (inst_iterator I=inst_begin(*FF), E=inst_end(*FF); I != E; ++I) {
223 if (!isa<PointerType>(I->getType()))
226 const SCEV *Limit, *Offset;
227 getPointerOffset(&*I, Base, Limit, Offset);
232 const SCEV *S = getAllocationElementCount(Base);
233 OS << *Base << " ==> " << *S << " elements, ";
234 OS << *Limit << " bytes allocated\n";
237 OS << &*I << " -- base: " << *Base;
238 OS << " offset: " << *Offset;
240 enum SolverResult res = PT.checkLimits(Offset, Limit, I->getParent());
243 OS << " always safe\n";
246 OS << " always unsafe\n";
249 OS << " <<unknown>>\n";
255 void PointerTracking::print(std::ostream &o, const Module* M) const {
256 raw_os_ostream OS(o);
260 static RegisterPass<PointerTracking> X("pointertracking",
261 "Track pointer bounds", false, true);