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      1 //===------ MemoryBuiltins.cpp - Identify calls to memory builtins --------===//
      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 // This family of functions identifies calls to builtin functions that allocate
     11 // or free memory.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #define DEBUG_TYPE "memory-builtins"
     16 #include "llvm/Analysis/MemoryBuiltins.h"
     17 #include "llvm/ADT/STLExtras.h"
     18 #include "llvm/ADT/Statistic.h"
     19 #include "llvm/Analysis/ValueTracking.h"
     20 #include "llvm/IR/DataLayout.h"
     21 #include "llvm/IR/GlobalVariable.h"
     22 #include "llvm/IR/Instructions.h"
     23 #include "llvm/IR/Intrinsics.h"
     24 #include "llvm/IR/Metadata.h"
     25 #include "llvm/IR/Module.h"
     26 #include "llvm/Support/Debug.h"
     27 #include "llvm/Support/MathExtras.h"
     28 #include "llvm/Support/raw_ostream.h"
     29 #include "llvm/Target/TargetLibraryInfo.h"
     30 #include "llvm/Transforms/Utils/Local.h"
     31 using namespace llvm;
     32 
     33 enum AllocType {
     34   MallocLike         = 1<<0, // allocates
     35   CallocLike         = 1<<1, // allocates + bzero
     36   ReallocLike        = 1<<2, // reallocates
     37   StrDupLike         = 1<<3,
     38   AllocLike          = MallocLike | CallocLike | StrDupLike,
     39   AnyAlloc           = MallocLike | CallocLike | ReallocLike | StrDupLike
     40 };
     41 
     42 struct AllocFnsTy {
     43   LibFunc::Func Func;
     44   AllocType AllocTy;
     45   unsigned char NumParams;
     46   // First and Second size parameters (or -1 if unused)
     47   signed char FstParam, SndParam;
     48 };
     49 
     50 // FIXME: certain users need more information. E.g., SimplifyLibCalls needs to
     51 // know which functions are nounwind, noalias, nocapture parameters, etc.
     52 static const AllocFnsTy AllocationFnData[] = {
     53   {LibFunc::malloc,              MallocLike,  1, 0,  -1},
     54   {LibFunc::valloc,              MallocLike,  1, 0,  -1},
     55   {LibFunc::Znwj,                MallocLike,  1, 0,  -1}, // new(unsigned int)
     56   {LibFunc::ZnwjRKSt9nothrow_t,  MallocLike,  2, 0,  -1}, // new(unsigned int, nothrow)
     57   {LibFunc::Znwm,                MallocLike,  1, 0,  -1}, // new(unsigned long)
     58   {LibFunc::ZnwmRKSt9nothrow_t,  MallocLike,  2, 0,  -1}, // new(unsigned long, nothrow)
     59   {LibFunc::Znaj,                MallocLike,  1, 0,  -1}, // new[](unsigned int)
     60   {LibFunc::ZnajRKSt9nothrow_t,  MallocLike,  2, 0,  -1}, // new[](unsigned int, nothrow)
     61   {LibFunc::Znam,                MallocLike,  1, 0,  -1}, // new[](unsigned long)
     62   {LibFunc::ZnamRKSt9nothrow_t,  MallocLike,  2, 0,  -1}, // new[](unsigned long, nothrow)
     63   {LibFunc::posix_memalign,      MallocLike,  3, 2,  -1},
     64   {LibFunc::calloc,              CallocLike,  2, 0,   1},
     65   {LibFunc::realloc,             ReallocLike, 2, 1,  -1},
     66   {LibFunc::reallocf,            ReallocLike, 2, 1,  -1},
     67   {LibFunc::strdup,              StrDupLike,  1, -1, -1},
     68   {LibFunc::strndup,             StrDupLike,  2, 1,  -1}
     69 };
     70 
     71 
     72 static Function *getCalledFunction(const Value *V, bool LookThroughBitCast) {
     73   if (LookThroughBitCast)
     74     V = V->stripPointerCasts();
     75 
     76   CallSite CS(const_cast<Value*>(V));
     77   if (!CS.getInstruction())
     78     return 0;
     79 
     80   Function *Callee = CS.getCalledFunction();
     81   if (!Callee || !Callee->isDeclaration())
     82     return 0;
     83   return Callee;
     84 }
     85 
     86 /// \brief Returns the allocation data for the given value if it is a call to a
     87 /// known allocation function, and NULL otherwise.
     88 static const AllocFnsTy *getAllocationData(const Value *V, AllocType AllocTy,
     89                                            const TargetLibraryInfo *TLI,
     90                                            bool LookThroughBitCast = false) {
     91   // Skip intrinsics
     92   if (isa<IntrinsicInst>(V))
     93     return 0;
     94 
     95   Function *Callee = getCalledFunction(V, LookThroughBitCast);
     96   if (!Callee)
     97     return 0;
     98 
     99   // Make sure that the function is available.
    100   StringRef FnName = Callee->getName();
    101   LibFunc::Func TLIFn;
    102   if (!TLI || !TLI->getLibFunc(FnName, TLIFn) || !TLI->has(TLIFn))
    103     return 0;
    104 
    105   unsigned i = 0;
    106   bool found = false;
    107   for ( ; i < array_lengthof(AllocationFnData); ++i) {
    108     if (AllocationFnData[i].Func == TLIFn) {
    109       found = true;
    110       break;
    111     }
    112   }
    113   if (!found)
    114     return 0;
    115 
    116   const AllocFnsTy *FnData = &AllocationFnData[i];
    117   if ((FnData->AllocTy & AllocTy) == 0)
    118     return 0;
    119 
    120   // Check function prototype.
    121   int FstParam = FnData->FstParam;
    122   int SndParam = FnData->SndParam;
    123   FunctionType *FTy = Callee->getFunctionType();
    124 
    125   if (FTy->getReturnType() == Type::getInt8PtrTy(FTy->getContext()) &&
    126       FTy->getNumParams() == FnData->NumParams &&
    127       (FstParam < 0 ||
    128        (FTy->getParamType(FstParam)->isIntegerTy(32) ||
    129         FTy->getParamType(FstParam)->isIntegerTy(64))) &&
    130       (SndParam < 0 ||
    131        FTy->getParamType(SndParam)->isIntegerTy(32) ||
    132        FTy->getParamType(SndParam)->isIntegerTy(64)))
    133     return FnData;
    134   return 0;
    135 }
    136 
    137 static bool hasNoAliasAttr(const Value *V, bool LookThroughBitCast) {
    138   ImmutableCallSite CS(LookThroughBitCast ? V->stripPointerCasts() : V);
    139   return CS && CS.hasFnAttr(Attribute::NoAlias);
    140 }
    141 
    142 
    143 /// \brief Tests if a value is a call or invoke to a library function that
    144 /// allocates or reallocates memory (either malloc, calloc, realloc, or strdup
    145 /// like).
    146 bool llvm::isAllocationFn(const Value *V, const TargetLibraryInfo *TLI,
    147                           bool LookThroughBitCast) {
    148   return getAllocationData(V, AnyAlloc, TLI, LookThroughBitCast);
    149 }
    150 
    151 /// \brief Tests if a value is a call or invoke to a function that returns a
    152 /// NoAlias pointer (including malloc/calloc/realloc/strdup-like functions).
    153 bool llvm::isNoAliasFn(const Value *V, const TargetLibraryInfo *TLI,
    154                        bool LookThroughBitCast) {
    155   // it's safe to consider realloc as noalias since accessing the original
    156   // pointer is undefined behavior
    157   return isAllocationFn(V, TLI, LookThroughBitCast) ||
    158          hasNoAliasAttr(V, LookThroughBitCast);
    159 }
    160 
    161 /// \brief Tests if a value is a call or invoke to a library function that
    162 /// allocates uninitialized memory (such as malloc).
    163 bool llvm::isMallocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
    164                           bool LookThroughBitCast) {
    165   return getAllocationData(V, MallocLike, TLI, LookThroughBitCast);
    166 }
    167 
    168 /// \brief Tests if a value is a call or invoke to a library function that
    169 /// allocates zero-filled memory (such as calloc).
    170 bool llvm::isCallocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
    171                           bool LookThroughBitCast) {
    172   return getAllocationData(V, CallocLike, TLI, LookThroughBitCast);
    173 }
    174 
    175 /// \brief Tests if a value is a call or invoke to a library function that
    176 /// allocates memory (either malloc, calloc, or strdup like).
    177 bool llvm::isAllocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
    178                          bool LookThroughBitCast) {
    179   return getAllocationData(V, AllocLike, TLI, LookThroughBitCast);
    180 }
    181 
    182 /// \brief Tests if a value is a call or invoke to a library function that
    183 /// reallocates memory (such as realloc).
    184 bool llvm::isReallocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
    185                            bool LookThroughBitCast) {
    186   return getAllocationData(V, ReallocLike, TLI, LookThroughBitCast);
    187 }
    188 
    189 /// extractMallocCall - Returns the corresponding CallInst if the instruction
    190 /// is a malloc call.  Since CallInst::CreateMalloc() only creates calls, we
    191 /// ignore InvokeInst here.
    192 const CallInst *llvm::extractMallocCall(const Value *I,
    193                                         const TargetLibraryInfo *TLI) {
    194   return isMallocLikeFn(I, TLI) ? dyn_cast<CallInst>(I) : 0;
    195 }
    196 
    197 static Value *computeArraySize(const CallInst *CI, const DataLayout *TD,
    198                                const TargetLibraryInfo *TLI,
    199                                bool LookThroughSExt = false) {
    200   if (!CI)
    201     return 0;
    202 
    203   // The size of the malloc's result type must be known to determine array size.
    204   Type *T = getMallocAllocatedType(CI, TLI);
    205   if (!T || !T->isSized() || !TD)
    206     return 0;
    207 
    208   unsigned ElementSize = TD->getTypeAllocSize(T);
    209   if (StructType *ST = dyn_cast<StructType>(T))
    210     ElementSize = TD->getStructLayout(ST)->getSizeInBytes();
    211 
    212   // If malloc call's arg can be determined to be a multiple of ElementSize,
    213   // return the multiple.  Otherwise, return NULL.
    214   Value *MallocArg = CI->getArgOperand(0);
    215   Value *Multiple = 0;
    216   if (ComputeMultiple(MallocArg, ElementSize, Multiple,
    217                       LookThroughSExt))
    218     return Multiple;
    219 
    220   return 0;
    221 }
    222 
    223 /// isArrayMalloc - Returns the corresponding CallInst if the instruction
    224 /// is a call to malloc whose array size can be determined and the array size
    225 /// is not constant 1.  Otherwise, return NULL.
    226 const CallInst *llvm::isArrayMalloc(const Value *I,
    227                                     const DataLayout *TD,
    228                                     const TargetLibraryInfo *TLI) {
    229   const CallInst *CI = extractMallocCall(I, TLI);
    230   Value *ArraySize = computeArraySize(CI, TD, TLI);
    231 
    232   if (ConstantInt *ConstSize = dyn_cast_or_null<ConstantInt>(ArraySize))
    233     if (ConstSize->isOne())
    234       return CI;
    235 
    236   // CI is a non-array malloc or we can't figure out that it is an array malloc.
    237   return 0;
    238 }
    239 
    240 /// getMallocType - Returns the PointerType resulting from the malloc call.
    241 /// The PointerType depends on the number of bitcast uses of the malloc call:
    242 ///   0: PointerType is the calls' return type.
    243 ///   1: PointerType is the bitcast's result type.
    244 ///  >1: Unique PointerType cannot be determined, return NULL.
    245 PointerType *llvm::getMallocType(const CallInst *CI,
    246                                  const TargetLibraryInfo *TLI) {
    247   assert(isMallocLikeFn(CI, TLI) && "getMallocType and not malloc call");
    248 
    249   PointerType *MallocType = 0;
    250   unsigned NumOfBitCastUses = 0;
    251 
    252   // Determine if CallInst has a bitcast use.
    253   for (Value::const_use_iterator UI = CI->use_begin(), E = CI->use_end();
    254        UI != E; )
    255     if (const BitCastInst *BCI = dyn_cast<BitCastInst>(*UI++)) {
    256       MallocType = cast<PointerType>(BCI->getDestTy());
    257       NumOfBitCastUses++;
    258     }
    259 
    260   // Malloc call has 1 bitcast use, so type is the bitcast's destination type.
    261   if (NumOfBitCastUses == 1)
    262     return MallocType;
    263 
    264   // Malloc call was not bitcast, so type is the malloc function's return type.
    265   if (NumOfBitCastUses == 0)
    266     return cast<PointerType>(CI->getType());
    267 
    268   // Type could not be determined.
    269   return 0;
    270 }
    271 
    272 /// getMallocAllocatedType - Returns the Type allocated by malloc call.
    273 /// The Type depends on the number of bitcast uses of the malloc call:
    274 ///   0: PointerType is the malloc calls' return type.
    275 ///   1: PointerType is the bitcast's result type.
    276 ///  >1: Unique PointerType cannot be determined, return NULL.
    277 Type *llvm::getMallocAllocatedType(const CallInst *CI,
    278                                    const TargetLibraryInfo *TLI) {
    279   PointerType *PT = getMallocType(CI, TLI);
    280   return PT ? PT->getElementType() : 0;
    281 }
    282 
    283 /// getMallocArraySize - Returns the array size of a malloc call.  If the
    284 /// argument passed to malloc is a multiple of the size of the malloced type,
    285 /// then return that multiple.  For non-array mallocs, the multiple is
    286 /// constant 1.  Otherwise, return NULL for mallocs whose array size cannot be
    287 /// determined.
    288 Value *llvm::getMallocArraySize(CallInst *CI, const DataLayout *TD,
    289                                 const TargetLibraryInfo *TLI,
    290                                 bool LookThroughSExt) {
    291   assert(isMallocLikeFn(CI, TLI) && "getMallocArraySize and not malloc call");
    292   return computeArraySize(CI, TD, TLI, LookThroughSExt);
    293 }
    294 
    295 
    296 /// extractCallocCall - Returns the corresponding CallInst if the instruction
    297 /// is a calloc call.
    298 const CallInst *llvm::extractCallocCall(const Value *I,
    299                                         const TargetLibraryInfo *TLI) {
    300   return isCallocLikeFn(I, TLI) ? cast<CallInst>(I) : 0;
    301 }
    302 
    303 
    304 /// isFreeCall - Returns non-null if the value is a call to the builtin free()
    305 const CallInst *llvm::isFreeCall(const Value *I, const TargetLibraryInfo *TLI) {
    306   const CallInst *CI = dyn_cast<CallInst>(I);
    307   if (!CI || isa<IntrinsicInst>(CI))
    308     return 0;
    309   Function *Callee = CI->getCalledFunction();
    310   if (Callee == 0 || !Callee->isDeclaration())
    311     return 0;
    312 
    313   StringRef FnName = Callee->getName();
    314   LibFunc::Func TLIFn;
    315   if (!TLI || !TLI->getLibFunc(FnName, TLIFn) || !TLI->has(TLIFn))
    316     return 0;
    317 
    318   if (TLIFn != LibFunc::free &&
    319       TLIFn != LibFunc::ZdlPv && // operator delete(void*)
    320       TLIFn != LibFunc::ZdaPv)   // operator delete[](void*)
    321     return 0;
    322 
    323   // Check free prototype.
    324   // FIXME: workaround for PR5130, this will be obsolete when a nobuiltin
    325   // attribute will exist.
    326   FunctionType *FTy = Callee->getFunctionType();
    327   if (!FTy->getReturnType()->isVoidTy())
    328     return 0;
    329   if (FTy->getNumParams() != 1)
    330     return 0;
    331   if (FTy->getParamType(0) != Type::getInt8PtrTy(Callee->getContext()))
    332     return 0;
    333 
    334   return CI;
    335 }
    336 
    337 
    338 
    339 //===----------------------------------------------------------------------===//
    340 //  Utility functions to compute size of objects.
    341 //
    342 
    343 
    344 /// \brief Compute the size of the object pointed by Ptr. Returns true and the
    345 /// object size in Size if successful, and false otherwise.
    346 /// If RoundToAlign is true, then Size is rounded up to the aligment of allocas,
    347 /// byval arguments, and global variables.
    348 bool llvm::getObjectSize(const Value *Ptr, uint64_t &Size, const DataLayout *TD,
    349                          const TargetLibraryInfo *TLI, bool RoundToAlign) {
    350   if (!TD)
    351     return false;
    352 
    353   ObjectSizeOffsetVisitor Visitor(TD, TLI, Ptr->getContext(), RoundToAlign);
    354   SizeOffsetType Data = Visitor.compute(const_cast<Value*>(Ptr));
    355   if (!Visitor.bothKnown(Data))
    356     return false;
    357 
    358   APInt ObjSize = Data.first, Offset = Data.second;
    359   // check for overflow
    360   if (Offset.slt(0) || ObjSize.ult(Offset))
    361     Size = 0;
    362   else
    363     Size = (ObjSize - Offset).getZExtValue();
    364   return true;
    365 }
    366 
    367 /// \brief Compute the size of the underlying object pointed by Ptr. Returns
    368 /// true and the object size in Size if successful, and false otherwise.
    369 /// If RoundToAlign is true, then Size is rounded up to the aligment of allocas,
    370 /// byval arguments, and global variables.
    371 bool llvm::getUnderlyingObjectSize(const Value *Ptr, uint64_t &Size,
    372                                    const DataLayout *TD,
    373                                    const TargetLibraryInfo *TLI,
    374                                    bool RoundToAlign) {
    375   if (!TD)
    376     return false;
    377 
    378   ObjectSizeOffsetVisitor Visitor(TD, TLI, Ptr->getContext(), RoundToAlign);
    379   SizeOffsetType Data = Visitor.compute(const_cast<Value*>(Ptr));
    380   if (!Visitor.knownSize(Data))
    381     return false;
    382 
    383   Size = Data.first.getZExtValue();
    384   return true;
    385 }
    386 
    387 
    388 STATISTIC(ObjectVisitorArgument,
    389           "Number of arguments with unsolved size and offset");
    390 STATISTIC(ObjectVisitorLoad,
    391           "Number of load instructions with unsolved size and offset");
    392 
    393 
    394 APInt ObjectSizeOffsetVisitor::align(APInt Size, uint64_t Align) {
    395   if (RoundToAlign && Align)
    396     return APInt(IntTyBits, RoundUpToAlignment(Size.getZExtValue(), Align));
    397   return Size;
    398 }
    399 
    400 ObjectSizeOffsetVisitor::ObjectSizeOffsetVisitor(const DataLayout *TD,
    401                                                  const TargetLibraryInfo *TLI,
    402                                                  LLVMContext &Context,
    403                                                  bool RoundToAlign)
    404 : TD(TD), TLI(TLI), RoundToAlign(RoundToAlign) {
    405   IntegerType *IntTy = TD->getIntPtrType(Context);
    406   IntTyBits = IntTy->getBitWidth();
    407   Zero = APInt::getNullValue(IntTyBits);
    408 }
    409 
    410 SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
    411   V = V->stripPointerCasts();
    412 
    413   if (isa<Instruction>(V) || isa<GEPOperator>(V)) {
    414     // Return cached value or insert unknown in cache if size of V was not
    415     // computed yet in order to avoid recursions in PHis.
    416     std::pair<CacheMapTy::iterator, bool> CacheVal =
    417       CacheMap.insert(std::make_pair(V, unknown()));
    418     if (!CacheVal.second)
    419       return CacheVal.first->second;
    420 
    421     SizeOffsetType Result;
    422     if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
    423       Result = visitGEPOperator(*GEP);
    424     else
    425       Result = visit(cast<Instruction>(*V));
    426     return CacheMap[V] = Result;
    427   }
    428 
    429   if (Argument *A = dyn_cast<Argument>(V))
    430     return visitArgument(*A);
    431   if (ConstantPointerNull *P = dyn_cast<ConstantPointerNull>(V))
    432     return visitConstantPointerNull(*P);
    433   if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V))
    434     return visitGlobalAlias(*GA);
    435   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
    436     return visitGlobalVariable(*GV);
    437   if (UndefValue *UV = dyn_cast<UndefValue>(V))
    438     return visitUndefValue(*UV);
    439   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
    440     if (CE->getOpcode() == Instruction::IntToPtr)
    441       return unknown(); // clueless
    442   }
    443 
    444   DEBUG(dbgs() << "ObjectSizeOffsetVisitor::compute() unhandled value: " << *V
    445         << '\n');
    446   return unknown();
    447 }
    448 
    449 SizeOffsetType ObjectSizeOffsetVisitor::visitAllocaInst(AllocaInst &I) {
    450   if (!I.getAllocatedType()->isSized())
    451     return unknown();
    452 
    453   APInt Size(IntTyBits, TD->getTypeAllocSize(I.getAllocatedType()));
    454   if (!I.isArrayAllocation())
    455     return std::make_pair(align(Size, I.getAlignment()), Zero);
    456 
    457   Value *ArraySize = I.getArraySize();
    458   if (const ConstantInt *C = dyn_cast<ConstantInt>(ArraySize)) {
    459     Size *= C->getValue().zextOrSelf(IntTyBits);
    460     return std::make_pair(align(Size, I.getAlignment()), Zero);
    461   }
    462   return unknown();
    463 }
    464 
    465 SizeOffsetType ObjectSizeOffsetVisitor::visitArgument(Argument &A) {
    466   // no interprocedural analysis is done at the moment
    467   if (!A.hasByValAttr()) {
    468     ++ObjectVisitorArgument;
    469     return unknown();
    470   }
    471   PointerType *PT = cast<PointerType>(A.getType());
    472   APInt Size(IntTyBits, TD->getTypeAllocSize(PT->getElementType()));
    473   return std::make_pair(align(Size, A.getParamAlignment()), Zero);
    474 }
    475 
    476 SizeOffsetType ObjectSizeOffsetVisitor::visitCallSite(CallSite CS) {
    477   const AllocFnsTy *FnData = getAllocationData(CS.getInstruction(), AnyAlloc,
    478                                                TLI);
    479   if (!FnData)
    480     return unknown();
    481 
    482   // handle strdup-like functions separately
    483   if (FnData->AllocTy == StrDupLike) {
    484     APInt Size(IntTyBits, GetStringLength(CS.getArgument(0)));
    485     if (!Size)
    486       return unknown();
    487 
    488     // strndup limits strlen
    489     if (FnData->FstParam > 0) {
    490       ConstantInt *Arg= dyn_cast<ConstantInt>(CS.getArgument(FnData->FstParam));
    491       if (!Arg)
    492         return unknown();
    493 
    494       APInt MaxSize = Arg->getValue().zextOrSelf(IntTyBits);
    495       if (Size.ugt(MaxSize))
    496         Size = MaxSize + 1;
    497     }
    498     return std::make_pair(Size, Zero);
    499   }
    500 
    501   ConstantInt *Arg = dyn_cast<ConstantInt>(CS.getArgument(FnData->FstParam));
    502   if (!Arg)
    503     return unknown();
    504 
    505   APInt Size = Arg->getValue().zextOrSelf(IntTyBits);
    506   // size determined by just 1 parameter
    507   if (FnData->SndParam < 0)
    508     return std::make_pair(Size, Zero);
    509 
    510   Arg = dyn_cast<ConstantInt>(CS.getArgument(FnData->SndParam));
    511   if (!Arg)
    512     return unknown();
    513 
    514   Size *= Arg->getValue().zextOrSelf(IntTyBits);
    515   return std::make_pair(Size, Zero);
    516 
    517   // TODO: handle more standard functions (+ wchar cousins):
    518   // - strdup / strndup
    519   // - strcpy / strncpy
    520   // - strcat / strncat
    521   // - memcpy / memmove
    522   // - strcat / strncat
    523   // - memset
    524 }
    525 
    526 SizeOffsetType
    527 ObjectSizeOffsetVisitor::visitConstantPointerNull(ConstantPointerNull&) {
    528   return std::make_pair(Zero, Zero);
    529 }
    530 
    531 SizeOffsetType
    532 ObjectSizeOffsetVisitor::visitExtractElementInst(ExtractElementInst&) {
    533   return unknown();
    534 }
    535 
    536 SizeOffsetType
    537 ObjectSizeOffsetVisitor::visitExtractValueInst(ExtractValueInst&) {
    538   // Easy cases were already folded by previous passes.
    539   return unknown();
    540 }
    541 
    542 SizeOffsetType ObjectSizeOffsetVisitor::visitGEPOperator(GEPOperator &GEP) {
    543   SizeOffsetType PtrData = compute(GEP.getPointerOperand());
    544   APInt Offset(IntTyBits, 0);
    545   if (!bothKnown(PtrData) || !GEP.accumulateConstantOffset(*TD, Offset))
    546     return unknown();
    547 
    548   return std::make_pair(PtrData.first, PtrData.second + Offset);
    549 }
    550 
    551 SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalAlias(GlobalAlias &GA) {
    552   if (GA.mayBeOverridden())
    553     return unknown();
    554   return compute(GA.getAliasee());
    555 }
    556 
    557 SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalVariable(GlobalVariable &GV){
    558   if (!GV.hasDefinitiveInitializer())
    559     return unknown();
    560 
    561   APInt Size(IntTyBits, TD->getTypeAllocSize(GV.getType()->getElementType()));
    562   return std::make_pair(align(Size, GV.getAlignment()), Zero);
    563 }
    564 
    565 SizeOffsetType ObjectSizeOffsetVisitor::visitIntToPtrInst(IntToPtrInst&) {
    566   // clueless
    567   return unknown();
    568 }
    569 
    570 SizeOffsetType ObjectSizeOffsetVisitor::visitLoadInst(LoadInst&) {
    571   ++ObjectVisitorLoad;
    572   return unknown();
    573 }
    574 
    575 SizeOffsetType ObjectSizeOffsetVisitor::visitPHINode(PHINode &PHI) {
    576   if (PHI.getNumIncomingValues() == 0)
    577     return unknown();
    578 
    579   SizeOffsetType Ret = compute(PHI.getIncomingValue(0));
    580   if (!bothKnown(Ret))
    581     return unknown();
    582 
    583   // Verify that all PHI incoming pointers have the same size and offset.
    584   for (unsigned i = 1, e = PHI.getNumIncomingValues(); i != e; ++i) {
    585     SizeOffsetType EdgeData = compute(PHI.getIncomingValue(i));
    586     if (!bothKnown(EdgeData) || EdgeData != Ret)
    587       return unknown();
    588   }
    589   return Ret;
    590 }
    591 
    592 SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
    593   SizeOffsetType TrueSide  = compute(I.getTrueValue());
    594   SizeOffsetType FalseSide = compute(I.getFalseValue());
    595   if (bothKnown(TrueSide) && bothKnown(FalseSide) && TrueSide == FalseSide)
    596     return TrueSide;
    597   return unknown();
    598 }
    599 
    600 SizeOffsetType ObjectSizeOffsetVisitor::visitUndefValue(UndefValue&) {
    601   return std::make_pair(Zero, Zero);
    602 }
    603 
    604 SizeOffsetType ObjectSizeOffsetVisitor::visitInstruction(Instruction &I) {
    605   DEBUG(dbgs() << "ObjectSizeOffsetVisitor unknown instruction:" << I << '\n');
    606   return unknown();
    607 }
    608 
    609 
    610 ObjectSizeOffsetEvaluator::ObjectSizeOffsetEvaluator(const DataLayout *TD,
    611                                                    const TargetLibraryInfo *TLI,
    612                                                      LLVMContext &Context)
    613 : TD(TD), TLI(TLI), Context(Context), Builder(Context, TargetFolder(TD)) {
    614   IntTy = TD->getIntPtrType(Context);
    615   Zero = ConstantInt::get(IntTy, 0);
    616 }
    617 
    618 SizeOffsetEvalType ObjectSizeOffsetEvaluator::compute(Value *V) {
    619   SizeOffsetEvalType Result = compute_(V);
    620 
    621   if (!bothKnown(Result)) {
    622     // erase everything that was computed in this iteration from the cache, so
    623     // that no dangling references are left behind. We could be a bit smarter if
    624     // we kept a dependency graph. It's probably not worth the complexity.
    625     for (PtrSetTy::iterator I=SeenVals.begin(), E=SeenVals.end(); I != E; ++I) {
    626       CacheMapTy::iterator CacheIt = CacheMap.find(*I);
    627       // non-computable results can be safely cached
    628       if (CacheIt != CacheMap.end() && anyKnown(CacheIt->second))
    629         CacheMap.erase(CacheIt);
    630     }
    631   }
    632 
    633   SeenVals.clear();
    634   return Result;
    635 }
    636 
    637 SizeOffsetEvalType ObjectSizeOffsetEvaluator::compute_(Value *V) {
    638   ObjectSizeOffsetVisitor Visitor(TD, TLI, Context);
    639   SizeOffsetType Const = Visitor.compute(V);
    640   if (Visitor.bothKnown(Const))
    641     return std::make_pair(ConstantInt::get(Context, Const.first),
    642                           ConstantInt::get(Context, Const.second));
    643 
    644   V = V->stripPointerCasts();
    645 
    646   // check cache
    647   CacheMapTy::iterator CacheIt = CacheMap.find(V);
    648   if (CacheIt != CacheMap.end())
    649     return CacheIt->second;
    650 
    651   // always generate code immediately before the instruction being
    652   // processed, so that the generated code dominates the same BBs
    653   Instruction *PrevInsertPoint = Builder.GetInsertPoint();
    654   if (Instruction *I = dyn_cast<Instruction>(V))
    655     Builder.SetInsertPoint(I);
    656 
    657   // record the pointers that were handled in this run, so that they can be
    658   // cleaned later if something fails
    659   SeenVals.insert(V);
    660 
    661   // now compute the size and offset
    662   SizeOffsetEvalType Result;
    663   if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
    664     Result = visitGEPOperator(*GEP);
    665   } else if (Instruction *I = dyn_cast<Instruction>(V)) {
    666     Result = visit(*I);
    667   } else if (isa<Argument>(V) ||
    668              (isa<ConstantExpr>(V) &&
    669               cast<ConstantExpr>(V)->getOpcode() == Instruction::IntToPtr) ||
    670              isa<GlobalAlias>(V) ||
    671              isa<GlobalVariable>(V)) {
    672     // ignore values where we cannot do more than what ObjectSizeVisitor can
    673     Result = unknown();
    674   } else {
    675     DEBUG(dbgs() << "ObjectSizeOffsetEvaluator::compute() unhandled value: "
    676           << *V << '\n');
    677     Result = unknown();
    678   }
    679 
    680   if (PrevInsertPoint)
    681     Builder.SetInsertPoint(PrevInsertPoint);
    682 
    683   // Don't reuse CacheIt since it may be invalid at this point.
    684   CacheMap[V] = Result;
    685   return Result;
    686 }
    687 
    688 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitAllocaInst(AllocaInst &I) {
    689   if (!I.getAllocatedType()->isSized())
    690     return unknown();
    691 
    692   // must be a VLA
    693   assert(I.isArrayAllocation());
    694   Value *ArraySize = I.getArraySize();
    695   Value *Size = ConstantInt::get(ArraySize->getType(),
    696                                  TD->getTypeAllocSize(I.getAllocatedType()));
    697   Size = Builder.CreateMul(Size, ArraySize);
    698   return std::make_pair(Size, Zero);
    699 }
    700 
    701 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitCallSite(CallSite CS) {
    702   const AllocFnsTy *FnData = getAllocationData(CS.getInstruction(), AnyAlloc,
    703                                                TLI);
    704   if (!FnData)
    705     return unknown();
    706 
    707   // handle strdup-like functions separately
    708   if (FnData->AllocTy == StrDupLike) {
    709     // TODO
    710     return unknown();
    711   }
    712 
    713   Value *FirstArg = CS.getArgument(FnData->FstParam);
    714   FirstArg = Builder.CreateZExt(FirstArg, IntTy);
    715   if (FnData->SndParam < 0)
    716     return std::make_pair(FirstArg, Zero);
    717 
    718   Value *SecondArg = CS.getArgument(FnData->SndParam);
    719   SecondArg = Builder.CreateZExt(SecondArg, IntTy);
    720   Value *Size = Builder.CreateMul(FirstArg, SecondArg);
    721   return std::make_pair(Size, Zero);
    722 
    723   // TODO: handle more standard functions (+ wchar cousins):
    724   // - strdup / strndup
    725   // - strcpy / strncpy
    726   // - strcat / strncat
    727   // - memcpy / memmove
    728   // - strcat / strncat
    729   // - memset
    730 }
    731 
    732 SizeOffsetEvalType
    733 ObjectSizeOffsetEvaluator::visitExtractElementInst(ExtractElementInst&) {
    734   return unknown();
    735 }
    736 
    737 SizeOffsetEvalType
    738 ObjectSizeOffsetEvaluator::visitExtractValueInst(ExtractValueInst&) {
    739   return unknown();
    740 }
    741 
    742 SizeOffsetEvalType
    743 ObjectSizeOffsetEvaluator::visitGEPOperator(GEPOperator &GEP) {
    744   SizeOffsetEvalType PtrData = compute_(GEP.getPointerOperand());
    745   if (!bothKnown(PtrData))
    746     return unknown();
    747 
    748   Value *Offset = EmitGEPOffset(&Builder, *TD, &GEP, /*NoAssumptions=*/true);
    749   Offset = Builder.CreateAdd(PtrData.second, Offset);
    750   return std::make_pair(PtrData.first, Offset);
    751 }
    752 
    753 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitIntToPtrInst(IntToPtrInst&) {
    754   // clueless
    755   return unknown();
    756 }
    757 
    758 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitLoadInst(LoadInst&) {
    759   return unknown();
    760 }
    761 
    762 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitPHINode(PHINode &PHI) {
    763   // create 2 PHIs: one for size and another for offset
    764   PHINode *SizePHI   = Builder.CreatePHI(IntTy, PHI.getNumIncomingValues());
    765   PHINode *OffsetPHI = Builder.CreatePHI(IntTy, PHI.getNumIncomingValues());
    766 
    767   // insert right away in the cache to handle recursive PHIs
    768   CacheMap[&PHI] = std::make_pair(SizePHI, OffsetPHI);
    769 
    770   // compute offset/size for each PHI incoming pointer
    771   for (unsigned i = 0, e = PHI.getNumIncomingValues(); i != e; ++i) {
    772     Builder.SetInsertPoint(PHI.getIncomingBlock(i)->getFirstInsertionPt());
    773     SizeOffsetEvalType EdgeData = compute_(PHI.getIncomingValue(i));
    774 
    775     if (!bothKnown(EdgeData)) {
    776       OffsetPHI->replaceAllUsesWith(UndefValue::get(IntTy));
    777       OffsetPHI->eraseFromParent();
    778       SizePHI->replaceAllUsesWith(UndefValue::get(IntTy));
    779       SizePHI->eraseFromParent();
    780       return unknown();
    781     }
    782     SizePHI->addIncoming(EdgeData.first, PHI.getIncomingBlock(i));
    783     OffsetPHI->addIncoming(EdgeData.second, PHI.getIncomingBlock(i));
    784   }
    785 
    786   Value *Size = SizePHI, *Offset = OffsetPHI, *Tmp;
    787   if ((Tmp = SizePHI->hasConstantValue())) {
    788     Size = Tmp;
    789     SizePHI->replaceAllUsesWith(Size);
    790     SizePHI->eraseFromParent();
    791   }
    792   if ((Tmp = OffsetPHI->hasConstantValue())) {
    793     Offset = Tmp;
    794     OffsetPHI->replaceAllUsesWith(Offset);
    795     OffsetPHI->eraseFromParent();
    796   }
    797   return std::make_pair(Size, Offset);
    798 }
    799 
    800 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitSelectInst(SelectInst &I) {
    801   SizeOffsetEvalType TrueSide  = compute_(I.getTrueValue());
    802   SizeOffsetEvalType FalseSide = compute_(I.getFalseValue());
    803 
    804   if (!bothKnown(TrueSide) || !bothKnown(FalseSide))
    805     return unknown();
    806   if (TrueSide == FalseSide)
    807     return TrueSide;
    808 
    809   Value *Size = Builder.CreateSelect(I.getCondition(), TrueSide.first,
    810                                      FalseSide.first);
    811   Value *Offset = Builder.CreateSelect(I.getCondition(), TrueSide.second,
    812                                        FalseSide.second);
    813   return std::make_pair(Size, Offset);
    814 }
    815 
    816 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitInstruction(Instruction &I) {
    817   DEBUG(dbgs() << "ObjectSizeOffsetEvaluator unknown instruction:" << I <<'\n');
    818   return unknown();
    819 }
    820