lib/Analysis/MemoryBuiltins.cpp

   1 //===- MemoryBuiltins.cpp - Identify calls to memory builtins -------------===//
   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 // This family of functions identifies calls to builtin functions that allocate
  10 // or free memory.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Analysis/MemoryBuiltins.h"
  15 #include "llvm/ADT/APInt.h"
  16 #include "llvm/ADT/None.h"
  17 #include "llvm/ADT/Optional.h"
  18 #include "llvm/ADT/STLExtras.h"
  19 #include "llvm/ADT/Statistic.h"
  20 #include "llvm/ADT/StringRef.h"
  21 #include "llvm/Analysis/TargetFolder.h"
  22 #include "llvm/Analysis/TargetLibraryInfo.h"
  23 #include "llvm/Analysis/Utils/Local.h"
  24 #include "llvm/Analysis/ValueTracking.h"
  25 #include "llvm/IR/Argument.h"
  26 #include "llvm/IR/Attributes.h"
  27 #include "llvm/IR/Constants.h"
  28 #include "llvm/IR/DataLayout.h"
  29 #include "llvm/IR/DerivedTypes.h"
  30 #include "llvm/IR/Function.h"
  31 #include "llvm/IR/GlobalAlias.h"
  32 #include "llvm/IR/GlobalVariable.h"
  33 #include "llvm/IR/Instruction.h"
  34 #include "llvm/IR/Instructions.h"
  35 #include "llvm/IR/IntrinsicInst.h"
  36 #include "llvm/IR/Operator.h"
  37 #include "llvm/IR/Type.h"
  38 #include "llvm/IR/Value.h"
  39 #include "llvm/Support/Casting.h"
  40 #include "llvm/Support/Debug.h"
  41 #include "llvm/Support/MathExtras.h"
  42 #include "llvm/Support/raw_ostream.h"
  43 #include <cassert>
  44 #include <cstdint>
  45 #include <iterator>
  46 #include <utility>
  47
  48 using namespace llvm;
  49
  50 #define DEBUG_TYPE "memory-builtins"
  51
  52 enum AllocType : uint8_t {
  53   OpNewLike          = 1<<0, // allocates; never returns null
  54   MallocLike         = 1<<1 | OpNewLike, // allocates; may return null
  55   CallocLike         = 1<<2, // allocates + bzero
  56   ReallocLike        = 1<<3, // reallocates
  57   StrDupLike         = 1<<4,
  58   MallocOrCallocLike = MallocLike | CallocLike,
  59   AllocLike          = MallocLike | CallocLike | StrDupLike,
  60   AnyAlloc           = AllocLike | ReallocLike
  61 };
  62
  63 struct AllocFnsTy {
  64   AllocType AllocTy;
  65   unsigned NumParams;
  66   // First and Second size parameters (or -1 if unused)
  67   int FstParam, SndParam;
  68 };
  69
  70 // FIXME: certain users need more information. E.g., SimplifyLibCalls needs to
  71 // know which functions are nounwind, noalias, nocapture parameters, etc.
  72 static const std::pair<LibFunc, AllocFnsTy> AllocationFnData[] = {
  73   {LibFunc_malloc,              {MallocLike,  1, 0,  -1}},
  74   {LibFunc_valloc,              {MallocLike,  1, 0,  -1}},
  75   {LibFunc_Znwj,                {OpNewLike,   1, 0,  -1}}, // new(unsigned int)
  76   {LibFunc_ZnwjRKSt9nothrow_t,  {MallocLike,  2, 0,  -1}}, // new(unsigned int, nothrow)
  77   {LibFunc_ZnwjSt11align_val_t, {OpNewLike,   2, 0,  -1}}, // new(unsigned int, align_val_t)
  78   {LibFunc_ZnwjSt11align_val_tRKSt9nothrow_t, // new(unsigned int, align_val_t, nothrow)
  79                                 {MallocLike,  3, 0,  -1}},
  80   {LibFunc_Znwm,                {OpNewLike,   1, 0,  -1}}, // new(unsigned long)
  81   {LibFunc_ZnwmRKSt9nothrow_t,  {MallocLike,  2, 0,  -1}}, // new(unsigned long, nothrow)
  82   {LibFunc_ZnwmSt11align_val_t, {OpNewLike,   2, 0,  -1}}, // new(unsigned long, align_val_t)
  83   {LibFunc_ZnwmSt11align_val_tRKSt9nothrow_t, // new(unsigned long, align_val_t, nothrow)
  84                                 {MallocLike,  3, 0,  -1}},
  85   {LibFunc_Znaj,                {OpNewLike,   1, 0,  -1}}, // new[](unsigned int)
  86   {LibFunc_ZnajRKSt9nothrow_t,  {MallocLike,  2, 0,  -1}}, // new[](unsigned int, nothrow)
  87   {LibFunc_ZnajSt11align_val_t, {OpNewLike,   2, 0,  -1}}, // new[](unsigned int, align_val_t)
  88   {LibFunc_ZnajSt11align_val_tRKSt9nothrow_t, // new[](unsigned int, align_val_t, nothrow)
  89                                 {MallocLike,  3, 0,  -1}},
  90   {LibFunc_Znam,                {OpNewLike,   1, 0,  -1}}, // new[](unsigned long)
  91   {LibFunc_ZnamRKSt9nothrow_t,  {MallocLike,  2, 0,  -1}}, // new[](unsigned long, nothrow)
  92   {LibFunc_ZnamSt11align_val_t, {OpNewLike,   2, 0,  -1}}, // new[](unsigned long, align_val_t)
  93   {LibFunc_ZnamSt11align_val_tRKSt9nothrow_t, // new[](unsigned long, align_val_t, nothrow)
  94                                  {MallocLike,  3, 0,  -1}},
  95   {LibFunc_msvc_new_int,         {OpNewLike,   1, 0,  -1}}, // new(unsigned int)
  96   {LibFunc_msvc_new_int_nothrow, {MallocLike,  2, 0,  -1}}, // new(unsigned int, nothrow)
  97   {LibFunc_msvc_new_longlong,         {OpNewLike,   1, 0,  -1}}, // new(unsigned long long)
  98   {LibFunc_msvc_new_longlong_nothrow, {MallocLike,  2, 0,  -1}}, // new(unsigned long long, nothrow)
  99   {LibFunc_msvc_new_array_int,         {OpNewLike,   1, 0,  -1}}, // new[](unsigned int)
 100   {LibFunc_msvc_new_array_int_nothrow, {MallocLike,  2, 0,  -1}}, // new[](unsigned int, nothrow)
 101   {LibFunc_msvc_new_array_longlong,         {OpNewLike,   1, 0,  -1}}, // new[](unsigned long long)
 102   {LibFunc_msvc_new_array_longlong_nothrow, {MallocLike,  2, 0,  -1}}, // new[](unsigned long long, nothrow)
 103   {LibFunc_calloc,              {CallocLike,  2, 0,   1}},
 104   {LibFunc_realloc,             {ReallocLike, 2, 1,  -1}},
 105   {LibFunc_reallocf,            {ReallocLike, 2, 1,  -1}},
 106   {LibFunc_strdup,              {StrDupLike,  1, -1, -1}},
 107   {LibFunc_strndup,             {StrDupLike,  2, 1,  -1}}
 108   // TODO: Handle "int posix_memalign(void **, size_t, size_t)"
 109 };
 110
 111 static const Function *getCalledFunction(const Value *V, bool LookThroughBitCast,
 112                                          bool &IsNoBuiltin) {
 113   // Don't care about intrinsics in this case.
 114   if (isa<IntrinsicInst>(V))
 115     return nullptr;
 116
 117   if (LookThroughBitCast)
 118     V = V->stripPointerCasts();
 119
 120   ImmutableCallSite CS(V);
 121   if (!CS.getInstruction())
 122     return nullptr;
 123
 124   IsNoBuiltin = CS.isNoBuiltin();
 125
 126   if (const Function *Callee = CS.getCalledFunction())
 127     return Callee;
 128   return nullptr;
 129 }
 130
 131 /// Returns the allocation data for the given value if it's either a call to a
 132 /// known allocation function, or a call to a function with the allocsize
 133 /// attribute.
 134 static Optional<AllocFnsTy>
 135 getAllocationDataForFunction(const Function *Callee, AllocType AllocTy,
 136                              const TargetLibraryInfo *TLI) {
 137   // Make sure that the function is available.
 138   StringRef FnName = Callee->getName();
 139   LibFunc TLIFn;
 140   if (!TLI || !TLI->getLibFunc(FnName, TLIFn) || !TLI->has(TLIFn))
 141     return None;
 142
 143   const auto *Iter = find_if(
 144       AllocationFnData, [TLIFn](const std::pair<LibFunc, AllocFnsTy> &P) {
 145         return P.first == TLIFn;
 146       });
 147
 148   if (Iter == std::end(AllocationFnData))
 149     return None;
 150
 151   const AllocFnsTy *FnData = &Iter->second;
 152   if ((FnData->AllocTy & AllocTy) != FnData->AllocTy)
 153     return None;
 154
 155   // Check function prototype.
 156   int FstParam = FnData->FstParam;
 157   int SndParam = FnData->SndParam;
 158   FunctionType *FTy = Callee->getFunctionType();
 159
 160   if (FTy->getReturnType() == Type::getInt8PtrTy(FTy->getContext()) &&
 161       FTy->getNumParams() == FnData->NumParams &&
 162       (FstParam < 0 ||
 163        (FTy->getParamType(FstParam)->isIntegerTy(32) ||
 164         FTy->getParamType(FstParam)->isIntegerTy(64))) &&
 165       (SndParam < 0 ||
 166        FTy->getParamType(SndParam)->isIntegerTy(32) ||
 167        FTy->getParamType(SndParam)->isIntegerTy(64)))
 168     return *FnData;
 169   return None;
 170 }
 171
 172 static Optional<AllocFnsTy> getAllocationData(const Value *V, AllocType AllocTy,
 173                                               const TargetLibraryInfo *TLI,
 174                                               bool LookThroughBitCast = false) {
 175   bool IsNoBuiltinCall;
 176   if (const Function *Callee =
 177           getCalledFunction(V, LookThroughBitCast, IsNoBuiltinCall))
 178     if (!IsNoBuiltinCall)
 179       return getAllocationDataForFunction(Callee, AllocTy, TLI);
 180   return None;
 181 }
 182
 183 static Optional<AllocFnsTy> getAllocationSize(const Value *V,
 184                                               const TargetLibraryInfo *TLI) {
 185   bool IsNoBuiltinCall;
 186   const Function *Callee =
 187       getCalledFunction(V, /*LookThroughBitCast=*/false, IsNoBuiltinCall);
 188   if (!Callee)
 189     return None;
 190
 191   // Prefer to use existing information over allocsize. This will give us an
 192   // accurate AllocTy.
 193   if (!IsNoBuiltinCall)
 194     if (Optional<AllocFnsTy> Data =
 195             getAllocationDataForFunction(Callee, AnyAlloc, TLI))
 196       return Data;
 197
 198   Attribute Attr = Callee->getFnAttribute(Attribute::AllocSize);
 199   if (Attr == Attribute())
 200     return None;
 201
 202   std::pair<unsigned, Optional<unsigned>> Args = Attr.getAllocSizeArgs();
 203
 204   AllocFnsTy Result;
 205   // Because allocsize only tells us how many bytes are allocated, we're not
 206   // really allowed to assume anything, so we use MallocLike.
 207   Result.AllocTy = MallocLike;
 208   Result.NumParams = Callee->getNumOperands();
 209   Result.FstParam = Args.first;
 210   Result.SndParam = Args.second.getValueOr(-1);
 211   return Result;
 212 }
 213
 214 static bool hasNoAliasAttr(const Value *V, bool LookThroughBitCast) {
 215   ImmutableCallSite CS(LookThroughBitCast ? V->stripPointerCasts() : V);
 216   return CS && CS.hasRetAttr(Attribute::NoAlias);
 217 }
 218
 219 /// Tests if a value is a call or invoke to a library function that
 220 /// allocates or reallocates memory (either malloc, calloc, realloc, or strdup
 221 /// like).
 222 bool llvm::isAllocationFn(const Value *V, const TargetLibraryInfo *TLI,
 223                           bool LookThroughBitCast) {
 224   return getAllocationData(V, AnyAlloc, TLI, LookThroughBitCast).hasValue();
 225 }
 226
 227 /// Tests if a value is a call or invoke to a function that returns a
 228 /// NoAlias pointer (including malloc/calloc/realloc/strdup-like functions).
 229 bool llvm::isNoAliasFn(const Value *V, const TargetLibraryInfo *TLI,
 230                        bool LookThroughBitCast) {
 231   // it's safe to consider realloc as noalias since accessing the original
 232   // pointer is undefined behavior
 233   return isAllocationFn(V, TLI, LookThroughBitCast) ||
 234          hasNoAliasAttr(V, LookThroughBitCast);
 235 }
 236
 237 /// Tests if a value is a call or invoke to a library function that
 238 /// allocates uninitialized memory (such as malloc).
 239 bool llvm::isMallocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
 240                           bool LookThroughBitCast) {
 241   return getAllocationData(V, MallocLike, TLI, LookThroughBitCast).hasValue();
 242 }
 243
 244 /// Tests if a value is a call or invoke to a library function that
 245 /// allocates zero-filled memory (such as calloc).
 246 bool llvm::isCallocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
 247                           bool LookThroughBitCast) {
 248   return getAllocationData(V, CallocLike, TLI, LookThroughBitCast).hasValue();
 249 }
 250
 251 /// Tests if a value is a call or invoke to a library function that
 252 /// allocates memory similar to malloc or calloc.
 253 bool llvm::isMallocOrCallocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
 254                                   bool LookThroughBitCast) {
 255   return getAllocationData(V, MallocOrCallocLike, TLI,
 256                            LookThroughBitCast).hasValue();
 257 }
 258
 259 /// Tests if a value is a call or invoke to a library function that
 260 /// allocates memory (either malloc, calloc, or strdup like).
 261 bool llvm::isAllocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
 262                          bool LookThroughBitCast) {
 263   return getAllocationData(V, AllocLike, TLI, LookThroughBitCast).hasValue();
 264 }
 265
 266 /// Tests if a value is a call or invoke to a library function that
 267 /// reallocates memory (e.g., realloc).
 268 bool llvm::isReallocLikeFn(const Value *V, const TargetLibraryInfo *TLI,
 269                      bool LookThroughBitCast) {
 270   return getAllocationData(V, ReallocLike, TLI, LookThroughBitCast).hasValue();
 271 }
 272
 273 /// Tests if a functions is a call or invoke to a library function that
 274 /// reallocates memory (e.g., realloc).
 275 bool llvm::isReallocLikeFn(const Function *F, const TargetLibraryInfo *TLI) {
 276   return getAllocationDataForFunction(F, ReallocLike, TLI).hasValue();
 277 }
 278
 279 /// Tests if a value is a call or invoke to a library function that
 280 /// allocates memory and throws if an allocation failed (e.g., new).
 281 bool llvm::isOpNewLikeFn(const Value *V, const TargetLibraryInfo *TLI,
 282                      bool LookThroughBitCast) {
 283   return getAllocationData(V, OpNewLike, TLI, LookThroughBitCast).hasValue();
 284 }
 285
 286 /// extractMallocCall - Returns the corresponding CallInst if the instruction
 287 /// is a malloc call.  Since CallInst::CreateMalloc() only creates calls, we
 288 /// ignore InvokeInst here.
 289 const CallInst *llvm::extractMallocCall(const Value *I,
 290                                         const TargetLibraryInfo *TLI) {
 291   return isMallocLikeFn(I, TLI) ? dyn_cast<CallInst>(I) : nullptr;
 292 }
 293
 294 static Value *computeArraySize(const CallInst *CI, const DataLayout &DL,
 295                                const TargetLibraryInfo *TLI,
 296                                bool LookThroughSExt = false) {
 297   if (!CI)
 298     return nullptr;
 299
 300   // The size of the malloc's result type must be known to determine array size.
 301   Type *T = getMallocAllocatedType(CI, TLI);
 302   if (!T || !T->isSized())
 303     return nullptr;
 304
 305   unsigned ElementSize = DL.getTypeAllocSize(T);
 306   if (StructType *ST = dyn_cast<StructType>(T))
 307     ElementSize = DL.getStructLayout(ST)->getSizeInBytes();
 308
 309   // If malloc call's arg can be determined to be a multiple of ElementSize,
 310   // return the multiple.  Otherwise, return NULL.
 311   Value *MallocArg = CI->getArgOperand(0);
 312   Value *Multiple = nullptr;
 313   if (ComputeMultiple(MallocArg, ElementSize, Multiple, LookThroughSExt))
 314     return Multiple;
 315
 316   return nullptr;
 317 }
 318
 319 /// getMallocType - Returns the PointerType resulting from the malloc call.
 320 /// The PointerType depends on the number of bitcast uses of the malloc call:
 321 ///   0: PointerType is the calls' return type.
 322 ///   1: PointerType is the bitcast's result type.
 323 ///  >1: Unique PointerType cannot be determined, return NULL.
 324 PointerType *llvm::getMallocType(const CallInst *CI,
 325                                  const TargetLibraryInfo *TLI) {
 326   assert(isMallocLikeFn(CI, TLI) && "getMallocType and not malloc call");
 327
 328   PointerType *MallocType = nullptr;
 329   unsigned NumOfBitCastUses = 0;
 330
 331   // Determine if CallInst has a bitcast use.
 332   for (Value::const_user_iterator UI = CI->user_begin(), E = CI->user_end();
 333        UI != E;)
 334     if (const BitCastInst *BCI = dyn_cast<BitCastInst>(*UI++)) {
 335       MallocType = cast<PointerType>(BCI->getDestTy());
 336       NumOfBitCastUses++;
 337     }
 338
 339   // Malloc call has 1 bitcast use, so type is the bitcast's destination type.
 340   if (NumOfBitCastUses == 1)
 341     return MallocType;
 342
 343   // Malloc call was not bitcast, so type is the malloc function's return type.
 344   if (NumOfBitCastUses == 0)
 345     return cast<PointerType>(CI->getType());
 346
 347   // Type could not be determined.
 348   return nullptr;
 349 }
 350
 351 /// getMallocAllocatedType - Returns the Type allocated by malloc call.
 352 /// The Type depends on the number of bitcast uses of the malloc call:
 353 ///   0: PointerType is the malloc calls' return type.
 354 ///   1: PointerType is the bitcast's result type.
 355 ///  >1: Unique PointerType cannot be determined, return NULL.
 356 Type *llvm::getMallocAllocatedType(const CallInst *CI,
 357                                    const TargetLibraryInfo *TLI) {
 358   PointerType *PT = getMallocType(CI, TLI);
 359   return PT ? PT->getElementType() : nullptr;
 360 }
 361
 362 /// getMallocArraySize - Returns the array size of a malloc call.  If the
 363 /// argument passed to malloc is a multiple of the size of the malloced type,
 364 /// then return that multiple.  For non-array mallocs, the multiple is
 365 /// constant 1.  Otherwise, return NULL for mallocs whose array size cannot be
 366 /// determined.
 367 Value *llvm::getMallocArraySize(CallInst *CI, const DataLayout &DL,
 368                                 const TargetLibraryInfo *TLI,
 369                                 bool LookThroughSExt) {
 370   assert(isMallocLikeFn(CI, TLI) && "getMallocArraySize and not malloc call");
 371   return computeArraySize(CI, DL, TLI, LookThroughSExt);
 372 }
 373
 374 /// extractCallocCall - Returns the corresponding CallInst if the instruction
 375 /// is a calloc call.
 376 const CallInst *llvm::extractCallocCall(const Value *I,
 377                                         const TargetLibraryInfo *TLI) {
 378   return isCallocLikeFn(I, TLI) ? cast<CallInst>(I) : nullptr;
 379 }
 380
 381 /// isLibFreeFunction - Returns true if the function is a builtin free()
 382 bool llvm::isLibFreeFunction(const Function *F, const LibFunc TLIFn) {
 383   unsigned ExpectedNumParams;
 384   if (TLIFn == LibFunc_free ||
 385       TLIFn == LibFunc_ZdlPv || // operator delete(void*)
 386       TLIFn == LibFunc_ZdaPv || // operator delete[](void*)
 387       TLIFn == LibFunc_msvc_delete_ptr32 || // operator delete(void*)
 388       TLIFn == LibFunc_msvc_delete_ptr64 || // operator delete(void*)
 389       TLIFn == LibFunc_msvc_delete_array_ptr32 || // operator delete[](void*)
 390       TLIFn == LibFunc_msvc_delete_array_ptr64)   // operator delete[](void*)
 391     ExpectedNumParams = 1;
 392   else if (TLIFn == LibFunc_ZdlPvj ||              // delete(void*, uint)
 393            TLIFn == LibFunc_ZdlPvm ||              // delete(void*, ulong)
 394            TLIFn == LibFunc_ZdlPvRKSt9nothrow_t || // delete(void*, nothrow)
 395            TLIFn == LibFunc_ZdlPvSt11align_val_t || // delete(void*, align_val_t)
 396            TLIFn == LibFunc_ZdaPvj ||              // delete[](void*, uint)
 397            TLIFn == LibFunc_ZdaPvm ||              // delete[](void*, ulong)
 398            TLIFn == LibFunc_ZdaPvRKSt9nothrow_t || // delete[](void*, nothrow)
 399            TLIFn == LibFunc_ZdaPvSt11align_val_t || // delete[](void*, align_val_t)
 400            TLIFn == LibFunc_msvc_delete_ptr32_int ||      // delete(void*, uint)
 401            TLIFn == LibFunc_msvc_delete_ptr64_longlong || // delete(void*, ulonglong)
 402            TLIFn == LibFunc_msvc_delete_ptr32_nothrow || // delete(void*, nothrow)
 403            TLIFn == LibFunc_msvc_delete_ptr64_nothrow || // delete(void*, nothrow)
 404            TLIFn == LibFunc_msvc_delete_array_ptr32_int ||      // delete[](void*, uint)
 405            TLIFn == LibFunc_msvc_delete_array_ptr64_longlong || // delete[](void*, ulonglong)
 406            TLIFn == LibFunc_msvc_delete_array_ptr32_nothrow || // delete[](void*, nothrow)
 407            TLIFn == LibFunc_msvc_delete_array_ptr64_nothrow)   // delete[](void*, nothrow)
 408     ExpectedNumParams = 2;
 409   else if (TLIFn == LibFunc_ZdaPvSt11align_val_tRKSt9nothrow_t || // delete(void*, align_val_t, nothrow)
 410            TLIFn == LibFunc_ZdlPvSt11align_val_tRKSt9nothrow_t) // delete[](void*, align_val_t, nothrow)
 411     ExpectedNumParams = 3;
 412   else
 413     return false;
 414
 415   // Check free prototype.
 416   // FIXME: workaround for PR5130, this will be obsolete when a nobuiltin
 417   // attribute will exist.
 418   FunctionType *FTy = F->getFunctionType();
 419   if (!FTy->getReturnType()->isVoidTy())
 420     return false;
 421   if (FTy->getNumParams() != ExpectedNumParams)
 422     return false;
 423   if (FTy->getParamType(0) != Type::getInt8PtrTy(F->getContext()))
 424     return false;
 425
 426   return true;
 427 }
 428
 429 /// isFreeCall - Returns non-null if the value is a call to the builtin free()
 430 const CallInst *llvm::isFreeCall(const Value *I, const TargetLibraryInfo *TLI) {
 431   bool IsNoBuiltinCall;
 432   const Function *Callee =
 433       getCalledFunction(I, /*LookThroughBitCast=*/false, IsNoBuiltinCall);
 434   if (Callee == nullptr || IsNoBuiltinCall)
 435     return nullptr;
 436
 437   StringRef FnName = Callee->getName();
 438   LibFunc TLIFn;
 439   if (!TLI || !TLI->getLibFunc(FnName, TLIFn) || !TLI->has(TLIFn))
 440     return nullptr;
 441
 442   return isLibFreeFunction(Callee, TLIFn) ? dyn_cast<CallInst>(I) : nullptr;
 443 }
 444
 445
 446 //===----------------------------------------------------------------------===//
 447 //  Utility functions to compute size of objects.
 448 //
 449 static APInt getSizeWithOverflow(const SizeOffsetType &Data) {
 450   if (Data.second.isNegative() || Data.first.ult(Data.second))
 451     return APInt(Data.first.getBitWidth(), 0);
 452   return Data.first - Data.second;
 453 }
 454
 455 /// Compute the size of the object pointed by Ptr. Returns true and the
 456 /// object size in Size if successful, and false otherwise.
 457 /// If RoundToAlign is true, then Size is rounded up to the alignment of
 458 /// allocas, byval arguments, and global variables.
 459 bool llvm::getObjectSize(const Value *Ptr, uint64_t &Size, const DataLayout &DL,
 460                          const TargetLibraryInfo *TLI, ObjectSizeOpts Opts) {
 461   ObjectSizeOffsetVisitor Visitor(DL, TLI, Ptr->getContext(), Opts);
 462   SizeOffsetType Data = Visitor.compute(const_cast<Value*>(Ptr));
 463   if (!Visitor.bothKnown(Data))
 464     return false;
 465
 466   Size = getSizeWithOverflow(Data).getZExtValue();
 467   return true;
 468 }
 469
 470 Value *llvm::lowerObjectSizeCall(IntrinsicInst *ObjectSize,
 471                                  const DataLayout &DL,
 472                                  const TargetLibraryInfo *TLI,
 473                                  bool MustSucceed) {
 474   assert(ObjectSize->getIntrinsicID() == Intrinsic::objectsize &&
 475          "ObjectSize must be a call to llvm.objectsize!");
 476
 477   bool MaxVal = cast<ConstantInt>(ObjectSize->getArgOperand(1))->isZero();
 478   ObjectSizeOpts EvalOptions;
 479   // Unless we have to fold this to something, try to be as accurate as
 480   // possible.
 481   if (MustSucceed)
 482     EvalOptions.EvalMode =
 483         MaxVal ? ObjectSizeOpts::Mode::Max : ObjectSizeOpts::Mode::Min;
 484   else
 485     EvalOptions.EvalMode = ObjectSizeOpts::Mode::Exact;
 486
 487   EvalOptions.NullIsUnknownSize =
 488       cast<ConstantInt>(ObjectSize->getArgOperand(2))->isOne();
 489
 490   auto *ResultType = cast<IntegerType>(ObjectSize->getType());
 491   bool StaticOnly = cast<ConstantInt>(ObjectSize->getArgOperand(3))->isZero();
 492   if (StaticOnly) {
 493     // FIXME: Does it make sense to just return a failure value if the size won't
 494     // fit in the output and `!MustSucceed`?
 495     uint64_t Size;
 496     if (getObjectSize(ObjectSize->getArgOperand(0), Size, DL, TLI, EvalOptions) &&
 497         isUIntN(ResultType->getBitWidth(), Size))
 498       return ConstantInt::get(ResultType, Size);
 499   } else {
 500     LLVMContext &Ctx = ObjectSize->getFunction()->getContext();
 501     ObjectSizeOffsetEvaluator Eval(DL, TLI, Ctx, EvalOptions);
 502     SizeOffsetEvalType SizeOffsetPair =
 503         Eval.compute(ObjectSize->getArgOperand(0));
 504
 505     if (SizeOffsetPair != ObjectSizeOffsetEvaluator::unknown()) {
 506       IRBuilder<TargetFolder> Builder(Ctx, TargetFolder(DL));
 507       Builder.SetInsertPoint(ObjectSize);
 508
 509       // If we've outside the end of the object, then we can always access
 510       // exactly 0 bytes.
 511       Value *ResultSize =
 512           Builder.CreateSub(SizeOffsetPair.first, SizeOffsetPair.second);
 513       Value *UseZero =
 514           Builder.CreateICmpULT(SizeOffsetPair.first, SizeOffsetPair.second);
 515       return Builder.CreateSelect(UseZero, ConstantInt::get(ResultType, 0),
 516                                   ResultSize);
 517     }
 518   }
 519
 520   if (!MustSucceed)
 521     return nullptr;
 522
 523   return ConstantInt::get(ResultType, MaxVal ? -1ULL : 0);
 524 }
 525
 526 STATISTIC(ObjectVisitorArgument,
 527           "Number of arguments with unsolved size and offset");
 528 STATISTIC(ObjectVisitorLoad,
 529           "Number of load instructions with unsolved size and offset");
 530
 531 APInt ObjectSizeOffsetVisitor::align(APInt Size, uint64_t Align) {
 532   if (Options.RoundToAlign && Align)
 533     return APInt(IntTyBits, alignTo(Size.getZExtValue(), llvm::Align(Align)));
 534   return Size;
 535 }
 536
 537 ObjectSizeOffsetVisitor::ObjectSizeOffsetVisitor(const DataLayout &DL,
 538                                                  const TargetLibraryInfo *TLI,
 539                                                  LLVMContext &Context,
 540                                                  ObjectSizeOpts Options)
 541     : DL(DL), TLI(TLI), Options(Options) {
 542   // Pointer size must be rechecked for each object visited since it could have
 543   // a different address space.
 544 }
 545
 546 SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
 547   IntTyBits = DL.getPointerTypeSizeInBits(V->getType());
 548   Zero = APInt::getNullValue(IntTyBits);
 549
 550   V = V->stripPointerCasts();
 551   if (Instruction *I = dyn_cast<Instruction>(V)) {
 552     // If we have already seen this instruction, bail out. Cycles can happen in
 553     // unreachable code after constant propagation.
 554     if (!SeenInsts.insert(I).second)
 555       return unknown();
 556
 557     if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
 558       return visitGEPOperator(*GEP);
 559     return visit(*I);
 560   }
 561   if (Argument *A = dyn_cast<Argument>(V))
 562     return visitArgument(*A);
 563   if (ConstantPointerNull *P = dyn_cast<ConstantPointerNull>(V))
 564     return visitConstantPointerNull(*P);
 565   if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V))
 566     return visitGlobalAlias(*GA);
 567   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
 568     return visitGlobalVariable(*GV);
 569   if (UndefValue *UV = dyn_cast<UndefValue>(V))
 570     return visitUndefValue(*UV);
 571   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
 572     if (CE->getOpcode() == Instruction::IntToPtr)
 573       return unknown(); // clueless
 574     if (CE->getOpcode() == Instruction::GetElementPtr)
 575       return visitGEPOperator(cast<GEPOperator>(*CE));
 576   }
 577
 578   LLVM_DEBUG(dbgs() << "ObjectSizeOffsetVisitor::compute() unhandled value: "
 579                     << *V << '\n');
 580   return unknown();
 581 }
 582
 583 /// When we're compiling N-bit code, and the user uses parameters that are
 584 /// greater than N bits (e.g. uint64_t on a 32-bit build), we can run into
 585 /// trouble with APInt size issues. This function handles resizing + overflow
 586 /// checks for us. Check and zext or trunc \p I depending on IntTyBits and
 587 /// I's value.
 588 bool ObjectSizeOffsetVisitor::CheckedZextOrTrunc(APInt &I) {
 589   // More bits than we can handle. Checking the bit width isn't necessary, but
 590   // it's faster than checking active bits, and should give `false` in the
 591   // vast majority of cases.
 592   if (I.getBitWidth() > IntTyBits && I.getActiveBits() > IntTyBits)
 593     return false;
 594   if (I.getBitWidth() != IntTyBits)
 595     I = I.zextOrTrunc(IntTyBits);
 596   return true;
 597 }
 598
 599 SizeOffsetType ObjectSizeOffsetVisitor::visitAllocaInst(AllocaInst &I) {
 600   if (!I.getAllocatedType()->isSized())
 601     return unknown();
 602
 603   APInt Size(IntTyBits, DL.getTypeAllocSize(I.getAllocatedType()));
 604   if (!I.isArrayAllocation())
 605     return std::make_pair(align(Size, I.getAlignment()), Zero);
 606
 607   Value *ArraySize = I.getArraySize();
 608   if (const ConstantInt *C = dyn_cast<ConstantInt>(ArraySize)) {
 609     APInt NumElems = C->getValue();
 610     if (!CheckedZextOrTrunc(NumElems))
 611       return unknown();
 612
 613     bool Overflow;
 614     Size = Size.umul_ov(NumElems, Overflow);
 615     return Overflow ? unknown() : std::make_pair(align(Size, I.getAlignment()),
 616                                                  Zero);
 617   }
 618   return unknown();
 619 }
 620
 621 SizeOffsetType ObjectSizeOffsetVisitor::visitArgument(Argument &A) {
 622   // No interprocedural analysis is done at the moment.
 623   if (!A.hasByValOrInAllocaAttr()) {
 624     ++ObjectVisitorArgument;
 625     return unknown();
 626   }
 627   PointerType *PT = cast<PointerType>(A.getType());
 628   APInt Size(IntTyBits, DL.getTypeAllocSize(PT->getElementType()));
 629   return std::make_pair(align(Size, A.getParamAlignment()), Zero);
 630 }
 631
 632 SizeOffsetType ObjectSizeOffsetVisitor::visitCallSite(CallSite CS) {
 633   Optional<AllocFnsTy> FnData = getAllocationSize(CS.getInstruction(), TLI);
 634   if (!FnData)
 635     return unknown();
 636
 637   // Handle strdup-like functions separately.
 638   if (FnData->AllocTy == StrDupLike) {
 639     APInt Size(IntTyBits, GetStringLength(CS.getArgument(0)));
 640     if (!Size)
 641       return unknown();
 642
 643     // Strndup limits strlen.
 644     if (FnData->FstParam > 0) {
 645       ConstantInt *Arg =
 646           dyn_cast<ConstantInt>(CS.getArgument(FnData->FstParam));
 647       if (!Arg)
 648         return unknown();
 649
 650       APInt MaxSize = Arg->getValue().zextOrSelf(IntTyBits);
 651       if (Size.ugt(MaxSize))
 652         Size = MaxSize + 1;
 653     }
 654     return std::make_pair(Size, Zero);
 655   }
 656
 657   ConstantInt *Arg = dyn_cast<ConstantInt>(CS.getArgument(FnData->FstParam));
 658   if (!Arg)
 659     return unknown();
 660
 661   APInt Size = Arg->getValue();
 662   if (!CheckedZextOrTrunc(Size))
 663     return unknown();
 664
 665   // Size is determined by just 1 parameter.
 666   if (FnData->SndParam < 0)
 667     return std::make_pair(Size, Zero);
 668
 669   Arg = dyn_cast<ConstantInt>(CS.getArgument(FnData->SndParam));
 670   if (!Arg)
 671     return unknown();
 672
 673   APInt NumElems = Arg->getValue();
 674   if (!CheckedZextOrTrunc(NumElems))
 675     return unknown();
 676
 677   bool Overflow;
 678   Size = Size.umul_ov(NumElems, Overflow);
 679   return Overflow ? unknown() : std::make_pair(Size, Zero);
 680
 681   // TODO: handle more standard functions (+ wchar cousins):
 682   // - strdup / strndup
 683   // - strcpy / strncpy
 684   // - strcat / strncat
 685   // - memcpy / memmove
 686   // - strcat / strncat
 687   // - memset
 688 }
 689
 690 SizeOffsetType
 691 ObjectSizeOffsetVisitor::visitConstantPointerNull(ConstantPointerNull& CPN) {
 692   // If null is unknown, there's nothing we can do. Additionally, non-zero
 693   // address spaces can make use of null, so we don't presume to know anything
 694   // about that.
 695   //
 696   // TODO: How should this work with address space casts? We currently just drop
 697   // them on the floor, but it's unclear what we should do when a NULL from
 698   // addrspace(1) gets casted to addrspace(0) (or vice-versa).
 699   if (Options.NullIsUnknownSize || CPN.getType()->getAddressSpace())
 700     return unknown();
 701   return std::make_pair(Zero, Zero);
 702 }
 703
 704 SizeOffsetType
 705 ObjectSizeOffsetVisitor::visitExtractElementInst(ExtractElementInst&) {
 706   return unknown();
 707 }
 708
 709 SizeOffsetType
 710 ObjectSizeOffsetVisitor::visitExtractValueInst(ExtractValueInst&) {
 711   // Easy cases were already folded by previous passes.
 712   return unknown();
 713 }
 714
 715 SizeOffsetType ObjectSizeOffsetVisitor::visitGEPOperator(GEPOperator &GEP) {
 716   SizeOffsetType PtrData = compute(GEP.getPointerOperand());
 717   APInt Offset(IntTyBits, 0);
 718   if (!bothKnown(PtrData) || !GEP.accumulateConstantOffset(DL, Offset))
 719     return unknown();
 720
 721   return std::make_pair(PtrData.first, PtrData.second + Offset);
 722 }
 723
 724 SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalAlias(GlobalAlias &GA) {
 725   if (GA.isInterposable())
 726     return unknown();
 727   return compute(GA.getAliasee());
 728 }
 729
 730 SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalVariable(GlobalVariable &GV){
 731   if (!GV.hasDefinitiveInitializer())
 732     return unknown();
 733
 734   APInt Size(IntTyBits, DL.getTypeAllocSize(GV.getValueType()));
 735   return std::make_pair(align(Size, GV.getAlignment()), Zero);
 736 }
 737
 738 SizeOffsetType ObjectSizeOffsetVisitor::visitIntToPtrInst(IntToPtrInst&) {
 739   // clueless
 740   return unknown();
 741 }
 742
 743 SizeOffsetType ObjectSizeOffsetVisitor::visitLoadInst(LoadInst&) {
 744   ++ObjectVisitorLoad;
 745   return unknown();
 746 }
 747
 748 SizeOffsetType ObjectSizeOffsetVisitor::visitPHINode(PHINode&) {
 749   // too complex to analyze statically.
 750   return unknown();
 751 }
 752
 753 SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
 754   SizeOffsetType TrueSide  = compute(I.getTrueValue());
 755   SizeOffsetType FalseSide = compute(I.getFalseValue());
 756   if (bothKnown(TrueSide) && bothKnown(FalseSide)) {
 757     if (TrueSide == FalseSide) {
 758         return TrueSide;
 759     }
 760
 761     APInt TrueResult = getSizeWithOverflow(TrueSide);
 762     APInt FalseResult = getSizeWithOverflow(FalseSide);
 763
 764     if (TrueResult == FalseResult) {
 765       return TrueSide;
 766     }
 767     if (Options.EvalMode == ObjectSizeOpts::Mode::Min) {
 768       if (TrueResult.slt(FalseResult))
 769         return TrueSide;
 770       return FalseSide;
 771     }
 772     if (Options.EvalMode == ObjectSizeOpts::Mode::Max) {
 773       if (TrueResult.sgt(FalseResult))
 774         return TrueSide;
 775       return FalseSide;
 776     }
 777   }
 778   return unknown();
 779 }
 780
 781 SizeOffsetType ObjectSizeOffsetVisitor::visitUndefValue(UndefValue&) {
 782   return std::make_pair(Zero, Zero);
 783 }
 784
 785 SizeOffsetType ObjectSizeOffsetVisitor::visitInstruction(Instruction &I) {
 786   LLVM_DEBUG(dbgs() << "ObjectSizeOffsetVisitor unknown instruction:" << I
 787                     << '\n');
 788   return unknown();
 789 }
 790
 791 ObjectSizeOffsetEvaluator::ObjectSizeOffsetEvaluator(
 792     const DataLayout &DL, const TargetLibraryInfo *TLI, LLVMContext &Context,
 793     ObjectSizeOpts EvalOpts)
 794     : DL(DL), TLI(TLI), Context(Context),
 795       Builder(Context, TargetFolder(DL),
 796               IRBuilderCallbackInserter(
 797                   [&](Instruction *I) { InsertedInstructions.insert(I); })),
 798       EvalOpts(EvalOpts) {
 799   // IntTy and Zero must be set for each compute() since the address space may
 800   // be different for later objects.
 801 }
 802
 803 SizeOffsetEvalType ObjectSizeOffsetEvaluator::compute(Value *V) {
 804   // XXX - Are vectors of pointers possible here?
 805   IntTy = cast<IntegerType>(DL.getIntPtrType(V->getType()));
 806   Zero = ConstantInt::get(IntTy, 0);
 807
 808   SizeOffsetEvalType Result = compute_(V);
 809
 810   if (!bothKnown(Result)) {
 811     // Erase everything that was computed in this iteration from the cache, so
 812     // that no dangling references are left behind. We could be a bit smarter if
 813     // we kept a dependency graph. It's probably not worth the complexity.
 814     for (const Value *SeenVal : SeenVals) {
 815       CacheMapTy::iterator CacheIt = CacheMap.find(SeenVal);
 816       // non-computable results can be safely cached
 817       if (CacheIt != CacheMap.end() && anyKnown(CacheIt->second))
 818         CacheMap.erase(CacheIt);
 819     }
 820
 821     // Erase any instructions we inserted as part of the traversal.
 822     for (Instruction *I : InsertedInstructions) {
 823       I->replaceAllUsesWith(UndefValue::get(I->getType()));
 824       I->eraseFromParent();
 825     }
 826   }
 827
 828   SeenVals.clear();
 829   InsertedInstructions.clear();
 830   return Result;
 831 }
 832
 833 SizeOffsetEvalType ObjectSizeOffsetEvaluator::compute_(Value *V) {
 834   ObjectSizeOffsetVisitor Visitor(DL, TLI, Context, EvalOpts);
 835   SizeOffsetType Const = Visitor.compute(V);
 836   if (Visitor.bothKnown(Const))
 837     return std::make_pair(ConstantInt::get(Context, Const.first),
 838                           ConstantInt::get(Context, Const.second));
 839
 840   V = V->stripPointerCasts();
 841
 842   // Check cache.
 843   CacheMapTy::iterator CacheIt = CacheMap.find(V);
 844   if (CacheIt != CacheMap.end())
 845     return CacheIt->second;
 846
 847   // Always generate code immediately before the instruction being
 848   // processed, so that the generated code dominates the same BBs.
 849   BuilderTy::InsertPointGuard Guard(Builder);
 850   if (Instruction *I = dyn_cast<Instruction>(V))
 851     Builder.SetInsertPoint(I);
 852
 853   // Now compute the size and offset.
 854   SizeOffsetEvalType Result;
 855
 856   // Record the pointers that were handled in this run, so that they can be
 857   // cleaned later if something fails. We also use this set to break cycles that
 858   // can occur in dead code.
 859   if (!SeenVals.insert(V).second) {
 860     Result = unknown();
 861   } else if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
 862     Result = visitGEPOperator(*GEP);
 863   } else if (Instruction *I = dyn_cast<Instruction>(V)) {
 864     Result = visit(*I);
 865   } else if (isa<Argument>(V) ||
 866              (isa<ConstantExpr>(V) &&
 867               cast<ConstantExpr>(V)->getOpcode() == Instruction::IntToPtr) ||
 868              isa<GlobalAlias>(V) ||
 869              isa<GlobalVariable>(V)) {
 870     // Ignore values where we cannot do more than ObjectSizeVisitor.
 871     Result = unknown();
 872   } else {
 873     LLVM_DEBUG(
 874         dbgs() << "ObjectSizeOffsetEvaluator::compute() unhandled value: " << *V
 875                << '\n');
 876     Result = unknown();
 877   }
 878
 879   // Don't reuse CacheIt since it may be invalid at this point.
 880   CacheMap[V] = Result;
 881   return Result;
 882 }
 883
 884 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitAllocaInst(AllocaInst &I) {
 885   if (!I.getAllocatedType()->isSized())
 886     return unknown();
 887
 888   // must be a VLA
 889   assert(I.isArrayAllocation());
 890   Value *ArraySize = I.getArraySize();
 891   Value *Size = ConstantInt::get(ArraySize->getType(),
 892                                  DL.getTypeAllocSize(I.getAllocatedType()));
 893   Size = Builder.CreateMul(Size, ArraySize);
 894   return std::make_pair(Size, Zero);
 895 }
 896
 897 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitCallSite(CallSite CS) {
 898   Optional<AllocFnsTy> FnData = getAllocationSize(CS.getInstruction(), TLI);
 899   if (!FnData)
 900     return unknown();
 901
 902   // Handle strdup-like functions separately.
 903   if (FnData->AllocTy == StrDupLike) {
 904     // TODO
 905     return unknown();
 906   }
 907
 908   Value *FirstArg = CS.getArgument(FnData->FstParam);
 909   FirstArg = Builder.CreateZExt(FirstArg, IntTy);
 910   if (FnData->SndParam < 0)
 911     return std::make_pair(FirstArg, Zero);
 912
 913   Value *SecondArg = CS.getArgument(FnData->SndParam);
 914   SecondArg = Builder.CreateZExt(SecondArg, IntTy);
 915   Value *Size = Builder.CreateMul(FirstArg, SecondArg);
 916   return std::make_pair(Size, Zero);
 917
 918   // TODO: handle more standard functions (+ wchar cousins):
 919   // - strdup / strndup
 920   // - strcpy / strncpy
 921   // - strcat / strncat
 922   // - memcpy / memmove
 923   // - strcat / strncat
 924   // - memset
 925 }
 926
 927 SizeOffsetEvalType
 928 ObjectSizeOffsetEvaluator::visitExtractElementInst(ExtractElementInst&) {
 929   return unknown();
 930 }
 931
 932 SizeOffsetEvalType
 933 ObjectSizeOffsetEvaluator::visitExtractValueInst(ExtractValueInst&) {
 934   return unknown();
 935 }
 936
 937 SizeOffsetEvalType
 938 ObjectSizeOffsetEvaluator::visitGEPOperator(GEPOperator &GEP) {
 939   SizeOffsetEvalType PtrData = compute_(GEP.getPointerOperand());
 940   if (!bothKnown(PtrData))
 941     return unknown();
 942
 943   Value *Offset = EmitGEPOffset(&Builder, DL, &GEP, /*NoAssumptions=*/true);
 944   Offset = Builder.CreateAdd(PtrData.second, Offset);
 945   return std::make_pair(PtrData.first, Offset);
 946 }
 947
 948 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitIntToPtrInst(IntToPtrInst&) {
 949   // clueless
 950   return unknown();
 951 }
 952
 953 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitLoadInst(LoadInst&) {
 954   return unknown();
 955 }
 956
 957 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitPHINode(PHINode &PHI) {
 958   // Create 2 PHIs: one for size and another for offset.
 959   PHINode *SizePHI   = Builder.CreatePHI(IntTy, PHI.getNumIncomingValues());
 960   PHINode *OffsetPHI = Builder.CreatePHI(IntTy, PHI.getNumIncomingValues());
 961
 962   // Insert right away in the cache to handle recursive PHIs.
 963   CacheMap[&PHI] = std::make_pair(SizePHI, OffsetPHI);
 964
 965   // Compute offset/size for each PHI incoming pointer.
 966   for (unsigned i = 0, e = PHI.getNumIncomingValues(); i != e; ++i) {
 967     Builder.SetInsertPoint(&*PHI.getIncomingBlock(i)->getFirstInsertionPt());
 968     SizeOffsetEvalType EdgeData = compute_(PHI.getIncomingValue(i));
 969
 970     if (!bothKnown(EdgeData)) {
 971       OffsetPHI->replaceAllUsesWith(UndefValue::get(IntTy));
 972       OffsetPHI->eraseFromParent();
 973       InsertedInstructions.erase(OffsetPHI);
 974       SizePHI->replaceAllUsesWith(UndefValue::get(IntTy));
 975       SizePHI->eraseFromParent();
 976       InsertedInstructions.erase(SizePHI);
 977       return unknown();
 978     }
 979     SizePHI->addIncoming(EdgeData.first, PHI.getIncomingBlock(i));
 980     OffsetPHI->addIncoming(EdgeData.second, PHI.getIncomingBlock(i));
 981   }
 982
 983   Value *Size = SizePHI, *Offset = OffsetPHI;
 984   if (Value *Tmp = SizePHI->hasConstantValue()) {
 985     Size = Tmp;
 986     SizePHI->replaceAllUsesWith(Size);
 987     SizePHI->eraseFromParent();
 988     InsertedInstructions.erase(SizePHI);
 989   }
 990   if (Value *Tmp = OffsetPHI->hasConstantValue()) {
 991     Offset = Tmp;
 992     OffsetPHI->replaceAllUsesWith(Offset);
 993     OffsetPHI->eraseFromParent();
 994     InsertedInstructions.erase(OffsetPHI);
 995   }
 996   return std::make_pair(Size, Offset);
 997 }
 998
 999 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitSelectInst(SelectInst &I) {
1000   SizeOffsetEvalType TrueSide  = compute_(I.getTrueValue());
1001   SizeOffsetEvalType FalseSide = compute_(I.getFalseValue());
1002
1003   if (!bothKnown(TrueSide) || !bothKnown(FalseSide))
1004     return unknown();
1005   if (TrueSide == FalseSide)
1006     return TrueSide;
1007
1008   Value *Size = Builder.CreateSelect(I.getCondition(), TrueSide.first,
1009                                      FalseSide.first);
1010   Value *Offset = Builder.CreateSelect(I.getCondition(), TrueSide.second,
1011                                        FalseSide.second);
1012   return std::make_pair(Size, Offset);
1013 }
1014
1015 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitInstruction(Instruction &I) {
1016   LLVM_DEBUG(dbgs() << "ObjectSizeOffsetEvaluator unknown instruction:" << I
1017                     << '\n');
1018   return unknown();
1019 }