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 /// extractMallocCall - Returns the corresponding CallInst if the instruction
 280 /// is a malloc call.  Since CallInst::CreateMalloc() only creates calls, we
 281 /// ignore InvokeInst here.
 282 const CallInst *llvm::extractMallocCall(const Value *I,
 283                                         const TargetLibraryInfo *TLI) {
 284   return isMallocLikeFn(I, TLI) ? dyn_cast<CallInst>(I) : nullptr;
 285 }
 286
 287 static Value *computeArraySize(const CallInst *CI, const DataLayout &DL,
 288                                const TargetLibraryInfo *TLI,
 289                                bool LookThroughSExt = false) {
 290   if (!CI)
 291     return nullptr;
 292
 293   // The size of the malloc's result type must be known to determine array size.
 294   Type *T = getMallocAllocatedType(CI, TLI);
 295   if (!T || !T->isSized())
 296     return nullptr;
 297
 298   unsigned ElementSize = DL.getTypeAllocSize(T);
 299   if (StructType *ST = dyn_cast<StructType>(T))
 300     ElementSize = DL.getStructLayout(ST)->getSizeInBytes();
 301
 302   // If malloc call's arg can be determined to be a multiple of ElementSize,
 303   // return the multiple.  Otherwise, return NULL.
 304   Value *MallocArg = CI->getArgOperand(0);
 305   Value *Multiple = nullptr;
 306   if (ComputeMultiple(MallocArg, ElementSize, Multiple, LookThroughSExt))
 307     return Multiple;
 308
 309   return nullptr;
 310 }
 311
 312 /// getMallocType - Returns the PointerType resulting from the malloc call.
 313 /// The PointerType depends on the number of bitcast uses of the malloc call:
 314 ///   0: PointerType is the calls' return type.
 315 ///   1: PointerType is the bitcast's result type.
 316 ///  >1: Unique PointerType cannot be determined, return NULL.
 317 PointerType *llvm::getMallocType(const CallInst *CI,
 318                                  const TargetLibraryInfo *TLI) {
 319   assert(isMallocLikeFn(CI, TLI) && "getMallocType and not malloc call");
 320
 321   PointerType *MallocType = nullptr;
 322   unsigned NumOfBitCastUses = 0;
 323
 324   // Determine if CallInst has a bitcast use.
 325   for (Value::const_user_iterator UI = CI->user_begin(), E = CI->user_end();
 326        UI != E;)
 327     if (const BitCastInst *BCI = dyn_cast<BitCastInst>(*UI++)) {
 328       MallocType = cast<PointerType>(BCI->getDestTy());
 329       NumOfBitCastUses++;
 330     }
 331
 332   // Malloc call has 1 bitcast use, so type is the bitcast's destination type.
 333   if (NumOfBitCastUses == 1)
 334     return MallocType;
 335
 336   // Malloc call was not bitcast, so type is the malloc function's return type.
 337   if (NumOfBitCastUses == 0)
 338     return cast<PointerType>(CI->getType());
 339
 340   // Type could not be determined.
 341   return nullptr;
 342 }
 343
 344 /// getMallocAllocatedType - Returns the Type allocated by malloc call.
 345 /// The Type depends on the number of bitcast uses of the malloc call:
 346 ///   0: PointerType is the malloc calls' return type.
 347 ///   1: PointerType is the bitcast's result type.
 348 ///  >1: Unique PointerType cannot be determined, return NULL.
 349 Type *llvm::getMallocAllocatedType(const CallInst *CI,
 350                                    const TargetLibraryInfo *TLI) {
 351   PointerType *PT = getMallocType(CI, TLI);
 352   return PT ? PT->getElementType() : nullptr;
 353 }
 354
 355 /// getMallocArraySize - Returns the array size of a malloc call.  If the
 356 /// argument passed to malloc is a multiple of the size of the malloced type,
 357 /// then return that multiple.  For non-array mallocs, the multiple is
 358 /// constant 1.  Otherwise, return NULL for mallocs whose array size cannot be
 359 /// determined.
 360 Value *llvm::getMallocArraySize(CallInst *CI, const DataLayout &DL,
 361                                 const TargetLibraryInfo *TLI,
 362                                 bool LookThroughSExt) {
 363   assert(isMallocLikeFn(CI, TLI) && "getMallocArraySize and not malloc call");
 364   return computeArraySize(CI, DL, TLI, LookThroughSExt);
 365 }
 366
 367 /// extractCallocCall - Returns the corresponding CallInst if the instruction
 368 /// is a calloc call.
 369 const CallInst *llvm::extractCallocCall(const Value *I,
 370                                         const TargetLibraryInfo *TLI) {
 371   return isCallocLikeFn(I, TLI) ? cast<CallInst>(I) : nullptr;
 372 }
 373
 374 /// isLibFreeFunction - Returns true if the function is a builtin free()
 375 bool llvm::isLibFreeFunction(const Function *F, const LibFunc TLIFn) {
 376   unsigned ExpectedNumParams;
 377   if (TLIFn == LibFunc_free ||
 378       TLIFn == LibFunc_ZdlPv || // operator delete(void*)
 379       TLIFn == LibFunc_ZdaPv || // operator delete[](void*)
 380       TLIFn == LibFunc_msvc_delete_ptr32 || // operator delete(void*)
 381       TLIFn == LibFunc_msvc_delete_ptr64 || // operator delete(void*)
 382       TLIFn == LibFunc_msvc_delete_array_ptr32 || // operator delete[](void*)
 383       TLIFn == LibFunc_msvc_delete_array_ptr64)   // operator delete[](void*)
 384     ExpectedNumParams = 1;
 385   else if (TLIFn == LibFunc_ZdlPvj ||              // delete(void*, uint)
 386            TLIFn == LibFunc_ZdlPvm ||              // delete(void*, ulong)
 387            TLIFn == LibFunc_ZdlPvRKSt9nothrow_t || // delete(void*, nothrow)
 388            TLIFn == LibFunc_ZdlPvSt11align_val_t || // delete(void*, align_val_t)
 389            TLIFn == LibFunc_ZdaPvj ||              // delete[](void*, uint)
 390            TLIFn == LibFunc_ZdaPvm ||              // delete[](void*, ulong)
 391            TLIFn == LibFunc_ZdaPvRKSt9nothrow_t || // delete[](void*, nothrow)
 392            TLIFn == LibFunc_ZdaPvSt11align_val_t || // delete[](void*, align_val_t)
 393            TLIFn == LibFunc_msvc_delete_ptr32_int ||      // delete(void*, uint)
 394            TLIFn == LibFunc_msvc_delete_ptr64_longlong || // delete(void*, ulonglong)
 395            TLIFn == LibFunc_msvc_delete_ptr32_nothrow || // delete(void*, nothrow)
 396            TLIFn == LibFunc_msvc_delete_ptr64_nothrow || // delete(void*, nothrow)
 397            TLIFn == LibFunc_msvc_delete_array_ptr32_int ||      // delete[](void*, uint)
 398            TLIFn == LibFunc_msvc_delete_array_ptr64_longlong || // delete[](void*, ulonglong)
 399            TLIFn == LibFunc_msvc_delete_array_ptr32_nothrow || // delete[](void*, nothrow)
 400            TLIFn == LibFunc_msvc_delete_array_ptr64_nothrow)   // delete[](void*, nothrow)
 401     ExpectedNumParams = 2;
 402   else if (TLIFn == LibFunc_ZdaPvSt11align_val_tRKSt9nothrow_t || // delete(void*, align_val_t, nothrow)
 403            TLIFn == LibFunc_ZdlPvSt11align_val_tRKSt9nothrow_t) // delete[](void*, align_val_t, nothrow)
 404     ExpectedNumParams = 3;
 405   else
 406     return false;
 407
 408   // Check free prototype.
 409   // FIXME: workaround for PR5130, this will be obsolete when a nobuiltin
 410   // attribute will exist.
 411   FunctionType *FTy = F->getFunctionType();
 412   if (!FTy->getReturnType()->isVoidTy())
 413     return false;
 414   if (FTy->getNumParams() != ExpectedNumParams)
 415     return false;
 416   if (FTy->getParamType(0) != Type::getInt8PtrTy(F->getContext()))
 417     return false;
 418
 419   return true;
 420 }
 421
 422 /// isFreeCall - Returns non-null if the value is a call to the builtin free()
 423 const CallInst *llvm::isFreeCall(const Value *I, const TargetLibraryInfo *TLI) {
 424   bool IsNoBuiltinCall;
 425   const Function *Callee =
 426       getCalledFunction(I, /*LookThroughBitCast=*/false, IsNoBuiltinCall);
 427   if (Callee == nullptr || IsNoBuiltinCall)
 428     return nullptr;
 429
 430   StringRef FnName = Callee->getName();
 431   LibFunc TLIFn;
 432   if (!TLI || !TLI->getLibFunc(FnName, TLIFn) || !TLI->has(TLIFn))
 433     return nullptr;
 434
 435   return isLibFreeFunction(Callee, TLIFn) ? dyn_cast<CallInst>(I) : nullptr;
 436 }
 437
 438
 439 //===----------------------------------------------------------------------===//
 440 //  Utility functions to compute size of objects.
 441 //
 442 static APInt getSizeWithOverflow(const SizeOffsetType &Data) {
 443   if (Data.second.isNegative() || Data.first.ult(Data.second))
 444     return APInt(Data.first.getBitWidth(), 0);
 445   return Data.first - Data.second;
 446 }
 447
 448 /// Compute the size of the object pointed by Ptr. Returns true and the
 449 /// object size in Size if successful, and false otherwise.
 450 /// If RoundToAlign is true, then Size is rounded up to the alignment of
 451 /// allocas, byval arguments, and global variables.
 452 bool llvm::getObjectSize(const Value *Ptr, uint64_t &Size, const DataLayout &DL,
 453                          const TargetLibraryInfo *TLI, ObjectSizeOpts Opts) {
 454   ObjectSizeOffsetVisitor Visitor(DL, TLI, Ptr->getContext(), Opts);
 455   SizeOffsetType Data = Visitor.compute(const_cast<Value*>(Ptr));
 456   if (!Visitor.bothKnown(Data))
 457     return false;
 458
 459   Size = getSizeWithOverflow(Data).getZExtValue();
 460   return true;
 461 }
 462
 463 Value *llvm::lowerObjectSizeCall(IntrinsicInst *ObjectSize,
 464                                  const DataLayout &DL,
 465                                  const TargetLibraryInfo *TLI,
 466                                  bool MustSucceed) {
 467   assert(ObjectSize->getIntrinsicID() == Intrinsic::objectsize &&
 468          "ObjectSize must be a call to llvm.objectsize!");
 469
 470   bool MaxVal = cast<ConstantInt>(ObjectSize->getArgOperand(1))->isZero();
 471   ObjectSizeOpts EvalOptions;
 472   // Unless we have to fold this to something, try to be as accurate as
 473   // possible.
 474   if (MustSucceed)
 475     EvalOptions.EvalMode =
 476         MaxVal ? ObjectSizeOpts::Mode::Max : ObjectSizeOpts::Mode::Min;
 477   else
 478     EvalOptions.EvalMode = ObjectSizeOpts::Mode::Exact;
 479
 480   EvalOptions.NullIsUnknownSize =
 481       cast<ConstantInt>(ObjectSize->getArgOperand(2))->isOne();
 482
 483   auto *ResultType = cast<IntegerType>(ObjectSize->getType());
 484   bool StaticOnly = cast<ConstantInt>(ObjectSize->getArgOperand(3))->isZero();
 485   if (StaticOnly) {
 486     // FIXME: Does it make sense to just return a failure value if the size won't
 487     // fit in the output and `!MustSucceed`?
 488     uint64_t Size;
 489     if (getObjectSize(ObjectSize->getArgOperand(0), Size, DL, TLI, EvalOptions) &&
 490         isUIntN(ResultType->getBitWidth(), Size))
 491       return ConstantInt::get(ResultType, Size);
 492   } else {
 493     LLVMContext &Ctx = ObjectSize->getFunction()->getContext();
 494     ObjectSizeOffsetEvaluator Eval(DL, TLI, Ctx, EvalOptions);
 495     SizeOffsetEvalType SizeOffsetPair =
 496         Eval.compute(ObjectSize->getArgOperand(0));
 497
 498     if (SizeOffsetPair != ObjectSizeOffsetEvaluator::unknown()) {
 499       IRBuilder<TargetFolder> Builder(Ctx, TargetFolder(DL));
 500       Builder.SetInsertPoint(ObjectSize);
 501
 502       // If we've outside the end of the object, then we can always access
 503       // exactly 0 bytes.
 504       Value *ResultSize =
 505           Builder.CreateSub(SizeOffsetPair.first, SizeOffsetPair.second);
 506       Value *UseZero =
 507           Builder.CreateICmpULT(SizeOffsetPair.first, SizeOffsetPair.second);
 508       return Builder.CreateSelect(UseZero, ConstantInt::get(ResultType, 0),
 509                                   ResultSize);
 510     }
 511   }
 512
 513   if (!MustSucceed)
 514     return nullptr;
 515
 516   return ConstantInt::get(ResultType, MaxVal ? -1ULL : 0);
 517 }
 518
 519 STATISTIC(ObjectVisitorArgument,
 520           "Number of arguments with unsolved size and offset");
 521 STATISTIC(ObjectVisitorLoad,
 522           "Number of load instructions with unsolved size and offset");
 523
 524 APInt ObjectSizeOffsetVisitor::align(APInt Size, uint64_t Align) {
 525   if (Options.RoundToAlign && Align)
 526     return APInt(IntTyBits, alignTo(Size.getZExtValue(), Align));
 527   return Size;
 528 }
 529
 530 ObjectSizeOffsetVisitor::ObjectSizeOffsetVisitor(const DataLayout &DL,
 531                                                  const TargetLibraryInfo *TLI,
 532                                                  LLVMContext &Context,
 533                                                  ObjectSizeOpts Options)
 534     : DL(DL), TLI(TLI), Options(Options) {
 535   // Pointer size must be rechecked for each object visited since it could have
 536   // a different address space.
 537 }
 538
 539 SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
 540   IntTyBits = DL.getPointerTypeSizeInBits(V->getType());
 541   Zero = APInt::getNullValue(IntTyBits);
 542
 543   V = V->stripPointerCasts();
 544   if (Instruction *I = dyn_cast<Instruction>(V)) {
 545     // If we have already seen this instruction, bail out. Cycles can happen in
 546     // unreachable code after constant propagation.
 547     if (!SeenInsts.insert(I).second)
 548       return unknown();
 549
 550     if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
 551       return visitGEPOperator(*GEP);
 552     return visit(*I);
 553   }
 554   if (Argument *A = dyn_cast<Argument>(V))
 555     return visitArgument(*A);
 556   if (ConstantPointerNull *P = dyn_cast<ConstantPointerNull>(V))
 557     return visitConstantPointerNull(*P);
 558   if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V))
 559     return visitGlobalAlias(*GA);
 560   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
 561     return visitGlobalVariable(*GV);
 562   if (UndefValue *UV = dyn_cast<UndefValue>(V))
 563     return visitUndefValue(*UV);
 564   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
 565     if (CE->getOpcode() == Instruction::IntToPtr)
 566       return unknown(); // clueless
 567     if (CE->getOpcode() == Instruction::GetElementPtr)
 568       return visitGEPOperator(cast<GEPOperator>(*CE));
 569   }
 570
 571   LLVM_DEBUG(dbgs() << "ObjectSizeOffsetVisitor::compute() unhandled value: "
 572                     << *V << '\n');
 573   return unknown();
 574 }
 575
 576 /// When we're compiling N-bit code, and the user uses parameters that are
 577 /// greater than N bits (e.g. uint64_t on a 32-bit build), we can run into
 578 /// trouble with APInt size issues. This function handles resizing + overflow
 579 /// checks for us. Check and zext or trunc \p I depending on IntTyBits and
 580 /// I's value.
 581 bool ObjectSizeOffsetVisitor::CheckedZextOrTrunc(APInt &I) {
 582   // More bits than we can handle. Checking the bit width isn't necessary, but
 583   // it's faster than checking active bits, and should give `false` in the
 584   // vast majority of cases.
 585   if (I.getBitWidth() > IntTyBits && I.getActiveBits() > IntTyBits)
 586     return false;
 587   if (I.getBitWidth() != IntTyBits)
 588     I = I.zextOrTrunc(IntTyBits);
 589   return true;
 590 }
 591
 592 SizeOffsetType ObjectSizeOffsetVisitor::visitAllocaInst(AllocaInst &I) {
 593   if (!I.getAllocatedType()->isSized())
 594     return unknown();
 595
 596   APInt Size(IntTyBits, DL.getTypeAllocSize(I.getAllocatedType()));
 597   if (!I.isArrayAllocation())
 598     return std::make_pair(align(Size, I.getAlignment()), Zero);
 599
 600   Value *ArraySize = I.getArraySize();
 601   if (const ConstantInt *C = dyn_cast<ConstantInt>(ArraySize)) {
 602     APInt NumElems = C->getValue();
 603     if (!CheckedZextOrTrunc(NumElems))
 604       return unknown();
 605
 606     bool Overflow;
 607     Size = Size.umul_ov(NumElems, Overflow);
 608     return Overflow ? unknown() : std::make_pair(align(Size, I.getAlignment()),
 609                                                  Zero);
 610   }
 611   return unknown();
 612 }
 613
 614 SizeOffsetType ObjectSizeOffsetVisitor::visitArgument(Argument &A) {
 615   // No interprocedural analysis is done at the moment.
 616   if (!A.hasByValOrInAllocaAttr()) {
 617     ++ObjectVisitorArgument;
 618     return unknown();
 619   }
 620   PointerType *PT = cast<PointerType>(A.getType());
 621   APInt Size(IntTyBits, DL.getTypeAllocSize(PT->getElementType()));
 622   return std::make_pair(align(Size, A.getParamAlignment()), Zero);
 623 }
 624
 625 SizeOffsetType ObjectSizeOffsetVisitor::visitCallSite(CallSite CS) {
 626   Optional<AllocFnsTy> FnData = getAllocationSize(CS.getInstruction(), TLI);
 627   if (!FnData)
 628     return unknown();
 629
 630   // Handle strdup-like functions separately.
 631   if (FnData->AllocTy == StrDupLike) {
 632     APInt Size(IntTyBits, GetStringLength(CS.getArgument(0)));
 633     if (!Size)
 634       return unknown();
 635
 636     // Strndup limits strlen.
 637     if (FnData->FstParam > 0) {
 638       ConstantInt *Arg =
 639           dyn_cast<ConstantInt>(CS.getArgument(FnData->FstParam));
 640       if (!Arg)
 641         return unknown();
 642
 643       APInt MaxSize = Arg->getValue().zextOrSelf(IntTyBits);
 644       if (Size.ugt(MaxSize))
 645         Size = MaxSize + 1;
 646     }
 647     return std::make_pair(Size, Zero);
 648   }
 649
 650   ConstantInt *Arg = dyn_cast<ConstantInt>(CS.getArgument(FnData->FstParam));
 651   if (!Arg)
 652     return unknown();
 653
 654   APInt Size = Arg->getValue();
 655   if (!CheckedZextOrTrunc(Size))
 656     return unknown();
 657
 658   // Size is determined by just 1 parameter.
 659   if (FnData->SndParam < 0)
 660     return std::make_pair(Size, Zero);
 661
 662   Arg = dyn_cast<ConstantInt>(CS.getArgument(FnData->SndParam));
 663   if (!Arg)
 664     return unknown();
 665
 666   APInt NumElems = Arg->getValue();
 667   if (!CheckedZextOrTrunc(NumElems))
 668     return unknown();
 669
 670   bool Overflow;
 671   Size = Size.umul_ov(NumElems, Overflow);
 672   return Overflow ? unknown() : std::make_pair(Size, Zero);
 673
 674   // TODO: handle more standard functions (+ wchar cousins):
 675   // - strdup / strndup
 676   // - strcpy / strncpy
 677   // - strcat / strncat
 678   // - memcpy / memmove
 679   // - strcat / strncat
 680   // - memset
 681 }
 682
 683 SizeOffsetType
 684 ObjectSizeOffsetVisitor::visitConstantPointerNull(ConstantPointerNull& CPN) {
 685   // If null is unknown, there's nothing we can do. Additionally, non-zero
 686   // address spaces can make use of null, so we don't presume to know anything
 687   // about that.
 688   //
 689   // TODO: How should this work with address space casts? We currently just drop
 690   // them on the floor, but it's unclear what we should do when a NULL from
 691   // addrspace(1) gets casted to addrspace(0) (or vice-versa).
 692   if (Options.NullIsUnknownSize || CPN.getType()->getAddressSpace())
 693     return unknown();
 694   return std::make_pair(Zero, Zero);
 695 }
 696
 697 SizeOffsetType
 698 ObjectSizeOffsetVisitor::visitExtractElementInst(ExtractElementInst&) {
 699   return unknown();
 700 }
 701
 702 SizeOffsetType
 703 ObjectSizeOffsetVisitor::visitExtractValueInst(ExtractValueInst&) {
 704   // Easy cases were already folded by previous passes.
 705   return unknown();
 706 }
 707
 708 SizeOffsetType ObjectSizeOffsetVisitor::visitGEPOperator(GEPOperator &GEP) {
 709   SizeOffsetType PtrData = compute(GEP.getPointerOperand());
 710   APInt Offset(IntTyBits, 0);
 711   if (!bothKnown(PtrData) || !GEP.accumulateConstantOffset(DL, Offset))
 712     return unknown();
 713
 714   return std::make_pair(PtrData.first, PtrData.second + Offset);
 715 }
 716
 717 SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalAlias(GlobalAlias &GA) {
 718   if (GA.isInterposable())
 719     return unknown();
 720   return compute(GA.getAliasee());
 721 }
 722
 723 SizeOffsetType ObjectSizeOffsetVisitor::visitGlobalVariable(GlobalVariable &GV){
 724   if (!GV.hasDefinitiveInitializer())
 725     return unknown();
 726
 727   APInt Size(IntTyBits, DL.getTypeAllocSize(GV.getValueType()));
 728   return std::make_pair(align(Size, GV.getAlignment()), Zero);
 729 }
 730
 731 SizeOffsetType ObjectSizeOffsetVisitor::visitIntToPtrInst(IntToPtrInst&) {
 732   // clueless
 733   return unknown();
 734 }
 735
 736 SizeOffsetType ObjectSizeOffsetVisitor::visitLoadInst(LoadInst&) {
 737   ++ObjectVisitorLoad;
 738   return unknown();
 739 }
 740
 741 SizeOffsetType ObjectSizeOffsetVisitor::visitPHINode(PHINode&) {
 742   // too complex to analyze statically.
 743   return unknown();
 744 }
 745
 746 SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
 747   SizeOffsetType TrueSide  = compute(I.getTrueValue());
 748   SizeOffsetType FalseSide = compute(I.getFalseValue());
 749   if (bothKnown(TrueSide) && bothKnown(FalseSide)) {
 750     if (TrueSide == FalseSide) {
 751         return TrueSide;
 752     }
 753
 754     APInt TrueResult = getSizeWithOverflow(TrueSide);
 755     APInt FalseResult = getSizeWithOverflow(FalseSide);
 756
 757     if (TrueResult == FalseResult) {
 758       return TrueSide;
 759     }
 760     if (Options.EvalMode == ObjectSizeOpts::Mode::Min) {
 761       if (TrueResult.slt(FalseResult))
 762         return TrueSide;
 763       return FalseSide;
 764     }
 765     if (Options.EvalMode == ObjectSizeOpts::Mode::Max) {
 766       if (TrueResult.sgt(FalseResult))
 767         return TrueSide;
 768       return FalseSide;
 769     }
 770   }
 771   return unknown();
 772 }
 773
 774 SizeOffsetType ObjectSizeOffsetVisitor::visitUndefValue(UndefValue&) {
 775   return std::make_pair(Zero, Zero);
 776 }
 777
 778 SizeOffsetType ObjectSizeOffsetVisitor::visitInstruction(Instruction &I) {
 779   LLVM_DEBUG(dbgs() << "ObjectSizeOffsetVisitor unknown instruction:" << I
 780                     << '\n');
 781   return unknown();
 782 }
 783
 784 ObjectSizeOffsetEvaluator::ObjectSizeOffsetEvaluator(
 785     const DataLayout &DL, const TargetLibraryInfo *TLI, LLVMContext &Context,
 786     ObjectSizeOpts EvalOpts)
 787     : DL(DL), TLI(TLI), Context(Context),
 788       Builder(Context, TargetFolder(DL),
 789               IRBuilderCallbackInserter(
 790                   [&](Instruction *I) { InsertedInstructions.insert(I); })),
 791       EvalOpts(EvalOpts) {
 792   // IntTy and Zero must be set for each compute() since the address space may
 793   // be different for later objects.
 794 }
 795
 796 SizeOffsetEvalType ObjectSizeOffsetEvaluator::compute(Value *V) {
 797   // XXX - Are vectors of pointers possible here?
 798   IntTy = cast<IntegerType>(DL.getIntPtrType(V->getType()));
 799   Zero = ConstantInt::get(IntTy, 0);
 800
 801   SizeOffsetEvalType Result = compute_(V);
 802
 803   if (!bothKnown(Result)) {
 804     // Erase everything that was computed in this iteration from the cache, so
 805     // that no dangling references are left behind. We could be a bit smarter if
 806     // we kept a dependency graph. It's probably not worth the complexity.
 807     for (const Value *SeenVal : SeenVals) {
 808       CacheMapTy::iterator CacheIt = CacheMap.find(SeenVal);
 809       // non-computable results can be safely cached
 810       if (CacheIt != CacheMap.end() && anyKnown(CacheIt->second))
 811         CacheMap.erase(CacheIt);
 812     }
 813
 814     // Erase any instructions we inserted as part of the traversal.
 815     for (Instruction *I : InsertedInstructions) {
 816       I->replaceAllUsesWith(UndefValue::get(I->getType()));
 817       I->eraseFromParent();
 818     }
 819   }
 820
 821   SeenVals.clear();
 822   InsertedInstructions.clear();
 823   return Result;
 824 }
 825
 826 SizeOffsetEvalType ObjectSizeOffsetEvaluator::compute_(Value *V) {
 827   ObjectSizeOffsetVisitor Visitor(DL, TLI, Context, EvalOpts);
 828   SizeOffsetType Const = Visitor.compute(V);
 829   if (Visitor.bothKnown(Const))
 830     return std::make_pair(ConstantInt::get(Context, Const.first),
 831                           ConstantInt::get(Context, Const.second));
 832
 833   V = V->stripPointerCasts();
 834
 835   // Check cache.
 836   CacheMapTy::iterator CacheIt = CacheMap.find(V);
 837   if (CacheIt != CacheMap.end())
 838     return CacheIt->second;
 839
 840   // Always generate code immediately before the instruction being
 841   // processed, so that the generated code dominates the same BBs.
 842   BuilderTy::InsertPointGuard Guard(Builder);
 843   if (Instruction *I = dyn_cast<Instruction>(V))
 844     Builder.SetInsertPoint(I);
 845
 846   // Now compute the size and offset.
 847   SizeOffsetEvalType Result;
 848
 849   // Record the pointers that were handled in this run, so that they can be
 850   // cleaned later if something fails. We also use this set to break cycles that
 851   // can occur in dead code.
 852   if (!SeenVals.insert(V).second) {
 853     Result = unknown();
 854   } else if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
 855     Result = visitGEPOperator(*GEP);
 856   } else if (Instruction *I = dyn_cast<Instruction>(V)) {
 857     Result = visit(*I);
 858   } else if (isa<Argument>(V) ||
 859              (isa<ConstantExpr>(V) &&
 860               cast<ConstantExpr>(V)->getOpcode() == Instruction::IntToPtr) ||
 861              isa<GlobalAlias>(V) ||
 862              isa<GlobalVariable>(V)) {
 863     // Ignore values where we cannot do more than ObjectSizeVisitor.
 864     Result = unknown();
 865   } else {
 866     LLVM_DEBUG(
 867         dbgs() << "ObjectSizeOffsetEvaluator::compute() unhandled value: " << *V
 868                << '\n');
 869     Result = unknown();
 870   }
 871
 872   // Don't reuse CacheIt since it may be invalid at this point.
 873   CacheMap[V] = Result;
 874   return Result;
 875 }
 876
 877 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitAllocaInst(AllocaInst &I) {
 878   if (!I.getAllocatedType()->isSized())
 879     return unknown();
 880
 881   // must be a VLA
 882   assert(I.isArrayAllocation());
 883   Value *ArraySize = I.getArraySize();
 884   Value *Size = ConstantInt::get(ArraySize->getType(),
 885                                  DL.getTypeAllocSize(I.getAllocatedType()));
 886   Size = Builder.CreateMul(Size, ArraySize);
 887   return std::make_pair(Size, Zero);
 888 }
 889
 890 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitCallSite(CallSite CS) {
 891   Optional<AllocFnsTy> FnData = getAllocationSize(CS.getInstruction(), TLI);
 892   if (!FnData)
 893     return unknown();
 894
 895   // Handle strdup-like functions separately.
 896   if (FnData->AllocTy == StrDupLike) {
 897     // TODO
 898     return unknown();
 899   }
 900
 901   Value *FirstArg = CS.getArgument(FnData->FstParam);
 902   FirstArg = Builder.CreateZExt(FirstArg, IntTy);
 903   if (FnData->SndParam < 0)
 904     return std::make_pair(FirstArg, Zero);
 905
 906   Value *SecondArg = CS.getArgument(FnData->SndParam);
 907   SecondArg = Builder.CreateZExt(SecondArg, IntTy);
 908   Value *Size = Builder.CreateMul(FirstArg, SecondArg);
 909   return std::make_pair(Size, Zero);
 910
 911   // TODO: handle more standard functions (+ wchar cousins):
 912   // - strdup / strndup
 913   // - strcpy / strncpy
 914   // - strcat / strncat
 915   // - memcpy / memmove
 916   // - strcat / strncat
 917   // - memset
 918 }
 919
 920 SizeOffsetEvalType
 921 ObjectSizeOffsetEvaluator::visitExtractElementInst(ExtractElementInst&) {
 922   return unknown();
 923 }
 924
 925 SizeOffsetEvalType
 926 ObjectSizeOffsetEvaluator::visitExtractValueInst(ExtractValueInst&) {
 927   return unknown();
 928 }
 929
 930 SizeOffsetEvalType
 931 ObjectSizeOffsetEvaluator::visitGEPOperator(GEPOperator &GEP) {
 932   SizeOffsetEvalType PtrData = compute_(GEP.getPointerOperand());
 933   if (!bothKnown(PtrData))
 934     return unknown();
 935
 936   Value *Offset = EmitGEPOffset(&Builder, DL, &GEP, /*NoAssumptions=*/true);
 937   Offset = Builder.CreateAdd(PtrData.second, Offset);
 938   return std::make_pair(PtrData.first, Offset);
 939 }
 940
 941 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitIntToPtrInst(IntToPtrInst&) {
 942   // clueless
 943   return unknown();
 944 }
 945
 946 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitLoadInst(LoadInst&) {
 947   return unknown();
 948 }
 949
 950 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitPHINode(PHINode &PHI) {
 951   // Create 2 PHIs: one for size and another for offset.
 952   PHINode *SizePHI   = Builder.CreatePHI(IntTy, PHI.getNumIncomingValues());
 953   PHINode *OffsetPHI = Builder.CreatePHI(IntTy, PHI.getNumIncomingValues());
 954
 955   // Insert right away in the cache to handle recursive PHIs.
 956   CacheMap[&PHI] = std::make_pair(SizePHI, OffsetPHI);
 957
 958   // Compute offset/size for each PHI incoming pointer.
 959   for (unsigned i = 0, e = PHI.getNumIncomingValues(); i != e; ++i) {
 960     Builder.SetInsertPoint(&*PHI.getIncomingBlock(i)->getFirstInsertionPt());
 961     SizeOffsetEvalType EdgeData = compute_(PHI.getIncomingValue(i));
 962
 963     if (!bothKnown(EdgeData)) {
 964       OffsetPHI->replaceAllUsesWith(UndefValue::get(IntTy));
 965       OffsetPHI->eraseFromParent();
 966       InsertedInstructions.erase(OffsetPHI);
 967       SizePHI->replaceAllUsesWith(UndefValue::get(IntTy));
 968       SizePHI->eraseFromParent();
 969       InsertedInstructions.erase(SizePHI);
 970       return unknown();
 971     }
 972     SizePHI->addIncoming(EdgeData.first, PHI.getIncomingBlock(i));
 973     OffsetPHI->addIncoming(EdgeData.second, PHI.getIncomingBlock(i));
 974   }
 975
 976   Value *Size = SizePHI, *Offset = OffsetPHI;
 977   if (Value *Tmp = SizePHI->hasConstantValue()) {
 978     Size = Tmp;
 979     SizePHI->replaceAllUsesWith(Size);
 980     SizePHI->eraseFromParent();
 981     InsertedInstructions.erase(SizePHI);
 982   }
 983   if (Value *Tmp = OffsetPHI->hasConstantValue()) {
 984     Offset = Tmp;
 985     OffsetPHI->replaceAllUsesWith(Offset);
 986     OffsetPHI->eraseFromParent();
 987     InsertedInstructions.erase(OffsetPHI);
 988   }
 989   return std::make_pair(Size, Offset);
 990 }
 991
 992 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitSelectInst(SelectInst &I) {
 993   SizeOffsetEvalType TrueSide  = compute_(I.getTrueValue());
 994   SizeOffsetEvalType FalseSide = compute_(I.getFalseValue());
 995
 996   if (!bothKnown(TrueSide) || !bothKnown(FalseSide))
 997     return unknown();
 998   if (TrueSide == FalseSide)
 999     return TrueSide;
1000
1001   Value *Size = Builder.CreateSelect(I.getCondition(), TrueSide.first,
1002                                      FalseSide.first);
1003   Value *Offset = Builder.CreateSelect(I.getCondition(), TrueSide.second,
1004                                        FalseSide.second);
1005   return std::make_pair(Size, Offset);
1006 }
1007
1008 SizeOffsetEvalType ObjectSizeOffsetEvaluator::visitInstruction(Instruction &I) {
1009   LLVM_DEBUG(dbgs() << "ObjectSizeOffsetEvaluator unknown instruction:" << I
1010                     << '\n');
1011   return unknown();
1012 }