llvm/lib/IR/Value.cpp

   1 //===-- Value.cpp - Implement the Value class -----------------------------===//
   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 file implements the Value, ValueHandle, and User classes.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/IR/Value.h"
  14 #include "LLVMContextImpl.h"
  15 #include "llvm/ADT/DenseMap.h"
  16 #include "llvm/ADT/SetVector.h"
  17 #include "llvm/ADT/SmallString.h"
  18 #include "llvm/IR/Constant.h"
  19 #include "llvm/IR/Constants.h"
  20 #include "llvm/IR/DataLayout.h"
  21 #include "llvm/IR/DebugInfo.h"
  22 #include "llvm/IR/DerivedTypes.h"
  23 #include "llvm/IR/DerivedUser.h"
  24 #include "llvm/IR/GetElementPtrTypeIterator.h"
  25 #include "llvm/IR/InstrTypes.h"
  26 #include "llvm/IR/Instructions.h"
  27 #include "llvm/IR/IntrinsicInst.h"
  28 #include "llvm/IR/Module.h"
  29 #include "llvm/IR/Operator.h"
  30 #include "llvm/IR/ValueHandle.h"
  31 #include "llvm/IR/ValueSymbolTable.h"
  32 #include "llvm/Support/CommandLine.h"
  33 #include "llvm/Support/Debug.h"
  34 #include "llvm/Support/ErrorHandling.h"
  35 #include "llvm/Support/ManagedStatic.h"
  36 #include "llvm/Support/raw_ostream.h"
  37 #include <algorithm>
  38
  39 using namespace llvm;
  40
  41 static cl::opt<unsigned> UseDerefAtPointSemantics(
  42     "use-dereferenceable-at-point-semantics", cl::Hidden, cl::init(false),
  43     cl::desc("Deref attributes and metadata infer facts at definition only"));
  44
  45 //===----------------------------------------------------------------------===//
  46 //                                Value Class
  47 //===----------------------------------------------------------------------===//
  48 static inline Type *checkType(Type *Ty) {
  49   assert(Ty && "Value defined with a null type: Error!");
  50   return Ty;
  51 }
  52
  53 Value::Value(Type *ty, unsigned scid)
  54     : VTy(checkType(ty)), UseList(nullptr), SubclassID(scid), HasValueHandle(0),
  55       SubclassOptionalData(0), SubclassData(0), NumUserOperands(0),
  56       IsUsedByMD(false), HasName(false), HasMetadata(false) {
  57   static_assert(ConstantFirstVal == 0, "!(SubclassID < ConstantFirstVal)");
  58   // FIXME: Why isn't this in the subclass gunk??
  59   // Note, we cannot call isa<CallInst> before the CallInst has been
  60   // constructed.
  61   unsigned OpCode = 0;
  62   if (SubclassID >= InstructionVal)
  63     OpCode = SubclassID - InstructionVal;
  64   if (OpCode == Instruction::Call || OpCode == Instruction::Invoke ||
  65       OpCode == Instruction::CallBr)
  66     assert((VTy->isFirstClassType() || VTy->isVoidTy() || VTy->isStructTy()) &&
  67            "invalid CallBase type!");
  68   else if (SubclassID != BasicBlockVal &&
  69            (/*SubclassID < ConstantFirstVal ||*/ SubclassID > ConstantLastVal))
  70     assert((VTy->isFirstClassType() || VTy->isVoidTy()) &&
  71            "Cannot create non-first-class values except for constants!");
  72   static_assert(sizeof(Value) == 2 * sizeof(void *) + 2 * sizeof(unsigned),
  73                 "Value too big");
  74 }
  75
  76 Value::~Value() {
  77   // Notify all ValueHandles (if present) that this value is going away.
  78   if (HasValueHandle)
  79     ValueHandleBase::ValueIsDeleted(this);
  80   if (isUsedByMetadata())
  81     ValueAsMetadata::handleDeletion(this);
  82
  83   // Remove associated metadata from context.
  84   if (HasMetadata)
  85     clearMetadata();
  86
  87 #ifndef NDEBUG      // Only in -g mode...
  88   // Check to make sure that there are no uses of this value that are still
  89   // around when the value is destroyed.  If there are, then we have a dangling
  90   // reference and something is wrong.  This code is here to print out where
  91   // the value is still being referenced.
  92   //
  93   // Note that use_empty() cannot be called here, as it eventually downcasts
  94   // 'this' to GlobalValue (derived class of Value), but GlobalValue has already
  95   // been destructed, so accessing it is UB.
  96   //
  97   if (!materialized_use_empty()) {
  98     dbgs() << "While deleting: " << *VTy << " %" << getName() << "\n";
  99     for (auto *U : users())
 100       dbgs() << "Use still stuck around after Def is destroyed:" << *U << "\n";
 101   }
 102 #endif
 103   assert(materialized_use_empty() && "Uses remain when a value is destroyed!");
 104
 105   // If this value is named, destroy the name.  This should not be in a symtab
 106   // at this point.
 107   destroyValueName();
 108 }
 109
 110 void Value::deleteValue() {
 111   switch (getValueID()) {
 112 #define HANDLE_VALUE(Name)                                                     \
 113   case Value::Name##Val:                                                       \
 114     delete static_cast<Name *>(this);                                          \
 115     break;
 116 #define HANDLE_MEMORY_VALUE(Name)                                              \
 117   case Value::Name##Val:                                                       \
 118     static_cast<DerivedUser *>(this)->DeleteValue(                             \
 119         static_cast<DerivedUser *>(this));                                     \
 120     break;
 121 #define HANDLE_CONSTANT(Name)                                                  \
 122   case Value::Name##Val:                                                       \
 123     llvm_unreachable("constants should be destroyed with destroyConstant");    \
 124     break;
 125 #define HANDLE_INSTRUCTION(Name)  /* nothing */
 126 #include "llvm/IR/Value.def"
 127
 128 #define HANDLE_INST(N, OPC, CLASS)                                             \
 129   case Value::InstructionVal + Instruction::OPC:                               \
 130     delete static_cast<CLASS *>(this);                                         \
 131     break;
 132 #define HANDLE_USER_INST(N, OPC, CLASS)
 133 #include "llvm/IR/Instruction.def"
 134
 135   default:
 136     llvm_unreachable("attempting to delete unknown value kind");
 137   }
 138 }
 139
 140 void Value::destroyValueName() {
 141   ValueName *Name = getValueName();
 142   if (Name) {
 143     MallocAllocator Allocator;
 144     Name->Destroy(Allocator);
 145   }
 146   setValueName(nullptr);
 147 }
 148
 149 bool Value::hasNUses(unsigned N) const {
 150   return hasNItems(use_begin(), use_end(), N);
 151 }
 152
 153 bool Value::hasNUsesOrMore(unsigned N) const {
 154   return hasNItemsOrMore(use_begin(), use_end(), N);
 155 }
 156
 157 bool Value::hasOneUser() const {
 158   if (use_empty())
 159     return false;
 160   if (hasOneUse())
 161     return true;
 162   return std::equal(++user_begin(), user_end(), user_begin());
 163 }
 164
 165 static bool isUnDroppableUser(const User *U) { return !U->isDroppable(); }
 166
 167 Use *Value::getSingleUndroppableUse() {
 168   Use *Result = nullptr;
 169   for (Use &U : uses()) {
 170     if (!U.getUser()->isDroppable()) {
 171       if (Result)
 172         return nullptr;
 173       Result = &U;
 174     }
 175   }
 176   return Result;
 177 }
 178
 179 bool Value::hasNUndroppableUses(unsigned int N) const {
 180   return hasNItems(user_begin(), user_end(), N, isUnDroppableUser);
 181 }
 182
 183 bool Value::hasNUndroppableUsesOrMore(unsigned int N) const {
 184   return hasNItemsOrMore(user_begin(), user_end(), N, isUnDroppableUser);
 185 }
 186
 187 void Value::dropDroppableUses(
 188     llvm::function_ref<bool(const Use *)> ShouldDrop) {
 189   SmallVector<Use *, 8> ToBeEdited;
 190   for (Use &U : uses())
 191     if (U.getUser()->isDroppable() && ShouldDrop(&U))
 192       ToBeEdited.push_back(&U);
 193   for (Use *U : ToBeEdited)
 194     dropDroppableUse(*U);
 195 }
 196
 197 void Value::dropDroppableUsesIn(User &Usr) {
 198   assert(Usr.isDroppable() && "Expected a droppable user!");
 199   for (Use &UsrOp : Usr.operands()) {
 200     if (UsrOp.get() == this)
 201       dropDroppableUse(UsrOp);
 202   }
 203 }
 204
 205 void Value::dropDroppableUse(Use &U) {
 206   U.removeFromList();
 207   if (auto *Assume = dyn_cast<AssumeInst>(U.getUser())) {
 208     unsigned OpNo = U.getOperandNo();
 209     if (OpNo == 0)
 210       U.set(ConstantInt::getTrue(Assume->getContext()));
 211     else {
 212       U.set(UndefValue::get(U.get()->getType()));
 213       CallInst::BundleOpInfo &BOI = Assume->getBundleOpInfoForOperand(OpNo);
 214       BOI.Tag = Assume->getContext().pImpl->getOrInsertBundleTag("ignore");
 215     }
 216     return;
 217   }
 218
 219   llvm_unreachable("unkown droppable use");
 220 }
 221
 222 bool Value::isUsedInBasicBlock(const BasicBlock *BB) const {
 223   // This can be computed either by scanning the instructions in BB, or by
 224   // scanning the use list of this Value. Both lists can be very long, but
 225   // usually one is quite short.
 226   //
 227   // Scan both lists simultaneously until one is exhausted. This limits the
 228   // search to the shorter list.
 229   BasicBlock::const_iterator BI = BB->begin(), BE = BB->end();
 230   const_user_iterator UI = user_begin(), UE = user_end();
 231   for (; BI != BE && UI != UE; ++BI, ++UI) {
 232     // Scan basic block: Check if this Value is used by the instruction at BI.
 233     if (is_contained(BI->operands(), this))
 234       return true;
 235     // Scan use list: Check if the use at UI is in BB.
 236     const auto *User = dyn_cast<Instruction>(*UI);
 237     if (User && User->getParent() == BB)
 238       return true;
 239   }
 240   return false;
 241 }
 242
 243 unsigned Value::getNumUses() const {
 244   return (unsigned)std::distance(use_begin(), use_end());
 245 }
 246
 247 static bool getSymTab(Value *V, ValueSymbolTable *&ST) {
 248   ST = nullptr;
 249   if (Instruction *I = dyn_cast<Instruction>(V)) {
 250     if (BasicBlock *P = I->getParent())
 251       if (Function *PP = P->getParent())
 252         ST = PP->getValueSymbolTable();
 253   } else if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
 254     if (Function *P = BB->getParent())
 255       ST = P->getValueSymbolTable();
 256   } else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
 257     if (Module *P = GV->getParent())
 258       ST = &P->getValueSymbolTable();
 259   } else if (Argument *A = dyn_cast<Argument>(V)) {
 260     if (Function *P = A->getParent())
 261       ST = P->getValueSymbolTable();
 262   } else {
 263     assert(isa<Constant>(V) && "Unknown value type!");
 264     return true;  // no name is setable for this.
 265   }
 266   return false;
 267 }
 268
 269 ValueName *Value::getValueName() const {
 270   if (!HasName) return nullptr;
 271
 272   LLVMContext &Ctx = getContext();
 273   auto I = Ctx.pImpl->ValueNames.find(this);
 274   assert(I != Ctx.pImpl->ValueNames.end() &&
 275          "No name entry found!");
 276
 277   return I->second;
 278 }
 279
 280 void Value::setValueName(ValueName *VN) {
 281   LLVMContext &Ctx = getContext();
 282
 283   assert(HasName == Ctx.pImpl->ValueNames.count(this) &&
 284          "HasName bit out of sync!");
 285
 286   if (!VN) {
 287     if (HasName)
 288       Ctx.pImpl->ValueNames.erase(this);
 289     HasName = false;
 290     return;
 291   }
 292
 293   HasName = true;
 294   Ctx.pImpl->ValueNames[this] = VN;
 295 }
 296
 297 StringRef Value::getName() const {
 298   // Make sure the empty string is still a C string. For historical reasons,
 299   // some clients want to call .data() on the result and expect it to be null
 300   // terminated.
 301   if (!hasName())
 302     return StringRef("", 0);
 303   return getValueName()->getKey();
 304 }
 305
 306 void Value::setNameImpl(const Twine &NewName) {
 307   // Fast-path: LLVMContext can be set to strip out non-GlobalValue names
 308   if (getContext().shouldDiscardValueNames() && !isa<GlobalValue>(this))
 309     return;
 310
 311   // Fast path for common IRBuilder case of setName("") when there is no name.
 312   if (NewName.isTriviallyEmpty() && !hasName())
 313     return;
 314
 315   SmallString<256> NameData;
 316   StringRef NameRef = NewName.toStringRef(NameData);
 317   assert(NameRef.find_first_of(0) == StringRef::npos &&
 318          "Null bytes are not allowed in names");
 319
 320   // Name isn't changing?
 321   if (getName() == NameRef)
 322     return;
 323
 324   assert(!getType()->isVoidTy() && "Cannot assign a name to void values!");
 325
 326   // Get the symbol table to update for this object.
 327   ValueSymbolTable *ST;
 328   if (getSymTab(this, ST))
 329     return;  // Cannot set a name on this value (e.g. constant).
 330
 331   if (!ST) { // No symbol table to update?  Just do the change.
 332     if (NameRef.empty()) {
 333       // Free the name for this value.
 334       destroyValueName();
 335       return;
 336     }
 337
 338     // NOTE: Could optimize for the case the name is shrinking to not deallocate
 339     // then reallocated.
 340     destroyValueName();
 341
 342     // Create the new name.
 343     MallocAllocator Allocator;
 344     setValueName(ValueName::Create(NameRef, Allocator));
 345     getValueName()->setValue(this);
 346     return;
 347   }
 348
 349   // NOTE: Could optimize for the case the name is shrinking to not deallocate
 350   // then reallocated.
 351   if (hasName()) {
 352     // Remove old name.
 353     ST->removeValueName(getValueName());
 354     destroyValueName();
 355
 356     if (NameRef.empty())
 357       return;
 358   }
 359
 360   // Name is changing to something new.
 361   setValueName(ST->createValueName(NameRef, this));
 362 }
 363
 364 void Value::setName(const Twine &NewName) {
 365   setNameImpl(NewName);
 366   if (Function *F = dyn_cast<Function>(this))
 367     F->recalculateIntrinsicID();
 368 }
 369
 370 void Value::takeName(Value *V) {
 371   ValueSymbolTable *ST = nullptr;
 372   // If this value has a name, drop it.
 373   if (hasName()) {
 374     // Get the symtab this is in.
 375     if (getSymTab(this, ST)) {
 376       // We can't set a name on this value, but we need to clear V's name if
 377       // it has one.
 378       if (V->hasName()) V->setName("");
 379       return;  // Cannot set a name on this value (e.g. constant).
 380     }
 381
 382     // Remove old name.
 383     if (ST)
 384       ST->removeValueName(getValueName());
 385     destroyValueName();
 386   }
 387
 388   // Now we know that this has no name.
 389
 390   // If V has no name either, we're done.
 391   if (!V->hasName()) return;
 392
 393   // Get this's symtab if we didn't before.
 394   if (!ST) {
 395     if (getSymTab(this, ST)) {
 396       // Clear V's name.
 397       V->setName("");
 398       return;  // Cannot set a name on this value (e.g. constant).
 399     }
 400   }
 401
 402   // Get V's ST, this should always succed, because V has a name.
 403   ValueSymbolTable *VST;
 404   bool Failure = getSymTab(V, VST);
 405   assert(!Failure && "V has a name, so it should have a ST!"); (void)Failure;
 406
 407   // If these values are both in the same symtab, we can do this very fast.
 408   // This works even if both values have no symtab yet.
 409   if (ST == VST) {
 410     // Take the name!
 411     setValueName(V->getValueName());
 412     V->setValueName(nullptr);
 413     getValueName()->setValue(this);
 414     return;
 415   }
 416
 417   // Otherwise, things are slightly more complex.  Remove V's name from VST and
 418   // then reinsert it into ST.
 419
 420   if (VST)
 421     VST->removeValueName(V->getValueName());
 422   setValueName(V->getValueName());
 423   V->setValueName(nullptr);
 424   getValueName()->setValue(this);
 425
 426   if (ST)
 427     ST->reinsertValue(this);
 428 }
 429
 430 #ifndef NDEBUG
 431 std::string Value::getNameOrAsOperand() const {
 432   if (!getName().empty())
 433     return std::string(getName());
 434
 435   std::string BBName;
 436   raw_string_ostream OS(BBName);
 437   printAsOperand(OS, false);
 438   return OS.str();
 439 }
 440 #endif
 441
 442 void Value::assertModuleIsMaterializedImpl() const {
 443 #ifndef NDEBUG
 444   const GlobalValue *GV = dyn_cast<GlobalValue>(this);
 445   if (!GV)
 446     return;
 447   const Module *M = GV->getParent();
 448   if (!M)
 449     return;
 450   assert(M->isMaterialized());
 451 #endif
 452 }
 453
 454 #ifndef NDEBUG
 455 static bool contains(SmallPtrSetImpl<ConstantExpr *> &Cache, ConstantExpr *Expr,
 456                      Constant *C) {
 457   if (!Cache.insert(Expr).second)
 458     return false;
 459
 460   for (auto &O : Expr->operands()) {
 461     if (O == C)
 462       return true;
 463     auto *CE = dyn_cast<ConstantExpr>(O);
 464     if (!CE)
 465       continue;
 466     if (contains(Cache, CE, C))
 467       return true;
 468   }
 469   return false;
 470 }
 471
 472 static bool contains(Value *Expr, Value *V) {
 473   if (Expr == V)
 474     return true;
 475
 476   auto *C = dyn_cast<Constant>(V);
 477   if (!C)
 478     return false;
 479
 480   auto *CE = dyn_cast<ConstantExpr>(Expr);
 481   if (!CE)
 482     return false;
 483
 484   SmallPtrSet<ConstantExpr *, 4> Cache;
 485   return contains(Cache, CE, C);
 486 }
 487 #endif // NDEBUG
 488
 489 void Value::doRAUW(Value *New, ReplaceMetadataUses ReplaceMetaUses) {
 490   assert(New && "Value::replaceAllUsesWith(<null>) is invalid!");
 491   assert(!contains(New, this) &&
 492          "this->replaceAllUsesWith(expr(this)) is NOT valid!");
 493   assert(New->getType() == getType() &&
 494          "replaceAllUses of value with new value of different type!");
 495
 496   // Notify all ValueHandles (if present) that this value is going away.
 497   if (HasValueHandle)
 498     ValueHandleBase::ValueIsRAUWd(this, New);
 499   if (ReplaceMetaUses == ReplaceMetadataUses::Yes && isUsedByMetadata())
 500     ValueAsMetadata::handleRAUW(this, New);
 501
 502   while (!materialized_use_empty()) {
 503     Use &U = *UseList;
 504     // Must handle Constants specially, we cannot call replaceUsesOfWith on a
 505     // constant because they are uniqued.
 506     if (auto *C = dyn_cast<Constant>(U.getUser())) {
 507       if (!isa<GlobalValue>(C)) {
 508         C->handleOperandChange(this, New);
 509         continue;
 510       }
 511     }
 512
 513     U.set(New);
 514   }
 515
 516   if (BasicBlock *BB = dyn_cast<BasicBlock>(this))
 517     BB->replaceSuccessorsPhiUsesWith(cast<BasicBlock>(New));
 518 }
 519
 520 void Value::replaceAllUsesWith(Value *New) {
 521   doRAUW(New, ReplaceMetadataUses::Yes);
 522 }
 523
 524 void Value::replaceNonMetadataUsesWith(Value *New) {
 525   doRAUW(New, ReplaceMetadataUses::No);
 526 }
 527
 528 void Value::replaceUsesWithIf(Value *New,
 529                               llvm::function_ref<bool(Use &U)> ShouldReplace) {
 530   assert(New && "Value::replaceUsesWithIf(<null>) is invalid!");
 531   assert(New->getType() == getType() &&
 532          "replaceUses of value with new value of different type!");
 533
 534   SmallVector<TrackingVH<Constant>, 8> Consts;
 535   SmallPtrSet<Constant *, 8> Visited;
 536
 537   for (use_iterator UI = use_begin(), E = use_end(); UI != E;) {
 538     Use &U = *UI;
 539     ++UI;
 540     if (!ShouldReplace(U))
 541       continue;
 542     // Must handle Constants specially, we cannot call replaceUsesOfWith on a
 543     // constant because they are uniqued.
 544     if (auto *C = dyn_cast<Constant>(U.getUser())) {
 545       if (!isa<GlobalValue>(C)) {
 546         if (Visited.insert(C).second)
 547           Consts.push_back(TrackingVH<Constant>(C));
 548         continue;
 549       }
 550     }
 551     U.set(New);
 552   }
 553
 554   while (!Consts.empty()) {
 555     // FIXME: handleOperandChange() updates all the uses in a given Constant,
 556     //        not just the one passed to ShouldReplace
 557     Consts.pop_back_val()->handleOperandChange(this, New);
 558   }
 559 }
 560
 561 /// Replace llvm.dbg.* uses of MetadataAsValue(ValueAsMetadata(V)) outside BB
 562 /// with New.
 563 static void replaceDbgUsesOutsideBlock(Value *V, Value *New, BasicBlock *BB) {
 564   SmallVector<DbgVariableIntrinsic *> DbgUsers;
 565   findDbgUsers(DbgUsers, V);
 566   for (auto *DVI : DbgUsers) {
 567     if (DVI->getParent() != BB)
 568       DVI->replaceVariableLocationOp(V, New);
 569   }
 570 }
 571
 572 // Like replaceAllUsesWith except it does not handle constants or basic blocks.
 573 // This routine leaves uses within BB.
 574 void Value::replaceUsesOutsideBlock(Value *New, BasicBlock *BB) {
 575   assert(New && "Value::replaceUsesOutsideBlock(<null>, BB) is invalid!");
 576   assert(!contains(New, this) &&
 577          "this->replaceUsesOutsideBlock(expr(this), BB) is NOT valid!");
 578   assert(New->getType() == getType() &&
 579          "replaceUses of value with new value of different type!");
 580   assert(BB && "Basic block that may contain a use of 'New' must be defined\n");
 581
 582   replaceDbgUsesOutsideBlock(this, New, BB);
 583   replaceUsesWithIf(New, [BB](Use &U) {
 584     auto *I = dyn_cast<Instruction>(U.getUser());
 585     // Don't replace if it's an instruction in the BB basic block.
 586     return !I || I->getParent() != BB;
 587   });
 588 }
 589
 590 namespace {
 591 // Various metrics for how much to strip off of pointers.
 592 enum PointerStripKind {
 593   PSK_ZeroIndices,
 594   PSK_ZeroIndicesAndAliases,
 595   PSK_ZeroIndicesSameRepresentation,
 596   PSK_ForAliasAnalysis,
 597   PSK_InBoundsConstantIndices,
 598   PSK_InBounds
 599 };
 600
 601 template <PointerStripKind StripKind> static void NoopCallback(const Value *) {}
 602
 603 template <PointerStripKind StripKind>
 604 static const Value *stripPointerCastsAndOffsets(
 605     const Value *V,
 606     function_ref<void(const Value *)> Func = NoopCallback<StripKind>) {
 607   if (!V->getType()->isPointerTy())
 608     return V;
 609
 610   // Even though we don't look through PHI nodes, we could be called on an
 611   // instruction in an unreachable block, which may be on a cycle.
 612   SmallPtrSet<const Value *, 4> Visited;
 613
 614   Visited.insert(V);
 615   do {
 616     Func(V);
 617     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 618       switch (StripKind) {
 619       case PSK_ZeroIndices:
 620       case PSK_ZeroIndicesAndAliases:
 621       case PSK_ZeroIndicesSameRepresentation:
 622       case PSK_ForAliasAnalysis:
 623         if (!GEP->hasAllZeroIndices())
 624           return V;
 625         break;
 626       case PSK_InBoundsConstantIndices:
 627         if (!GEP->hasAllConstantIndices())
 628           return V;
 629         LLVM_FALLTHROUGH;
 630       case PSK_InBounds:
 631         if (!GEP->isInBounds())
 632           return V;
 633         break;
 634       }
 635       V = GEP->getPointerOperand();
 636     } else if (Operator::getOpcode(V) == Instruction::BitCast) {
 637       V = cast<Operator>(V)->getOperand(0);
 638       if (!V->getType()->isPointerTy())
 639         return V;
 640     } else if (StripKind != PSK_ZeroIndicesSameRepresentation &&
 641                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
 642       // TODO: If we know an address space cast will not change the
 643       //       representation we could look through it here as well.
 644       V = cast<Operator>(V)->getOperand(0);
 645     } else if (StripKind == PSK_ZeroIndicesAndAliases && isa<GlobalAlias>(V)) {
 646       V = cast<GlobalAlias>(V)->getAliasee();
 647     } else if (StripKind == PSK_ForAliasAnalysis && isa<PHINode>(V) &&
 648                cast<PHINode>(V)->getNumIncomingValues() == 1) {
 649       V = cast<PHINode>(V)->getIncomingValue(0);
 650     } else {
 651       if (const auto *Call = dyn_cast<CallBase>(V)) {
 652         if (const Value *RV = Call->getReturnedArgOperand()) {
 653           V = RV;
 654           continue;
 655         }
 656         // The result of launder.invariant.group must alias it's argument,
 657         // but it can't be marked with returned attribute, that's why it needs
 658         // special case.
 659         if (StripKind == PSK_ForAliasAnalysis &&
 660             (Call->getIntrinsicID() == Intrinsic::launder_invariant_group ||
 661              Call->getIntrinsicID() == Intrinsic::strip_invariant_group)) {
 662           V = Call->getArgOperand(0);
 663           continue;
 664         }
 665       }
 666       return V;
 667     }
 668     assert(V->getType()->isPointerTy() && "Unexpected operand type!");
 669   } while (Visited.insert(V).second);
 670
 671   return V;
 672 }
 673 } // end anonymous namespace
 674
 675 const Value *Value::stripPointerCasts() const {
 676   return stripPointerCastsAndOffsets<PSK_ZeroIndices>(this);
 677 }
 678
 679 const Value *Value::stripPointerCastsAndAliases() const {
 680   return stripPointerCastsAndOffsets<PSK_ZeroIndicesAndAliases>(this);
 681 }
 682
 683 const Value *Value::stripPointerCastsSameRepresentation() const {
 684   return stripPointerCastsAndOffsets<PSK_ZeroIndicesSameRepresentation>(this);
 685 }
 686
 687 const Value *Value::stripInBoundsConstantOffsets() const {
 688   return stripPointerCastsAndOffsets<PSK_InBoundsConstantIndices>(this);
 689 }
 690
 691 const Value *Value::stripPointerCastsForAliasAnalysis() const {
 692   return stripPointerCastsAndOffsets<PSK_ForAliasAnalysis>(this);
 693 }
 694
 695 const Value *Value::stripAndAccumulateConstantOffsets(
 696     const DataLayout &DL, APInt &Offset, bool AllowNonInbounds,
 697     function_ref<bool(Value &, APInt &)> ExternalAnalysis) const {
 698   if (!getType()->isPtrOrPtrVectorTy())
 699     return this;
 700
 701   unsigned BitWidth = Offset.getBitWidth();
 702   assert(BitWidth == DL.getIndexTypeSizeInBits(getType()) &&
 703          "The offset bit width does not match the DL specification.");
 704
 705   // Even though we don't look through PHI nodes, we could be called on an
 706   // instruction in an unreachable block, which may be on a cycle.
 707   SmallPtrSet<const Value *, 4> Visited;
 708   Visited.insert(this);
 709   const Value *V = this;
 710   do {
 711     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 712       // If in-bounds was requested, we do not strip non-in-bounds GEPs.
 713       if (!AllowNonInbounds && !GEP->isInBounds())
 714         return V;
 715
 716       // If one of the values we have visited is an addrspacecast, then
 717       // the pointer type of this GEP may be different from the type
 718       // of the Ptr parameter which was passed to this function.  This
 719       // means when we construct GEPOffset, we need to use the size
 720       // of GEP's pointer type rather than the size of the original
 721       // pointer type.
 722       APInt GEPOffset(DL.getIndexTypeSizeInBits(V->getType()), 0);
 723       if (!GEP->accumulateConstantOffset(DL, GEPOffset, ExternalAnalysis))
 724         return V;
 725
 726       // Stop traversal if the pointer offset wouldn't fit in the bit-width
 727       // provided by the Offset argument. This can happen due to AddrSpaceCast
 728       // stripping.
 729       if (GEPOffset.getMinSignedBits() > BitWidth)
 730         return V;
 731
 732       // External Analysis can return a result higher/lower than the value
 733       // represents. We need to detect overflow/underflow.
 734       APInt GEPOffsetST = GEPOffset.sextOrTrunc(BitWidth);
 735       if (!ExternalAnalysis) {
 736         Offset += GEPOffsetST;
 737       } else {
 738         bool Overflow = false;
 739         APInt OldOffset = Offset;
 740         Offset = Offset.sadd_ov(GEPOffsetST, Overflow);
 741         if (Overflow) {
 742           Offset = OldOffset;
 743           return V;
 744         }
 745       }
 746       V = GEP->getPointerOperand();
 747     } else if (Operator::getOpcode(V) == Instruction::BitCast ||
 748                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
 749       V = cast<Operator>(V)->getOperand(0);
 750     } else if (auto *GA = dyn_cast<GlobalAlias>(V)) {
 751       if (!GA->isInterposable())
 752         V = GA->getAliasee();
 753     } else if (const auto *Call = dyn_cast<CallBase>(V)) {
 754         if (const Value *RV = Call->getReturnedArgOperand())
 755           V = RV;
 756     }
 757     assert(V->getType()->isPtrOrPtrVectorTy() && "Unexpected operand type!");
 758   } while (Visited.insert(V).second);
 759
 760   return V;
 761 }
 762
 763 const Value *
 764 Value::stripInBoundsOffsets(function_ref<void(const Value *)> Func) const {
 765   return stripPointerCastsAndOffsets<PSK_InBounds>(this, Func);
 766 }
 767
 768 bool Value::canBeFreed() const {
 769   assert(getType()->isPointerTy());
 770
 771   // Cases that can simply never be deallocated
 772   // *) Constants aren't allocated per se, thus not deallocated either.
 773   if (isa<Constant>(this))
 774     return false;
 775
 776   // Handle byval/byref/sret/inalloca/preallocated arguments.  The storage
 777   // lifetime is guaranteed to be longer than the callee's lifetime.
 778   if (auto *A = dyn_cast<Argument>(this)) {
 779     if (A->hasPointeeInMemoryValueAttr())
 780       return false;
 781     // A pointer to an object in a function which neither frees, nor can arrange
 782     // for another thread to free on its behalf, can not be freed in the scope
 783     // of the function.  Note that this logic is restricted to memory
 784     // allocations in existance before the call; a nofree function *is* allowed
 785     // to free memory it allocated.
 786     const Function *F = A->getParent();
 787     if (F->doesNotFreeMemory() && F->hasNoSync())
 788       return false;
 789   }
 790
 791   const Function *F = nullptr;
 792   if (auto *I = dyn_cast<Instruction>(this))
 793     F = I->getFunction();
 794   if (auto *A = dyn_cast<Argument>(this))
 795     F = A->getParent();
 796
 797   if (!F)
 798     return true;
 799
 800   // With garbage collection, deallocation typically occurs solely at or after
 801   // safepoints.  If we're compiling for a collector which uses the
 802   // gc.statepoint infrastructure, safepoints aren't explicitly present
 803   // in the IR until after lowering from abstract to physical machine model.
 804   // The collector could chose to mix explicit deallocation and gc'd objects
 805   // which is why we need the explicit opt in on a per collector basis.
 806   if (!F->hasGC())
 807     return true;
 808
 809   const auto &GCName = F->getGC();
 810   if (GCName == "statepoint-example") {
 811     auto *PT = cast<PointerType>(this->getType());
 812     if (PT->getAddressSpace() != 1)
 813       // For the sake of this example GC, we arbitrarily pick addrspace(1) as
 814       // our GC managed heap.  This must match the same check in
 815       // RewriteStatepointsForGC (and probably needs better factored.)
 816       return true;
 817
 818     // It is cheaper to scan for a declaration than to scan for a use in this
 819     // function.  Note that gc.statepoint is a type overloaded function so the
 820     // usual trick of requesting declaration of the intrinsic from the module
 821     // doesn't work.
 822     for (auto &Fn : *F->getParent())
 823       if (Fn.getIntrinsicID() == Intrinsic::experimental_gc_statepoint)
 824         return true;
 825     return false;
 826   }
 827   return true;
 828 }
 829
 830 uint64_t Value::getPointerDereferenceableBytes(const DataLayout &DL,
 831                                                bool &CanBeNull,
 832                                                bool &CanBeFreed) const {
 833   assert(getType()->isPointerTy() && "must be pointer");
 834
 835   uint64_t DerefBytes = 0;
 836   CanBeNull = false;
 837   CanBeFreed = UseDerefAtPointSemantics && canBeFreed();
 838   if (const Argument *A = dyn_cast<Argument>(this)) {
 839     DerefBytes = A->getDereferenceableBytes();
 840     if (DerefBytes == 0) {
 841       // Handle byval/byref/inalloca/preallocated arguments
 842       if (Type *ArgMemTy = A->getPointeeInMemoryValueType()) {
 843         if (ArgMemTy->isSized()) {
 844           // FIXME: Why isn't this the type alloc size?
 845           DerefBytes = DL.getTypeStoreSize(ArgMemTy).getKnownMinSize();
 846         }
 847       }
 848     }
 849
 850     if (DerefBytes == 0) {
 851       DerefBytes = A->getDereferenceableOrNullBytes();
 852       CanBeNull = true;
 853     }
 854   } else if (const auto *Call = dyn_cast<CallBase>(this)) {
 855     DerefBytes = Call->getRetDereferenceableBytes();
 856     if (DerefBytes == 0) {
 857       DerefBytes = Call->getRetDereferenceableOrNullBytes();
 858       CanBeNull = true;
 859     }
 860   } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
 861     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) {
 862       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 863       DerefBytes = CI->getLimitedValue();
 864     }
 865     if (DerefBytes == 0) {
 866       if (MDNode *MD =
 867               LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
 868         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 869         DerefBytes = CI->getLimitedValue();
 870       }
 871       CanBeNull = true;
 872     }
 873   } else if (auto *IP = dyn_cast<IntToPtrInst>(this)) {
 874     if (MDNode *MD = IP->getMetadata(LLVMContext::MD_dereferenceable)) {
 875       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 876       DerefBytes = CI->getLimitedValue();
 877     }
 878     if (DerefBytes == 0) {
 879       if (MDNode *MD =
 880               IP->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
 881         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 882         DerefBytes = CI->getLimitedValue();
 883       }
 884       CanBeNull = true;
 885     }
 886   } else if (auto *AI = dyn_cast<AllocaInst>(this)) {
 887     if (!AI->isArrayAllocation()) {
 888       DerefBytes =
 889           DL.getTypeStoreSize(AI->getAllocatedType()).getKnownMinSize();
 890       CanBeNull = false;
 891       CanBeFreed = false;
 892     }
 893   } else if (auto *GV = dyn_cast<GlobalVariable>(this)) {
 894     if (GV->getValueType()->isSized() && !GV->hasExternalWeakLinkage()) {
 895       // TODO: Don't outright reject hasExternalWeakLinkage but set the
 896       // CanBeNull flag.
 897       DerefBytes = DL.getTypeStoreSize(GV->getValueType()).getFixedSize();
 898       CanBeNull = false;
 899       CanBeFreed = false;
 900     }
 901   }
 902   return DerefBytes;
 903 }
 904
 905 Align Value::getPointerAlignment(const DataLayout &DL) const {
 906   assert(getType()->isPointerTy() && "must be pointer");
 907   if (auto *GO = dyn_cast<GlobalObject>(this)) {
 908     if (isa<Function>(GO)) {
 909       Align FunctionPtrAlign = DL.getFunctionPtrAlign().valueOrOne();
 910       switch (DL.getFunctionPtrAlignType()) {
 911       case DataLayout::FunctionPtrAlignType::Independent:
 912         return FunctionPtrAlign;
 913       case DataLayout::FunctionPtrAlignType::MultipleOfFunctionAlign:
 914         return std::max(FunctionPtrAlign, GO->getAlign().valueOrOne());
 915       }
 916       llvm_unreachable("Unhandled FunctionPtrAlignType");
 917     }
 918     const MaybeAlign Alignment(GO->getAlignment());
 919     if (!Alignment) {
 920       if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
 921         Type *ObjectType = GVar->getValueType();
 922         if (ObjectType->isSized()) {
 923           // If the object is defined in the current Module, we'll be giving
 924           // it the preferred alignment. Otherwise, we have to assume that it
 925           // may only have the minimum ABI alignment.
 926           if (GVar->isStrongDefinitionForLinker())
 927             return DL.getPreferredAlign(GVar);
 928           else
 929             return DL.getABITypeAlign(ObjectType);
 930         }
 931       }
 932     }
 933     return Alignment.valueOrOne();
 934   } else if (const Argument *A = dyn_cast<Argument>(this)) {
 935     const MaybeAlign Alignment = A->getParamAlign();
 936     if (!Alignment && A->hasStructRetAttr()) {
 937       // An sret parameter has at least the ABI alignment of the return type.
 938       Type *EltTy = A->getParamStructRetType();
 939       if (EltTy->isSized())
 940         return DL.getABITypeAlign(EltTy);
 941     }
 942     return Alignment.valueOrOne();
 943   } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(this)) {
 944     return AI->getAlign();
 945   } else if (const auto *Call = dyn_cast<CallBase>(this)) {
 946     MaybeAlign Alignment = Call->getRetAlign();
 947     if (!Alignment && Call->getCalledFunction())
 948       Alignment = Call->getCalledFunction()->getAttributes().getRetAlignment();
 949     return Alignment.valueOrOne();
 950   } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
 951     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_align)) {
 952       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 953       return Align(CI->getLimitedValue());
 954     }
 955   } else if (auto *CstPtr = dyn_cast<Constant>(this)) {
 956     if (auto *CstInt = dyn_cast_or_null<ConstantInt>(ConstantExpr::getPtrToInt(
 957             const_cast<Constant *>(CstPtr), DL.getIntPtrType(getType()),
 958             /*OnlyIfReduced=*/true))) {
 959       size_t TrailingZeros = CstInt->getValue().countTrailingZeros();
 960       // While the actual alignment may be large, elsewhere we have
 961       // an arbitrary upper alignmet limit, so let's clamp to it.
 962       return Align(TrailingZeros < Value::MaxAlignmentExponent
 963                        ? uint64_t(1) << TrailingZeros
 964                        : Value::MaximumAlignment);
 965     }
 966   }
 967   return Align(1);
 968 }
 969
 970 const Value *Value::DoPHITranslation(const BasicBlock *CurBB,
 971                                      const BasicBlock *PredBB) const {
 972   auto *PN = dyn_cast<PHINode>(this);
 973   if (PN && PN->getParent() == CurBB)
 974     return PN->getIncomingValueForBlock(PredBB);
 975   return this;
 976 }
 977
 978 LLVMContext &Value::getContext() const { return VTy->getContext(); }
 979
 980 void Value::reverseUseList() {
 981   if (!UseList || !UseList->Next)
 982     // No need to reverse 0 or 1 uses.
 983     return;
 984
 985   Use *Head = UseList;
 986   Use *Current = UseList->Next;
 987   Head->Next = nullptr;
 988   while (Current) {
 989     Use *Next = Current->Next;
 990     Current->Next = Head;
 991     Head->Prev = &Current->Next;
 992     Head = Current;
 993     Current = Next;
 994   }
 995   UseList = Head;
 996   Head->Prev = &UseList;
 997 }
 998
 999 bool Value::isSwiftError() const {
1000   auto *Arg = dyn_cast<Argument>(this);
1001   if (Arg)
1002     return Arg->hasSwiftErrorAttr();
1003   auto *Alloca = dyn_cast<AllocaInst>(this);
1004   if (!Alloca)
1005     return false;
1006   return Alloca->isSwiftError();
1007 }
1008
1009 bool Value::isTransitiveUsedByMetadataOnly() const {
1010   if (use_empty())
1011     return false;
1012   llvm::SmallVector<const User *, 32> WorkList;
1013   llvm::SmallPtrSet<const User *, 32> Visited;
1014   WorkList.insert(WorkList.begin(), user_begin(), user_end());
1015   while (!WorkList.empty()) {
1016     const User *U = WorkList.back();
1017     WorkList.pop_back();
1018     Visited.insert(U);
1019     // If it is transitively used by a global value or a non-constant value,
1020     // it's obviously not only used by metadata.
1021     if (!isa<Constant>(U) || isa<GlobalValue>(U))
1022       return false;
1023     for (const User *UU : U->users())
1024       if (!Visited.count(UU))
1025         WorkList.push_back(UU);
1026   }
1027   return true;
1028 }
1029
1030 //===----------------------------------------------------------------------===//
1031 //                             ValueHandleBase Class
1032 //===----------------------------------------------------------------------===//
1033
1034 void ValueHandleBase::AddToExistingUseList(ValueHandleBase **List) {
1035   assert(List && "Handle list is null?");
1036
1037   // Splice ourselves into the list.
1038   Next = *List;
1039   *List = this;
1040   setPrevPtr(List);
1041   if (Next) {
1042     Next->setPrevPtr(&Next);
1043     assert(getValPtr() == Next->getValPtr() && "Added to wrong list?");
1044   }
1045 }
1046
1047 void ValueHandleBase::AddToExistingUseListAfter(ValueHandleBase *List) {
1048   assert(List && "Must insert after existing node");
1049
1050   Next = List->Next;
1051   setPrevPtr(&List->Next);
1052   List->Next = this;
1053   if (Next)
1054     Next->setPrevPtr(&Next);
1055 }
1056
1057 void ValueHandleBase::AddToUseList() {
1058   assert(getValPtr() && "Null pointer doesn't have a use list!");
1059
1060   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
1061
1062   if (getValPtr()->HasValueHandle) {
1063     // If this value already has a ValueHandle, then it must be in the
1064     // ValueHandles map already.
1065     ValueHandleBase *&Entry = pImpl->ValueHandles[getValPtr()];
1066     assert(Entry && "Value doesn't have any handles?");
1067     AddToExistingUseList(&Entry);
1068     return;
1069   }
1070
1071   // Ok, it doesn't have any handles yet, so we must insert it into the
1072   // DenseMap.  However, doing this insertion could cause the DenseMap to
1073   // reallocate itself, which would invalidate all of the PrevP pointers that
1074   // point into the old table.  Handle this by checking for reallocation and
1075   // updating the stale pointers only if needed.
1076   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
1077   const void *OldBucketPtr = Handles.getPointerIntoBucketsArray();
1078
1079   ValueHandleBase *&Entry = Handles[getValPtr()];
1080   assert(!Entry && "Value really did already have handles?");
1081   AddToExistingUseList(&Entry);
1082   getValPtr()->HasValueHandle = true;
1083
1084   // If reallocation didn't happen or if this was the first insertion, don't
1085   // walk the table.
1086   if (Handles.isPointerIntoBucketsArray(OldBucketPtr) ||
1087       Handles.size() == 1) {
1088     return;
1089   }
1090
1091   // Okay, reallocation did happen.  Fix the Prev Pointers.
1092   for (DenseMap<Value*, ValueHandleBase*>::iterator I = Handles.begin(),
1093        E = Handles.end(); I != E; ++I) {
1094     assert(I->second && I->first == I->second->getValPtr() &&
1095            "List invariant broken!");
1096     I->second->setPrevPtr(&I->second);
1097   }
1098 }
1099
1100 void ValueHandleBase::RemoveFromUseList() {
1101   assert(getValPtr() && getValPtr()->HasValueHandle &&
1102          "Pointer doesn't have a use list!");
1103
1104   // Unlink this from its use list.
1105   ValueHandleBase **PrevPtr = getPrevPtr();
1106   assert(*PrevPtr == this && "List invariant broken");
1107
1108   *PrevPtr = Next;
1109   if (Next) {
1110     assert(Next->getPrevPtr() == &Next && "List invariant broken");
1111     Next->setPrevPtr(PrevPtr);
1112     return;
1113   }
1114
1115   // If the Next pointer was null, then it is possible that this was the last
1116   // ValueHandle watching VP.  If so, delete its entry from the ValueHandles
1117   // map.
1118   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
1119   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
1120   if (Handles.isPointerIntoBucketsArray(PrevPtr)) {
1121     Handles.erase(getValPtr());
1122     getValPtr()->HasValueHandle = false;
1123   }
1124 }
1125
1126 void ValueHandleBase::ValueIsDeleted(Value *V) {
1127   assert(V->HasValueHandle && "Should only be called if ValueHandles present");
1128
1129   // Get the linked list base, which is guaranteed to exist since the
1130   // HasValueHandle flag is set.
1131   LLVMContextImpl *pImpl = V->getContext().pImpl;
1132   ValueHandleBase *Entry = pImpl->ValueHandles[V];
1133   assert(Entry && "Value bit set but no entries exist");
1134
1135   // We use a local ValueHandleBase as an iterator so that ValueHandles can add
1136   // and remove themselves from the list without breaking our iteration.  This
1137   // is not really an AssertingVH; we just have to give ValueHandleBase a kind.
1138   // Note that we deliberately do not the support the case when dropping a value
1139   // handle results in a new value handle being permanently added to the list
1140   // (as might occur in theory for CallbackVH's): the new value handle will not
1141   // be processed and the checking code will mete out righteous punishment if
1142   // the handle is still present once we have finished processing all the other
1143   // value handles (it is fine to momentarily add then remove a value handle).
1144   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
1145     Iterator.RemoveFromUseList();
1146     Iterator.AddToExistingUseListAfter(Entry);
1147     assert(Entry->Next == &Iterator && "Loop invariant broken.");
1148
1149     switch (Entry->getKind()) {
1150     case Assert:
1151       break;
1152     case Weak:
1153     case WeakTracking:
1154       // WeakTracking and Weak just go to null, which unlinks them
1155       // from the list.
1156       Entry->operator=(nullptr);
1157       break;
1158     case Callback:
1159       // Forward to the subclass's implementation.
1160       static_cast<CallbackVH*>(Entry)->deleted();
1161       break;
1162     }
1163   }
1164
1165   // All callbacks, weak references, and assertingVHs should be dropped by now.
1166   if (V->HasValueHandle) {
1167 #ifndef NDEBUG      // Only in +Asserts mode...
1168     dbgs() << "While deleting: " << *V->getType() << " %" << V->getName()
1169            << "\n";
1170     if (pImpl->ValueHandles[V]->getKind() == Assert)
1171       llvm_unreachable("An asserting value handle still pointed to this"
1172                        " value!");
1173
1174 #endif
1175     llvm_unreachable("All references to V were not removed?");
1176   }
1177 }
1178
1179 void ValueHandleBase::ValueIsRAUWd(Value *Old, Value *New) {
1180   assert(Old->HasValueHandle &&"Should only be called if ValueHandles present");
1181   assert(Old != New && "Changing value into itself!");
1182   assert(Old->getType() == New->getType() &&
1183          "replaceAllUses of value with new value of different type!");
1184
1185   // Get the linked list base, which is guaranteed to exist since the
1186   // HasValueHandle flag is set.
1187   LLVMContextImpl *pImpl = Old->getContext().pImpl;
1188   ValueHandleBase *Entry = pImpl->ValueHandles[Old];
1189
1190   assert(Entry && "Value bit set but no entries exist");
1191
1192   // We use a local ValueHandleBase as an iterator so that
1193   // ValueHandles can add and remove themselves from the list without
1194   // breaking our iteration.  This is not really an AssertingVH; we
1195   // just have to give ValueHandleBase some kind.
1196   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
1197     Iterator.RemoveFromUseList();
1198     Iterator.AddToExistingUseListAfter(Entry);
1199     assert(Entry->Next == &Iterator && "Loop invariant broken.");
1200
1201     switch (Entry->getKind()) {
1202     case Assert:
1203     case Weak:
1204       // Asserting and Weak handles do not follow RAUW implicitly.
1205       break;
1206     case WeakTracking:
1207       // Weak goes to the new value, which will unlink it from Old's list.
1208       Entry->operator=(New);
1209       break;
1210     case Callback:
1211       // Forward to the subclass's implementation.
1212       static_cast<CallbackVH*>(Entry)->allUsesReplacedWith(New);
1213       break;
1214     }
1215   }
1216
1217 #ifndef NDEBUG
1218   // If any new weak value handles were added while processing the
1219   // list, then complain about it now.
1220   if (Old->HasValueHandle)
1221     for (Entry = pImpl->ValueHandles[Old]; Entry; Entry = Entry->Next)
1222       switch (Entry->getKind()) {
1223       case WeakTracking:
1224         dbgs() << "After RAUW from " << *Old->getType() << " %"
1225                << Old->getName() << " to " << *New->getType() << " %"
1226                << New->getName() << "\n";
1227         llvm_unreachable(
1228             "A weak tracking value handle still pointed to the old value!\n");
1229       default:
1230         break;
1231       }
1232 #endif
1233 }
1234
1235 // Pin the vtable to this file.
1236 void CallbackVH::anchor() {}