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/SmallString.h"
  17 #include "llvm/IR/Constant.h"
  18 #include "llvm/IR/Constants.h"
  19 #include "llvm/IR/DataLayout.h"
  20 #include "llvm/IR/DebugInfo.h"
  21 #include "llvm/IR/DerivedTypes.h"
  22 #include "llvm/IR/DerivedUser.h"
  23 #include "llvm/IR/GetElementPtrTypeIterator.h"
  24 #include "llvm/IR/InstrTypes.h"
  25 #include "llvm/IR/Instructions.h"
  26 #include "llvm/IR/IntrinsicInst.h"
  27 #include "llvm/IR/Module.h"
  28 #include "llvm/IR/Operator.h"
  29 #include "llvm/IR/TypedPointerType.h"
  30 #include "llvm/IR/ValueHandle.h"
  31 #include "llvm/IR/ValueSymbolTable.h"
  32 #include "llvm/Support/CommandLine.h"
  33 #include "llvm/Support/ErrorHandling.h"
  34 #include "llvm/Support/raw_ostream.h"
  35 #include <algorithm>
  36
  37 using namespace llvm;
  38
  39 static cl::opt<unsigned> UseDerefAtPointSemantics(
  40     "use-dereferenceable-at-point-semantics", cl::Hidden, cl::init(false),
  41     cl::desc("Deref attributes and metadata infer facts at definition only"));
  42
  43 //===----------------------------------------------------------------------===//
  44 //                                Value Class
  45 //===----------------------------------------------------------------------===//
  46 static inline Type *checkType(Type *Ty) {
  47   assert(Ty && "Value defined with a null type: Error!");
  48   assert(!isa<TypedPointerType>(Ty->getScalarType()) &&
  49          "Cannot have values with typed pointer types");
  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 User *Value::getUniqueUndroppableUser() {
 180   User *Result = nullptr;
 181   for (auto *U : users()) {
 182     if (!U->isDroppable()) {
 183       if (Result && Result != U)
 184         return nullptr;
 185       Result = U;
 186     }
 187   }
 188   return Result;
 189 }
 190
 191 bool Value::hasNUndroppableUses(unsigned int N) const {
 192   return hasNItems(user_begin(), user_end(), N, isUnDroppableUser);
 193 }
 194
 195 bool Value::hasNUndroppableUsesOrMore(unsigned int N) const {
 196   return hasNItemsOrMore(user_begin(), user_end(), N, isUnDroppableUser);
 197 }
 198
 199 void Value::dropDroppableUses(
 200     llvm::function_ref<bool(const Use *)> ShouldDrop) {
 201   SmallVector<Use *, 8> ToBeEdited;
 202   for (Use &U : uses())
 203     if (U.getUser()->isDroppable() && ShouldDrop(&U))
 204       ToBeEdited.push_back(&U);
 205   for (Use *U : ToBeEdited)
 206     dropDroppableUse(*U);
 207 }
 208
 209 void Value::dropDroppableUsesIn(User &Usr) {
 210   assert(Usr.isDroppable() && "Expected a droppable user!");
 211   for (Use &UsrOp : Usr.operands()) {
 212     if (UsrOp.get() == this)
 213       dropDroppableUse(UsrOp);
 214   }
 215 }
 216
 217 void Value::dropDroppableUse(Use &U) {
 218   U.removeFromList();
 219   if (auto *Assume = dyn_cast<AssumeInst>(U.getUser())) {
 220     unsigned OpNo = U.getOperandNo();
 221     if (OpNo == 0)
 222       U.set(ConstantInt::getTrue(Assume->getContext()));
 223     else {
 224       U.set(UndefValue::get(U.get()->getType()));
 225       CallInst::BundleOpInfo &BOI = Assume->getBundleOpInfoForOperand(OpNo);
 226       BOI.Tag = Assume->getContext().pImpl->getOrInsertBundleTag("ignore");
 227     }
 228     return;
 229   }
 230
 231   llvm_unreachable("unkown droppable use");
 232 }
 233
 234 bool Value::isUsedInBasicBlock(const BasicBlock *BB) const {
 235   // This can be computed either by scanning the instructions in BB, or by
 236   // scanning the use list of this Value. Both lists can be very long, but
 237   // usually one is quite short.
 238   //
 239   // Scan both lists simultaneously until one is exhausted. This limits the
 240   // search to the shorter list.
 241   BasicBlock::const_iterator BI = BB->begin(), BE = BB->end();
 242   const_user_iterator UI = user_begin(), UE = user_end();
 243   for (; BI != BE && UI != UE; ++BI, ++UI) {
 244     // Scan basic block: Check if this Value is used by the instruction at BI.
 245     if (is_contained(BI->operands(), this))
 246       return true;
 247     // Scan use list: Check if the use at UI is in BB.
 248     const auto *User = dyn_cast<Instruction>(*UI);
 249     if (User && User->getParent() == BB)
 250       return true;
 251   }
 252   return false;
 253 }
 254
 255 unsigned Value::getNumUses() const {
 256   return (unsigned)std::distance(use_begin(), use_end());
 257 }
 258
 259 static bool getSymTab(Value *V, ValueSymbolTable *&ST) {
 260   ST = nullptr;
 261   if (Instruction *I = dyn_cast<Instruction>(V)) {
 262     if (BasicBlock *P = I->getParent())
 263       if (Function *PP = P->getParent())
 264         ST = PP->getValueSymbolTable();
 265   } else if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
 266     if (Function *P = BB->getParent())
 267       ST = P->getValueSymbolTable();
 268   } else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
 269     if (Module *P = GV->getParent())
 270       ST = &P->getValueSymbolTable();
 271   } else if (Argument *A = dyn_cast<Argument>(V)) {
 272     if (Function *P = A->getParent())
 273       ST = P->getValueSymbolTable();
 274   } else {
 275     assert(isa<Constant>(V) && "Unknown value type!");
 276     return true;  // no name is setable for this.
 277   }
 278   return false;
 279 }
 280
 281 ValueName *Value::getValueName() const {
 282   if (!HasName) return nullptr;
 283
 284   LLVMContext &Ctx = getContext();
 285   auto I = Ctx.pImpl->ValueNames.find(this);
 286   assert(I != Ctx.pImpl->ValueNames.end() &&
 287          "No name entry found!");
 288
 289   return I->second;
 290 }
 291
 292 void Value::setValueName(ValueName *VN) {
 293   LLVMContext &Ctx = getContext();
 294
 295   assert(HasName == Ctx.pImpl->ValueNames.count(this) &&
 296          "HasName bit out of sync!");
 297
 298   if (!VN) {
 299     if (HasName)
 300       Ctx.pImpl->ValueNames.erase(this);
 301     HasName = false;
 302     return;
 303   }
 304
 305   HasName = true;
 306   Ctx.pImpl->ValueNames[this] = VN;
 307 }
 308
 309 StringRef Value::getName() const {
 310   // Make sure the empty string is still a C string. For historical reasons,
 311   // some clients want to call .data() on the result and expect it to be null
 312   // terminated.
 313   if (!hasName())
 314     return StringRef("", 0);
 315   return getValueName()->getKey();
 316 }
 317
 318 void Value::setNameImpl(const Twine &NewName) {
 319   bool NeedNewName =
 320       !getContext().shouldDiscardValueNames() || isa<GlobalValue>(this);
 321
 322   // Fast-path: LLVMContext can be set to strip out non-GlobalValue names
 323   // and there is no need to delete the old name.
 324   if (!NeedNewName && !hasName())
 325     return;
 326
 327   // Fast path for common IRBuilder case of setName("") when there is no name.
 328   if (NewName.isTriviallyEmpty() && !hasName())
 329     return;
 330
 331   SmallString<256> NameData;
 332   StringRef NameRef = NeedNewName ? NewName.toStringRef(NameData) : "";
 333   assert(!NameRef.contains(0) && "Null bytes are not allowed in names");
 334
 335   // Name isn't changing?
 336   if (getName() == NameRef)
 337     return;
 338
 339   assert(!getType()->isVoidTy() && "Cannot assign a name to void values!");
 340
 341   // Get the symbol table to update for this object.
 342   ValueSymbolTable *ST;
 343   if (getSymTab(this, ST))
 344     return;  // Cannot set a name on this value (e.g. constant).
 345
 346   if (!ST) { // No symbol table to update?  Just do the change.
 347     // NOTE: Could optimize for the case the name is shrinking to not deallocate
 348     // then reallocated.
 349     destroyValueName();
 350
 351     if (!NameRef.empty()) {
 352       // Create the new name.
 353       assert(NeedNewName);
 354       MallocAllocator Allocator;
 355       setValueName(ValueName::create(NameRef, Allocator));
 356       getValueName()->setValue(this);
 357     }
 358     return;
 359   }
 360
 361   // NOTE: Could optimize for the case the name is shrinking to not deallocate
 362   // then reallocated.
 363   if (hasName()) {
 364     // Remove old name.
 365     ST->removeValueName(getValueName());
 366     destroyValueName();
 367
 368     if (NameRef.empty())
 369       return;
 370   }
 371
 372   // Name is changing to something new.
 373   assert(NeedNewName);
 374   setValueName(ST->createValueName(NameRef, this));
 375 }
 376
 377 void Value::setName(const Twine &NewName) {
 378   setNameImpl(NewName);
 379   if (Function *F = dyn_cast<Function>(this))
 380     F->recalculateIntrinsicID();
 381 }
 382
 383 void Value::takeName(Value *V) {
 384   assert(V != this && "Illegal call to this->takeName(this)!");
 385   ValueSymbolTable *ST = nullptr;
 386   // If this value has a name, drop it.
 387   if (hasName()) {
 388     // Get the symtab this is in.
 389     if (getSymTab(this, ST)) {
 390       // We can't set a name on this value, but we need to clear V's name if
 391       // it has one.
 392       if (V->hasName()) V->setName("");
 393       return;  // Cannot set a name on this value (e.g. constant).
 394     }
 395
 396     // Remove old name.
 397     if (ST)
 398       ST->removeValueName(getValueName());
 399     destroyValueName();
 400   }
 401
 402   // Now we know that this has no name.
 403
 404   // If V has no name either, we're done.
 405   if (!V->hasName()) return;
 406
 407   // Get this's symtab if we didn't before.
 408   if (!ST) {
 409     if (getSymTab(this, ST)) {
 410       // Clear V's name.
 411       V->setName("");
 412       return;  // Cannot set a name on this value (e.g. constant).
 413     }
 414   }
 415
 416   // Get V's ST, this should always succeed, because V has a name.
 417   ValueSymbolTable *VST;
 418   bool Failure = getSymTab(V, VST);
 419   assert(!Failure && "V has a name, so it should have a ST!"); (void)Failure;
 420
 421   // If these values are both in the same symtab, we can do this very fast.
 422   // This works even if both values have no symtab yet.
 423   if (ST == VST) {
 424     // Take the name!
 425     setValueName(V->getValueName());
 426     V->setValueName(nullptr);
 427     getValueName()->setValue(this);
 428     return;
 429   }
 430
 431   // Otherwise, things are slightly more complex.  Remove V's name from VST and
 432   // then reinsert it into ST.
 433
 434   if (VST)
 435     VST->removeValueName(V->getValueName());
 436   setValueName(V->getValueName());
 437   V->setValueName(nullptr);
 438   getValueName()->setValue(this);
 439
 440   if (ST)
 441     ST->reinsertValue(this);
 442 }
 443
 444 #ifndef NDEBUG
 445 std::string Value::getNameOrAsOperand() const {
 446   if (!getName().empty())
 447     return std::string(getName());
 448
 449   std::string BBName;
 450   raw_string_ostream OS(BBName);
 451   printAsOperand(OS, false);
 452   return OS.str();
 453 }
 454 #endif
 455
 456 void Value::assertModuleIsMaterializedImpl() const {
 457 #ifndef NDEBUG
 458   const GlobalValue *GV = dyn_cast<GlobalValue>(this);
 459   if (!GV)
 460     return;
 461   const Module *M = GV->getParent();
 462   if (!M)
 463     return;
 464   assert(M->isMaterialized());
 465 #endif
 466 }
 467
 468 #ifndef NDEBUG
 469 static bool contains(SmallPtrSetImpl<ConstantExpr *> &Cache, ConstantExpr *Expr,
 470                      Constant *C) {
 471   if (!Cache.insert(Expr).second)
 472     return false;
 473
 474   for (auto &O : Expr->operands()) {
 475     if (O == C)
 476       return true;
 477     auto *CE = dyn_cast<ConstantExpr>(O);
 478     if (!CE)
 479       continue;
 480     if (contains(Cache, CE, C))
 481       return true;
 482   }
 483   return false;
 484 }
 485
 486 static bool contains(Value *Expr, Value *V) {
 487   if (Expr == V)
 488     return true;
 489
 490   auto *C = dyn_cast<Constant>(V);
 491   if (!C)
 492     return false;
 493
 494   auto *CE = dyn_cast<ConstantExpr>(Expr);
 495   if (!CE)
 496     return false;
 497
 498   SmallPtrSet<ConstantExpr *, 4> Cache;
 499   return contains(Cache, CE, C);
 500 }
 501 #endif // NDEBUG
 502
 503 void Value::doRAUW(Value *New, ReplaceMetadataUses ReplaceMetaUses) {
 504   assert(New && "Value::replaceAllUsesWith(<null>) is invalid!");
 505   assert(!contains(New, this) &&
 506          "this->replaceAllUsesWith(expr(this)) is NOT valid!");
 507   assert(New->getType() == getType() &&
 508          "replaceAllUses of value with new value of different type!");
 509
 510   // Notify all ValueHandles (if present) that this value is going away.
 511   if (HasValueHandle)
 512     ValueHandleBase::ValueIsRAUWd(this, New);
 513   if (ReplaceMetaUses == ReplaceMetadataUses::Yes && isUsedByMetadata())
 514     ValueAsMetadata::handleRAUW(this, New);
 515
 516   while (!materialized_use_empty()) {
 517     Use &U = *UseList;
 518     // Must handle Constants specially, we cannot call replaceUsesOfWith on a
 519     // constant because they are uniqued.
 520     if (auto *C = dyn_cast<Constant>(U.getUser())) {
 521       if (!isa<GlobalValue>(C)) {
 522         C->handleOperandChange(this, New);
 523         continue;
 524       }
 525     }
 526
 527     U.set(New);
 528   }
 529
 530   if (BasicBlock *BB = dyn_cast<BasicBlock>(this))
 531     BB->replaceSuccessorsPhiUsesWith(cast<BasicBlock>(New));
 532 }
 533
 534 void Value::replaceAllUsesWith(Value *New) {
 535   doRAUW(New, ReplaceMetadataUses::Yes);
 536 }
 537
 538 void Value::replaceNonMetadataUsesWith(Value *New) {
 539   doRAUW(New, ReplaceMetadataUses::No);
 540 }
 541
 542 void Value::replaceUsesWithIf(Value *New,
 543                               llvm::function_ref<bool(Use &U)> ShouldReplace) {
 544   assert(New && "Value::replaceUsesWithIf(<null>) is invalid!");
 545   assert(New->getType() == getType() &&
 546          "replaceUses of value with new value of different type!");
 547
 548   SmallVector<TrackingVH<Constant>, 8> Consts;
 549   SmallPtrSet<Constant *, 8> Visited;
 550
 551   for (Use &U : llvm::make_early_inc_range(uses())) {
 552     if (!ShouldReplace(U))
 553       continue;
 554     // Must handle Constants specially, we cannot call replaceUsesOfWith on a
 555     // constant because they are uniqued.
 556     if (auto *C = dyn_cast<Constant>(U.getUser())) {
 557       if (!isa<GlobalValue>(C)) {
 558         if (Visited.insert(C).second)
 559           Consts.push_back(TrackingVH<Constant>(C));
 560         continue;
 561       }
 562     }
 563     U.set(New);
 564   }
 565
 566   while (!Consts.empty()) {
 567     // FIXME: handleOperandChange() updates all the uses in a given Constant,
 568     //        not just the one passed to ShouldReplace
 569     Consts.pop_back_val()->handleOperandChange(this, New);
 570   }
 571 }
 572
 573 /// Replace llvm.dbg.* uses of MetadataAsValue(ValueAsMetadata(V)) outside BB
 574 /// with New.
 575 static void replaceDbgUsesOutsideBlock(Value *V, Value *New, BasicBlock *BB) {
 576   SmallVector<DbgVariableIntrinsic *> DbgUsers;
 577   findDbgUsers(DbgUsers, V);
 578   for (auto *DVI : DbgUsers) {
 579     if (DVI->getParent() != BB)
 580       DVI->replaceVariableLocationOp(V, New);
 581   }
 582 }
 583
 584 // Like replaceAllUsesWith except it does not handle constants or basic blocks.
 585 // This routine leaves uses within BB.
 586 void Value::replaceUsesOutsideBlock(Value *New, BasicBlock *BB) {
 587   assert(New && "Value::replaceUsesOutsideBlock(<null>, BB) is invalid!");
 588   assert(!contains(New, this) &&
 589          "this->replaceUsesOutsideBlock(expr(this), BB) is NOT valid!");
 590   assert(New->getType() == getType() &&
 591          "replaceUses of value with new value of different type!");
 592   assert(BB && "Basic block that may contain a use of 'New' must be defined\n");
 593
 594   replaceDbgUsesOutsideBlock(this, New, BB);
 595   replaceUsesWithIf(New, [BB](Use &U) {
 596     auto *I = dyn_cast<Instruction>(U.getUser());
 597     // Don't replace if it's an instruction in the BB basic block.
 598     return !I || I->getParent() != BB;
 599   });
 600 }
 601
 602 namespace {
 603 // Various metrics for how much to strip off of pointers.
 604 enum PointerStripKind {
 605   PSK_ZeroIndices,
 606   PSK_ZeroIndicesAndAliases,
 607   PSK_ZeroIndicesSameRepresentation,
 608   PSK_ForAliasAnalysis,
 609   PSK_InBoundsConstantIndices,
 610   PSK_InBounds
 611 };
 612
 613 template <PointerStripKind StripKind> static void NoopCallback(const Value *) {}
 614
 615 template <PointerStripKind StripKind>
 616 static const Value *stripPointerCastsAndOffsets(
 617     const Value *V,
 618     function_ref<void(const Value *)> Func = NoopCallback<StripKind>) {
 619   if (!V->getType()->isPointerTy())
 620     return V;
 621
 622   // Even though we don't look through PHI nodes, we could be called on an
 623   // instruction in an unreachable block, which may be on a cycle.
 624   SmallPtrSet<const Value *, 4> Visited;
 625
 626   Visited.insert(V);
 627   do {
 628     Func(V);
 629     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 630       switch (StripKind) {
 631       case PSK_ZeroIndices:
 632       case PSK_ZeroIndicesAndAliases:
 633       case PSK_ZeroIndicesSameRepresentation:
 634       case PSK_ForAliasAnalysis:
 635         if (!GEP->hasAllZeroIndices())
 636           return V;
 637         break;
 638       case PSK_InBoundsConstantIndices:
 639         if (!GEP->hasAllConstantIndices())
 640           return V;
 641         [[fallthrough]];
 642       case PSK_InBounds:
 643         if (!GEP->isInBounds())
 644           return V;
 645         break;
 646       }
 647       V = GEP->getPointerOperand();
 648     } else if (Operator::getOpcode(V) == Instruction::BitCast) {
 649       V = cast<Operator>(V)->getOperand(0);
 650       if (!V->getType()->isPointerTy())
 651         return V;
 652     } else if (StripKind != PSK_ZeroIndicesSameRepresentation &&
 653                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
 654       // TODO: If we know an address space cast will not change the
 655       //       representation we could look through it here as well.
 656       V = cast<Operator>(V)->getOperand(0);
 657     } else if (StripKind == PSK_ZeroIndicesAndAliases && isa<GlobalAlias>(V)) {
 658       V = cast<GlobalAlias>(V)->getAliasee();
 659     } else if (StripKind == PSK_ForAliasAnalysis && isa<PHINode>(V) &&
 660                cast<PHINode>(V)->getNumIncomingValues() == 1) {
 661       V = cast<PHINode>(V)->getIncomingValue(0);
 662     } else {
 663       if (const auto *Call = dyn_cast<CallBase>(V)) {
 664         if (const Value *RV = Call->getReturnedArgOperand()) {
 665           V = RV;
 666           continue;
 667         }
 668         // The result of launder.invariant.group must alias it's argument,
 669         // but it can't be marked with returned attribute, that's why it needs
 670         // special case.
 671         if (StripKind == PSK_ForAliasAnalysis &&
 672             (Call->getIntrinsicID() == Intrinsic::launder_invariant_group ||
 673              Call->getIntrinsicID() == Intrinsic::strip_invariant_group)) {
 674           V = Call->getArgOperand(0);
 675           continue;
 676         }
 677       }
 678       return V;
 679     }
 680     assert(V->getType()->isPointerTy() && "Unexpected operand type!");
 681   } while (Visited.insert(V).second);
 682
 683   return V;
 684 }
 685 } // end anonymous namespace
 686
 687 const Value *Value::stripPointerCasts() const {
 688   return stripPointerCastsAndOffsets<PSK_ZeroIndices>(this);
 689 }
 690
 691 const Value *Value::stripPointerCastsAndAliases() const {
 692   return stripPointerCastsAndOffsets<PSK_ZeroIndicesAndAliases>(this);
 693 }
 694
 695 const Value *Value::stripPointerCastsSameRepresentation() const {
 696   return stripPointerCastsAndOffsets<PSK_ZeroIndicesSameRepresentation>(this);
 697 }
 698
 699 const Value *Value::stripInBoundsConstantOffsets() const {
 700   return stripPointerCastsAndOffsets<PSK_InBoundsConstantIndices>(this);
 701 }
 702
 703 const Value *Value::stripPointerCastsForAliasAnalysis() const {
 704   return stripPointerCastsAndOffsets<PSK_ForAliasAnalysis>(this);
 705 }
 706
 707 const Value *Value::stripAndAccumulateConstantOffsets(
 708     const DataLayout &DL, APInt &Offset, bool AllowNonInbounds,
 709     bool AllowInvariantGroup,
 710     function_ref<bool(Value &, APInt &)> ExternalAnalysis) const {
 711   if (!getType()->isPtrOrPtrVectorTy())
 712     return this;
 713
 714   unsigned BitWidth = Offset.getBitWidth();
 715   assert(BitWidth == DL.getIndexTypeSizeInBits(getType()) &&
 716          "The offset bit width does not match the DL specification.");
 717
 718   // Even though we don't look through PHI nodes, we could be called on an
 719   // instruction in an unreachable block, which may be on a cycle.
 720   SmallPtrSet<const Value *, 4> Visited;
 721   Visited.insert(this);
 722   const Value *V = this;
 723   do {
 724     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 725       // If in-bounds was requested, we do not strip non-in-bounds GEPs.
 726       if (!AllowNonInbounds && !GEP->isInBounds())
 727         return V;
 728
 729       // If one of the values we have visited is an addrspacecast, then
 730       // the pointer type of this GEP may be different from the type
 731       // of the Ptr parameter which was passed to this function.  This
 732       // means when we construct GEPOffset, we need to use the size
 733       // of GEP's pointer type rather than the size of the original
 734       // pointer type.
 735       APInt GEPOffset(DL.getIndexTypeSizeInBits(V->getType()), 0);
 736       if (!GEP->accumulateConstantOffset(DL, GEPOffset, ExternalAnalysis))
 737         return V;
 738
 739       // Stop traversal if the pointer offset wouldn't fit in the bit-width
 740       // provided by the Offset argument. This can happen due to AddrSpaceCast
 741       // stripping.
 742       if (GEPOffset.getSignificantBits() > BitWidth)
 743         return V;
 744
 745       // External Analysis can return a result higher/lower than the value
 746       // represents. We need to detect overflow/underflow.
 747       APInt GEPOffsetST = GEPOffset.sextOrTrunc(BitWidth);
 748       if (!ExternalAnalysis) {
 749         Offset += GEPOffsetST;
 750       } else {
 751         bool Overflow = false;
 752         APInt OldOffset = Offset;
 753         Offset = Offset.sadd_ov(GEPOffsetST, Overflow);
 754         if (Overflow) {
 755           Offset = OldOffset;
 756           return V;
 757         }
 758       }
 759       V = GEP->getPointerOperand();
 760     } else if (Operator::getOpcode(V) == Instruction::BitCast ||
 761                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
 762       V = cast<Operator>(V)->getOperand(0);
 763     } else if (auto *GA = dyn_cast<GlobalAlias>(V)) {
 764       if (!GA->isInterposable())
 765         V = GA->getAliasee();
 766     } else if (const auto *Call = dyn_cast<CallBase>(V)) {
 767         if (const Value *RV = Call->getReturnedArgOperand())
 768           V = RV;
 769         if (AllowInvariantGroup && Call->isLaunderOrStripInvariantGroup())
 770           V = Call->getArgOperand(0);
 771     }
 772     assert(V->getType()->isPtrOrPtrVectorTy() && "Unexpected operand type!");
 773   } while (Visited.insert(V).second);
 774
 775   return V;
 776 }
 777
 778 const Value *
 779 Value::stripInBoundsOffsets(function_ref<void(const Value *)> Func) const {
 780   return stripPointerCastsAndOffsets<PSK_InBounds>(this, Func);
 781 }
 782
 783 bool Value::canBeFreed() const {
 784   assert(getType()->isPointerTy());
 785
 786   // Cases that can simply never be deallocated
 787   // *) Constants aren't allocated per se, thus not deallocated either.
 788   if (isa<Constant>(this))
 789     return false;
 790
 791   // Handle byval/byref/sret/inalloca/preallocated arguments.  The storage
 792   // lifetime is guaranteed to be longer than the callee's lifetime.
 793   if (auto *A = dyn_cast<Argument>(this)) {
 794     if (A->hasPointeeInMemoryValueAttr())
 795       return false;
 796     // A pointer to an object in a function which neither frees, nor can arrange
 797     // for another thread to free on its behalf, can not be freed in the scope
 798     // of the function.  Note that this logic is restricted to memory
 799     // allocations in existance before the call; a nofree function *is* allowed
 800     // to free memory it allocated.
 801     const Function *F = A->getParent();
 802     if (F->doesNotFreeMemory() && F->hasNoSync())
 803       return false;
 804   }
 805
 806   const Function *F = nullptr;
 807   if (auto *I = dyn_cast<Instruction>(this))
 808     F = I->getFunction();
 809   if (auto *A = dyn_cast<Argument>(this))
 810     F = A->getParent();
 811
 812   if (!F)
 813     return true;
 814
 815   // With garbage collection, deallocation typically occurs solely at or after
 816   // safepoints.  If we're compiling for a collector which uses the
 817   // gc.statepoint infrastructure, safepoints aren't explicitly present
 818   // in the IR until after lowering from abstract to physical machine model.
 819   // The collector could chose to mix explicit deallocation and gc'd objects
 820   // which is why we need the explicit opt in on a per collector basis.
 821   if (!F->hasGC())
 822     return true;
 823
 824   const auto &GCName = F->getGC();
 825   if (GCName == "statepoint-example") {
 826     auto *PT = cast<PointerType>(this->getType());
 827     if (PT->getAddressSpace() != 1)
 828       // For the sake of this example GC, we arbitrarily pick addrspace(1) as
 829       // our GC managed heap.  This must match the same check in
 830       // RewriteStatepointsForGC (and probably needs better factored.)
 831       return true;
 832
 833     // It is cheaper to scan for a declaration than to scan for a use in this
 834     // function.  Note that gc.statepoint is a type overloaded function so the
 835     // usual trick of requesting declaration of the intrinsic from the module
 836     // doesn't work.
 837     for (auto &Fn : *F->getParent())
 838       if (Fn.getIntrinsicID() == Intrinsic::experimental_gc_statepoint)
 839         return true;
 840     return false;
 841   }
 842   return true;
 843 }
 844
 845 uint64_t Value::getPointerDereferenceableBytes(const DataLayout &DL,
 846                                                bool &CanBeNull,
 847                                                bool &CanBeFreed) const {
 848   assert(getType()->isPointerTy() && "must be pointer");
 849
 850   uint64_t DerefBytes = 0;
 851   CanBeNull = false;
 852   CanBeFreed = UseDerefAtPointSemantics && canBeFreed();
 853   if (const Argument *A = dyn_cast<Argument>(this)) {
 854     DerefBytes = A->getDereferenceableBytes();
 855     if (DerefBytes == 0) {
 856       // Handle byval/byref/inalloca/preallocated arguments
 857       if (Type *ArgMemTy = A->getPointeeInMemoryValueType()) {
 858         if (ArgMemTy->isSized()) {
 859           // FIXME: Why isn't this the type alloc size?
 860           DerefBytes = DL.getTypeStoreSize(ArgMemTy).getKnownMinValue();
 861         }
 862       }
 863     }
 864
 865     if (DerefBytes == 0) {
 866       DerefBytes = A->getDereferenceableOrNullBytes();
 867       CanBeNull = true;
 868     }
 869   } else if (const auto *Call = dyn_cast<CallBase>(this)) {
 870     DerefBytes = Call->getRetDereferenceableBytes();
 871     if (DerefBytes == 0) {
 872       DerefBytes = Call->getRetDereferenceableOrNullBytes();
 873       CanBeNull = true;
 874     }
 875   } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
 876     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) {
 877       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 878       DerefBytes = CI->getLimitedValue();
 879     }
 880     if (DerefBytes == 0) {
 881       if (MDNode *MD =
 882               LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
 883         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 884         DerefBytes = CI->getLimitedValue();
 885       }
 886       CanBeNull = true;
 887     }
 888   } else if (auto *IP = dyn_cast<IntToPtrInst>(this)) {
 889     if (MDNode *MD = IP->getMetadata(LLVMContext::MD_dereferenceable)) {
 890       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 891       DerefBytes = CI->getLimitedValue();
 892     }
 893     if (DerefBytes == 0) {
 894       if (MDNode *MD =
 895               IP->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
 896         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 897         DerefBytes = CI->getLimitedValue();
 898       }
 899       CanBeNull = true;
 900     }
 901   } else if (auto *AI = dyn_cast<AllocaInst>(this)) {
 902     if (!AI->isArrayAllocation()) {
 903       DerefBytes =
 904           DL.getTypeStoreSize(AI->getAllocatedType()).getKnownMinValue();
 905       CanBeNull = false;
 906       CanBeFreed = false;
 907     }
 908   } else if (auto *GV = dyn_cast<GlobalVariable>(this)) {
 909     if (GV->getValueType()->isSized() && !GV->hasExternalWeakLinkage()) {
 910       // TODO: Don't outright reject hasExternalWeakLinkage but set the
 911       // CanBeNull flag.
 912       DerefBytes = DL.getTypeStoreSize(GV->getValueType()).getFixedValue();
 913       CanBeNull = false;
 914       CanBeFreed = false;
 915     }
 916   }
 917   return DerefBytes;
 918 }
 919
 920 Align Value::getPointerAlignment(const DataLayout &DL) const {
 921   assert(getType()->isPointerTy() && "must be pointer");
 922   if (auto *GO = dyn_cast<GlobalObject>(this)) {
 923     if (isa<Function>(GO)) {
 924       Align FunctionPtrAlign = DL.getFunctionPtrAlign().valueOrOne();
 925       switch (DL.getFunctionPtrAlignType()) {
 926       case DataLayout::FunctionPtrAlignType::Independent:
 927         return FunctionPtrAlign;
 928       case DataLayout::FunctionPtrAlignType::MultipleOfFunctionAlign:
 929         return std::max(FunctionPtrAlign, GO->getAlign().valueOrOne());
 930       }
 931       llvm_unreachable("Unhandled FunctionPtrAlignType");
 932     }
 933     const MaybeAlign Alignment(GO->getAlign());
 934     if (!Alignment) {
 935       if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
 936         Type *ObjectType = GVar->getValueType();
 937         if (ObjectType->isSized()) {
 938           // If the object is defined in the current Module, we'll be giving
 939           // it the preferred alignment. Otherwise, we have to assume that it
 940           // may only have the minimum ABI alignment.
 941           if (GVar->isStrongDefinitionForLinker())
 942             return DL.getPreferredAlign(GVar);
 943           else
 944             return DL.getABITypeAlign(ObjectType);
 945         }
 946       }
 947     }
 948     return Alignment.valueOrOne();
 949   } else if (const Argument *A = dyn_cast<Argument>(this)) {
 950     const MaybeAlign Alignment = A->getParamAlign();
 951     if (!Alignment && A->hasStructRetAttr()) {
 952       // An sret parameter has at least the ABI alignment of the return type.
 953       Type *EltTy = A->getParamStructRetType();
 954       if (EltTy->isSized())
 955         return DL.getABITypeAlign(EltTy);
 956     }
 957     return Alignment.valueOrOne();
 958   } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(this)) {
 959     return AI->getAlign();
 960   } else if (const auto *Call = dyn_cast<CallBase>(this)) {
 961     MaybeAlign Alignment = Call->getRetAlign();
 962     if (!Alignment && Call->getCalledFunction())
 963       Alignment = Call->getCalledFunction()->getAttributes().getRetAlignment();
 964     return Alignment.valueOrOne();
 965   } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
 966     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_align)) {
 967       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 968       return Align(CI->getLimitedValue());
 969     }
 970   } else if (auto *CstPtr = dyn_cast<Constant>(this)) {
 971     // Strip pointer casts to avoid creating unnecessary ptrtoint expression
 972     // if the only "reduction" is combining a bitcast + ptrtoint.
 973     CstPtr = CstPtr->stripPointerCasts();
 974     if (auto *CstInt = dyn_cast_or_null<ConstantInt>(ConstantExpr::getPtrToInt(
 975             const_cast<Constant *>(CstPtr), DL.getIntPtrType(getType()),
 976             /*OnlyIfReduced=*/true))) {
 977       size_t TrailingZeros = CstInt->getValue().countr_zero();
 978       // While the actual alignment may be large, elsewhere we have
 979       // an arbitrary upper alignmet limit, so let's clamp to it.
 980       return Align(TrailingZeros < Value::MaxAlignmentExponent
 981                        ? uint64_t(1) << TrailingZeros
 982                        : Value::MaximumAlignment);
 983     }
 984   }
 985   return Align(1);
 986 }
 987
 988 static std::optional<int64_t>
 989 getOffsetFromIndex(const GEPOperator *GEP, unsigned Idx, const DataLayout &DL) {
 990   // Skip over the first indices.
 991   gep_type_iterator GTI = gep_type_begin(GEP);
 992   for (unsigned i = 1; i != Idx; ++i, ++GTI)
 993     /*skip along*/;
 994
 995   // Compute the offset implied by the rest of the indices.
 996   int64_t Offset = 0;
 997   for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
 998     ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
 999     if (!OpC)
1000       return std::nullopt;
1001     if (OpC->isZero())
1002       continue; // No offset.
1003
1004     // Handle struct indices, which add their field offset to the pointer.
1005     if (StructType *STy = GTI.getStructTypeOrNull()) {
1006       Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
1007       continue;
1008     }
1009
1010     // Otherwise, we have a sequential type like an array or fixed-length
1011     // vector. Multiply the index by the ElementSize.
1012     TypeSize Size = DL.getTypeAllocSize(GTI.getIndexedType());
1013     if (Size.isScalable())
1014       return std::nullopt;
1015     Offset += Size.getFixedValue() * OpC->getSExtValue();
1016   }
1017
1018   return Offset;
1019 }
1020
1021 std::optional<int64_t> Value::getPointerOffsetFrom(const Value *Other,
1022                                                    const DataLayout &DL) const {
1023   const Value *Ptr1 = Other;
1024   const Value *Ptr2 = this;
1025   APInt Offset1(DL.getIndexTypeSizeInBits(Ptr1->getType()), 0);
1026   APInt Offset2(DL.getIndexTypeSizeInBits(Ptr2->getType()), 0);
1027   Ptr1 = Ptr1->stripAndAccumulateConstantOffsets(DL, Offset1, true);
1028   Ptr2 = Ptr2->stripAndAccumulateConstantOffsets(DL, Offset2, true);
1029
1030   // Handle the trivial case first.
1031   if (Ptr1 == Ptr2)
1032     return Offset2.getSExtValue() - Offset1.getSExtValue();
1033
1034   const GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
1035   const GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);
1036
1037   // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
1038   // base.  After that base, they may have some number of common (and
1039   // potentially variable) indices.  After that they handle some constant
1040   // offset, which determines their offset from each other.  At this point, we
1041   // handle no other case.
1042   if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0) ||
1043       GEP1->getSourceElementType() != GEP2->getSourceElementType())
1044     return std::nullopt;
1045
1046   // Skip any common indices and track the GEP types.
1047   unsigned Idx = 1;
1048   for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
1049     if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
1050       break;
1051
1052   auto IOffset1 = getOffsetFromIndex(GEP1, Idx, DL);
1053   auto IOffset2 = getOffsetFromIndex(GEP2, Idx, DL);
1054   if (!IOffset1 || !IOffset2)
1055     return std::nullopt;
1056   return *IOffset2 - *IOffset1 + Offset2.getSExtValue() -
1057          Offset1.getSExtValue();
1058 }
1059
1060 const Value *Value::DoPHITranslation(const BasicBlock *CurBB,
1061                                      const BasicBlock *PredBB) const {
1062   auto *PN = dyn_cast<PHINode>(this);
1063   if (PN && PN->getParent() == CurBB)
1064     return PN->getIncomingValueForBlock(PredBB);
1065   return this;
1066 }
1067
1068 LLVMContext &Value::getContext() const { return VTy->getContext(); }
1069
1070 void Value::reverseUseList() {
1071   if (!UseList || !UseList->Next)
1072     // No need to reverse 0 or 1 uses.
1073     return;
1074
1075   Use *Head = UseList;
1076   Use *Current = UseList->Next;
1077   Head->Next = nullptr;
1078   while (Current) {
1079     Use *Next = Current->Next;
1080     Current->Next = Head;
1081     Head->Prev = &Current->Next;
1082     Head = Current;
1083     Current = Next;
1084   }
1085   UseList = Head;
1086   Head->Prev = &UseList;
1087 }
1088
1089 bool Value::isSwiftError() const {
1090   auto *Arg = dyn_cast<Argument>(this);
1091   if (Arg)
1092     return Arg->hasSwiftErrorAttr();
1093   auto *Alloca = dyn_cast<AllocaInst>(this);
1094   if (!Alloca)
1095     return false;
1096   return Alloca->isSwiftError();
1097 }
1098
1099 //===----------------------------------------------------------------------===//
1100 //                             ValueHandleBase Class
1101 //===----------------------------------------------------------------------===//
1102
1103 void ValueHandleBase::AddToExistingUseList(ValueHandleBase **List) {
1104   assert(List && "Handle list is null?");
1105
1106   // Splice ourselves into the list.
1107   Next = *List;
1108   *List = this;
1109   setPrevPtr(List);
1110   if (Next) {
1111     Next->setPrevPtr(&Next);
1112     assert(getValPtr() == Next->getValPtr() && "Added to wrong list?");
1113   }
1114 }
1115
1116 void ValueHandleBase::AddToExistingUseListAfter(ValueHandleBase *List) {
1117   assert(List && "Must insert after existing node");
1118
1119   Next = List->Next;
1120   setPrevPtr(&List->Next);
1121   List->Next = this;
1122   if (Next)
1123     Next->setPrevPtr(&Next);
1124 }
1125
1126 void ValueHandleBase::AddToUseList() {
1127   assert(getValPtr() && "Null pointer doesn't have a use list!");
1128
1129   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
1130
1131   if (getValPtr()->HasValueHandle) {
1132     // If this value already has a ValueHandle, then it must be in the
1133     // ValueHandles map already.
1134     ValueHandleBase *&Entry = pImpl->ValueHandles[getValPtr()];
1135     assert(Entry && "Value doesn't have any handles?");
1136     AddToExistingUseList(&Entry);
1137     return;
1138   }
1139
1140   // Ok, it doesn't have any handles yet, so we must insert it into the
1141   // DenseMap.  However, doing this insertion could cause the DenseMap to
1142   // reallocate itself, which would invalidate all of the PrevP pointers that
1143   // point into the old table.  Handle this by checking for reallocation and
1144   // updating the stale pointers only if needed.
1145   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
1146   const void *OldBucketPtr = Handles.getPointerIntoBucketsArray();
1147
1148   ValueHandleBase *&Entry = Handles[getValPtr()];
1149   assert(!Entry && "Value really did already have handles?");
1150   AddToExistingUseList(&Entry);
1151   getValPtr()->HasValueHandle = true;
1152
1153   // If reallocation didn't happen or if this was the first insertion, don't
1154   // walk the table.
1155   if (Handles.isPointerIntoBucketsArray(OldBucketPtr) ||
1156       Handles.size() == 1) {
1157     return;
1158   }
1159
1160   // Okay, reallocation did happen.  Fix the Prev Pointers.
1161   for (DenseMap<Value*, ValueHandleBase*>::iterator I = Handles.begin(),
1162        E = Handles.end(); I != E; ++I) {
1163     assert(I->second && I->first == I->second->getValPtr() &&
1164            "List invariant broken!");
1165     I->second->setPrevPtr(&I->second);
1166   }
1167 }
1168
1169 void ValueHandleBase::RemoveFromUseList() {
1170   assert(getValPtr() && getValPtr()->HasValueHandle &&
1171          "Pointer doesn't have a use list!");
1172
1173   // Unlink this from its use list.
1174   ValueHandleBase **PrevPtr = getPrevPtr();
1175   assert(*PrevPtr == this && "List invariant broken");
1176
1177   *PrevPtr = Next;
1178   if (Next) {
1179     assert(Next->getPrevPtr() == &Next && "List invariant broken");
1180     Next->setPrevPtr(PrevPtr);
1181     return;
1182   }
1183
1184   // If the Next pointer was null, then it is possible that this was the last
1185   // ValueHandle watching VP.  If so, delete its entry from the ValueHandles
1186   // map.
1187   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
1188   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
1189   if (Handles.isPointerIntoBucketsArray(PrevPtr)) {
1190     Handles.erase(getValPtr());
1191     getValPtr()->HasValueHandle = false;
1192   }
1193 }
1194
1195 void ValueHandleBase::ValueIsDeleted(Value *V) {
1196   assert(V->HasValueHandle && "Should only be called if ValueHandles present");
1197
1198   // Get the linked list base, which is guaranteed to exist since the
1199   // HasValueHandle flag is set.
1200   LLVMContextImpl *pImpl = V->getContext().pImpl;
1201   ValueHandleBase *Entry = pImpl->ValueHandles[V];
1202   assert(Entry && "Value bit set but no entries exist");
1203
1204   // We use a local ValueHandleBase as an iterator so that ValueHandles can add
1205   // and remove themselves from the list without breaking our iteration.  This
1206   // is not really an AssertingVH; we just have to give ValueHandleBase a kind.
1207   // Note that we deliberately do not the support the case when dropping a value
1208   // handle results in a new value handle being permanently added to the list
1209   // (as might occur in theory for CallbackVH's): the new value handle will not
1210   // be processed and the checking code will mete out righteous punishment if
1211   // the handle is still present once we have finished processing all the other
1212   // value handles (it is fine to momentarily add then remove a value handle).
1213   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
1214     Iterator.RemoveFromUseList();
1215     Iterator.AddToExistingUseListAfter(Entry);
1216     assert(Entry->Next == &Iterator && "Loop invariant broken.");
1217
1218     switch (Entry->getKind()) {
1219     case Assert:
1220       break;
1221     case Weak:
1222     case WeakTracking:
1223       // WeakTracking and Weak just go to null, which unlinks them
1224       // from the list.
1225       Entry->operator=(nullptr);
1226       break;
1227     case Callback:
1228       // Forward to the subclass's implementation.
1229       static_cast<CallbackVH*>(Entry)->deleted();
1230       break;
1231     }
1232   }
1233
1234   // All callbacks, weak references, and assertingVHs should be dropped by now.
1235   if (V->HasValueHandle) {
1236 #ifndef NDEBUG      // Only in +Asserts mode...
1237     dbgs() << "While deleting: " << *V->getType() << " %" << V->getName()
1238            << "\n";
1239     if (pImpl->ValueHandles[V]->getKind() == Assert)
1240       llvm_unreachable("An asserting value handle still pointed to this"
1241                        " value!");
1242
1243 #endif
1244     llvm_unreachable("All references to V were not removed?");
1245   }
1246 }
1247
1248 void ValueHandleBase::ValueIsRAUWd(Value *Old, Value *New) {
1249   assert(Old->HasValueHandle &&"Should only be called if ValueHandles present");
1250   assert(Old != New && "Changing value into itself!");
1251   assert(Old->getType() == New->getType() &&
1252          "replaceAllUses of value with new value of different type!");
1253
1254   // Get the linked list base, which is guaranteed to exist since the
1255   // HasValueHandle flag is set.
1256   LLVMContextImpl *pImpl = Old->getContext().pImpl;
1257   ValueHandleBase *Entry = pImpl->ValueHandles[Old];
1258
1259   assert(Entry && "Value bit set but no entries exist");
1260
1261   // We use a local ValueHandleBase as an iterator so that
1262   // ValueHandles can add and remove themselves from the list without
1263   // breaking our iteration.  This is not really an AssertingVH; we
1264   // just have to give ValueHandleBase some kind.
1265   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
1266     Iterator.RemoveFromUseList();
1267     Iterator.AddToExistingUseListAfter(Entry);
1268     assert(Entry->Next == &Iterator && "Loop invariant broken.");
1269
1270     switch (Entry->getKind()) {
1271     case Assert:
1272     case Weak:
1273       // Asserting and Weak handles do not follow RAUW implicitly.
1274       break;
1275     case WeakTracking:
1276       // Weak goes to the new value, which will unlink it from Old's list.
1277       Entry->operator=(New);
1278       break;
1279     case Callback:
1280       // Forward to the subclass's implementation.
1281       static_cast<CallbackVH*>(Entry)->allUsesReplacedWith(New);
1282       break;
1283     }
1284   }
1285
1286 #ifndef NDEBUG
1287   // If any new weak value handles were added while processing the
1288   // list, then complain about it now.
1289   if (Old->HasValueHandle)
1290     for (Entry = pImpl->ValueHandles[Old]; Entry; Entry = Entry->Next)
1291       switch (Entry->getKind()) {
1292       case WeakTracking:
1293         dbgs() << "After RAUW from " << *Old->getType() << " %"
1294                << Old->getName() << " to " << *New->getType() << " %"
1295                << New->getName() << "\n";
1296         llvm_unreachable(
1297             "A weak tracking value handle still pointed to the old value!\n");
1298       default:
1299         break;
1300       }
1301 #endif
1302 }
1303
1304 // Pin the vtable to this file.
1305 void CallbackVH::anchor() {}