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 cl::opt<bool> 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     : SubclassID(scid), HasValueHandle(0), SubclassOptionalData(0),
  55       SubclassData(0), NumUserOperands(0), IsUsedByMD(false), HasName(false),
  56       HasMetadata(false), VTy(checkType(ty)), UseList(nullptr) {
  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->updateAfterNameChange();
 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   SmallVector<DbgVariableRecord *> DPUsers;
 578   findDbgUsers(DbgUsers, V, &DPUsers);
 579   for (auto *DVI : DbgUsers) {
 580     if (DVI->getParent() != BB)
 581       DVI->replaceVariableLocationOp(V, New);
 582   }
 583   for (auto *DVR : DPUsers) {
 584     DbgMarker *Marker = DVR->getMarker();
 585     if (Marker->getParent() != BB)
 586       DVR->replaceVariableLocationOp(V, New);
 587   }
 588 }
 589
 590 // Like replaceAllUsesWith except it does not handle constants or basic blocks.
 591 // This routine leaves uses within BB.
 592 void Value::replaceUsesOutsideBlock(Value *New, BasicBlock *BB) {
 593   assert(New && "Value::replaceUsesOutsideBlock(<null>, BB) is invalid!");
 594   assert(!contains(New, this) &&
 595          "this->replaceUsesOutsideBlock(expr(this), BB) is NOT valid!");
 596   assert(New->getType() == getType() &&
 597          "replaceUses of value with new value of different type!");
 598   assert(BB && "Basic block that may contain a use of 'New' must be defined\n");
 599
 600   replaceDbgUsesOutsideBlock(this, New, BB);
 601   replaceUsesWithIf(New, [BB](Use &U) {
 602     auto *I = dyn_cast<Instruction>(U.getUser());
 603     // Don't replace if it's an instruction in the BB basic block.
 604     return !I || I->getParent() != BB;
 605   });
 606 }
 607
 608 namespace {
 609 // Various metrics for how much to strip off of pointers.
 610 enum PointerStripKind {
 611   PSK_ZeroIndices,
 612   PSK_ZeroIndicesAndAliases,
 613   PSK_ZeroIndicesSameRepresentation,
 614   PSK_ForAliasAnalysis,
 615   PSK_InBoundsConstantIndices,
 616   PSK_InBounds
 617 };
 618
 619 template <PointerStripKind StripKind> static void NoopCallback(const Value *) {}
 620
 621 template <PointerStripKind StripKind>
 622 static const Value *stripPointerCastsAndOffsets(
 623     const Value *V,
 624     function_ref<void(const Value *)> Func = NoopCallback<StripKind>) {
 625   if (!V->getType()->isPointerTy())
 626     return V;
 627
 628   // Even though we don't look through PHI nodes, we could be called on an
 629   // instruction in an unreachable block, which may be on a cycle.
 630   SmallPtrSet<const Value *, 4> Visited;
 631
 632   Visited.insert(V);
 633   do {
 634     Func(V);
 635     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 636       switch (StripKind) {
 637       case PSK_ZeroIndices:
 638       case PSK_ZeroIndicesAndAliases:
 639       case PSK_ZeroIndicesSameRepresentation:
 640       case PSK_ForAliasAnalysis:
 641         if (!GEP->hasAllZeroIndices())
 642           return V;
 643         break;
 644       case PSK_InBoundsConstantIndices:
 645         if (!GEP->hasAllConstantIndices())
 646           return V;
 647         [[fallthrough]];
 648       case PSK_InBounds:
 649         if (!GEP->isInBounds())
 650           return V;
 651         break;
 652       }
 653       V = GEP->getPointerOperand();
 654     } else if (Operator::getOpcode(V) == Instruction::BitCast) {
 655       Value *NewV = cast<Operator>(V)->getOperand(0);
 656       if (!NewV->getType()->isPointerTy())
 657         return V;
 658       V = NewV;
 659     } else if (StripKind != PSK_ZeroIndicesSameRepresentation &&
 660                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
 661       // TODO: If we know an address space cast will not change the
 662       //       representation we could look through it here as well.
 663       V = cast<Operator>(V)->getOperand(0);
 664     } else if (StripKind == PSK_ZeroIndicesAndAliases && isa<GlobalAlias>(V)) {
 665       V = cast<GlobalAlias>(V)->getAliasee();
 666     } else if (StripKind == PSK_ForAliasAnalysis && isa<PHINode>(V) &&
 667                cast<PHINode>(V)->getNumIncomingValues() == 1) {
 668       V = cast<PHINode>(V)->getIncomingValue(0);
 669     } else {
 670       if (const auto *Call = dyn_cast<CallBase>(V)) {
 671         if (const Value *RV = Call->getReturnedArgOperand()) {
 672           V = RV;
 673           continue;
 674         }
 675         // The result of launder.invariant.group must alias it's argument,
 676         // but it can't be marked with returned attribute, that's why it needs
 677         // special case.
 678         if (StripKind == PSK_ForAliasAnalysis &&
 679             (Call->getIntrinsicID() == Intrinsic::launder_invariant_group ||
 680              Call->getIntrinsicID() == Intrinsic::strip_invariant_group)) {
 681           V = Call->getArgOperand(0);
 682           continue;
 683         }
 684       }
 685       return V;
 686     }
 687     assert(V->getType()->isPointerTy() && "Unexpected operand type!");
 688   } while (Visited.insert(V).second);
 689
 690   return V;
 691 }
 692 } // end anonymous namespace
 693
 694 const Value *Value::stripPointerCasts() const {
 695   return stripPointerCastsAndOffsets<PSK_ZeroIndices>(this);
 696 }
 697
 698 const Value *Value::stripPointerCastsAndAliases() const {
 699   return stripPointerCastsAndOffsets<PSK_ZeroIndicesAndAliases>(this);
 700 }
 701
 702 const Value *Value::stripPointerCastsSameRepresentation() const {
 703   return stripPointerCastsAndOffsets<PSK_ZeroIndicesSameRepresentation>(this);
 704 }
 705
 706 const Value *Value::stripInBoundsConstantOffsets() const {
 707   return stripPointerCastsAndOffsets<PSK_InBoundsConstantIndices>(this);
 708 }
 709
 710 const Value *Value::stripPointerCastsForAliasAnalysis() const {
 711   return stripPointerCastsAndOffsets<PSK_ForAliasAnalysis>(this);
 712 }
 713
 714 const Value *Value::stripAndAccumulateConstantOffsets(
 715     const DataLayout &DL, APInt &Offset, bool AllowNonInbounds,
 716     bool AllowInvariantGroup,
 717     function_ref<bool(Value &, APInt &)> ExternalAnalysis,
 718     bool LookThroughIntToPtr) const {
 719   if (!getType()->isPtrOrPtrVectorTy())
 720     return this;
 721
 722   unsigned BitWidth = Offset.getBitWidth();
 723   assert(BitWidth == DL.getIndexTypeSizeInBits(getType()) &&
 724          "The offset bit width does not match the DL specification.");
 725
 726   // Even though we don't look through PHI nodes, we could be called on an
 727   // instruction in an unreachable block, which may be on a cycle.
 728   SmallPtrSet<const Value *, 4> Visited;
 729   Visited.insert(this);
 730   const Value *V = this;
 731   do {
 732     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 733       // If in-bounds was requested, we do not strip non-in-bounds GEPs.
 734       if (!AllowNonInbounds && !GEP->isInBounds())
 735         return V;
 736
 737       // If one of the values we have visited is an addrspacecast, then
 738       // the pointer type of this GEP may be different from the type
 739       // of the Ptr parameter which was passed to this function.  This
 740       // means when we construct GEPOffset, we need to use the size
 741       // of GEP's pointer type rather than the size of the original
 742       // pointer type.
 743       APInt GEPOffset(DL.getIndexTypeSizeInBits(V->getType()), 0);
 744       if (!GEP->accumulateConstantOffset(DL, GEPOffset, ExternalAnalysis))
 745         return V;
 746
 747       // Stop traversal if the pointer offset wouldn't fit in the bit-width
 748       // provided by the Offset argument. This can happen due to AddrSpaceCast
 749       // stripping.
 750       if (GEPOffset.getSignificantBits() > BitWidth)
 751         return V;
 752
 753       // External Analysis can return a result higher/lower than the value
 754       // represents. We need to detect overflow/underflow.
 755       APInt GEPOffsetST = GEPOffset.sextOrTrunc(BitWidth);
 756       if (!ExternalAnalysis) {
 757         Offset += GEPOffsetST;
 758       } else {
 759         bool Overflow = false;
 760         APInt OldOffset = Offset;
 761         Offset = Offset.sadd_ov(GEPOffsetST, Overflow);
 762         if (Overflow) {
 763           Offset = OldOffset;
 764           return V;
 765         }
 766       }
 767       V = GEP->getPointerOperand();
 768     } else if (Operator::getOpcode(V) == Instruction::BitCast ||
 769                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
 770       V = cast<Operator>(V)->getOperand(0);
 771     } else if (auto *GA = dyn_cast<GlobalAlias>(V)) {
 772       if (!GA->isInterposable())
 773         V = GA->getAliasee();
 774     } else if (const auto *Call = dyn_cast<CallBase>(V)) {
 775         if (const Value *RV = Call->getReturnedArgOperand())
 776           V = RV;
 777         if (AllowInvariantGroup && Call->isLaunderOrStripInvariantGroup())
 778           V = Call->getArgOperand(0);
 779     } else if (auto *Int2Ptr = dyn_cast<Operator>(V)) {
 780       // Try to accumulate across (inttoptr (add (ptrtoint p), off)).
 781       if (!AllowNonInbounds || !LookThroughIntToPtr || !Int2Ptr ||
 782           Int2Ptr->getOpcode() != Instruction::IntToPtr ||
 783           Int2Ptr->getOperand(0)->getType()->getScalarSizeInBits() != BitWidth)
 784         return V;
 785
 786       auto *Add = dyn_cast<AddOperator>(Int2Ptr->getOperand(0));
 787       if (!Add)
 788         return V;
 789
 790       auto *Ptr2Int = dyn_cast<PtrToIntOperator>(Add->getOperand(0));
 791       auto *CI = dyn_cast<ConstantInt>(Add->getOperand(1));
 792       if (!Ptr2Int || !CI)
 793         return V;
 794
 795       Offset += CI->getValue();
 796       V = Ptr2Int->getOperand(0);
 797     }
 798     assert(V->getType()->isPtrOrPtrVectorTy() && "Unexpected operand type!");
 799   } while (Visited.insert(V).second);
 800
 801   return V;
 802 }
 803
 804 const Value *
 805 Value::stripInBoundsOffsets(function_ref<void(const Value *)> Func) const {
 806   return stripPointerCastsAndOffsets<PSK_InBounds>(this, Func);
 807 }
 808
 809 bool Value::canBeFreed() const {
 810   assert(getType()->isPointerTy());
 811
 812   // Cases that can simply never be deallocated
 813   // *) Constants aren't allocated per se, thus not deallocated either.
 814   if (isa<Constant>(this))
 815     return false;
 816
 817   // Handle byval/byref/sret/inalloca/preallocated arguments.  The storage
 818   // lifetime is guaranteed to be longer than the callee's lifetime.
 819   if (auto *A = dyn_cast<Argument>(this)) {
 820     if (A->hasPointeeInMemoryValueAttr())
 821       return false;
 822     // A pointer to an object in a function which neither frees, nor can arrange
 823     // for another thread to free on its behalf, can not be freed in the scope
 824     // of the function.  Note that this logic is restricted to memory
 825     // allocations in existance before the call; a nofree function *is* allowed
 826     // to free memory it allocated.
 827     const Function *F = A->getParent();
 828     if (F->doesNotFreeMemory() && F->hasNoSync())
 829       return false;
 830   }
 831
 832   const Function *F = nullptr;
 833   if (auto *I = dyn_cast<Instruction>(this))
 834     F = I->getFunction();
 835   if (auto *A = dyn_cast<Argument>(this))
 836     F = A->getParent();
 837
 838   if (!F)
 839     return true;
 840
 841   // With garbage collection, deallocation typically occurs solely at or after
 842   // safepoints.  If we're compiling for a collector which uses the
 843   // gc.statepoint infrastructure, safepoints aren't explicitly present
 844   // in the IR until after lowering from abstract to physical machine model.
 845   // The collector could chose to mix explicit deallocation and gc'd objects
 846   // which is why we need the explicit opt in on a per collector basis.
 847   if (!F->hasGC())
 848     return true;
 849
 850   const auto &GCName = F->getGC();
 851   if (GCName == "statepoint-example") {
 852     auto *PT = cast<PointerType>(this->getType());
 853     if (PT->getAddressSpace() != 1)
 854       // For the sake of this example GC, we arbitrarily pick addrspace(1) as
 855       // our GC managed heap.  This must match the same check in
 856       // RewriteStatepointsForGC (and probably needs better factored.)
 857       return true;
 858
 859     // It is cheaper to scan for a declaration than to scan for a use in this
 860     // function.  Note that gc.statepoint is a type overloaded function so the
 861     // usual trick of requesting declaration of the intrinsic from the module
 862     // doesn't work.
 863     for (auto &Fn : *F->getParent())
 864       if (Fn.getIntrinsicID() == Intrinsic::experimental_gc_statepoint)
 865         return true;
 866     return false;
 867   }
 868   return true;
 869 }
 870
 871 uint64_t Value::getPointerDereferenceableBytes(const DataLayout &DL,
 872                                                bool &CanBeNull,
 873                                                bool &CanBeFreed) const {
 874   assert(getType()->isPointerTy() && "must be pointer");
 875
 876   uint64_t DerefBytes = 0;
 877   CanBeNull = false;
 878   CanBeFreed = UseDerefAtPointSemantics && canBeFreed();
 879   if (const Argument *A = dyn_cast<Argument>(this)) {
 880     DerefBytes = A->getDereferenceableBytes();
 881     if (DerefBytes == 0) {
 882       // Handle byval/byref/inalloca/preallocated arguments
 883       if (Type *ArgMemTy = A->getPointeeInMemoryValueType()) {
 884         if (ArgMemTy->isSized()) {
 885           // FIXME: Why isn't this the type alloc size?
 886           DerefBytes = DL.getTypeStoreSize(ArgMemTy).getKnownMinValue();
 887         }
 888       }
 889     }
 890
 891     if (DerefBytes == 0) {
 892       DerefBytes = A->getDereferenceableOrNullBytes();
 893       CanBeNull = true;
 894     }
 895   } else if (const auto *Call = dyn_cast<CallBase>(this)) {
 896     DerefBytes = Call->getRetDereferenceableBytes();
 897     if (DerefBytes == 0) {
 898       DerefBytes = Call->getRetDereferenceableOrNullBytes();
 899       CanBeNull = true;
 900     }
 901   } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
 902     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) {
 903       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 904       DerefBytes = CI->getLimitedValue();
 905     }
 906     if (DerefBytes == 0) {
 907       if (MDNode *MD =
 908               LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
 909         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 910         DerefBytes = CI->getLimitedValue();
 911       }
 912       CanBeNull = true;
 913     }
 914   } else if (auto *IP = dyn_cast<IntToPtrInst>(this)) {
 915     if (MDNode *MD = IP->getMetadata(LLVMContext::MD_dereferenceable)) {
 916       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 917       DerefBytes = CI->getLimitedValue();
 918     }
 919     if (DerefBytes == 0) {
 920       if (MDNode *MD =
 921               IP->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
 922         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 923         DerefBytes = CI->getLimitedValue();
 924       }
 925       CanBeNull = true;
 926     }
 927   } else if (auto *AI = dyn_cast<AllocaInst>(this)) {
 928     if (!AI->isArrayAllocation()) {
 929       DerefBytes =
 930           DL.getTypeStoreSize(AI->getAllocatedType()).getKnownMinValue();
 931       CanBeNull = false;
 932       CanBeFreed = false;
 933     }
 934   } else if (auto *GV = dyn_cast<GlobalVariable>(this)) {
 935     if (GV->getValueType()->isSized() && !GV->hasExternalWeakLinkage()) {
 936       // TODO: Don't outright reject hasExternalWeakLinkage but set the
 937       // CanBeNull flag.
 938       DerefBytes = DL.getTypeStoreSize(GV->getValueType()).getFixedValue();
 939       CanBeNull = false;
 940       CanBeFreed = false;
 941     }
 942   }
 943   return DerefBytes;
 944 }
 945
 946 Align Value::getPointerAlignment(const DataLayout &DL) const {
 947   assert(getType()->isPointerTy() && "must be pointer");
 948   if (auto *GO = dyn_cast<GlobalObject>(this)) {
 949     if (isa<Function>(GO)) {
 950       Align FunctionPtrAlign = DL.getFunctionPtrAlign().valueOrOne();
 951       switch (DL.getFunctionPtrAlignType()) {
 952       case DataLayout::FunctionPtrAlignType::Independent:
 953         return FunctionPtrAlign;
 954       case DataLayout::FunctionPtrAlignType::MultipleOfFunctionAlign:
 955         return std::max(FunctionPtrAlign, GO->getAlign().valueOrOne());
 956       }
 957       llvm_unreachable("Unhandled FunctionPtrAlignType");
 958     }
 959     const MaybeAlign Alignment(GO->getAlign());
 960     if (!Alignment) {
 961       if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
 962         Type *ObjectType = GVar->getValueType();
 963         if (ObjectType->isSized()) {
 964           // If the object is defined in the current Module, we'll be giving
 965           // it the preferred alignment. Otherwise, we have to assume that it
 966           // may only have the minimum ABI alignment.
 967           if (GVar->isStrongDefinitionForLinker())
 968             return DL.getPreferredAlign(GVar);
 969           else
 970             return DL.getABITypeAlign(ObjectType);
 971         }
 972       }
 973     }
 974     return Alignment.valueOrOne();
 975   } else if (const Argument *A = dyn_cast<Argument>(this)) {
 976     const MaybeAlign Alignment = A->getParamAlign();
 977     if (!Alignment && A->hasStructRetAttr()) {
 978       // An sret parameter has at least the ABI alignment of the return type.
 979       Type *EltTy = A->getParamStructRetType();
 980       if (EltTy->isSized())
 981         return DL.getABITypeAlign(EltTy);
 982     }
 983     return Alignment.valueOrOne();
 984   } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(this)) {
 985     return AI->getAlign();
 986   } else if (const auto *Call = dyn_cast<CallBase>(this)) {
 987     MaybeAlign Alignment = Call->getRetAlign();
 988     if (!Alignment && Call->getCalledFunction())
 989       Alignment = Call->getCalledFunction()->getAttributes().getRetAlignment();
 990     return Alignment.valueOrOne();
 991   } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
 992     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_align)) {
 993       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 994       return Align(CI->getLimitedValue());
 995     }
 996   } else if (auto *CstPtr = dyn_cast<Constant>(this)) {
 997     // Strip pointer casts to avoid creating unnecessary ptrtoint expression
 998     // if the only "reduction" is combining a bitcast + ptrtoint.
 999     CstPtr = CstPtr->stripPointerCasts();
1000     if (auto *CstInt = dyn_cast_or_null<ConstantInt>(ConstantExpr::getPtrToInt(
1001             const_cast<Constant *>(CstPtr), DL.getIntPtrType(getType()),
1002             /*OnlyIfReduced=*/true))) {
1003       size_t TrailingZeros = CstInt->getValue().countr_zero();
1004       // While the actual alignment may be large, elsewhere we have
1005       // an arbitrary upper alignmet limit, so let's clamp to it.
1006       return Align(TrailingZeros < Value::MaxAlignmentExponent
1007                        ? uint64_t(1) << TrailingZeros
1008                        : Value::MaximumAlignment);
1009     }
1010   }
1011   return Align(1);
1012 }
1013
1014 static std::optional<int64_t>
1015 getOffsetFromIndex(const GEPOperator *GEP, unsigned Idx, const DataLayout &DL) {
1016   // Skip over the first indices.
1017   gep_type_iterator GTI = gep_type_begin(GEP);
1018   for (unsigned i = 1; i != Idx; ++i, ++GTI)
1019     /*skip along*/;
1020
1021   // Compute the offset implied by the rest of the indices.
1022   int64_t Offset = 0;
1023   for (unsigned i = Idx, e = GEP->getNumOperands(); i != e; ++i, ++GTI) {
1024     ConstantInt *OpC = dyn_cast<ConstantInt>(GEP->getOperand(i));
1025     if (!OpC)
1026       return std::nullopt;
1027     if (OpC->isZero())
1028       continue; // No offset.
1029
1030     // Handle struct indices, which add their field offset to the pointer.
1031     if (StructType *STy = GTI.getStructTypeOrNull()) {
1032       Offset += DL.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
1033       continue;
1034     }
1035
1036     // Otherwise, we have a sequential type like an array or fixed-length
1037     // vector. Multiply the index by the ElementSize.
1038     TypeSize Size = GTI.getSequentialElementStride(DL);
1039     if (Size.isScalable())
1040       return std::nullopt;
1041     Offset += Size.getFixedValue() * OpC->getSExtValue();
1042   }
1043
1044   return Offset;
1045 }
1046
1047 std::optional<int64_t> Value::getPointerOffsetFrom(const Value *Other,
1048                                                    const DataLayout &DL) const {
1049   const Value *Ptr1 = Other;
1050   const Value *Ptr2 = this;
1051   APInt Offset1(DL.getIndexTypeSizeInBits(Ptr1->getType()), 0);
1052   APInt Offset2(DL.getIndexTypeSizeInBits(Ptr2->getType()), 0);
1053   Ptr1 = Ptr1->stripAndAccumulateConstantOffsets(DL, Offset1, true);
1054   Ptr2 = Ptr2->stripAndAccumulateConstantOffsets(DL, Offset2, true);
1055
1056   // Handle the trivial case first.
1057   if (Ptr1 == Ptr2)
1058     return Offset2.getSExtValue() - Offset1.getSExtValue();
1059
1060   const GEPOperator *GEP1 = dyn_cast<GEPOperator>(Ptr1);
1061   const GEPOperator *GEP2 = dyn_cast<GEPOperator>(Ptr2);
1062
1063   // Right now we handle the case when Ptr1/Ptr2 are both GEPs with an identical
1064   // base.  After that base, they may have some number of common (and
1065   // potentially variable) indices.  After that they handle some constant
1066   // offset, which determines their offset from each other.  At this point, we
1067   // handle no other case.
1068   if (!GEP1 || !GEP2 || GEP1->getOperand(0) != GEP2->getOperand(0) ||
1069       GEP1->getSourceElementType() != GEP2->getSourceElementType())
1070     return std::nullopt;
1071
1072   // Skip any common indices and track the GEP types.
1073   unsigned Idx = 1;
1074   for (; Idx != GEP1->getNumOperands() && Idx != GEP2->getNumOperands(); ++Idx)
1075     if (GEP1->getOperand(Idx) != GEP2->getOperand(Idx))
1076       break;
1077
1078   auto IOffset1 = getOffsetFromIndex(GEP1, Idx, DL);
1079   auto IOffset2 = getOffsetFromIndex(GEP2, Idx, DL);
1080   if (!IOffset1 || !IOffset2)
1081     return std::nullopt;
1082   return *IOffset2 - *IOffset1 + Offset2.getSExtValue() -
1083          Offset1.getSExtValue();
1084 }
1085
1086 const Value *Value::DoPHITranslation(const BasicBlock *CurBB,
1087                                      const BasicBlock *PredBB) const {
1088   auto *PN = dyn_cast<PHINode>(this);
1089   if (PN && PN->getParent() == CurBB)
1090     return PN->getIncomingValueForBlock(PredBB);
1091   return this;
1092 }
1093
1094 LLVMContext &Value::getContext() const { return VTy->getContext(); }
1095
1096 void Value::reverseUseList() {
1097   if (!UseList || !UseList->Next)
1098     // No need to reverse 0 or 1 uses.
1099     return;
1100
1101   Use *Head = UseList;
1102   Use *Current = UseList->Next;
1103   Head->Next = nullptr;
1104   while (Current) {
1105     Use *Next = Current->Next;
1106     Current->Next = Head;
1107     Head->Prev = &Current->Next;
1108     Head = Current;
1109     Current = Next;
1110   }
1111   UseList = Head;
1112   Head->Prev = &UseList;
1113 }
1114
1115 bool Value::isSwiftError() const {
1116   auto *Arg = dyn_cast<Argument>(this);
1117   if (Arg)
1118     return Arg->hasSwiftErrorAttr();
1119   auto *Alloca = dyn_cast<AllocaInst>(this);
1120   if (!Alloca)
1121     return false;
1122   return Alloca->isSwiftError();
1123 }
1124
1125 //===----------------------------------------------------------------------===//
1126 //                             ValueHandleBase Class
1127 //===----------------------------------------------------------------------===//
1128
1129 void ValueHandleBase::AddToExistingUseList(ValueHandleBase **List) {
1130   assert(List && "Handle list is null?");
1131
1132   // Splice ourselves into the list.
1133   Next = *List;
1134   *List = this;
1135   setPrevPtr(List);
1136   if (Next) {
1137     Next->setPrevPtr(&Next);
1138     assert(getValPtr() == Next->getValPtr() && "Added to wrong list?");
1139   }
1140 }
1141
1142 void ValueHandleBase::AddToExistingUseListAfter(ValueHandleBase *List) {
1143   assert(List && "Must insert after existing node");
1144
1145   Next = List->Next;
1146   setPrevPtr(&List->Next);
1147   List->Next = this;
1148   if (Next)
1149     Next->setPrevPtr(&Next);
1150 }
1151
1152 void ValueHandleBase::AddToUseList() {
1153   assert(getValPtr() && "Null pointer doesn't have a use list!");
1154
1155   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
1156
1157   if (getValPtr()->HasValueHandle) {
1158     // If this value already has a ValueHandle, then it must be in the
1159     // ValueHandles map already.
1160     ValueHandleBase *&Entry = pImpl->ValueHandles[getValPtr()];
1161     assert(Entry && "Value doesn't have any handles?");
1162     AddToExistingUseList(&Entry);
1163     return;
1164   }
1165
1166   // Ok, it doesn't have any handles yet, so we must insert it into the
1167   // DenseMap.  However, doing this insertion could cause the DenseMap to
1168   // reallocate itself, which would invalidate all of the PrevP pointers that
1169   // point into the old table.  Handle this by checking for reallocation and
1170   // updating the stale pointers only if needed.
1171   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
1172   const void *OldBucketPtr = Handles.getPointerIntoBucketsArray();
1173
1174   ValueHandleBase *&Entry = Handles[getValPtr()];
1175   assert(!Entry && "Value really did already have handles?");
1176   AddToExistingUseList(&Entry);
1177   getValPtr()->HasValueHandle = true;
1178
1179   // If reallocation didn't happen or if this was the first insertion, don't
1180   // walk the table.
1181   if (Handles.isPointerIntoBucketsArray(OldBucketPtr) ||
1182       Handles.size() == 1) {
1183     return;
1184   }
1185
1186   // Okay, reallocation did happen.  Fix the Prev Pointers.
1187   for (DenseMap<Value*, ValueHandleBase*>::iterator I = Handles.begin(),
1188        E = Handles.end(); I != E; ++I) {
1189     assert(I->second && I->first == I->second->getValPtr() &&
1190            "List invariant broken!");
1191     I->second->setPrevPtr(&I->second);
1192   }
1193 }
1194
1195 void ValueHandleBase::RemoveFromUseList() {
1196   assert(getValPtr() && getValPtr()->HasValueHandle &&
1197          "Pointer doesn't have a use list!");
1198
1199   // Unlink this from its use list.
1200   ValueHandleBase **PrevPtr = getPrevPtr();
1201   assert(*PrevPtr == this && "List invariant broken");
1202
1203   *PrevPtr = Next;
1204   if (Next) {
1205     assert(Next->getPrevPtr() == &Next && "List invariant broken");
1206     Next->setPrevPtr(PrevPtr);
1207     return;
1208   }
1209
1210   // If the Next pointer was null, then it is possible that this was the last
1211   // ValueHandle watching VP.  If so, delete its entry from the ValueHandles
1212   // map.
1213   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
1214   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
1215   if (Handles.isPointerIntoBucketsArray(PrevPtr)) {
1216     Handles.erase(getValPtr());
1217     getValPtr()->HasValueHandle = false;
1218   }
1219 }
1220
1221 void ValueHandleBase::ValueIsDeleted(Value *V) {
1222   assert(V->HasValueHandle && "Should only be called if ValueHandles present");
1223
1224   // Get the linked list base, which is guaranteed to exist since the
1225   // HasValueHandle flag is set.
1226   LLVMContextImpl *pImpl = V->getContext().pImpl;
1227   ValueHandleBase *Entry = pImpl->ValueHandles[V];
1228   assert(Entry && "Value bit set but no entries exist");
1229
1230   // We use a local ValueHandleBase as an iterator so that ValueHandles can add
1231   // and remove themselves from the list without breaking our iteration.  This
1232   // is not really an AssertingVH; we just have to give ValueHandleBase a kind.
1233   // Note that we deliberately do not the support the case when dropping a value
1234   // handle results in a new value handle being permanently added to the list
1235   // (as might occur in theory for CallbackVH's): the new value handle will not
1236   // be processed and the checking code will mete out righteous punishment if
1237   // the handle is still present once we have finished processing all the other
1238   // value handles (it is fine to momentarily add then remove a value handle).
1239   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
1240     Iterator.RemoveFromUseList();
1241     Iterator.AddToExistingUseListAfter(Entry);
1242     assert(Entry->Next == &Iterator && "Loop invariant broken.");
1243
1244     switch (Entry->getKind()) {
1245     case Assert:
1246       break;
1247     case Weak:
1248     case WeakTracking:
1249       // WeakTracking and Weak just go to null, which unlinks them
1250       // from the list.
1251       Entry->operator=(nullptr);
1252       break;
1253     case Callback:
1254       // Forward to the subclass's implementation.
1255       static_cast<CallbackVH*>(Entry)->deleted();
1256       break;
1257     }
1258   }
1259
1260   // All callbacks, weak references, and assertingVHs should be dropped by now.
1261   if (V->HasValueHandle) {
1262 #ifndef NDEBUG      // Only in +Asserts mode...
1263     dbgs() << "While deleting: " << *V->getType() << " %" << V->getName()
1264            << "\n";
1265     if (pImpl->ValueHandles[V]->getKind() == Assert)
1266       llvm_unreachable("An asserting value handle still pointed to this"
1267                        " value!");
1268
1269 #endif
1270     llvm_unreachable("All references to V were not removed?");
1271   }
1272 }
1273
1274 void ValueHandleBase::ValueIsRAUWd(Value *Old, Value *New) {
1275   assert(Old->HasValueHandle &&"Should only be called if ValueHandles present");
1276   assert(Old != New && "Changing value into itself!");
1277   assert(Old->getType() == New->getType() &&
1278          "replaceAllUses of value with new value of different type!");
1279
1280   // Get the linked list base, which is guaranteed to exist since the
1281   // HasValueHandle flag is set.
1282   LLVMContextImpl *pImpl = Old->getContext().pImpl;
1283   ValueHandleBase *Entry = pImpl->ValueHandles[Old];
1284
1285   assert(Entry && "Value bit set but no entries exist");
1286
1287   // We use a local ValueHandleBase as an iterator so that
1288   // ValueHandles can add and remove themselves from the list without
1289   // breaking our iteration.  This is not really an AssertingVH; we
1290   // just have to give ValueHandleBase some kind.
1291   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
1292     Iterator.RemoveFromUseList();
1293     Iterator.AddToExistingUseListAfter(Entry);
1294     assert(Entry->Next == &Iterator && "Loop invariant broken.");
1295
1296     switch (Entry->getKind()) {
1297     case Assert:
1298     case Weak:
1299       // Asserting and Weak handles do not follow RAUW implicitly.
1300       break;
1301     case WeakTracking:
1302       // Weak goes to the new value, which will unlink it from Old's list.
1303       Entry->operator=(New);
1304       break;
1305     case Callback:
1306       // Forward to the subclass's implementation.
1307       static_cast<CallbackVH*>(Entry)->allUsesReplacedWith(New);
1308       break;
1309     }
1310   }
1311
1312 #ifndef NDEBUG
1313   // If any new weak value handles were added while processing the
1314   // list, then complain about it now.
1315   if (Old->HasValueHandle)
1316     for (Entry = pImpl->ValueHandles[Old]; Entry; Entry = Entry->Next)
1317       switch (Entry->getKind()) {
1318       case WeakTracking:
1319         dbgs() << "After RAUW from " << *Old->getType() << " %"
1320                << Old->getName() << " to " << *New->getType() << " %"
1321                << New->getName() << "\n";
1322         llvm_unreachable(
1323             "A weak tracking value handle still pointed to the old value!\n");
1324       default:
1325         break;
1326       }
1327 #endif
1328 }
1329
1330 // Pin the vtable to this file.
1331 void CallbackVH::anchor() {}