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/ADT/SetVector.h"
  18 #include "llvm/IR/Constant.h"
  19 #include "llvm/IR/Constants.h"
  20 #include "llvm/IR/DataLayout.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/Statepoint.h"
  30 #include "llvm/IR/ValueHandle.h"
  31 #include "llvm/IR/ValueSymbolTable.h"
  32 #include "llvm/Support/Debug.h"
  33 #include "llvm/Support/ErrorHandling.h"
  34 #include "llvm/Support/ManagedStatic.h"
  35 #include "llvm/Support/raw_ostream.h"
  36 #include <algorithm>
  37
  38 using namespace llvm;
  39
  40 static cl::opt<unsigned> NonGlobalValueMaxNameSize(
  41     "non-global-value-max-name-size", cl::Hidden, cl::init(1024),
  42     cl::desc("Maximum size for the name of non-global values."));
  43
  44 //===----------------------------------------------------------------------===//
  45 //                                Value Class
  46 //===----------------------------------------------------------------------===//
  47 static inline Type *checkType(Type *Ty) {
  48   assert(Ty && "Value defined with a null type: Error!");
  49   return Ty;
  50 }
  51
  52 Value::Value(Type *ty, unsigned scid)
  53     : VTy(checkType(ty)), UseList(nullptr), SubclassID(scid),
  54       HasValueHandle(0), SubclassOptionalData(0), SubclassData(0),
  55       NumUserOperands(0), IsUsedByMD(false), HasName(false) {
  56   static_assert(ConstantFirstVal == 0, "!(SubclassID < ConstantFirstVal)");
  57   // FIXME: Why isn't this in the subclass gunk??
  58   // Note, we cannot call isa<CallInst> before the CallInst has been
  59   // constructed.
  60   if (SubclassID == Instruction::Call || SubclassID == Instruction::Invoke ||
  61       SubclassID == Instruction::CallBr)
  62     assert((VTy->isFirstClassType() || VTy->isVoidTy() || VTy->isStructTy()) &&
  63            "invalid CallInst type!");
  64   else if (SubclassID != BasicBlockVal &&
  65            (/*SubclassID < ConstantFirstVal ||*/ SubclassID > ConstantLastVal))
  66     assert((VTy->isFirstClassType() || VTy->isVoidTy()) &&
  67            "Cannot create non-first-class values except for constants!");
  68   static_assert(sizeof(Value) == 2 * sizeof(void *) + 2 * sizeof(unsigned),
  69                 "Value too big");
  70 }
  71
  72 Value::~Value() {
  73   // Notify all ValueHandles (if present) that this value is going away.
  74   if (HasValueHandle)
  75     ValueHandleBase::ValueIsDeleted(this);
  76   if (isUsedByMetadata())
  77     ValueAsMetadata::handleDeletion(this);
  78
  79 #ifndef NDEBUG      // Only in -g mode...
  80   // Check to make sure that there are no uses of this value that are still
  81   // around when the value is destroyed.  If there are, then we have a dangling
  82   // reference and something is wrong.  This code is here to print out where
  83   // the value is still being referenced.
  84   //
  85   if (!use_empty()) {
  86     dbgs() << "While deleting: " << *VTy << " %" << getName() << "\n";
  87     for (auto *U : users())
  88       dbgs() << "Use still stuck around after Def is destroyed:" << *U << "\n";
  89   }
  90 #endif
  91   assert(use_empty() && "Uses remain when a value is destroyed!");
  92
  93   // If this value is named, destroy the name.  This should not be in a symtab
  94   // at this point.
  95   destroyValueName();
  96 }
  97
  98 void Value::deleteValue() {
  99   switch (getValueID()) {
 100 #define HANDLE_VALUE(Name)                                                     \
 101   case Value::Name##Val:                                                       \
 102     delete static_cast<Name *>(this);                                          \
 103     break;
 104 #define HANDLE_MEMORY_VALUE(Name)                                              \
 105   case Value::Name##Val:                                                       \
 106     static_cast<DerivedUser *>(this)->DeleteValue(                             \
 107         static_cast<DerivedUser *>(this));                                     \
 108     break;
 109 #define HANDLE_INSTRUCTION(Name)  /* nothing */
 110 #include "llvm/IR/Value.def"
 111
 112 #define HANDLE_INST(N, OPC, CLASS)                                             \
 113   case Value::InstructionVal + Instruction::OPC:                               \
 114     delete static_cast<CLASS *>(this);                                         \
 115     break;
 116 #define HANDLE_USER_INST(N, OPC, CLASS)
 117 #include "llvm/IR/Instruction.def"
 118
 119   default:
 120     llvm_unreachable("attempting to delete unknown value kind");
 121   }
 122 }
 123
 124 void Value::destroyValueName() {
 125   ValueName *Name = getValueName();
 126   if (Name)
 127     Name->Destroy();
 128   setValueName(nullptr);
 129 }
 130
 131 bool Value::hasNUses(unsigned N) const {
 132   return hasNItems(use_begin(), use_end(), N);
 133 }
 134
 135 bool Value::hasNUsesOrMore(unsigned N) const {
 136   return hasNItemsOrMore(use_begin(), use_end(), N);
 137 }
 138
 139 bool Value::isUsedInBasicBlock(const BasicBlock *BB) const {
 140   // This can be computed either by scanning the instructions in BB, or by
 141   // scanning the use list of this Value. Both lists can be very long, but
 142   // usually one is quite short.
 143   //
 144   // Scan both lists simultaneously until one is exhausted. This limits the
 145   // search to the shorter list.
 146   BasicBlock::const_iterator BI = BB->begin(), BE = BB->end();
 147   const_user_iterator UI = user_begin(), UE = user_end();
 148   for (; BI != BE && UI != UE; ++BI, ++UI) {
 149     // Scan basic block: Check if this Value is used by the instruction at BI.
 150     if (is_contained(BI->operands(), this))
 151       return true;
 152     // Scan use list: Check if the use at UI is in BB.
 153     const auto *User = dyn_cast<Instruction>(*UI);
 154     if (User && User->getParent() == BB)
 155       return true;
 156   }
 157   return false;
 158 }
 159
 160 unsigned Value::getNumUses() const {
 161   return (unsigned)std::distance(use_begin(), use_end());
 162 }
 163
 164 static bool getSymTab(Value *V, ValueSymbolTable *&ST) {
 165   ST = nullptr;
 166   if (Instruction *I = dyn_cast<Instruction>(V)) {
 167     if (BasicBlock *P = I->getParent())
 168       if (Function *PP = P->getParent())
 169         ST = PP->getValueSymbolTable();
 170   } else if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
 171     if (Function *P = BB->getParent())
 172       ST = P->getValueSymbolTable();
 173   } else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
 174     if (Module *P = GV->getParent())
 175       ST = &P->getValueSymbolTable();
 176   } else if (Argument *A = dyn_cast<Argument>(V)) {
 177     if (Function *P = A->getParent())
 178       ST = P->getValueSymbolTable();
 179   } else {
 180     assert(isa<Constant>(V) && "Unknown value type!");
 181     return true;  // no name is setable for this.
 182   }
 183   return false;
 184 }
 185
 186 ValueName *Value::getValueName() const {
 187   if (!HasName) return nullptr;
 188
 189   LLVMContext &Ctx = getContext();
 190   auto I = Ctx.pImpl->ValueNames.find(this);
 191   assert(I != Ctx.pImpl->ValueNames.end() &&
 192          "No name entry found!");
 193
 194   return I->second;
 195 }
 196
 197 void Value::setValueName(ValueName *VN) {
 198   LLVMContext &Ctx = getContext();
 199
 200   assert(HasName == Ctx.pImpl->ValueNames.count(this) &&
 201          "HasName bit out of sync!");
 202
 203   if (!VN) {
 204     if (HasName)
 205       Ctx.pImpl->ValueNames.erase(this);
 206     HasName = false;
 207     return;
 208   }
 209
 210   HasName = true;
 211   Ctx.pImpl->ValueNames[this] = VN;
 212 }
 213
 214 StringRef Value::getName() const {
 215   // Make sure the empty string is still a C string. For historical reasons,
 216   // some clients want to call .data() on the result and expect it to be null
 217   // terminated.
 218   if (!hasName())
 219     return StringRef("", 0);
 220   return getValueName()->getKey();
 221 }
 222
 223 void Value::setNameImpl(const Twine &NewName) {
 224   // Fast-path: LLVMContext can be set to strip out non-GlobalValue names
 225   if (getContext().shouldDiscardValueNames() && !isa<GlobalValue>(this))
 226     return;
 227
 228   // Fast path for common IRBuilder case of setName("") when there is no name.
 229   if (NewName.isTriviallyEmpty() && !hasName())
 230     return;
 231
 232   SmallString<256> NameData;
 233   StringRef NameRef = NewName.toStringRef(NameData);
 234   assert(NameRef.find_first_of(0) == StringRef::npos &&
 235          "Null bytes are not allowed in names");
 236
 237   // Name isn't changing?
 238   if (getName() == NameRef)
 239     return;
 240
 241   // Cap the size of non-GlobalValue names.
 242   if (NameRef.size() > NonGlobalValueMaxNameSize && !isa<GlobalValue>(this))
 243     NameRef =
 244         NameRef.substr(0, std::max(1u, (unsigned)NonGlobalValueMaxNameSize));
 245
 246   assert(!getType()->isVoidTy() && "Cannot assign a name to void values!");
 247
 248   // Get the symbol table to update for this object.
 249   ValueSymbolTable *ST;
 250   if (getSymTab(this, ST))
 251     return;  // Cannot set a name on this value (e.g. constant).
 252
 253   if (!ST) { // No symbol table to update?  Just do the change.
 254     if (NameRef.empty()) {
 255       // Free the name for this value.
 256       destroyValueName();
 257       return;
 258     }
 259
 260     // NOTE: Could optimize for the case the name is shrinking to not deallocate
 261     // then reallocated.
 262     destroyValueName();
 263
 264     // Create the new name.
 265     setValueName(ValueName::Create(NameRef));
 266     getValueName()->setValue(this);
 267     return;
 268   }
 269
 270   // NOTE: Could optimize for the case the name is shrinking to not deallocate
 271   // then reallocated.
 272   if (hasName()) {
 273     // Remove old name.
 274     ST->removeValueName(getValueName());
 275     destroyValueName();
 276
 277     if (NameRef.empty())
 278       return;
 279   }
 280
 281   // Name is changing to something new.
 282   setValueName(ST->createValueName(NameRef, this));
 283 }
 284
 285 void Value::setName(const Twine &NewName) {
 286   setNameImpl(NewName);
 287   if (Function *F = dyn_cast<Function>(this))
 288     F->recalculateIntrinsicID();
 289 }
 290
 291 void Value::takeName(Value *V) {
 292   ValueSymbolTable *ST = nullptr;
 293   // If this value has a name, drop it.
 294   if (hasName()) {
 295     // Get the symtab this is in.
 296     if (getSymTab(this, ST)) {
 297       // We can't set a name on this value, but we need to clear V's name if
 298       // it has one.
 299       if (V->hasName()) V->setName("");
 300       return;  // Cannot set a name on this value (e.g. constant).
 301     }
 302
 303     // Remove old name.
 304     if (ST)
 305       ST->removeValueName(getValueName());
 306     destroyValueName();
 307   }
 308
 309   // Now we know that this has no name.
 310
 311   // If V has no name either, we're done.
 312   if (!V->hasName()) return;
 313
 314   // Get this's symtab if we didn't before.
 315   if (!ST) {
 316     if (getSymTab(this, ST)) {
 317       // Clear V's name.
 318       V->setName("");
 319       return;  // Cannot set a name on this value (e.g. constant).
 320     }
 321   }
 322
 323   // Get V's ST, this should always succed, because V has a name.
 324   ValueSymbolTable *VST;
 325   bool Failure = getSymTab(V, VST);
 326   assert(!Failure && "V has a name, so it should have a ST!"); (void)Failure;
 327
 328   // If these values are both in the same symtab, we can do this very fast.
 329   // This works even if both values have no symtab yet.
 330   if (ST == VST) {
 331     // Take the name!
 332     setValueName(V->getValueName());
 333     V->setValueName(nullptr);
 334     getValueName()->setValue(this);
 335     return;
 336   }
 337
 338   // Otherwise, things are slightly more complex.  Remove V's name from VST and
 339   // then reinsert it into ST.
 340
 341   if (VST)
 342     VST->removeValueName(V->getValueName());
 343   setValueName(V->getValueName());
 344   V->setValueName(nullptr);
 345   getValueName()->setValue(this);
 346
 347   if (ST)
 348     ST->reinsertValue(this);
 349 }
 350
 351 void Value::assertModuleIsMaterializedImpl() const {
 352 #ifndef NDEBUG
 353   const GlobalValue *GV = dyn_cast<GlobalValue>(this);
 354   if (!GV)
 355     return;
 356   const Module *M = GV->getParent();
 357   if (!M)
 358     return;
 359   assert(M->isMaterialized());
 360 #endif
 361 }
 362
 363 #ifndef NDEBUG
 364 static bool contains(SmallPtrSetImpl<ConstantExpr *> &Cache, ConstantExpr *Expr,
 365                      Constant *C) {
 366   if (!Cache.insert(Expr).second)
 367     return false;
 368
 369   for (auto &O : Expr->operands()) {
 370     if (O == C)
 371       return true;
 372     auto *CE = dyn_cast<ConstantExpr>(O);
 373     if (!CE)
 374       continue;
 375     if (contains(Cache, CE, C))
 376       return true;
 377   }
 378   return false;
 379 }
 380
 381 static bool contains(Value *Expr, Value *V) {
 382   if (Expr == V)
 383     return true;
 384
 385   auto *C = dyn_cast<Constant>(V);
 386   if (!C)
 387     return false;
 388
 389   auto *CE = dyn_cast<ConstantExpr>(Expr);
 390   if (!CE)
 391     return false;
 392
 393   SmallPtrSet<ConstantExpr *, 4> Cache;
 394   return contains(Cache, CE, C);
 395 }
 396 #endif // NDEBUG
 397
 398 void Value::doRAUW(Value *New, ReplaceMetadataUses ReplaceMetaUses) {
 399   assert(New && "Value::replaceAllUsesWith(<null>) is invalid!");
 400   assert(!contains(New, this) &&
 401          "this->replaceAllUsesWith(expr(this)) is NOT valid!");
 402   assert(New->getType() == getType() &&
 403          "replaceAllUses of value with new value of different type!");
 404
 405   // Notify all ValueHandles (if present) that this value is going away.
 406   if (HasValueHandle)
 407     ValueHandleBase::ValueIsRAUWd(this, New);
 408   if (ReplaceMetaUses == ReplaceMetadataUses::Yes && isUsedByMetadata())
 409     ValueAsMetadata::handleRAUW(this, New);
 410
 411   while (!materialized_use_empty()) {
 412     Use &U = *UseList;
 413     // Must handle Constants specially, we cannot call replaceUsesOfWith on a
 414     // constant because they are uniqued.
 415     if (auto *C = dyn_cast<Constant>(U.getUser())) {
 416       if (!isa<GlobalValue>(C)) {
 417         C->handleOperandChange(this, New);
 418         continue;
 419       }
 420     }
 421
 422     U.set(New);
 423   }
 424
 425   if (BasicBlock *BB = dyn_cast<BasicBlock>(this))
 426     BB->replaceSuccessorsPhiUsesWith(cast<BasicBlock>(New));
 427 }
 428
 429 void Value::replaceAllUsesWith(Value *New) {
 430   doRAUW(New, ReplaceMetadataUses::Yes);
 431 }
 432
 433 void Value::replaceNonMetadataUsesWith(Value *New) {
 434   doRAUW(New, ReplaceMetadataUses::No);
 435 }
 436
 437 // Like replaceAllUsesWith except it does not handle constants or basic blocks.
 438 // This routine leaves uses within BB.
 439 void Value::replaceUsesOutsideBlock(Value *New, BasicBlock *BB) {
 440   assert(New && "Value::replaceUsesOutsideBlock(<null>, BB) is invalid!");
 441   assert(!contains(New, this) &&
 442          "this->replaceUsesOutsideBlock(expr(this), BB) is NOT valid!");
 443   assert(New->getType() == getType() &&
 444          "replaceUses of value with new value of different type!");
 445   assert(BB && "Basic block that may contain a use of 'New' must be defined\n");
 446
 447   replaceUsesWithIf(New, [BB](Use &U) {
 448     auto *I = dyn_cast<Instruction>(U.getUser());
 449     // Don't replace if it's an instruction in the BB basic block.
 450     return !I || I->getParent() != BB;
 451   });
 452 }
 453
 454 namespace {
 455 // Various metrics for how much to strip off of pointers.
 456 enum PointerStripKind {
 457   PSK_ZeroIndices,
 458   PSK_ZeroIndicesAndAliases,
 459   PSK_ZeroIndicesSameRepresentation,
 460   PSK_ZeroIndicesAndInvariantGroups,
 461   PSK_InBoundsConstantIndices,
 462   PSK_InBounds
 463 };
 464
 465 template <PointerStripKind StripKind>
 466 static const Value *stripPointerCastsAndOffsets(const Value *V) {
 467   if (!V->getType()->isPointerTy())
 468     return V;
 469
 470   // Even though we don't look through PHI nodes, we could be called on an
 471   // instruction in an unreachable block, which may be on a cycle.
 472   SmallPtrSet<const Value *, 4> Visited;
 473
 474   Visited.insert(V);
 475   do {
 476     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 477       switch (StripKind) {
 478       case PSK_ZeroIndices:
 479       case PSK_ZeroIndicesAndAliases:
 480       case PSK_ZeroIndicesSameRepresentation:
 481       case PSK_ZeroIndicesAndInvariantGroups:
 482         if (!GEP->hasAllZeroIndices())
 483           return V;
 484         break;
 485       case PSK_InBoundsConstantIndices:
 486         if (!GEP->hasAllConstantIndices())
 487           return V;
 488         LLVM_FALLTHROUGH;
 489       case PSK_InBounds:
 490         if (!GEP->isInBounds())
 491           return V;
 492         break;
 493       }
 494       V = GEP->getPointerOperand();
 495     } else if (Operator::getOpcode(V) == Instruction::BitCast) {
 496       V = cast<Operator>(V)->getOperand(0);
 497     } else if (StripKind != PSK_ZeroIndicesSameRepresentation &&
 498                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
 499       // TODO: If we know an address space cast will not change the
 500       //       representation we could look through it here as well.
 501       V = cast<Operator>(V)->getOperand(0);
 502     } else if (StripKind == PSK_ZeroIndicesAndAliases && isa<GlobalAlias>(V)) {
 503       V = cast<GlobalAlias>(V)->getAliasee();
 504     } else {
 505       if (const auto *Call = dyn_cast<CallBase>(V)) {
 506         if (const Value *RV = Call->getReturnedArgOperand()) {
 507           V = RV;
 508           continue;
 509         }
 510         // The result of launder.invariant.group must alias it's argument,
 511         // but it can't be marked with returned attribute, that's why it needs
 512         // special case.
 513         if (StripKind == PSK_ZeroIndicesAndInvariantGroups &&
 514             (Call->getIntrinsicID() == Intrinsic::launder_invariant_group ||
 515              Call->getIntrinsicID() == Intrinsic::strip_invariant_group)) {
 516           V = Call->getArgOperand(0);
 517           continue;
 518         }
 519       }
 520       return V;
 521     }
 522     assert(V->getType()->isPointerTy() && "Unexpected operand type!");
 523   } while (Visited.insert(V).second);
 524
 525   return V;
 526 }
 527 } // end anonymous namespace
 528
 529 const Value *Value::stripPointerCasts() const {
 530   return stripPointerCastsAndOffsets<PSK_ZeroIndices>(this);
 531 }
 532
 533 const Value *Value::stripPointerCastsAndAliases() const {
 534   return stripPointerCastsAndOffsets<PSK_ZeroIndicesAndAliases>(this);
 535 }
 536
 537 const Value *Value::stripPointerCastsSameRepresentation() const {
 538   return stripPointerCastsAndOffsets<PSK_ZeroIndicesSameRepresentation>(this);
 539 }
 540
 541 const Value *Value::stripInBoundsConstantOffsets() const {
 542   return stripPointerCastsAndOffsets<PSK_InBoundsConstantIndices>(this);
 543 }
 544
 545 const Value *Value::stripPointerCastsAndInvariantGroups() const {
 546   return stripPointerCastsAndOffsets<PSK_ZeroIndicesAndInvariantGroups>(this);
 547 }
 548
 549 const Value *
 550 Value::stripAndAccumulateConstantOffsets(const DataLayout &DL, APInt &Offset,
 551                                          bool AllowNonInbounds) const {
 552   if (!getType()->isPtrOrPtrVectorTy())
 553     return this;
 554
 555   unsigned BitWidth = Offset.getBitWidth();
 556   assert(BitWidth == DL.getIndexTypeSizeInBits(getType()) &&
 557          "The offset bit width does not match the DL specification.");
 558
 559   // Even though we don't look through PHI nodes, we could be called on an
 560   // instruction in an unreachable block, which may be on a cycle.
 561   SmallPtrSet<const Value *, 4> Visited;
 562   Visited.insert(this);
 563   const Value *V = this;
 564   do {
 565     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 566       // If in-bounds was requested, we do not strip non-in-bounds GEPs.
 567       if (!AllowNonInbounds && !GEP->isInBounds())
 568         return V;
 569
 570       // If one of the values we have visited is an addrspacecast, then
 571       // the pointer type of this GEP may be different from the type
 572       // of the Ptr parameter which was passed to this function.  This
 573       // means when we construct GEPOffset, we need to use the size
 574       // of GEP's pointer type rather than the size of the original
 575       // pointer type.
 576       APInt GEPOffset(DL.getIndexTypeSizeInBits(V->getType()), 0);
 577       if (!GEP->accumulateConstantOffset(DL, GEPOffset))
 578         return V;
 579
 580       // Stop traversal if the pointer offset wouldn't fit in the bit-width
 581       // provided by the Offset argument. This can happen due to AddrSpaceCast
 582       // stripping.
 583       if (GEPOffset.getMinSignedBits() > BitWidth)
 584         return V;
 585
 586       Offset += GEPOffset.sextOrTrunc(BitWidth);
 587       V = GEP->getPointerOperand();
 588     } else if (Operator::getOpcode(V) == Instruction::BitCast ||
 589                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
 590       V = cast<Operator>(V)->getOperand(0);
 591     } else if (auto *GA = dyn_cast<GlobalAlias>(V)) {
 592       if (!GA->isInterposable())
 593         V = GA->getAliasee();
 594     } else if (const auto *Call = dyn_cast<CallBase>(V)) {
 595         if (const Value *RV = Call->getReturnedArgOperand())
 596           V = RV;
 597     }
 598     assert(V->getType()->isPtrOrPtrVectorTy() && "Unexpected operand type!");
 599   } while (Visited.insert(V).second);
 600
 601   return V;
 602 }
 603
 604 const Value *Value::stripInBoundsOffsets() const {
 605   return stripPointerCastsAndOffsets<PSK_InBounds>(this);
 606 }
 607
 608 uint64_t Value::getPointerDereferenceableBytes(const DataLayout &DL,
 609                                                bool &CanBeNull) const {
 610   assert(getType()->isPointerTy() && "must be pointer");
 611
 612   uint64_t DerefBytes = 0;
 613   CanBeNull = false;
 614   if (const Argument *A = dyn_cast<Argument>(this)) {
 615     DerefBytes = A->getDereferenceableBytes();
 616     if (DerefBytes == 0 && (A->hasByValAttr() || A->hasStructRetAttr())) {
 617       Type *PT = cast<PointerType>(A->getType())->getElementType();
 618       if (PT->isSized())
 619         DerefBytes = DL.getTypeStoreSize(PT);
 620     }
 621     if (DerefBytes == 0) {
 622       DerefBytes = A->getDereferenceableOrNullBytes();
 623       CanBeNull = true;
 624     }
 625   } else if (const auto *Call = dyn_cast<CallBase>(this)) {
 626     DerefBytes = Call->getDereferenceableBytes(AttributeList::ReturnIndex);
 627     if (DerefBytes == 0) {
 628       DerefBytes =
 629           Call->getDereferenceableOrNullBytes(AttributeList::ReturnIndex);
 630       CanBeNull = true;
 631     }
 632   } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
 633     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) {
 634       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 635       DerefBytes = CI->getLimitedValue();
 636     }
 637     if (DerefBytes == 0) {
 638       if (MDNode *MD =
 639               LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
 640         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 641         DerefBytes = CI->getLimitedValue();
 642       }
 643       CanBeNull = true;
 644     }
 645   } else if (auto *IP = dyn_cast<IntToPtrInst>(this)) {
 646     if (MDNode *MD = IP->getMetadata(LLVMContext::MD_dereferenceable)) {
 647       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 648       DerefBytes = CI->getLimitedValue();
 649     }
 650     if (DerefBytes == 0) {
 651       if (MDNode *MD =
 652               IP->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
 653         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 654         DerefBytes = CI->getLimitedValue();
 655       }
 656       CanBeNull = true;
 657     }
 658   } else if (auto *AI = dyn_cast<AllocaInst>(this)) {
 659     if (!AI->isArrayAllocation()) {
 660       DerefBytes = DL.getTypeStoreSize(AI->getAllocatedType());
 661       CanBeNull = false;
 662     }
 663   } else if (auto *GV = dyn_cast<GlobalVariable>(this)) {
 664     if (GV->getValueType()->isSized() && !GV->hasExternalWeakLinkage()) {
 665       // TODO: Don't outright reject hasExternalWeakLinkage but set the
 666       // CanBeNull flag.
 667       DerefBytes = DL.getTypeStoreSize(GV->getValueType());
 668       CanBeNull = false;
 669     }
 670   }
 671   return DerefBytes;
 672 }
 673
 674 MaybeAlign Value::getPointerAlignment(const DataLayout &DL) const {
 675   assert(getType()->isPointerTy() && "must be pointer");
 676   if (auto *GO = dyn_cast<GlobalObject>(this)) {
 677     if (isa<Function>(GO)) {
 678       const MaybeAlign FunctionPtrAlign = DL.getFunctionPtrAlign();
 679       switch (DL.getFunctionPtrAlignType()) {
 680       case DataLayout::FunctionPtrAlignType::Independent:
 681         return FunctionPtrAlign;
 682       case DataLayout::FunctionPtrAlignType::MultipleOfFunctionAlign:
 683         return std::max(FunctionPtrAlign, MaybeAlign(GO->getAlignment()));
 684       }
 685       llvm_unreachable("Unhandled FunctionPtrAlignType");
 686     }
 687     const MaybeAlign Alignment(GO->getAlignment());
 688     if (!Alignment) {
 689       if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
 690         Type *ObjectType = GVar->getValueType();
 691         if (ObjectType->isSized()) {
 692           // If the object is defined in the current Module, we'll be giving
 693           // it the preferred alignment. Otherwise, we have to assume that it
 694           // may only have the minimum ABI alignment.
 695           if (GVar->isStrongDefinitionForLinker())
 696             return MaybeAlign(DL.getPreferredAlignment(GVar));
 697           else
 698             return Align(DL.getABITypeAlignment(ObjectType));
 699         }
 700       }
 701     }
 702     return Alignment;
 703   } else if (const Argument *A = dyn_cast<Argument>(this)) {
 704     const MaybeAlign Alignment(A->getParamAlignment());
 705     if (!Alignment && A->hasStructRetAttr()) {
 706       // An sret parameter has at least the ABI alignment of the return type.
 707       Type *EltTy = cast<PointerType>(A->getType())->getElementType();
 708       if (EltTy->isSized())
 709         return Align(DL.getABITypeAlignment(EltTy));
 710     }
 711     return Alignment;
 712   } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(this)) {
 713     const MaybeAlign Alignment(AI->getAlignment());
 714     if (!Alignment) {
 715       Type *AllocatedType = AI->getAllocatedType();
 716       if (AllocatedType->isSized())
 717         return MaybeAlign(DL.getPrefTypeAlignment(AllocatedType));
 718     }
 719     return Alignment;
 720   } else if (const auto *Call = dyn_cast<CallBase>(this)) {
 721     const MaybeAlign Alignment(Call->getRetAlignment());
 722     if (!Alignment && Call->getCalledFunction())
 723       return MaybeAlign(
 724           Call->getCalledFunction()->getAttributes().getRetAlignment());
 725     return Alignment;
 726   } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
 727     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_align)) {
 728       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 729       return MaybeAlign(CI->getLimitedValue());
 730     }
 731   }
 732   return llvm::None;
 733 }
 734
 735 const Value *Value::DoPHITranslation(const BasicBlock *CurBB,
 736                                      const BasicBlock *PredBB) const {
 737   auto *PN = dyn_cast<PHINode>(this);
 738   if (PN && PN->getParent() == CurBB)
 739     return PN->getIncomingValueForBlock(PredBB);
 740   return this;
 741 }
 742
 743 LLVMContext &Value::getContext() const { return VTy->getContext(); }
 744
 745 void Value::reverseUseList() {
 746   if (!UseList || !UseList->Next)
 747     // No need to reverse 0 or 1 uses.
 748     return;
 749
 750   Use *Head = UseList;
 751   Use *Current = UseList->Next;
 752   Head->Next = nullptr;
 753   while (Current) {
 754     Use *Next = Current->Next;
 755     Current->Next = Head;
 756     Head->setPrev(&Current->Next);
 757     Head = Current;
 758     Current = Next;
 759   }
 760   UseList = Head;
 761   Head->setPrev(&UseList);
 762 }
 763
 764 bool Value::isSwiftError() const {
 765   auto *Arg = dyn_cast<Argument>(this);
 766   if (Arg)
 767     return Arg->hasSwiftErrorAttr();
 768   auto *Alloca = dyn_cast<AllocaInst>(this);
 769   if (!Alloca)
 770     return false;
 771   return Alloca->isSwiftError();
 772 }
 773
 774 //===----------------------------------------------------------------------===//
 775 //                             ValueHandleBase Class
 776 //===----------------------------------------------------------------------===//
 777
 778 void ValueHandleBase::AddToExistingUseList(ValueHandleBase **List) {
 779   assert(List && "Handle list is null?");
 780
 781   // Splice ourselves into the list.
 782   Next = *List;
 783   *List = this;
 784   setPrevPtr(List);
 785   if (Next) {
 786     Next->setPrevPtr(&Next);
 787     assert(getValPtr() == Next->getValPtr() && "Added to wrong list?");
 788   }
 789 }
 790
 791 void ValueHandleBase::AddToExistingUseListAfter(ValueHandleBase *List) {
 792   assert(List && "Must insert after existing node");
 793
 794   Next = List->Next;
 795   setPrevPtr(&List->Next);
 796   List->Next = this;
 797   if (Next)
 798     Next->setPrevPtr(&Next);
 799 }
 800
 801 void ValueHandleBase::AddToUseList() {
 802   assert(getValPtr() && "Null pointer doesn't have a use list!");
 803
 804   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
 805
 806   if (getValPtr()->HasValueHandle) {
 807     // If this value already has a ValueHandle, then it must be in the
 808     // ValueHandles map already.
 809     ValueHandleBase *&Entry = pImpl->ValueHandles[getValPtr()];
 810     assert(Entry && "Value doesn't have any handles?");
 811     AddToExistingUseList(&Entry);
 812     return;
 813   }
 814
 815   // Ok, it doesn't have any handles yet, so we must insert it into the
 816   // DenseMap.  However, doing this insertion could cause the DenseMap to
 817   // reallocate itself, which would invalidate all of the PrevP pointers that
 818   // point into the old table.  Handle this by checking for reallocation and
 819   // updating the stale pointers only if needed.
 820   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
 821   const void *OldBucketPtr = Handles.getPointerIntoBucketsArray();
 822
 823   ValueHandleBase *&Entry = Handles[getValPtr()];
 824   assert(!Entry && "Value really did already have handles?");
 825   AddToExistingUseList(&Entry);
 826   getValPtr()->HasValueHandle = true;
 827
 828   // If reallocation didn't happen or if this was the first insertion, don't
 829   // walk the table.
 830   if (Handles.isPointerIntoBucketsArray(OldBucketPtr) ||
 831       Handles.size() == 1) {
 832     return;
 833   }
 834
 835   // Okay, reallocation did happen.  Fix the Prev Pointers.
 836   for (DenseMap<Value*, ValueHandleBase*>::iterator I = Handles.begin(),
 837        E = Handles.end(); I != E; ++I) {
 838     assert(I->second && I->first == I->second->getValPtr() &&
 839            "List invariant broken!");
 840     I->second->setPrevPtr(&I->second);
 841   }
 842 }
 843
 844 void ValueHandleBase::RemoveFromUseList() {
 845   assert(getValPtr() && getValPtr()->HasValueHandle &&
 846          "Pointer doesn't have a use list!");
 847
 848   // Unlink this from its use list.
 849   ValueHandleBase **PrevPtr = getPrevPtr();
 850   assert(*PrevPtr == this && "List invariant broken");
 851
 852   *PrevPtr = Next;
 853   if (Next) {
 854     assert(Next->getPrevPtr() == &Next && "List invariant broken");
 855     Next->setPrevPtr(PrevPtr);
 856     return;
 857   }
 858
 859   // If the Next pointer was null, then it is possible that this was the last
 860   // ValueHandle watching VP.  If so, delete its entry from the ValueHandles
 861   // map.
 862   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
 863   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
 864   if (Handles.isPointerIntoBucketsArray(PrevPtr)) {
 865     Handles.erase(getValPtr());
 866     getValPtr()->HasValueHandle = false;
 867   }
 868 }
 869
 870 void ValueHandleBase::ValueIsDeleted(Value *V) {
 871   assert(V->HasValueHandle && "Should only be called if ValueHandles present");
 872
 873   // Get the linked list base, which is guaranteed to exist since the
 874   // HasValueHandle flag is set.
 875   LLVMContextImpl *pImpl = V->getContext().pImpl;
 876   ValueHandleBase *Entry = pImpl->ValueHandles[V];
 877   assert(Entry && "Value bit set but no entries exist");
 878
 879   // We use a local ValueHandleBase as an iterator so that ValueHandles can add
 880   // and remove themselves from the list without breaking our iteration.  This
 881   // is not really an AssertingVH; we just have to give ValueHandleBase a kind.
 882   // Note that we deliberately do not the support the case when dropping a value
 883   // handle results in a new value handle being permanently added to the list
 884   // (as might occur in theory for CallbackVH's): the new value handle will not
 885   // be processed and the checking code will mete out righteous punishment if
 886   // the handle is still present once we have finished processing all the other
 887   // value handles (it is fine to momentarily add then remove a value handle).
 888   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
 889     Iterator.RemoveFromUseList();
 890     Iterator.AddToExistingUseListAfter(Entry);
 891     assert(Entry->Next == &Iterator && "Loop invariant broken.");
 892
 893     switch (Entry->getKind()) {
 894     case Assert:
 895       break;
 896     case Weak:
 897     case WeakTracking:
 898       // WeakTracking and Weak just go to null, which unlinks them
 899       // from the list.
 900       Entry->operator=(nullptr);
 901       break;
 902     case Callback:
 903       // Forward to the subclass's implementation.
 904       static_cast<CallbackVH*>(Entry)->deleted();
 905       break;
 906     }
 907   }
 908
 909   // All callbacks, weak references, and assertingVHs should be dropped by now.
 910   if (V->HasValueHandle) {
 911 #ifndef NDEBUG      // Only in +Asserts mode...
 912     dbgs() << "While deleting: " << *V->getType() << " %" << V->getName()
 913            << "\n";
 914     if (pImpl->ValueHandles[V]->getKind() == Assert)
 915       llvm_unreachable("An asserting value handle still pointed to this"
 916                        " value!");
 917
 918 #endif
 919     llvm_unreachable("All references to V were not removed?");
 920   }
 921 }
 922
 923 void ValueHandleBase::ValueIsRAUWd(Value *Old, Value *New) {
 924   assert(Old->HasValueHandle &&"Should only be called if ValueHandles present");
 925   assert(Old != New && "Changing value into itself!");
 926   assert(Old->getType() == New->getType() &&
 927          "replaceAllUses of value with new value of different type!");
 928
 929   // Get the linked list base, which is guaranteed to exist since the
 930   // HasValueHandle flag is set.
 931   LLVMContextImpl *pImpl = Old->getContext().pImpl;
 932   ValueHandleBase *Entry = pImpl->ValueHandles[Old];
 933
 934   assert(Entry && "Value bit set but no entries exist");
 935
 936   // We use a local ValueHandleBase as an iterator so that
 937   // ValueHandles can add and remove themselves from the list without
 938   // breaking our iteration.  This is not really an AssertingVH; we
 939   // just have to give ValueHandleBase some kind.
 940   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
 941     Iterator.RemoveFromUseList();
 942     Iterator.AddToExistingUseListAfter(Entry);
 943     assert(Entry->Next == &Iterator && "Loop invariant broken.");
 944
 945     switch (Entry->getKind()) {
 946     case Assert:
 947     case Weak:
 948       // Asserting and Weak handles do not follow RAUW implicitly.
 949       break;
 950     case WeakTracking:
 951       // Weak goes to the new value, which will unlink it from Old's list.
 952       Entry->operator=(New);
 953       break;
 954     case Callback:
 955       // Forward to the subclass's implementation.
 956       static_cast<CallbackVH*>(Entry)->allUsesReplacedWith(New);
 957       break;
 958     }
 959   }
 960
 961 #ifndef NDEBUG
 962   // If any new weak value handles were added while processing the
 963   // list, then complain about it now.
 964   if (Old->HasValueHandle)
 965     for (Entry = pImpl->ValueHandles[Old]; Entry; Entry = Entry->Next)
 966       switch (Entry->getKind()) {
 967       case WeakTracking:
 968         dbgs() << "After RAUW from " << *Old->getType() << " %"
 969                << Old->getName() << " to " << *New->getType() << " %"
 970                << New->getName() << "\n";
 971         llvm_unreachable(
 972             "A weak tracking value handle still pointed to the old value!\n");
 973       default:
 974         break;
 975       }
 976 #endif
 977 }
 978
 979 // Pin the vtable to this file.
 980 void CallbackVH::anchor() {}