lib/IR/Value.cpp

   1 //===-- Value.cpp - Implement the Value class -----------------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the Value, ValueHandle, and User classes.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/IR/Value.h"
  15 #include "LLVMContextImpl.h"
  16 #include "llvm/ADT/DenseMap.h"
  17 #include "llvm/ADT/SmallString.h"
  18 #include "llvm/ADT/SetVector.h"
  19 #include "llvm/IR/CallSite.h"
  20 #include "llvm/IR/Constant.h"
  21 #include "llvm/IR/Constants.h"
  22 #include "llvm/IR/DataLayout.h"
  23 #include "llvm/IR/DerivedTypes.h"
  24 #include "llvm/IR/DerivedUser.h"
  25 #include "llvm/IR/GetElementPtrTypeIterator.h"
  26 #include "llvm/IR/InstrTypes.h"
  27 #include "llvm/IR/Instructions.h"
  28 #include "llvm/IR/IntrinsicInst.h"
  29 #include "llvm/IR/Module.h"
  30 #include "llvm/IR/Operator.h"
  31 #include "llvm/IR/Statepoint.h"
  32 #include "llvm/IR/ValueHandle.h"
  33 #include "llvm/IR/ValueSymbolTable.h"
  34 #include "llvm/Support/Debug.h"
  35 #include "llvm/Support/ErrorHandling.h"
  36 #include "llvm/Support/ManagedStatic.h"
  37 #include "llvm/Support/raw_ostream.h"
  38 #include <algorithm>
  39
  40 using namespace llvm;
  41
  42 static cl::opt<unsigned> NonGlobalValueMaxNameSize(
  43     "non-global-value-max-name-size", cl::Hidden, cl::init(1024),
  44     cl::desc("Maximum size for the name of non-global values."));
  45
  46 //===----------------------------------------------------------------------===//
  47 //                                Value Class
  48 //===----------------------------------------------------------------------===//
  49 static inline Type *checkType(Type *Ty) {
  50   assert(Ty && "Value defined with a null type: Error!");
  51   return Ty;
  52 }
  53
  54 Value::Value(Type *ty, unsigned scid)
  55     : VTy(checkType(ty)), UseList(nullptr), SubclassID(scid),
  56       HasValueHandle(0), SubclassOptionalData(0), SubclassData(0),
  57       NumUserOperands(0), IsUsedByMD(false), HasName(false) {
  58   static_assert(ConstantFirstVal == 0, "!(SubclassID < ConstantFirstVal)");
  59   // FIXME: Why isn't this in the subclass gunk??
  60   // Note, we cannot call isa<CallInst> before the CallInst has been
  61   // constructed.
  62   if (SubclassID == Instruction::Call || SubclassID == Instruction::Invoke)
  63     assert((VTy->isFirstClassType() || VTy->isVoidTy() || VTy->isStructTy()) &&
  64            "invalid CallInst type!");
  65   else if (SubclassID != BasicBlockVal &&
  66            (/*SubclassID < ConstantFirstVal ||*/ SubclassID > ConstantLastVal))
  67     assert((VTy->isFirstClassType() || VTy->isVoidTy()) &&
  68            "Cannot create non-first-class values except for constants!");
  69   static_assert(sizeof(Value) == 2 * sizeof(void *) + 2 * sizeof(unsigned),
  70                 "Value too big");
  71 }
  72
  73 Value::~Value() {
  74   // Notify all ValueHandles (if present) that this value is going away.
  75   if (HasValueHandle)
  76     ValueHandleBase::ValueIsDeleted(this);
  77   if (isUsedByMetadata())
  78     ValueAsMetadata::handleDeletion(this);
  79
  80 #ifndef NDEBUG      // Only in -g mode...
  81   // Check to make sure that there are no uses of this value that are still
  82   // around when the value is destroyed.  If there are, then we have a dangling
  83   // reference and something is wrong.  This code is here to print out where
  84   // the value is still being referenced.
  85   //
  86   if (!use_empty()) {
  87     dbgs() << "While deleting: " << *VTy << " %" << getName() << "\n";
  88     for (auto *U : users())
  89       dbgs() << "Use still stuck around after Def is destroyed:" << *U << "\n";
  90   }
  91 #endif
  92   assert(use_empty() && "Uses remain when a value is destroyed!");
  93
  94   // If this value is named, destroy the name.  This should not be in a symtab
  95   // at this point.
  96   destroyValueName();
  97 }
  98
  99 void Value::deleteValue() {
 100   switch (getValueID()) {
 101 #define HANDLE_VALUE(Name)                                                     \
 102   case Value::Name##Val:                                                       \
 103     delete static_cast<Name *>(this);                                          \
 104     break;
 105 #define HANDLE_MEMORY_VALUE(Name)                                              \
 106   case Value::Name##Val:                                                       \
 107     static_cast<DerivedUser *>(this)->DeleteValue(                             \
 108         static_cast<DerivedUser *>(this));                                     \
 109     break;
 110 #define HANDLE_INSTRUCTION(Name)  /* nothing */
 111 #include "llvm/IR/Value.def"
 112
 113 #define HANDLE_INST(N, OPC, CLASS)                                             \
 114   case Value::InstructionVal + Instruction::OPC:                               \
 115     delete static_cast<CLASS *>(this);                                         \
 116     break;
 117 #define HANDLE_USER_INST(N, OPC, CLASS)
 118 #include "llvm/IR/Instruction.def"
 119
 120   default:
 121     llvm_unreachable("attempting to delete unknown value kind");
 122   }
 123 }
 124
 125 void Value::destroyValueName() {
 126   ValueName *Name = getValueName();
 127   if (Name)
 128     Name->Destroy();
 129   setValueName(nullptr);
 130 }
 131
 132 bool Value::hasNUses(unsigned N) const {
 133   const_use_iterator UI = use_begin(), E = use_end();
 134
 135   for (; N; --N, ++UI)
 136     if (UI == E) return false;  // Too few.
 137   return UI == E;
 138 }
 139
 140 bool Value::hasNUsesOrMore(unsigned N) const {
 141   const_use_iterator UI = use_begin(), E = use_end();
 142
 143   for (; N; --N, ++UI)
 144     if (UI == E) return false;  // Too few.
 145
 146   return true;
 147 }
 148
 149 bool Value::isUsedInBasicBlock(const BasicBlock *BB) const {
 150   // This can be computed either by scanning the instructions in BB, or by
 151   // scanning the use list of this Value. Both lists can be very long, but
 152   // usually one is quite short.
 153   //
 154   // Scan both lists simultaneously until one is exhausted. This limits the
 155   // search to the shorter list.
 156   BasicBlock::const_iterator BI = BB->begin(), BE = BB->end();
 157   const_user_iterator UI = user_begin(), UE = user_end();
 158   for (; BI != BE && UI != UE; ++BI, ++UI) {
 159     // Scan basic block: Check if this Value is used by the instruction at BI.
 160     if (is_contained(BI->operands(), this))
 161       return true;
 162     // Scan use list: Check if the use at UI is in BB.
 163     const auto *User = dyn_cast<Instruction>(*UI);
 164     if (User && User->getParent() == BB)
 165       return true;
 166   }
 167   return false;
 168 }
 169
 170 unsigned Value::getNumUses() const {
 171   return (unsigned)std::distance(use_begin(), use_end());
 172 }
 173
 174 static bool getSymTab(Value *V, ValueSymbolTable *&ST) {
 175   ST = nullptr;
 176   if (Instruction *I = dyn_cast<Instruction>(V)) {
 177     if (BasicBlock *P = I->getParent())
 178       if (Function *PP = P->getParent())
 179         ST = PP->getValueSymbolTable();
 180   } else if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
 181     if (Function *P = BB->getParent())
 182       ST = P->getValueSymbolTable();
 183   } else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
 184     if (Module *P = GV->getParent())
 185       ST = &P->getValueSymbolTable();
 186   } else if (Argument *A = dyn_cast<Argument>(V)) {
 187     if (Function *P = A->getParent())
 188       ST = P->getValueSymbolTable();
 189   } else {
 190     assert(isa<Constant>(V) && "Unknown value type!");
 191     return true;  // no name is setable for this.
 192   }
 193   return false;
 194 }
 195
 196 ValueName *Value::getValueName() const {
 197   if (!HasName) return nullptr;
 198
 199   LLVMContext &Ctx = getContext();
 200   auto I = Ctx.pImpl->ValueNames.find(this);
 201   assert(I != Ctx.pImpl->ValueNames.end() &&
 202          "No name entry found!");
 203
 204   return I->second;
 205 }
 206
 207 void Value::setValueName(ValueName *VN) {
 208   LLVMContext &Ctx = getContext();
 209
 210   assert(HasName == Ctx.pImpl->ValueNames.count(this) &&
 211          "HasName bit out of sync!");
 212
 213   if (!VN) {
 214     if (HasName)
 215       Ctx.pImpl->ValueNames.erase(this);
 216     HasName = false;
 217     return;
 218   }
 219
 220   HasName = true;
 221   Ctx.pImpl->ValueNames[this] = VN;
 222 }
 223
 224 StringRef Value::getName() const {
 225   // Make sure the empty string is still a C string. For historical reasons,
 226   // some clients want to call .data() on the result and expect it to be null
 227   // terminated.
 228   if (!hasName())
 229     return StringRef("", 0);
 230   return getValueName()->getKey();
 231 }
 232
 233 void Value::setNameImpl(const Twine &NewName) {
 234   // Fast-path: LLVMContext can be set to strip out non-GlobalValue names
 235   if (getContext().shouldDiscardValueNames() && !isa<GlobalValue>(this))
 236     return;
 237
 238   // Fast path for common IRBuilder case of setName("") when there is no name.
 239   if (NewName.isTriviallyEmpty() && !hasName())
 240     return;
 241
 242   SmallString<256> NameData;
 243   StringRef NameRef = NewName.toStringRef(NameData);
 244   assert(NameRef.find_first_of(0) == StringRef::npos &&
 245          "Null bytes are not allowed in names");
 246
 247   // Name isn't changing?
 248   if (getName() == NameRef)
 249     return;
 250
 251   // Cap the size of non-GlobalValue names.
 252   if (NameRef.size() > NonGlobalValueMaxNameSize && !isa<GlobalValue>(this))
 253     NameRef =
 254         NameRef.substr(0, std::max(1u, (unsigned)NonGlobalValueMaxNameSize));
 255
 256   assert(!getType()->isVoidTy() && "Cannot assign a name to void values!");
 257
 258   // Get the symbol table to update for this object.
 259   ValueSymbolTable *ST;
 260   if (getSymTab(this, ST))
 261     return;  // Cannot set a name on this value (e.g. constant).
 262
 263   if (!ST) { // No symbol table to update?  Just do the change.
 264     if (NameRef.empty()) {
 265       // Free the name for this value.
 266       destroyValueName();
 267       return;
 268     }
 269
 270     // NOTE: Could optimize for the case the name is shrinking to not deallocate
 271     // then reallocated.
 272     destroyValueName();
 273
 274     // Create the new name.
 275     setValueName(ValueName::Create(NameRef));
 276     getValueName()->setValue(this);
 277     return;
 278   }
 279
 280   // NOTE: Could optimize for the case the name is shrinking to not deallocate
 281   // then reallocated.
 282   if (hasName()) {
 283     // Remove old name.
 284     ST->removeValueName(getValueName());
 285     destroyValueName();
 286
 287     if (NameRef.empty())
 288       return;
 289   }
 290
 291   // Name is changing to something new.
 292   setValueName(ST->createValueName(NameRef, this));
 293 }
 294
 295 void Value::setName(const Twine &NewName) {
 296   setNameImpl(NewName);
 297   if (Function *F = dyn_cast<Function>(this))
 298     F->recalculateIntrinsicID();
 299 }
 300
 301 void Value::takeName(Value *V) {
 302   ValueSymbolTable *ST = nullptr;
 303   // If this value has a name, drop it.
 304   if (hasName()) {
 305     // Get the symtab this is in.
 306     if (getSymTab(this, ST)) {
 307       // We can't set a name on this value, but we need to clear V's name if
 308       // it has one.
 309       if (V->hasName()) V->setName("");
 310       return;  // Cannot set a name on this value (e.g. constant).
 311     }
 312
 313     // Remove old name.
 314     if (ST)
 315       ST->removeValueName(getValueName());
 316     destroyValueName();
 317   }
 318
 319   // Now we know that this has no name.
 320
 321   // If V has no name either, we're done.
 322   if (!V->hasName()) return;
 323
 324   // Get this's symtab if we didn't before.
 325   if (!ST) {
 326     if (getSymTab(this, ST)) {
 327       // Clear V's name.
 328       V->setName("");
 329       return;  // Cannot set a name on this value (e.g. constant).
 330     }
 331   }
 332
 333   // Get V's ST, this should always succed, because V has a name.
 334   ValueSymbolTable *VST;
 335   bool Failure = getSymTab(V, VST);
 336   assert(!Failure && "V has a name, so it should have a ST!"); (void)Failure;
 337
 338   // If these values are both in the same symtab, we can do this very fast.
 339   // This works even if both values have no symtab yet.
 340   if (ST == VST) {
 341     // Take the name!
 342     setValueName(V->getValueName());
 343     V->setValueName(nullptr);
 344     getValueName()->setValue(this);
 345     return;
 346   }
 347
 348   // Otherwise, things are slightly more complex.  Remove V's name from VST and
 349   // then reinsert it into ST.
 350
 351   if (VST)
 352     VST->removeValueName(V->getValueName());
 353   setValueName(V->getValueName());
 354   V->setValueName(nullptr);
 355   getValueName()->setValue(this);
 356
 357   if (ST)
 358     ST->reinsertValue(this);
 359 }
 360
 361 void Value::assertModuleIsMaterializedImpl() const {
 362 #ifndef NDEBUG
 363   const GlobalValue *GV = dyn_cast<GlobalValue>(this);
 364   if (!GV)
 365     return;
 366   const Module *M = GV->getParent();
 367   if (!M)
 368     return;
 369   assert(M->isMaterialized());
 370 #endif
 371 }
 372
 373 #ifndef NDEBUG
 374 static bool contains(SmallPtrSetImpl<ConstantExpr *> &Cache, ConstantExpr *Expr,
 375                      Constant *C) {
 376   if (!Cache.insert(Expr).second)
 377     return false;
 378
 379   for (auto &O : Expr->operands()) {
 380     if (O == C)
 381       return true;
 382     auto *CE = dyn_cast<ConstantExpr>(O);
 383     if (!CE)
 384       continue;
 385     if (contains(Cache, CE, C))
 386       return true;
 387   }
 388   return false;
 389 }
 390
 391 static bool contains(Value *Expr, Value *V) {
 392   if (Expr == V)
 393     return true;
 394
 395   auto *C = dyn_cast<Constant>(V);
 396   if (!C)
 397     return false;
 398
 399   auto *CE = dyn_cast<ConstantExpr>(Expr);
 400   if (!CE)
 401     return false;
 402
 403   SmallPtrSet<ConstantExpr *, 4> Cache;
 404   return contains(Cache, CE, C);
 405 }
 406 #endif // NDEBUG
 407
 408 void Value::doRAUW(Value *New, ReplaceMetadataUses ReplaceMetaUses) {
 409   assert(New && "Value::replaceAllUsesWith(<null>) is invalid!");
 410   assert(!contains(New, this) &&
 411          "this->replaceAllUsesWith(expr(this)) is NOT valid!");
 412   assert(New->getType() == getType() &&
 413          "replaceAllUses of value with new value of different type!");
 414
 415   // Notify all ValueHandles (if present) that this value is going away.
 416   if (HasValueHandle)
 417     ValueHandleBase::ValueIsRAUWd(this, New);
 418   if (ReplaceMetaUses == ReplaceMetadataUses::Yes && isUsedByMetadata())
 419     ValueAsMetadata::handleRAUW(this, New);
 420
 421   while (!materialized_use_empty()) {
 422     Use &U = *UseList;
 423     // Must handle Constants specially, we cannot call replaceUsesOfWith on a
 424     // constant because they are uniqued.
 425     if (auto *C = dyn_cast<Constant>(U.getUser())) {
 426       if (!isa<GlobalValue>(C)) {
 427         C->handleOperandChange(this, New);
 428         continue;
 429       }
 430     }
 431
 432     U.set(New);
 433   }
 434
 435   if (BasicBlock *BB = dyn_cast<BasicBlock>(this))
 436     BB->replaceSuccessorsPhiUsesWith(cast<BasicBlock>(New));
 437 }
 438
 439 void Value::replaceAllUsesWith(Value *New) {
 440   doRAUW(New, ReplaceMetadataUses::Yes);
 441 }
 442
 443 void Value::replaceNonMetadataUsesWith(Value *New) {
 444   doRAUW(New, ReplaceMetadataUses::No);
 445 }
 446
 447 // Like replaceAllUsesWith except it does not handle constants or basic blocks.
 448 // This routine leaves uses within BB.
 449 void Value::replaceUsesOutsideBlock(Value *New, BasicBlock *BB) {
 450   assert(New && "Value::replaceUsesOutsideBlock(<null>, BB) is invalid!");
 451   assert(!contains(New, this) &&
 452          "this->replaceUsesOutsideBlock(expr(this), BB) is NOT valid!");
 453   assert(New->getType() == getType() &&
 454          "replaceUses of value with new value of different type!");
 455   assert(BB && "Basic block that may contain a use of 'New' must be defined\n");
 456
 457   use_iterator UI = use_begin(), E = use_end();
 458   for (; UI != E;) {
 459     Use &U = *UI;
 460     ++UI;
 461     auto *Usr = dyn_cast<Instruction>(U.getUser());
 462     if (Usr && Usr->getParent() == BB)
 463       continue;
 464     U.set(New);
 465   }
 466 }
 467
 468 namespace {
 469 // Various metrics for how much to strip off of pointers.
 470 enum PointerStripKind {
 471   PSK_ZeroIndices,
 472   PSK_ZeroIndicesAndAliases,
 473   PSK_ZeroIndicesAndAliasesAndInvariantGroups,
 474   PSK_InBoundsConstantIndices,
 475   PSK_InBounds
 476 };
 477
 478 template <PointerStripKind StripKind>
 479 static const Value *stripPointerCastsAndOffsets(const Value *V) {
 480   if (!V->getType()->isPointerTy())
 481     return V;
 482
 483   // Even though we don't look through PHI nodes, we could be called on an
 484   // instruction in an unreachable block, which may be on a cycle.
 485   SmallPtrSet<const Value *, 4> Visited;
 486
 487   Visited.insert(V);
 488   do {
 489     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 490       switch (StripKind) {
 491       case PSK_ZeroIndicesAndAliases:
 492       case PSK_ZeroIndicesAndAliasesAndInvariantGroups:
 493       case PSK_ZeroIndices:
 494         if (!GEP->hasAllZeroIndices())
 495           return V;
 496         break;
 497       case PSK_InBoundsConstantIndices:
 498         if (!GEP->hasAllConstantIndices())
 499           return V;
 500         LLVM_FALLTHROUGH;
 501       case PSK_InBounds:
 502         if (!GEP->isInBounds())
 503           return V;
 504         break;
 505       }
 506       V = GEP->getPointerOperand();
 507     } else if (Operator::getOpcode(V) == Instruction::BitCast ||
 508                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
 509       V = cast<Operator>(V)->getOperand(0);
 510     } else if (auto *GA = dyn_cast<GlobalAlias>(V)) {
 511       if (StripKind == PSK_ZeroIndices || GA->isInterposable())
 512         return V;
 513       V = GA->getAliasee();
 514     } else {
 515       if (auto CS = ImmutableCallSite(V)) {
 516         if (const Value *RV = CS.getReturnedArgOperand()) {
 517           V = RV;
 518           continue;
 519         }
 520         // The result of launder.invariant.group must alias it's argument,
 521         // but it can't be marked with returned attribute, that's why it needs
 522         // special case.
 523         if (StripKind == PSK_ZeroIndicesAndAliasesAndInvariantGroups &&
 524             (CS.getIntrinsicID() == Intrinsic::launder_invariant_group ||
 525              CS.getIntrinsicID() == Intrinsic::strip_invariant_group)) {
 526           V = CS.getArgOperand(0);
 527           continue;
 528         }
 529       }
 530       return V;
 531     }
 532     assert(V->getType()->isPointerTy() && "Unexpected operand type!");
 533   } while (Visited.insert(V).second);
 534
 535   return V;
 536 }
 537 } // end anonymous namespace
 538
 539 const Value *Value::stripPointerCasts() const {
 540   return stripPointerCastsAndOffsets<PSK_ZeroIndicesAndAliases>(this);
 541 }
 542
 543 const Value *Value::stripPointerCastsNoFollowAliases() const {
 544   return stripPointerCastsAndOffsets<PSK_ZeroIndices>(this);
 545 }
 546
 547 const Value *Value::stripInBoundsConstantOffsets() const {
 548   return stripPointerCastsAndOffsets<PSK_InBoundsConstantIndices>(this);
 549 }
 550
 551 const Value *Value::stripPointerCastsAndInvariantGroups() const {
 552   return stripPointerCastsAndOffsets<PSK_ZeroIndicesAndAliasesAndInvariantGroups>(
 553       this);
 554 }
 555
 556 const Value *
 557 Value::stripAndAccumulateInBoundsConstantOffsets(const DataLayout &DL,
 558                                                  APInt &Offset) const {
 559   if (!getType()->isPointerTy())
 560     return this;
 561
 562   assert(Offset.getBitWidth() == DL.getIndexSizeInBits(cast<PointerType>(
 563                                      getType())->getAddressSpace()) &&
 564          "The offset bit width does not match the DL specification.");
 565
 566   // Even though we don't look through PHI nodes, we could be called on an
 567   // instruction in an unreachable block, which may be on a cycle.
 568   SmallPtrSet<const Value *, 4> Visited;
 569   Visited.insert(this);
 570   const Value *V = this;
 571   do {
 572     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
 573       if (!GEP->isInBounds())
 574         return V;
 575       APInt GEPOffset(Offset);
 576       if (!GEP->accumulateConstantOffset(DL, GEPOffset))
 577         return V;
 578       Offset = GEPOffset;
 579       V = GEP->getPointerOperand();
 580     } else if (Operator::getOpcode(V) == Instruction::BitCast) {
 581       V = cast<Operator>(V)->getOperand(0);
 582     } else if (auto *GA = dyn_cast<GlobalAlias>(V)) {
 583       V = GA->getAliasee();
 584     } else {
 585       if (auto CS = ImmutableCallSite(V))
 586         if (const Value *RV = CS.getReturnedArgOperand()) {
 587           V = RV;
 588           continue;
 589         }
 590
 591       return V;
 592     }
 593     assert(V->getType()->isPointerTy() && "Unexpected operand type!");
 594   } while (Visited.insert(V).second);
 595
 596   return V;
 597 }
 598
 599 const Value *Value::stripInBoundsOffsets() const {
 600   return stripPointerCastsAndOffsets<PSK_InBounds>(this);
 601 }
 602
 603 uint64_t Value::getPointerDereferenceableBytes(const DataLayout &DL,
 604                                                bool &CanBeNull) const {
 605   assert(getType()->isPointerTy() && "must be pointer");
 606
 607   uint64_t DerefBytes = 0;
 608   CanBeNull = false;
 609   if (const Argument *A = dyn_cast<Argument>(this)) {
 610     DerefBytes = A->getDereferenceableBytes();
 611     if (DerefBytes == 0 && (A->hasByValAttr() || A->hasStructRetAttr())) {
 612       Type *PT = cast<PointerType>(A->getType())->getElementType();
 613       if (PT->isSized())
 614         DerefBytes = DL.getTypeStoreSize(PT);
 615     }
 616     if (DerefBytes == 0) {
 617       DerefBytes = A->getDereferenceableOrNullBytes();
 618       CanBeNull = true;
 619     }
 620   } else if (auto CS = ImmutableCallSite(this)) {
 621     DerefBytes = CS.getDereferenceableBytes(AttributeList::ReturnIndex);
 622     if (DerefBytes == 0) {
 623       DerefBytes = CS.getDereferenceableOrNullBytes(AttributeList::ReturnIndex);
 624       CanBeNull = true;
 625     }
 626   } else if (const LoadInst *LI = dyn_cast<LoadInst>(this)) {
 627     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) {
 628       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 629       DerefBytes = CI->getLimitedValue();
 630     }
 631     if (DerefBytes == 0) {
 632       if (MDNode *MD =
 633               LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
 634         ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 635         DerefBytes = CI->getLimitedValue();
 636       }
 637       CanBeNull = true;
 638     }
 639   } else if (auto *AI = dyn_cast<AllocaInst>(this)) {
 640     if (!AI->isArrayAllocation()) {
 641       DerefBytes = DL.getTypeStoreSize(AI->getAllocatedType());
 642       CanBeNull = false;
 643     }
 644   } else if (auto *GV = dyn_cast<GlobalVariable>(this)) {
 645     if (GV->getValueType()->isSized() && !GV->hasExternalWeakLinkage()) {
 646       // TODO: Don't outright reject hasExternalWeakLinkage but set the
 647       // CanBeNull flag.
 648       DerefBytes = DL.getTypeStoreSize(GV->getValueType());
 649       CanBeNull = false;
 650     }
 651   }
 652   return DerefBytes;
 653 }
 654
 655 unsigned Value::getPointerAlignment(const DataLayout &DL) const {
 656   assert(getType()->isPointerTy() && "must be pointer");
 657
 658   unsigned Align = 0;
 659   if (auto *GO = dyn_cast<GlobalObject>(this)) {
 660     // Don't make any assumptions about function pointer alignment. Some
 661     // targets use the LSBs to store additional information.
 662     if (isa<Function>(GO))
 663       return 0;
 664     Align = GO->getAlignment();
 665     if (Align == 0) {
 666       if (auto *GVar = dyn_cast<GlobalVariable>(GO)) {
 667         Type *ObjectType = GVar->getValueType();
 668         if (ObjectType->isSized()) {
 669           // If the object is defined in the current Module, we'll be giving
 670           // it the preferred alignment. Otherwise, we have to assume that it
 671           // may only have the minimum ABI alignment.
 672           if (GVar->isStrongDefinitionForLinker())
 673             Align = DL.getPreferredAlignment(GVar);
 674           else
 675             Align = DL.getABITypeAlignment(ObjectType);
 676         }
 677       }
 678     }
 679   } else if (const Argument *A = dyn_cast<Argument>(this)) {
 680     Align = A->getParamAlignment();
 681
 682     if (!Align && A->hasStructRetAttr()) {
 683       // An sret parameter has at least the ABI alignment of the return type.
 684       Type *EltTy = cast<PointerType>(A->getType())->getElementType();
 685       if (EltTy->isSized())
 686         Align = DL.getABITypeAlignment(EltTy);
 687     }
 688   } else if (const AllocaInst *AI = dyn_cast<AllocaInst>(this)) {
 689     Align = AI->getAlignment();
 690     if (Align == 0) {
 691       Type *AllocatedType = AI->getAllocatedType();
 692       if (AllocatedType->isSized())
 693         Align = DL.getPrefTypeAlignment(AllocatedType);
 694     }
 695   } else if (auto CS = ImmutableCallSite(this))
 696     Align = CS.getAttributes().getRetAlignment();
 697   else if (const LoadInst *LI = dyn_cast<LoadInst>(this))
 698     if (MDNode *MD = LI->getMetadata(LLVMContext::MD_align)) {
 699       ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
 700       Align = CI->getLimitedValue();
 701     }
 702
 703   return Align;
 704 }
 705
 706 const Value *Value::DoPHITranslation(const BasicBlock *CurBB,
 707                                      const BasicBlock *PredBB) const {
 708   auto *PN = dyn_cast<PHINode>(this);
 709   if (PN && PN->getParent() == CurBB)
 710     return PN->getIncomingValueForBlock(PredBB);
 711   return this;
 712 }
 713
 714 LLVMContext &Value::getContext() const { return VTy->getContext(); }
 715
 716 void Value::reverseUseList() {
 717   if (!UseList || !UseList->Next)
 718     // No need to reverse 0 or 1 uses.
 719     return;
 720
 721   Use *Head = UseList;
 722   Use *Current = UseList->Next;
 723   Head->Next = nullptr;
 724   while (Current) {
 725     Use *Next = Current->Next;
 726     Current->Next = Head;
 727     Head->setPrev(&Current->Next);
 728     Head = Current;
 729     Current = Next;
 730   }
 731   UseList = Head;
 732   Head->setPrev(&UseList);
 733 }
 734
 735 bool Value::isSwiftError() const {
 736   auto *Arg = dyn_cast<Argument>(this);
 737   if (Arg)
 738     return Arg->hasSwiftErrorAttr();
 739   auto *Alloca = dyn_cast<AllocaInst>(this);
 740   if (!Alloca)
 741     return false;
 742   return Alloca->isSwiftError();
 743 }
 744
 745 //===----------------------------------------------------------------------===//
 746 //                             ValueHandleBase Class
 747 //===----------------------------------------------------------------------===//
 748
 749 void ValueHandleBase::AddToExistingUseList(ValueHandleBase **List) {
 750   assert(List && "Handle list is null?");
 751
 752   // Splice ourselves into the list.
 753   Next = *List;
 754   *List = this;
 755   setPrevPtr(List);
 756   if (Next) {
 757     Next->setPrevPtr(&Next);
 758     assert(getValPtr() == Next->getValPtr() && "Added to wrong list?");
 759   }
 760 }
 761
 762 void ValueHandleBase::AddToExistingUseListAfter(ValueHandleBase *List) {
 763   assert(List && "Must insert after existing node");
 764
 765   Next = List->Next;
 766   setPrevPtr(&List->Next);
 767   List->Next = this;
 768   if (Next)
 769     Next->setPrevPtr(&Next);
 770 }
 771
 772 void ValueHandleBase::AddToUseList() {
 773   assert(getValPtr() && "Null pointer doesn't have a use list!");
 774
 775   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
 776
 777   if (getValPtr()->HasValueHandle) {
 778     // If this value already has a ValueHandle, then it must be in the
 779     // ValueHandles map already.
 780     ValueHandleBase *&Entry = pImpl->ValueHandles[getValPtr()];
 781     assert(Entry && "Value doesn't have any handles?");
 782     AddToExistingUseList(&Entry);
 783     return;
 784   }
 785
 786   // Ok, it doesn't have any handles yet, so we must insert it into the
 787   // DenseMap.  However, doing this insertion could cause the DenseMap to
 788   // reallocate itself, which would invalidate all of the PrevP pointers that
 789   // point into the old table.  Handle this by checking for reallocation and
 790   // updating the stale pointers only if needed.
 791   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
 792   const void *OldBucketPtr = Handles.getPointerIntoBucketsArray();
 793
 794   ValueHandleBase *&Entry = Handles[getValPtr()];
 795   assert(!Entry && "Value really did already have handles?");
 796   AddToExistingUseList(&Entry);
 797   getValPtr()->HasValueHandle = true;
 798
 799   // If reallocation didn't happen or if this was the first insertion, don't
 800   // walk the table.
 801   if (Handles.isPointerIntoBucketsArray(OldBucketPtr) ||
 802       Handles.size() == 1) {
 803     return;
 804   }
 805
 806   // Okay, reallocation did happen.  Fix the Prev Pointers.
 807   for (DenseMap<Value*, ValueHandleBase*>::iterator I = Handles.begin(),
 808        E = Handles.end(); I != E; ++I) {
 809     assert(I->second && I->first == I->second->getValPtr() &&
 810            "List invariant broken!");
 811     I->second->setPrevPtr(&I->second);
 812   }
 813 }
 814
 815 void ValueHandleBase::RemoveFromUseList() {
 816   assert(getValPtr() && getValPtr()->HasValueHandle &&
 817          "Pointer doesn't have a use list!");
 818
 819   // Unlink this from its use list.
 820   ValueHandleBase **PrevPtr = getPrevPtr();
 821   assert(*PrevPtr == this && "List invariant broken");
 822
 823   *PrevPtr = Next;
 824   if (Next) {
 825     assert(Next->getPrevPtr() == &Next && "List invariant broken");
 826     Next->setPrevPtr(PrevPtr);
 827     return;
 828   }
 829
 830   // If the Next pointer was null, then it is possible that this was the last
 831   // ValueHandle watching VP.  If so, delete its entry from the ValueHandles
 832   // map.
 833   LLVMContextImpl *pImpl = getValPtr()->getContext().pImpl;
 834   DenseMap<Value*, ValueHandleBase*> &Handles = pImpl->ValueHandles;
 835   if (Handles.isPointerIntoBucketsArray(PrevPtr)) {
 836     Handles.erase(getValPtr());
 837     getValPtr()->HasValueHandle = false;
 838   }
 839 }
 840
 841 void ValueHandleBase::ValueIsDeleted(Value *V) {
 842   assert(V->HasValueHandle && "Should only be called if ValueHandles present");
 843
 844   // Get the linked list base, which is guaranteed to exist since the
 845   // HasValueHandle flag is set.
 846   LLVMContextImpl *pImpl = V->getContext().pImpl;
 847   ValueHandleBase *Entry = pImpl->ValueHandles[V];
 848   assert(Entry && "Value bit set but no entries exist");
 849
 850   // We use a local ValueHandleBase as an iterator so that ValueHandles can add
 851   // and remove themselves from the list without breaking our iteration.  This
 852   // is not really an AssertingVH; we just have to give ValueHandleBase a kind.
 853   // Note that we deliberately do not the support the case when dropping a value
 854   // handle results in a new value handle being permanently added to the list
 855   // (as might occur in theory for CallbackVH's): the new value handle will not
 856   // be processed and the checking code will mete out righteous punishment if
 857   // the handle is still present once we have finished processing all the other
 858   // value handles (it is fine to momentarily add then remove a value handle).
 859   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
 860     Iterator.RemoveFromUseList();
 861     Iterator.AddToExistingUseListAfter(Entry);
 862     assert(Entry->Next == &Iterator && "Loop invariant broken.");
 863
 864     switch (Entry->getKind()) {
 865     case Assert:
 866       break;
 867     case Weak:
 868     case WeakTracking:
 869       // WeakTracking and Weak just go to null, which unlinks them
 870       // from the list.
 871       Entry->operator=(nullptr);
 872       break;
 873     case Callback:
 874       // Forward to the subclass's implementation.
 875       static_cast<CallbackVH*>(Entry)->deleted();
 876       break;
 877     }
 878   }
 879
 880   // All callbacks, weak references, and assertingVHs should be dropped by now.
 881   if (V->HasValueHandle) {
 882 #ifndef NDEBUG      // Only in +Asserts mode...
 883     dbgs() << "While deleting: " << *V->getType() << " %" << V->getName()
 884            << "\n";
 885     if (pImpl->ValueHandles[V]->getKind() == Assert)
 886       llvm_unreachable("An asserting value handle still pointed to this"
 887                        " value!");
 888
 889 #endif
 890     llvm_unreachable("All references to V were not removed?");
 891   }
 892 }
 893
 894 void ValueHandleBase::ValueIsRAUWd(Value *Old, Value *New) {
 895   assert(Old->HasValueHandle &&"Should only be called if ValueHandles present");
 896   assert(Old != New && "Changing value into itself!");
 897   assert(Old->getType() == New->getType() &&
 898          "replaceAllUses of value with new value of different type!");
 899
 900   // Get the linked list base, which is guaranteed to exist since the
 901   // HasValueHandle flag is set.
 902   LLVMContextImpl *pImpl = Old->getContext().pImpl;
 903   ValueHandleBase *Entry = pImpl->ValueHandles[Old];
 904
 905   assert(Entry && "Value bit set but no entries exist");
 906
 907   // We use a local ValueHandleBase as an iterator so that
 908   // ValueHandles can add and remove themselves from the list without
 909   // breaking our iteration.  This is not really an AssertingVH; we
 910   // just have to give ValueHandleBase some kind.
 911   for (ValueHandleBase Iterator(Assert, *Entry); Entry; Entry = Iterator.Next) {
 912     Iterator.RemoveFromUseList();
 913     Iterator.AddToExistingUseListAfter(Entry);
 914     assert(Entry->Next == &Iterator && "Loop invariant broken.");
 915
 916     switch (Entry->getKind()) {
 917     case Assert:
 918     case Weak:
 919       // Asserting and Weak handles do not follow RAUW implicitly.
 920       break;
 921     case WeakTracking:
 922       // Weak goes to the new value, which will unlink it from Old's list.
 923       Entry->operator=(New);
 924       break;
 925     case Callback:
 926       // Forward to the subclass's implementation.
 927       static_cast<CallbackVH*>(Entry)->allUsesReplacedWith(New);
 928       break;
 929     }
 930   }
 931
 932 #ifndef NDEBUG
 933   // If any new weak value handles were added while processing the
 934   // list, then complain about it now.
 935   if (Old->HasValueHandle)
 936     for (Entry = pImpl->ValueHandles[Old]; Entry; Entry = Entry->Next)
 937       switch (Entry->getKind()) {
 938       case WeakTracking:
 939         dbgs() << "After RAUW from " << *Old->getType() << " %"
 940                << Old->getName() << " to " << *New->getType() << " %"
 941                << New->getName() << "\n";
 942         llvm_unreachable(
 943             "A weak tracking value handle still pointed to the  old value!\n");
 944       default:
 945         break;
 946       }
 947 #endif
 948 }
 949
 950 // Pin the vtable to this file.
 951 void CallbackVH::anchor() {}