text: //===- Metadata.cpp - Implement Metadata classes --------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements the Metadata classes.
  //
  //===----------------------------------------------------------------------===//
  
  #include "LLVMContextImpl.h"
  #include "MetadataImpl.h"
  #include "SymbolTableListTraitsImpl.h"
  #include "llvm/ADT/APFloat.h"
  #include "llvm/ADT/APInt.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/DenseSet.h"
  #include "llvm/ADT/None.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/SetVector.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/StringMap.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/ADT/Twine.h"
  #include "llvm/IR/Argument.h"
  #include "llvm/IR/BasicBlock.h"
  #include "llvm/IR/Constant.h"
  #include "llvm/IR/ConstantRange.h"
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DebugInfoMetadata.h"
  #include "llvm/IR/DebugLoc.h"
  #include "llvm/IR/Function.h"
  #include "llvm/IR/GlobalObject.h"
  #include "llvm/IR/GlobalVariable.h"
  #include "llvm/IR/Instruction.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/IR/Metadata.h"
  #include "llvm/IR/Module.h"
  #include "llvm/IR/TrackingMDRef.h"
  #include "llvm/IR/Type.h"
  #include "llvm/IR/Value.h"
  #include "llvm/IR/ValueHandle.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/MathExtras.h"
  #include <algorithm>
  #include <cassert>
  #include <cstddef>
  #include <cstdint>
  #include <iterator>
  #include <tuple>
  #include <type_traits>
  #include <utility>
  #include <vector>
  
  using namespace llvm;
  
  MetadataAsValue::MetadataAsValue(Type *Ty, Metadata *MD)
      : Value(Ty, MetadataAsValueVal), MD(MD) {
    track();
  }
  
  MetadataAsValue::~MetadataAsValue() {
    getType()->getContext().pImpl->MetadataAsValues.erase(MD);
    untrack();
  }
  
  /// Canonicalize metadata arguments to intrinsics.
  ///
  /// To support bitcode upgrades (and assembly semantic sugar) for \a
  /// MetadataAsValue, we need to canonicalize certain metadata.
  ///
  ///   - nullptr is replaced by an empty MDNode.
  ///   - An MDNode with a single null operand is replaced by an empty MDNode.
  ///   - An MDNode whose only operand is a \a ConstantAsMetadata gets skipped.
  ///
  /// This maintains readability of bitcode from when metadata was a type of
  /// value, and these bridges were unnecessary.
  static Metadata *canonicalizeMetadataForValue(LLVMContext &Context,
                                                Metadata *MD) {
    if (!MD)
      // !{}
      return MDNode::get(Context, None);
  
    // Return early if this isn't a single-operand MDNode.
    auto *N = dyn_cast<MDNode>(MD);
    if (!N || N->getNumOperands() != 1)
      return MD;
  
    if (!N->getOperand(0))
      // !{}
      return MDNode::get(Context, None);
  
    if (auto *C = dyn_cast<ConstantAsMetadata>(N->getOperand(0)))
      // Look through the MDNode.
      return C;
  
    return MD;
  }
  
  MetadataAsValue *MetadataAsValue::get(LLVMContext &Context, Metadata *MD) {
    MD = canonicalizeMetadataForValue(Context, MD);
    auto *&Entry = Context.pImpl->MetadataAsValues[MD];
    if (!Entry)
      Entry = new MetadataAsValue(Type::getMetadataTy(Context), MD);
    return Entry;
  }
  
  MetadataAsValue *MetadataAsValue::getIfExists(LLVMContext &Context,
                                                Metadata *MD) {
    MD = canonicalizeMetadataForValue(Context, MD);
    auto &Store = Context.pImpl->MetadataAsValues;
    return Store.lookup(MD);
  }
  
  void MetadataAsValue::handleChangedMetadata(Metadata *MD) {
    LLVMContext &Context = getContext();
    MD = canonicalizeMetadataForValue(Context, MD);
    auto &Store = Context.pImpl->MetadataAsValues;
  
    // Stop tracking the old metadata.
    Store.erase(this->MD);
    untrack();
    this->MD = nullptr;
  
    // Start tracking MD, or RAUW if necessary.
    auto *&Entry = Store[MD];
    if (Entry) {
      replaceAllUsesWith(Entry);
      delete this;
      return;
    }
  
    this->MD = MD;
    track();
    Entry = this;
  }
  
  void MetadataAsValue::track() {
    if (MD)
      MetadataTracking::track(&MD, *MD, *this);
  }
  
  void MetadataAsValue::untrack() {
    if (MD)
      MetadataTracking::untrack(MD);
  }
  
  bool MetadataTracking::track(void *Ref, Metadata &MD, OwnerTy Owner) {
    assert(Ref && "Expected live reference");
    assert((Owner || *static_cast<Metadata **>(Ref) == &MD) &&
           "Reference without owner must be direct");
    if (auto *R = ReplaceableMetadataImpl::getOrCreate(MD)) {
      R->addRef(Ref, Owner);
      return true;
    }
    if (auto *PH = dyn_cast<DistinctMDOperandPlaceholder>(&MD)) {
      assert(!PH->Use && "Placeholders can only be used once");
      assert(!Owner && "Unexpected callback to owner");
      PH->Use = static_cast<Metadata **>(Ref);
      return true;
    }
    return false;
  }
  
  void MetadataTracking::untrack(void *Ref, Metadata &MD) {
    assert(Ref && "Expected live reference");
    if (auto *R = ReplaceableMetadataImpl::getIfExists(MD))
      R->dropRef(Ref);
    else if (auto *PH = dyn_cast<DistinctMDOperandPlaceholder>(&MD))
      PH->Use = nullptr;
  }
  
  bool MetadataTracking::retrack(void *Ref, Metadata &MD, void *New) {
    assert(Ref && "Expected live reference");
    assert(New && "Expected live reference");
    assert(Ref != New && "Expected change");
    if (auto *R = ReplaceableMetadataImpl::getIfExists(MD)) {
      R->moveRef(Ref, New, MD);
      return true;
    }
    assert(!isa<DistinctMDOperandPlaceholder>(MD) &&
           "Unexpected move of an MDOperand");
    assert(!isReplaceable(MD) &&
           "Expected un-replaceable metadata, since we didn't move a reference");
    return false;
  }
  
  bool MetadataTracking::isReplaceable(const Metadata &MD) {
    return ReplaceableMetadataImpl::isReplaceable(MD);
  }
  
  void ReplaceableMetadataImpl::addRef(void *Ref, OwnerTy Owner) {
    bool WasInserted =
        UseMap.insert(std::make_pair(Ref, std::make_pair(Owner, NextIndex)))
            .second;
    (void)WasInserted;
    assert(WasInserted && "Expected to add a reference");
  
    ++NextIndex;
    assert(NextIndex != 0 && "Unexpected overflow");
  }
  
  void ReplaceableMetadataImpl::dropRef(void *Ref) {
    bool WasErased = UseMap.erase(Ref);
    (void)WasErased;
    assert(WasErased && "Expected to drop a reference");
  }
  
  void ReplaceableMetadataImpl::moveRef(void *Ref, void *New,
                                        const Metadata &MD) {
    auto I = UseMap.find(Ref);
    assert(I != UseMap.end() && "Expected to move a reference");
    auto OwnerAndIndex = I->second;
    UseMap.erase(I);
    bool WasInserted = UseMap.insert(std::make_pair(New, OwnerAndIndex)).second;
    (void)WasInserted;
    assert(WasInserted && "Expected to add a reference");
  
    // Check that the references are direct if there's no owner.
    (void)MD;
    assert((OwnerAndIndex.first || *static_cast<Metadata **>(Ref) == &MD) &&
           "Reference without owner must be direct");
    assert((OwnerAndIndex.first || *static_cast<Metadata **>(New) == &MD) &&
           "Reference without owner must be direct");
  }
  
  void ReplaceableMetadataImpl::replaceAllUsesWith(Metadata *MD) {
    if (UseMap.empty())
      return;
  
    // Copy out uses since UseMap will get touched below.
    using UseTy = std::pair<void *, std::pair<OwnerTy, uint64_t>>;
    SmallVector<UseTy, 8> Uses(UseMap.begin(), UseMap.end());
    llvm::sort(Uses, [](const UseTy &L, const UseTy &R) {
      return L.second.second < R.second.second;
    });
    for (const auto &Pair : Uses) {
      // Check that this Ref hasn't disappeared after RAUW (when updating a
      // previous Ref).
      if (!UseMap.count(Pair.first))
        continue;
  
      OwnerTy Owner = Pair.second.first;
      if (!Owner) {
        // Update unowned tracking references directly.
        Metadata *&Ref = *static_cast<Metadata **>(Pair.first);
        Ref = MD;
        if (MD)
          MetadataTracking::track(Ref);
        UseMap.erase(Pair.first);
        continue;
      }
  
      // Check for MetadataAsValue.
      if (Owner.is<MetadataAsValue *>()) {
        Owner.get<MetadataAsValue *>()->handleChangedMetadata(MD);
        continue;
      }
  
      // There's a Metadata owner -- dispatch.
      Metadata *OwnerMD = Owner.get<Metadata *>();
      switch (OwnerMD->getMetadataID()) {
  #define HANDLE_METADATA_LEAF(CLASS)                                            \
    case Metadata::CLASS##Kind:                                                  \
      cast<CLASS>(OwnerMD)->handleChangedOperand(Pair.first, MD);                \
      continue;
  #include "llvm/IR/Metadata.def"
      default:
        llvm_unreachable("Invalid metadata subclass");
      }
    }
    assert(UseMap.empty() && "Expected all uses to be replaced");
  }
  
  void ReplaceableMetadataImpl::resolveAllUses(bool ResolveUsers) {
    if (UseMap.empty())
      return;
  
    if (!ResolveUsers) {
      UseMap.clear();
      return;
    }
  
    // Copy out uses since UseMap could get touched below.
    using UseTy = std::pair<void *, std::pair<OwnerTy, uint64_t>>;
    SmallVector<UseTy, 8> Uses(UseMap.begin(), UseMap.end());
    llvm::sort(Uses, [](const UseTy &L, const UseTy &R) {
      return L.second.second < R.second.second;
    });
    UseMap.clear();
    for (const auto &Pair : Uses) {
      auto Owner = Pair.second.first;
      if (!Owner)
        continue;
      if (Owner.is<MetadataAsValue *>())
        continue;
  
      // Resolve MDNodes that point at this.
      auto *OwnerMD = dyn_cast<MDNode>(Owner.get<Metadata *>());
      if (!OwnerMD)
        continue;
      if (OwnerMD->isResolved())
        continue;
      OwnerMD->decrementUnresolvedOperandCount();
    }
  }
  
  ReplaceableMetadataImpl *ReplaceableMetadataImpl::getOrCreate(Metadata &MD) {
    if (auto *N = dyn_cast<MDNode>(&MD))
      return N->isResolved() ? nullptr : N->Context.getOrCreateReplaceableUses();
    return dyn_cast<ValueAsMetadata>(&MD);
  }
  
  ReplaceableMetadataImpl *ReplaceableMetadataImpl::getIfExists(Metadata &MD) {
    if (auto *N = dyn_cast<MDNode>(&MD))
      return N->isResolved() ? nullptr : N->Context.getReplaceableUses();
    return dyn_cast<ValueAsMetadata>(&MD);
  }
  
  bool ReplaceableMetadataImpl::isReplaceable(const Metadata &MD) {
    if (auto *N = dyn_cast<MDNode>(&MD))
      return !N->isResolved();
    return dyn_cast<ValueAsMetadata>(&MD);
  }
  
  static DISubprogram *getLocalFunctionMetadata(Value *V) {
    assert(V && "Expected value");
    if (auto *A = dyn_cast<Argument>(V)) {
      if (auto *Fn = A->getParent())
        return Fn->getSubprogram();
      return nullptr;
    }
  
    if (BasicBlock *BB = cast<Instruction>(V)->getParent()) {
      if (auto *Fn = BB->getParent())
        return Fn->getSubprogram();
      return nullptr;
    }
  
    return nullptr;
  }
  
  ValueAsMetadata *ValueAsMetadata::get(Value *V) {
    assert(V && "Unexpected null Value");
  
    auto &Context = V->getContext();
    auto *&Entry = Context.pImpl->ValuesAsMetadata[V];
    if (!Entry) {
      assert((isa<Constant>(V) || isa<Argument>(V) || isa<Instruction>(V)) &&
             "Expected constant or function-local value");
      assert(!V->IsUsedByMD && "Expected this to be the only metadata use");
      V->IsUsedByMD = true;
      if (auto *C = dyn_cast<Constant>(V))
        Entry = new ConstantAsMetadata(C);
      else
        Entry = new LocalAsMetadata(V);
    }
  
    return Entry;
  }
  
  ValueAsMetadata *ValueAsMetadata::getIfExists(Value *V) {
    assert(V && "Unexpected null Value");
    return V->getContext().pImpl->ValuesAsMetadata.lookup(V);
  }
  
  void ValueAsMetadata::handleDeletion(Value *V) {
    assert(V && "Expected valid value");
  
    auto &Store = V->getType()->getContext().pImpl->ValuesAsMetadata;
    auto I = Store.find(V);
    if (I == Store.end())
      return;
  
    // Remove old entry from the map.
    ValueAsMetadata *MD = I->second;
    assert(MD && "Expected valid metadata");
    assert(MD->getValue() == V && "Expected valid mapping");
    Store.erase(I);
  
    // Delete the metadata.
    MD->replaceAllUsesWith(nullptr);
    delete MD;
  }
  
  void ValueAsMetadata::handleRAUW(Value *From, Value *To) {
    assert(From && "Expected valid value");
    assert(To && "Expected valid value");
    assert(From != To && "Expected changed value");
    assert(From->getType() == To->getType() && "Unexpected type change");
  
    LLVMContext &Context = From->getType()->getContext();
    auto &Store = Context.pImpl->ValuesAsMetadata;
    auto I = Store.find(From);
    if (I == Store.end()) {
      assert(!From->IsUsedByMD && "Expected From not to be used by metadata");
      return;
    }
  
    // Remove old entry from the map.
    assert(From->IsUsedByMD && "Expected From to be used by metadata");
    From->IsUsedByMD = false;
    ValueAsMetadata *MD = I->second;
    assert(MD && "Expected valid metadata");
    assert(MD->getValue() == From && "Expected valid mapping");
    Store.erase(I);
  
    if (isa<LocalAsMetadata>(MD)) {
      if (auto *C = dyn_cast<Constant>(To)) {
        // Local became a constant.
        MD->replaceAllUsesWith(ConstantAsMetadata::get(C));
        delete MD;
        return;
      }
      if (getLocalFunctionMetadata(From) && getLocalFunctionMetadata(To) &&
          getLocalFunctionMetadata(From) != getLocalFunctionMetadata(To)) {
        // DISubprogram changed.
        MD->replaceAllUsesWith(nullptr);
        delete MD;
        return;
      }
    } else if (!isa<Constant>(To)) {
      // Changed to function-local value.
      MD->replaceAllUsesWith(nullptr);
      delete MD;
      return;
    }
  
    auto *&Entry = Store[To];
    if (Entry) {
      // The target already exists.
      MD->replaceAllUsesWith(Entry);
      delete MD;
      return;
    }
  
    // Update MD in place (and update the map entry).
    assert(!To->IsUsedByMD && "Expected this to be the only metadata use");
    To->IsUsedByMD = true;
    MD->V = To;
    Entry = MD;
  }
  
  //===----------------------------------------------------------------------===//
  // MDString implementation.
  //
  
  MDString *MDString::get(LLVMContext &Context, StringRef Str) {
    auto &Store = Context.pImpl->MDStringCache;
    auto I = Store.try_emplace(Str);
    auto &MapEntry = I.first->getValue();
    if (!I.second)
      return &MapEntry;
    MapEntry.Entry = &*I.first;
    return &MapEntry;
  }
  
  StringRef MDString::getString() const {
    assert(Entry && "Expected to find string map entry");
    return Entry->first();
  }
  
  //===----------------------------------------------------------------------===//
  // MDNode implementation.
  //
  
  // Assert that the MDNode types will not be unaligned by the objects
  // prepended to them.
  #define HANDLE_MDNODE_LEAF(CLASS)                                              \
    static_assert(                                                               \
        alignof(uint64_t) >= alignof(CLASS),                                     \
        "Alignment is insufficient after objects prepended to " #CLASS);
  #include "llvm/IR/Metadata.def"
  
  void *MDNode::operator new(size_t Size, unsigned NumOps) {
    size_t OpSize = NumOps * sizeof(MDOperand);
    // uint64_t is the most aligned type we need support (ensured by static_assert
    // above)
    OpSize = alignTo(OpSize, alignof(uint64_t));
    void *Ptr = reinterpret_cast<char *>(::operator new(OpSize + Size)) + OpSize;
    MDOperand *O = static_cast<MDOperand *>(Ptr);
    for (MDOperand *E = O - NumOps; O != E; --O)
      (void)new (O - 1) MDOperand;
    return Ptr;
  }
  
  // Repress memory sanitization, due to use-after-destroy by operator
  // delete. Bug report 24578 identifies this issue.
  LLVM_NO_SANITIZE_MEMORY_ATTRIBUTE void MDNode::operator delete(void *Mem) {
    MDNode *N = static_cast<MDNode *>(Mem);
    size_t OpSize = N->NumOperands * sizeof(MDOperand);
    OpSize = alignTo(OpSize, alignof(uint64_t));
  
    MDOperand *O = static_cast<MDOperand *>(Mem);
    for (MDOperand *E = O - N->NumOperands; O != E; --O)
      (O - 1)->~MDOperand();
    ::operator delete(reinterpret_cast<char *>(Mem) - OpSize);
  }
  
  MDNode::MDNode(LLVMContext &Context, unsigned ID, StorageType Storage,
                 ArrayRef<Metadata *> Ops1, ArrayRef<Metadata *> Ops2)
      : Metadata(ID, Storage), NumOperands(Ops1.size() + Ops2.size()),
        NumUnresolved(0), Context(Context) {
    unsigned Op = 0;
    for (Metadata *MD : Ops1)
      setOperand(Op++, MD);
    for (Metadata *MD : Ops2)
      setOperand(Op++, MD);
  
    if (!isUniqued())
      return;
  
    // Count the unresolved operands.  If there are any, RAUW support will be
    // added lazily on first reference.
    countUnresolvedOperands();
  }
  
  TempMDNode MDNode::clone() const {
    switch (getMetadataID()) {
    default:
      llvm_unreachable("Invalid MDNode subclass");
  #define HANDLE_MDNODE_LEAF(CLASS)                                              \
    case CLASS##Kind:                                                            \
      return cast<CLASS>(this)->cloneImpl();
  #include "llvm/IR/Metadata.def"
    }
  }
  
  static bool isOperandUnresolved(Metadata *Op) {
    if (auto *N = dyn_cast_or_null<MDNode>(Op))
      return !N->isResolved();
    return false;
  }
  
  void MDNode::countUnresolvedOperands() {
    assert(NumUnresolved == 0 && "Expected unresolved ops to be uncounted");
    assert(isUniqued() && "Expected this to be uniqued");
    NumUnresolved = count_if(operands(), isOperandUnresolved);
  }
  
  void MDNode::makeUniqued() {
    assert(isTemporary() && "Expected this to be temporary");
    assert(!isResolved() && "Expected this to be unresolved");
  
    // Enable uniquing callbacks.
    for (auto &Op : mutable_operands())
      Op.reset(Op.get(), this);
  
    // Make this 'uniqued'.
    Storage = Uniqued;
    countUnresolvedOperands();
    if (!NumUnresolved) {
      dropReplaceableUses();
      assert(isResolved() && "Expected this to be resolved");
    }
  
    assert(isUniqued() && "Expected this to be uniqued");
  }
  
  void MDNode::makeDistinct() {
    assert(isTemporary() && "Expected this to be temporary");
    assert(!isResolved() && "Expected this to be unresolved");
  
    // Drop RAUW support and store as a distinct node.
    dropReplaceableUses();
    storeDistinctInContext();
  
    assert(isDistinct() && "Expected this to be distinct");
    assert(isResolved() && "Expected this to be resolved");
  }
  
  void MDNode::resolve() {
    assert(isUniqued() && "Expected this to be uniqued");
    assert(!isResolved() && "Expected this to be unresolved");
  
    NumUnresolved = 0;
    dropReplaceableUses();
  
    assert(isResolved() && "Expected this to be resolved");
  }
  
  void MDNode::dropReplaceableUses() {
    assert(!NumUnresolved && "Unexpected unresolved operand");
  
    // Drop any RAUW support.
    if (Context.hasReplaceableUses())
      Context.takeReplaceableUses()->resolveAllUses();
  }
  
  void MDNode::resolveAfterOperandChange(Metadata *Old, Metadata *New) {
    assert(isUniqued() && "Expected this to be uniqued");
    assert(NumUnresolved != 0 && "Expected unresolved operands");
  
    // Check if an operand was resolved.
    if (!isOperandUnresolved(Old)) {
      if (isOperandUnresolved(New))
        // An operand was un-resolved!
        ++NumUnresolved;
    } else if (!isOperandUnresolved(New))
      decrementUnresolvedOperandCount();
  }
  
  void MDNode::decrementUnresolvedOperandCount() {
    assert(!isResolved() && "Expected this to be unresolved");
    if (isTemporary())
      return;
  
    assert(isUniqued() && "Expected this to be uniqued");
    if (--NumUnresolved)
      return;
  
    // Last unresolved operand has just been resolved.
    dropReplaceableUses();
    assert(isResolved() && "Expected this to become resolved");
  }
  
  void MDNode::resolveCycles() {
    if (isResolved())
      return;
  
    // Resolve this node immediately.
    resolve();
  
    // Resolve all operands.
    for (const auto &Op : operands()) {
      auto *N = dyn_cast_or_null<MDNode>(Op);
      if (!N)
        continue;
  
      assert(!N->isTemporary() &&
             "Expected all forward declarations to be resolved");
      if (!N->isResolved())
        N->resolveCycles();
    }
  }
  
  static bool hasSelfReference(MDNode *N) {
    for (Metadata *MD : N->operands())
      if (MD == N)
        return true;
    return false;
  }
  
  MDNode *MDNode::replaceWithPermanentImpl() {
    switch (getMetadataID()) {
    default:
      // If this type isn't uniquable, replace with a distinct node.
      return replaceWithDistinctImpl();
  
  #define HANDLE_MDNODE_LEAF_UNIQUABLE(CLASS)                                    \
    case CLASS##Kind:                                                            \
      break;
  #include "llvm/IR/Metadata.def"
    }
  
    // Even if this type is uniquable, self-references have to be distinct.
    if (hasSelfReference(this))
      return replaceWithDistinctImpl();
    return replaceWithUniquedImpl();
  }
  
  MDNode *MDNode::replaceWithUniquedImpl() {
    // Try to uniquify in place.
    MDNode *UniquedNode = uniquify();
  
    if (UniquedNode == this) {
      makeUniqued();
      return this;
    }
  
    // Collision, so RAUW instead.
    replaceAllUsesWith(UniquedNode);
    deleteAsSubclass();
    return UniquedNode;
  }
  
  MDNode *MDNode::replaceWithDistinctImpl() {
    makeDistinct();
    return this;
  }
  
  void MDTuple::recalculateHash() {
    setHash(MDTupleInfo::KeyTy::calculateHash(this));
  }
  
  void MDNode::dropAllReferences() {
    for (unsigned I = 0, E = NumOperands; I != E; ++I)
      setOperand(I, nullptr);
    if (Context.hasReplaceableUses()) {
      Context.getReplaceableUses()->resolveAllUses(/* ResolveUsers */ false);
      (void)Context.takeReplaceableUses();
    }
  }
  
  void MDNode::handleChangedOperand(void *Ref, Metadata *New) {
    unsigned Op = static_cast<MDOperand *>(Ref) - op_begin();
    assert(Op < getNumOperands() && "Expected valid operand");
  
    if (!isUniqued()) {
      // This node is not uniqued.  Just set the operand and be done with it.
      setOperand(Op, New);
      return;
    }
  
    // This node is uniqued.
    eraseFromStore();
  
    Metadata *Old = getOperand(Op);
    setOperand(Op, New);
  
    // Drop uniquing for self-reference cycles and deleted constants.
    if (New == this || (!New && Old && isa<ConstantAsMetadata>(Old))) {
      if (!isResolved())
        resolve();
      storeDistinctInContext();
      return;
    }
  
    // Re-unique the node.
    auto *Uniqued = uniquify();
    if (Uniqued == this) {
      if (!isResolved())
        resolveAfterOperandChange(Old, New);
      return;
    }
  
    // Collision.
    if (!isResolved()) {
      // Still unresolved, so RAUW.
      //
      // First, clear out all operands to prevent any recursion (similar to
      // dropAllReferences(), but we still need the use-list).
      for (unsigned O = 0, E = getNumOperands(); O != E; ++O)
        setOperand(O, nullptr);
      if (Context.hasReplaceableUses())
        Context.getReplaceableUses()->replaceAllUsesWith(Uniqued);
      deleteAsSubclass();
      return;
    }
  
    // Store in non-uniqued form if RAUW isn't possible.
    storeDistinctInContext();
  }
  
  void MDNode::deleteAsSubclass() {
    switch (getMetadataID()) {
    default:
      llvm_unreachable("Invalid subclass of MDNode");
  #define HANDLE_MDNODE_LEAF(CLASS)                                              \
    case CLASS##Kind:                                                            \
      delete cast<CLASS>(this);                                                  \
      break;
  #include "llvm/IR/Metadata.def"
    }
  }
  
  template <class T, class InfoT>
  static T *uniquifyImpl(T *N, DenseSet<T *, InfoT> &Store) {
    if (T *U = getUniqued(Store, N))
      return U;
  
    Store.insert(N);
    return N;
  }
  
  template <class NodeTy> struct MDNode::HasCachedHash {
    using Yes = char[1];
    using No = char[2];
    template <class U, U Val> struct SFINAE {};
  
    template <class U>
    static Yes &check(SFINAE<void (U::*)(unsigned), &U::setHash> *);
    template <class U> static No &check(...);
  
    static const bool value = sizeof(check<NodeTy>(nullptr)) == sizeof(Yes);
  };
  
  MDNode *MDNode::uniquify() {
    assert(!hasSelfReference(this) && "Cannot uniquify a self-referencing node");
  
    // Try to insert into uniquing store.
    switch (getMetadataID()) {
    default:
      llvm_unreachable("Invalid or non-uniquable subclass of MDNode");
  #define HANDLE_MDNODE_LEAF_UNIQUABLE(CLASS)                                    \
    case CLASS##Kind: {                                                          \
      CLASS *SubclassThis = cast<CLASS>(this);                                   \
      std::integral_constant<bool, HasCachedHash<CLASS>::value>                  \
          ShouldRecalculateHash;                                                 \
      dispatchRecalculateHash(SubclassThis, ShouldRecalculateHash);              \
      return uniquifyImpl(SubclassThis, getContext().pImpl->CLASS##s);           \
    }
  #include "llvm/IR/Metadata.def"
    }
  }
  
  void MDNode::eraseFromStore() {
    switch (getMetadataID()) {
    default:
      llvm_unreachable("Invalid or non-uniquable subclass of MDNode");
  #define HANDLE_MDNODE_LEAF_UNIQUABLE(CLASS)                                    \
    case CLASS##Kind:                                                            \
      getContext().pImpl->CLASS##s.erase(cast<CLASS>(this));                     \
      break;
  #include "llvm/IR/Metadata.def"
    }
  }
  
  MDTuple *MDTuple::getImpl(LLVMContext &Context, ArrayRef<Metadata *> MDs,
                            StorageType Storage, bool ShouldCreate) {
    unsigned Hash = 0;
    if (Storage == Uniqued) {
      MDTupleInfo::KeyTy Key(MDs);
      if (auto *N = getUniqued(Context.pImpl->MDTuples, Key))
        return N;
      if (!ShouldCreate)
        return nullptr;
      Hash = Key.getHash();
    } else {
      assert(ShouldCreate && "Expected non-uniqued nodes to always be created");
    }
  
    return storeImpl(new (MDs.size()) MDTuple(Context, Storage, Hash, MDs),
                     Storage, Context.pImpl->MDTuples);
  }
  
  void MDNode::deleteTemporary(MDNode *N) {
    assert(N->isTemporary() && "Expected temporary node");
    N->replaceAllUsesWith(nullptr);
    N->deleteAsSubclass();
  }
  
  void MDNode::storeDistinctInContext() {
    assert(!Context.hasReplaceableUses() && "Unexpected replaceable uses");
    assert(!NumUnresolved && "Unexpected unresolved nodes");
    Storage = Distinct;
    assert(isResolved() && "Expected this to be resolved");
  
    // Reset the hash.
    switch (getMetadataID()) {
    default:
      llvm_unreachable("Invalid subclass of MDNode");
  #define HANDLE_MDNODE_LEAF(CLASS)                                              \
    case CLASS##Kind: {                                                          \
      std::integral_constant<bool, HasCachedHash<CLASS>::value> ShouldResetHash; \
      dispatchResetHash(cast<CLASS>(this), ShouldResetHash);                     \
      break;                                                                     \
    }
  #include "llvm/IR/Metadata.def"
    }
  
    getContext().pImpl->DistinctMDNodes.push_back(this);
  }
  
  void MDNode::replaceOperandWith(unsigned I, Metadata *New) {
    if (getOperand(I) == New)
      return;
  
    if (!isUniqued()) {
      setOperand(I, New);
      return;
    }
  
    handleChangedOperand(mutable_begin() + I, New);
  }
  
  void MDNode::setOperand(unsigned I, Metadata *New) {
    assert(I < NumOperands);
    mutable_begin()[I].reset(New, isUniqued() ? this : nullptr);
  }
  
  /// Get a node or a self-reference that looks like it.
  ///
  /// Special handling for finding self-references, for use by \a
  /// MDNode::concatenate() and \a MDNode::intersect() to maintain behaviour from
  /// when self-referencing nodes were still uniqued.  If the first operand has
  /// the same operands as \c Ops, return the first operand instead.
  static MDNode *getOrSelfReference(LLVMContext &Context,
                                    ArrayRef<Metadata *> Ops) {
    if (!Ops.empty())
      if (MDNode *N = dyn_cast_or_null<MDNode>(Ops[0]))
        if (N->getNumOperands() == Ops.size() && N == N->getOperand(0)) {
          for (unsigned I = 1, E = Ops.size(); I != E; ++I)
            if (Ops[I] != N->getOperand(I))
              return MDNode::get(Context, Ops);
          return N;
        }
  
    return MDNode::get(Context, Ops);
  }
  
  MDNode *MDNode::concatenate(MDNode *A, MDNode *B) {
    if (!A)
      return B;
    if (!B)
      return A;
  
    SmallSetVector<Metadata *, 4> MDs(A->op_begin(), A->op_end());
    MDs.insert(B->op_begin(), B->op_end());
  
    // FIXME: This preserves long-standing behaviour, but is it really the right
    // behaviour?  Or was that an unintended side-effect of node uniquing?
    return getOrSelfReference(A->getContext(), MDs.getArrayRef());
  }
  
  MDNode *MDNode::intersect(MDNode *A, MDNode *B) {
    if (!A || !B)
      return nullptr;
  
    SmallSetVector<Metadata *, 4> MDs(A->op_begin(), A->op_end());
    SmallPtrSet<Metadata *, 4> BSet(B->op_begin(), B->op_end());
    MDs.remove_if([&](Metadata *MD) { return !BSet.count(MD); });
  
    // FIXME: This preserves long-standing behaviour, but is it really the right
    // behaviour?  Or was that an unintended side-effect of node uniquing?
    return getOrSelfReference(A->getContext(), MDs.getArrayRef());
  }
  
  MDNode *MDNode::getMostGenericAliasScope(MDNode *A, MDNode *B) {
    if (!A || !B)
      return nullptr;
  
    return concatenate(A, B);
  }
  
  MDNode *MDNode::getMostGenericFPMath(MDNode *A, MDNode *B) {
    if (!A || !B)
      return nullptr;
  
    APFloat AVal = mdconst::extract<ConstantFP>(A->getOperand(0))->getValueAPF();
    APFloat BVal = mdconst::extract<ConstantFP>(B->getOperand(0))->getValueAPF();
    if (AVal < BVal)
      return A;
    return B;
  }
  
  static bool isContiguous(const ConstantRange &A, const ConstantRange &B) {
    return A.getUpper() == B.getLower() || A.getLower() == B.getUpper();
  }
  
  static bool canBeMerged(const ConstantRange &A, const ConstantRange &B) {
    return !A.intersectWith(B).isEmptySet() || isContiguous(A, B);
  }
  
  static bool tryMergeRange(SmallVectorImpl<ConstantInt *> &EndPoints,
                            ConstantInt *Low, ConstantInt *High) {
    ConstantRange NewRange(Low->getValue(), High->getValue());
    unsigned Size = EndPoints.size();
    APInt LB = EndPoints[Size - 2]->getValue();
    APInt LE = EndPoints[Size - 1]->getValue();
    ConstantRange LastRange(LB, LE);
    if (canBeMerged(NewRange, LastRange)) {
      ConstantRange Union = LastRange.unionWith(NewRange);
      Type *Ty = High->getType();
      EndPoints[Size - 2] =
          cast<ConstantInt>(ConstantInt::get(Ty, Union.getLower()));
      EndPoints[Size - 1] =
          cast<ConstantInt>(ConstantInt::get(Ty, Union.getUpper()));
      return true;
    }
    return false;
  }
  
  static void addRange(SmallVectorImpl<ConstantInt *> &EndPoints,
                       ConstantInt *Low, ConstantInt *High) {
    if (!EndPoints.empty())
      if (tryMergeRange(EndPoints, Low, High))
        return;
  
    EndPoints.push_back(Low);
    EndPoints.push_back(High);
  }
  
  MDNode *MDNode::getMostGenericRange(MDNode *A, MDNode *B) {
    // Given two ranges, we want to compute the union of the ranges. This
    // is slightly complicated by having to combine the intervals and merge
    // the ones that overlap.
  
    if (!A || !B)
      return nullptr;
  
    if (A == B)
      return A;
  
    // First, walk both lists in order of the lower boundary of each interval.
    // At each step, try to merge the new interval to the last one we adedd.
    SmallVector<ConstantInt *, 4> EndPoints;
    int AI = 0;
    int BI = 0;
    int AN = A->getNumOperands() / 2;
    int BN = B->getNumOperands() / 2;
    while (AI < AN && BI < BN) {
      ConstantInt *ALow = mdconst::extract<ConstantInt>(A->getOperand(2 * AI));
      ConstantInt *BLow = mdconst::extract<ConstantInt>(B->getOperand(2 * BI));
  
      if (ALow->getValue().slt(BLow->getValue())) {
        addRange(EndPoints, ALow,
                 mdconst::extract<ConstantInt>(A->getOperand(2 * AI + 1)));
        ++AI;
      } else {
        addRange(EndPoints, BLow,
                 mdconst::extract<ConstantInt>(B->getOperand(2 * BI + 1)));
        ++BI;
      }
    }
    while (AI < AN) {
      addRange(EndPoints, mdconst::extract<ConstantInt>(A->getOperand(2 * AI)),
               mdconst::extract<ConstantInt>(A->getOperand(2 * AI + 1)));
      ++AI;
    }
    while (BI < BN) {
      addRange(EndPoints, mdconst::extract<ConstantInt>(B->getOperand(2 * BI)),
               mdconst::extract<ConstantInt>(B->getOperand(2 * BI + 1)));
      ++BI;
    }
  
    // If we have more than 2 ranges (4 endpoints) we have to try to merge
    // the last and first ones.
    unsigned Size = EndPoints.size();
    if (Size > 4) {
      ConstantInt *FB = EndPoints[0];
      ConstantInt *FE = EndPoints[1];
      if (tryMergeRange(EndPoints, FB, FE)) {
        for (unsigned i = 0; i < Size - 2; ++i) {
          EndPoints[i] = EndPoints[i + 2];
        }
        EndPoints.resize(Size - 2);
      }
    }
  
    // If in the end we have a single range, it is possible that it is now the
    // full range. Just drop the metadata in that case.
    if (EndPoints.size() == 2) {
      ConstantRange Range(EndPoints[0]->getValue(), EndPoints[1]->getValue());
      if (Range.isFullSet())
        return nullptr;
    }
  
    SmallVector<Metadata *, 4> MDs;
    MDs.reserve(EndPoints.size());
    for (auto *I : EndPoints)
      MDs.push_back(ConstantAsMetadata::get(I));
    return MDNode::get(A->getContext(), MDs);
  }
  
  MDNode *MDNode::getMostGenericAlignmentOrDereferenceable(MDNode *A, MDNode *B) {
    if (!A || !B)
      return nullptr;
  
    ConstantInt *AVal = mdconst::extract<ConstantInt>(A->getOperand(0));
    ConstantInt *BVal = mdconst::extract<ConstantInt>(B->getOperand(0));
    if (AVal->getZExtValue() < BVal->getZExtValue())
      return A;
    return B;
  }
  
  //===----------------------------------------------------------------------===//
  // NamedMDNode implementation.
  //
  
  static SmallVector<TrackingMDRef, 4> &getNMDOps(void *Operands) {
    return *(SmallVector<TrackingMDRef, 4> *)Operands;
  }
  
  NamedMDNode::NamedMDNode(const Twine &N)
      : Name(N.str()), Operands(new SmallVector<TrackingMDRef, 4>()) {}
  
  NamedMDNode::~NamedMDNode() {
    dropAllReferences();
    delete &getNMDOps(Operands);
  }
  
  unsigned NamedMDNode::getNumOperands() const {
    return (unsigned)getNMDOps(Operands).size();
  }
  
  MDNode *NamedMDNode::getOperand(unsigned i) const {
    assert(i < getNumOperands() && "Invalid Operand number!");
    auto *N = getNMDOps(Operands)[i].get();
    return cast_or_null<MDNode>(N);
  }
  
  void NamedMDNode::addOperand(MDNode *M) { getNMDOps(Operands).emplace_back(M); }
  
  void NamedMDNode::setOperand(unsigned I, MDNode *New) {
    assert(I < getNumOperands() && "Invalid operand number");
    getNMDOps(Operands)[I].reset(New);
  }
  
  void NamedMDNode::eraseFromParent() { getParent()->eraseNamedMetadata(this); }
  
  void NamedMDNode::clearOperands() { getNMDOps(Operands).clear(); }
  
  StringRef NamedMDNode::getName() const { return StringRef(Name); }
  
  //===----------------------------------------------------------------------===//
  // Instruction Metadata method implementations.
  //
  
  MDNode *MDAttachments::lookup(unsigned ID) const {
    for (const auto &A : Attachments)
      if (A.MDKind == ID)
        return A.Node;
    return nullptr;
  }
  
  void MDAttachments::get(unsigned ID, SmallVectorImpl<MDNode *> &Result) const {
    for (const auto &A : Attachments)
      if (A.MDKind == ID)
        Result.push_back(A.Node);
  }
  
  void MDAttachments::getAll(
      SmallVectorImpl<std::pair<unsigned, MDNode *>> &Result) const {
    for (const auto &A : Attachments)
      Result.emplace_back(A.MDKind, A.Node);
  
    // Sort the resulting array so it is stable with respect to metadata IDs. We
    // need to preserve the original insertion order though.
    if (Result.size() > 1)
      llvm::stable_sort(Result, less_first());
  }
  
  void MDAttachments::set(unsigned ID, MDNode *MD) {
    erase(ID);
    if (MD)
      insert(ID, *MD);
  }
  
  void MDAttachments::insert(unsigned ID, MDNode &MD) {
    Attachments.push_back({ID, TrackingMDNodeRef(&MD)});
  }
  
  bool MDAttachments::erase(unsigned ID) {
    if (empty())
      return false;
  
    // Common case is one value.
    if (Attachments.size() == 1 && Attachments.back().MDKind == ID) {
      Attachments.pop_back();
      return true;
    }
  
    auto I = std::remove_if(Attachments.begin(), Attachments.end(),
                            [ID](const Attachment &A) { return A.MDKind == ID; });
    bool Changed = I != Attachments.end();
    Attachments.erase(I, Attachments.end());
    return Changed;
  }
  
  MDNode *Value::getMetadata(unsigned KindID) const {
    if (!hasMetadata())
      return nullptr;
    const auto &Info = getContext().pImpl->ValueMetadata[this];
    assert(!Info.empty() && "bit out of sync with hash table");
    return Info.lookup(KindID);
  }
  
  MDNode *Value::getMetadata(StringRef Kind) const {
    if (!hasMetadata())
      return nullptr;
    const auto &Info = getContext().pImpl->ValueMetadata[this];
    assert(!Info.empty() && "bit out of sync with hash table");
    return Info.lookup(getContext().getMDKindID(Kind));
  }
  
  void Value::getMetadata(unsigned KindID, SmallVectorImpl<MDNode *> &MDs) const {
    if (hasMetadata())
      getContext().pImpl->ValueMetadata[this].get(KindID, MDs);
  }
  
  void Value::getMetadata(StringRef Kind, SmallVectorImpl<MDNode *> &MDs) const {
    if (hasMetadata())
      getMetadata(getContext().getMDKindID(Kind), MDs);
  }
  
  void Value::getAllMetadata(
      SmallVectorImpl<std::pair<unsigned, MDNode *>> &MDs) const {
    if (hasMetadata()) {
      assert(getContext().pImpl->ValueMetadata.count(this) &&
             "bit out of sync with hash table");
      const auto &Info = getContext().pImpl->ValueMetadata.find(this)->second;
      assert(!Info.empty() && "Shouldn't have called this");
      Info.getAll(MDs);
    }
  }
  
  void Value::setMetadata(unsigned KindID, MDNode *Node) {
    assert(isa<Instruction>(this) || isa<GlobalObject>(this));
  
    // Handle the case when we're adding/updating metadata on a value.
    if (Node) {
      auto &Info = getContext().pImpl->ValueMetadata[this];
      assert(!Info.empty() == HasMetadata && "bit out of sync with hash table");
      if (Info.empty())
        HasMetadata = true;
      Info.set(KindID, Node);
      return;
    }
  
    // Otherwise, we're removing metadata from an instruction.
    assert((HasMetadata == (getContext().pImpl->ValueMetadata.count(this) > 0)) &&
           "bit out of sync with hash table");
    if (!HasMetadata)
      return; // Nothing to remove!
    auto &Info = getContext().pImpl->ValueMetadata[this];
  
    // Handle removal of an existing value.
    Info.erase(KindID);
    if (!Info.empty())
      return;
    getContext().pImpl->ValueMetadata.erase(this);
    HasMetadata = false;
  }
  
  void Value::setMetadata(StringRef Kind, MDNode *Node) {
    if (!Node && !HasMetadata)
      return;
    setMetadata(getContext().getMDKindID(Kind), Node);
  }
  
  void Value::addMetadata(unsigned KindID, MDNode &MD) {
    assert(isa<Instruction>(this) || isa<GlobalObject>(this));
    if (!HasMetadata)
      HasMetadata = true;
    getContext().pImpl->ValueMetadata[this].insert(KindID, MD);
  }
  
  void Value::addMetadata(StringRef Kind, MDNode &MD) {
    addMetadata(getContext().getMDKindID(Kind), MD);
  }
  
  bool Value::eraseMetadata(unsigned KindID) {
    // Nothing to unset.
    if (!HasMetadata)
      return false;
  
    auto &Store = getContext().pImpl->ValueMetadata[this];
    bool Changed = Store.erase(KindID);
    if (Store.empty())
      clearMetadata();
    return Changed;
  }
  
  void Value::clearMetadata() {
    if (!HasMetadata)
      return;
    assert(getContext().pImpl->ValueMetadata.count(this) &&
           "bit out of sync with hash table");
    getContext().pImpl->ValueMetadata.erase(this);
    HasMetadata = false;
  }
  
  void Instruction::setMetadata(StringRef Kind, MDNode *Node) {
    if (!Node && !hasMetadata())
      return;
    setMetadata(getContext().getMDKindID(Kind), Node);
  }
  
  MDNode *Instruction::getMetadataImpl(StringRef Kind) const {
    return getMetadataImpl(getContext().getMDKindID(Kind));
  }
  
  void Instruction::dropUnknownNonDebugMetadata(ArrayRef<unsigned> KnownIDs) {
    if (!Value::hasMetadata())
      return; // Nothing to remove!
  
    if (KnownIDs.empty()) {
      // Just drop our entry at the store.
      clearMetadata();
      return;
    }
  
    SmallSet<unsigned, 4> KnownSet;
    KnownSet.insert(KnownIDs.begin(), KnownIDs.end());
  
    auto &MetadataStore = getContext().pImpl->ValueMetadata;
    auto &Info = MetadataStore[this];
    assert(!Info.empty() && "bit out of sync with hash table");
    Info.remove_if([&KnownSet](const MDAttachments::Attachment &I) {
      return !KnownSet.count(I.MDKind);
    });
  
    if (Info.empty()) {
      // Drop our entry at the store.
      clearMetadata();
    }
  }
  
  void Instruction::setMetadata(unsigned KindID, MDNode *Node) {
    if (!Node && !hasMetadata())
      return;
  
    // Handle 'dbg' as a special case since it is not stored in the hash table.
    if (KindID == LLVMContext::MD_dbg) {
      DbgLoc = DebugLoc(Node);
      return;
    }
  
    Value::setMetadata(KindID, Node);
  }
  
  void Instruction::setAAMetadata(const AAMDNodes &N) {
    setMetadata(LLVMContext::MD_tbaa, N.TBAA);
    setMetadata(LLVMContext::MD_tbaa_struct, N.TBAAStruct);
    setMetadata(LLVMContext::MD_alias_scope, N.Scope);
    setMetadata(LLVMContext::MD_noalias, N.NoAlias);
  }
  
  MDNode *Instruction::getMetadataImpl(unsigned KindID) const {
    // Handle 'dbg' as a special case since it is not stored in the hash table.
    if (KindID == LLVMContext::MD_dbg)
      return DbgLoc.getAsMDNode();
    return Value::getMetadata(KindID);
  }
  
  void Instruction::getAllMetadataImpl(
      SmallVectorImpl<std::pair<unsigned, MDNode *>> &Result) const {
    Result.clear();
  
    // Handle 'dbg' as a special case since it is not stored in the hash table.
    if (DbgLoc) {
      Result.push_back(
          std::make_pair((unsigned)LLVMContext::MD_dbg, DbgLoc.getAsMDNode()));
    }
    Value::getAllMetadata(Result);
  }
  
  bool Instruction::extractProfMetadata(uint64_t &TrueVal,
                                        uint64_t &FalseVal) const {
    assert(
        (getOpcode() == Instruction::Br || getOpcode() == Instruction::Select) &&
        "Looking for branch weights on something besides branch or select");
  
    auto *ProfileData = getMetadata(LLVMContext::MD_prof);
    if (!ProfileData || ProfileData->getNumOperands() != 3)
      return false;
  
    auto *ProfDataName = dyn_cast<MDString>(ProfileData->getOperand(0));
    if (!ProfDataName || !ProfDataName->getString().equals("branch_weights"))
      return false;
  
    auto *CITrue = mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(1));
    auto *CIFalse = mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(2));
    if (!CITrue || !CIFalse)
      return false;
  
    TrueVal = CITrue->getValue().getZExtValue();
    FalseVal = CIFalse->getValue().getZExtValue();
  
    return true;
  }
  
  bool Instruction::extractProfTotalWeight(uint64_t &TotalVal) const {
    assert((getOpcode() == Instruction::Br ||
            getOpcode() == Instruction::Select ||
            getOpcode() == Instruction::Call ||
            getOpcode() == Instruction::Invoke ||
            getOpcode() == Instruction::Switch) &&
           "Looking for branch weights on something besides branch");
  
    TotalVal = 0;
    auto *ProfileData = getMetadata(LLVMContext::MD_prof);
    if (!ProfileData)
      return false;
  
    auto *ProfDataName = dyn_cast<MDString>(ProfileData->getOperand(0));
    if (!ProfDataName)
      return false;
  
    if (ProfDataName->getString().equals("branch_weights")) {
      TotalVal = 0;
      for (unsigned i = 1; i < ProfileData->getNumOperands(); i++) {
        auto *V = mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(i));
        if (!V)
          return false;
        TotalVal += V->getValue().getZExtValue();
      }
      return true;
    } else if (ProfDataName->getString().equals("VP") &&
               ProfileData->getNumOperands() > 3) {
      TotalVal = mdconst::dyn_extract<ConstantInt>(ProfileData->getOperand(2))
                     ->getValue()
                     .getZExtValue();
      return true;
    }
    return false;
  }
  
  void GlobalObject::copyMetadata(const GlobalObject *Other, unsigned Offset) {
    SmallVector<std::pair<unsigned, MDNode *>, 8> MDs;
    Other->getAllMetadata(MDs);
    for (auto &MD : MDs) {
      // We need to adjust the type metadata offset.
      if (Offset != 0 && MD.first == LLVMContext::MD_type) {
        auto *OffsetConst = cast<ConstantInt>(
            cast<ConstantAsMetadata>(MD.second->getOperand(0))->getValue());
        Metadata *TypeId = MD.second->getOperand(1);
        auto *NewOffsetMD = ConstantAsMetadata::get(ConstantInt::get(
            OffsetConst->getType(), OffsetConst->getValue() + Offset));
        addMetadata(LLVMContext::MD_type,
                    *MDNode::get(getContext(), {NewOffsetMD, TypeId}));
        continue;
      }
      // If an offset adjustment was specified we need to modify the DIExpression
      // to prepend the adjustment:
      // !DIExpression(DW_OP_plus, Offset, [original expr])
      auto *Attachment = MD.second;
      if (Offset != 0 && MD.first == LLVMContext::MD_dbg) {
        DIGlobalVariable *GV = dyn_cast<DIGlobalVariable>(Attachment);
        DIExpression *E = nullptr;
        if (!GV) {
          auto *GVE = cast<DIGlobalVariableExpression>(Attachment);
          GV = GVE->getVariable();
          E = GVE->getExpression();
        }
        ArrayRef<uint64_t> OrigElements;
        if (E)
          OrigElements = E->getElements();
        std::vector<uint64_t> Elements(OrigElements.size() + 2);
        Elements[0] = dwarf::DW_OP_plus_uconst;
        Elements[1] = Offset;
        llvm::copy(OrigElements, Elements.begin() + 2);
        E = DIExpression::get(getContext(), Elements);
        Attachment = DIGlobalVariableExpression::get(getContext(), GV, E);
      }
      addMetadata(MD.first, *Attachment);
    }
  }
  
  void GlobalObject::addTypeMetadata(unsigned Offset, Metadata *TypeID) {
    addMetadata(
        LLVMContext::MD_type,
        *MDTuple::get(getContext(),
                      {ConstantAsMetadata::get(ConstantInt::get(
                           Type::getInt64Ty(getContext()), Offset)),
                       TypeID}));
  }
  
  void GlobalObject::setVCallVisibilityMetadata(VCallVisibility Visibility) {
    // Remove any existing vcall visibility metadata first in case we are
    // updating.
    eraseMetadata(LLVMContext::MD_vcall_visibility);
    addMetadata(LLVMContext::MD_vcall_visibility,
                *MDNode::get(getContext(),
                             {ConstantAsMetadata::get(ConstantInt::get(
                                 Type::getInt64Ty(getContext()), Visibility))}));
  }
  
  GlobalObject::VCallVisibility GlobalObject::getVCallVisibility() const {
    if (MDNode *MD = getMetadata(LLVMContext::MD_vcall_visibility)) {
      uint64_t Val = cast<ConstantInt>(
                         cast<ConstantAsMetadata>(MD->getOperand(0))->getValue())
                         ->getZExtValue();
      assert(Val <= 2 && "unknown vcall visibility!");
      return (VCallVisibility)Val;
    }
    return VCallVisibility::VCallVisibilityPublic;
  }
  
  void Function::setSubprogram(DISubprogram *SP) {
    setMetadata(LLVMContext::MD_dbg, SP);
  }
  
  DISubprogram *Function::getSubprogram() const {
    return cast_or_null<DISubprogram>(getMetadata(LLVMContext::MD_dbg));
  }
  
  bool Function::isDebugInfoForProfiling() const {
    if (DISubprogram *SP = getSubprogram()) {
      if (DICompileUnit *CU = SP->getUnit()) {
        return CU->getDebugInfoForProfiling();
      }
    }
    return false;
  }
  
  void GlobalVariable::addDebugInfo(DIGlobalVariableExpression *GV) {
    addMetadata(LLVMContext::MD_dbg, *GV);
  }
  
  void GlobalVariable::getDebugInfo(
      SmallVectorImpl<DIGlobalVariableExpression *> &GVs) const {
    SmallVector<MDNode *, 1> MDs;
    getMetadata(LLVMContext::MD_dbg, MDs);
    for (MDNode *MD : MDs)
      GVs.push_back(cast<DIGlobalVariableExpression>(MD));
  }
  