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 //===--- ImmutableSet.h - Immutable (functional) set interface --*- C++ -*-===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
 /// This file defines the ImutAVLTree and ImmutableSet classes.
 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_IMMUTABLESET_H
 #define LLVM_ADT_IMMUTABLESET_H
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/iterator.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/ErrorHandling.h"
 #include <cassert>
 #include <cstdint>
 #include <functional>
 #include <iterator>
 #include <new>
 #include <vector>
 
 namespace llvm {
 
 //===----------------------------------------------------------------------===//
 // Immutable AVL-Tree Definition.
 //===----------------------------------------------------------------------===//
 
 template <typename ImutInfo> class ImutAVLFactory;
 template <typename ImutInfo> class ImutIntervalAVLFactory;
 template <typename ImutInfo> class ImutAVLTreeInOrderIterator;
 template <typename ImutInfo> class ImutAVLTreeGenericIterator;
 
 template <typename ImutInfo >
 class ImutAVLTree {
 public:
   using key_type_ref = typename ImutInfo::key_type_ref;
   using value_type = typename ImutInfo::value_type;
   using value_type_ref = typename ImutInfo::value_type_ref;
   using Factory = ImutAVLFactory<ImutInfo>;
   using iterator = ImutAVLTreeInOrderIterator<ImutInfo>;
 
   friend class ImutAVLFactory<ImutInfo>;
   friend class ImutIntervalAVLFactory<ImutInfo>;
   friend class ImutAVLTreeGenericIterator<ImutInfo>;
 
   //===----------------------------------------------------===//
   // Public Interface.
   //===----------------------------------------------------===//
 
   /// Return a pointer to the left subtree.  This value
   ///  is NULL if there is no left subtree.
   ImutAVLTree *getLeft() const { return left; }
 
   /// Return a pointer to the right subtree.  This value is
   ///  NULL if there is no right subtree.
   ImutAVLTree *getRight() const { return right; }
 
   /// getHeight - Returns the height of the tree.  A tree with no subtrees
   ///  has a height of 1.
   unsigned getHeight() const { return height; }
 
   /// getValue - Returns the data value associated with the tree node.
   const value_type& getValue() const { return value; }
 
   /// find - Finds the subtree associated with the specified key value.
   ///  This method returns NULL if no matching subtree is found.
   ImutAVLTree* find(key_type_ref K) {
     ImutAVLTree *T = this;
     while (T) {
       key_type_ref CurrentKey = ImutInfo::KeyOfValue(T->getValue());
       if (ImutInfo::isEqual(K,CurrentKey))
         return T;
       else if (ImutInfo::isLess(K,CurrentKey))
         T = T->getLeft();
       else
         T = T->getRight();
     }
     return nullptr;
   }
 
   /// getMaxElement - Find the subtree associated with the highest ranged
   ///  key value.
   ImutAVLTree* getMaxElement() {
     ImutAVLTree *T = this;
     ImutAVLTree *Right = T->getRight();
     while (Right) { T = Right; Right = T->getRight(); }
     return T;
   }
 
   /// size - Returns the number of nodes in the tree, which includes
   ///  both leaves and non-leaf nodes.
   unsigned size() const {
     unsigned n = 1;
     if (const ImutAVLTree* L = getLeft())
       n += L->size();
     if (const ImutAVLTree* R = getRight())
       n += R->size();
     return n;
   }
 
   /// begin - Returns an iterator that iterates over the nodes of the tree
   ///  in an inorder traversal.  The returned iterator thus refers to the
   ///  the tree node with the minimum data element.
   iterator begin() const { return iterator(this); }
 
   /// end - Returns an iterator for the tree that denotes the end of an
   ///  inorder traversal.
   iterator end() const { return iterator(); }
 
   bool isElementEqual(value_type_ref V) const {
     // Compare the keys.
     if (!ImutInfo::isEqual(ImutInfo::KeyOfValue(getValue()),
                            ImutInfo::KeyOfValue(V)))
       return false;
 
     // Also compare the data values.
     if (!ImutInfo::isDataEqual(ImutInfo::DataOfValue(getValue()),
                                ImutInfo::DataOfValue(V)))
       return false;
 
     return true;
   }
 
   bool isElementEqual(const ImutAVLTree* RHS) const {
     return isElementEqual(RHS->getValue());
   }
 
   /// isEqual - Compares two trees for structural equality and returns true
   ///   if they are equal.  This worst case performance of this operation is
   //    linear in the sizes of the trees.
   bool isEqual(const ImutAVLTree& RHS) const {
     if (&RHS == this)
       return true;
 
     iterator LItr = begin(), LEnd = end();
     iterator RItr = RHS.begin(), REnd = RHS.end();
 
     while (LItr != LEnd && RItr != REnd) {
       if (&*LItr == &*RItr) {
         LItr.skipSubTree();
         RItr.skipSubTree();
         continue;
       }
 
       if (!LItr->isElementEqual(&*RItr))
         return false;
 
       ++LItr;
       ++RItr;
     }
 
     return LItr == LEnd && RItr == REnd;
   }
 
   /// isNotEqual - Compares two trees for structural inequality.  Performance
   ///  is the same is isEqual.
   bool isNotEqual(const ImutAVLTree& RHS) const { return !isEqual(RHS); }
 
   /// contains - Returns true if this tree contains a subtree (node) that
   ///  has an data element that matches the specified key.  Complexity
   ///  is logarithmic in the size of the tree.
   bool contains(key_type_ref K) { return (bool) find(K); }
 
   /// validateTree - A utility method that checks that the balancing and
   ///  ordering invariants of the tree are satisfied.  It is a recursive
   ///  method that returns the height of the tree, which is then consumed
   ///  by the enclosing validateTree call.  External callers should ignore the
   ///  return value.  An invalid tree will cause an assertion to fire in
   ///  a debug build.
   unsigned validateTree() const {
     unsigned HL = getLeft() ? getLeft()->validateTree() : 0;
     unsigned HR = getRight() ? getRight()->validateTree() : 0;
     (void) HL;
     (void) HR;
 
     assert(getHeight() == ( HL > HR ? HL : HR ) + 1
             && "Height calculation wrong");
 
     assert((HL > HR ? HL-HR : HR-HL) <= 2
            && "Balancing invariant violated");
 
     assert((!getLeft() ||
             ImutInfo::isLess(ImutInfo::KeyOfValue(getLeft()->getValue()),
                              ImutInfo::KeyOfValue(getValue()))) &&
            "Value in left child is not less that current value");
 
     assert((!getRight() ||
              ImutInfo::isLess(ImutInfo::KeyOfValue(getValue()),
                               ImutInfo::KeyOfValue(getRight()->getValue()))) &&
            "Current value is not less that value of right child");
 
     return getHeight();
   }
 
   //===----------------------------------------------------===//
   // Internal values.
   //===----------------------------------------------------===//
 
 private:
   Factory *factory;
   ImutAVLTree *left;
   ImutAVLTree *right;
   ImutAVLTree *prev = nullptr;
   ImutAVLTree *next = nullptr;
 
   unsigned height : 28;
   bool IsMutable : 1;
   bool IsDigestCached : 1;
   bool IsCanonicalized : 1;
 
   value_type value;
   uint32_t digest = 0;
   uint32_t refCount = 0;
 
   //===----------------------------------------------------===//
   // Internal methods (node manipulation; used by Factory).
   //===----------------------------------------------------===//
 
 private:
   /// ImutAVLTree - Internal constructor that is only called by
   ///   ImutAVLFactory.
   ImutAVLTree(Factory *f, ImutAVLTree* l, ImutAVLTree* r, value_type_ref v,
               unsigned height)
     : factory(f), left(l), right(r), height(height), IsMutable(true),
       IsDigestCached(false), IsCanonicalized(false), value(v)
   {
     if (left) left->retain();
     if (right) right->retain();
   }
 
   /// isMutable - Returns true if the left and right subtree references
   ///  (as well as height) can be changed.  If this method returns false,
   ///  the tree is truly immutable.  Trees returned from an ImutAVLFactory
   ///  object should always have this method return true.  Further, if this
   ///  method returns false for an instance of ImutAVLTree, all subtrees
   ///  will also have this method return false.  The converse is not true.
   bool isMutable() const { return IsMutable; }
 
   /// hasCachedDigest - Returns true if the digest for this tree is cached.
   ///  This can only be true if the tree is immutable.
   bool hasCachedDigest() const { return IsDigestCached; }
 
   //===----------------------------------------------------===//
   // Mutating operations.  A tree root can be manipulated as
   // long as its reference has not "escaped" from internal
   // methods of a factory object (see below).  When a tree
   // pointer is externally viewable by client code, the
   // internal "mutable bit" is cleared to mark the tree
   // immutable.  Note that a tree that still has its mutable
   // bit set may have children (subtrees) that are themselves
   // immutable.
   //===----------------------------------------------------===//
 
   /// markImmutable - Clears the mutable flag for a tree.  After this happens,
   ///   it is an error to call setLeft(), setRight(), and setHeight().
   void markImmutable() {
     assert(isMutable() && "Mutable flag already removed.");
     IsMutable = false;
   }
 
   /// markedCachedDigest - Clears the NoCachedDigest flag for a tree.
   void markedCachedDigest() {
     assert(!hasCachedDigest() && "NoCachedDigest flag already removed.");
     IsDigestCached = true;
   }
 
   /// setHeight - Changes the height of the tree.  Used internally by
   ///  ImutAVLFactory.
   void setHeight(unsigned h) {
     assert(isMutable() && "Only a mutable tree can have its height changed.");
     height = h;
   }
 
   static uint32_t computeDigest(ImutAVLTree *L, ImutAVLTree *R,
                                 value_type_ref V) {
     uint32_t digest = 0;
 
     if (L)
       digest += L->computeDigest();
 
     // Compute digest of stored data.
     FoldingSetNodeID ID;
     ImutInfo::Profile(ID,V);
     digest += ID.ComputeHash();
 
     if (R)
       digest += R->computeDigest();
 
     return digest;
   }
 
   uint32_t computeDigest() {
     // Check the lowest bit to determine if digest has actually been
     // pre-computed.
     if (hasCachedDigest())
       return digest;
 
     uint32_t X = computeDigest(getLeft(), getRight(), getValue());
     digest = X;
     markedCachedDigest();
     return X;
   }
 
   //===----------------------------------------------------===//
   // Reference count operations.
   //===----------------------------------------------------===//
 
 public:
   void retain() { ++refCount; }
 
   void release() {
     assert(refCount > 0);
     if (--refCount == 0)
       destroy();
   }
 
   void destroy() {
     if (left)
       left->release();
     if (right)
       right->release();
     if (IsCanonicalized) {
       if (next)
         next->prev = prev;
 
       if (prev)
         prev->next = next;
       else
         factory->Cache[factory->maskCacheIndex(computeDigest())] = next;
     }
 
     // We need to clear the mutability bit in case we are
     // destroying the node as part of a sweep in ImutAVLFactory::recoverNodes().
     IsMutable = false;
     factory->freeNodes.push_back(this);
   }
 };
 
 template <typename ImutInfo>
 struct IntrusiveRefCntPtrInfo<ImutAVLTree<ImutInfo>> {
   static void retain(ImutAVLTree<ImutInfo> *Tree) { Tree->retain(); }
   static void release(ImutAVLTree<ImutInfo> *Tree) { Tree->release(); }
 };
 
 //===----------------------------------------------------------------------===//
 // Immutable AVL-Tree Factory class.
 //===----------------------------------------------------------------------===//
 
 template <typename ImutInfo >
 class ImutAVLFactory {
   friend class ImutAVLTree<ImutInfo>;
 
   using TreeTy = ImutAVLTree<ImutInfo>;
   using value_type_ref = typename TreeTy::value_type_ref;
   using key_type_ref = typename TreeTy::key_type_ref;
   using CacheTy = DenseMap<unsigned, TreeTy*>;
 
   CacheTy Cache;
   uintptr_t Allocator;
   std::vector<TreeTy*> createdNodes;
   std::vector<TreeTy*> freeNodes;
 
   bool ownsAllocator() const {
     return (Allocator & 0x1) == 0;
   }
 
   BumpPtrAllocator& getAllocator() const {
     return *reinterpret_cast<BumpPtrAllocator*>(Allocator & ~0x1);
   }
 
   //===--------------------------------------------------===//
   // Public interface.
   //===--------------------------------------------------===//
 
 public:
   ImutAVLFactory()
     : Allocator(reinterpret_cast<uintptr_t>(new BumpPtrAllocator())) {}
 
   ImutAVLFactory(BumpPtrAllocator& Alloc)
     : Allocator(reinterpret_cast<uintptr_t>(&Alloc) | 0x1) {}
 
   ~ImutAVLFactory() {
     if (ownsAllocator()) delete &getAllocator();
   }
 
   TreeTy* add(TreeTy* T, value_type_ref V) {
     T = add_internal(V,T);
     markImmutable(T);
     recoverNodes();
     return T;
   }
 
   TreeTy* remove(TreeTy* T, key_type_ref V) {
     T = remove_internal(V,T);
     markImmutable(T);
     recoverNodes();
     return T;
   }
 
   TreeTy* getEmptyTree() const { return nullptr; }
 
 protected:
   //===--------------------------------------------------===//
   // A bunch of quick helper functions used for reasoning
   // about the properties of trees and their children.
   // These have succinct names so that the balancing code
   // is as terse (and readable) as possible.
   //===--------------------------------------------------===//
 
   bool            isEmpty(TreeTy* T) const { return !T; }
   unsigned        getHeight(TreeTy* T) const { return T ? T->getHeight() : 0; }
   TreeTy*         getLeft(TreeTy* T) const { return T->getLeft(); }
   TreeTy*         getRight(TreeTy* T) const { return T->getRight(); }
   value_type_ref  getValue(TreeTy* T) const { return T->value; }
 
   // Make sure the index is not the Tombstone or Entry key of the DenseMap.
   static unsigned maskCacheIndex(unsigned I) { return (I & ~0x02); }
 
   unsigned incrementHeight(TreeTy* L, TreeTy* R) const {
     unsigned hl = getHeight(L);
     unsigned hr = getHeight(R);
     return (hl > hr ? hl : hr) + 1;
   }
 
   static bool compareTreeWithSection(TreeTy* T,
                                      typename TreeTy::iterator& TI,
                                      typename TreeTy::iterator& TE) {
     typename TreeTy::iterator I = T->begin(), E = T->end();
     for ( ; I!=E ; ++I, ++TI) {
       if (TI == TE || !I->isElementEqual(&*TI))
         return false;
     }
     return true;
   }
 
   //===--------------------------------------------------===//
   // "createNode" is used to generate new tree roots that link
   // to other trees.  The function may also simply move links
   // in an existing root if that root is still marked mutable.
   // This is necessary because otherwise our balancing code
   // would leak memory as it would create nodes that are
   // then discarded later before the finished tree is
   // returned to the caller.
   //===--------------------------------------------------===//
 
   TreeTy* createNode(TreeTy* L, value_type_ref V, TreeTy* R) {
     BumpPtrAllocator& A = getAllocator();
     TreeTy* T;
     if (!freeNodes.empty()) {
       T = freeNodes.back();
       freeNodes.pop_back();
       assert(T != L);
       assert(T != R);
     } else {
       T = (TreeTy*) A.Allocate<TreeTy>();
     }
     new (T) TreeTy(this, L, R, V, incrementHeight(L,R));
     createdNodes.push_back(T);
     return T;
   }
 
   TreeTy* createNode(TreeTy* newLeft, TreeTy* oldTree, TreeTy* newRight) {
     return createNode(newLeft, getValue(oldTree), newRight);
   }
 
   void recoverNodes() {
     for (unsigned i = 0, n = createdNodes.size(); i < n; ++i) {
       TreeTy *N = createdNodes[i];
       if (N->isMutable() && N->refCount == 0)
         N->destroy();
     }
     createdNodes.clear();
   }
 
   /// balanceTree - Used by add_internal and remove_internal to
   ///  balance a newly created tree.
   TreeTy* balanceTree(TreeTy* L, value_type_ref V, TreeTy* R) {
     unsigned hl = getHeight(L);
     unsigned hr = getHeight(R);
 
     if (hl > hr + 2) {
       assert(!isEmpty(L) && "Left tree cannot be empty to have a height >= 2");
 
       TreeTy *LL = getLeft(L);
       TreeTy *LR = getRight(L);
 
       if (getHeight(LL) >= getHeight(LR))
         return createNode(LL, L, createNode(LR,V,R));
 
       assert(!isEmpty(LR) && "LR cannot be empty because it has a height >= 1");
 
       TreeTy *LRL = getLeft(LR);
       TreeTy *LRR = getRight(LR);
 
       return createNode(createNode(LL,L,LRL), LR, createNode(LRR,V,R));
     }
 
     if (hr > hl + 2) {
       assert(!isEmpty(R) && "Right tree cannot be empty to have a height >= 2");
 
       TreeTy *RL = getLeft(R);
       TreeTy *RR = getRight(R);
 
       if (getHeight(RR) >= getHeight(RL))
         return createNode(createNode(L,V,RL), R, RR);
 
       assert(!isEmpty(RL) && "RL cannot be empty because it has a height >= 1");
 
       TreeTy *RLL = getLeft(RL);
       TreeTy *RLR = getRight(RL);
 
       return createNode(createNode(L,V,RLL), RL, createNode(RLR,R,RR));
     }
 
     return createNode(L,V,R);
   }
 
   /// add_internal - Creates a new tree that includes the specified
   ///  data and the data from the original tree.  If the original tree
   ///  already contained the data item, the original tree is returned.
   TreeTy* add_internal(value_type_ref V, TreeTy* T) {
     if (isEmpty(T))
       return createNode(T, V, T);
     assert(!T->isMutable());
 
     key_type_ref K = ImutInfo::KeyOfValue(V);
     key_type_ref KCurrent = ImutInfo::KeyOfValue(getValue(T));
 
     if (ImutInfo::isEqual(K,KCurrent))
       return createNode(getLeft(T), V, getRight(T));
     else if (ImutInfo::isLess(K,KCurrent))
       return balanceTree(add_internal(V, getLeft(T)), getValue(T), getRight(T));
     else
       return balanceTree(getLeft(T), getValue(T), add_internal(V, getRight(T)));
   }
 
   /// remove_internal - Creates a new tree that includes all the data
   ///  from the original tree except the specified data.  If the
   ///  specified data did not exist in the original tree, the original
   ///  tree is returned.
   TreeTy* remove_internal(key_type_ref K, TreeTy* T) {
     if (isEmpty(T))
       return T;
 
     assert(!T->isMutable());
 
     key_type_ref KCurrent = ImutInfo::KeyOfValue(getValue(T));
 
     if (ImutInfo::isEqual(K,KCurrent)) {
       return combineTrees(getLeft(T), getRight(T));
     } else if (ImutInfo::isLess(K,KCurrent)) {
       return balanceTree(remove_internal(K, getLeft(T)),
                                             getValue(T), getRight(T));
     } else {
       return balanceTree(getLeft(T), getValue(T),
                          remove_internal(K, getRight(T)));
     }
   }
 
   TreeTy* combineTrees(TreeTy* L, TreeTy* R) {
     if (isEmpty(L))
       return R;
     if (isEmpty(R))
       return L;
     TreeTy* OldNode;
     TreeTy* newRight = removeMinBinding(R,OldNode);
     return balanceTree(L, getValue(OldNode), newRight);
   }
 
   TreeTy* removeMinBinding(TreeTy* T, TreeTy*& Noderemoved) {
     assert(!isEmpty(T));
     if (isEmpty(getLeft(T))) {
       Noderemoved = T;
       return getRight(T);
     }
     return balanceTree(removeMinBinding(getLeft(T), Noderemoved),
                        getValue(T), getRight(T));
   }
 
   /// markImmutable - Clears the mutable bits of a root and all of its
   ///  descendants.
   void markImmutable(TreeTy* T) {
     if (!T || !T->isMutable())
       return;
     T->markImmutable();
     markImmutable(getLeft(T));
     markImmutable(getRight(T));
   }
 
 public:
   TreeTy *getCanonicalTree(TreeTy *TNew) {
     if (!TNew)
       return nullptr;
 
     if (TNew->IsCanonicalized)
       return TNew;
 
     // Search the hashtable for another tree with the same digest, and
     // if find a collision compare those trees by their contents.
     unsigned digest = TNew->computeDigest();
     TreeTy *&entry = Cache[maskCacheIndex(digest)];
     do {
       if (!entry)
         break;
       for (TreeTy *T = entry ; T != nullptr; T = T->next) {
         // Compare the Contents('T') with Contents('TNew')
         typename TreeTy::iterator TI = T->begin(), TE = T->end();
         if (!compareTreeWithSection(TNew, TI, TE))
           continue;
         if (TI != TE)
           continue; // T has more contents than TNew.
         // Trees did match!  Return 'T'.
         if (TNew->refCount == 0)
           TNew->destroy();
         return T;
       }
       entry->prev = TNew;
       TNew->next = entry;
     }
     while (false);
 
     entry = TNew;
     TNew->IsCanonicalized = true;
     return TNew;
   }
 };
 
 //===----------------------------------------------------------------------===//
 // Immutable AVL-Tree Iterators.
 //===----------------------------------------------------------------------===//
 
 template <typename ImutInfo> class ImutAVLTreeGenericIterator {
   SmallVector<uintptr_t,20> stack;
 
 public:
   using iterator_category = std::bidirectional_iterator_tag;
   using value_type = ImutAVLTree<ImutInfo>;
   using difference_type = std::ptrdiff_t;
   using pointer = value_type *;
   using reference = value_type &;
 
   enum VisitFlag { VisitedNone=0x0, VisitedLeft=0x1, VisitedRight=0x3,
                    Flags=0x3 };
 
   using TreeTy = ImutAVLTree<ImutInfo>;
 
   ImutAVLTreeGenericIterator() = default;
   ImutAVLTreeGenericIterator(const TreeTy *Root) {
     if (Root) stack.push_back(reinterpret_cast<uintptr_t>(Root));
   }
 
   TreeTy &operator*() const {
     assert(!stack.empty());
     return *reinterpret_cast<TreeTy *>(stack.back() & ~Flags);
   }
   TreeTy *operator->() const { return &*this; }
 
   uintptr_t getVisitState() const {
     assert(!stack.empty());
     return stack.back() & Flags;
   }
 
   bool atEnd() const { return stack.empty(); }
 
   bool atBeginning() const {
     return stack.size() == 1 && getVisitState() == VisitedNone;
   }
 
   void skipToParent() {
     assert(!stack.empty());
     stack.pop_back();
     if (stack.empty())
       return;
     switch (getVisitState()) {
       case VisitedNone:
         stack.back() |= VisitedLeft;
         break;
       case VisitedLeft:
         stack.back() |= VisitedRight;
         break;
       default:
         llvm_unreachable("Unreachable.");
     }
   }
 
   bool operator==(const ImutAVLTreeGenericIterator &x) const {
     return stack == x.stack;
   }
 
   bool operator!=(const ImutAVLTreeGenericIterator &x) const {
     return !(*this == x);
   }
 
   ImutAVLTreeGenericIterator &operator++() {
     assert(!stack.empty());
     TreeTy* Current = reinterpret_cast<TreeTy*>(stack.back() & ~Flags);
     assert(Current);
     switch (getVisitState()) {
       case VisitedNone:
         if (TreeTy* L = Current->getLeft())
           stack.push_back(reinterpret_cast<uintptr_t>(L));
         else
           stack.back() |= VisitedLeft;
         break;
       case VisitedLeft:
         if (TreeTy* R = Current->getRight())
           stack.push_back(reinterpret_cast<uintptr_t>(R));
         else
           stack.back() |= VisitedRight;
         break;
       case VisitedRight:
         skipToParent();
         break;
       default:
         llvm_unreachable("Unreachable.");
     }
     return *this;
   }
 
   ImutAVLTreeGenericIterator &operator--() {
     assert(!stack.empty());
     TreeTy* Current = reinterpret_cast<TreeTy*>(stack.back() & ~Flags);
     assert(Current);
     switch (getVisitState()) {
       case VisitedNone:
         stack.pop_back();
         break;
       case VisitedLeft:
         stack.back() &= ~Flags; // Set state to "VisitedNone."
         if (TreeTy* L = Current->getLeft())
           stack.push_back(reinterpret_cast<uintptr_t>(L) | VisitedRight);
         break;
       case VisitedRight:
         stack.back() &= ~Flags;
         stack.back() |= VisitedLeft;
         if (TreeTy* R = Current->getRight())
           stack.push_back(reinterpret_cast<uintptr_t>(R) | VisitedRight);
         break;
       default:
         llvm_unreachable("Unreachable.");
     }
     return *this;
   }
 };
 
 template <typename ImutInfo> class ImutAVLTreeInOrderIterator {
   using InternalIteratorTy = ImutAVLTreeGenericIterator<ImutInfo>;
 
   InternalIteratorTy InternalItr;
 
 public:
   using iterator_category = std::bidirectional_iterator_tag;
   using value_type = ImutAVLTree<ImutInfo>;
   using difference_type = std::ptrdiff_t;
   using pointer = value_type *;
   using reference = value_type &;
 
   using TreeTy = ImutAVLTree<ImutInfo>;
 
   ImutAVLTreeInOrderIterator(const TreeTy* Root) : InternalItr(Root) {
     if (Root)
       ++*this; // Advance to first element.
   }
 
   ImutAVLTreeInOrderIterator() : InternalItr() {}
 
   bool operator==(const ImutAVLTreeInOrderIterator &x) const {
     return InternalItr == x.InternalItr;
   }
 
   bool operator!=(const ImutAVLTreeInOrderIterator &x) const {
     return !(*this == x);
   }
 
   TreeTy &operator*() const { return *InternalItr; }
   TreeTy *operator->() const { return &*InternalItr; }
 
   ImutAVLTreeInOrderIterator &operator++() {
     do ++InternalItr;
     while (!InternalItr.atEnd() &&
            InternalItr.getVisitState() != InternalIteratorTy::VisitedLeft);
 
     return *this;
   }
 
   ImutAVLTreeInOrderIterator &operator--() {
     do --InternalItr;
     while (!InternalItr.atBeginning() &&
            InternalItr.getVisitState() != InternalIteratorTy::VisitedLeft);
 
     return *this;
   }
 
   void skipSubTree() {
     InternalItr.skipToParent();
 
     while (!InternalItr.atEnd() &&
            InternalItr.getVisitState() != InternalIteratorTy::VisitedLeft)
       ++InternalItr;
   }
 };
 
 /// Generic iterator that wraps a T::TreeTy::iterator and exposes
 /// iterator::getValue() on dereference.
 template <typename T>
 struct ImutAVLValueIterator
     : iterator_adaptor_base<
           ImutAVLValueIterator<T>, typename T::TreeTy::iterator,
           typename std::iterator_traits<
               typename T::TreeTy::iterator>::iterator_category,
           const typename T::value_type> {
   ImutAVLValueIterator() = default;
   explicit ImutAVLValueIterator(typename T::TreeTy *Tree)
       : ImutAVLValueIterator::iterator_adaptor_base(Tree) {}
 
   typename ImutAVLValueIterator::reference operator*() const {
     return this->I->getValue();
   }
 };
 
 //===----------------------------------------------------------------------===//
 // Trait classes for Profile information.
 //===----------------------------------------------------------------------===//
 
 /// Generic profile template.  The default behavior is to invoke the
 /// profile method of an object.  Specializations for primitive integers
 /// and generic handling of pointers is done below.
 template <typename T>
 struct ImutProfileInfo {
   using value_type = const T;
   using value_type_ref = const T&;
 
   static void Profile(FoldingSetNodeID &ID, value_type_ref X) {
     FoldingSetTrait<T>::Profile(X,ID);
   }
 };
 
 /// Profile traits for integers.
 template <typename T>
 struct ImutProfileInteger {
   using value_type = const T;
   using value_type_ref = const T&;
 
   static void Profile(FoldingSetNodeID &ID, value_type_ref X) {
     ID.AddInteger(X);
   }
 };
 
 #define PROFILE_INTEGER_INFO(X)\
 template<> struct ImutProfileInfo<X> : ImutProfileInteger<X> {};
 
 PROFILE_INTEGER_INFO(char)
 PROFILE_INTEGER_INFO(unsigned char)
 PROFILE_INTEGER_INFO(short)
 PROFILE_INTEGER_INFO(unsigned short)
 PROFILE_INTEGER_INFO(unsigned)
 PROFILE_INTEGER_INFO(signed)
 PROFILE_INTEGER_INFO(long)
 PROFILE_INTEGER_INFO(unsigned long)
 PROFILE_INTEGER_INFO(long long)
 PROFILE_INTEGER_INFO(unsigned long long)
 
 #undef PROFILE_INTEGER_INFO
 
 /// Profile traits for booleans.
 template <>
 struct ImutProfileInfo<bool> {
   using value_type = const bool;
   using value_type_ref = const bool&;
 
   static void Profile(FoldingSetNodeID &ID, value_type_ref X) {
     ID.AddBoolean(X);
   }
 };
 
 /// Generic profile trait for pointer types.  We treat pointers as
 /// references to unique objects.
 template <typename T>
 struct ImutProfileInfo<T*> {
   using value_type = const T*;
   using value_type_ref = value_type;
 
   static void Profile(FoldingSetNodeID &ID, value_type_ref X) {
     ID.AddPointer(X);
   }
 };
 
 //===----------------------------------------------------------------------===//
 // Trait classes that contain element comparison operators and type
 //  definitions used by ImutAVLTree, ImmutableSet, and ImmutableMap.  These
 //  inherit from the profile traits (ImutProfileInfo) to include operations
 //  for element profiling.
 //===----------------------------------------------------------------------===//
 
 /// ImutContainerInfo - Generic definition of comparison operations for
 ///   elements of immutable containers that defaults to using
 ///   std::equal_to<> and std::less<> to perform comparison of elements.
 template <typename T>
 struct ImutContainerInfo : public ImutProfileInfo<T> {
   using value_type = typename ImutProfileInfo<T>::value_type;
   using value_type_ref = typename ImutProfileInfo<T>::value_type_ref;
   using key_type = value_type;
   using key_type_ref = value_type_ref;
   using data_type = bool;
   using data_type_ref = bool;
 
   static key_type_ref KeyOfValue(value_type_ref D) { return D; }
   static data_type_ref DataOfValue(value_type_ref) { return true; }
 
   static bool isEqual(key_type_ref LHS, key_type_ref RHS) {
     return std::equal_to<key_type>()(LHS,RHS);
   }
 
   static bool isLess(key_type_ref LHS, key_type_ref RHS) {
     return std::less<key_type>()(LHS,RHS);
   }
 
   static bool isDataEqual(data_type_ref, data_type_ref) { return true; }
 };
 
 /// ImutContainerInfo - Specialization for pointer values to treat pointers
 ///  as references to unique objects.  Pointers are thus compared by
 ///  their addresses.
 template <typename T>
 struct ImutContainerInfo<T*> : public ImutProfileInfo<T*> {
   using value_type = typename ImutProfileInfo<T*>::value_type;
   using value_type_ref = typename ImutProfileInfo<T*>::value_type_ref;
   using key_type = value_type;
   using key_type_ref = value_type_ref;
   using data_type = bool;
   using data_type_ref = bool;
 
   static key_type_ref KeyOfValue(value_type_ref D) { return D; }
   static data_type_ref DataOfValue(value_type_ref) { return true; }
 
   static bool isEqual(key_type_ref LHS, key_type_ref RHS) { return LHS == RHS; }
 
   static bool isLess(key_type_ref LHS, key_type_ref RHS) { return LHS < RHS; }
 
   static bool isDataEqual(data_type_ref, data_type_ref) { return true; }
 };
 
 //===----------------------------------------------------------------------===//
 // Immutable Set
 //===----------------------------------------------------------------------===//
 
 template <typename ValT, typename ValInfo = ImutContainerInfo<ValT>>
 class ImmutableSet {
 public:
   using value_type = typename ValInfo::value_type;
   using value_type_ref = typename ValInfo::value_type_ref;
   using TreeTy = ImutAVLTree<ValInfo>;
 
 private:
   IntrusiveRefCntPtr<TreeTy> Root;
 
 public:
   /// Constructs a set from a pointer to a tree root.  In general one
   /// should use a Factory object to create sets instead of directly
   /// invoking the constructor, but there are cases where make this
   /// constructor public is useful.
   explicit ImmutableSet(TreeTy *R) : Root(R) {}
 
   class Factory {
     typename TreeTy::Factory F;
     const bool Canonicalize;
 
   public:
     Factory(bool canonicalize = true)
       : Canonicalize(canonicalize) {}
 
     Factory(BumpPtrAllocator& Alloc, bool canonicalize = true)
       : F(Alloc), Canonicalize(canonicalize) {}
 
     Factory(const Factory& RHS) = delete;
     void operator=(const Factory& RHS) = delete;
 
     /// getEmptySet - Returns an immutable set that contains no elements.
     ImmutableSet getEmptySet() {
       return ImmutableSet(F.getEmptyTree());
     }
 
     /// add - Creates a new immutable set that contains all of the values
     ///  of the original set with the addition of the specified value.  If
     ///  the original set already included the value, then the original set is
     ///  returned and no memory is allocated.  The time and space complexity
     ///  of this operation is logarithmic in the size of the original set.
     ///  The memory allocated to represent the set is released when the
     ///  factory object that created the set is destroyed.
     [[nodiscard]] ImmutableSet add(ImmutableSet Old, value_type_ref V) {
       TreeTy *NewT = F.add(Old.Root.get(), V);
       return ImmutableSet(Canonicalize ? F.getCanonicalTree(NewT) : NewT);
     }
 
     /// remove - Creates a new immutable set that contains all of the values
     ///  of the original set with the exception of the specified value.  If
     ///  the original set did not contain the value, the original set is
     ///  returned and no memory is allocated.  The time and space complexity
     ///  of this operation is logarithmic in the size of the original set.
     ///  The memory allocated to represent the set is released when the
     ///  factory object that created the set is destroyed.
     [[nodiscard]] ImmutableSet remove(ImmutableSet Old, value_type_ref V) {
       TreeTy *NewT = F.remove(Old.Root.get(), V);
       return ImmutableSet(Canonicalize ? F.getCanonicalTree(NewT) : NewT);
     }
 
     BumpPtrAllocator& getAllocator() { return F.getAllocator(); }
 
     typename TreeTy::Factory *getTreeFactory() const {
       return const_cast<typename TreeTy::Factory *>(&F);
     }
   };
 
   friend class Factory;
 
   /// Returns true if the set contains the specified value.
   bool contains(value_type_ref V) const {
     return Root ? Root->contains(V) : false;
   }
 
   bool operator==(const ImmutableSet &RHS) const {
     return Root && RHS.Root ? Root->isEqual(*RHS.Root.get()) : Root == RHS.Root;
   }
 
   bool operator!=(const ImmutableSet &RHS) const {
     return Root && RHS.Root ? Root->isNotEqual(*RHS.Root.get())
                             : Root != RHS.Root;
   }
 
   TreeTy *getRoot() {
     if (Root) { Root->retain(); }
     return Root.get();
   }
 
   TreeTy *getRootWithoutRetain() const { return Root.get(); }
 
   /// isEmpty - Return true if the set contains no elements.
   bool isEmpty() const { return !Root; }
 
   /// isSingleton - Return true if the set contains exactly one element.
   ///   This method runs in constant time.
   bool isSingleton() const { return getHeight() == 1; }
 
   //===--------------------------------------------------===//
   // Iterators.
   //===--------------------------------------------------===//
 
   using iterator = ImutAVLValueIterator<ImmutableSet>;
 
   iterator begin() const { return iterator(Root.get()); }
   iterator end() const { return iterator(); }
 
   //===--------------------------------------------------===//
   // Utility methods.
   //===--------------------------------------------------===//
 
   unsigned getHeight() const { return Root ? Root->getHeight() : 0; }
 
   static void Profile(FoldingSetNodeID &ID, const ImmutableSet &S) {
     ID.AddPointer(S.Root.get());
   }
 
   void Profile(FoldingSetNodeID &ID) const { return Profile(ID, *this); }
 
   //===--------------------------------------------------===//
   // For testing.
   //===--------------------------------------------------===//
 
   void validateTree() const { if (Root) Root->validateTree(); }
 };
 
 // NOTE: This may some day replace the current ImmutableSet.
 template <typename ValT, typename ValInfo = ImutContainerInfo<ValT>>
 class ImmutableSetRef {
 public:
   using value_type = typename ValInfo::value_type;
   using value_type_ref = typename ValInfo::value_type_ref;
   using TreeTy = ImutAVLTree<ValInfo>;
   using FactoryTy = typename TreeTy::Factory;
 
 private:
   IntrusiveRefCntPtr<TreeTy> Root;
   FactoryTy *Factory;
 
 public:
   /// Constructs a set from a pointer to a tree root.  In general one
   /// should use a Factory object to create sets instead of directly
   /// invoking the constructor, but there are cases where make this
   /// constructor public is useful.
   ImmutableSetRef(TreeTy *R, FactoryTy *F) : Root(R), Factory(F) {}
 
   static ImmutableSetRef getEmptySet(FactoryTy *F) {
     return ImmutableSetRef(0, F);
   }
 
   ImmutableSetRef add(value_type_ref V) {
     return ImmutableSetRef(Factory->add(Root.get(), V), Factory);
   }
 
   ImmutableSetRef remove(value_type_ref V) {
     return ImmutableSetRef(Factory->remove(Root.get(), V), Factory);
   }
 
   /// Returns true if the set contains the specified value.
   bool contains(value_type_ref V) const {
     return Root ? Root->contains(V) : false;
   }
 
   ImmutableSet<ValT> asImmutableSet(bool canonicalize = true) const {
     return ImmutableSet<ValT>(
         canonicalize ? Factory->getCanonicalTree(Root.get()) : Root.get());
   }
 
   TreeTy *getRootWithoutRetain() const { return Root.get(); }
 
   bool operator==(const ImmutableSetRef &RHS) const {
     return Root && RHS.Root ? Root->isEqual(*RHS.Root.get()) : Root == RHS.Root;
   }
 
   bool operator!=(const ImmutableSetRef &RHS) const {
     return Root && RHS.Root ? Root->isNotEqual(*RHS.Root.get())
                             : Root != RHS.Root;
   }
 
   /// isEmpty - Return true if the set contains no elements.
   bool isEmpty() const { return !Root; }
 
   /// isSingleton - Return true if the set contains exactly one element.
   ///   This method runs in constant time.
   bool isSingleton() const { return getHeight() == 1; }
 
   //===--------------------------------------------------===//
   // Iterators.
   //===--------------------------------------------------===//
 
   using iterator = ImutAVLValueIterator<ImmutableSetRef>;
 
   iterator begin() const { return iterator(Root.get()); }
   iterator end() const { return iterator(); }
 
   //===--------------------------------------------------===//
   // Utility methods.
   //===--------------------------------------------------===//
 
   unsigned getHeight() const { return Root ? Root->getHeight() : 0; }
 
   static void Profile(FoldingSetNodeID &ID, const ImmutableSetRef &S) {
     ID.AddPointer(S.Root.get());
   }
 
   void Profile(FoldingSetNodeID &ID) const { return Profile(ID, *this); }
 
   //===--------------------------------------------------===//
   // For testing.
   //===--------------------------------------------------===//
 
   void validateTree() const { if (Root) Root->validateTree(); }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_ADT_IMMUTABLESET_H

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