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diff --git a/llvm/lib/Bitcode/Writer/ValueEnumerator.h b/llvm/lib/Bitcode/Writer/ValueEnumerator.h
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+++ b/llvm/lib/Bitcode/Writer/ValueEnumerator.h
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+//===- Bitcode/Writer/ValueEnumerator.h - Number values ---------*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This class gives values and types Unique ID's.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_BITCODE_WRITER_VALUEENUMERATOR_H
+#define LLVM_LIB_BITCODE_WRITER_VALUEENUMERATOR_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/UniqueVector.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/UseListOrder.h"
+#include <cassert>
+#include <cstdint>
+#include <utility>
+#include <vector>
+
+namespace llvm {
+
+class BasicBlock;
+class Comdat;
+class Function;
+class Instruction;
+class LocalAsMetadata;
+class MDNode;
+class Metadata;
+class Module;
+class NamedMDNode;
+class raw_ostream;
+class Type;
+class Value;
+class ValueSymbolTable;
+
+class ValueEnumerator {
+public:
+  using TypeList = std::vector<Type *>;
+
+  // For each value, we remember its Value* and occurrence frequency.
+  using ValueList = std::vector<std::pair<const Value *, unsigned>>;
+
+  /// Attribute groups as encoded in bitcode are almost AttributeSets, but they
+  /// include the AttributeList index, so we have to track that in our map.
+  using IndexAndAttrSet = std::pair<unsigned, AttributeSet>;
+
+  UseListOrderStack UseListOrders;
+
+private:
+  using TypeMapType = DenseMap<Type *, unsigned>;
+  TypeMapType TypeMap;
+  TypeList Types;
+
+  using ValueMapType = DenseMap<const Value *, unsigned>;
+  ValueMapType ValueMap;
+  ValueList Values;
+
+  using ComdatSetType = UniqueVector<const Comdat *>;
+  ComdatSetType Comdats;
+
+  std::vector<const Metadata *> MDs;
+  std::vector<const Metadata *> FunctionMDs;
+
+  /// Index of information about a piece of metadata.
+  struct MDIndex {
+    unsigned F = 0;  ///< The ID of the function for this metadata, if any.
+    unsigned ID = 0; ///< The implicit ID of this metadata in bitcode.
+
+    MDIndex() = default;
+    explicit MDIndex(unsigned F) : F(F) {}
+
+    /// Check if this has a function tag, and it's different from NewF.
+    bool hasDifferentFunction(unsigned NewF) const { return F && F != NewF; }
+
+    /// Fetch the MD this references out of the given metadata array.
+    const Metadata *get(ArrayRef<const Metadata *> MDs) const {
+      assert(ID && "Expected non-zero ID");
+      assert(ID <= MDs.size() && "Expected valid ID");
+      return MDs[ID - 1];
+    }
+  };
+
+  using MetadataMapType = DenseMap<const Metadata *, MDIndex>;
+  MetadataMapType MetadataMap;
+
+  /// Range of metadata IDs, as a half-open range.
+  struct MDRange {
+    unsigned First = 0;
+    unsigned Last = 0;
+
+    /// Number of strings in the prefix of the metadata range.
+    unsigned NumStrings = 0;
+
+    MDRange() = default;
+    explicit MDRange(unsigned First) : First(First) {}
+  };
+  SmallDenseMap<unsigned, MDRange, 1> FunctionMDInfo;
+
+  bool ShouldPreserveUseListOrder;
+
+  using AttributeGroupMapType = DenseMap<IndexAndAttrSet, unsigned>;
+  AttributeGroupMapType AttributeGroupMap;
+  std::vector<IndexAndAttrSet> AttributeGroups;
+
+  using AttributeListMapType = DenseMap<AttributeList, unsigned>;
+  AttributeListMapType AttributeListMap;
+  std::vector<AttributeList> AttributeLists;
+
+  /// GlobalBasicBlockIDs - This map memoizes the basic block ID's referenced by
+  /// the "getGlobalBasicBlockID" method.
+  mutable DenseMap<const BasicBlock*, unsigned> GlobalBasicBlockIDs;
+
+  using InstructionMapType = DenseMap<const Instruction *, unsigned>;
+  InstructionMapType InstructionMap;
+  unsigned InstructionCount;
+
+  /// BasicBlocks - This contains all the basic blocks for the currently
+  /// incorporated function.  Their reverse mapping is stored in ValueMap.
+  std::vector<const BasicBlock*> BasicBlocks;
+
+  /// When a function is incorporated, this is the size of the Values list
+  /// before incorporation.
+  unsigned NumModuleValues;
+
+  /// When a function is incorporated, this is the size of the Metadatas list
+  /// before incorporation.
+  unsigned NumModuleMDs = 0;
+  unsigned NumMDStrings = 0;
+
+  unsigned FirstFuncConstantID;
+  unsigned FirstInstID;
+
+public:
+  ValueEnumerator(const Module &M, bool ShouldPreserveUseListOrder);
+  ValueEnumerator(const ValueEnumerator &) = delete;
+  ValueEnumerator &operator=(const ValueEnumerator &) = delete;
+
+  void dump() const;
+  void print(raw_ostream &OS, const ValueMapType &Map, const char *Name) const;
+  void print(raw_ostream &OS, const MetadataMapType &Map,
+             const char *Name) const;
+
+  unsigned getValueID(const Value *V) const;
+
+  unsigned getMetadataID(const Metadata *MD) const {
+    auto ID = getMetadataOrNullID(MD);
+    assert(ID != 0 && "Metadata not in slotcalculator!");
+    return ID - 1;
+  }
+
+  unsigned getMetadataOrNullID(const Metadata *MD) const {
+    return MetadataMap.lookup(MD).ID;
+  }
+
+  unsigned numMDs() const { return MDs.size(); }
+
+  bool shouldPreserveUseListOrder() const { return ShouldPreserveUseListOrder; }
+
+  unsigned getTypeID(Type *T) const {
+    TypeMapType::const_iterator I = TypeMap.find(T);
+    assert(I != TypeMap.end() && "Type not in ValueEnumerator!");
+    return I->second-1;
+  }
+
+  unsigned getInstructionID(const Instruction *I) const;
+  void setInstructionID(const Instruction *I);
+
+  unsigned getAttributeListID(AttributeList PAL) const {
+    if (PAL.isEmpty()) return 0;  // Null maps to zero.
+    AttributeListMapType::const_iterator I = AttributeListMap.find(PAL);
+    assert(I != AttributeListMap.end() && "Attribute not in ValueEnumerator!");
+    return I->second;
+  }
+
+  unsigned getAttributeGroupID(IndexAndAttrSet Group) const {
+    if (!Group.second.hasAttributes())
+      return 0; // Null maps to zero.
+    AttributeGroupMapType::const_iterator I = AttributeGroupMap.find(Group);
+    assert(I != AttributeGroupMap.end() && "Attribute not in ValueEnumerator!");
+    return I->second;
+  }
+
+  /// getFunctionConstantRange - Return the range of values that corresponds to
+  /// function-local constants.
+  void getFunctionConstantRange(unsigned &Start, unsigned &End) const {
+    Start = FirstFuncConstantID;
+    End = FirstInstID;
+  }
+
+  const ValueList &getValues() const { return Values; }
+
+  /// Check whether the current block has any metadata to emit.
+  bool hasMDs() const { return NumModuleMDs < MDs.size(); }
+
+  /// Get the MDString metadata for this block.
+  ArrayRef<const Metadata *> getMDStrings() const {
+    return makeArrayRef(MDs).slice(NumModuleMDs, NumMDStrings);
+  }
+
+  /// Get the non-MDString metadata for this block.
+  ArrayRef<const Metadata *> getNonMDStrings() const {
+    return makeArrayRef(MDs).slice(NumModuleMDs).slice(NumMDStrings);
+  }
+
+  const TypeList &getTypes() const { return Types; }
+
+  const std::vector<const BasicBlock*> &getBasicBlocks() const {
+    return BasicBlocks;
+  }
+
+  const std::vector<AttributeList> &getAttributeLists() const { return AttributeLists; }
+
+  const std::vector<IndexAndAttrSet> &getAttributeGroups() const {
+    return AttributeGroups;
+  }
+
+  const ComdatSetType &getComdats() const { return Comdats; }
+  unsigned getComdatID(const Comdat *C) const;
+
+  /// getGlobalBasicBlockID - This returns the function-specific ID for the
+  /// specified basic block.  This is relatively expensive information, so it
+  /// should only be used by rare constructs such as address-of-label.
+  unsigned getGlobalBasicBlockID(const BasicBlock *BB) const;
+
+  /// incorporateFunction/purgeFunction - If you'd like to deal with a function,
+  /// use these two methods to get its data into the ValueEnumerator!
+  void incorporateFunction(const Function &F);
+
+  void purgeFunction();
+  uint64_t computeBitsRequiredForTypeIndicies() const;
+
+private:
+  void OptimizeConstants(unsigned CstStart, unsigned CstEnd);
+
+  /// Reorder the reachable metadata.
+  ///
+  /// This is not just an optimization, but is mandatory for emitting MDString
+  /// correctly.
+  void organizeMetadata();
+
+  /// Drop the function tag from the transitive operands of the given node.
+  void dropFunctionFromMetadata(MetadataMapType::value_type &FirstMD);
+
+  /// Incorporate the function metadata.
+  ///
+  /// This should be called before enumerating LocalAsMetadata for the
+  /// function.
+  void incorporateFunctionMetadata(const Function &F);
+
+  /// Enumerate a single instance of metadata with the given function tag.
+  ///
+  /// If \c MD has already been enumerated, check that \c F matches its
+  /// function tag.  If not, call \a dropFunctionFromMetadata().
+  ///
+  /// Otherwise, mark \c MD as visited.  Assign it an ID, or just return it if
+  /// it's an \a MDNode.
+  const MDNode *enumerateMetadataImpl(unsigned F, const Metadata *MD);
+
+  unsigned getMetadataFunctionID(const Function *F) const;
+
+  /// Enumerate reachable metadata in (almost) post-order.
+  ///
+  /// Enumerate all the metadata reachable from MD.  We want to minimize the
+  /// cost of reading bitcode records, and so the primary consideration is that
+  /// operands of uniqued nodes are resolved before the nodes are read.  This
+  /// avoids re-uniquing them on the context and factors away RAUW support.
+  ///
+  /// This algorithm guarantees that subgraphs of uniqued nodes are in
+  /// post-order.  Distinct subgraphs reachable only from a single uniqued node
+  /// will be in post-order.
+  ///
+  /// \note The relative order of a distinct and uniqued node is irrelevant.
+  /// \a organizeMetadata() will later partition distinct nodes ahead of
+  /// uniqued ones.
+  ///{
+  void EnumerateMetadata(const Function *F, const Metadata *MD);
+  void EnumerateMetadata(unsigned F, const Metadata *MD);
+  ///}
+
+  void EnumerateFunctionLocalMetadata(const Function &F,
+                                      const LocalAsMetadata *Local);
+  void EnumerateFunctionLocalMetadata(unsigned F, const LocalAsMetadata *Local);
+  void EnumerateNamedMDNode(const NamedMDNode *NMD);
+  void EnumerateValue(const Value *V);
+  void EnumerateType(Type *T);
+  void EnumerateOperandType(const Value *V);
+  void EnumerateAttributes(AttributeList PAL);
+
+  void EnumerateValueSymbolTable(const ValueSymbolTable &ST);
+  void EnumerateNamedMetadata(const Module &M);
+};
+
+} // end namespace llvm
+
+#endif // LLVM_LIB_BITCODE_WRITER_VALUEENUMERATOR_H