llvm16 targets

1 files changed, 5240 insertions, 0 deletions

diff --git a/contrib/libs/llvm16/lib/Bitcode/Writer/BitcodeWriter.cpp b/contrib/libs/llvm16/lib/Bitcode/Writer/BitcodeWriter.cpp
new file mode 100644
index 00000000000..f85fd86c114
--- /dev/null
+++ b/contrib/libs/llvm16/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -0,0 +1,5240 @@
+//===- Bitcode/Writer/BitcodeWriter.cpp - Bitcode Writer ------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Bitcode writer implementation.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Bitcode/BitcodeWriter.h"
+#include "ValueEnumerator.h"
+#include "llvm/ADT/APFloat.h"
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/Bitcode/BitcodeCommon.h"
+#include "llvm/Bitcode/BitcodeReader.h"
+#include "llvm/Bitcode/LLVMBitCodes.h"
+#include "llvm/Bitstream/BitCodes.h"
+#include "llvm/Bitstream/BitstreamWriter.h"
+#include "llvm/Config/llvm-config.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Comdat.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/DebugLoc.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GlobalAlias.h"
+#include "llvm/IR/GlobalIFunc.h"
+#include "llvm/IR/GlobalObject.h"
+#include "llvm/IR/GlobalValue.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/InlineAsm.h"
+#include "llvm/IR/InstrTypes.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/ModuleSummaryIndex.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/UseListOrder.h"
+#include "llvm/IR/Value.h"
+#include "llvm/IR/ValueSymbolTable.h"
+#include "llvm/MC/StringTableBuilder.h"
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/Object/IRSymtab.h"
+#include "llvm/Support/AtomicOrdering.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/SHA1.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <iterator>
+#include <map>
+#include <memory>
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+using namespace llvm;
+
+static cl::opt<unsigned>
+    IndexThreshold("bitcode-mdindex-threshold", cl::Hidden, cl::init(25),
+                   cl::desc("Number of metadatas above which we emit an index "
+                            "to enable lazy-loading"));
+static cl::opt<uint32_t> FlushThreshold(
+    "bitcode-flush-threshold", cl::Hidden, cl::init(512),
+    cl::desc("The threshold (unit M) for flushing LLVM bitcode."));
+
+static cl::opt<bool> WriteRelBFToSummary(
+    "write-relbf-to-summary", cl::Hidden, cl::init(false),
+    cl::desc("Write relative block frequency to function summary "));
+
+namespace llvm {
+extern FunctionSummary::ForceSummaryHotnessType ForceSummaryEdgesCold;
+}
+
+namespace {
+
+/// These are manifest constants used by the bitcode writer. They do not need to
+/// be kept in sync with the reader, but need to be consistent within this file.
+enum {
+  // VALUE_SYMTAB_BLOCK abbrev id's.
+  VST_ENTRY_8_ABBREV = bitc::FIRST_APPLICATION_ABBREV,
+  VST_ENTRY_7_ABBREV,
+  VST_ENTRY_6_ABBREV,
+  VST_BBENTRY_6_ABBREV,
+
+  // CONSTANTS_BLOCK abbrev id's.
+  CONSTANTS_SETTYPE_ABBREV = bitc::FIRST_APPLICATION_ABBREV,
+  CONSTANTS_INTEGER_ABBREV,
+  CONSTANTS_CE_CAST_Abbrev,
+  CONSTANTS_NULL_Abbrev,
+
+  // FUNCTION_BLOCK abbrev id's.
+  FUNCTION_INST_LOAD_ABBREV = bitc::FIRST_APPLICATION_ABBREV,
+  FUNCTION_INST_UNOP_ABBREV,
+  FUNCTION_INST_UNOP_FLAGS_ABBREV,
+  FUNCTION_INST_BINOP_ABBREV,
+  FUNCTION_INST_BINOP_FLAGS_ABBREV,
+  FUNCTION_INST_CAST_ABBREV,
+  FUNCTION_INST_RET_VOID_ABBREV,
+  FUNCTION_INST_RET_VAL_ABBREV,
+  FUNCTION_INST_UNREACHABLE_ABBREV,
+  FUNCTION_INST_GEP_ABBREV,
+};
+
+/// Abstract class to manage the bitcode writing, subclassed for each bitcode
+/// file type.
+class BitcodeWriterBase {
+protected:
+  /// The stream created and owned by the client.
+  BitstreamWriter &Stream;
+
+  StringTableBuilder &StrtabBuilder;
+
+public:
+  /// Constructs a BitcodeWriterBase object that writes to the provided
+  /// \p Stream.
+  BitcodeWriterBase(BitstreamWriter &Stream, StringTableBuilder &StrtabBuilder)
+      : Stream(Stream), StrtabBuilder(StrtabBuilder) {}
+
+protected:
+  void writeModuleVersion();
+};
+
+void BitcodeWriterBase::writeModuleVersion() {
+  // VERSION: [version#]
+  Stream.EmitRecord(bitc::MODULE_CODE_VERSION, ArrayRef<uint64_t>{2});
+}
+
+/// Base class to manage the module bitcode writing, currently subclassed for
+/// ModuleBitcodeWriter and ThinLinkBitcodeWriter.
+class ModuleBitcodeWriterBase : public BitcodeWriterBase {
+protected:
+  /// The Module to write to bitcode.
+  const Module &M;
+
+  /// Enumerates ids for all values in the module.
+  ValueEnumerator VE;
+
+  /// Optional per-module index to write for ThinLTO.
+  const ModuleSummaryIndex *Index;
+
+  /// Map that holds the correspondence between GUIDs in the summary index,
+  /// that came from indirect call profiles, and a value id generated by this
+  /// class to use in the VST and summary block records.
+  std::map<GlobalValue::GUID, unsigned> GUIDToValueIdMap;
+
+  /// Tracks the last value id recorded in the GUIDToValueMap.
+  unsigned GlobalValueId;
+
+  /// Saves the offset of the VSTOffset record that must eventually be
+  /// backpatched with the offset of the actual VST.
+  uint64_t VSTOffsetPlaceholder = 0;
+
+public:
+  /// Constructs a ModuleBitcodeWriterBase object for the given Module,
+  /// writing to the provided \p Buffer.
+  ModuleBitcodeWriterBase(const Module &M, StringTableBuilder &StrtabBuilder,
+                          BitstreamWriter &Stream,
+                          bool ShouldPreserveUseListOrder,
+                          const ModuleSummaryIndex *Index)
+      : BitcodeWriterBase(Stream, StrtabBuilder), M(M),
+        VE(M, ShouldPreserveUseListOrder), Index(Index) {
+    // Assign ValueIds to any callee values in the index that came from
+    // indirect call profiles and were recorded as a GUID not a Value*
+    // (which would have been assigned an ID by the ValueEnumerator).
+    // The starting ValueId is just after the number of values in the
+    // ValueEnumerator, so that they can be emitted in the VST.
+    GlobalValueId = VE.getValues().size();
+    if (!Index)
+      return;
+    for (const auto &GUIDSummaryLists : *Index)
+      // Examine all summaries for this GUID.
+      for (auto &Summary : GUIDSummaryLists.second.SummaryList)
+        if (auto FS = dyn_cast<FunctionSummary>(Summary.get()))
+          // For each call in the function summary, see if the call
+          // is to a GUID (which means it is for an indirect call,
+          // otherwise we would have a Value for it). If so, synthesize
+          // a value id.
+          for (auto &CallEdge : FS->calls())
+            if (!CallEdge.first.haveGVs() || !CallEdge.first.getValue())
+              assignValueId(CallEdge.first.getGUID());
+  }
+
+protected:
+  void writePerModuleGlobalValueSummary();
+
+private:
+  void writePerModuleFunctionSummaryRecord(
+      SmallVector<uint64_t, 64> &NameVals, GlobalValueSummary *Summary,
+      unsigned ValueID, unsigned FSCallsAbbrev, unsigned FSCallsProfileAbbrev,
+      unsigned CallsiteAbbrev, unsigned AllocAbbrev, const Function &F);
+  void writeModuleLevelReferences(const GlobalVariable &V,
+                                  SmallVector<uint64_t, 64> &NameVals,
+                                  unsigned FSModRefsAbbrev,
+                                  unsigned FSModVTableRefsAbbrev);
+
+  void assignValueId(GlobalValue::GUID ValGUID) {
+    GUIDToValueIdMap[ValGUID] = ++GlobalValueId;
+  }
+
+  unsigned getValueId(GlobalValue::GUID ValGUID) {
+    const auto &VMI = GUIDToValueIdMap.find(ValGUID);
+    // Expect that any GUID value had a value Id assigned by an
+    // earlier call to assignValueId.
+    assert(VMI != GUIDToValueIdMap.end() &&
+           "GUID does not have assigned value Id");
+    return VMI->second;
+  }
+
+  // Helper to get the valueId for the type of value recorded in VI.
+  unsigned getValueId(ValueInfo VI) {
+    if (!VI.haveGVs() || !VI.getValue())
+      return getValueId(VI.getGUID());
+    return VE.getValueID(VI.getValue());
+  }
+
+  std::map<GlobalValue::GUID, unsigned> &valueIds() { return GUIDToValueIdMap; }
+};
+
+/// Class to manage the bitcode writing for a module.
+class ModuleBitcodeWriter : public ModuleBitcodeWriterBase {
+  /// Pointer to the buffer allocated by caller for bitcode writing.
+  const SmallVectorImpl<char> &Buffer;
+
+  /// True if a module hash record should be written.
+  bool GenerateHash;
+
+  /// If non-null, when GenerateHash is true, the resulting hash is written
+  /// into ModHash.
+  ModuleHash *ModHash;
+
+  SHA1 Hasher;
+
+  /// The start bit of the identification block.
+  uint64_t BitcodeStartBit;
+
+public:
+  /// Constructs a ModuleBitcodeWriter object for the given Module,
+  /// writing to the provided \p Buffer.
+  ModuleBitcodeWriter(const Module &M, SmallVectorImpl<char> &Buffer,
+                      StringTableBuilder &StrtabBuilder,
+                      BitstreamWriter &Stream, bool ShouldPreserveUseListOrder,
+                      const ModuleSummaryIndex *Index, bool GenerateHash,
+                      ModuleHash *ModHash = nullptr)
+      : ModuleBitcodeWriterBase(M, StrtabBuilder, Stream,
+                                ShouldPreserveUseListOrder, Index),
+        Buffer(Buffer), GenerateHash(GenerateHash), ModHash(ModHash),
+        BitcodeStartBit(Stream.GetCurrentBitNo()) {}
+
+  /// Emit the current module to the bitstream.
+  void write();
+
+private:
+  uint64_t bitcodeStartBit() { return BitcodeStartBit; }
+
+  size_t addToStrtab(StringRef Str);
+
+  void writeAttributeGroupTable();
+  void writeAttributeTable();
+  void writeTypeTable();
+  void writeComdats();
+  void writeValueSymbolTableForwardDecl();
+  void writeModuleInfo();
+  void writeValueAsMetadata(const ValueAsMetadata *MD,
+                            SmallVectorImpl<uint64_t> &Record);
+  void writeMDTuple(const MDTuple *N, SmallVectorImpl<uint64_t> &Record,
+                    unsigned Abbrev);
+  unsigned createDILocationAbbrev();
+  void writeDILocation(const DILocation *N, SmallVectorImpl<uint64_t> &Record,
+                       unsigned &Abbrev);
+  unsigned createGenericDINodeAbbrev();
+  void writeGenericDINode(const GenericDINode *N,
+                          SmallVectorImpl<uint64_t> &Record, unsigned &Abbrev);
+  void writeDISubrange(const DISubrange *N, SmallVectorImpl<uint64_t> &Record,
+                       unsigned Abbrev);
+  void writeDIGenericSubrange(const DIGenericSubrange *N,
+                              SmallVectorImpl<uint64_t> &Record,
+                              unsigned Abbrev);
+  void writeDIEnumerator(const DIEnumerator *N,
+                         SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDIBasicType(const DIBasicType *N, SmallVectorImpl<uint64_t> &Record,
+                        unsigned Abbrev);
+  void writeDIStringType(const DIStringType *N,
+                         SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDIDerivedType(const DIDerivedType *N,
+                          SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDICompositeType(const DICompositeType *N,
+                            SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDISubroutineType(const DISubroutineType *N,
+                             SmallVectorImpl<uint64_t> &Record,
+                             unsigned Abbrev);
+  void writeDIFile(const DIFile *N, SmallVectorImpl<uint64_t> &Record,
+                   unsigned Abbrev);
+  void writeDICompileUnit(const DICompileUnit *N,
+                          SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDISubprogram(const DISubprogram *N,
+                         SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDILexicalBlock(const DILexicalBlock *N,
+                           SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDILexicalBlockFile(const DILexicalBlockFile *N,
+                               SmallVectorImpl<uint64_t> &Record,
+                               unsigned Abbrev);
+  void writeDICommonBlock(const DICommonBlock *N,
+                          SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDINamespace(const DINamespace *N, SmallVectorImpl<uint64_t> &Record,
+                        unsigned Abbrev);
+  void writeDIMacro(const DIMacro *N, SmallVectorImpl<uint64_t> &Record,
+                    unsigned Abbrev);
+  void writeDIMacroFile(const DIMacroFile *N, SmallVectorImpl<uint64_t> &Record,
+                        unsigned Abbrev);
+  void writeDIArgList(const DIArgList *N, SmallVectorImpl<uint64_t> &Record,
+                      unsigned Abbrev);
+  void writeDIModule(const DIModule *N, SmallVectorImpl<uint64_t> &Record,
+                     unsigned Abbrev);
+  void writeDIAssignID(const DIAssignID *N, SmallVectorImpl<uint64_t> &Record,
+                       unsigned Abbrev);
+  void writeDITemplateTypeParameter(const DITemplateTypeParameter *N,
+                                    SmallVectorImpl<uint64_t> &Record,
+                                    unsigned Abbrev);
+  void writeDITemplateValueParameter(const DITemplateValueParameter *N,
+                                     SmallVectorImpl<uint64_t> &Record,
+                                     unsigned Abbrev);
+  void writeDIGlobalVariable(const DIGlobalVariable *N,
+                             SmallVectorImpl<uint64_t> &Record,
+                             unsigned Abbrev);
+  void writeDILocalVariable(const DILocalVariable *N,
+                            SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDILabel(const DILabel *N,
+                    SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDIExpression(const DIExpression *N,
+                         SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDIGlobalVariableExpression(const DIGlobalVariableExpression *N,
+                                       SmallVectorImpl<uint64_t> &Record,
+                                       unsigned Abbrev);
+  void writeDIObjCProperty(const DIObjCProperty *N,
+                           SmallVectorImpl<uint64_t> &Record, unsigned Abbrev);
+  void writeDIImportedEntity(const DIImportedEntity *N,
+                             SmallVectorImpl<uint64_t> &Record,
+                             unsigned Abbrev);
+  unsigned createNamedMetadataAbbrev();
+  void writeNamedMetadata(SmallVectorImpl<uint64_t> &Record);
+  unsigned createMetadataStringsAbbrev();
+  void writeMetadataStrings(ArrayRef<const Metadata *> Strings,
+                            SmallVectorImpl<uint64_t> &Record);
+  void writeMetadataRecords(ArrayRef<const Metadata *> MDs,
+                            SmallVectorImpl<uint64_t> &Record,
+                            std::vector<unsigned> *MDAbbrevs = nullptr,
+                            std::vector<uint64_t> *IndexPos = nullptr);
+  void writeModuleMetadata();
+  void writeFunctionMetadata(const Function &F);
+  void writeFunctionMetadataAttachment(const Function &F);
+  void pushGlobalMetadataAttachment(SmallVectorImpl<uint64_t> &Record,
+                                    const GlobalObject &GO);
+  void writeModuleMetadataKinds();
+  void writeOperandBundleTags();
+  void writeSyncScopeNames();
+  void writeConstants(unsigned FirstVal, unsigned LastVal, bool isGlobal);
+  void writeModuleConstants();
+  bool pushValueAndType(const Value *V, unsigned InstID,
+                        SmallVectorImpl<unsigned> &Vals);
+  void writeOperandBundles(const CallBase &CB, unsigned InstID);
+  void pushValue(const Value *V, unsigned InstID,
+                 SmallVectorImpl<unsigned> &Vals);
+  void pushValueSigned(const Value *V, unsigned InstID,
+                       SmallVectorImpl<uint64_t> &Vals);
+  void writeInstruction(const Instruction &I, unsigned InstID,
+                        SmallVectorImpl<unsigned> &Vals);
+  void writeFunctionLevelValueSymbolTable(const ValueSymbolTable &VST);
+  void writeGlobalValueSymbolTable(
+      DenseMap<const Function *, uint64_t> &FunctionToBitcodeIndex);
+  void writeUseList(UseListOrder &&Order);
+  void writeUseListBlock(const Function *F);
+  void
+  writeFunction(const Function &F,
+                DenseMap<const Function *, uint64_t> &FunctionToBitcodeIndex);
+  void writeBlockInfo();
+  void writeModuleHash(size_t BlockStartPos);
+
+  unsigned getEncodedSyncScopeID(SyncScope::ID SSID) {
+    return unsigned(SSID);
+  }
+
+  unsigned getEncodedAlign(MaybeAlign Alignment) { return encode(Alignment); }
+};
+
+/// Class to manage the bitcode writing for a combined index.
+class IndexBitcodeWriter : public BitcodeWriterBase {
+  /// The combined index to write to bitcode.
+  const ModuleSummaryIndex &Index;
+
+  /// When writing a subset of the index for distributed backends, client
+  /// provides a map of modules to the corresponding GUIDs/summaries to write.
+  const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex;
+
+  /// Map that holds the correspondence between the GUID used in the combined
+  /// index and a value id generated by this class to use in references.
+  std::map<GlobalValue::GUID, unsigned> GUIDToValueIdMap;
+
+  // The sorted stack id indices actually used in the summary entries being
+  // written, which will be a subset of those in the full index in the case of
+  // distributed indexes.
+  std::vector<unsigned> StackIdIndices;
+
+  /// Tracks the last value id recorded in the GUIDToValueMap.
+  unsigned GlobalValueId = 0;
+
+public:
+  /// Constructs a IndexBitcodeWriter object for the given combined index,
+  /// writing to the provided \p Buffer. When writing a subset of the index
+  /// for a distributed backend, provide a \p ModuleToSummariesForIndex map.
+  IndexBitcodeWriter(BitstreamWriter &Stream, StringTableBuilder &StrtabBuilder,
+                     const ModuleSummaryIndex &Index,
+                     const std::map<std::string, GVSummaryMapTy>
+                         *ModuleToSummariesForIndex = nullptr)
+      : BitcodeWriterBase(Stream, StrtabBuilder), Index(Index),
+        ModuleToSummariesForIndex(ModuleToSummariesForIndex) {
+    // Assign unique value ids to all summaries to be written, for use
+    // in writing out the call graph edges. Save the mapping from GUID
+    // to the new global value id to use when writing those edges, which
+    // are currently saved in the index in terms of GUID.
+    forEachSummary([&](GVInfo I, bool IsAliasee) {
+      GUIDToValueIdMap[I.first] = ++GlobalValueId;
+      if (IsAliasee)
+        return;
+      auto *FS = dyn_cast<FunctionSummary>(I.second);
+      if (!FS)
+        return;
+      // Record all stack id indices actually used in the summary entries being
+      // written, so that we can compact them in the case of distributed ThinLTO
+      // indexes.
+      for (auto &CI : FS->callsites())
+        for (auto Idx : CI.StackIdIndices)
+          StackIdIndices.push_back(Idx);
+      for (auto &AI : FS->allocs())
+        for (auto &MIB : AI.MIBs)
+          for (auto Idx : MIB.StackIdIndices)
+            StackIdIndices.push_back(Idx);
+    });
+    llvm::sort(StackIdIndices);
+    StackIdIndices.erase(
+        std::unique(StackIdIndices.begin(), StackIdIndices.end()),
+        StackIdIndices.end());
+  }
+
+  /// The below iterator returns the GUID and associated summary.
+  using GVInfo = std::pair<GlobalValue::GUID, GlobalValueSummary *>;
+
+  /// Calls the callback for each value GUID and summary to be written to
+  /// bitcode. This hides the details of whether they are being pulled from the
+  /// entire index or just those in a provided ModuleToSummariesForIndex map.
+  template<typename Functor>
+  void forEachSummary(Functor Callback) {
+    if (ModuleToSummariesForIndex) {
+      for (auto &M : *ModuleToSummariesForIndex)
+        for (auto &Summary : M.second) {
+          Callback(Summary, false);
+          // Ensure aliasee is handled, e.g. for assigning a valueId,
+          // even if we are not importing the aliasee directly (the
+          // imported alias will contain a copy of aliasee).
+          if (auto *AS = dyn_cast<AliasSummary>(Summary.getSecond()))
+            Callback({AS->getAliaseeGUID(), &AS->getAliasee()}, true);
+        }
+    } else {
+      for (auto &Summaries : Index)
+        for (auto &Summary : Summaries.second.SummaryList)
+          Callback({Summaries.first, Summary.get()}, false);
+    }
+  }
+
+  /// Calls the callback for each entry in the modulePaths StringMap that
+  /// should be written to the module path string table. This hides the details
+  /// of whether they are being pulled from the entire index or just those in a
+  /// provided ModuleToSummariesForIndex map.
+  template <typename Functor> void forEachModule(Functor Callback) {
+    if (ModuleToSummariesForIndex) {
+      for (const auto &M : *ModuleToSummariesForIndex) {
+        const auto &MPI = Index.modulePaths().find(M.first);
+        if (MPI == Index.modulePaths().end()) {
+          // This should only happen if the bitcode file was empty, in which
+          // case we shouldn't be importing (the ModuleToSummariesForIndex
+          // would only include the module we are writing and index for).
+          assert(ModuleToSummariesForIndex->size() == 1);
+          continue;
+        }
+        Callback(*MPI);
+      }
+    } else {
+      for (const auto &MPSE : Index.modulePaths())
+        Callback(MPSE);
+    }
+  }
+
+  /// Main entry point for writing a combined index to bitcode.
+  void write();
+
+private:
+  void writeModStrings();
+  void writeCombinedGlobalValueSummary();
+
+  std::optional<unsigned> getValueId(GlobalValue::GUID ValGUID) {
+    auto VMI = GUIDToValueIdMap.find(ValGUID);
+    if (VMI == GUIDToValueIdMap.end())
+      return std::nullopt;
+    return VMI->second;
+  }
+
+  std::map<GlobalValue::GUID, unsigned> &valueIds() { return GUIDToValueIdMap; }
+};
+
+} // end anonymous namespace
+
+static unsigned getEncodedCastOpcode(unsigned Opcode) {
+  switch (Opcode) {
+  default: llvm_unreachable("Unknown cast instruction!");
+  case Instruction::Trunc   : return bitc::CAST_TRUNC;
+  case Instruction::ZExt    : return bitc::CAST_ZEXT;
+  case Instruction::SExt    : return bitc::CAST_SEXT;
+  case Instruction::FPToUI  : return bitc::CAST_FPTOUI;
+  case Instruction::FPToSI  : return bitc::CAST_FPTOSI;
+  case Instruction::UIToFP  : return bitc::CAST_UITOFP;
+  case Instruction::SIToFP  : return bitc::CAST_SITOFP;
+  case Instruction::FPTrunc : return bitc::CAST_FPTRUNC;
+  case Instruction::FPExt   : return bitc::CAST_FPEXT;
+  case Instruction::PtrToInt: return bitc::CAST_PTRTOINT;
+  case Instruction::IntToPtr: return bitc::CAST_INTTOPTR;
+  case Instruction::BitCast : return bitc::CAST_BITCAST;
+  case Instruction::AddrSpaceCast: return bitc::CAST_ADDRSPACECAST;
+  }
+}
+
+static unsigned getEncodedUnaryOpcode(unsigned Opcode) {
+  switch (Opcode) {
+  default: llvm_unreachable("Unknown binary instruction!");
+  case Instruction::FNeg: return bitc::UNOP_FNEG;
+  }
+}
+
+static unsigned getEncodedBinaryOpcode(unsigned Opcode) {
+  switch (Opcode) {
+  default: llvm_unreachable("Unknown binary instruction!");
+  case Instruction::Add:
+  case Instruction::FAdd: return bitc::BINOP_ADD;
+  case Instruction::Sub:
+  case Instruction::FSub: return bitc::BINOP_SUB;
+  case Instruction::Mul:
+  case Instruction::FMul: return bitc::BINOP_MUL;
+  case Instruction::UDiv: return bitc::BINOP_UDIV;
+  case Instruction::FDiv:
+  case Instruction::SDiv: return bitc::BINOP_SDIV;
+  case Instruction::URem: return bitc::BINOP_UREM;
+  case Instruction::FRem:
+  case Instruction::SRem: return bitc::BINOP_SREM;
+  case Instruction::Shl:  return bitc::BINOP_SHL;
+  case Instruction::LShr: return bitc::BINOP_LSHR;
+  case Instruction::AShr: return bitc::BINOP_ASHR;
+  case Instruction::And:  return bitc::BINOP_AND;
+  case Instruction::Or:   return bitc::BINOP_OR;
+  case Instruction::Xor:  return bitc::BINOP_XOR;
+  }
+}
+
+static unsigned getEncodedRMWOperation(AtomicRMWInst::BinOp Op) {
+  switch (Op) {
+  default: llvm_unreachable("Unknown RMW operation!");
+  case AtomicRMWInst::Xchg: return bitc::RMW_XCHG;
+  case AtomicRMWInst::Add: return bitc::RMW_ADD;
+  case AtomicRMWInst::Sub: return bitc::RMW_SUB;
+  case AtomicRMWInst::And: return bitc::RMW_AND;
+  case AtomicRMWInst::Nand: return bitc::RMW_NAND;
+  case AtomicRMWInst::Or: return bitc::RMW_OR;
+  case AtomicRMWInst::Xor: return bitc::RMW_XOR;
+  case AtomicRMWInst::Max: return bitc::RMW_MAX;
+  case AtomicRMWInst::Min: return bitc::RMW_MIN;
+  case AtomicRMWInst::UMax: return bitc::RMW_UMAX;
+  case AtomicRMWInst::UMin: return bitc::RMW_UMIN;
+  case AtomicRMWInst::FAdd: return bitc::RMW_FADD;
+  case AtomicRMWInst::FSub: return bitc::RMW_FSUB;
+  case AtomicRMWInst::FMax: return bitc::RMW_FMAX;
+  case AtomicRMWInst::FMin: return bitc::RMW_FMIN;
+  case AtomicRMWInst::UIncWrap:
+    return bitc::RMW_UINC_WRAP;
+  case AtomicRMWInst::UDecWrap:
+    return bitc::RMW_UDEC_WRAP;
+  }
+}
+
+static unsigned getEncodedOrdering(AtomicOrdering Ordering) {
+  switch (Ordering) {
+  case AtomicOrdering::NotAtomic: return bitc::ORDERING_NOTATOMIC;
+  case AtomicOrdering::Unordered: return bitc::ORDERING_UNORDERED;
+  case AtomicOrdering::Monotonic: return bitc::ORDERING_MONOTONIC;
+  case AtomicOrdering::Acquire: return bitc::ORDERING_ACQUIRE;
+  case AtomicOrdering::Release: return bitc::ORDERING_RELEASE;
+  case AtomicOrdering::AcquireRelease: return bitc::ORDERING_ACQREL;
+  case AtomicOrdering::SequentiallyConsistent: return bitc::ORDERING_SEQCST;
+  }
+  llvm_unreachable("Invalid ordering");
+}
+
+static void writeStringRecord(BitstreamWriter &Stream, unsigned Code,
+                              StringRef Str, unsigned AbbrevToUse) {
+  SmallVector<unsigned, 64> Vals;
+
+  // Code: [strchar x N]
+  for (char C : Str) {
+    if (AbbrevToUse && !BitCodeAbbrevOp::isChar6(C))
+      AbbrevToUse = 0;
+    Vals.push_back(C);
+  }
+
+  // Emit the finished record.
+  Stream.EmitRecord(Code, Vals, AbbrevToUse);
+}
+
+static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
+  switch (Kind) {
+  case Attribute::Alignment:
+    return bitc::ATTR_KIND_ALIGNMENT;
+  case Attribute::AllocAlign:
+    return bitc::ATTR_KIND_ALLOC_ALIGN;
+  case Attribute::AllocSize:
+    return bitc::ATTR_KIND_ALLOC_SIZE;
+  case Attribute::AlwaysInline:
+    return bitc::ATTR_KIND_ALWAYS_INLINE;
+  case Attribute::Builtin:
+    return bitc::ATTR_KIND_BUILTIN;
+  case Attribute::ByVal:
+    return bitc::ATTR_KIND_BY_VAL;
+  case Attribute::Convergent:
+    return bitc::ATTR_KIND_CONVERGENT;
+  case Attribute::InAlloca:
+    return bitc::ATTR_KIND_IN_ALLOCA;
+  case Attribute::Cold:
+    return bitc::ATTR_KIND_COLD;
+  case Attribute::DisableSanitizerInstrumentation:
+    return bitc::ATTR_KIND_DISABLE_SANITIZER_INSTRUMENTATION;
+  case Attribute::FnRetThunkExtern:
+    return bitc::ATTR_KIND_FNRETTHUNK_EXTERN;
+  case Attribute::Hot:
+    return bitc::ATTR_KIND_HOT;
+  case Attribute::ElementType:
+    return bitc::ATTR_KIND_ELEMENTTYPE;
+  case Attribute::InlineHint:
+    return bitc::ATTR_KIND_INLINE_HINT;
+  case Attribute::InReg:
+    return bitc::ATTR_KIND_IN_REG;
+  case Attribute::JumpTable:
+    return bitc::ATTR_KIND_JUMP_TABLE;
+  case Attribute::MinSize:
+    return bitc::ATTR_KIND_MIN_SIZE;
+  case Attribute::AllocatedPointer:
+    return bitc::ATTR_KIND_ALLOCATED_POINTER;
+  case Attribute::AllocKind:
+    return bitc::ATTR_KIND_ALLOC_KIND;
+  case Attribute::Memory:
+    return bitc::ATTR_KIND_MEMORY;
+  case Attribute::Naked:
+    return bitc::ATTR_KIND_NAKED;
+  case Attribute::Nest:
+    return bitc::ATTR_KIND_NEST;
+  case Attribute::NoAlias:
+    return bitc::ATTR_KIND_NO_ALIAS;
+  case Attribute::NoBuiltin:
+    return bitc::ATTR_KIND_NO_BUILTIN;
+  case Attribute::NoCallback:
+    return bitc::ATTR_KIND_NO_CALLBACK;
+  case Attribute::NoCapture:
+    return bitc::ATTR_KIND_NO_CAPTURE;
+  case Attribute::NoDuplicate:
+    return bitc::ATTR_KIND_NO_DUPLICATE;
+  case Attribute::NoFree:
+    return bitc::ATTR_KIND_NOFREE;
+  case Attribute::NoImplicitFloat:
+    return bitc::ATTR_KIND_NO_IMPLICIT_FLOAT;
+  case Attribute::NoInline:
+    return bitc::ATTR_KIND_NO_INLINE;
+  case Attribute::NoRecurse:
+    return bitc::ATTR_KIND_NO_RECURSE;
+  case Attribute::NoMerge:
+    return bitc::ATTR_KIND_NO_MERGE;
+  case Attribute::NonLazyBind:
+    return bitc::ATTR_KIND_NON_LAZY_BIND;
+  case Attribute::NonNull:
+    return bitc::ATTR_KIND_NON_NULL;
+  case Attribute::Dereferenceable:
+    return bitc::ATTR_KIND_DEREFERENCEABLE;
+  case Attribute::DereferenceableOrNull:
+    return bitc::ATTR_KIND_DEREFERENCEABLE_OR_NULL;
+  case Attribute::NoRedZone:
+    return bitc::ATTR_KIND_NO_RED_ZONE;
+  case Attribute::NoReturn:
+    return bitc::ATTR_KIND_NO_RETURN;
+  case Attribute::NoSync:
+    return bitc::ATTR_KIND_NOSYNC;
+  case Attribute::NoCfCheck:
+    return bitc::ATTR_KIND_NOCF_CHECK;
+  case Attribute::NoProfile:
+    return bitc::ATTR_KIND_NO_PROFILE;
+  case Attribute::SkipProfile:
+    return bitc::ATTR_KIND_SKIP_PROFILE;
+  case Attribute::NoUnwind:
+    return bitc::ATTR_KIND_NO_UNWIND;
+  case Attribute::NoSanitizeBounds:
+    return bitc::ATTR_KIND_NO_SANITIZE_BOUNDS;
+  case Attribute::NoSanitizeCoverage:
+    return bitc::ATTR_KIND_NO_SANITIZE_COVERAGE;
+  case Attribute::NullPointerIsValid:
+    return bitc::ATTR_KIND_NULL_POINTER_IS_VALID;
+  case Attribute::OptForFuzzing:
+    return bitc::ATTR_KIND_OPT_FOR_FUZZING;
+  case Attribute::OptimizeForSize:
+    return bitc::ATTR_KIND_OPTIMIZE_FOR_SIZE;
+  case Attribute::OptimizeNone:
+    return bitc::ATTR_KIND_OPTIMIZE_NONE;
+  case Attribute::ReadNone:
+    return bitc::ATTR_KIND_READ_NONE;
+  case Attribute::ReadOnly:
+    return bitc::ATTR_KIND_READ_ONLY;
+  case Attribute::Returned:
+    return bitc::ATTR_KIND_RETURNED;
+  case Attribute::ReturnsTwice:
+    return bitc::ATTR_KIND_RETURNS_TWICE;
+  case Attribute::SExt:
+    return bitc::ATTR_KIND_S_EXT;
+  case Attribute::Speculatable:
+    return bitc::ATTR_KIND_SPECULATABLE;
+  case Attribute::StackAlignment:
+    return bitc::ATTR_KIND_STACK_ALIGNMENT;
+  case Attribute::StackProtect:
+    return bitc::ATTR_KIND_STACK_PROTECT;
+  case Attribute::StackProtectReq:
+    return bitc::ATTR_KIND_STACK_PROTECT_REQ;
+  case Attribute::StackProtectStrong:
+    return bitc::ATTR_KIND_STACK_PROTECT_STRONG;
+  case Attribute::SafeStack:
+    return bitc::ATTR_KIND_SAFESTACK;
+  case Attribute::ShadowCallStack:
+    return bitc::ATTR_KIND_SHADOWCALLSTACK;
+  case Attribute::StrictFP:
+    return bitc::ATTR_KIND_STRICT_FP;
+  case Attribute::StructRet:
+    return bitc::ATTR_KIND_STRUCT_RET;
+  case Attribute::SanitizeAddress:
+    return bitc::ATTR_KIND_SANITIZE_ADDRESS;
+  case Attribute::SanitizeHWAddress:
+    return bitc::ATTR_KIND_SANITIZE_HWADDRESS;
+  case Attribute::SanitizeThread:
+    return bitc::ATTR_KIND_SANITIZE_THREAD;
+  case Attribute::SanitizeMemory:
+    return bitc::ATTR_KIND_SANITIZE_MEMORY;
+  case Attribute::SpeculativeLoadHardening:
+    return bitc::ATTR_KIND_SPECULATIVE_LOAD_HARDENING;
+  case Attribute::SwiftError:
+    return bitc::ATTR_KIND_SWIFT_ERROR;
+  case Attribute::SwiftSelf:
+    return bitc::ATTR_KIND_SWIFT_SELF;
+  case Attribute::SwiftAsync:
+    return bitc::ATTR_KIND_SWIFT_ASYNC;
+  case Attribute::UWTable:
+    return bitc::ATTR_KIND_UW_TABLE;
+  case Attribute::VScaleRange:
+    return bitc::ATTR_KIND_VSCALE_RANGE;
+  case Attribute::WillReturn:
+    return bitc::ATTR_KIND_WILLRETURN;
+  case Attribute::WriteOnly:
+    return bitc::ATTR_KIND_WRITEONLY;
+  case Attribute::ZExt:
+    return bitc::ATTR_KIND_Z_EXT;
+  case Attribute::ImmArg:
+    return bitc::ATTR_KIND_IMMARG;
+  case Attribute::SanitizeMemTag:
+    return bitc::ATTR_KIND_SANITIZE_MEMTAG;
+  case Attribute::Preallocated:
+    return bitc::ATTR_KIND_PREALLOCATED;
+  case Attribute::NoUndef:
+    return bitc::ATTR_KIND_NOUNDEF;
+  case Attribute::ByRef:
+    return bitc::ATTR_KIND_BYREF;
+  case Attribute::MustProgress:
+    return bitc::ATTR_KIND_MUSTPROGRESS;
+  case Attribute::PresplitCoroutine:
+    return bitc::ATTR_KIND_PRESPLIT_COROUTINE;
+  case Attribute::EndAttrKinds:
+    llvm_unreachable("Can not encode end-attribute kinds marker.");
+  case Attribute::None:
+    llvm_unreachable("Can not encode none-attribute.");
+  case Attribute::EmptyKey:
+  case Attribute::TombstoneKey:
+    llvm_unreachable("Trying to encode EmptyKey/TombstoneKey");
+  }
+
+  llvm_unreachable("Trying to encode unknown attribute");
+}
+
+void ModuleBitcodeWriter::writeAttributeGroupTable() {
+  const std::vector<ValueEnumerator::IndexAndAttrSet> &AttrGrps =
+      VE.getAttributeGroups();
+  if (AttrGrps.empty()) return;
+
+  Stream.EnterSubblock(bitc::PARAMATTR_GROUP_BLOCK_ID, 3);
+
+  SmallVector<uint64_t, 64> Record;
+  for (ValueEnumerator::IndexAndAttrSet Pair : AttrGrps) {
+    unsigned AttrListIndex = Pair.first;
+    AttributeSet AS = Pair.second;
+    Record.push_back(VE.getAttributeGroupID(Pair));
+    Record.push_back(AttrListIndex);
+
+    for (Attribute Attr : AS) {
+      if (Attr.isEnumAttribute()) {
+        Record.push_back(0);
+        Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
+      } else if (Attr.isIntAttribute()) {
+        Record.push_back(1);
+        Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
+        Record.push_back(Attr.getValueAsInt());
+      } else if (Attr.isStringAttribute()) {
+        StringRef Kind = Attr.getKindAsString();
+        StringRef Val = Attr.getValueAsString();
+
+        Record.push_back(Val.empty() ? 3 : 4);
+        Record.append(Kind.begin(), Kind.end());
+        Record.push_back(0);
+        if (!Val.empty()) {
+          Record.append(Val.begin(), Val.end());
+          Record.push_back(0);
+        }
+      } else {
+        assert(Attr.isTypeAttribute());
+        Type *Ty = Attr.getValueAsType();
+        Record.push_back(Ty ? 6 : 5);
+        Record.push_back(getAttrKindEncoding(Attr.getKindAsEnum()));
+        if (Ty)
+          Record.push_back(VE.getTypeID(Attr.getValueAsType()));
+      }
+    }
+
+    Stream.EmitRecord(bitc::PARAMATTR_GRP_CODE_ENTRY, Record);
+    Record.clear();
+  }
+
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::writeAttributeTable() {
+  const std::vector<AttributeList> &Attrs = VE.getAttributeLists();
+  if (Attrs.empty()) return;
+
+  Stream.EnterSubblock(bitc::PARAMATTR_BLOCK_ID, 3);
+
+  SmallVector<uint64_t, 64> Record;
+  for (const AttributeList &AL : Attrs) {
+    for (unsigned i : AL.indexes()) {
+      AttributeSet AS = AL.getAttributes(i);
+      if (AS.hasAttributes())
+        Record.push_back(VE.getAttributeGroupID({i, AS}));
+    }
+
+    Stream.EmitRecord(bitc::PARAMATTR_CODE_ENTRY, Record);
+    Record.clear();
+  }
+
+  Stream.ExitBlock();
+}
+
+/// WriteTypeTable - Write out the type table for a module.
+void ModuleBitcodeWriter::writeTypeTable() {
+  const ValueEnumerator::TypeList &TypeList = VE.getTypes();
+
+  Stream.EnterSubblock(bitc::TYPE_BLOCK_ID_NEW, 4 /*count from # abbrevs */);
+  SmallVector<uint64_t, 64> TypeVals;
+
+  uint64_t NumBits = VE.computeBitsRequiredForTypeIndicies();
+
+  // Abbrev for TYPE_CODE_POINTER.
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::TYPE_CODE_POINTER));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, NumBits));
+  Abbv->Add(BitCodeAbbrevOp(0));  // Addrspace = 0
+  unsigned PtrAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for TYPE_CODE_OPAQUE_POINTER.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::TYPE_CODE_OPAQUE_POINTER));
+  Abbv->Add(BitCodeAbbrevOp(0)); // Addrspace = 0
+  unsigned OpaquePtrAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for TYPE_CODE_FUNCTION.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::TYPE_CODE_FUNCTION));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));  // isvararg
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, NumBits));
+  unsigned FunctionAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for TYPE_CODE_STRUCT_ANON.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::TYPE_CODE_STRUCT_ANON));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));  // ispacked
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, NumBits));
+  unsigned StructAnonAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for TYPE_CODE_STRUCT_NAME.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::TYPE_CODE_STRUCT_NAME));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Char6));
+  unsigned StructNameAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for TYPE_CODE_STRUCT_NAMED.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::TYPE_CODE_STRUCT_NAMED));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));  // ispacked
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, NumBits));
+  unsigned StructNamedAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for TYPE_CODE_ARRAY.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::TYPE_CODE_ARRAY));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // size
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, NumBits));
+  unsigned ArrayAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Emit an entry count so the reader can reserve space.
+  TypeVals.push_back(TypeList.size());
+  Stream.EmitRecord(bitc::TYPE_CODE_NUMENTRY, TypeVals);
+  TypeVals.clear();
+
+  // Loop over all of the types, emitting each in turn.
+  for (Type *T : TypeList) {
+    int AbbrevToUse = 0;
+    unsigned Code = 0;
+
+    switch (T->getTypeID()) {
+    case Type::VoidTyID:      Code = bitc::TYPE_CODE_VOID;      break;
+    case Type::HalfTyID:      Code = bitc::TYPE_CODE_HALF;      break;
+    case Type::BFloatTyID:    Code = bitc::TYPE_CODE_BFLOAT;    break;
+    case Type::FloatTyID:     Code = bitc::TYPE_CODE_FLOAT;     break;
+    case Type::DoubleTyID:    Code = bitc::TYPE_CODE_DOUBLE;    break;
+    case Type::X86_FP80TyID:  Code = bitc::TYPE_CODE_X86_FP80;  break;
+    case Type::FP128TyID:     Code = bitc::TYPE_CODE_FP128;     break;
+    case Type::PPC_FP128TyID: Code = bitc::TYPE_CODE_PPC_FP128; break;
+    case Type::LabelTyID:     Code = bitc::TYPE_CODE_LABEL;     break;
+    case Type::MetadataTyID:  Code = bitc::TYPE_CODE_METADATA;  break;
+    case Type::X86_MMXTyID:   Code = bitc::TYPE_CODE_X86_MMX;   break;
+    case Type::X86_AMXTyID:   Code = bitc::TYPE_CODE_X86_AMX;   break;
+    case Type::TokenTyID:     Code = bitc::TYPE_CODE_TOKEN;     break;
+    case Type::IntegerTyID:
+      // INTEGER: [width]
+      Code = bitc::TYPE_CODE_INTEGER;
+      TypeVals.push_back(cast<IntegerType>(T)->getBitWidth());
+      break;
+    case Type::PointerTyID: {
+      PointerType *PTy = cast<PointerType>(T);
+      unsigned AddressSpace = PTy->getAddressSpace();
+      if (PTy->isOpaque()) {
+        // OPAQUE_POINTER: [address space]
+        Code = bitc::TYPE_CODE_OPAQUE_POINTER;
+        TypeVals.push_back(AddressSpace);
+        if (AddressSpace == 0)
+          AbbrevToUse = OpaquePtrAbbrev;
+      } else {
+        // POINTER: [pointee type, address space]
+        Code = bitc::TYPE_CODE_POINTER;
+        TypeVals.push_back(VE.getTypeID(PTy->getNonOpaquePointerElementType()));
+        TypeVals.push_back(AddressSpace);
+        if (AddressSpace == 0)
+          AbbrevToUse = PtrAbbrev;
+      }
+      break;
+    }
+    case Type::FunctionTyID: {
+      FunctionType *FT = cast<FunctionType>(T);
+      // FUNCTION: [isvararg, retty, paramty x N]
+      Code = bitc::TYPE_CODE_FUNCTION;
+      TypeVals.push_back(FT->isVarArg());
+      TypeVals.push_back(VE.getTypeID(FT->getReturnType()));
+      for (unsigned i = 0, e = FT->getNumParams(); i != e; ++i)
+        TypeVals.push_back(VE.getTypeID(FT->getParamType(i)));
+      AbbrevToUse = FunctionAbbrev;
+      break;
+    }
+    case Type::StructTyID: {
+      StructType *ST = cast<StructType>(T);
+      // STRUCT: [ispacked, eltty x N]
+      TypeVals.push_back(ST->isPacked());
+      // Output all of the element types.
+      for (Type *ET : ST->elements())
+        TypeVals.push_back(VE.getTypeID(ET));
+
+      if (ST->isLiteral()) {
+        Code = bitc::TYPE_CODE_STRUCT_ANON;
+        AbbrevToUse = StructAnonAbbrev;
+      } else {
+        if (ST->isOpaque()) {
+          Code = bitc::TYPE_CODE_OPAQUE;
+        } else {
+          Code = bitc::TYPE_CODE_STRUCT_NAMED;
+          AbbrevToUse = StructNamedAbbrev;
+        }
+
+        // Emit the name if it is present.
+        if (!ST->getName().empty())
+          writeStringRecord(Stream, bitc::TYPE_CODE_STRUCT_NAME, ST->getName(),
+                            StructNameAbbrev);
+      }
+      break;
+    }
+    case Type::ArrayTyID: {
+      ArrayType *AT = cast<ArrayType>(T);
+      // ARRAY: [numelts, eltty]
+      Code = bitc::TYPE_CODE_ARRAY;
+      TypeVals.push_back(AT->getNumElements());
+      TypeVals.push_back(VE.getTypeID(AT->getElementType()));
+      AbbrevToUse = ArrayAbbrev;
+      break;
+    }
+    case Type::FixedVectorTyID:
+    case Type::ScalableVectorTyID: {
+      VectorType *VT = cast<VectorType>(T);
+      // VECTOR [numelts, eltty] or
+      //        [numelts, eltty, scalable]
+      Code = bitc::TYPE_CODE_VECTOR;
+      TypeVals.push_back(VT->getElementCount().getKnownMinValue());
+      TypeVals.push_back(VE.getTypeID(VT->getElementType()));
+      if (isa<ScalableVectorType>(VT))
+        TypeVals.push_back(true);
+      break;
+    }
+    case Type::TargetExtTyID: {
+      TargetExtType *TET = cast<TargetExtType>(T);
+      Code = bitc::TYPE_CODE_TARGET_TYPE;
+      writeStringRecord(Stream, bitc::TYPE_CODE_STRUCT_NAME, TET->getName(),
+                        StructNameAbbrev);
+      TypeVals.push_back(TET->getNumTypeParameters());
+      for (Type *InnerTy : TET->type_params())
+        TypeVals.push_back(VE.getTypeID(InnerTy));
+      for (unsigned IntParam : TET->int_params())
+        TypeVals.push_back(IntParam);
+      break;
+    }
+    case Type::TypedPointerTyID:
+      llvm_unreachable("Typed pointers cannot be added to IR modules");
+    }
+
+    // Emit the finished record.
+    Stream.EmitRecord(Code, TypeVals, AbbrevToUse);
+    TypeVals.clear();
+  }
+
+  Stream.ExitBlock();
+}
+
+static unsigned getEncodedLinkage(const GlobalValue::LinkageTypes Linkage) {
+  switch (Linkage) {
+  case GlobalValue::ExternalLinkage:
+    return 0;
+  case GlobalValue::WeakAnyLinkage:
+    return 16;
+  case GlobalValue::AppendingLinkage:
+    return 2;
+  case GlobalValue::InternalLinkage:
+    return 3;
+  case GlobalValue::LinkOnceAnyLinkage:
+    return 18;
+  case GlobalValue::ExternalWeakLinkage:
+    return 7;
+  case GlobalValue::CommonLinkage:
+    return 8;
+  case GlobalValue::PrivateLinkage:
+    return 9;
+  case GlobalValue::WeakODRLinkage:
+    return 17;
+  case GlobalValue::LinkOnceODRLinkage:
+    return 19;
+  case GlobalValue::AvailableExternallyLinkage:
+    return 12;
+  }
+  llvm_unreachable("Invalid linkage");
+}
+
+static unsigned getEncodedLinkage(const GlobalValue &GV) {
+  return getEncodedLinkage(GV.getLinkage());
+}
+
+static uint64_t getEncodedFFlags(FunctionSummary::FFlags Flags) {
+  uint64_t RawFlags = 0;
+  RawFlags |= Flags.ReadNone;
+  RawFlags |= (Flags.ReadOnly << 1);
+  RawFlags |= (Flags.NoRecurse << 2);
+  RawFlags |= (Flags.ReturnDoesNotAlias << 3);
+  RawFlags |= (Flags.NoInline << 4);
+  RawFlags |= (Flags.AlwaysInline << 5);
+  RawFlags |= (Flags.NoUnwind << 6);
+  RawFlags |= (Flags.MayThrow << 7);
+  RawFlags |= (Flags.HasUnknownCall << 8);
+  RawFlags |= (Flags.MustBeUnreachable << 9);
+  return RawFlags;
+}
+
+// Decode the flags for GlobalValue in the summary. See getDecodedGVSummaryFlags
+// in BitcodeReader.cpp.
+static uint64_t getEncodedGVSummaryFlags(GlobalValueSummary::GVFlags Flags) {
+  uint64_t RawFlags = 0;
+
+  RawFlags |= Flags.NotEligibleToImport; // bool
+  RawFlags |= (Flags.Live << 1);
+  RawFlags |= (Flags.DSOLocal << 2);
+  RawFlags |= (Flags.CanAutoHide << 3);
+
+  // Linkage don't need to be remapped at that time for the summary. Any future
+  // change to the getEncodedLinkage() function will need to be taken into
+  // account here as well.
+  RawFlags = (RawFlags << 4) | Flags.Linkage; // 4 bits
+
+  RawFlags |= (Flags.Visibility << 8); // 2 bits
+
+  return RawFlags;
+}
+
+static uint64_t getEncodedGVarFlags(GlobalVarSummary::GVarFlags Flags) {
+  uint64_t RawFlags = Flags.MaybeReadOnly | (Flags.MaybeWriteOnly << 1) |
+                      (Flags.Constant << 2) | Flags.VCallVisibility << 3;
+  return RawFlags;
+}
+
+static unsigned getEncodedVisibility(const GlobalValue &GV) {
+  switch (GV.getVisibility()) {
+  case GlobalValue::DefaultVisibility:   return 0;
+  case GlobalValue::HiddenVisibility:    return 1;
+  case GlobalValue::ProtectedVisibility: return 2;
+  }
+  llvm_unreachable("Invalid visibility");
+}
+
+static unsigned getEncodedDLLStorageClass(const GlobalValue &GV) {
+  switch (GV.getDLLStorageClass()) {
+  case GlobalValue::DefaultStorageClass:   return 0;
+  case GlobalValue::DLLImportStorageClass: return 1;
+  case GlobalValue::DLLExportStorageClass: return 2;
+  }
+  llvm_unreachable("Invalid DLL storage class");
+}
+
+static unsigned getEncodedThreadLocalMode(const GlobalValue &GV) {
+  switch (GV.getThreadLocalMode()) {
+    case GlobalVariable::NotThreadLocal:         return 0;
+    case GlobalVariable::GeneralDynamicTLSModel: return 1;
+    case GlobalVariable::LocalDynamicTLSModel:   return 2;
+    case GlobalVariable::InitialExecTLSModel:    return 3;
+    case GlobalVariable::LocalExecTLSModel:      return 4;
+  }
+  llvm_unreachable("Invalid TLS model");
+}
+
+static unsigned getEncodedComdatSelectionKind(const Comdat &C) {
+  switch (C.getSelectionKind()) {
+  case Comdat::Any:
+    return bitc::COMDAT_SELECTION_KIND_ANY;
+  case Comdat::ExactMatch:
+    return bitc::COMDAT_SELECTION_KIND_EXACT_MATCH;
+  case Comdat::Largest:
+    return bitc::COMDAT_SELECTION_KIND_LARGEST;
+  case Comdat::NoDeduplicate:
+    return bitc::COMDAT_SELECTION_KIND_NO_DUPLICATES;
+  case Comdat::SameSize:
+    return bitc::COMDAT_SELECTION_KIND_SAME_SIZE;
+  }
+  llvm_unreachable("Invalid selection kind");
+}
+
+static unsigned getEncodedUnnamedAddr(const GlobalValue &GV) {
+  switch (GV.getUnnamedAddr()) {
+  case GlobalValue::UnnamedAddr::None:   return 0;
+  case GlobalValue::UnnamedAddr::Local:  return 2;
+  case GlobalValue::UnnamedAddr::Global: return 1;
+  }
+  llvm_unreachable("Invalid unnamed_addr");
+}
+
+size_t ModuleBitcodeWriter::addToStrtab(StringRef Str) {
+  if (GenerateHash)
+    Hasher.update(Str);
+  return StrtabBuilder.add(Str);
+}
+
+void ModuleBitcodeWriter::writeComdats() {
+  SmallVector<unsigned, 64> Vals;
+  for (const Comdat *C : VE.getComdats()) {
+    // COMDAT: [strtab offset, strtab size, selection_kind]
+    Vals.push_back(addToStrtab(C->getName()));
+    Vals.push_back(C->getName().size());
+    Vals.push_back(getEncodedComdatSelectionKind(*C));
+    Stream.EmitRecord(bitc::MODULE_CODE_COMDAT, Vals, /*AbbrevToUse=*/0);
+    Vals.clear();
+  }
+}
+
+/// Write a record that will eventually hold the word offset of the
+/// module-level VST. For now the offset is 0, which will be backpatched
+/// after the real VST is written. Saves the bit offset to backpatch.
+void ModuleBitcodeWriter::writeValueSymbolTableForwardDecl() {
+  // Write a placeholder value in for the offset of the real VST,
+  // which is written after the function blocks so that it can include
+  // the offset of each function. The placeholder offset will be
+  // updated when the real VST is written.
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::MODULE_CODE_VSTOFFSET));
+  // Blocks are 32-bit aligned, so we can use a 32-bit word offset to
+  // hold the real VST offset. Must use fixed instead of VBR as we don't
+  // know how many VBR chunks to reserve ahead of time.
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+  unsigned VSTOffsetAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Emit the placeholder
+  uint64_t Vals[] = {bitc::MODULE_CODE_VSTOFFSET, 0};
+  Stream.EmitRecordWithAbbrev(VSTOffsetAbbrev, Vals);
+
+  // Compute and save the bit offset to the placeholder, which will be
+  // patched when the real VST is written. We can simply subtract the 32-bit
+  // fixed size from the current bit number to get the location to backpatch.
+  VSTOffsetPlaceholder = Stream.GetCurrentBitNo() - 32;
+}
+
+enum StringEncoding { SE_Char6, SE_Fixed7, SE_Fixed8 };
+
+/// Determine the encoding to use for the given string name and length.
+static StringEncoding getStringEncoding(StringRef Str) {
+  bool isChar6 = true;
+  for (char C : Str) {
+    if (isChar6)
+      isChar6 = BitCodeAbbrevOp::isChar6(C);
+    if ((unsigned char)C & 128)
+      // don't bother scanning the rest.
+      return SE_Fixed8;
+  }
+  if (isChar6)
+    return SE_Char6;
+  return SE_Fixed7;
+}
+
+static_assert(sizeof(GlobalValue::SanitizerMetadata) <= sizeof(unsigned),
+              "Sanitizer Metadata is too large for naive serialization.");
+static unsigned
+serializeSanitizerMetadata(const GlobalValue::SanitizerMetadata &Meta) {
+  return Meta.NoAddress | (Meta.NoHWAddress << 1) |
+         (Meta.Memtag << 2) | (Meta.IsDynInit << 3);
+}
+
+/// Emit top-level description of module, including target triple, inline asm,
+/// descriptors for global variables, and function prototype info.
+/// Returns the bit offset to backpatch with the location of the real VST.
+void ModuleBitcodeWriter::writeModuleInfo() {
+  // Emit various pieces of data attached to a module.
+  if (!M.getTargetTriple().empty())
+    writeStringRecord(Stream, bitc::MODULE_CODE_TRIPLE, M.getTargetTriple(),
+                      0 /*TODO*/);
+  const std::string &DL = M.getDataLayoutStr();
+  if (!DL.empty())
+    writeStringRecord(Stream, bitc::MODULE_CODE_DATALAYOUT, DL, 0 /*TODO*/);
+  if (!M.getModuleInlineAsm().empty())
+    writeStringRecord(Stream, bitc::MODULE_CODE_ASM, M.getModuleInlineAsm(),
+                      0 /*TODO*/);
+
+  // Emit information about sections and GC, computing how many there are. Also
+  // compute the maximum alignment value.
+  std::map<std::string, unsigned> SectionMap;
+  std::map<std::string, unsigned> GCMap;
+  MaybeAlign MaxAlignment;
+  unsigned MaxGlobalType = 0;
+  const auto UpdateMaxAlignment = [&MaxAlignment](const MaybeAlign A) {
+    if (A)
+      MaxAlignment = !MaxAlignment ? *A : std::max(*MaxAlignment, *A);
+  };
+  for (const GlobalVariable &GV : M.globals()) {
+    UpdateMaxAlignment(GV.getAlign());
+    MaxGlobalType = std::max(MaxGlobalType, VE.getTypeID(GV.getValueType()));
+    if (GV.hasSection()) {
+      // Give section names unique ID's.
+      unsigned &Entry = SectionMap[std::string(GV.getSection())];
+      if (!Entry) {
+        writeStringRecord(Stream, bitc::MODULE_CODE_SECTIONNAME, GV.getSection(),
+                          0 /*TODO*/);
+        Entry = SectionMap.size();
+      }
+    }
+  }
+  for (const Function &F : M) {
+    UpdateMaxAlignment(F.getAlign());
+    if (F.hasSection()) {
+      // Give section names unique ID's.
+      unsigned &Entry = SectionMap[std::string(F.getSection())];
+      if (!Entry) {
+        writeStringRecord(Stream, bitc::MODULE_CODE_SECTIONNAME, F.getSection(),
+                          0 /*TODO*/);
+        Entry = SectionMap.size();
+      }
+    }
+    if (F.hasGC()) {
+      // Same for GC names.
+      unsigned &Entry = GCMap[F.getGC()];
+      if (!Entry) {
+        writeStringRecord(Stream, bitc::MODULE_CODE_GCNAME, F.getGC(),
+                          0 /*TODO*/);
+        Entry = GCMap.size();
+      }
+    }
+  }
+
+  // Emit abbrev for globals, now that we know # sections and max alignment.
+  unsigned SimpleGVarAbbrev = 0;
+  if (!M.global_empty()) {
+    // Add an abbrev for common globals with no visibility or thread localness.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::MODULE_CODE_GLOBALVAR));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed,
+                              Log2_32_Ceil(MaxGlobalType+1)));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // AddrSpace << 2
+                                                           //| explicitType << 1
+                                                           //| constant
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // Initializer.
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 5)); // Linkage.
+    if (!MaxAlignment)                                     // Alignment.
+      Abbv->Add(BitCodeAbbrevOp(0));
+    else {
+      unsigned MaxEncAlignment = getEncodedAlign(MaxAlignment);
+      Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed,
+                               Log2_32_Ceil(MaxEncAlignment+1)));
+    }
+    if (SectionMap.empty())                                    // Section.
+      Abbv->Add(BitCodeAbbrevOp(0));
+    else
+      Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed,
+                               Log2_32_Ceil(SectionMap.size()+1)));
+    // Don't bother emitting vis + thread local.
+    SimpleGVarAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+  }
+
+  SmallVector<unsigned, 64> Vals;
+  // Emit the module's source file name.
+  {
+    StringEncoding Bits = getStringEncoding(M.getSourceFileName());
+    BitCodeAbbrevOp AbbrevOpToUse = BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8);
+    if (Bits == SE_Char6)
+      AbbrevOpToUse = BitCodeAbbrevOp(BitCodeAbbrevOp::Char6);
+    else if (Bits == SE_Fixed7)
+      AbbrevOpToUse = BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 7);
+
+    // MODULE_CODE_SOURCE_FILENAME: [namechar x N]
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::MODULE_CODE_SOURCE_FILENAME));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(AbbrevOpToUse);
+    unsigned FilenameAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+    for (const auto P : M.getSourceFileName())
+      Vals.push_back((unsigned char)P);
+
+    // Emit the finished record.
+    Stream.EmitRecord(bitc::MODULE_CODE_SOURCE_FILENAME, Vals, FilenameAbbrev);
+    Vals.clear();
+  }
+
+  // Emit the global variable information.
+  for (const GlobalVariable &GV : M.globals()) {
+    unsigned AbbrevToUse = 0;
+
+    // GLOBALVAR: [strtab offset, strtab size, type, isconst, initid,
+    //             linkage, alignment, section, visibility, threadlocal,
+    //             unnamed_addr, externally_initialized, dllstorageclass,
+    //             comdat, attributes, DSO_Local, GlobalSanitizer]
+    Vals.push_back(addToStrtab(GV.getName()));
+    Vals.push_back(GV.getName().size());
+    Vals.push_back(VE.getTypeID(GV.getValueType()));
+    Vals.push_back(GV.getType()->getAddressSpace() << 2 | 2 | GV.isConstant());
+    Vals.push_back(GV.isDeclaration() ? 0 :
+                   (VE.getValueID(GV.getInitializer()) + 1));
+    Vals.push_back(getEncodedLinkage(GV));
+    Vals.push_back(getEncodedAlign(GV.getAlign()));
+    Vals.push_back(GV.hasSection() ? SectionMap[std::string(GV.getSection())]
+                                   : 0);
+    if (GV.isThreadLocal() ||
+        GV.getVisibility() != GlobalValue::DefaultVisibility ||
+        GV.getUnnamedAddr() != GlobalValue::UnnamedAddr::None ||
+        GV.isExternallyInitialized() ||
+        GV.getDLLStorageClass() != GlobalValue::DefaultStorageClass ||
+        GV.hasComdat() || GV.hasAttributes() || GV.isDSOLocal() ||
+        GV.hasPartition() || GV.hasSanitizerMetadata()) {
+      Vals.push_back(getEncodedVisibility(GV));
+      Vals.push_back(getEncodedThreadLocalMode(GV));
+      Vals.push_back(getEncodedUnnamedAddr(GV));
+      Vals.push_back(GV.isExternallyInitialized());
+      Vals.push_back(getEncodedDLLStorageClass(GV));
+      Vals.push_back(GV.hasComdat() ? VE.getComdatID(GV.getComdat()) : 0);
+
+      auto AL = GV.getAttributesAsList(AttributeList::FunctionIndex);
+      Vals.push_back(VE.getAttributeListID(AL));
+
+      Vals.push_back(GV.isDSOLocal());
+      Vals.push_back(addToStrtab(GV.getPartition()));
+      Vals.push_back(GV.getPartition().size());
+
+      Vals.push_back((GV.hasSanitizerMetadata() ? serializeSanitizerMetadata(
+                                                      GV.getSanitizerMetadata())
+                                                : 0));
+    } else {
+      AbbrevToUse = SimpleGVarAbbrev;
+    }
+
+    Stream.EmitRecord(bitc::MODULE_CODE_GLOBALVAR, Vals, AbbrevToUse);
+    Vals.clear();
+  }
+
+  // Emit the function proto information.
+  for (const Function &F : M) {
+    // FUNCTION:  [strtab offset, strtab size, type, callingconv, isproto,
+    //             linkage, paramattrs, alignment, section, visibility, gc,
+    //             unnamed_addr, prologuedata, dllstorageclass, comdat,
+    //             prefixdata, personalityfn, DSO_Local, addrspace]
+    Vals.push_back(addToStrtab(F.getName()));
+    Vals.push_back(F.getName().size());
+    Vals.push_back(VE.getTypeID(F.getFunctionType()));
+    Vals.push_back(F.getCallingConv());
+    Vals.push_back(F.isDeclaration());
+    Vals.push_back(getEncodedLinkage(F));
+    Vals.push_back(VE.getAttributeListID(F.getAttributes()));
+    Vals.push_back(getEncodedAlign(F.getAlign()));
+    Vals.push_back(F.hasSection() ? SectionMap[std::string(F.getSection())]
+                                  : 0);
+    Vals.push_back(getEncodedVisibility(F));
+    Vals.push_back(F.hasGC() ? GCMap[F.getGC()] : 0);
+    Vals.push_back(getEncodedUnnamedAddr(F));
+    Vals.push_back(F.hasPrologueData() ? (VE.getValueID(F.getPrologueData()) + 1)
+                                       : 0);
+    Vals.push_back(getEncodedDLLStorageClass(F));
+    Vals.push_back(F.hasComdat() ? VE.getComdatID(F.getComdat()) : 0);
+    Vals.push_back(F.hasPrefixData() ? (VE.getValueID(F.getPrefixData()) + 1)
+                                     : 0);
+    Vals.push_back(
+        F.hasPersonalityFn() ? (VE.getValueID(F.getPersonalityFn()) + 1) : 0);
+
+    Vals.push_back(F.isDSOLocal());
+    Vals.push_back(F.getAddressSpace());
+    Vals.push_back(addToStrtab(F.getPartition()));
+    Vals.push_back(F.getPartition().size());
+
+    unsigned AbbrevToUse = 0;
+    Stream.EmitRecord(bitc::MODULE_CODE_FUNCTION, Vals, AbbrevToUse);
+    Vals.clear();
+  }
+
+  // Emit the alias information.
+  for (const GlobalAlias &A : M.aliases()) {
+    // ALIAS: [strtab offset, strtab size, alias type, aliasee val#, linkage,
+    //         visibility, dllstorageclass, threadlocal, unnamed_addr,
+    //         DSO_Local]
+    Vals.push_back(addToStrtab(A.getName()));
+    Vals.push_back(A.getName().size());
+    Vals.push_back(VE.getTypeID(A.getValueType()));
+    Vals.push_back(A.getType()->getAddressSpace());
+    Vals.push_back(VE.getValueID(A.getAliasee()));
+    Vals.push_back(getEncodedLinkage(A));
+    Vals.push_back(getEncodedVisibility(A));
+    Vals.push_back(getEncodedDLLStorageClass(A));
+    Vals.push_back(getEncodedThreadLocalMode(A));
+    Vals.push_back(getEncodedUnnamedAddr(A));
+    Vals.push_back(A.isDSOLocal());
+    Vals.push_back(addToStrtab(A.getPartition()));
+    Vals.push_back(A.getPartition().size());
+
+    unsigned AbbrevToUse = 0;
+    Stream.EmitRecord(bitc::MODULE_CODE_ALIAS, Vals, AbbrevToUse);
+    Vals.clear();
+  }
+
+  // Emit the ifunc information.
+  for (const GlobalIFunc &I : M.ifuncs()) {
+    // IFUNC: [strtab offset, strtab size, ifunc type, address space, resolver
+    //         val#, linkage, visibility, DSO_Local]
+    Vals.push_back(addToStrtab(I.getName()));
+    Vals.push_back(I.getName().size());
+    Vals.push_back(VE.getTypeID(I.getValueType()));
+    Vals.push_back(I.getType()->getAddressSpace());
+    Vals.push_back(VE.getValueID(I.getResolver()));
+    Vals.push_back(getEncodedLinkage(I));
+    Vals.push_back(getEncodedVisibility(I));
+    Vals.push_back(I.isDSOLocal());
+    Vals.push_back(addToStrtab(I.getPartition()));
+    Vals.push_back(I.getPartition().size());
+    Stream.EmitRecord(bitc::MODULE_CODE_IFUNC, Vals);
+    Vals.clear();
+  }
+
+  writeValueSymbolTableForwardDecl();
+}
+
+static uint64_t getOptimizationFlags(const Value *V) {
+  uint64_t Flags = 0;
+
+  if (const auto *OBO = dyn_cast<OverflowingBinaryOperator>(V)) {
+    if (OBO->hasNoSignedWrap())
+      Flags |= 1 << bitc::OBO_NO_SIGNED_WRAP;
+    if (OBO->hasNoUnsignedWrap())
+      Flags |= 1 << bitc::OBO_NO_UNSIGNED_WRAP;
+  } else if (const auto *PEO = dyn_cast<PossiblyExactOperator>(V)) {
+    if (PEO->isExact())
+      Flags |= 1 << bitc::PEO_EXACT;
+  } else if (const auto *FPMO = dyn_cast<FPMathOperator>(V)) {
+    if (FPMO->hasAllowReassoc())
+      Flags |= bitc::AllowReassoc;
+    if (FPMO->hasNoNaNs())
+      Flags |= bitc::NoNaNs;
+    if (FPMO->hasNoInfs())
+      Flags |= bitc::NoInfs;
+    if (FPMO->hasNoSignedZeros())
+      Flags |= bitc::NoSignedZeros;
+    if (FPMO->hasAllowReciprocal())
+      Flags |= bitc::AllowReciprocal;
+    if (FPMO->hasAllowContract())
+      Flags |= bitc::AllowContract;
+    if (FPMO->hasApproxFunc())
+      Flags |= bitc::ApproxFunc;
+  }
+
+  return Flags;
+}
+
+void ModuleBitcodeWriter::writeValueAsMetadata(
+    const ValueAsMetadata *MD, SmallVectorImpl<uint64_t> &Record) {
+  // Mimic an MDNode with a value as one operand.
+  Value *V = MD->getValue();
+  Record.push_back(VE.getTypeID(V->getType()));
+  Record.push_back(VE.getValueID(V));
+  Stream.EmitRecord(bitc::METADATA_VALUE, Record, 0);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeMDTuple(const MDTuple *N,
+                                       SmallVectorImpl<uint64_t> &Record,
+                                       unsigned Abbrev) {
+  for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+    Metadata *MD = N->getOperand(i);
+    assert(!(MD && isa<LocalAsMetadata>(MD)) &&
+           "Unexpected function-local metadata");
+    Record.push_back(VE.getMetadataOrNullID(MD));
+  }
+  Stream.EmitRecord(N->isDistinct() ? bitc::METADATA_DISTINCT_NODE
+                                    : bitc::METADATA_NODE,
+                    Record, Abbrev);
+  Record.clear();
+}
+
+unsigned ModuleBitcodeWriter::createDILocationAbbrev() {
+  // Assume the column is usually under 128, and always output the inlined-at
+  // location (it's never more expensive than building an array size 1).
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::METADATA_LOCATION));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));
+  return Stream.EmitAbbrev(std::move(Abbv));
+}
+
+void ModuleBitcodeWriter::writeDILocation(const DILocation *N,
+                                          SmallVectorImpl<uint64_t> &Record,
+                                          unsigned &Abbrev) {
+  if (!Abbrev)
+    Abbrev = createDILocationAbbrev();
+
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getLine());
+  Record.push_back(N->getColumn());
+  Record.push_back(VE.getMetadataID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getInlinedAt()));
+  Record.push_back(N->isImplicitCode());
+
+  Stream.EmitRecord(bitc::METADATA_LOCATION, Record, Abbrev);
+  Record.clear();
+}
+
+unsigned ModuleBitcodeWriter::createGenericDINodeAbbrev() {
+  // Assume the column is usually under 128, and always output the inlined-at
+  // location (it's never more expensive than building an array size 1).
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::METADATA_GENERIC_DEBUG));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
+  return Stream.EmitAbbrev(std::move(Abbv));
+}
+
+void ModuleBitcodeWriter::writeGenericDINode(const GenericDINode *N,
+                                             SmallVectorImpl<uint64_t> &Record,
+                                             unsigned &Abbrev) {
+  if (!Abbrev)
+    Abbrev = createGenericDINodeAbbrev();
+
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getTag());
+  Record.push_back(0); // Per-tag version field; unused for now.
+
+  for (auto &I : N->operands())
+    Record.push_back(VE.getMetadataOrNullID(I));
+
+  Stream.EmitRecord(bitc::METADATA_GENERIC_DEBUG, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDISubrange(const DISubrange *N,
+                                          SmallVectorImpl<uint64_t> &Record,
+                                          unsigned Abbrev) {
+  const uint64_t Version = 2 << 1;
+  Record.push_back((uint64_t)N->isDistinct() | Version);
+  Record.push_back(VE.getMetadataOrNullID(N->getRawCountNode()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawLowerBound()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawUpperBound()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawStride()));
+
+  Stream.EmitRecord(bitc::METADATA_SUBRANGE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIGenericSubrange(
+    const DIGenericSubrange *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  Record.push_back((uint64_t)N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawCountNode()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawLowerBound()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawUpperBound()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawStride()));
+
+  Stream.EmitRecord(bitc::METADATA_GENERIC_SUBRANGE, Record, Abbrev);
+  Record.clear();
+}
+
+static void emitSignedInt64(SmallVectorImpl<uint64_t> &Vals, uint64_t V) {
+  if ((int64_t)V >= 0)
+    Vals.push_back(V << 1);
+  else
+    Vals.push_back((-V << 1) | 1);
+}
+
+static void emitWideAPInt(SmallVectorImpl<uint64_t> &Vals, const APInt &A) {
+  // We have an arbitrary precision integer value to write whose
+  // bit width is > 64. However, in canonical unsigned integer
+  // format it is likely that the high bits are going to be zero.
+  // So, we only write the number of active words.
+  unsigned NumWords = A.getActiveWords();
+  const uint64_t *RawData = A.getRawData();
+  for (unsigned i = 0; i < NumWords; i++)
+    emitSignedInt64(Vals, RawData[i]);
+}
+
+void ModuleBitcodeWriter::writeDIEnumerator(const DIEnumerator *N,
+                                            SmallVectorImpl<uint64_t> &Record,
+                                            unsigned Abbrev) {
+  const uint64_t IsBigInt = 1 << 2;
+  Record.push_back(IsBigInt | (N->isUnsigned() << 1) | N->isDistinct());
+  Record.push_back(N->getValue().getBitWidth());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  emitWideAPInt(Record, N->getValue());
+
+  Stream.EmitRecord(bitc::METADATA_ENUMERATOR, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIBasicType(const DIBasicType *N,
+                                           SmallVectorImpl<uint64_t> &Record,
+                                           unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getTag());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(N->getSizeInBits());
+  Record.push_back(N->getAlignInBits());
+  Record.push_back(N->getEncoding());
+  Record.push_back(N->getFlags());
+
+  Stream.EmitRecord(bitc::METADATA_BASIC_TYPE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIStringType(const DIStringType *N,
+                                            SmallVectorImpl<uint64_t> &Record,
+                                            unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getTag());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getStringLength()));
+  Record.push_back(VE.getMetadataOrNullID(N->getStringLengthExp()));
+  Record.push_back(VE.getMetadataOrNullID(N->getStringLocationExp()));
+  Record.push_back(N->getSizeInBits());
+  Record.push_back(N->getAlignInBits());
+  Record.push_back(N->getEncoding());
+
+  Stream.EmitRecord(bitc::METADATA_STRING_TYPE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIDerivedType(const DIDerivedType *N,
+                                             SmallVectorImpl<uint64_t> &Record,
+                                             unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getTag());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getBaseType()));
+  Record.push_back(N->getSizeInBits());
+  Record.push_back(N->getAlignInBits());
+  Record.push_back(N->getOffsetInBits());
+  Record.push_back(N->getFlags());
+  Record.push_back(VE.getMetadataOrNullID(N->getExtraData()));
+
+  // DWARF address space is encoded as N->getDWARFAddressSpace() + 1. 0 means
+  // that there is no DWARF address space associated with DIDerivedType.
+  if (const auto &DWARFAddressSpace = N->getDWARFAddressSpace())
+    Record.push_back(*DWARFAddressSpace + 1);
+  else
+    Record.push_back(0);
+
+  Record.push_back(VE.getMetadataOrNullID(N->getAnnotations().get()));
+
+  Stream.EmitRecord(bitc::METADATA_DERIVED_TYPE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDICompositeType(
+    const DICompositeType *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  const unsigned IsNotUsedInOldTypeRef = 0x2;
+  Record.push_back(IsNotUsedInOldTypeRef | (unsigned)N->isDistinct());
+  Record.push_back(N->getTag());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getBaseType()));
+  Record.push_back(N->getSizeInBits());
+  Record.push_back(N->getAlignInBits());
+  Record.push_back(N->getOffsetInBits());
+  Record.push_back(N->getFlags());
+  Record.push_back(VE.getMetadataOrNullID(N->getElements().get()));
+  Record.push_back(N->getRuntimeLang());
+  Record.push_back(VE.getMetadataOrNullID(N->getVTableHolder()));
+  Record.push_back(VE.getMetadataOrNullID(N->getTemplateParams().get()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawIdentifier()));
+  Record.push_back(VE.getMetadataOrNullID(N->getDiscriminator()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawDataLocation()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawAssociated()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawAllocated()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawRank()));
+  Record.push_back(VE.getMetadataOrNullID(N->getAnnotations().get()));
+
+  Stream.EmitRecord(bitc::METADATA_COMPOSITE_TYPE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDISubroutineType(
+    const DISubroutineType *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  const unsigned HasNoOldTypeRefs = 0x2;
+  Record.push_back(HasNoOldTypeRefs | (unsigned)N->isDistinct());
+  Record.push_back(N->getFlags());
+  Record.push_back(VE.getMetadataOrNullID(N->getTypeArray().get()));
+  Record.push_back(N->getCC());
+
+  Stream.EmitRecord(bitc::METADATA_SUBROUTINE_TYPE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIFile(const DIFile *N,
+                                      SmallVectorImpl<uint64_t> &Record,
+                                      unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawFilename()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawDirectory()));
+  if (N->getRawChecksum()) {
+    Record.push_back(N->getRawChecksum()->Kind);
+    Record.push_back(VE.getMetadataOrNullID(N->getRawChecksum()->Value));
+  } else {
+    // Maintain backwards compatibility with the old internal representation of
+    // CSK_None in ChecksumKind by writing nulls here when Checksum is None.
+    Record.push_back(0);
+    Record.push_back(VE.getMetadataOrNullID(nullptr));
+  }
+  auto Source = N->getRawSource();
+  if (Source)
+    Record.push_back(VE.getMetadataOrNullID(Source));
+
+  Stream.EmitRecord(bitc::METADATA_FILE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDICompileUnit(const DICompileUnit *N,
+                                             SmallVectorImpl<uint64_t> &Record,
+                                             unsigned Abbrev) {
+  assert(N->isDistinct() && "Expected distinct compile units");
+  Record.push_back(/* IsDistinct */ true);
+  Record.push_back(N->getSourceLanguage());
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawProducer()));
+  Record.push_back(N->isOptimized());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawFlags()));
+  Record.push_back(N->getRuntimeVersion());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSplitDebugFilename()));
+  Record.push_back(N->getEmissionKind());
+  Record.push_back(VE.getMetadataOrNullID(N->getEnumTypes().get()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRetainedTypes().get()));
+  Record.push_back(/* subprograms */ 0);
+  Record.push_back(VE.getMetadataOrNullID(N->getGlobalVariables().get()));
+  Record.push_back(VE.getMetadataOrNullID(N->getImportedEntities().get()));
+  Record.push_back(N->getDWOId());
+  Record.push_back(VE.getMetadataOrNullID(N->getMacros().get()));
+  Record.push_back(N->getSplitDebugInlining());
+  Record.push_back(N->getDebugInfoForProfiling());
+  Record.push_back((unsigned)N->getNameTableKind());
+  Record.push_back(N->getRangesBaseAddress());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSysRoot()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSDK()));
+
+  Stream.EmitRecord(bitc::METADATA_COMPILE_UNIT, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDISubprogram(const DISubprogram *N,
+                                            SmallVectorImpl<uint64_t> &Record,
+                                            unsigned Abbrev) {
+  const uint64_t HasUnitFlag = 1 << 1;
+  const uint64_t HasSPFlagsFlag = 1 << 2;
+  Record.push_back(uint64_t(N->isDistinct()) | HasUnitFlag | HasSPFlagsFlag);
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawLinkageName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getType()));
+  Record.push_back(N->getScopeLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getContainingType()));
+  Record.push_back(N->getSPFlags());
+  Record.push_back(N->getVirtualIndex());
+  Record.push_back(N->getFlags());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawUnit()));
+  Record.push_back(VE.getMetadataOrNullID(N->getTemplateParams().get()));
+  Record.push_back(VE.getMetadataOrNullID(N->getDeclaration()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRetainedNodes().get()));
+  Record.push_back(N->getThisAdjustment());
+  Record.push_back(VE.getMetadataOrNullID(N->getThrownTypes().get()));
+  Record.push_back(VE.getMetadataOrNullID(N->getAnnotations().get()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawTargetFuncName()));
+
+  Stream.EmitRecord(bitc::METADATA_SUBPROGRAM, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDILexicalBlock(const DILexicalBlock *N,
+                                              SmallVectorImpl<uint64_t> &Record,
+                                              unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLine());
+  Record.push_back(N->getColumn());
+
+  Stream.EmitRecord(bitc::METADATA_LEXICAL_BLOCK, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDILexicalBlockFile(
+    const DILexicalBlockFile *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getDiscriminator());
+
+  Stream.EmitRecord(bitc::METADATA_LEXICAL_BLOCK_FILE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDICommonBlock(const DICommonBlock *N,
+                                             SmallVectorImpl<uint64_t> &Record,
+                                             unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getDecl()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLineNo());
+
+  Stream.EmitRecord(bitc::METADATA_COMMON_BLOCK, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDINamespace(const DINamespace *N,
+                                           SmallVectorImpl<uint64_t> &Record,
+                                           unsigned Abbrev) {
+  Record.push_back(N->isDistinct() | N->getExportSymbols() << 1);
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+
+  Stream.EmitRecord(bitc::METADATA_NAMESPACE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIMacro(const DIMacro *N,
+                                       SmallVectorImpl<uint64_t> &Record,
+                                       unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getMacinfoType());
+  Record.push_back(N->getLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawValue()));
+
+  Stream.EmitRecord(bitc::METADATA_MACRO, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIMacroFile(const DIMacroFile *N,
+                                           SmallVectorImpl<uint64_t> &Record,
+                                           unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getMacinfoType());
+  Record.push_back(N->getLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(VE.getMetadataOrNullID(N->getElements().get()));
+
+  Stream.EmitRecord(bitc::METADATA_MACRO_FILE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIArgList(const DIArgList *N,
+                                         SmallVectorImpl<uint64_t> &Record,
+                                         unsigned Abbrev) {
+  Record.reserve(N->getArgs().size());
+  for (ValueAsMetadata *MD : N->getArgs())
+    Record.push_back(VE.getMetadataID(MD));
+
+  Stream.EmitRecord(bitc::METADATA_ARG_LIST, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIModule(const DIModule *N,
+                                        SmallVectorImpl<uint64_t> &Record,
+                                        unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  for (auto &I : N->operands())
+    Record.push_back(VE.getMetadataOrNullID(I));
+  Record.push_back(N->getLineNo());
+  Record.push_back(N->getIsDecl());
+
+  Stream.EmitRecord(bitc::METADATA_MODULE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIAssignID(const DIAssignID *N,
+                                          SmallVectorImpl<uint64_t> &Record,
+                                          unsigned Abbrev) {
+  // There are no arguments for this metadata type.
+  Record.push_back(N->isDistinct());
+  Stream.EmitRecord(bitc::METADATA_ASSIGN_ID, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDITemplateTypeParameter(
+    const DITemplateTypeParameter *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getType()));
+  Record.push_back(N->isDefault());
+
+  Stream.EmitRecord(bitc::METADATA_TEMPLATE_TYPE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDITemplateValueParameter(
+    const DITemplateValueParameter *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getTag());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getType()));
+  Record.push_back(N->isDefault());
+  Record.push_back(VE.getMetadataOrNullID(N->getValue()));
+
+  Stream.EmitRecord(bitc::METADATA_TEMPLATE_VALUE, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIGlobalVariable(
+    const DIGlobalVariable *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  const uint64_t Version = 2 << 1;
+  Record.push_back((uint64_t)N->isDistinct() | Version);
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawLinkageName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getType()));
+  Record.push_back(N->isLocalToUnit());
+  Record.push_back(N->isDefinition());
+  Record.push_back(VE.getMetadataOrNullID(N->getStaticDataMemberDeclaration()));
+  Record.push_back(VE.getMetadataOrNullID(N->getTemplateParams()));
+  Record.push_back(N->getAlignInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getAnnotations().get()));
+
+  Stream.EmitRecord(bitc::METADATA_GLOBAL_VAR, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDILocalVariable(
+    const DILocalVariable *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  // In order to support all possible bitcode formats in BitcodeReader we need
+  // to distinguish the following cases:
+  // 1) Record has no artificial tag (Record[1]),
+  //   has no obsolete inlinedAt field (Record[9]).
+  //   In this case Record size will be 8, HasAlignment flag is false.
+  // 2) Record has artificial tag (Record[1]),
+  //   has no obsolete inlignedAt field (Record[9]).
+  //   In this case Record size will be 9, HasAlignment flag is false.
+  // 3) Record has both artificial tag (Record[1]) and
+  //   obsolete inlignedAt field (Record[9]).
+  //   In this case Record size will be 10, HasAlignment flag is false.
+  // 4) Record has neither artificial tag, nor inlignedAt field, but
+  //   HasAlignment flag is true and Record[8] contains alignment value.
+  const uint64_t HasAlignmentFlag = 1 << 1;
+  Record.push_back((uint64_t)N->isDistinct() | HasAlignmentFlag);
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getType()));
+  Record.push_back(N->getArg());
+  Record.push_back(N->getFlags());
+  Record.push_back(N->getAlignInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getAnnotations().get()));
+
+  Stream.EmitRecord(bitc::METADATA_LOCAL_VAR, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDILabel(
+    const DILabel *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  Record.push_back((uint64_t)N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLine());
+
+  Stream.EmitRecord(bitc::METADATA_LABEL, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIExpression(const DIExpression *N,
+                                            SmallVectorImpl<uint64_t> &Record,
+                                            unsigned Abbrev) {
+  Record.reserve(N->getElements().size() + 1);
+  const uint64_t Version = 3 << 1;
+  Record.push_back((uint64_t)N->isDistinct() | Version);
+  Record.append(N->elements_begin(), N->elements_end());
+
+  Stream.EmitRecord(bitc::METADATA_EXPRESSION, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIGlobalVariableExpression(
+    const DIGlobalVariableExpression *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getVariable()));
+  Record.push_back(VE.getMetadataOrNullID(N->getExpression()));
+
+  Stream.EmitRecord(bitc::METADATA_GLOBAL_VAR_EXPR, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIObjCProperty(const DIObjCProperty *N,
+                                              SmallVectorImpl<uint64_t> &Record,
+                                              unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getFile()));
+  Record.push_back(N->getLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawSetterName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawGetterName()));
+  Record.push_back(N->getAttributes());
+  Record.push_back(VE.getMetadataOrNullID(N->getType()));
+
+  Stream.EmitRecord(bitc::METADATA_OBJC_PROPERTY, Record, Abbrev);
+  Record.clear();
+}
+
+void ModuleBitcodeWriter::writeDIImportedEntity(
+    const DIImportedEntity *N, SmallVectorImpl<uint64_t> &Record,
+    unsigned Abbrev) {
+  Record.push_back(N->isDistinct());
+  Record.push_back(N->getTag());
+  Record.push_back(VE.getMetadataOrNullID(N->getScope()));
+  Record.push_back(VE.getMetadataOrNullID(N->getEntity()));
+  Record.push_back(N->getLine());
+  Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
+  Record.push_back(VE.getMetadataOrNullID(N->getRawFile()));
+  Record.push_back(VE.getMetadataOrNullID(N->getElements().get()));
+
+  Stream.EmitRecord(bitc::METADATA_IMPORTED_ENTITY, Record, Abbrev);
+  Record.clear();
+}
+
+unsigned ModuleBitcodeWriter::createNamedMetadataAbbrev() {
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::METADATA_NAME));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8));
+  return Stream.EmitAbbrev(std::move(Abbv));
+}
+
+void ModuleBitcodeWriter::writeNamedMetadata(
+    SmallVectorImpl<uint64_t> &Record) {
+  if (M.named_metadata_empty())
+    return;
+
+  unsigned Abbrev = createNamedMetadataAbbrev();
+  for (const NamedMDNode &NMD : M.named_metadata()) {
+    // Write name.
+    StringRef Str = NMD.getName();
+    Record.append(Str.bytes_begin(), Str.bytes_end());
+    Stream.EmitRecord(bitc::METADATA_NAME, Record, Abbrev);
+    Record.clear();
+
+    // Write named metadata operands.
+    for (const MDNode *N : NMD.operands())
+      Record.push_back(VE.getMetadataID(N));
+    Stream.EmitRecord(bitc::METADATA_NAMED_NODE, Record, 0);
+    Record.clear();
+  }
+}
+
+unsigned ModuleBitcodeWriter::createMetadataStringsAbbrev() {
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::METADATA_STRINGS));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // # of strings
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // offset to chars
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob));
+  return Stream.EmitAbbrev(std::move(Abbv));
+}
+
+/// Write out a record for MDString.
+///
+/// All the metadata strings in a metadata block are emitted in a single
+/// record.  The sizes and strings themselves are shoved into a blob.
+void ModuleBitcodeWriter::writeMetadataStrings(
+    ArrayRef<const Metadata *> Strings, SmallVectorImpl<uint64_t> &Record) {
+  if (Strings.empty())
+    return;
+
+  // Start the record with the number of strings.
+  Record.push_back(bitc::METADATA_STRINGS);
+  Record.push_back(Strings.size());
+
+  // Emit the sizes of the strings in the blob.
+  SmallString<256> Blob;
+  {
+    BitstreamWriter W(Blob);
+    for (const Metadata *MD : Strings)
+      W.EmitVBR(cast<MDString>(MD)->getLength(), 6);
+    W.FlushToWord();
+  }
+
+  // Add the offset to the strings to the record.
+  Record.push_back(Blob.size());
+
+  // Add the strings to the blob.
+  for (const Metadata *MD : Strings)
+    Blob.append(cast<MDString>(MD)->getString());
+
+  // Emit the final record.
+  Stream.EmitRecordWithBlob(createMetadataStringsAbbrev(), Record, Blob);
+  Record.clear();
+}
+
+// Generates an enum to use as an index in the Abbrev array of Metadata record.
+enum MetadataAbbrev : unsigned {
+#define HANDLE_MDNODE_LEAF(CLASS) CLASS##AbbrevID,
+#include "llvm/IR/Metadata.def"
+  LastPlusOne
+};
+
+void ModuleBitcodeWriter::writeMetadataRecords(
+    ArrayRef<const Metadata *> MDs, SmallVectorImpl<uint64_t> &Record,
+    std::vector<unsigned> *MDAbbrevs, std::vector<uint64_t> *IndexPos) {
+  if (MDs.empty())
+    return;
+
+  // Initialize MDNode abbreviations.
+#define HANDLE_MDNODE_LEAF(CLASS) unsigned CLASS##Abbrev = 0;
+#include "llvm/IR/Metadata.def"
+
+  for (const Metadata *MD : MDs) {
+    if (IndexPos)
+      IndexPos->push_back(Stream.GetCurrentBitNo());
+    if (const MDNode *N = dyn_cast<MDNode>(MD)) {
+      assert(N->isResolved() && "Expected forward references to be resolved");
+
+      switch (N->getMetadataID()) {
+      default:
+        llvm_unreachable("Invalid MDNode subclass");
+#define HANDLE_MDNODE_LEAF(CLASS)                                              \
+  case Metadata::CLASS##Kind:                                                  \
+    if (MDAbbrevs)                                                             \
+      write##CLASS(cast<CLASS>(N), Record,                                     \
+                   (*MDAbbrevs)[MetadataAbbrev::CLASS##AbbrevID]);             \
+    else                                                                       \
+      write##CLASS(cast<CLASS>(N), Record, CLASS##Abbrev);                     \
+    continue;
+#include "llvm/IR/Metadata.def"
+      }
+    }
+    writeValueAsMetadata(cast<ValueAsMetadata>(MD), Record);
+  }
+}
+
+void ModuleBitcodeWriter::writeModuleMetadata() {
+  if (!VE.hasMDs() && M.named_metadata_empty())
+    return;
+
+  Stream.EnterSubblock(bitc::METADATA_BLOCK_ID, 4);
+  SmallVector<uint64_t, 64> Record;
+
+  // Emit all abbrevs upfront, so that the reader can jump in the middle of the
+  // block and load any metadata.
+  std::vector<unsigned> MDAbbrevs;
+
+  MDAbbrevs.resize(MetadataAbbrev::LastPlusOne);
+  MDAbbrevs[MetadataAbbrev::DILocationAbbrevID] = createDILocationAbbrev();
+  MDAbbrevs[MetadataAbbrev::GenericDINodeAbbrevID] =
+      createGenericDINodeAbbrev();
+
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::METADATA_INDEX_OFFSET));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+  unsigned OffsetAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::METADATA_INDEX));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
+  unsigned IndexAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Emit MDStrings together upfront.
+  writeMetadataStrings(VE.getMDStrings(), Record);
+
+  // We only emit an index for the metadata record if we have more than a given
+  // (naive) threshold of metadatas, otherwise it is not worth it.
+  if (VE.getNonMDStrings().size() > IndexThreshold) {
+    // Write a placeholder value in for the offset of the metadata index,
+    // which is written after the records, so that it can include
+    // the offset of each entry. The placeholder offset will be
+    // updated after all records are emitted.
+    uint64_t Vals[] = {0, 0};
+    Stream.EmitRecord(bitc::METADATA_INDEX_OFFSET, Vals, OffsetAbbrev);
+  }
+
+  // Compute and save the bit offset to the current position, which will be
+  // patched when we emit the index later. We can simply subtract the 64-bit
+  // fixed size from the current bit number to get the location to backpatch.
+  uint64_t IndexOffsetRecordBitPos = Stream.GetCurrentBitNo();
+
+  // This index will contain the bitpos for each individual record.
+  std::vector<uint64_t> IndexPos;
+  IndexPos.reserve(VE.getNonMDStrings().size());
+
+  // Write all the records
+  writeMetadataRecords(VE.getNonMDStrings(), Record, &MDAbbrevs, &IndexPos);
+
+  if (VE.getNonMDStrings().size() > IndexThreshold) {
+    // Now that we have emitted all the records we will emit the index. But
+    // first
+    // backpatch the forward reference so that the reader can skip the records
+    // efficiently.
+    Stream.BackpatchWord64(IndexOffsetRecordBitPos - 64,
+                           Stream.GetCurrentBitNo() - IndexOffsetRecordBitPos);
+
+    // Delta encode the index.
+    uint64_t PreviousValue = IndexOffsetRecordBitPos;
+    for (auto &Elt : IndexPos) {
+      auto EltDelta = Elt - PreviousValue;
+      PreviousValue = Elt;
+      Elt = EltDelta;
+    }
+    // Emit the index record.
+    Stream.EmitRecord(bitc::METADATA_INDEX, IndexPos, IndexAbbrev);
+    IndexPos.clear();
+  }
+
+  // Write the named metadata now.
+  writeNamedMetadata(Record);
+
+  auto AddDeclAttachedMetadata = [&](const GlobalObject &GO) {
+    SmallVector<uint64_t, 4> Record;
+    Record.push_back(VE.getValueID(&GO));
+    pushGlobalMetadataAttachment(Record, GO);
+    Stream.EmitRecord(bitc::METADATA_GLOBAL_DECL_ATTACHMENT, Record);
+  };
+  for (const Function &F : M)
+    if (F.isDeclaration() && F.hasMetadata())
+      AddDeclAttachedMetadata(F);
+  // FIXME: Only store metadata for declarations here, and move data for global
+  // variable definitions to a separate block (PR28134).
+  for (const GlobalVariable &GV : M.globals())
+    if (GV.hasMetadata())
+      AddDeclAttachedMetadata(GV);
+
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::writeFunctionMetadata(const Function &F) {
+  if (!VE.hasMDs())
+    return;
+
+  Stream.EnterSubblock(bitc::METADATA_BLOCK_ID, 3);
+  SmallVector<uint64_t, 64> Record;
+  writeMetadataStrings(VE.getMDStrings(), Record);
+  writeMetadataRecords(VE.getNonMDStrings(), Record);
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::pushGlobalMetadataAttachment(
+    SmallVectorImpl<uint64_t> &Record, const GlobalObject &GO) {
+  // [n x [id, mdnode]]
+  SmallVector<std::pair<unsigned, MDNode *>, 4> MDs;
+  GO.getAllMetadata(MDs);
+  for (const auto &I : MDs) {
+    Record.push_back(I.first);
+    Record.push_back(VE.getMetadataID(I.second));
+  }
+}
+
+void ModuleBitcodeWriter::writeFunctionMetadataAttachment(const Function &F) {
+  Stream.EnterSubblock(bitc::METADATA_ATTACHMENT_ID, 3);
+
+  SmallVector<uint64_t, 64> Record;
+
+  if (F.hasMetadata()) {
+    pushGlobalMetadataAttachment(Record, F);
+    Stream.EmitRecord(bitc::METADATA_ATTACHMENT, Record, 0);
+    Record.clear();
+  }
+
+  // Write metadata attachments
+  // METADATA_ATTACHMENT - [m x [value, [n x [id, mdnode]]]
+  SmallVector<std::pair<unsigned, MDNode *>, 4> MDs;
+  for (const BasicBlock &BB : F)
+    for (const Instruction &I : BB) {
+      MDs.clear();
+      I.getAllMetadataOtherThanDebugLoc(MDs);
+
+      // If no metadata, ignore instruction.
+      if (MDs.empty()) continue;
+
+      Record.push_back(VE.getInstructionID(&I));
+
+      for (unsigned i = 0, e = MDs.size(); i != e; ++i) {
+        Record.push_back(MDs[i].first);
+        Record.push_back(VE.getMetadataID(MDs[i].second));
+      }
+      Stream.EmitRecord(bitc::METADATA_ATTACHMENT, Record, 0);
+      Record.clear();
+    }
+
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::writeModuleMetadataKinds() {
+  SmallVector<uint64_t, 64> Record;
+
+  // Write metadata kinds
+  // METADATA_KIND - [n x [id, name]]
+  SmallVector<StringRef, 8> Names;
+  M.getMDKindNames(Names);
+
+  if (Names.empty()) return;
+
+  Stream.EnterSubblock(bitc::METADATA_KIND_BLOCK_ID, 3);
+
+  for (unsigned MDKindID = 0, e = Names.size(); MDKindID != e; ++MDKindID) {
+    Record.push_back(MDKindID);
+    StringRef KName = Names[MDKindID];
+    Record.append(KName.begin(), KName.end());
+
+    Stream.EmitRecord(bitc::METADATA_KIND, Record, 0);
+    Record.clear();
+  }
+
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::writeOperandBundleTags() {
+  // Write metadata kinds
+  //
+  // OPERAND_BUNDLE_TAGS_BLOCK_ID : N x OPERAND_BUNDLE_TAG
+  //
+  // OPERAND_BUNDLE_TAG - [strchr x N]
+
+  SmallVector<StringRef, 8> Tags;
+  M.getOperandBundleTags(Tags);
+
+  if (Tags.empty())
+    return;
+
+  Stream.EnterSubblock(bitc::OPERAND_BUNDLE_TAGS_BLOCK_ID, 3);
+
+  SmallVector<uint64_t, 64> Record;
+
+  for (auto Tag : Tags) {
+    Record.append(Tag.begin(), Tag.end());
+
+    Stream.EmitRecord(bitc::OPERAND_BUNDLE_TAG, Record, 0);
+    Record.clear();
+  }
+
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::writeSyncScopeNames() {
+  SmallVector<StringRef, 8> SSNs;
+  M.getContext().getSyncScopeNames(SSNs);
+  if (SSNs.empty())
+    return;
+
+  Stream.EnterSubblock(bitc::SYNC_SCOPE_NAMES_BLOCK_ID, 2);
+
+  SmallVector<uint64_t, 64> Record;
+  for (auto SSN : SSNs) {
+    Record.append(SSN.begin(), SSN.end());
+    Stream.EmitRecord(bitc::SYNC_SCOPE_NAME, Record, 0);
+    Record.clear();
+  }
+
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::writeConstants(unsigned FirstVal, unsigned LastVal,
+                                         bool isGlobal) {
+  if (FirstVal == LastVal) return;
+
+  Stream.EnterSubblock(bitc::CONSTANTS_BLOCK_ID, 4);
+
+  unsigned AggregateAbbrev = 0;
+  unsigned String8Abbrev = 0;
+  unsigned CString7Abbrev = 0;
+  unsigned CString6Abbrev = 0;
+  // If this is a constant pool for the module, emit module-specific abbrevs.
+  if (isGlobal) {
+    // Abbrev for CST_CODE_AGGREGATE.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::CST_CODE_AGGREGATE));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, Log2_32_Ceil(LastVal+1)));
+    AggregateAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+    // Abbrev for CST_CODE_STRING.
+    Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::CST_CODE_STRING));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8));
+    String8Abbrev = Stream.EmitAbbrev(std::move(Abbv));
+    // Abbrev for CST_CODE_CSTRING.
+    Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::CST_CODE_CSTRING));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 7));
+    CString7Abbrev = Stream.EmitAbbrev(std::move(Abbv));
+    // Abbrev for CST_CODE_CSTRING.
+    Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::CST_CODE_CSTRING));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Char6));
+    CString6Abbrev = Stream.EmitAbbrev(std::move(Abbv));
+  }
+
+  SmallVector<uint64_t, 64> Record;
+
+  const ValueEnumerator::ValueList &Vals = VE.getValues();
+  Type *LastTy = nullptr;
+  for (unsigned i = FirstVal; i != LastVal; ++i) {
+    const Value *V = Vals[i].first;
+    // If we need to switch types, do so now.
+    if (V->getType() != LastTy) {
+      LastTy = V->getType();
+      Record.push_back(VE.getTypeID(LastTy));
+      Stream.EmitRecord(bitc::CST_CODE_SETTYPE, Record,
+                        CONSTANTS_SETTYPE_ABBREV);
+      Record.clear();
+    }
+
+    if (const InlineAsm *IA = dyn_cast<InlineAsm>(V)) {
+      Record.push_back(VE.getTypeID(IA->getFunctionType()));
+      Record.push_back(
+          unsigned(IA->hasSideEffects()) | unsigned(IA->isAlignStack()) << 1 |
+          unsigned(IA->getDialect() & 1) << 2 | unsigned(IA->canThrow()) << 3);
+
+      // Add the asm string.
+      const std::string &AsmStr = IA->getAsmString();
+      Record.push_back(AsmStr.size());
+      Record.append(AsmStr.begin(), AsmStr.end());
+
+      // Add the constraint string.
+      const std::string &ConstraintStr = IA->getConstraintString();
+      Record.push_back(ConstraintStr.size());
+      Record.append(ConstraintStr.begin(), ConstraintStr.end());
+      Stream.EmitRecord(bitc::CST_CODE_INLINEASM, Record);
+      Record.clear();
+      continue;
+    }
+    const Constant *C = cast<Constant>(V);
+    unsigned Code = -1U;
+    unsigned AbbrevToUse = 0;
+    if (C->isNullValue()) {
+      Code = bitc::CST_CODE_NULL;
+    } else if (isa<PoisonValue>(C)) {
+      Code = bitc::CST_CODE_POISON;
+    } else if (isa<UndefValue>(C)) {
+      Code = bitc::CST_CODE_UNDEF;
+    } else if (const ConstantInt *IV = dyn_cast<ConstantInt>(C)) {
+      if (IV->getBitWidth() <= 64) {
+        uint64_t V = IV->getSExtValue();
+        emitSignedInt64(Record, V);
+        Code = bitc::CST_CODE_INTEGER;
+        AbbrevToUse = CONSTANTS_INTEGER_ABBREV;
+      } else {                             // Wide integers, > 64 bits in size.
+        emitWideAPInt(Record, IV->getValue());
+        Code = bitc::CST_CODE_WIDE_INTEGER;
+      }
+    } else if (const ConstantFP *CFP = dyn_cast<ConstantFP>(C)) {
+      Code = bitc::CST_CODE_FLOAT;
+      Type *Ty = CFP->getType();
+      if (Ty->isHalfTy() || Ty->isBFloatTy() || Ty->isFloatTy() ||
+          Ty->isDoubleTy()) {
+        Record.push_back(CFP->getValueAPF().bitcastToAPInt().getZExtValue());
+      } else if (Ty->isX86_FP80Ty()) {
+        // api needed to prevent premature destruction
+        // bits are not in the same order as a normal i80 APInt, compensate.
+        APInt api = CFP->getValueAPF().bitcastToAPInt();
+        const uint64_t *p = api.getRawData();
+        Record.push_back((p[1] << 48) | (p[0] >> 16));
+        Record.push_back(p[0] & 0xffffLL);
+      } else if (Ty->isFP128Ty() || Ty->isPPC_FP128Ty()) {
+        APInt api = CFP->getValueAPF().bitcastToAPInt();
+        const uint64_t *p = api.getRawData();
+        Record.push_back(p[0]);
+        Record.push_back(p[1]);
+      } else {
+        assert(0 && "Unknown FP type!");
+      }
+    } else if (isa<ConstantDataSequential>(C) &&
+               cast<ConstantDataSequential>(C)->isString()) {
+      const ConstantDataSequential *Str = cast<ConstantDataSequential>(C);
+      // Emit constant strings specially.
+      unsigned NumElts = Str->getNumElements();
+      // If this is a null-terminated string, use the denser CSTRING encoding.
+      if (Str->isCString()) {
+        Code = bitc::CST_CODE_CSTRING;
+        --NumElts;  // Don't encode the null, which isn't allowed by char6.
+      } else {
+        Code = bitc::CST_CODE_STRING;
+        AbbrevToUse = String8Abbrev;
+      }
+      bool isCStr7 = Code == bitc::CST_CODE_CSTRING;
+      bool isCStrChar6 = Code == bitc::CST_CODE_CSTRING;
+      for (unsigned i = 0; i != NumElts; ++i) {
+        unsigned char V = Str->getElementAsInteger(i);
+        Record.push_back(V);
+        isCStr7 &= (V & 128) == 0;
+        if (isCStrChar6)
+          isCStrChar6 = BitCodeAbbrevOp::isChar6(V);
+      }
+
+      if (isCStrChar6)
+        AbbrevToUse = CString6Abbrev;
+      else if (isCStr7)
+        AbbrevToUse = CString7Abbrev;
+    } else if (const ConstantDataSequential *CDS =
+                  dyn_cast<ConstantDataSequential>(C)) {
+      Code = bitc::CST_CODE_DATA;
+      Type *EltTy = CDS->getElementType();
+      if (isa<IntegerType>(EltTy)) {
+        for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i)
+          Record.push_back(CDS->getElementAsInteger(i));
+      } else {
+        for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i)
+          Record.push_back(
+              CDS->getElementAsAPFloat(i).bitcastToAPInt().getLimitedValue());
+      }
+    } else if (isa<ConstantAggregate>(C)) {
+      Code = bitc::CST_CODE_AGGREGATE;
+      for (const Value *Op : C->operands())
+        Record.push_back(VE.getValueID(Op));
+      AbbrevToUse = AggregateAbbrev;
+    } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
+      switch (CE->getOpcode()) {
+      default:
+        if (Instruction::isCast(CE->getOpcode())) {
+          Code = bitc::CST_CODE_CE_CAST;
+          Record.push_back(getEncodedCastOpcode(CE->getOpcode()));
+          Record.push_back(VE.getTypeID(C->getOperand(0)->getType()));
+          Record.push_back(VE.getValueID(C->getOperand(0)));
+          AbbrevToUse = CONSTANTS_CE_CAST_Abbrev;
+        } else {
+          assert(CE->getNumOperands() == 2 && "Unknown constant expr!");
+          Code = bitc::CST_CODE_CE_BINOP;
+          Record.push_back(getEncodedBinaryOpcode(CE->getOpcode()));
+          Record.push_back(VE.getValueID(C->getOperand(0)));
+          Record.push_back(VE.getValueID(C->getOperand(1)));
+          uint64_t Flags = getOptimizationFlags(CE);
+          if (Flags != 0)
+            Record.push_back(Flags);
+        }
+        break;
+      case Instruction::FNeg: {
+        assert(CE->getNumOperands() == 1 && "Unknown constant expr!");
+        Code = bitc::CST_CODE_CE_UNOP;
+        Record.push_back(getEncodedUnaryOpcode(CE->getOpcode()));
+        Record.push_back(VE.getValueID(C->getOperand(0)));
+        uint64_t Flags = getOptimizationFlags(CE);
+        if (Flags != 0)
+          Record.push_back(Flags);
+        break;
+      }
+      case Instruction::GetElementPtr: {
+        Code = bitc::CST_CODE_CE_GEP;
+        const auto *GO = cast<GEPOperator>(C);
+        Record.push_back(VE.getTypeID(GO->getSourceElementType()));
+        if (std::optional<unsigned> Idx = GO->getInRangeIndex()) {
+          Code = bitc::CST_CODE_CE_GEP_WITH_INRANGE_INDEX;
+          Record.push_back((*Idx << 1) | GO->isInBounds());
+        } else if (GO->isInBounds())
+          Code = bitc::CST_CODE_CE_INBOUNDS_GEP;
+        for (unsigned i = 0, e = CE->getNumOperands(); i != e; ++i) {
+          Record.push_back(VE.getTypeID(C->getOperand(i)->getType()));
+          Record.push_back(VE.getValueID(C->getOperand(i)));
+        }
+        break;
+      }
+      case Instruction::Select:
+        Code = bitc::CST_CODE_CE_SELECT;
+        Record.push_back(VE.getValueID(C->getOperand(0)));
+        Record.push_back(VE.getValueID(C->getOperand(1)));
+        Record.push_back(VE.getValueID(C->getOperand(2)));
+        break;
+      case Instruction::ExtractElement:
+        Code = bitc::CST_CODE_CE_EXTRACTELT;
+        Record.push_back(VE.getTypeID(C->getOperand(0)->getType()));
+        Record.push_back(VE.getValueID(C->getOperand(0)));
+        Record.push_back(VE.getTypeID(C->getOperand(1)->getType()));
+        Record.push_back(VE.getValueID(C->getOperand(1)));
+        break;
+      case Instruction::InsertElement:
+        Code = bitc::CST_CODE_CE_INSERTELT;
+        Record.push_back(VE.getValueID(C->getOperand(0)));
+        Record.push_back(VE.getValueID(C->getOperand(1)));
+        Record.push_back(VE.getTypeID(C->getOperand(2)->getType()));
+        Record.push_back(VE.getValueID(C->getOperand(2)));
+        break;
+      case Instruction::ShuffleVector:
+        // If the return type and argument types are the same, this is a
+        // standard shufflevector instruction.  If the types are different,
+        // then the shuffle is widening or truncating the input vectors, and
+        // the argument type must also be encoded.
+        if (C->getType() == C->getOperand(0)->getType()) {
+          Code = bitc::CST_CODE_CE_SHUFFLEVEC;
+        } else {
+          Code = bitc::CST_CODE_CE_SHUFVEC_EX;
+          Record.push_back(VE.getTypeID(C->getOperand(0)->getType()));
+        }
+        Record.push_back(VE.getValueID(C->getOperand(0)));
+        Record.push_back(VE.getValueID(C->getOperand(1)));
+        Record.push_back(VE.getValueID(CE->getShuffleMaskForBitcode()));
+        break;
+      case Instruction::ICmp:
+      case Instruction::FCmp:
+        Code = bitc::CST_CODE_CE_CMP;
+        Record.push_back(VE.getTypeID(C->getOperand(0)->getType()));
+        Record.push_back(VE.getValueID(C->getOperand(0)));
+        Record.push_back(VE.getValueID(C->getOperand(1)));
+        Record.push_back(CE->getPredicate());
+        break;
+      }
+    } else if (const BlockAddress *BA = dyn_cast<BlockAddress>(C)) {
+      Code = bitc::CST_CODE_BLOCKADDRESS;
+      Record.push_back(VE.getTypeID(BA->getFunction()->getType()));
+      Record.push_back(VE.getValueID(BA->getFunction()));
+      Record.push_back(VE.getGlobalBasicBlockID(BA->getBasicBlock()));
+    } else if (const auto *Equiv = dyn_cast<DSOLocalEquivalent>(C)) {
+      Code = bitc::CST_CODE_DSO_LOCAL_EQUIVALENT;
+      Record.push_back(VE.getTypeID(Equiv->getGlobalValue()->getType()));
+      Record.push_back(VE.getValueID(Equiv->getGlobalValue()));
+    } else if (const auto *NC = dyn_cast<NoCFIValue>(C)) {
+      Code = bitc::CST_CODE_NO_CFI_VALUE;
+      Record.push_back(VE.getTypeID(NC->getGlobalValue()->getType()));
+      Record.push_back(VE.getValueID(NC->getGlobalValue()));
+    } else {
+#ifndef NDEBUG
+      C->dump();
+#endif
+      llvm_unreachable("Unknown constant!");
+    }
+    Stream.EmitRecord(Code, Record, AbbrevToUse);
+    Record.clear();
+  }
+
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::writeModuleConstants() {
+  const ValueEnumerator::ValueList &Vals = VE.getValues();
+
+  // Find the first constant to emit, which is the first non-globalvalue value.
+  // We know globalvalues have been emitted by WriteModuleInfo.
+  for (unsigned i = 0, e = Vals.size(); i != e; ++i) {
+    if (!isa<GlobalValue>(Vals[i].first)) {
+      writeConstants(i, Vals.size(), true);
+      return;
+    }
+  }
+}
+
+/// pushValueAndType - The file has to encode both the value and type id for
+/// many values, because we need to know what type to create for forward
+/// references.  However, most operands are not forward references, so this type
+/// field is not needed.
+///
+/// This function adds V's value ID to Vals.  If the value ID is higher than the
+/// instruction ID, then it is a forward reference, and it also includes the
+/// type ID.  The value ID that is written is encoded relative to the InstID.
+bool ModuleBitcodeWriter::pushValueAndType(const Value *V, unsigned InstID,
+                                           SmallVectorImpl<unsigned> &Vals) {
+  unsigned ValID = VE.getValueID(V);
+  // Make encoding relative to the InstID.
+  Vals.push_back(InstID - ValID);
+  if (ValID >= InstID) {
+    Vals.push_back(VE.getTypeID(V->getType()));
+    return true;
+  }
+  return false;
+}
+
+void ModuleBitcodeWriter::writeOperandBundles(const CallBase &CS,
+                                              unsigned InstID) {
+  SmallVector<unsigned, 64> Record;
+  LLVMContext &C = CS.getContext();
+
+  for (unsigned i = 0, e = CS.getNumOperandBundles(); i != e; ++i) {
+    const auto &Bundle = CS.getOperandBundleAt(i);
+    Record.push_back(C.getOperandBundleTagID(Bundle.getTagName()));
+
+    for (auto &Input : Bundle.Inputs)
+      pushValueAndType(Input, InstID, Record);
+
+    Stream.EmitRecord(bitc::FUNC_CODE_OPERAND_BUNDLE, Record);
+    Record.clear();
+  }
+}
+
+/// pushValue - Like pushValueAndType, but where the type of the value is
+/// omitted (perhaps it was already encoded in an earlier operand).
+void ModuleBitcodeWriter::pushValue(const Value *V, unsigned InstID,
+                                    SmallVectorImpl<unsigned> &Vals) {
+  unsigned ValID = VE.getValueID(V);
+  Vals.push_back(InstID - ValID);
+}
+
+void ModuleBitcodeWriter::pushValueSigned(const Value *V, unsigned InstID,
+                                          SmallVectorImpl<uint64_t> &Vals) {
+  unsigned ValID = VE.getValueID(V);
+  int64_t diff = ((int32_t)InstID - (int32_t)ValID);
+  emitSignedInt64(Vals, diff);
+}
+
+/// WriteInstruction - Emit an instruction to the specified stream.
+void ModuleBitcodeWriter::writeInstruction(const Instruction &I,
+                                           unsigned InstID,
+                                           SmallVectorImpl<unsigned> &Vals) {
+  unsigned Code = 0;
+  unsigned AbbrevToUse = 0;
+  VE.setInstructionID(&I);
+  switch (I.getOpcode()) {
+  default:
+    if (Instruction::isCast(I.getOpcode())) {
+      Code = bitc::FUNC_CODE_INST_CAST;
+      if (!pushValueAndType(I.getOperand(0), InstID, Vals))
+        AbbrevToUse = FUNCTION_INST_CAST_ABBREV;
+      Vals.push_back(VE.getTypeID(I.getType()));
+      Vals.push_back(getEncodedCastOpcode(I.getOpcode()));
+    } else {
+      assert(isa<BinaryOperator>(I) && "Unknown instruction!");
+      Code = bitc::FUNC_CODE_INST_BINOP;
+      if (!pushValueAndType(I.getOperand(0), InstID, Vals))
+        AbbrevToUse = FUNCTION_INST_BINOP_ABBREV;
+      pushValue(I.getOperand(1), InstID, Vals);
+      Vals.push_back(getEncodedBinaryOpcode(I.getOpcode()));
+      uint64_t Flags = getOptimizationFlags(&I);
+      if (Flags != 0) {
+        if (AbbrevToUse == FUNCTION_INST_BINOP_ABBREV)
+          AbbrevToUse = FUNCTION_INST_BINOP_FLAGS_ABBREV;
+        Vals.push_back(Flags);
+      }
+    }
+    break;
+  case Instruction::FNeg: {
+    Code = bitc::FUNC_CODE_INST_UNOP;
+    if (!pushValueAndType(I.getOperand(0), InstID, Vals))
+      AbbrevToUse = FUNCTION_INST_UNOP_ABBREV;
+    Vals.push_back(getEncodedUnaryOpcode(I.getOpcode()));
+    uint64_t Flags = getOptimizationFlags(&I);
+    if (Flags != 0) {
+      if (AbbrevToUse == FUNCTION_INST_UNOP_ABBREV)
+        AbbrevToUse = FUNCTION_INST_UNOP_FLAGS_ABBREV;
+      Vals.push_back(Flags);
+    }
+    break;
+  }
+  case Instruction::GetElementPtr: {
+    Code = bitc::FUNC_CODE_INST_GEP;
+    AbbrevToUse = FUNCTION_INST_GEP_ABBREV;
+    auto &GEPInst = cast<GetElementPtrInst>(I);
+    Vals.push_back(GEPInst.isInBounds());
+    Vals.push_back(VE.getTypeID(GEPInst.getSourceElementType()));
+    for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i)
+      pushValueAndType(I.getOperand(i), InstID, Vals);
+    break;
+  }
+  case Instruction::ExtractValue: {
+    Code = bitc::FUNC_CODE_INST_EXTRACTVAL;
+    pushValueAndType(I.getOperand(0), InstID, Vals);
+    const ExtractValueInst *EVI = cast<ExtractValueInst>(&I);
+    Vals.append(EVI->idx_begin(), EVI->idx_end());
+    break;
+  }
+  case Instruction::InsertValue: {
+    Code = bitc::FUNC_CODE_INST_INSERTVAL;
+    pushValueAndType(I.getOperand(0), InstID, Vals);
+    pushValueAndType(I.getOperand(1), InstID, Vals);
+    const InsertValueInst *IVI = cast<InsertValueInst>(&I);
+    Vals.append(IVI->idx_begin(), IVI->idx_end());
+    break;
+  }
+  case Instruction::Select: {
+    Code = bitc::FUNC_CODE_INST_VSELECT;
+    pushValueAndType(I.getOperand(1), InstID, Vals);
+    pushValue(I.getOperand(2), InstID, Vals);
+    pushValueAndType(I.getOperand(0), InstID, Vals);
+    uint64_t Flags = getOptimizationFlags(&I);
+    if (Flags != 0)
+      Vals.push_back(Flags);
+    break;
+  }
+  case Instruction::ExtractElement:
+    Code = bitc::FUNC_CODE_INST_EXTRACTELT;
+    pushValueAndType(I.getOperand(0), InstID, Vals);
+    pushValueAndType(I.getOperand(1), InstID, Vals);
+    break;
+  case Instruction::InsertElement:
+    Code = bitc::FUNC_CODE_INST_INSERTELT;
+    pushValueAndType(I.getOperand(0), InstID, Vals);
+    pushValue(I.getOperand(1), InstID, Vals);
+    pushValueAndType(I.getOperand(2), InstID, Vals);
+    break;
+  case Instruction::ShuffleVector:
+    Code = bitc::FUNC_CODE_INST_SHUFFLEVEC;
+    pushValueAndType(I.getOperand(0), InstID, Vals);
+    pushValue(I.getOperand(1), InstID, Vals);
+    pushValue(cast<ShuffleVectorInst>(I).getShuffleMaskForBitcode(), InstID,
+              Vals);
+    break;
+  case Instruction::ICmp:
+  case Instruction::FCmp: {
+    // compare returning Int1Ty or vector of Int1Ty
+    Code = bitc::FUNC_CODE_INST_CMP2;
+    pushValueAndType(I.getOperand(0), InstID, Vals);
+    pushValue(I.getOperand(1), InstID, Vals);
+    Vals.push_back(cast<CmpInst>(I).getPredicate());
+    uint64_t Flags = getOptimizationFlags(&I);
+    if (Flags != 0)
+      Vals.push_back(Flags);
+    break;
+  }
+
+  case Instruction::Ret:
+    {
+      Code = bitc::FUNC_CODE_INST_RET;
+      unsigned NumOperands = I.getNumOperands();
+      if (NumOperands == 0)
+        AbbrevToUse = FUNCTION_INST_RET_VOID_ABBREV;
+      else if (NumOperands == 1) {
+        if (!pushValueAndType(I.getOperand(0), InstID, Vals))
+          AbbrevToUse = FUNCTION_INST_RET_VAL_ABBREV;
+      } else {
+        for (unsigned i = 0, e = NumOperands; i != e; ++i)
+          pushValueAndType(I.getOperand(i), InstID, Vals);
+      }
+    }
+    break;
+  case Instruction::Br:
+    {
+      Code = bitc::FUNC_CODE_INST_BR;
+      const BranchInst &II = cast<BranchInst>(I);
+      Vals.push_back(VE.getValueID(II.getSuccessor(0)));
+      if (II.isConditional()) {
+        Vals.push_back(VE.getValueID(II.getSuccessor(1)));
+        pushValue(II.getCondition(), InstID, Vals);
+      }
+    }
+    break;
+  case Instruction::Switch:
+    {
+      Code = bitc::FUNC_CODE_INST_SWITCH;
+      const SwitchInst &SI = cast<SwitchInst>(I);
+      Vals.push_back(VE.getTypeID(SI.getCondition()->getType()));
+      pushValue(SI.getCondition(), InstID, Vals);
+      Vals.push_back(VE.getValueID(SI.getDefaultDest()));
+      for (auto Case : SI.cases()) {
+        Vals.push_back(VE.getValueID(Case.getCaseValue()));
+        Vals.push_back(VE.getValueID(Case.getCaseSuccessor()));
+      }
+    }
+    break;
+  case Instruction::IndirectBr:
+    Code = bitc::FUNC_CODE_INST_INDIRECTBR;
+    Vals.push_back(VE.getTypeID(I.getOperand(0)->getType()));
+    // Encode the address operand as relative, but not the basic blocks.
+    pushValue(I.getOperand(0), InstID, Vals);
+    for (unsigned i = 1, e = I.getNumOperands(); i != e; ++i)
+      Vals.push_back(VE.getValueID(I.getOperand(i)));
+    break;
+
+  case Instruction::Invoke: {
+    const InvokeInst *II = cast<InvokeInst>(&I);
+    const Value *Callee = II->getCalledOperand();
+    FunctionType *FTy = II->getFunctionType();
+
+    if (II->hasOperandBundles())
+      writeOperandBundles(*II, InstID);
+
+    Code = bitc::FUNC_CODE_INST_INVOKE;
+
+    Vals.push_back(VE.getAttributeListID(II->getAttributes()));
+    Vals.push_back(II->getCallingConv() | 1 << 13);
+    Vals.push_back(VE.getValueID(II->getNormalDest()));
+    Vals.push_back(VE.getValueID(II->getUnwindDest()));
+    Vals.push_back(VE.getTypeID(FTy));
+    pushValueAndType(Callee, InstID, Vals);
+
+    // Emit value #'s for the fixed parameters.
+    for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
+      pushValue(I.getOperand(i), InstID, Vals); // fixed param.
+
+    // Emit type/value pairs for varargs params.
+    if (FTy->isVarArg()) {
+      for (unsigned i = FTy->getNumParams(), e = II->arg_size(); i != e; ++i)
+        pushValueAndType(I.getOperand(i), InstID, Vals); // vararg
+    }
+    break;
+  }
+  case Instruction::Resume:
+    Code = bitc::FUNC_CODE_INST_RESUME;
+    pushValueAndType(I.getOperand(0), InstID, Vals);
+    break;
+  case Instruction::CleanupRet: {
+    Code = bitc::FUNC_CODE_INST_CLEANUPRET;
+    const auto &CRI = cast<CleanupReturnInst>(I);
+    pushValue(CRI.getCleanupPad(), InstID, Vals);
+    if (CRI.hasUnwindDest())
+      Vals.push_back(VE.getValueID(CRI.getUnwindDest()));
+    break;
+  }
+  case Instruction::CatchRet: {
+    Code = bitc::FUNC_CODE_INST_CATCHRET;
+    const auto &CRI = cast<CatchReturnInst>(I);
+    pushValue(CRI.getCatchPad(), InstID, Vals);
+    Vals.push_back(VE.getValueID(CRI.getSuccessor()));
+    break;
+  }
+  case Instruction::CleanupPad:
+  case Instruction::CatchPad: {
+    const auto &FuncletPad = cast<FuncletPadInst>(I);
+    Code = isa<CatchPadInst>(FuncletPad) ? bitc::FUNC_CODE_INST_CATCHPAD
+                                         : bitc::FUNC_CODE_INST_CLEANUPPAD;
+    pushValue(FuncletPad.getParentPad(), InstID, Vals);
+
+    unsigned NumArgOperands = FuncletPad.arg_size();
+    Vals.push_back(NumArgOperands);
+    for (unsigned Op = 0; Op != NumArgOperands; ++Op)
+      pushValueAndType(FuncletPad.getArgOperand(Op), InstID, Vals);
+    break;
+  }
+  case Instruction::CatchSwitch: {
+    Code = bitc::FUNC_CODE_INST_CATCHSWITCH;
+    const auto &CatchSwitch = cast<CatchSwitchInst>(I);
+
+    pushValue(CatchSwitch.getParentPad(), InstID, Vals);
+
+    unsigned NumHandlers = CatchSwitch.getNumHandlers();
+    Vals.push_back(NumHandlers);
+    for (const BasicBlock *CatchPadBB : CatchSwitch.handlers())
+      Vals.push_back(VE.getValueID(CatchPadBB));
+
+    if (CatchSwitch.hasUnwindDest())
+      Vals.push_back(VE.getValueID(CatchSwitch.getUnwindDest()));
+    break;
+  }
+  case Instruction::CallBr: {
+    const CallBrInst *CBI = cast<CallBrInst>(&I);
+    const Value *Callee = CBI->getCalledOperand();
+    FunctionType *FTy = CBI->getFunctionType();
+
+    if (CBI->hasOperandBundles())
+      writeOperandBundles(*CBI, InstID);
+
+    Code = bitc::FUNC_CODE_INST_CALLBR;
+
+    Vals.push_back(VE.getAttributeListID(CBI->getAttributes()));
+
+    Vals.push_back(CBI->getCallingConv() << bitc::CALL_CCONV |
+                   1 << bitc::CALL_EXPLICIT_TYPE);
+
+    Vals.push_back(VE.getValueID(CBI->getDefaultDest()));
+    Vals.push_back(CBI->getNumIndirectDests());
+    for (unsigned i = 0, e = CBI->getNumIndirectDests(); i != e; ++i)
+      Vals.push_back(VE.getValueID(CBI->getIndirectDest(i)));
+
+    Vals.push_back(VE.getTypeID(FTy));
+    pushValueAndType(Callee, InstID, Vals);
+
+    // Emit value #'s for the fixed parameters.
+    for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i)
+      pushValue(I.getOperand(i), InstID, Vals); // fixed param.
+
+    // Emit type/value pairs for varargs params.
+    if (FTy->isVarArg()) {
+      for (unsigned i = FTy->getNumParams(), e = CBI->arg_size(); i != e; ++i)
+        pushValueAndType(I.getOperand(i), InstID, Vals); // vararg
+    }
+    break;
+  }
+  case Instruction::Unreachable:
+    Code = bitc::FUNC_CODE_INST_UNREACHABLE;
+    AbbrevToUse = FUNCTION_INST_UNREACHABLE_ABBREV;
+    break;
+
+  case Instruction::PHI: {
+    const PHINode &PN = cast<PHINode>(I);
+    Code = bitc::FUNC_CODE_INST_PHI;
+    // With the newer instruction encoding, forward references could give
+    // negative valued IDs.  This is most common for PHIs, so we use
+    // signed VBRs.
+    SmallVector<uint64_t, 128> Vals64;
+    Vals64.push_back(VE.getTypeID(PN.getType()));
+    for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
+      pushValueSigned(PN.getIncomingValue(i), InstID, Vals64);
+      Vals64.push_back(VE.getValueID(PN.getIncomingBlock(i)));
+    }
+
+    uint64_t Flags = getOptimizationFlags(&I);
+    if (Flags != 0)
+      Vals64.push_back(Flags);
+
+    // Emit a Vals64 vector and exit.
+    Stream.EmitRecord(Code, Vals64, AbbrevToUse);
+    Vals64.clear();
+    return;
+  }
+
+  case Instruction::LandingPad: {
+    const LandingPadInst &LP = cast<LandingPadInst>(I);
+    Code = bitc::FUNC_CODE_INST_LANDINGPAD;
+    Vals.push_back(VE.getTypeID(LP.getType()));
+    Vals.push_back(LP.isCleanup());
+    Vals.push_back(LP.getNumClauses());
+    for (unsigned I = 0, E = LP.getNumClauses(); I != E; ++I) {
+      if (LP.isCatch(I))
+        Vals.push_back(LandingPadInst::Catch);
+      else
+        Vals.push_back(LandingPadInst::Filter);
+      pushValueAndType(LP.getClause(I), InstID, Vals);
+    }
+    break;
+  }
+
+  case Instruction::Alloca: {
+    Code = bitc::FUNC_CODE_INST_ALLOCA;
+    const AllocaInst &AI = cast<AllocaInst>(I);
+    Vals.push_back(VE.getTypeID(AI.getAllocatedType()));
+    Vals.push_back(VE.getTypeID(I.getOperand(0)->getType()));
+    Vals.push_back(VE.getValueID(I.getOperand(0))); // size.
+    using APV = AllocaPackedValues;
+    unsigned Record = 0;
+    unsigned EncodedAlign = getEncodedAlign(AI.getAlign());
+    Bitfield::set<APV::AlignLower>(
+        Record, EncodedAlign & ((1 << APV::AlignLower::Bits) - 1));
+    Bitfield::set<APV::AlignUpper>(Record,
+                                   EncodedAlign >> APV::AlignLower::Bits);
+    Bitfield::set<APV::UsedWithInAlloca>(Record, AI.isUsedWithInAlloca());
+    Bitfield::set<APV::ExplicitType>(Record, true);
+    Bitfield::set<APV::SwiftError>(Record, AI.isSwiftError());
+    Vals.push_back(Record);
+
+    unsigned AS = AI.getAddressSpace();
+    if (AS != M.getDataLayout().getAllocaAddrSpace())
+      Vals.push_back(AS);
+    break;
+  }
+
+  case Instruction::Load:
+    if (cast<LoadInst>(I).isAtomic()) {
+      Code = bitc::FUNC_CODE_INST_LOADATOMIC;
+      pushValueAndType(I.getOperand(0), InstID, Vals);
+    } else {
+      Code = bitc::FUNC_CODE_INST_LOAD;
+      if (!pushValueAndType(I.getOperand(0), InstID, Vals)) // ptr
+        AbbrevToUse = FUNCTION_INST_LOAD_ABBREV;
+    }
+    Vals.push_back(VE.getTypeID(I.getType()));
+    Vals.push_back(getEncodedAlign(cast<LoadInst>(I).getAlign()));
+    Vals.push_back(cast<LoadInst>(I).isVolatile());
+    if (cast<LoadInst>(I).isAtomic()) {
+      Vals.push_back(getEncodedOrdering(cast<LoadInst>(I).getOrdering()));
+      Vals.push_back(getEncodedSyncScopeID(cast<LoadInst>(I).getSyncScopeID()));
+    }
+    break;
+  case Instruction::Store:
+    if (cast<StoreInst>(I).isAtomic())
+      Code = bitc::FUNC_CODE_INST_STOREATOMIC;
+    else
+      Code = bitc::FUNC_CODE_INST_STORE;
+    pushValueAndType(I.getOperand(1), InstID, Vals); // ptrty + ptr
+    pushValueAndType(I.getOperand(0), InstID, Vals); // valty + val
+    Vals.push_back(getEncodedAlign(cast<StoreInst>(I).getAlign()));
+    Vals.push_back(cast<StoreInst>(I).isVolatile());
+    if (cast<StoreInst>(I).isAtomic()) {
+      Vals.push_back(getEncodedOrdering(cast<StoreInst>(I).getOrdering()));
+      Vals.push_back(
+          getEncodedSyncScopeID(cast<StoreInst>(I).getSyncScopeID()));
+    }
+    break;
+  case Instruction::AtomicCmpXchg:
+    Code = bitc::FUNC_CODE_INST_CMPXCHG;
+    pushValueAndType(I.getOperand(0), InstID, Vals); // ptrty + ptr
+    pushValueAndType(I.getOperand(1), InstID, Vals); // cmp.
+    pushValue(I.getOperand(2), InstID, Vals);        // newval.
+    Vals.push_back(cast<AtomicCmpXchgInst>(I).isVolatile());
+    Vals.push_back(
+        getEncodedOrdering(cast<AtomicCmpXchgInst>(I).getSuccessOrdering()));
+    Vals.push_back(
+        getEncodedSyncScopeID(cast<AtomicCmpXchgInst>(I).getSyncScopeID()));
+    Vals.push_back(
+        getEncodedOrdering(cast<AtomicCmpXchgInst>(I).getFailureOrdering()));
+    Vals.push_back(cast<AtomicCmpXchgInst>(I).isWeak());
+    Vals.push_back(getEncodedAlign(cast<AtomicCmpXchgInst>(I).getAlign()));
+    break;
+  case Instruction::AtomicRMW:
+    Code = bitc::FUNC_CODE_INST_ATOMICRMW;
+    pushValueAndType(I.getOperand(0), InstID, Vals); // ptrty + ptr
+    pushValueAndType(I.getOperand(1), InstID, Vals); // valty + val
+    Vals.push_back(
+        getEncodedRMWOperation(cast<AtomicRMWInst>(I).getOperation()));
+    Vals.push_back(cast<AtomicRMWInst>(I).isVolatile());
+    Vals.push_back(getEncodedOrdering(cast<AtomicRMWInst>(I).getOrdering()));
+    Vals.push_back(
+        getEncodedSyncScopeID(cast<AtomicRMWInst>(I).getSyncScopeID()));
+    Vals.push_back(getEncodedAlign(cast<AtomicRMWInst>(I).getAlign()));
+    break;
+  case Instruction::Fence:
+    Code = bitc::FUNC_CODE_INST_FENCE;
+    Vals.push_back(getEncodedOrdering(cast<FenceInst>(I).getOrdering()));
+    Vals.push_back(getEncodedSyncScopeID(cast<FenceInst>(I).getSyncScopeID()));
+    break;
+  case Instruction::Call: {
+    const CallInst &CI = cast<CallInst>(I);
+    FunctionType *FTy = CI.getFunctionType();
+
+    if (CI.hasOperandBundles())
+      writeOperandBundles(CI, InstID);
+
+    Code = bitc::FUNC_CODE_INST_CALL;
+
+    Vals.push_back(VE.getAttributeListID(CI.getAttributes()));
+
+    unsigned Flags = getOptimizationFlags(&I);
+    Vals.push_back(CI.getCallingConv() << bitc::CALL_CCONV |
+                   unsigned(CI.isTailCall()) << bitc::CALL_TAIL |
+                   unsigned(CI.isMustTailCall()) << bitc::CALL_MUSTTAIL |
+                   1 << bitc::CALL_EXPLICIT_TYPE |
+                   unsigned(CI.isNoTailCall()) << bitc::CALL_NOTAIL |
+                   unsigned(Flags != 0) << bitc::CALL_FMF);
+    if (Flags != 0)
+      Vals.push_back(Flags);
+
+    Vals.push_back(VE.getTypeID(FTy));
+    pushValueAndType(CI.getCalledOperand(), InstID, Vals); // Callee
+
+    // Emit value #'s for the fixed parameters.
+    for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i) {
+      // Check for labels (can happen with asm labels).
+      if (FTy->getParamType(i)->isLabelTy())
+        Vals.push_back(VE.getValueID(CI.getArgOperand(i)));
+      else
+        pushValue(CI.getArgOperand(i), InstID, Vals); // fixed param.
+    }
+
+    // Emit type/value pairs for varargs params.
+    if (FTy->isVarArg()) {
+      for (unsigned i = FTy->getNumParams(), e = CI.arg_size(); i != e; ++i)
+        pushValueAndType(CI.getArgOperand(i), InstID, Vals); // varargs
+    }
+    break;
+  }
+  case Instruction::VAArg:
+    Code = bitc::FUNC_CODE_INST_VAARG;
+    Vals.push_back(VE.getTypeID(I.getOperand(0)->getType()));   // valistty
+    pushValue(I.getOperand(0), InstID, Vals);                   // valist.
+    Vals.push_back(VE.getTypeID(I.getType())); // restype.
+    break;
+  case Instruction::Freeze:
+    Code = bitc::FUNC_CODE_INST_FREEZE;
+    pushValueAndType(I.getOperand(0), InstID, Vals);
+    break;
+  }
+
+  Stream.EmitRecord(Code, Vals, AbbrevToUse);
+  Vals.clear();
+}
+
+/// Write a GlobalValue VST to the module. The purpose of this data structure is
+/// to allow clients to efficiently find the function body.
+void ModuleBitcodeWriter::writeGlobalValueSymbolTable(
+  DenseMap<const Function *, uint64_t> &FunctionToBitcodeIndex) {
+  // Get the offset of the VST we are writing, and backpatch it into
+  // the VST forward declaration record.
+  uint64_t VSTOffset = Stream.GetCurrentBitNo();
+  // The BitcodeStartBit was the stream offset of the identification block.
+  VSTOffset -= bitcodeStartBit();
+  assert((VSTOffset & 31) == 0 && "VST block not 32-bit aligned");
+  // Note that we add 1 here because the offset is relative to one word
+  // before the start of the identification block, which was historically
+  // always the start of the regular bitcode header.
+  Stream.BackpatchWord(VSTOffsetPlaceholder, VSTOffset / 32 + 1);
+
+  Stream.EnterSubblock(bitc::VALUE_SYMTAB_BLOCK_ID, 4);
+
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::VST_CODE_FNENTRY));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // value id
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // funcoffset
+  unsigned FnEntryAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  for (const Function &F : M) {
+    uint64_t Record[2];
+
+    if (F.isDeclaration())
+      continue;
+
+    Record[0] = VE.getValueID(&F);
+
+    // Save the word offset of the function (from the start of the
+    // actual bitcode written to the stream).
+    uint64_t BitcodeIndex = FunctionToBitcodeIndex[&F] - bitcodeStartBit();
+    assert((BitcodeIndex & 31) == 0 && "function block not 32-bit aligned");
+    // Note that we add 1 here because the offset is relative to one word
+    // before the start of the identification block, which was historically
+    // always the start of the regular bitcode header.
+    Record[1] = BitcodeIndex / 32 + 1;
+
+    Stream.EmitRecord(bitc::VST_CODE_FNENTRY, Record, FnEntryAbbrev);
+  }
+
+  Stream.ExitBlock();
+}
+
+/// Emit names for arguments, instructions and basic blocks in a function.
+void ModuleBitcodeWriter::writeFunctionLevelValueSymbolTable(
+    const ValueSymbolTable &VST) {
+  if (VST.empty())
+    return;
+
+  Stream.EnterSubblock(bitc::VALUE_SYMTAB_BLOCK_ID, 4);
+
+  // FIXME: Set up the abbrev, we know how many values there are!
+  // FIXME: We know if the type names can use 7-bit ascii.
+  SmallVector<uint64_t, 64> NameVals;
+
+  for (const ValueName &Name : VST) {
+    // Figure out the encoding to use for the name.
+    StringEncoding Bits = getStringEncoding(Name.getKey());
+
+    unsigned AbbrevToUse = VST_ENTRY_8_ABBREV;
+    NameVals.push_back(VE.getValueID(Name.getValue()));
+
+    // VST_CODE_ENTRY:   [valueid, namechar x N]
+    // VST_CODE_BBENTRY: [bbid, namechar x N]
+    unsigned Code;
+    if (isa<BasicBlock>(Name.getValue())) {
+      Code = bitc::VST_CODE_BBENTRY;
+      if (Bits == SE_Char6)
+        AbbrevToUse = VST_BBENTRY_6_ABBREV;
+    } else {
+      Code = bitc::VST_CODE_ENTRY;
+      if (Bits == SE_Char6)
+        AbbrevToUse = VST_ENTRY_6_ABBREV;
+      else if (Bits == SE_Fixed7)
+        AbbrevToUse = VST_ENTRY_7_ABBREV;
+    }
+
+    for (const auto P : Name.getKey())
+      NameVals.push_back((unsigned char)P);
+
+    // Emit the finished record.
+    Stream.EmitRecord(Code, NameVals, AbbrevToUse);
+    NameVals.clear();
+  }
+
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::writeUseList(UseListOrder &&Order) {
+  assert(Order.Shuffle.size() >= 2 && "Shuffle too small");
+  unsigned Code;
+  if (isa<BasicBlock>(Order.V))
+    Code = bitc::USELIST_CODE_BB;
+  else
+    Code = bitc::USELIST_CODE_DEFAULT;
+
+  SmallVector<uint64_t, 64> Record(Order.Shuffle.begin(), Order.Shuffle.end());
+  Record.push_back(VE.getValueID(Order.V));
+  Stream.EmitRecord(Code, Record);
+}
+
+void ModuleBitcodeWriter::writeUseListBlock(const Function *F) {
+  assert(VE.shouldPreserveUseListOrder() &&
+         "Expected to be preserving use-list order");
+
+  auto hasMore = [&]() {
+    return !VE.UseListOrders.empty() && VE.UseListOrders.back().F == F;
+  };
+  if (!hasMore())
+    // Nothing to do.
+    return;
+
+  Stream.EnterSubblock(bitc::USELIST_BLOCK_ID, 3);
+  while (hasMore()) {
+    writeUseList(std::move(VE.UseListOrders.back()));
+    VE.UseListOrders.pop_back();
+  }
+  Stream.ExitBlock();
+}
+
+/// Emit a function body to the module stream.
+void ModuleBitcodeWriter::writeFunction(
+    const Function &F,
+    DenseMap<const Function *, uint64_t> &FunctionToBitcodeIndex) {
+  // Save the bitcode index of the start of this function block for recording
+  // in the VST.
+  FunctionToBitcodeIndex[&F] = Stream.GetCurrentBitNo();
+
+  Stream.EnterSubblock(bitc::FUNCTION_BLOCK_ID, 4);
+  VE.incorporateFunction(F);
+
+  SmallVector<unsigned, 64> Vals;
+
+  // Emit the number of basic blocks, so the reader can create them ahead of
+  // time.
+  Vals.push_back(VE.getBasicBlocks().size());
+  Stream.EmitRecord(bitc::FUNC_CODE_DECLAREBLOCKS, Vals);
+  Vals.clear();
+
+  // If there are function-local constants, emit them now.
+  unsigned CstStart, CstEnd;
+  VE.getFunctionConstantRange(CstStart, CstEnd);
+  writeConstants(CstStart, CstEnd, false);
+
+  // If there is function-local metadata, emit it now.
+  writeFunctionMetadata(F);
+
+  // Keep a running idea of what the instruction ID is.
+  unsigned InstID = CstEnd;
+
+  bool NeedsMetadataAttachment = F.hasMetadata();
+
+  DILocation *LastDL = nullptr;
+  SmallSetVector<Function *, 4> BlockAddressUsers;
+
+  // Finally, emit all the instructions, in order.
+  for (const BasicBlock &BB : F) {
+    for (const Instruction &I : BB) {
+      writeInstruction(I, InstID, Vals);
+
+      if (!I.getType()->isVoidTy())
+        ++InstID;
+
+      // If the instruction has metadata, write a metadata attachment later.
+      NeedsMetadataAttachment |= I.hasMetadataOtherThanDebugLoc();
+
+      // If the instruction has a debug location, emit it.
+      DILocation *DL = I.getDebugLoc();
+      if (!DL)
+        continue;
+
+      if (DL == LastDL) {
+        // Just repeat the same debug loc as last time.
+        Stream.EmitRecord(bitc::FUNC_CODE_DEBUG_LOC_AGAIN, Vals);
+        continue;
+      }
+
+      Vals.push_back(DL->getLine());
+      Vals.push_back(DL->getColumn());
+      Vals.push_back(VE.getMetadataOrNullID(DL->getScope()));
+      Vals.push_back(VE.getMetadataOrNullID(DL->getInlinedAt()));
+      Vals.push_back(DL->isImplicitCode());
+      Stream.EmitRecord(bitc::FUNC_CODE_DEBUG_LOC, Vals);
+      Vals.clear();
+
+      LastDL = DL;
+    }
+
+    if (BlockAddress *BA = BlockAddress::lookup(&BB)) {
+      SmallVector<Value *> Worklist{BA};
+      SmallPtrSet<Value *, 8> Visited{BA};
+      while (!Worklist.empty()) {
+        Value *V = Worklist.pop_back_val();
+        for (User *U : V->users()) {
+          if (auto *I = dyn_cast<Instruction>(U)) {
+            Function *P = I->getFunction();
+            if (P != &F)
+              BlockAddressUsers.insert(P);
+          } else if (isa<Constant>(U) && !isa<GlobalValue>(U) &&
+                     Visited.insert(U).second)
+            Worklist.push_back(U);
+        }
+      }
+    }
+  }
+
+  if (!BlockAddressUsers.empty()) {
+    Vals.resize(BlockAddressUsers.size());
+    for (auto I : llvm::enumerate(BlockAddressUsers))
+      Vals[I.index()] = VE.getValueID(I.value());
+    Stream.EmitRecord(bitc::FUNC_CODE_BLOCKADDR_USERS, Vals);
+    Vals.clear();
+  }
+
+  // Emit names for all the instructions etc.
+  if (auto *Symtab = F.getValueSymbolTable())
+    writeFunctionLevelValueSymbolTable(*Symtab);
+
+  if (NeedsMetadataAttachment)
+    writeFunctionMetadataAttachment(F);
+  if (VE.shouldPreserveUseListOrder())
+    writeUseListBlock(&F);
+  VE.purgeFunction();
+  Stream.ExitBlock();
+}
+
+// Emit blockinfo, which defines the standard abbreviations etc.
+void ModuleBitcodeWriter::writeBlockInfo() {
+  // We only want to emit block info records for blocks that have multiple
+  // instances: CONSTANTS_BLOCK, FUNCTION_BLOCK and VALUE_SYMTAB_BLOCK.
+  // Other blocks can define their abbrevs inline.
+  Stream.EnterBlockInfoBlock();
+
+  { // 8-bit fixed-width VST_CODE_ENTRY/VST_CODE_BBENTRY strings.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 3));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8));
+    if (Stream.EmitBlockInfoAbbrev(bitc::VALUE_SYMTAB_BLOCK_ID, Abbv) !=
+        VST_ENTRY_8_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+
+  { // 7-bit fixed width VST_CODE_ENTRY strings.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::VST_CODE_ENTRY));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 7));
+    if (Stream.EmitBlockInfoAbbrev(bitc::VALUE_SYMTAB_BLOCK_ID, Abbv) !=
+        VST_ENTRY_7_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // 6-bit char6 VST_CODE_ENTRY strings.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::VST_CODE_ENTRY));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Char6));
+    if (Stream.EmitBlockInfoAbbrev(bitc::VALUE_SYMTAB_BLOCK_ID, Abbv) !=
+        VST_ENTRY_6_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // 6-bit char6 VST_CODE_BBENTRY strings.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::VST_CODE_BBENTRY));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Char6));
+    if (Stream.EmitBlockInfoAbbrev(bitc::VALUE_SYMTAB_BLOCK_ID, Abbv) !=
+        VST_BBENTRY_6_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+
+  { // SETTYPE abbrev for CONSTANTS_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::CST_CODE_SETTYPE));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed,
+                              VE.computeBitsRequiredForTypeIndicies()));
+    if (Stream.EmitBlockInfoAbbrev(bitc::CONSTANTS_BLOCK_ID, Abbv) !=
+        CONSTANTS_SETTYPE_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+
+  { // INTEGER abbrev for CONSTANTS_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::CST_CODE_INTEGER));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    if (Stream.EmitBlockInfoAbbrev(bitc::CONSTANTS_BLOCK_ID, Abbv) !=
+        CONSTANTS_INTEGER_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+
+  { // CE_CAST abbrev for CONSTANTS_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::CST_CODE_CE_CAST));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 4));  // cast opc
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed,       // typeid
+                              VE.computeBitsRequiredForTypeIndicies()));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));    // value id
+
+    if (Stream.EmitBlockInfoAbbrev(bitc::CONSTANTS_BLOCK_ID, Abbv) !=
+        CONSTANTS_CE_CAST_Abbrev)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // NULL abbrev for CONSTANTS_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::CST_CODE_NULL));
+    if (Stream.EmitBlockInfoAbbrev(bitc::CONSTANTS_BLOCK_ID, Abbv) !=
+        CONSTANTS_NULL_Abbrev)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+
+  // FIXME: This should only use space for first class types!
+
+  { // INST_LOAD abbrev for FUNCTION_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_LOAD));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Ptr
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed,    // dest ty
+                              VE.computeBitsRequiredForTypeIndicies()));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // Align
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // volatile
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_LOAD_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // INST_UNOP abbrev for FUNCTION_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_UNOP));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LHS
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 4)); // opc
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_UNOP_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // INST_UNOP_FLAGS abbrev for FUNCTION_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_UNOP));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LHS
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 4)); // opc
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8)); // flags
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_UNOP_FLAGS_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // INST_BINOP abbrev for FUNCTION_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_BINOP));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LHS
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // RHS
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 4)); // opc
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_BINOP_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // INST_BINOP_FLAGS abbrev for FUNCTION_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_BINOP));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // LHS
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // RHS
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 4)); // opc
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8)); // flags
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_BINOP_FLAGS_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // INST_CAST abbrev for FUNCTION_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_CAST));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));    // OpVal
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed,       // dest ty
+                              VE.computeBitsRequiredForTypeIndicies()));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 4));  // opc
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_CAST_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+
+  { // INST_RET abbrev for FUNCTION_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_RET));
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_RET_VOID_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // INST_RET abbrev for FUNCTION_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_RET));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // ValID
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_RET_VAL_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // INST_UNREACHABLE abbrev for FUNCTION_BLOCK.
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_UNREACHABLE));
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_UNREACHABLE_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  {
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_GEP));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, // dest ty
+                              Log2_32_Ceil(VE.getTypes().size() + 1)));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
+    if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID, Abbv) !=
+        FUNCTION_INST_GEP_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+
+  Stream.ExitBlock();
+}
+
+/// Write the module path strings, currently only used when generating
+/// a combined index file.
+void IndexBitcodeWriter::writeModStrings() {
+  Stream.EnterSubblock(bitc::MODULE_STRTAB_BLOCK_ID, 3);
+
+  // TODO: See which abbrev sizes we actually need to emit
+
+  // 8-bit fixed-width MST_ENTRY strings.
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::MST_CODE_ENTRY));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8));
+  unsigned Abbrev8Bit = Stream.EmitAbbrev(std::move(Abbv));
+
+  // 7-bit fixed width MST_ENTRY strings.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::MST_CODE_ENTRY));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 7));
+  unsigned Abbrev7Bit = Stream.EmitAbbrev(std::move(Abbv));
+
+  // 6-bit char6 MST_ENTRY strings.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::MST_CODE_ENTRY));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Char6));
+  unsigned Abbrev6Bit = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Module Hash, 160 bits SHA1. Optionally, emitted after each MST_CODE_ENTRY.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::MST_CODE_HASH));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+  unsigned AbbrevHash = Stream.EmitAbbrev(std::move(Abbv));
+
+  SmallVector<unsigned, 64> Vals;
+  forEachModule(
+      [&](const StringMapEntry<std::pair<uint64_t, ModuleHash>> &MPSE) {
+        StringRef Key = MPSE.getKey();
+        const auto &Value = MPSE.getValue();
+        StringEncoding Bits = getStringEncoding(Key);
+        unsigned AbbrevToUse = Abbrev8Bit;
+        if (Bits == SE_Char6)
+          AbbrevToUse = Abbrev6Bit;
+        else if (Bits == SE_Fixed7)
+          AbbrevToUse = Abbrev7Bit;
+
+        Vals.push_back(Value.first);
+        Vals.append(Key.begin(), Key.end());
+
+        // Emit the finished record.
+        Stream.EmitRecord(bitc::MST_CODE_ENTRY, Vals, AbbrevToUse);
+
+        // Emit an optional hash for the module now
+        const auto &Hash = Value.second;
+        if (llvm::any_of(Hash, [](uint32_t H) { return H; })) {
+          Vals.assign(Hash.begin(), Hash.end());
+          // Emit the hash record.
+          Stream.EmitRecord(bitc::MST_CODE_HASH, Vals, AbbrevHash);
+        }
+
+        Vals.clear();
+      });
+  Stream.ExitBlock();
+}
+
+/// Write the function type metadata related records that need to appear before
+/// a function summary entry (whether per-module or combined).
+template <typename Fn>
+static void writeFunctionTypeMetadataRecords(BitstreamWriter &Stream,
+                                             FunctionSummary *FS,
+                                             Fn GetValueID) {
+  if (!FS->type_tests().empty())
+    Stream.EmitRecord(bitc::FS_TYPE_TESTS, FS->type_tests());
+
+  SmallVector<uint64_t, 64> Record;
+
+  auto WriteVFuncIdVec = [&](uint64_t Ty,
+                             ArrayRef<FunctionSummary::VFuncId> VFs) {
+    if (VFs.empty())
+      return;
+    Record.clear();
+    for (auto &VF : VFs) {
+      Record.push_back(VF.GUID);
+      Record.push_back(VF.Offset);
+    }
+    Stream.EmitRecord(Ty, Record);
+  };
+
+  WriteVFuncIdVec(bitc::FS_TYPE_TEST_ASSUME_VCALLS,
+                  FS->type_test_assume_vcalls());
+  WriteVFuncIdVec(bitc::FS_TYPE_CHECKED_LOAD_VCALLS,
+                  FS->type_checked_load_vcalls());
+
+  auto WriteConstVCallVec = [&](uint64_t Ty,
+                                ArrayRef<FunctionSummary::ConstVCall> VCs) {
+    for (auto &VC : VCs) {
+      Record.clear();
+      Record.push_back(VC.VFunc.GUID);
+      Record.push_back(VC.VFunc.Offset);
+      llvm::append_range(Record, VC.Args);
+      Stream.EmitRecord(Ty, Record);
+    }
+  };
+
+  WriteConstVCallVec(bitc::FS_TYPE_TEST_ASSUME_CONST_VCALL,
+                     FS->type_test_assume_const_vcalls());
+  WriteConstVCallVec(bitc::FS_TYPE_CHECKED_LOAD_CONST_VCALL,
+                     FS->type_checked_load_const_vcalls());
+
+  auto WriteRange = [&](ConstantRange Range) {
+    Range = Range.sextOrTrunc(FunctionSummary::ParamAccess::RangeWidth);
+    assert(Range.getLower().getNumWords() == 1);
+    assert(Range.getUpper().getNumWords() == 1);
+    emitSignedInt64(Record, *Range.getLower().getRawData());
+    emitSignedInt64(Record, *Range.getUpper().getRawData());
+  };
+
+  if (!FS->paramAccesses().empty()) {
+    Record.clear();
+    for (auto &Arg : FS->paramAccesses()) {
+      size_t UndoSize = Record.size();
+      Record.push_back(Arg.ParamNo);
+      WriteRange(Arg.Use);
+      Record.push_back(Arg.Calls.size());
+      for (auto &Call : Arg.Calls) {
+        Record.push_back(Call.ParamNo);
+        std::optional<unsigned> ValueID = GetValueID(Call.Callee);
+        if (!ValueID) {
+          // If ValueID is unknown we can't drop just this call, we must drop
+          // entire parameter.
+          Record.resize(UndoSize);
+          break;
+        }
+        Record.push_back(*ValueID);
+        WriteRange(Call.Offsets);
+      }
+    }
+    if (!Record.empty())
+      Stream.EmitRecord(bitc::FS_PARAM_ACCESS, Record);
+  }
+}
+
+/// Collect type IDs from type tests used by function.
+static void
+getReferencedTypeIds(FunctionSummary *FS,
+                     std::set<GlobalValue::GUID> &ReferencedTypeIds) {
+  if (!FS->type_tests().empty())
+    for (auto &TT : FS->type_tests())
+      ReferencedTypeIds.insert(TT);
+
+  auto GetReferencedTypesFromVFuncIdVec =
+      [&](ArrayRef<FunctionSummary::VFuncId> VFs) {
+        for (auto &VF : VFs)
+          ReferencedTypeIds.insert(VF.GUID);
+      };
+
+  GetReferencedTypesFromVFuncIdVec(FS->type_test_assume_vcalls());
+  GetReferencedTypesFromVFuncIdVec(FS->type_checked_load_vcalls());
+
+  auto GetReferencedTypesFromConstVCallVec =
+      [&](ArrayRef<FunctionSummary::ConstVCall> VCs) {
+        for (auto &VC : VCs)
+          ReferencedTypeIds.insert(VC.VFunc.GUID);
+      };
+
+  GetReferencedTypesFromConstVCallVec(FS->type_test_assume_const_vcalls());
+  GetReferencedTypesFromConstVCallVec(FS->type_checked_load_const_vcalls());
+}
+
+static void writeWholeProgramDevirtResolutionByArg(
+    SmallVector<uint64_t, 64> &NameVals, const std::vector<uint64_t> &args,
+    const WholeProgramDevirtResolution::ByArg &ByArg) {
+  NameVals.push_back(args.size());
+  llvm::append_range(NameVals, args);
+
+  NameVals.push_back(ByArg.TheKind);
+  NameVals.push_back(ByArg.Info);
+  NameVals.push_back(ByArg.Byte);
+  NameVals.push_back(ByArg.Bit);
+}
+
+static void writeWholeProgramDevirtResolution(
+    SmallVector<uint64_t, 64> &NameVals, StringTableBuilder &StrtabBuilder,
+    uint64_t Id, const WholeProgramDevirtResolution &Wpd) {
+  NameVals.push_back(Id);
+
+  NameVals.push_back(Wpd.TheKind);
+  NameVals.push_back(StrtabBuilder.add(Wpd.SingleImplName));
+  NameVals.push_back(Wpd.SingleImplName.size());
+
+  NameVals.push_back(Wpd.ResByArg.size());
+  for (auto &A : Wpd.ResByArg)
+    writeWholeProgramDevirtResolutionByArg(NameVals, A.first, A.second);
+}
+
+static void writeTypeIdSummaryRecord(SmallVector<uint64_t, 64> &NameVals,
+                                     StringTableBuilder &StrtabBuilder,
+                                     const std::string &Id,
+                                     const TypeIdSummary &Summary) {
+  NameVals.push_back(StrtabBuilder.add(Id));
+  NameVals.push_back(Id.size());
+
+  NameVals.push_back(Summary.TTRes.TheKind);
+  NameVals.push_back(Summary.TTRes.SizeM1BitWidth);
+  NameVals.push_back(Summary.TTRes.AlignLog2);
+  NameVals.push_back(Summary.TTRes.SizeM1);
+  NameVals.push_back(Summary.TTRes.BitMask);
+  NameVals.push_back(Summary.TTRes.InlineBits);
+
+  for (auto &W : Summary.WPDRes)
+    writeWholeProgramDevirtResolution(NameVals, StrtabBuilder, W.first,
+                                      W.second);
+}
+
+static void writeTypeIdCompatibleVtableSummaryRecord(
+    SmallVector<uint64_t, 64> &NameVals, StringTableBuilder &StrtabBuilder,
+    const std::string &Id, const TypeIdCompatibleVtableInfo &Summary,
+    ValueEnumerator &VE) {
+  NameVals.push_back(StrtabBuilder.add(Id));
+  NameVals.push_back(Id.size());
+
+  for (auto &P : Summary) {
+    NameVals.push_back(P.AddressPointOffset);
+    NameVals.push_back(VE.getValueID(P.VTableVI.getValue()));
+  }
+}
+
+static void writeFunctionHeapProfileRecords(
+    BitstreamWriter &Stream, FunctionSummary *FS, unsigned CallsiteAbbrev,
+    unsigned AllocAbbrev, bool PerModule,
+    std::function<unsigned(const ValueInfo &VI)> GetValueID,
+    std::function<unsigned(unsigned)> GetStackIndex) {
+  SmallVector<uint64_t> Record;
+
+  for (auto &CI : FS->callsites()) {
+    Record.clear();
+    // Per module callsite clones should always have a single entry of
+    // value 0.
+    assert(!PerModule || (CI.Clones.size() == 1 && CI.Clones[0] == 0));
+    Record.push_back(GetValueID(CI.Callee));
+    if (!PerModule) {
+      Record.push_back(CI.StackIdIndices.size());
+      Record.push_back(CI.Clones.size());
+    }
+    for (auto Id : CI.StackIdIndices)
+      Record.push_back(GetStackIndex(Id));
+    if (!PerModule) {
+      for (auto V : CI.Clones)
+        Record.push_back(V);
+    }
+    Stream.EmitRecord(PerModule ? bitc::FS_PERMODULE_CALLSITE_INFO
+                                : bitc::FS_COMBINED_CALLSITE_INFO,
+                      Record, CallsiteAbbrev);
+  }
+
+  for (auto &AI : FS->allocs()) {
+    Record.clear();
+    // Per module alloc versions should always have a single entry of
+    // value 0.
+    assert(!PerModule || (AI.Versions.size() == 1 && AI.Versions[0] == 0));
+    if (!PerModule) {
+      Record.push_back(AI.MIBs.size());
+      Record.push_back(AI.Versions.size());
+    }
+    for (auto &MIB : AI.MIBs) {
+      Record.push_back((uint8_t)MIB.AllocType);
+      Record.push_back(MIB.StackIdIndices.size());
+      for (auto Id : MIB.StackIdIndices)
+        Record.push_back(GetStackIndex(Id));
+    }
+    if (!PerModule) {
+      for (auto V : AI.Versions)
+        Record.push_back(V);
+    }
+    Stream.EmitRecord(PerModule ? bitc::FS_PERMODULE_ALLOC_INFO
+                                : bitc::FS_COMBINED_ALLOC_INFO,
+                      Record, AllocAbbrev);
+  }
+}
+
+// Helper to emit a single function summary record.
+void ModuleBitcodeWriterBase::writePerModuleFunctionSummaryRecord(
+    SmallVector<uint64_t, 64> &NameVals, GlobalValueSummary *Summary,
+    unsigned ValueID, unsigned FSCallsAbbrev, unsigned FSCallsProfileAbbrev,
+    unsigned CallsiteAbbrev, unsigned AllocAbbrev, const Function &F) {
+  NameVals.push_back(ValueID);
+
+  FunctionSummary *FS = cast<FunctionSummary>(Summary);
+
+  writeFunctionTypeMetadataRecords(
+      Stream, FS, [&](const ValueInfo &VI) -> std::optional<unsigned> {
+        return {VE.getValueID(VI.getValue())};
+      });
+
+  writeFunctionHeapProfileRecords(
+      Stream, FS, CallsiteAbbrev, AllocAbbrev,
+      /*PerModule*/ true,
+      /*GetValueId*/ [&](const ValueInfo &VI) { return getValueId(VI); },
+      /*GetStackIndex*/ [&](unsigned I) { return I; });
+
+  auto SpecialRefCnts = FS->specialRefCounts();
+  NameVals.push_back(getEncodedGVSummaryFlags(FS->flags()));
+  NameVals.push_back(FS->instCount());
+  NameVals.push_back(getEncodedFFlags(FS->fflags()));
+  NameVals.push_back(FS->refs().size());
+  NameVals.push_back(SpecialRefCnts.first);  // rorefcnt
+  NameVals.push_back(SpecialRefCnts.second); // worefcnt
+
+  for (auto &RI : FS->refs())
+    NameVals.push_back(VE.getValueID(RI.getValue()));
+
+  bool HasProfileData =
+      F.hasProfileData() || ForceSummaryEdgesCold != FunctionSummary::FSHT_None;
+  for (auto &ECI : FS->calls()) {
+    NameVals.push_back(getValueId(ECI.first));
+    if (HasProfileData)
+      NameVals.push_back(static_cast<uint8_t>(ECI.second.Hotness));
+    else if (WriteRelBFToSummary)
+      NameVals.push_back(ECI.second.RelBlockFreq);
+  }
+
+  unsigned FSAbbrev = (HasProfileData ? FSCallsProfileAbbrev : FSCallsAbbrev);
+  unsigned Code =
+      (HasProfileData ? bitc::FS_PERMODULE_PROFILE
+                      : (WriteRelBFToSummary ? bitc::FS_PERMODULE_RELBF
+                                             : bitc::FS_PERMODULE));
+
+  // Emit the finished record.
+  Stream.EmitRecord(Code, NameVals, FSAbbrev);
+  NameVals.clear();
+}
+
+// Collect the global value references in the given variable's initializer,
+// and emit them in a summary record.
+void ModuleBitcodeWriterBase::writeModuleLevelReferences(
+    const GlobalVariable &V, SmallVector<uint64_t, 64> &NameVals,
+    unsigned FSModRefsAbbrev, unsigned FSModVTableRefsAbbrev) {
+  auto VI = Index->getValueInfo(V.getGUID());
+  if (!VI || VI.getSummaryList().empty()) {
+    // Only declarations should not have a summary (a declaration might however
+    // have a summary if the def was in module level asm).
+    assert(V.isDeclaration());
+    return;
+  }
+  auto *Summary = VI.getSummaryList()[0].get();
+  NameVals.push_back(VE.getValueID(&V));
+  GlobalVarSummary *VS = cast<GlobalVarSummary>(Summary);
+  NameVals.push_back(getEncodedGVSummaryFlags(VS->flags()));
+  NameVals.push_back(getEncodedGVarFlags(VS->varflags()));
+
+  auto VTableFuncs = VS->vTableFuncs();
+  if (!VTableFuncs.empty())
+    NameVals.push_back(VS->refs().size());
+
+  unsigned SizeBeforeRefs = NameVals.size();
+  for (auto &RI : VS->refs())
+    NameVals.push_back(VE.getValueID(RI.getValue()));
+  // Sort the refs for determinism output, the vector returned by FS->refs() has
+  // been initialized from a DenseSet.
+  llvm::sort(drop_begin(NameVals, SizeBeforeRefs));
+
+  if (VTableFuncs.empty())
+    Stream.EmitRecord(bitc::FS_PERMODULE_GLOBALVAR_INIT_REFS, NameVals,
+                      FSModRefsAbbrev);
+  else {
+    // VTableFuncs pairs should already be sorted by offset.
+    for (auto &P : VTableFuncs) {
+      NameVals.push_back(VE.getValueID(P.FuncVI.getValue()));
+      NameVals.push_back(P.VTableOffset);
+    }
+
+    Stream.EmitRecord(bitc::FS_PERMODULE_VTABLE_GLOBALVAR_INIT_REFS, NameVals,
+                      FSModVTableRefsAbbrev);
+  }
+  NameVals.clear();
+}
+
+/// Emit the per-module summary section alongside the rest of
+/// the module's bitcode.
+void ModuleBitcodeWriterBase::writePerModuleGlobalValueSummary() {
+  // By default we compile with ThinLTO if the module has a summary, but the
+  // client can request full LTO with a module flag.
+  bool IsThinLTO = true;
+  if (auto *MD =
+          mdconst::extract_or_null<ConstantInt>(M.getModuleFlag("ThinLTO")))
+    IsThinLTO = MD->getZExtValue();
+  Stream.EnterSubblock(IsThinLTO ? bitc::GLOBALVAL_SUMMARY_BLOCK_ID
+                                 : bitc::FULL_LTO_GLOBALVAL_SUMMARY_BLOCK_ID,
+                       4);
+
+  Stream.EmitRecord(
+      bitc::FS_VERSION,
+      ArrayRef<uint64_t>{ModuleSummaryIndex::BitcodeSummaryVersion});
+
+  // Write the index flags.
+  uint64_t Flags = 0;
+  // Bits 1-3 are set only in the combined index, skip them.
+  if (Index->enableSplitLTOUnit())
+    Flags |= 0x8;
+  Stream.EmitRecord(bitc::FS_FLAGS, ArrayRef<uint64_t>{Flags});
+
+  if (Index->begin() == Index->end()) {
+    Stream.ExitBlock();
+    return;
+  }
+
+  for (const auto &GVI : valueIds()) {
+    Stream.EmitRecord(bitc::FS_VALUE_GUID,
+                      ArrayRef<uint64_t>{GVI.second, GVI.first});
+  }
+
+  if (!Index->stackIds().empty()) {
+    auto StackIdAbbv = std::make_shared<BitCodeAbbrev>();
+    StackIdAbbv->Add(BitCodeAbbrevOp(bitc::FS_STACK_IDS));
+    // numids x stackid
+    StackIdAbbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    StackIdAbbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    unsigned StackIdAbbvId = Stream.EmitAbbrev(std::move(StackIdAbbv));
+    Stream.EmitRecord(bitc::FS_STACK_IDS, Index->stackIds(), StackIdAbbvId);
+  }
+
+  // Abbrev for FS_PERMODULE_PROFILE.
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_PERMODULE_PROFILE));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // fflags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // rorefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // worefcnt
+  // numrefs x valueid, n x (valueid, hotness)
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned FSCallsProfileAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for FS_PERMODULE or FS_PERMODULE_RELBF.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  if (WriteRelBFToSummary)
+    Abbv->Add(BitCodeAbbrevOp(bitc::FS_PERMODULE_RELBF));
+  else
+    Abbv->Add(BitCodeAbbrevOp(bitc::FS_PERMODULE));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // fflags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // rorefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // worefcnt
+  // numrefs x valueid, n x (valueid [, rel_block_freq])
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned FSCallsAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for FS_PERMODULE_GLOBALVAR_INIT_REFS.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_PERMODULE_GLOBALVAR_INIT_REFS));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // flags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));  // valueids
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned FSModRefsAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for FS_PERMODULE_VTABLE_GLOBALVAR_INIT_REFS.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_PERMODULE_VTABLE_GLOBALVAR_INIT_REFS));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // flags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // numrefs
+  // numrefs x valueid, n x (valueid , offset)
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned FSModVTableRefsAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for FS_ALIAS.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_ALIAS));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
+  unsigned FSAliasAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for FS_TYPE_ID_METADATA
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_TYPE_ID_METADATA));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // typeid strtab index
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // typeid length
+  // n x (valueid , offset)
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned TypeIdCompatibleVtableAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_PERMODULE_CALLSITE_INFO));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // valueid
+  // n x stackidindex
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned CallsiteAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_PERMODULE_ALLOC_INFO));
+  // n x (alloc type, numstackids, numstackids x stackidindex)
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned AllocAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  SmallVector<uint64_t, 64> NameVals;
+  // Iterate over the list of functions instead of the Index to
+  // ensure the ordering is stable.
+  for (const Function &F : M) {
+    // Summary emission does not support anonymous functions, they have to
+    // renamed using the anonymous function renaming pass.
+    if (!F.hasName())
+      report_fatal_error("Unexpected anonymous function when writing summary");
+
+    ValueInfo VI = Index->getValueInfo(F.getGUID());
+    if (!VI || VI.getSummaryList().empty()) {
+      // Only declarations should not have a summary (a declaration might
+      // however have a summary if the def was in module level asm).
+      assert(F.isDeclaration());
+      continue;
+    }
+    auto *Summary = VI.getSummaryList()[0].get();
+    writePerModuleFunctionSummaryRecord(NameVals, Summary, VE.getValueID(&F),
+                                        FSCallsAbbrev, FSCallsProfileAbbrev,
+                                        CallsiteAbbrev, AllocAbbrev, F);
+  }
+
+  // Capture references from GlobalVariable initializers, which are outside
+  // of a function scope.
+  for (const GlobalVariable &G : M.globals())
+    writeModuleLevelReferences(G, NameVals, FSModRefsAbbrev,
+                               FSModVTableRefsAbbrev);
+
+  for (const GlobalAlias &A : M.aliases()) {
+    auto *Aliasee = A.getAliaseeObject();
+    // Skip ifunc and nameless functions which don't have an entry in the
+    // summary.
+    if (!Aliasee->hasName() || isa<GlobalIFunc>(Aliasee))
+      continue;
+    auto AliasId = VE.getValueID(&A);
+    auto AliaseeId = VE.getValueID(Aliasee);
+    NameVals.push_back(AliasId);
+    auto *Summary = Index->getGlobalValueSummary(A);
+    AliasSummary *AS = cast<AliasSummary>(Summary);
+    NameVals.push_back(getEncodedGVSummaryFlags(AS->flags()));
+    NameVals.push_back(AliaseeId);
+    Stream.EmitRecord(bitc::FS_ALIAS, NameVals, FSAliasAbbrev);
+    NameVals.clear();
+  }
+
+  for (auto &S : Index->typeIdCompatibleVtableMap()) {
+    writeTypeIdCompatibleVtableSummaryRecord(NameVals, StrtabBuilder, S.first,
+                                             S.second, VE);
+    Stream.EmitRecord(bitc::FS_TYPE_ID_METADATA, NameVals,
+                      TypeIdCompatibleVtableAbbrev);
+    NameVals.clear();
+  }
+
+  Stream.EmitRecord(bitc::FS_BLOCK_COUNT,
+                    ArrayRef<uint64_t>{Index->getBlockCount()});
+
+  Stream.ExitBlock();
+}
+
+/// Emit the combined summary section into the combined index file.
+void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
+  Stream.EnterSubblock(bitc::GLOBALVAL_SUMMARY_BLOCK_ID, 4);
+  Stream.EmitRecord(
+      bitc::FS_VERSION,
+      ArrayRef<uint64_t>{ModuleSummaryIndex::BitcodeSummaryVersion});
+
+  // Write the index flags.
+  Stream.EmitRecord(bitc::FS_FLAGS, ArrayRef<uint64_t>{Index.getFlags()});
+
+  for (const auto &GVI : valueIds()) {
+    Stream.EmitRecord(bitc::FS_VALUE_GUID,
+                      ArrayRef<uint64_t>{GVI.second, GVI.first});
+  }
+
+  if (!StackIdIndices.empty()) {
+    auto StackIdAbbv = std::make_shared<BitCodeAbbrev>();
+    StackIdAbbv->Add(BitCodeAbbrevOp(bitc::FS_STACK_IDS));
+    // numids x stackid
+    StackIdAbbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    StackIdAbbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    unsigned StackIdAbbvId = Stream.EmitAbbrev(std::move(StackIdAbbv));
+    // Write the stack ids used by this index, which will be a subset of those in
+    // the full index in the case of distributed indexes.
+    std::vector<uint64_t> StackIds;
+    for (auto &I : StackIdIndices)
+      StackIds.push_back(Index.getStackIdAtIndex(I));
+    Stream.EmitRecord(bitc::FS_STACK_IDS, StackIds, StackIdAbbvId);
+  }
+
+  // Abbrev for FS_COMBINED.
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // modid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // fflags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // entrycount
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // rorefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // worefcnt
+  // numrefs x valueid, n x (valueid)
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned FSCallsAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for FS_COMBINED_PROFILE.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED_PROFILE));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // modid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // fflags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // entrycount
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // rorefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // worefcnt
+  // numrefs x valueid, n x (valueid, hotness)
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned FSCallsProfileAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for FS_COMBINED_GLOBALVAR_INIT_REFS.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED_GLOBALVAR_INIT_REFS));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // modid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));    // valueids
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned FSModRefsAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // Abbrev for FS_COMBINED_ALIAS.
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED_ALIAS));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // modid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
+  unsigned FSAliasAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED_CALLSITE_INFO));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // valueid
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // numstackindices
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // numver
+  // numstackindices x stackidindex, numver x version
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned CallsiteAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED_ALLOC_INFO));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // nummib
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // numver
+  // nummib x (alloc type, numstackids, numstackids x stackidindex),
+  // numver x version
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+  unsigned AllocAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+  // The aliases are emitted as a post-pass, and will point to the value
+  // id of the aliasee. Save them in a vector for post-processing.
+  SmallVector<AliasSummary *, 64> Aliases;
+
+  // Save the value id for each summary for alias emission.
+  DenseMap<const GlobalValueSummary *, unsigned> SummaryToValueIdMap;
+
+  SmallVector<uint64_t, 64> NameVals;
+
+  // Set that will be populated during call to writeFunctionTypeMetadataRecords
+  // with the type ids referenced by this index file.
+  std::set<GlobalValue::GUID> ReferencedTypeIds;
+
+  // For local linkage, we also emit the original name separately
+  // immediately after the record.
+  auto MaybeEmitOriginalName = [&](GlobalValueSummary &S) {
+    // We don't need to emit the original name if we are writing the index for
+    // distributed backends (in which case ModuleToSummariesForIndex is
+    // non-null). The original name is only needed during the thin link, since
+    // for SamplePGO the indirect call targets for local functions have
+    // have the original name annotated in profile.
+    // Continue to emit it when writing out the entire combined index, which is
+    // used in testing the thin link via llvm-lto.
+    if (ModuleToSummariesForIndex || !GlobalValue::isLocalLinkage(S.linkage()))
+      return;
+    NameVals.push_back(S.getOriginalName());
+    Stream.EmitRecord(bitc::FS_COMBINED_ORIGINAL_NAME, NameVals);
+    NameVals.clear();
+  };
+
+  std::set<GlobalValue::GUID> DefOrUseGUIDs;
+  forEachSummary([&](GVInfo I, bool IsAliasee) {
+    GlobalValueSummary *S = I.second;
+    assert(S);
+    DefOrUseGUIDs.insert(I.first);
+    for (const ValueInfo &VI : S->refs())
+      DefOrUseGUIDs.insert(VI.getGUID());
+
+    auto ValueId = getValueId(I.first);
+    assert(ValueId);
+    SummaryToValueIdMap[S] = *ValueId;
+
+    // If this is invoked for an aliasee, we want to record the above
+    // mapping, but then not emit a summary entry (if the aliasee is
+    // to be imported, we will invoke this separately with IsAliasee=false).
+    if (IsAliasee)
+      return;
+
+    if (auto *AS = dyn_cast<AliasSummary>(S)) {
+      // Will process aliases as a post-pass because the reader wants all
+      // global to be loaded first.
+      Aliases.push_back(AS);
+      return;
+    }
+
+    if (auto *VS = dyn_cast<GlobalVarSummary>(S)) {
+      NameVals.push_back(*ValueId);
+      NameVals.push_back(Index.getModuleId(VS->modulePath()));
+      NameVals.push_back(getEncodedGVSummaryFlags(VS->flags()));
+      NameVals.push_back(getEncodedGVarFlags(VS->varflags()));
+      for (auto &RI : VS->refs()) {
+        auto RefValueId = getValueId(RI.getGUID());
+        if (!RefValueId)
+          continue;
+        NameVals.push_back(*RefValueId);
+      }
+
+      // Emit the finished record.
+      Stream.EmitRecord(bitc::FS_COMBINED_GLOBALVAR_INIT_REFS, NameVals,
+                        FSModRefsAbbrev);
+      NameVals.clear();
+      MaybeEmitOriginalName(*S);
+      return;
+    }
+
+    auto GetValueId = [&](const ValueInfo &VI) -> std::optional<unsigned> {
+      if (!VI)
+        return std::nullopt;
+      return getValueId(VI.getGUID());
+    };
+
+    auto *FS = cast<FunctionSummary>(S);
+    writeFunctionTypeMetadataRecords(Stream, FS, GetValueId);
+    getReferencedTypeIds(FS, ReferencedTypeIds);
+
+    writeFunctionHeapProfileRecords(
+        Stream, FS, CallsiteAbbrev, AllocAbbrev,
+        /*PerModule*/ false,
+        /*GetValueId*/ [&](const ValueInfo &VI) -> unsigned {
+          std::optional<unsigned> ValueID = GetValueId(VI);
+          // This can happen in shared index files for distributed ThinLTO if
+          // the callee function summary is not included. Record 0 which we
+          // will have to deal with conservatively when doing any kind of
+          // validation in the ThinLTO backends.
+          if (!ValueID)
+            return 0;
+          return *ValueID;
+        },
+        /*GetStackIndex*/ [&](unsigned I) {
+          // Get the corresponding index into the list of StackIdIndices
+          // actually being written for this combined index (which may be a
+          // subset in the case of distributed indexes).
+          auto Lower = llvm::lower_bound(StackIdIndices, I);
+          return std::distance(StackIdIndices.begin(), Lower);
+        });
+
+    NameVals.push_back(*ValueId);
+    NameVals.push_back(Index.getModuleId(FS->modulePath()));
+    NameVals.push_back(getEncodedGVSummaryFlags(FS->flags()));
+    NameVals.push_back(FS->instCount());
+    NameVals.push_back(getEncodedFFlags(FS->fflags()));
+    NameVals.push_back(FS->entryCount());
+
+    // Fill in below
+    NameVals.push_back(0); // numrefs
+    NameVals.push_back(0); // rorefcnt
+    NameVals.push_back(0); // worefcnt
+
+    unsigned Count = 0, RORefCnt = 0, WORefCnt = 0;
+    for (auto &RI : FS->refs()) {
+      auto RefValueId = getValueId(RI.getGUID());
+      if (!RefValueId)
+        continue;
+      NameVals.push_back(*RefValueId);
+      if (RI.isReadOnly())
+        RORefCnt++;
+      else if (RI.isWriteOnly())
+        WORefCnt++;
+      Count++;
+    }
+    NameVals[6] = Count;
+    NameVals[7] = RORefCnt;
+    NameVals[8] = WORefCnt;
+
+    bool HasProfileData = false;
+    for (auto &EI : FS->calls()) {
+      HasProfileData |=
+          EI.second.getHotness() != CalleeInfo::HotnessType::Unknown;
+      if (HasProfileData)
+        break;
+    }
+
+    for (auto &EI : FS->calls()) {
+      // If this GUID doesn't have a value id, it doesn't have a function
+      // summary and we don't need to record any calls to it.
+      std::optional<unsigned> CallValueId = GetValueId(EI.first);
+      if (!CallValueId)
+        continue;
+      NameVals.push_back(*CallValueId);
+      if (HasProfileData)
+        NameVals.push_back(static_cast<uint8_t>(EI.second.Hotness));
+    }
+
+    unsigned FSAbbrev = (HasProfileData ? FSCallsProfileAbbrev : FSCallsAbbrev);
+    unsigned Code =
+        (HasProfileData ? bitc::FS_COMBINED_PROFILE : bitc::FS_COMBINED);
+
+    // Emit the finished record.
+    Stream.EmitRecord(Code, NameVals, FSAbbrev);
+    NameVals.clear();
+    MaybeEmitOriginalName(*S);
+  });
+
+  for (auto *AS : Aliases) {
+    auto AliasValueId = SummaryToValueIdMap[AS];
+    assert(AliasValueId);
+    NameVals.push_back(AliasValueId);
+    NameVals.push_back(Index.getModuleId(AS->modulePath()));
+    NameVals.push_back(getEncodedGVSummaryFlags(AS->flags()));
+    auto AliaseeValueId = SummaryToValueIdMap[&AS->getAliasee()];
+    assert(AliaseeValueId);
+    NameVals.push_back(AliaseeValueId);
+
+    // Emit the finished record.
+    Stream.EmitRecord(bitc::FS_COMBINED_ALIAS, NameVals, FSAliasAbbrev);
+    NameVals.clear();
+    MaybeEmitOriginalName(*AS);
+
+    if (auto *FS = dyn_cast<FunctionSummary>(&AS->getAliasee()))
+      getReferencedTypeIds(FS, ReferencedTypeIds);
+  }
+
+  if (!Index.cfiFunctionDefs().empty()) {
+    for (auto &S : Index.cfiFunctionDefs()) {
+      if (DefOrUseGUIDs.count(
+              GlobalValue::getGUID(GlobalValue::dropLLVMManglingEscape(S)))) {
+        NameVals.push_back(StrtabBuilder.add(S));
+        NameVals.push_back(S.size());
+      }
+    }
+    if (!NameVals.empty()) {
+      Stream.EmitRecord(bitc::FS_CFI_FUNCTION_DEFS, NameVals);
+      NameVals.clear();
+    }
+  }
+
+  if (!Index.cfiFunctionDecls().empty()) {
+    for (auto &S : Index.cfiFunctionDecls()) {
+      if (DefOrUseGUIDs.count(
+              GlobalValue::getGUID(GlobalValue::dropLLVMManglingEscape(S)))) {
+        NameVals.push_back(StrtabBuilder.add(S));
+        NameVals.push_back(S.size());
+      }
+    }
+    if (!NameVals.empty()) {
+      Stream.EmitRecord(bitc::FS_CFI_FUNCTION_DECLS, NameVals);
+      NameVals.clear();
+    }
+  }
+
+  // Walk the GUIDs that were referenced, and write the
+  // corresponding type id records.
+  for (auto &T : ReferencedTypeIds) {
+    auto TidIter = Index.typeIds().equal_range(T);
+    for (auto It = TidIter.first; It != TidIter.second; ++It) {
+      writeTypeIdSummaryRecord(NameVals, StrtabBuilder, It->second.first,
+                               It->second.second);
+      Stream.EmitRecord(bitc::FS_TYPE_ID, NameVals);
+      NameVals.clear();
+    }
+  }
+
+  Stream.EmitRecord(bitc::FS_BLOCK_COUNT,
+                    ArrayRef<uint64_t>{Index.getBlockCount()});
+
+  Stream.ExitBlock();
+}
+
+/// Create the "IDENTIFICATION_BLOCK_ID" containing a single string with the
+/// current llvm version, and a record for the epoch number.
+static void writeIdentificationBlock(BitstreamWriter &Stream) {
+  Stream.EnterSubblock(bitc::IDENTIFICATION_BLOCK_ID, 5);
+
+  // Write the "user readable" string identifying the bitcode producer
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::IDENTIFICATION_CODE_STRING));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Char6));
+  auto StringAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+  writeStringRecord(Stream, bitc::IDENTIFICATION_CODE_STRING,
+                    "LLVM" LLVM_VERSION_STRING, StringAbbrev);
+
+  // Write the epoch version
+  Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(bitc::IDENTIFICATION_CODE_EPOCH));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));
+  auto EpochAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+  constexpr std::array<unsigned, 1> Vals = {{bitc::BITCODE_CURRENT_EPOCH}};
+  Stream.EmitRecord(bitc::IDENTIFICATION_CODE_EPOCH, Vals, EpochAbbrev);
+  Stream.ExitBlock();
+}
+
+void ModuleBitcodeWriter::writeModuleHash(size_t BlockStartPos) {
+  // Emit the module's hash.
+  // MODULE_CODE_HASH: [5*i32]
+  if (GenerateHash) {
+    uint32_t Vals[5];
+    Hasher.update(ArrayRef<uint8_t>((const uint8_t *)&(Buffer)[BlockStartPos],
+                                    Buffer.size() - BlockStartPos));
+    std::array<uint8_t, 20> Hash = Hasher.result();
+    for (int Pos = 0; Pos < 20; Pos += 4) {
+      Vals[Pos / 4] = support::endian::read32be(Hash.data() + Pos);
+    }
+
+    // Emit the finished record.
+    Stream.EmitRecord(bitc::MODULE_CODE_HASH, Vals);
+
+    if (ModHash)
+      // Save the written hash value.
+      llvm::copy(Vals, std::begin(*ModHash));
+  }
+}
+
+void ModuleBitcodeWriter::write() {
+  writeIdentificationBlock(Stream);
+
+  Stream.EnterSubblock(bitc::MODULE_BLOCK_ID, 3);
+  size_t BlockStartPos = Buffer.size();
+
+  writeModuleVersion();
+
+  // Emit blockinfo, which defines the standard abbreviations etc.
+  writeBlockInfo();
+
+  // Emit information describing all of the types in the module.
+  writeTypeTable();
+
+  // Emit information about attribute groups.
+  writeAttributeGroupTable();
+
+  // Emit information about parameter attributes.
+  writeAttributeTable();
+
+  writeComdats();
+
+  // Emit top-level description of module, including target triple, inline asm,
+  // descriptors for global variables, and function prototype info.
+  writeModuleInfo();
+
+  // Emit constants.
+  writeModuleConstants();
+
+  // Emit metadata kind names.
+  writeModuleMetadataKinds();
+
+  // Emit metadata.
+  writeModuleMetadata();
+
+  // Emit module-level use-lists.
+  if (VE.shouldPreserveUseListOrder())
+    writeUseListBlock(nullptr);
+
+  writeOperandBundleTags();
+  writeSyncScopeNames();
+
+  // Emit function bodies.
+  DenseMap<const Function *, uint64_t> FunctionToBitcodeIndex;
+  for (const Function &F : M)
+    if (!F.isDeclaration())
+      writeFunction(F, FunctionToBitcodeIndex);
+
+  // Need to write after the above call to WriteFunction which populates
+  // the summary information in the index.
+  if (Index)
+    writePerModuleGlobalValueSummary();
+
+  writeGlobalValueSymbolTable(FunctionToBitcodeIndex);
+
+  writeModuleHash(BlockStartPos);
+
+  Stream.ExitBlock();
+}
+
+static void writeInt32ToBuffer(uint32_t Value, SmallVectorImpl<char> &Buffer,
+                               uint32_t &Position) {
+  support::endian::write32le(&Buffer[Position], Value);
+  Position += 4;
+}
+
+/// If generating a bc file on darwin, we have to emit a
+/// header and trailer to make it compatible with the system archiver.  To do
+/// this we emit the following header, and then emit a trailer that pads the
+/// file out to be a multiple of 16 bytes.
+///
+/// struct bc_header {
+///   uint32_t Magic;         // 0x0B17C0DE
+///   uint32_t Version;       // Version, currently always 0.
+///   uint32_t BitcodeOffset; // Offset to traditional bitcode file.
+///   uint32_t BitcodeSize;   // Size of traditional bitcode file.
+///   uint32_t CPUType;       // CPU specifier.
+///   ... potentially more later ...
+/// };
+static void emitDarwinBCHeaderAndTrailer(SmallVectorImpl<char> &Buffer,
+                                         const Triple &TT) {
+  unsigned CPUType = ~0U;
+
+  // Match x86_64-*, i[3-9]86-*, powerpc-*, powerpc64-*, arm-*, thumb-*,
+  // armv[0-9]-*, thumbv[0-9]-*, armv5te-*, or armv6t2-*. The CPUType is a magic
+  // number from /usr/include/mach/machine.h.  It is ok to reproduce the
+  // specific constants here because they are implicitly part of the Darwin ABI.
+  enum {
+    DARWIN_CPU_ARCH_ABI64      = 0x01000000,
+    DARWIN_CPU_TYPE_X86        = 7,
+    DARWIN_CPU_TYPE_ARM        = 12,
+    DARWIN_CPU_TYPE_POWERPC    = 18
+  };
+
+  Triple::ArchType Arch = TT.getArch();
+  if (Arch == Triple::x86_64)
+    CPUType = DARWIN_CPU_TYPE_X86 | DARWIN_CPU_ARCH_ABI64;
+  else if (Arch == Triple::x86)
+    CPUType = DARWIN_CPU_TYPE_X86;
+  else if (Arch == Triple::ppc)
+    CPUType = DARWIN_CPU_TYPE_POWERPC;
+  else if (Arch == Triple::ppc64)
+    CPUType = DARWIN_CPU_TYPE_POWERPC | DARWIN_CPU_ARCH_ABI64;
+  else if (Arch == Triple::arm || Arch == Triple::thumb)
+    CPUType = DARWIN_CPU_TYPE_ARM;
+
+  // Traditional Bitcode starts after header.
+  assert(Buffer.size() >= BWH_HeaderSize &&
+         "Expected header size to be reserved");
+  unsigned BCOffset = BWH_HeaderSize;
+  unsigned BCSize = Buffer.size() - BWH_HeaderSize;
+
+  // Write the magic and version.
+  unsigned Position = 0;
+  writeInt32ToBuffer(0x0B17C0DE, Buffer, Position);
+  writeInt32ToBuffer(0, Buffer, Position); // Version.
+  writeInt32ToBuffer(BCOffset, Buffer, Position);
+  writeInt32ToBuffer(BCSize, Buffer, Position);
+  writeInt32ToBuffer(CPUType, Buffer, Position);
+
+  // If the file is not a multiple of 16 bytes, insert dummy padding.
+  while (Buffer.size() & 15)
+    Buffer.push_back(0);
+}
+
+/// Helper to write the header common to all bitcode files.
+static void writeBitcodeHeader(BitstreamWriter &Stream) {
+  // Emit the file header.
+  Stream.Emit((unsigned)'B', 8);
+  Stream.Emit((unsigned)'C', 8);
+  Stream.Emit(0x0, 4);
+  Stream.Emit(0xC, 4);
+  Stream.Emit(0xE, 4);
+  Stream.Emit(0xD, 4);
+}
+
+BitcodeWriter::BitcodeWriter(SmallVectorImpl<char> &Buffer, raw_fd_stream *FS)
+    : Buffer(Buffer), Stream(new BitstreamWriter(Buffer, FS, FlushThreshold)) {
+  writeBitcodeHeader(*Stream);
+}
+
+BitcodeWriter::~BitcodeWriter() { assert(WroteStrtab); }
+
+void BitcodeWriter::writeBlob(unsigned Block, unsigned Record, StringRef Blob) {
+  Stream->EnterSubblock(Block, 3);
+
+  auto Abbv = std::make_shared<BitCodeAbbrev>();
+  Abbv->Add(BitCodeAbbrevOp(Record));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob));
+  auto AbbrevNo = Stream->EmitAbbrev(std::move(Abbv));
+
+  Stream->EmitRecordWithBlob(AbbrevNo, ArrayRef<uint64_t>{Record}, Blob);
+
+  Stream->ExitBlock();
+}
+
+void BitcodeWriter::writeSymtab() {
+  assert(!WroteStrtab && !WroteSymtab);
+
+  // If any module has module-level inline asm, we will require a registered asm
+  // parser for the target so that we can create an accurate symbol table for
+  // the module.
+  for (Module *M : Mods) {
+    if (M->getModuleInlineAsm().empty())
+      continue;
+
+    std::string Err;
+    const Triple TT(M->getTargetTriple());
+    const Target *T = TargetRegistry::lookupTarget(TT.str(), Err);
+    if (!T || !T->hasMCAsmParser())
+      return;
+  }
+
+  WroteSymtab = true;
+  SmallVector<char, 0> Symtab;
+  // The irsymtab::build function may be unable to create a symbol table if the
+  // module is malformed (e.g. it contains an invalid alias). Writing a symbol
+  // table is not required for correctness, but we still want to be able to
+  // write malformed modules to bitcode files, so swallow the error.
+  if (Error E = irsymtab::build(Mods, Symtab, StrtabBuilder, Alloc)) {
+    consumeError(std::move(E));
+    return;
+  }
+
+  writeBlob(bitc::SYMTAB_BLOCK_ID, bitc::SYMTAB_BLOB,
+            {Symtab.data(), Symtab.size()});
+}
+
+void BitcodeWriter::writeStrtab() {
+  assert(!WroteStrtab);
+
+  std::vector<char> Strtab;
+  StrtabBuilder.finalizeInOrder();
+  Strtab.resize(StrtabBuilder.getSize());
+  StrtabBuilder.write((uint8_t *)Strtab.data());
+
+  writeBlob(bitc::STRTAB_BLOCK_ID, bitc::STRTAB_BLOB,
+            {Strtab.data(), Strtab.size()});
+
+  WroteStrtab = true;
+}
+
+void BitcodeWriter::copyStrtab(StringRef Strtab) {
+  writeBlob(bitc::STRTAB_BLOCK_ID, bitc::STRTAB_BLOB, Strtab);
+  WroteStrtab = true;
+}
+
+void BitcodeWriter::writeModule(const Module &M,
+                                bool ShouldPreserveUseListOrder,
+                                const ModuleSummaryIndex *Index,
+                                bool GenerateHash, ModuleHash *ModHash) {
+  assert(!WroteStrtab);
+
+  // The Mods vector is used by irsymtab::build, which requires non-const
+  // Modules in case it needs to materialize metadata. But the bitcode writer
+  // requires that the module is materialized, so we can cast to non-const here,
+  // after checking that it is in fact materialized.
+  assert(M.isMaterialized());
+  Mods.push_back(const_cast<Module *>(&M));
+
+  ModuleBitcodeWriter ModuleWriter(M, Buffer, StrtabBuilder, *Stream,
+                                   ShouldPreserveUseListOrder, Index,
+                                   GenerateHash, ModHash);
+  ModuleWriter.write();
+}
+
+void BitcodeWriter::writeIndex(
+    const ModuleSummaryIndex *Index,
+    const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex) {
+  IndexBitcodeWriter IndexWriter(*Stream, StrtabBuilder, *Index,
+                                 ModuleToSummariesForIndex);
+  IndexWriter.write();
+}
+
+/// Write the specified module to the specified output stream.
+void llvm::WriteBitcodeToFile(const Module &M, raw_ostream &Out,
+                              bool ShouldPreserveUseListOrder,
+                              const ModuleSummaryIndex *Index,
+                              bool GenerateHash, ModuleHash *ModHash) {
+  SmallVector<char, 0> Buffer;
+  Buffer.reserve(256*1024);
+
+  // If this is darwin or another generic macho target, reserve space for the
+  // header.
+  Triple TT(M.getTargetTriple());
+  if (TT.isOSDarwin() || TT.isOSBinFormatMachO())
+    Buffer.insert(Buffer.begin(), BWH_HeaderSize, 0);
+
+  BitcodeWriter Writer(Buffer, dyn_cast<raw_fd_stream>(&Out));
+  Writer.writeModule(M, ShouldPreserveUseListOrder, Index, GenerateHash,
+                     ModHash);
+  Writer.writeSymtab();
+  Writer.writeStrtab();
+
+  if (TT.isOSDarwin() || TT.isOSBinFormatMachO())
+    emitDarwinBCHeaderAndTrailer(Buffer, TT);
+
+  // Write the generated bitstream to "Out".
+  if (!Buffer.empty())
+    Out.write((char *)&Buffer.front(), Buffer.size());
+}
+
+void IndexBitcodeWriter::write() {
+  Stream.EnterSubblock(bitc::MODULE_BLOCK_ID, 3);
+
+  writeModuleVersion();
+
+  // Write the module paths in the combined index.
+  writeModStrings();
+
+  // Write the summary combined index records.
+  writeCombinedGlobalValueSummary();
+
+  Stream.ExitBlock();
+}
+
+// Write the specified module summary index to the given raw output stream,
+// where it will be written in a new bitcode block. This is used when
+// writing the combined index file for ThinLTO. When writing a subset of the
+// index for a distributed backend, provide a \p ModuleToSummariesForIndex map.
+void llvm::writeIndexToFile(
+    const ModuleSummaryIndex &Index, raw_ostream &Out,
+    const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex) {
+  SmallVector<char, 0> Buffer;
+  Buffer.reserve(256 * 1024);
+
+  BitcodeWriter Writer(Buffer);
+  Writer.writeIndex(&Index, ModuleToSummariesForIndex);
+  Writer.writeStrtab();
+
+  Out.write((char *)&Buffer.front(), Buffer.size());
+}
+
+namespace {
+
+/// Class to manage the bitcode writing for a thin link bitcode file.
+class ThinLinkBitcodeWriter : public ModuleBitcodeWriterBase {
+  /// ModHash is for use in ThinLTO incremental build, generated while writing
+  /// the module bitcode file.
+  const ModuleHash *ModHash;
+
+public:
+  ThinLinkBitcodeWriter(const Module &M, StringTableBuilder &StrtabBuilder,
+                        BitstreamWriter &Stream,
+                        const ModuleSummaryIndex &Index,
+                        const ModuleHash &ModHash)
+      : ModuleBitcodeWriterBase(M, StrtabBuilder, Stream,
+                                /*ShouldPreserveUseListOrder=*/false, &Index),
+        ModHash(&ModHash) {}
+
+  void write();
+
+private:
+  void writeSimplifiedModuleInfo();
+};
+
+} // end anonymous namespace
+
+// This function writes a simpilified module info for thin link bitcode file.
+// It only contains the source file name along with the name(the offset and
+// size in strtab) and linkage for global values. For the global value info
+// entry, in order to keep linkage at offset 5, there are three zeros used
+// as padding.
+void ThinLinkBitcodeWriter::writeSimplifiedModuleInfo() {
+  SmallVector<unsigned, 64> Vals;
+  // Emit the module's source file name.
+  {
+    StringEncoding Bits = getStringEncoding(M.getSourceFileName());
+    BitCodeAbbrevOp AbbrevOpToUse = BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8);
+    if (Bits == SE_Char6)
+      AbbrevOpToUse = BitCodeAbbrevOp(BitCodeAbbrevOp::Char6);
+    else if (Bits == SE_Fixed7)
+      AbbrevOpToUse = BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 7);
+
+    // MODULE_CODE_SOURCE_FILENAME: [namechar x N]
+    auto Abbv = std::make_shared<BitCodeAbbrev>();
+    Abbv->Add(BitCodeAbbrevOp(bitc::MODULE_CODE_SOURCE_FILENAME));
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    Abbv->Add(AbbrevOpToUse);
+    unsigned FilenameAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+
+    for (const auto P : M.getSourceFileName())
+      Vals.push_back((unsigned char)P);
+
+    Stream.EmitRecord(bitc::MODULE_CODE_SOURCE_FILENAME, Vals, FilenameAbbrev);
+    Vals.clear();
+  }
+
+  // Emit the global variable information.
+  for (const GlobalVariable &GV : M.globals()) {
+    // GLOBALVAR: [strtab offset, strtab size, 0, 0, 0, linkage]
+    Vals.push_back(StrtabBuilder.add(GV.getName()));
+    Vals.push_back(GV.getName().size());
+    Vals.push_back(0);
+    Vals.push_back(0);
+    Vals.push_back(0);
+    Vals.push_back(getEncodedLinkage(GV));
+
+    Stream.EmitRecord(bitc::MODULE_CODE_GLOBALVAR, Vals);
+    Vals.clear();
+  }
+
+  // Emit the function proto information.
+  for (const Function &F : M) {
+    // FUNCTION:  [strtab offset, strtab size, 0, 0, 0, linkage]
+    Vals.push_back(StrtabBuilder.add(F.getName()));
+    Vals.push_back(F.getName().size());
+    Vals.push_back(0);
+    Vals.push_back(0);
+    Vals.push_back(0);
+    Vals.push_back(getEncodedLinkage(F));
+
+    Stream.EmitRecord(bitc::MODULE_CODE_FUNCTION, Vals);
+    Vals.clear();
+  }
+
+  // Emit the alias information.
+  for (const GlobalAlias &A : M.aliases()) {
+    // ALIAS: [strtab offset, strtab size, 0, 0, 0, linkage]
+    Vals.push_back(StrtabBuilder.add(A.getName()));
+    Vals.push_back(A.getName().size());
+    Vals.push_back(0);
+    Vals.push_back(0);
+    Vals.push_back(0);
+    Vals.push_back(getEncodedLinkage(A));
+
+    Stream.EmitRecord(bitc::MODULE_CODE_ALIAS, Vals);
+    Vals.clear();
+  }
+
+  // Emit the ifunc information.
+  for (const GlobalIFunc &I : M.ifuncs()) {
+    // IFUNC: [strtab offset, strtab size, 0, 0, 0, linkage]
+    Vals.push_back(StrtabBuilder.add(I.getName()));
+    Vals.push_back(I.getName().size());
+    Vals.push_back(0);
+    Vals.push_back(0);
+    Vals.push_back(0);
+    Vals.push_back(getEncodedLinkage(I));
+
+    Stream.EmitRecord(bitc::MODULE_CODE_IFUNC, Vals);
+    Vals.clear();
+  }
+}
+
+void ThinLinkBitcodeWriter::write() {
+  Stream.EnterSubblock(bitc::MODULE_BLOCK_ID, 3);
+
+  writeModuleVersion();
+
+  writeSimplifiedModuleInfo();
+
+  writePerModuleGlobalValueSummary();
+
+  // Write module hash.
+  Stream.EmitRecord(bitc::MODULE_CODE_HASH, ArrayRef<uint32_t>(*ModHash));
+
+  Stream.ExitBlock();
+}
+
+void BitcodeWriter::writeThinLinkBitcode(const Module &M,
+                                         const ModuleSummaryIndex &Index,
+                                         const ModuleHash &ModHash) {
+  assert(!WroteStrtab);
+
+  // The Mods vector is used by irsymtab::build, which requires non-const
+  // Modules in case it needs to materialize metadata. But the bitcode writer
+  // requires that the module is materialized, so we can cast to non-const here,
+  // after checking that it is in fact materialized.
+  assert(M.isMaterialized());
+  Mods.push_back(const_cast<Module *>(&M));
+
+  ThinLinkBitcodeWriter ThinLinkWriter(M, StrtabBuilder, *Stream, Index,
+                                       ModHash);
+  ThinLinkWriter.write();
+}
+
+// Write the specified thin link bitcode file to the given raw output stream,
+// where it will be written in a new bitcode block. This is used when
+// writing the per-module index file for ThinLTO.
+void llvm::writeThinLinkBitcodeToFile(const Module &M, raw_ostream &Out,
+                                      const ModuleSummaryIndex &Index,
+                                      const ModuleHash &ModHash) {
+  SmallVector<char, 0> Buffer;
+  Buffer.reserve(256 * 1024);
+
+  BitcodeWriter Writer(Buffer);
+  Writer.writeThinLinkBitcode(M, Index, ModHash);
+  Writer.writeSymtab();
+  Writer.writeStrtab();
+
+  Out.write((char *)&Buffer.front(), Buffer.size());
+}
+
+static const char *getSectionNameForBitcode(const Triple &T) {
+  switch (T.getObjectFormat()) {
+  case Triple::MachO:
+    return "__LLVM,__bitcode";
+  case Triple::COFF:
+  case Triple::ELF:
+  case Triple::Wasm:
+  case Triple::UnknownObjectFormat:
+    return ".llvmbc";
+  case Triple::GOFF:
+    llvm_unreachable("GOFF is not yet implemented");
+    break;
+  case Triple::SPIRV:
+    llvm_unreachable("SPIRV is not yet implemented");
+    break;
+  case Triple::XCOFF:
+    llvm_unreachable("XCOFF is not yet implemented");
+    break;
+  case Triple::DXContainer:
+    llvm_unreachable("DXContainer is not yet implemented");
+    break;
+  }
+  llvm_unreachable("Unimplemented ObjectFormatType");
+}
+
+static const char *getSectionNameForCommandline(const Triple &T) {
+  switch (T.getObjectFormat()) {
+  case Triple::MachO:
+    return "__LLVM,__cmdline";
+  case Triple::COFF:
+  case Triple::ELF:
+  case Triple::Wasm:
+  case Triple::UnknownObjectFormat:
+    return ".llvmcmd";
+  case Triple::GOFF:
+    llvm_unreachable("GOFF is not yet implemented");
+    break;
+  case Triple::SPIRV:
+    llvm_unreachable("SPIRV is not yet implemented");
+    break;
+  case Triple::XCOFF:
+    llvm_unreachable("XCOFF is not yet implemented");
+    break;
+  case Triple::DXContainer:
+    llvm_unreachable("DXC is not yet implemented");
+    break;
+  }
+  llvm_unreachable("Unimplemented ObjectFormatType");
+}
+
+void llvm::embedBitcodeInModule(llvm::Module &M, llvm::MemoryBufferRef Buf,
+                                bool EmbedBitcode, bool EmbedCmdline,
+                                const std::vector<uint8_t> &CmdArgs) {
+  // Save llvm.compiler.used and remove it.
+  SmallVector<Constant *, 2> UsedArray;
+  SmallVector<GlobalValue *, 4> UsedGlobals;
+  Type *UsedElementType = Type::getInt8Ty(M.getContext())->getPointerTo(0);
+  GlobalVariable *Used = collectUsedGlobalVariables(M, UsedGlobals, true);
+  for (auto *GV : UsedGlobals) {
+    if (GV->getName() != "llvm.embedded.module" &&
+        GV->getName() != "llvm.cmdline")
+      UsedArray.push_back(
+          ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
+  }
+  if (Used)
+    Used->eraseFromParent();
+
+  // Embed the bitcode for the llvm module.
+  std::string Data;
+  ArrayRef<uint8_t> ModuleData;
+  Triple T(M.getTargetTriple());
+
+  if (EmbedBitcode) {
+    if (Buf.getBufferSize() == 0 ||
+        !isBitcode((const unsigned char *)Buf.getBufferStart(),
+                   (const unsigned char *)Buf.getBufferEnd())) {
+      // If the input is LLVM Assembly, bitcode is produced by serializing
+      // the module. Use-lists order need to be preserved in this case.
+      llvm::raw_string_ostream OS(Data);
+      llvm::WriteBitcodeToFile(M, OS, /* ShouldPreserveUseListOrder */ true);
+      ModuleData =
+          ArrayRef<uint8_t>((const uint8_t *)OS.str().data(), OS.str().size());
+    } else
+      // If the input is LLVM bitcode, write the input byte stream directly.
+      ModuleData = ArrayRef<uint8_t>((const uint8_t *)Buf.getBufferStart(),
+                                     Buf.getBufferSize());
+  }
+  llvm::Constant *ModuleConstant =
+      llvm::ConstantDataArray::get(M.getContext(), ModuleData);
+  llvm::GlobalVariable *GV = new llvm::GlobalVariable(
+      M, ModuleConstant->getType(), true, llvm::GlobalValue::PrivateLinkage,
+      ModuleConstant);
+  GV->setSection(getSectionNameForBitcode(T));
+  // Set alignment to 1 to prevent padding between two contributions from input
+  // sections after linking.
+  GV->setAlignment(Align(1));
+  UsedArray.push_back(
+      ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
+  if (llvm::GlobalVariable *Old =
+          M.getGlobalVariable("llvm.embedded.module", true)) {
+    assert(Old->hasZeroLiveUses() &&
+           "llvm.embedded.module can only be used once in llvm.compiler.used");
+    GV->takeName(Old);
+    Old->eraseFromParent();
+  } else {
+    GV->setName("llvm.embedded.module");
+  }
+
+  // Skip if only bitcode needs to be embedded.
+  if (EmbedCmdline) {
+    // Embed command-line options.
+    ArrayRef<uint8_t> CmdData(const_cast<uint8_t *>(CmdArgs.data()),
+                              CmdArgs.size());
+    llvm::Constant *CmdConstant =
+        llvm::ConstantDataArray::get(M.getContext(), CmdData);
+    GV = new llvm::GlobalVariable(M, CmdConstant->getType(), true,
+                                  llvm::GlobalValue::PrivateLinkage,
+                                  CmdConstant);
+    GV->setSection(getSectionNameForCommandline(T));
+    GV->setAlignment(Align(1));
+    UsedArray.push_back(
+        ConstantExpr::getPointerBitCastOrAddrSpaceCast(GV, UsedElementType));
+    if (llvm::GlobalVariable *Old = M.getGlobalVariable("llvm.cmdline", true)) {
+      assert(Old->hasZeroLiveUses() &&
+             "llvm.cmdline can only be used once in llvm.compiler.used");
+      GV->takeName(Old);
+      Old->eraseFromParent();
+    } else {
+      GV->setName("llvm.cmdline");
+    }
+  }
+
+  if (UsedArray.empty())
+    return;
+
+  // Recreate llvm.compiler.used.
+  ArrayType *ATy = ArrayType::get(UsedElementType, UsedArray.size());
+  auto *NewUsed = new GlobalVariable(
+      M, ATy, false, llvm::GlobalValue::AppendingLinkage,
+      llvm::ConstantArray::get(ATy, UsedArray), "llvm.compiler.used");
+  NewUsed->setSection("llvm.metadata");
+}