Bitcode: Add a string table to the bitcode format.

[pcc]

Summary

Add a top-level STRTAB block containing a string table blob, and start storing
strings for module codes FUNCTION, GLOBALVAR, ALIAS, IFUNC and COMDAT in
the string table.

This change allows us to share names between globals and comdats as well
as between modules, and improves the efficiency of loading bitcode files by
no longer using a bit encoding for symbol names. Once we start writing the
irsymtab to the bitcode file we will also be able to share strings between
it and the module.

On my machine, link time for Chromium for Linux with ThinLTO decreases by
about 7% for no-op incremental builds or about 1% for full builds. Total
bitcode file size decreases by about 3%.

As discussed on llvm-dev:
http://lists.llvm.org/pipermail/llvm-dev/2017-April/111732.html

Depends on D31828

Depends on D31829

[pcc]

• Update some comments
• Move writing the version into a function

[tejohnson]

I got through the end of the BitcodeReader.cpp, sending comments so far.

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

390

Document, especially return value.

1805

We don't have namecharXN anymore, right?

1806

Can this block be refactored out of here and parseValueSymbolTable? I guess that requires some change to recordValue too if we want to share the accessing of the Function pointer, but it would at least be nice to refactor and share the rest.

2732

Maybe add comment here and in parseFunctionRecord and parseGlobalIndirectSymbolRecord that in v1 the name will be added to the value later when the old style VST is parsed.

4904

refactor out and share with analogous parseValueSymbolTable handling?

[vsk]

I've got a collection of old bitcode files which I'll try recompiling with this patch applied, once the review winds down.

llvm/tools/llvm-modextract/llvm-modextract.cpp

65

I see two places where we need to perform a byte-for-byte copy of a BitcodeModule's buffer, and then copy the strtab. Is there any reason to perform such a copy and not copy the strtab? If not, we could reduce the duplication by adding a 'writeCopyOfModule(BitcodeModule &)' helper to BitcodeWriter.

[pcc]

• Address review comments

[pcc]

llvm/tools/llvm-modextract/llvm-modextract.cpp

65

Is there any reason to perform such a copy and not copy the strtab?

In principle you could concatenate multi-module bitcode files by copying only unique strtabs instead of potentially copying the same strtab multiple times.

If not, we could reduce the duplication by adding a 'writeCopyOfModule(BitcodeModule &)' helper to BitcodeWriter.

Maybe, but we only need to perform these copies in low level tools, so I'm not sure if we want to support their operations at the API level. That would also create a direct dependency from the bitcode writer to the bitcode reader, and I'd like to avoid adding any new such dependencies. Maybe we can reconsider if we need to do this elsewhere (i.e. rule of 3).

[tejohnson]

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

5015

Add comment with record format above here (see other cases).

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

1285

Why does this move?

1310

Why does this go away?

2902–2906

Comment needs updating.

2905

Maybe rename to writeFunctionLevelValueSymbolTable or something like that to distinguish from the other one.

2922–2923

This one goes away I think

3537

Can getValueId be split into two, part that does the assignment if it doesn't exist in map and returns nothing (called from this code), and one that asserts it exists in map and returns the value (called from where we originally called getValueId further down? Presumably by the time we reach there we will always have them assigned due to this code.

llvm/tools/llvm-cat/llvm-cat.cpp

54

Needed because string in string table owned by parsed modules?

llvm/tools/llvm-modextract/llvm-modextract.cpp

62–67

Rename variable? "Header" no longer seems appropriate.

[pcc]

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

1285

We now create the summary entries as we read MODULE_CODE_* records. That means that we need the source file name to compute the GUID correctly.

1310

We now create a VST unconditionally. Avoiding creating a VST if the module is empty seems like a micro-optimization that is not worth it.

llvm/tools/llvm-cat/llvm-cat.cpp

54

Yes, comment added.

[pcc]

• Address review comments

[pcc]

Hmm, I somehow managed to revert my changes from the first round of review comments. Uploading a new patch shortly.

[pcc]

Re-applying changes from first round of review comments

[tejohnson]

LGTM

llvm/docs/BitCodeFormat.rst

 
 * 15 --- `METADATA_BLOCK`_ --- This describes metadata items.
 
 * 16 --- `METADATA_ATTACHMENT`_ --- This contains records associating metadata
   with function instruction values.
 
 * 17 --- `TYPE_BLOCK`_ --- This describes all of the types in the module.
 
+* 23 --- `STRTAB_BLOCK`_ --- The bitcode file's string table.
+
 .. _MODULE_BLOCK:
 
 MODULE_BLOCK Contents
 ---------------------
 
 The ``MODULE_BLOCK`` block (id 8) is the top-level block for LLVM bitcode files,
 and each bitcode file must contain exactly one. In addition to records
 (described below) containing information about the module, a ``MODULE_BLOCK``

 .. _MODULE_CODE_VERSION:
 
 MODULE_CODE_VERSION Record
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 ``[VERSION, version#]``
 
 The ``VERSION`` record (code 1) contains a single value indicating the format
-version. Versions 0 and 1 are supported at this time. The difference between
+version. Versions 0, 1 and 2 are supported at this time. The difference between
 version 0 and 1 is in the encoding of instruction operands in
 each `FUNCTION_BLOCK`_.
 
 In version 0, each value defined by an instruction is assigned an ID
 unique to the function. Function-level value IDs are assigned starting from
 ``NumModuleValues`` since they share the same namespace as module-level
 values. The value enumerator resets after each function. When a value is
 an operand of an instruction, the value ID is used to represent the operand.

 do not use the relative encoding.
 
 Forward references will result in a negative value.
 This can be inefficient, as operands are normally encoded
 as unsigned VBRs. However, forward references are rare, except in the
 case of phi instructions. For phi instructions, operands are encoded as
 `Signed VBRs`_ to deal with forward references.
 
+In version 2, the meaning of module records ``FUNCTION``, ``GLOBALVAR``,
+``ALIAS``, ``IFUNC`` and ``COMDAT`` change such that the first two operands
+specify an offset and size of a string in a string table (see `STRTAB_BLOCK
+Contents`_), the function name is removed from the ``FNENTRY`` record in the
+value symbol table, and the top-level ``VALUE_SYMTAB_BLOCK`` may only contain
+``FNENTRY`` records.
 
 MODULE_CODE_TRIPLE Record
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 ``[TRIPLE, ...string...]``
 
 The ``TRIPLE`` record (code 2) contains a variable number of values representing
 the bytes of the ``target triple`` specification string.

 The ``DEPLIB`` record (code 6) contains a variable number of values representing
 the bytes of a single dependent library name string, one of the libraries
 mentioned in a ``deplibs`` declaration.  There should be one ``DEPLIB`` record
 for each library name referenced.
 
 MODULE_CODE_GLOBALVAR Record
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-``[GLOBALVAR, pointer type, isconst, initid, linkage, alignment, section, visibility, threadlocal, unnamed_addr, externally_initialized, dllstorageclass, comdat]``
+``[GLOBALVAR, strtab offset, strtab size, pointer type, isconst, initid, linkage, alignment, section, visibility, threadlocal, unnamed_addr, externally_initialized, dllstorageclass, comdat]``
 
 The ``GLOBALVAR`` record (code 7) marks the declaration or definition of a
 global variable. The operand fields are:
 
+* *strtab offset*, *strtab size*: Specifies the name of the global variable.
+  See `STRTAB_BLOCK Contents`_.
+
 * *pointer type*: The type index of the pointer type used to point to this
   global variable
 
 * *isconst*: Non-zero if the variable is treated as constant within the module,
   or zero if it is not
 
 * *initid*: If non-zero, the value index of the initializer for this variable,
   plus 1.

 
 * *comdat*: An encoding of the COMDAT of this function
 
 .. _FUNCTION:
 
 MODULE_CODE_FUNCTION Record
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-``[FUNCTION, type, callingconv, isproto, linkage, paramattr, alignment, section, visibility, gc, prologuedata, dllstorageclass, comdat, prefixdata, personalityfn]``
+``[FUNCTION, strtab offset, strtab size, type, callingconv, isproto, linkage, paramattr, alignment, section, visibility, gc, prologuedata, dllstorageclass, comdat, prefixdata, personalityfn]``
 
 The ``FUNCTION`` record (code 8) marks the declaration or definition of a
 function. The operand fields are:
 
+* *strtab offset*, *strtab size*: Specifies the name of the function.
+  See `STRTAB_BLOCK Contents`_.
+
 * *type*: The type index of the function type describing this function
 
 * *callingconv*: The calling convention number:
   * ``ccc``: code 0
   * ``fastcc``: code 8
   * ``coldcc``: code 9
   * ``webkit_jscc``: code 12
   * ``anyregcc``: code 13
* *prefixdata*: If non-zero, the value index of the prefix data for this function,
   plus 1.
 
 * *personalityfn*: If non-zero, the value index of the personality function for this function,
   plus 1.
 
 MODULE_CODE_ALIAS Record
 ^^^^^^^^^^^^^^^^^^^^^^^^
 
-``[ALIAS, alias type, aliasee val#, linkage, visibility, dllstorageclass, threadlocal, unnamed_addr]``
+``[ALIAS, strtab offset, strtab size, alias type, aliasee val#, linkage, visibility, dllstorageclass, threadlocal, unnamed_addr]``
 
 The ``ALIAS`` record (code 9) marks the definition of an alias. The operand
 fields are
 
+* *strtab offset*, *strtab size*: Specifies the name of the alias.
+  See `STRTAB_BLOCK Contents`_.
+
 * *alias type*: The type index of the alias
 
 * *aliasee val#*: The value index of the aliased value
 
 * *linkage*: An encoding of the `linkage type`_ for this alias
 
 * *visibility*: If present, an encoding of the `visibility`_ of the alias
 

 The ``METADATA_BLOCK`` block (id 15) ...
 
 .. _METADATA_ATTACHMENT:
 
 METADATA_ATTACHMENT Contents
 ----------------------------
 
 The ``METADATA_ATTACHMENT`` block (id 16) ...
+
+.. _STRTAB_BLOCK:
+
+STRTAB_BLOCK Contents
+---------------------
+
+The ``STRTAB`` block (id 23) contains a single record (``STRTAB_BLOB``, id 1)
+with a single blob operand containing the bitcode file's string table.
+
+Strings in the string table are not null terminated. A record's *strtab
+offset* and *strtab size* operands specify the byte offset and size of a
+string within the string table.
+
+The string table is used by all preceding blocks in the bitcode file that are
+not succeeded by another intervening ``STRTAB`` block. Normally a bitcode
+file will have a single string table, but it may have more than one if it
+was created by binary concatenation of multiple bitcode files.

llvm/include/llvm/Bitcode/BitcodeReader.h

namespace llvm {
   }
 
   /// Represents a module in a bitcode file.
   class BitcodeModule {
     // This covers the identification (if present) and module blocks.
     ArrayRef<uint8_t> Buffer;
     StringRef ModuleIdentifier;
 
+    // The string table used to interpret this module.
+    StringRef Strtab;
+
     // The bitstream location of the IDENTIFICATION_BLOCK.
     uint64_t IdentificationBit;
 
     // The bitstream location of this module's MODULE_BLOCK.
     uint64_t ModuleBit;
 
     BitcodeModule(ArrayRef<uint8_t> Buffer, StringRef ModuleIdentifier,
                   uint64_t IdentificationBit, uint64_t ModuleBit)
         : Buffer(Buffer), ModuleIdentifier(ModuleIdentifier),
           IdentificationBit(IdentificationBit), ModuleBit(ModuleBit) {}
 
     // Calls the ctor.
     friend Expected<std::vector<BitcodeModule>>
     getBitcodeModuleList(MemoryBufferRef Buffer);
 
     Expected<std::unique_ptr<Module>> getModuleImpl(LLVMContext &Context,
                                                     bool MaterializeAll,
                                                     bool ShouldLazyLoadMetadata,
                                                     bool IsImporting);
 
   public:
     StringRef getBuffer() const {
       return StringRef((const char *)Buffer.begin(), Buffer.size());
     }
+    StringRef getStrtab() const { return Strtab; }
 
     StringRef getModuleIdentifier() const { return ModuleIdentifier; }
 
     /// Read the bitcode module and prepare for lazy deserialization of function
     /// bodies. If ShouldLazyLoadMetadata is true, lazily load metadata as well.
     /// If IsImporting is true, this module is being parsed for ThinLTO
     /// importing into another module.
     Expected<std::unique_ptr<Module>> getLazyModule(LLVMContext &Context,

llvm/include/llvm/Bitcode/BitcodeWriter.h

 // This header defines interfaces to write LLVM bitcode files/streams.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_BITCODE_BITCODEWRITER_H
 #define LLVM_BITCODE_BITCODEWRITER_H
 
 #include "llvm/IR/ModuleSummaryIndex.h"
+#include "llvm/MC/StringTableBuilder.h"
 #include <string>
 
 namespace llvm {
   class BitstreamWriter;
   class Module;
   class raw_ostream;
 
   class BitcodeWriter {
     SmallVectorImpl<char> &Buffer;
     std::unique_ptr<BitstreamWriter> Stream;
 
+    StringTableBuilder StrtabBuilder{StringTableBuilder::RAW};
+    bool WroteStrtab = false;
+
+    void writeBlob(unsigned Block, unsigned Record, StringRef Blob);
+
    public:
     /// Create a BitcodeWriter that writes to Buffer.
     BitcodeWriter(SmallVectorImpl<char> &Buffer);
 
     ~BitcodeWriter();
 
+    /// Write the bitcode file's string table. This must be called exactly once
+    /// after all modules have been written.
+    void writeStrtab();
+
+    /// Copy the string table for another module into this bitcode file. This
+    /// should be called after copying the module itself into the bitcode file.
+    void copyStrtab(StringRef Strtab);
+
     /// Write the specified module to the buffer specified at construction time.
     ///
     /// If \c ShouldPreserveUseListOrder, encode the use-list order for each \a
     /// Value in \c M.  These will be reconstructed exactly when \a M is
     /// deserialized.
     ///
     /// If \c Index is supplied, the bitcode will contain the summary index
     /// (currently for use in ThinLTO optimization).

llvm/include/llvm/Bitcode/LLVMBitCodes.h

 
 #ifndef LLVM_BITCODE_LLVMBITCODES_H
 #define LLVM_BITCODE_LLVMBITCODES_H
 
 #include "llvm/Bitcode/BitCodes.h"
 
 namespace llvm {
 namespace bitc {
-// The only top-level block type defined is for a module.
+// The only top-level block types are MODULE, IDENTIFICATION and STRTAB.
 enum BlockIDs {
   // Blocks
   MODULE_BLOCK_ID = FIRST_APPLICATION_BLOCKID,
 
   // Module sub-block id's.
   PARAMATTR_BLOCK_ID,
   PARAMATTR_GROUP_BLOCK_ID,
 
enum BlockIDs {
 
   USELIST_BLOCK_ID,
 
   MODULE_STRTAB_BLOCK_ID,
   GLOBALVAL_SUMMARY_BLOCK_ID,
 
   OPERAND_BUNDLE_TAGS_BLOCK_ID,
 
-  METADATA_KIND_BLOCK_ID
+  METADATA_KIND_BLOCK_ID,
+
+  STRTAB_BLOCK_ID,
 };
 
 /// Identification block contains a string that describes the producer details,
 /// and an epoch that defines the auto-upgrade capability.
 enum IdentificationCodes {
   IDENTIFICATION_CODE_STRING = 1, // IDENTIFICATION:      [strchr x N]
   IDENTIFICATION_CODE_EPOCH = 2,  // EPOCH:               [epoch#]
 };
enum GlobalValueSummarySymtabCodes {
   // Identifies a virtual call made by this function using an
   // llvm.assume(llvm.type.test) intrinsic with all constant integer arguments.
   // [typeid, offset, n x arg]
   FS_TYPE_TEST_ASSUME_CONST_VCALL = 14,
   // Identifies a virtual call made by this function using an
   // llvm.type.checked.load intrinsic with all constant integer arguments.
   // [typeid, offset, n x arg]
   FS_TYPE_CHECKED_LOAD_CONST_VCALL = 15,
+  // Assigns a GUID to a value ID. This normally appears only in combined
+  // summaries, but it can also appear in per-module summaries for PGO data.
+  // [valueid, guid]
+  FS_VALUE_GUID = 16,
 };
 
 enum MetadataCodes {
   METADATA_STRING_OLD = 1,     // MDSTRING:      [values]
   METADATA_VALUE = 2,          // VALUE:         [type num, value num]
   METADATA_NODE = 3,           // NODE:          [n x md num]
   METADATA_NAME = 4,           // STRING:        [values]
   METADATA_DISTINCT_NODE = 5,  // DISTINCT_NODE: [n x md num]

 enum ComdatSelectionKindCodes {
   COMDAT_SELECTION_KIND_ANY = 1,
   COMDAT_SELECTION_KIND_EXACT_MATCH = 2,
   COMDAT_SELECTION_KIND_LARGEST = 3,
   COMDAT_SELECTION_KIND_NO_DUPLICATES = 4,
   COMDAT_SELECTION_KIND_SAME_SIZE = 5,
 };
 
+enum StrtabCodes {
+  STRTAB_BLOB = 1,
+};
+
 } // End bitc namespace
 } // End llvm namespace
 
 #endif

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

case BitstreamEntry::Record:
       Stream.skipRecord(Entry.ID);
       continue;
     }
   }
 }
 
 class BitcodeReaderBase {
 protected:
-  BitcodeReaderBase(BitstreamCursor Stream) : Stream(std::move(Stream)) {
+  BitcodeReaderBase(BitstreamCursor Stream, StringRef Strtab)
+      : Stream(std::move(Stream)), Strtab(Strtab) {
     this->Stream.setBlockInfo(&BlockInfo);
   }
 
   BitstreamBlockInfo BlockInfo;
   BitstreamCursor Stream;
+  StringRef Strtab;
+
+  /// In version 2 of the bitcode we store names of global values and comdats in
+  /// a string table rather than in the VST.
+  bool UseStrtab = false;
 
   Expected<unsigned> parseVersionRecord(ArrayRef<uint64_t> Record);
 
+  /// If this module uses a string table, pop the reference to the string table
+  /// and return the referenced string and the rest of the record. Otherwise
+  /// just return the record itself.
+  std::pair<StringRef, ArrayRef<uint64_t>>
+  readNameFromStrtab(ArrayRef<uint64_t> Record);
+
   bool readBlockInfo();
 
   // Contains an arbitrary and optional string identifying the bitcode producer
   std::string ProducerIdentification;
 
   Error error(const Twine &Message);
 };
 
 Error BitcodeReaderBase::error(const Twine &Message) {
   std::string FullMsg = Message.str();
   if (!ProducerIdentification.empty())
     FullMsg += " (Producer: '" + ProducerIdentification + "' Reader: 'LLVM " +
                LLVM_VERSION_STRING "')";
   return ::error(FullMsg);
 }
 
 Expected<unsigned>
 BitcodeReaderBase::parseVersionRecord(ArrayRef<uint64_t> Record) {
   if (Record.size() < 1)
     return error("Invalid record");
   unsigned ModuleVersion = Record[0];
-  if (ModuleVersion > 1)
+  if (ModuleVersion > 2)
     return error("Invalid value");
+  UseStrtab = ModuleVersion >= 2;
   return ModuleVersion;
 }
 
+std::pair<StringRef, ArrayRef<uint64_t>>
+BitcodeReaderBase::readNameFromStrtab(ArrayRef<uint64_t> Record) {
+  if (!UseStrtab)
+    return {"", Record};
+  // Invalid reference. Let the caller complain about the record being empty.
+  if (Record[0] + Record[1] > Strtab.size())
+    return {"", {}};
+  return {StringRef(Strtab.data() + Record[0], Record[1]), Record.slice(2)};
+}
+
 class BitcodeReader : public BitcodeReaderBase, public GVMaterializer {
   LLVMContext &Context;
   Module *TheModule = nullptr;
   // Next offset to start scanning for lazy parsing of function bodies.
   uint64_t NextUnreadBit = 0;
   // Last function offset found in the VST.
   uint64_t LastFunctionBlockBit = 0;
   bool SeenValueSymbolTable = false;
class BitcodeReader : public BitcodeReaderBase, public GVMaterializer {
   bool WillMaterializeAllForwardRefs = false;
 
   bool StripDebugInfo = false;
   TBAAVerifier TBAAVerifyHelper;
 
   std::vector<std::string> BundleTags;
 
 public:
-  BitcodeReader(BitstreamCursor Stream, StringRef ProducerIdentification,
-                LLVMContext &Context);
+  BitcodeReader(BitstreamCursor Stream, StringRef Strtab,
+                StringRef ProducerIdentification, LLVMContext &Context);
 
   Error materializeForwardReferencedFunctions();
 
   Error materialize(GlobalValue *GV) override;
   Error materializeModule() override;
   std::vector<StructType *> getIdentifiedStructTypes() const override;
 
   /// \brief Main interface to parsing a bitcode buffer.
private:
   Error parseAttributeBlock();
   Error parseAttributeGroupBlock();
   Error parseTypeTable();
   Error parseTypeTableBody();
   Error parseOperandBundleTags();
 
   Expected<Value *> recordValue(SmallVectorImpl<uint64_t> &Record,
                                 unsigned NameIndex, Triple &TT);
+  void setDeferredFunctionInfo(unsigned FuncBitcodeOffsetDelta, Function *F,
+                               ArrayRef<uint64_t> Record);
   Error parseValueSymbolTable(uint64_t Offset = 0);
+  Error parseGlobalValueSymbolTable();
   Error parseConstants();
   Error rememberAndSkipFunctionBodies();
   Error rememberAndSkipFunctionBody();
   /// Save the positions of the Metadata blocks and skip parsing the blocks.
   Error rememberAndSkipMetadata();
   Error typeCheckLoadStoreInst(Type *ValType, Type *PtrType);
   Error parseFunctionBody(Function *F);
   Error globalCleanup();
class ModuleSummaryIndexBitcodeReader : public BitcodeReaderBase {
   /// path string table, used to correlate with combined index
   /// summary records.
   DenseMap<uint64_t, StringRef> ModuleIdMap;
 
   /// Original source file name recorded in a bitcode record.
   std::string SourceFileName;
 
 public:
-  ModuleSummaryIndexBitcodeReader(
-      BitstreamCursor Stream, ModuleSummaryIndex &TheIndex);
+  ModuleSummaryIndexBitcodeReader(BitstreamCursor Stream, StringRef Strtab,
+                                  ModuleSummaryIndex &TheIndex);
 
   Error parseModule(StringRef ModulePath);
 
 private:
+  void setValueGUID(uint64_t ValueID, StringRef ValueName,
+                    GlobalValue::LinkageTypes Linkage,
+                    StringRef SourceFileName);
   Error parseValueSymbolTable(
       uint64_t Offset,
       DenseMap<unsigned, GlobalValue::LinkageTypes> &ValueIdToLinkageMap);
   std::vector<ValueInfo> makeRefList(ArrayRef<uint64_t> Record);
   std::vector<FunctionSummary::EdgeTy> makeCallList(ArrayRef<uint64_t> Record,
                                                     bool IsOldProfileFormat,
                                                     bool HasProfile);
   Error parseEntireSummary(StringRef ModulePath);
handleAllErrors(std::move(Err), [&](ErrorInfoBase &EIB) {
       EC = EIB.convertToErrorCode();
       Ctx.emitError(EIB.message());
     });
     return EC;
   }
   return std::error_code();
 }
 
-BitcodeReader::BitcodeReader(BitstreamCursor Stream,
+BitcodeReader::BitcodeReader(BitstreamCursor Stream, StringRef Strtab,
                              StringRef ProducerIdentification,
                              LLVMContext &Context)
-    : BitcodeReaderBase(std::move(Stream)), Context(Context),
+    : BitcodeReaderBase(std::move(Stream), Strtab), Context(Context),
       ValueList(Context) {
   this->ProducerIdentification = ProducerIdentification;
 }
 
 Error BitcodeReader::materializeForwardReferencedFunctions() {
   if (WillMaterializeAllForwardRefs)
     return Error::success();
 

 #else
   // In NDEBUG mode ignore the output so we don't get an unused variable
   // warning.
   Stream.advance();
 #endif
   return CurrentBit;
 }
 
+void BitcodeReader::setDeferredFunctionInfo(unsigned FuncBitcodeOffsetDelta,
+                                            Function *F,
+                                            ArrayRef<uint64_t> Record) {
+  // Note that we subtract 1 here because the offset is relative to one word
+  // before the start of the identification or module block, which was
+  // historically always the start of the regular bitcode header.
+  uint64_t FuncWordOffset = Record[1] - 1;
+  uint64_t FuncBitOffset = FuncWordOffset * 32;
+  DeferredFunctionInfo[F] = FuncBitOffset + FuncBitcodeOffsetDelta;
+  // Set the LastFunctionBlockBit to point to the last function block.
+  // Later when parsing is resumed after function materialization,
+  // we can simply skip that last function block.
+  if (FuncBitOffset > LastFunctionBlockBit)
+    LastFunctionBlockBit = FuncBitOffset;
+}
+
+/// Read a new-style GlobalValue symbol table.
+Error BitcodeReader::parseGlobalValueSymbolTable() {
+  unsigned FuncBitcodeOffsetDelta =
+      Stream.getAbbrevIDWidth() + bitc::BlockIDWidth;
+
+  if (Stream.EnterSubBlock(bitc::VALUE_SYMTAB_BLOCK_ID))
+    return error("Invalid record");
+
+  SmallVector<uint64_t, 64> Record;
+  while (true) {
+    BitstreamEntry Entry = Stream.advanceSkippingSubblocks();
+
+    switch (Entry.Kind) {
+    case BitstreamEntry::SubBlock:
+    case BitstreamEntry::Error:
+      return error("Malformed block");
+    case BitstreamEntry::EndBlock:
+      return Error::success();
+    case BitstreamEntry::Record:
+      break;
+    }
+
+    Record.clear();
+    switch (Stream.readRecord(Entry.ID, Record)) {
+    case bitc::VST_CODE_FNENTRY: // [valueid, offset]
+      setDeferredFunctionInfo(FuncBitcodeOffsetDelta,
+                              cast<Function>(ValueList[Record[0]]), Record);
+      break;
+    }
+  }
+}
+
 /// Parse the value symbol table at either the current parsing location or
 /// at the given bit offset if provided.
 Error BitcodeReader::parseValueSymbolTable(uint64_t Offset) {
   uint64_t CurrentBit;
   // Pass in the Offset to distinguish between calling for the module-level
   // VST (where we want to jump to the VST offset) and the function-level
   // VST (where we don't).
-  if (Offset > 0)
+  if (Offset > 0) {
     CurrentBit = jumpToValueSymbolTable(Offset, Stream);
+    // If this module uses a string table, read this as a module-level VST.
+    if (UseStrtab) {
+      if (Error Err = parseGlobalValueSymbolTable())
+        return Err;
+      Stream.JumpToBit(CurrentBit);
+      return Error::success();
+    }
+    // Otherwise, the VST will be in a similar format to a function-level VST,
+    // and will contain symbol names.
+  }
 
   // Compute the delta between the bitcode indices in the VST (the word offset
   // to the word-aligned ENTER_SUBBLOCK for the function block, and that
   // expected by the lazy reader. The reader's EnterSubBlock expects to have
   // already read the ENTER_SUBBLOCK code (size getAbbrevIDWidth) and BlockID
   // (size BlockIDWidth). Note that we access the stream's AbbrevID width here
   // just before entering the VST subblock because: 1) the EnterSubBlock
   // changes the AbbrevID width; 2) the VST block is nested within the same
while (true) {
     }
     case bitc::VST_CODE_FNENTRY: {
       // VST_CODE_FNENTRY: [valueid, offset, namechar x N]
       Expected<Value *> ValOrErr = recordValue(Record, 2, TT);
       if (Error Err = ValOrErr.takeError())
         return Err;
       Value *V = ValOrErr.get();
 
-      auto *F = dyn_cast<Function>(V);
       // Ignore function offsets emitted for aliases of functions in older
       // versions of LLVM.
-      if (!F)
-        break;
-
-      // Note that we subtract 1 here because the offset is relative to one word
-      // before the start of the identification or module block, which was
-      // historically always the start of the regular bitcode header.
-      uint64_t FuncWordOffset = Record[1] - 1;
-      uint64_t FuncBitOffset = FuncWordOffset * 32;
-      DeferredFunctionInfo[F] = FuncBitOffset + FuncBitcodeOffsetDelta;
-      // Set the LastFunctionBlockBit to point to the last function block.
-      // Later when parsing is resumed after function materialization,
-      // we can simply skip that last function block.
-      if (FuncBitOffset > LastFunctionBlockBit)
-        LastFunctionBlockBit = FuncBitOffset;
+      if (auto *F = dyn_cast<Function>(V))
+        setDeferredFunctionInfo(FuncBitcodeOffsetDelta, F, Record);
       break;
     }
     case bitc::VST_CODE_BBENTRY: {
       if (convertToString(Record, 1, ValueName))
         return error("Invalid record");
       BasicBlock *BB = getBasicBlock(Record[0]);
       if (!BB)
         return error("Invalid record");
bool BitcodeReaderBase::readBlockInfo() {
   Optional<BitstreamBlockInfo> NewBlockInfo = Stream.ReadBlockInfoBlock();
   if (!NewBlockInfo)
     return true;
   BlockInfo = std::move(*NewBlockInfo);
   return false;
 }
 
 Error BitcodeReader::parseComdatRecord(ArrayRef<uint64_t> Record) {
-  // [selection_kind, name]
-  if (Record.size() < 2)
+  // v1: [selection_kind, name]
+  // v2: [strtab_offset, strtab_size, selection_kind]
+  StringRef Name;
+  std::tie(Name, Record) = readNameFromStrtab(Record);
+
+  if (Record.size() < 1)
     return error("Invalid record");
   Comdat::SelectionKind SK = getDecodedComdatSelectionKind(Record[0]);
-  std::string Name;
+  std::string OldFormatName;
+  if (!UseStrtab) {
+    if (Record.size() < 2)
+      return error("Invalid record");
     unsigned ComdatNameSize = Record[1];
-  Name.reserve(ComdatNameSize);
+    OldFormatName.reserve(ComdatNameSize);
     for (unsigned i = 0; i != ComdatNameSize; ++i)
-    Name += (char)Record[2 + i];
+      OldFormatName += (char)Record[2 + i];
+    Name = OldFormatName;
+  }
   Comdat *C = TheModule->getOrInsertComdat(Name);
   C->setSelectionKind(SK);
   ComdatList.push_back(C);
   return Error::success();
 }
 
 Error BitcodeReader::parseGlobalVarRecord(ArrayRef<uint64_t> Record) {
-  // [pointer type, isconst, initid, linkage, alignment, section,
+  // v1: [pointer type, isconst, initid, linkage, alignment, section,
   // visibility, threadlocal, unnamed_addr, externally_initialized,
-  // dllstorageclass, comdat]
+  // dllstorageclass, comdat] (name in VST)
+  // v2: [strtab_offset, strtab_size, v1]
+  StringRef Name;
+  std::tie(Name, Record) = readNameFromStrtab(Record);
+
   if (Record.size() < 6)
     return error("Invalid record");
   Type *Ty = getTypeByID(Record[0]);
   if (!Ty)
     return error("Invalid record");
   bool isConstant = Record[1] & 1;
   bool explicitType = Record[1] & 2;
   unsigned AddressSpace;
Error BitcodeReader::parseGlobalVarRecord(ArrayRef<uint64_t> Record) {
   if (Record.size() > 8)
     UnnamedAddr = getDecodedUnnamedAddrType(Record[8]);
 
   bool ExternallyInitialized = false;
   if (Record.size() > 9)
     ExternallyInitialized = Record[9];
 
   GlobalVariable *NewGV =
-      new GlobalVariable(*TheModule, Ty, isConstant, Linkage, nullptr, "",
+      new GlobalVariable(*TheModule, Ty, isConstant, Linkage, nullptr, Name,
                          nullptr, TLM, AddressSpace, ExternallyInitialized);
   NewGV->setAlignment(Alignment);
   if (!Section.empty())
     NewGV->setSection(Section);
   NewGV->setVisibility(Visibility);
   NewGV->setUnnamedAddr(UnnamedAddr);
 
   if (Record.size() > 10)
if (Record.size() > 11) {
     }
   } else if (hasImplicitComdat(RawLinkage)) {
     NewGV->setComdat(reinterpret_cast<Comdat *>(1));
   }
   return Error::success();
 }
 
 Error BitcodeReader::parseFunctionRecord(ArrayRef<uint64_t> Record) {
-  // [type, callingconv, isproto, linkage, paramattr, alignment, section,
+  // v1: [type, callingconv, isproto, linkage, paramattr, alignment, section,
   // visibility, gc, unnamed_addr, prologuedata, dllstorageclass, comdat,
-  // prefixdata]
+  // prefixdata] (name in VST)
+  // v2: [strtab_offset, strtab_size, v1]
+  StringRef Name;
+  std::tie(Name, Record) = readNameFromStrtab(Record);
+
   if (Record.size() < 8)
     return error("Invalid record");
   Type *Ty = getTypeByID(Record[0]);
   if (!Ty)
     return error("Invalid record");
   if (auto *PTy = dyn_cast<PointerType>(Ty))
     Ty = PTy->getElementType();
   auto *FTy = dyn_cast<FunctionType>(Ty);
   if (!FTy)
     return error("Invalid type for value");
   auto CC = static_cast<CallingConv::ID>(Record[1]);
   if (CC & ~CallingConv::MaxID)
     return error("Invalid calling convention ID");
 
   Function *Func =
-      Function::Create(FTy, GlobalValue::ExternalLinkage, "", TheModule);
+      Function::Create(FTy, GlobalValue::ExternalLinkage, Name, TheModule);
 
   Func->setCallingConv(CC);
   bool isProto = Record[2];
   uint64_t RawLinkage = Record[3];
   Func->setLinkage(getDecodedLinkage(RawLinkage));
   Func->setAttributes(getAttributes(Record[4]));
 
   unsigned Alignment;
if (!isProto) {
     FunctionsWithBodies.push_back(Func);
     DeferredFunctionInfo[Func] = 0;
   }
   return Error::success();
 }
 
 Error BitcodeReader::parseGlobalIndirectSymbolRecord(
     unsigned BitCode, ArrayRef<uint64_t> Record) {
-  // ALIAS_OLD: [alias type, aliasee val#, linkage]
-  // ALIAS: [alias type, addrspace, aliasee val#, linkage, visibility,
-  // dllstorageclass]
-  // IFUNC: [alias type, addrspace, aliasee val#, linkage,
-  // visibility, dllstorageclass]
+  // v1 ALIAS_OLD: [alias type, aliasee val#, linkage] (name in VST)
+  // v1 ALIAS: [alias type, addrspace, aliasee val#, linkage, visibility,
+  // dllstorageclass] (name in VST)
+  // v1 IFUNC: [alias type, addrspace, aliasee val#, linkage,
+  // visibility, dllstorageclass] (name in VST)
+  // v2: [strtab_offset, strtab_size, v1]
+  StringRef Name;
+  std::tie(Name, Record) = readNameFromStrtab(Record);
+
   bool NewRecord = BitCode != bitc::MODULE_CODE_ALIAS_OLD;
   if (Record.size() < (3 + (unsigned)NewRecord))
     return error("Invalid record");
   unsigned OpNum = 0;
   Type *Ty = getTypeByID(Record[OpNum++]);
   if (!Ty)
     return error("Invalid record");
 
   unsigned AddrSpace;
   if (!NewRecord) {
     auto *PTy = dyn_cast<PointerType>(Ty);
     if (!PTy)
       return error("Invalid type for value");
     Ty = PTy->getElementType();
     AddrSpace = PTy->getAddressSpace();
   } else {
     AddrSpace = Record[OpNum++];
   }
 
   auto Val = Record[OpNum++];
   auto Linkage = Record[OpNum++];
   GlobalIndirectSymbol *NewGA;
   if (BitCode == bitc::MODULE_CODE_ALIAS ||
       BitCode == bitc::MODULE_CODE_ALIAS_OLD)
-    NewGA = GlobalAlias::create(Ty, AddrSpace, getDecodedLinkage(Linkage), "",
+    NewGA = GlobalAlias::create(Ty, AddrSpace, getDecodedLinkage(Linkage), Name,
                                 TheModule);
   else
-    NewGA = GlobalIFunc::create(Ty, AddrSpace, getDecodedLinkage(Linkage), "",
+    NewGA = GlobalIFunc::create(Ty, AddrSpace, getDecodedLinkage(Linkage), Name,
                                 nullptr, TheModule);
   // Old bitcode files didn't have visibility field.
   // Local linkage must have default visibility.
   if (OpNum != Record.size()) {
     auto VisInd = OpNum++;
     if (!NewGA->hasLocalLinkage())
       // FIXME: Change to an error if non-default in 4.0.
       NewGA->setVisibility(getDecodedVisibility(Record[VisInd]));
Error BitcodeReader::materializeModule() {
   return Error::success();
 }
 
 std::vector<StructType *> BitcodeReader::getIdentifiedStructTypes() const {
   return IdentifiedStructTypes;
 }
 
 ModuleSummaryIndexBitcodeReader::ModuleSummaryIndexBitcodeReader(
-    BitstreamCursor Cursor, ModuleSummaryIndex &TheIndex)
-    : BitcodeReaderBase(std::move(Cursor)), TheIndex(TheIndex) {}
+    BitstreamCursor Cursor, StringRef Strtab, ModuleSummaryIndex &TheIndex)
+    : BitcodeReaderBase(std::move(Cursor), Strtab), TheIndex(TheIndex) {}
 
 std::pair<GlobalValue::GUID, GlobalValue::GUID>
 ModuleSummaryIndexBitcodeReader::getGUIDFromValueId(unsigned ValueId) {
   auto VGI = ValueIdToCallGraphGUIDMap.find(ValueId);
   assert(VGI != ValueIdToCallGraphGUIDMap.end());
   return VGI->second;
 }
 
+void ModuleSummaryIndexBitcodeReader::setValueGUID(
+    uint64_t ValueID, StringRef ValueName, GlobalValue::LinkageTypes Linkage,
+    StringRef SourceFileName) {
+  std::string GlobalId =
+      GlobalValue::getGlobalIdentifier(ValueName, Linkage, SourceFileName);
+  auto ValueGUID = GlobalValue::getGUID(GlobalId);
+  auto OriginalNameID = ValueGUID;
+  if (GlobalValue::isLocalLinkage(Linkage))
+    OriginalNameID = GlobalValue::getGUID(ValueName);
+  if (PrintSummaryGUIDs)
+    dbgs() << "GUID " << ValueGUID << "(" << OriginalNameID << ") is "
+           << ValueName << "\n";
+  ValueIdToCallGraphGUIDMap[ValueID] =
+      std::make_pair(ValueGUID, OriginalNameID);
+}
+
 // Specialized value symbol table parser used when reading module index
 // blocks where we don't actually create global values. The parsed information
 // is saved in the bitcode reader for use when later parsing summaries.
 Error ModuleSummaryIndexBitcodeReader::parseValueSymbolTable(
     uint64_t Offset,
     DenseMap<unsigned, GlobalValue::LinkageTypes> &ValueIdToLinkageMap) {
+  // With a strtab the VST is not required to parse the summary.
+  if (UseStrtab)
+    return Error::success();
+
   assert(Offset > 0 && "Expected non-zero VST offset");
   uint64_t CurrentBit = jumpToValueSymbolTable(Offset, Stream);
 
   if (Stream.EnterSubBlock(bitc::VALUE_SYMTAB_BLOCK_ID))
     return error("Invalid record");
 
   SmallVector<uint64_t, 64> Record;
 
case bitc::VST_CODE_ENTRY: { // VST_CODE_ENTRY: [valueid, namechar x N]
       if (convertToString(Record, 1, ValueName))
         return error("Invalid record");
       unsigned ValueID = Record[0];
       assert(!SourceFileName.empty());
       auto VLI = ValueIdToLinkageMap.find(ValueID);
       assert(VLI != ValueIdToLinkageMap.end() &&
              "No linkage found for VST entry?");
       auto Linkage = VLI->second;
-      std::string GlobalId =
-          GlobalValue::getGlobalIdentifier(ValueName, Linkage, SourceFileName);
-      auto ValueGUID = GlobalValue::getGUID(GlobalId);
-      auto OriginalNameID = ValueGUID;
-      if (GlobalValue::isLocalLinkage(Linkage))
-        OriginalNameID = GlobalValue::getGUID(ValueName);
-      if (PrintSummaryGUIDs)
-        dbgs() << "GUID " << ValueGUID << "(" << OriginalNameID << ") is "
-               << ValueName << "\n";
-      ValueIdToCallGraphGUIDMap[ValueID] =
-          std::make_pair(ValueGUID, OriginalNameID);
+      setValueGUID(ValueID, ValueName, Linkage, SourceFileName);
       ValueName.clear();
       break;
     }
     case bitc::VST_CODE_FNENTRY: {
       // VST_CODE_FNENTRY: [valueid, offset, namechar x N]
       if (convertToString(Record, 2, ValueName))
         return error("Invalid record");
       unsigned ValueID = Record[0];
       assert(!SourceFileName.empty());
       auto VLI = ValueIdToLinkageMap.find(ValueID);
       assert(VLI != ValueIdToLinkageMap.end() &&
              "No linkage found for VST entry?");
       auto Linkage = VLI->second;
-      std::string FunctionGlobalId = GlobalValue::getGlobalIdentifier(
-          ValueName, VLI->second, SourceFileName);
-      auto FunctionGUID = GlobalValue::getGUID(FunctionGlobalId);
-      auto OriginalNameID = FunctionGUID;
-      if (GlobalValue::isLocalLinkage(Linkage))
-        OriginalNameID = GlobalValue::getGUID(ValueName);
-      if (PrintSummaryGUIDs)
-        dbgs() << "GUID " << FunctionGUID << "(" << OriginalNameID << ") is "
-               << ValueName << "\n";
-      ValueIdToCallGraphGUIDMap[ValueID] =
-          std::make_pair(FunctionGUID, OriginalNameID);
-
+      setValueGUID(ValueID, ValueName, Linkage, SourceFileName);
       ValueName.clear();
       break;
     }
     case bitc::VST_CODE_COMBINED_ENTRY: {
       // VST_CODE_COMBINED_ENTRY: [valueid, refguid]
       unsigned ValueID = Record[0];
       GlobalValue::GUID RefGUID = Record[1];
       // The "original name", which is the second value of the pair will be
case BitstreamEntry::SubBlock:
       continue;
 
     case BitstreamEntry::Record: {
         Record.clear();
         auto BitCode = Stream.readRecord(Entry.ID, Record);
         switch (BitCode) {
         default:
           break; // Default behavior, ignore unknown content.
+        case bitc::MODULE_CODE_VERSION: {
+          if (Error Err = parseVersionRecord(Record).takeError())
+            return Err;
+          break;
+        }
         /// MODULE_CODE_SOURCE_FILENAME: [namechar x N]
         case bitc::MODULE_CODE_SOURCE_FILENAME: {
           SmallString<128> ValueName;
           if (convertToString(Record, 0, ValueName))
             return error("Invalid record");
           SourceFileName = ValueName.c_str();
           break;
         }
case BitstreamEntry::Record: {
         case bitc::MODULE_CODE_VSTOFFSET:
           if (Record.size() < 1)
             return error("Invalid record");
           // Note that we subtract 1 here because the offset is relative to one
           // word before the start of the identification or module block, which
           // was historically always the start of the regular bitcode header.
           VSTOffset = Record[0] - 1;
           break;
-        // GLOBALVAR: [pointer type, isconst,     initid,       linkage, ...]
-        // FUNCTION:  [type,         callingconv, isproto,      linkage, ...]
-        // ALIAS:     [alias type,   addrspace,   aliasee val#, linkage, ...]
+        // v1 GLOBALVAR: [pointer type, isconst,     initid,       linkage, ...]
+        // v1 FUNCTION:  [type,         callingconv, isproto,      linkage, ...]
+        // v1 ALIAS:     [alias type,   addrspace,   aliasee val#, linkage, ...]
+        // v2: [strtab offset, strtab size, v1]
         case bitc::MODULE_CODE_GLOBALVAR:
         case bitc::MODULE_CODE_FUNCTION:
         case bitc::MODULE_CODE_ALIAS: {
-          if (Record.size() <= 3)
+          StringRef Name;
+          ArrayRef<uint64_t> GVRecord;
+          std::tie(Name, GVRecord) = readNameFromStrtab(Record);
+          if (GVRecord.size() <= 3)
             return error("Invalid record");
-          uint64_t RawLinkage = Record[3];
+          uint64_t RawLinkage = GVRecord[3];
           GlobalValue::LinkageTypes Linkage = getDecodedLinkage(RawLinkage);
+          if (!UseStrtab) {
             ValueIdToLinkageMap[ValueId++] = Linkage;
             break;
           }
+
+          setValueGUID(ValueId++, Name, Linkage, SourceFileName);
+          break;
+        }
         }
       }
       continue;
     }
   }
 }
 
 std::vector<ValueInfo>
while (true) {
     // via the bitcode offset of the summary records (which were saved
     // in the combined index VST entries). The records also contain
     // information used for ThinLTO renaming and importing.
     Record.clear();
     auto BitCode = Stream.readRecord(Entry.ID, Record);
     switch (BitCode) {
     default: // Default behavior: ignore.
       break;
+    case bitc::FS_VALUE_GUID: { // [valueid, refguid]
+      uint64_t ValueID = Record[0];
+      GlobalValue::GUID RefGUID = Record[1];
+      ValueIdToCallGraphGUIDMap[ValueID] = std::make_pair(RefGUID, RefGUID);
+      break;
+    }
     // FS_PERMODULE: [valueid, flags, instcount, numrefs, numrefs x valueid,
     //                n x (valueid)]
     // FS_PERMODULE_PROFILE: [valueid, flags, instcount, numrefs,
     //                        numrefs x valueid,
     //                        n x (valueid, hotness)]
     case bitc::FS_PERMODULE:
     case bitc::FS_PERMODULE_PROFILE: {
       unsigned ValueID = Record[0];

 } // end anonymous namespace
 
 static ManagedStatic<BitcodeErrorCategoryType> ErrorCategory;
 
 const std::error_category &llvm::BitcodeErrorCategory() {
   return *ErrorCategory;
 }
 
+static Expected<StringRef> readStrtab(BitstreamCursor &Stream) {
+  if (Stream.EnterSubBlock(bitc::STRTAB_BLOCK_ID))
+    return error("Invalid record");
+
+  StringRef Strtab;
+  while (1) {
+    BitstreamEntry Entry = Stream.advance();
+    switch (Entry.Kind) {
+    case BitstreamEntry::EndBlock:
+      return Strtab;
+
+    case BitstreamEntry::Error:
+      return error("Malformed block");
+
+    case BitstreamEntry::SubBlock:
+      if (Stream.SkipBlock())
+        return error("Malformed block");
+      break;
+
+    case BitstreamEntry::Record:
+      StringRef Blob;
+      SmallVector<uint64_t, 1> Record;
+      if (Stream.readRecord(Entry.ID, Record, &Blob) == bitc::STRTAB_BLOB)
+        Strtab = Blob;
+      break;
+    }
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // External interface
 //===----------------------------------------------------------------------===//
 
 Expected<std::vector<BitcodeModule>>
 llvm::getBitcodeModuleList(MemoryBufferRef Buffer) {
   Expected<BitstreamCursor> StreamOrErr = initStream(Buffer);
   if (!StreamOrErr)
case BitstreamEntry::SubBlock: {
 
         Modules.push_back({Stream.getBitcodeBytes().slice(
                                BCBegin, Stream.getCurrentByteNo() - BCBegin),
                            Buffer.getBufferIdentifier(), IdentificationBit,
                            ModuleBit});
         continue;
       }
 
+      if (Entry.ID == bitc::STRTAB_BLOCK_ID) {
+        Expected<StringRef> Strtab = readStrtab(Stream);
+        if (!Strtab)
+          return Strtab.takeError();
+        // This string table is used by every preceding bitcode module that does
+        // not have its own string table. A bitcode file may have multiple
+        // string tables if it was created by binary concatenation, for example
+        // with "llvm-cat -b".
+        for (auto I = Modules.rbegin(), E = Modules.rend(); I != E; ++I) {
+          if (!I->Strtab.empty())
+            break;
+          I->Strtab = *Strtab;
+        }
+        continue;
+      }
+
       if (Stream.SkipBlock())
         return error("Malformed block");
       continue;
     }
     case BitstreamEntry::Record:
       Stream.skipRecord(Entry.ID);
       continue;
     }
Expected<std::string> ProducerIdentificationOrErr =
         readIdentificationBlock(Stream);
     if (!ProducerIdentificationOrErr)
       return ProducerIdentificationOrErr.takeError();
 
     ProducerIdentification = *ProducerIdentificationOrErr;
   }
 
   Stream.JumpToBit(ModuleBit);
-  auto *R =
-      new BitcodeReader(std::move(Stream), ProducerIdentification, Context);
+  auto *R = new BitcodeReader(std::move(Stream), Strtab, ProducerIdentification,
+                              Context);
 
   std::unique_ptr<Module> M =
       llvm::make_unique<Module>(ModuleIdentifier, Context);
   M->setMaterializer(R);
 
   // Delay parsing Metadata if ShouldLazyLoadMetadata is true.
   if (Error Err =
           R->parseBitcodeInto(M.get(), ShouldLazyLoadMetadata, IsImporting))

 }
 
 // Parse the specified bitcode buffer, returning the function info index.
 Expected<std::unique_ptr<ModuleSummaryIndex>> BitcodeModule::getSummary() {
   BitstreamCursor Stream(Buffer);
   Stream.JumpToBit(ModuleBit);
 
   auto Index = llvm::make_unique<ModuleSummaryIndex>();
-  ModuleSummaryIndexBitcodeReader R(std::move(Stream), *Index);
+  ModuleSummaryIndexBitcodeReader R(std::move(Stream), Strtab, *Index);
 
   if (Error Err = R.parseModule(ModuleIdentifier))
     return std::move(Err);
 
   return std::move(Index);
 }
 
 // Check if the given bitcode buffer contains a global value summary block.

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/IR/UseListOrder.h"
 #include "llvm/IR/ValueSymbolTable.h"
+#include "llvm/MC/StringTableBuilder.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/SHA1.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cctype>
 #include <map>
 using namespace llvm;

 
 /// 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;
 
-  /// 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 BitcodeWriterBase object that writes to the provided
   /// \p Stream.
   BitcodeWriterBase(BitstreamWriter &Stream) : Stream(Stream) {}
 
 protected:
-  bool hasVSTOffsetPlaceholder() { return VSTOffsetPlaceholder != 0; }
-  void writeValueSymbolTableForwardDecl();
   void writeBitcodeHeader();
+  void writeModuleVersion();
 };
 
+void BitcodeWriterBase::writeModuleVersion() {
+  // VERSION: [version#]
+  Stream.EmitRecord(bitc::MODULE_CODE_VERSION, ArrayRef<uint64_t>{2});
+}
+
 /// Class to manage the bitcode writing for a module.
 class ModuleBitcodeWriter : public BitcodeWriterBase {
   /// Pointer to the buffer allocated by caller for bitcode writing.
   const SmallVectorImpl<char> &Buffer;
 
+  StringTableBuilder &StrtabBuilder;
+
   /// 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;
class ModuleBitcodeWriter : public BitcodeWriterBase {
   /// 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 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)
-      : BitcodeWriterBase(Stream), Buffer(Buffer), M(*M),
-        VE(*M, ShouldPreserveUseListOrder), Index(Index),
+      : BitcodeWriterBase(Stream), Buffer(Buffer), StrtabBuilder(StrtabBuilder),
+        M(*M), VE(*M, ShouldPreserveUseListOrder), Index(Index),
         GenerateHash(GenerateHash), ModHash(ModHash),
         BitcodeStartBit(Stream.GetCurrentBitNo()) {
     // 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();

 
 private:
   uint64_t bitcodeStartBit() { return BitcodeStartBit; }
 
   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);
bool pushValueAndType(const Value *V, unsigned InstID,
                         SmallVectorImpl<unsigned> &Vals);
   void writeOperandBundles(ImmutableCallSite CS, 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 writeValueSymbolTable(
-      const ValueSymbolTable &VST, bool IsModuleLevel = false,
-      DenseMap<const Function *, uint64_t> *FunctionToBitcodeIndex = nullptr);
+  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 writePerModuleFunctionSummaryRecord(SmallVector<uint64_t, 64> &NameVals,
                                            GlobalValueSummary *Summary,
public:
   /// Obtain the end iterator over the summaries to be written.
   iterator end() { return iterator(*this, /*IsAtEnd=*/true); }
 
   /// Main entry point for writing a combined index to bitcode.
   void write();
 
 private:
   void writeModStrings();
-  void writeCombinedValueSymbolTable();
   void writeCombinedGlobalValueSummary();
 
   /// Indicates whether the provided \p ModulePath should be written into
   /// the module string table, e.g. if full index written or if it is in
   /// the provided subset.
   bool doIncludeModule(StringRef ModulePath) {
     return !ModuleToSummariesForIndex ||
            ModuleToSummariesForIndex->count(ModulePath);
   }
 
   bool hasValueId(GlobalValue::GUID ValGUID) {
     const auto &VMI = GUIDToValueIdMap.find(ValGUID);
     return VMI != GUIDToValueIdMap.end();
   }
+  void assignValueId(GlobalValue::GUID ValGUID) {
+    unsigned &ValueId = GUIDToValueIdMap[ValGUID];
+    if (ValueId == 0)
+      ValueId = ++GlobalValueId;
+  }
   unsigned getValueId(GlobalValue::GUID ValGUID) {
-    const auto &VMI = GUIDToValueIdMap.find(ValGUID);
-    // If this GUID doesn't have an entry, assign one.
-    if (VMI == GUIDToValueIdMap.end()) {
-      GUIDToValueIdMap[ValGUID] = ++GlobalValueId;
-      return GlobalValueId;
-    } else {
-      return VMI->second;
-    }
-  }
+    auto VMI = GUIDToValueIdMap.find(ValGUID);
+    assert(VMI != GUIDToValueIdMap.end());
   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;
static unsigned getEncodedUnnamedAddr(const GlobalValue &GV) {
   case GlobalValue::UnnamedAddr::Global: return 1;
   }
   llvm_unreachable("Invalid unnamed_addr");
 }
 
 void ModuleBitcodeWriter::writeComdats() {
   SmallVector<unsigned, 64> Vals;
   for (const Comdat *C : VE.getComdats()) {
-    // COMDAT: [selection_kind, name]
+    // COMDAT: [strtab offset, strtab size, selection_kind]
+    Vals.push_back(StrtabBuilder.add(C->getName()));
+    Vals.push_back(C->getName().size());
     Vals.push_back(getEncodedComdatSelectionKind(*C));
-    size_t Size = C->getName().size();
-    assert(isUInt<32>(Size));
-    Vals.push_back(Size);
-    for (char Chr : C->getName())
-      Vals.push_back((unsigned char)Chr);
     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 BitcodeWriterBase::writeValueSymbolTableForwardDecl() {
+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
void ModuleBitcodeWriter::writeModuleInfo() {
   }
 
   // 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 == 0)                                 // Alignment.
       Abbv->Add(BitCodeAbbrevOp(0));
     else {
       unsigned MaxEncAlignment = Log2_32(MaxAlignment)+1;
       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));
   }
 
-  // Emit the global variable information.
   SmallVector<unsigned, 64> Vals;
+  // Emit the module's source file name.
+  {
+    StringEncoding Bits = getStringEncoding(M.getSourceFileName().data(),
+                                            M.getSourceFileName().size());
+    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: [type, isconst, initid,
+    // GLOBALVAR: [strtab offset, strtab size, type, isconst, initid,
     //             linkage, alignment, section, visibility, threadlocal,
     //             unnamed_addr, externally_initialized, dllstorageclass,
     //             comdat]
+    Vals.push_back(StrtabBuilder.add(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(Log2_32(GV.getAlignment())+1);
     Vals.push_back(GV.hasSection() ? SectionMap[GV.getSection()] : 0);
     if (GV.isThreadLocal() ||
for (const GlobalVariable &GV : M.globals()) {
     }
 
     Stream.EmitRecord(bitc::MODULE_CODE_GLOBALVAR, Vals, AbbrevToUse);
     Vals.clear();
   }
 
   // Emit the function proto information.
   for (const Function &F : M) {
-    // FUNCTION:  [type, callingconv, isproto, linkage, paramattrs, alignment,
-    //             section, visibility, gc, unnamed_addr, prologuedata,
-    //             dllstorageclass, comdat, prefixdata, personalityfn]
+    // FUNCTION:  [strtab offset, strtab size, type, callingconv, isproto,
+    //             linkage, paramattrs, alignment, section, visibility, gc,
+    //             unnamed_addr, prologuedata, dllstorageclass, comdat,
+    //             prefixdata, personalityfn]
+    Vals.push_back(StrtabBuilder.add(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.getAttributeID(F.getAttributes()));
     Vals.push_back(Log2_32(F.getAlignment())+1);
     Vals.push_back(F.hasSection() ? SectionMap[F.getSection()] : 0);
     Vals.push_back(getEncodedVisibility(F));
for (const Function &F : M) {
 
     unsigned AbbrevToUse = 0;
     Stream.EmitRecord(bitc::MODULE_CODE_FUNCTION, Vals, AbbrevToUse);
     Vals.clear();
   }
 
   // Emit the alias information.
   for (const GlobalAlias &A : M.aliases()) {
-    // ALIAS: [alias type, aliasee val#, linkage, visibility, dllstorageclass,
-    //         threadlocal, unnamed_addr]
+    // ALIAS: [strtab offset, strtab size, alias type, aliasee val#, linkage,
+    //         visibility, dllstorageclass, threadlocal, unnamed_addr]
+    Vals.push_back(StrtabBuilder.add(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));
     unsigned AbbrevToUse = 0;
     Stream.EmitRecord(bitc::MODULE_CODE_ALIAS, Vals, AbbrevToUse);
     Vals.clear();
   }
 
   // Emit the ifunc information.
   for (const GlobalIFunc &I : M.ifuncs()) {
-    // IFUNC: [ifunc type, address space, resolver val#, linkage, visibility]
+    // IFUNC: [strtab offset, strtab size, ifunc type, address space, resolver
+    //         val#, linkage, visibility]
+    Vals.push_back(StrtabBuilder.add(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));
     Stream.EmitRecord(bitc::MODULE_CODE_IFUNC, Vals);
     Vals.clear();
   }
 
-  // Emit the module's source file name.
-  {
-    StringEncoding Bits = getStringEncoding(M.getSourceFileName().data(),
-                                            M.getSourceFileName().size());
-    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();
-  }
-
-  // If we have a VST, write the VSTOFFSET record placeholder.
-  if (M.getValueSymbolTable().empty())
-    return;
   writeValueSymbolTableForwardDecl();
 }
 
 static uint64_t getOptimizationFlags(const Value *V) {
   uint64_t Flags = 0;
 
   if (const auto *OBO = dyn_cast<OverflowingBinaryOperator>(V)) {
     if (OBO->hasNoSignedWrap())
case Instruction::VAArg:
     Vals.push_back(VE.getTypeID(I.getType())); // restype.
     break;
   }
 
   Stream.EmitRecord(Code, Vals, AbbrevToUse);
   Vals.clear();
 }
 
-/// Emit names for globals/functions etc. \p IsModuleLevel is true when
-/// we are writing the module-level VST, where we are including a function
-/// bitcode index and need to backpatch the VST forward declaration record.
-void ModuleBitcodeWriter::writeValueSymbolTable(
-    const ValueSymbolTable &VST, bool IsModuleLevel,
-    DenseMap<const Function *, uint64_t> *FunctionToBitcodeIndex) {
-  if (VST.empty()) {
-    // writeValueSymbolTableForwardDecl should have returned early as
-    // well. Ensure this handling remains in sync by asserting that
-    // the placeholder offset is not set.
-    assert(!IsModuleLevel || !hasVSTOffsetPlaceholder());
-    return;
-  }
-
-  if (IsModuleLevel && hasVSTOffsetPlaceholder()) {
-    // 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);
-  }
+/// 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) {
 
   Stream.EnterSubblock(bitc::VALUE_SYMTAB_BLOCK_ID, 4);
 
-  // For the module-level VST, add abbrev Ids for the VST_CODE_FNENTRY
-  // records, which are not used in the per-function VSTs.
-  unsigned FnEntry8BitAbbrev;
-  unsigned FnEntry7BitAbbrev;
-  unsigned FnEntry6BitAbbrev;
-  unsigned GUIDEntryAbbrev;
-  if (IsModuleLevel && hasVSTOffsetPlaceholder()) {
-    // 8-bit fixed-width VST_CODE_FNENTRY function strings.
-    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
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8));
-    FnEntry8BitAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+  unsigned FnEntryAbbrev = Stream.EmitAbbrev(std::move(Abbv));
 
-    // 7-bit fixed width VST_CODE_FNENTRY function strings.
-    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
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 7));
-    FnEntry7BitAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+  for (const Function &F : M) {
+    uint64_t Record[2];
 
-    // 6-bit char6 VST_CODE_FNENTRY function strings.
-    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
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Char6));
-    FnEntry6BitAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+    if (F.isDeclaration())
+      continue;
 
-    // FIXME: Change the name of this record as it is now used by
-    // the per-module index as well.
-    Abbv = std::make_shared<BitCodeAbbrev>();
-    Abbv->Add(BitCodeAbbrevOp(bitc::VST_CODE_COMBINED_ENTRY));
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // valueid
-    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // refguid
-    GUIDEntryAbbrev = Stream.EmitAbbrev(std::move(Abbv));
+    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.getKeyData(), Name.getKeyLength());
 
     unsigned AbbrevToUse = VST_ENTRY_8_ABBREV;
     NameVals.push_back(VE.getValueID(Name.getValue()));
 
-    Function *F = dyn_cast<Function>(Name.getValue());
-
     // VST_CODE_ENTRY:   [valueid, namechar x N]
-    // VST_CODE_FNENTRY: [valueid, funcoffset, 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 if (F && !F->isDeclaration()) {
-      // Must be the module-level VST, where we pass in the Index and
-      // have a VSTOffsetPlaceholder. The function-level VST should not
-      // contain any Function symbols.
-      assert(FunctionToBitcodeIndex);
-      assert(hasVSTOffsetPlaceholder());
-
-      // 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.
-      NameVals.push_back(BitcodeIndex / 32 + 1);
-
-      Code = bitc::VST_CODE_FNENTRY;
-      AbbrevToUse = FnEntry8BitAbbrev;
-      if (Bits == SE_Char6)
-        AbbrevToUse = FnEntry6BitAbbrev;
-      else if (Bits == SE_Fixed7)
-        AbbrevToUse = FnEntry7BitAbbrev;
     } 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();
   }
-  // Emit any GUID valueIDs created for indirect call edges into the
-  // module-level VST.
-  if (IsModuleLevel && hasVSTOffsetPlaceholder())
-    for (const auto &GI : valueIds()) {
-      NameVals.push_back(GI.second);
-      NameVals.push_back(GI.first);
-      Stream.EmitRecord(bitc::VST_CODE_COMBINED_ENTRY, NameVals,
-                        GUIDEntryAbbrev);
-      NameVals.clear();
-    }
-  Stream.ExitBlock();
-}
-
-/// Emit function names and summary offsets for the combined index
-/// used by ThinLTO.
-void IndexBitcodeWriter::writeCombinedValueSymbolTable() {
-  assert(hasVSTOffsetPlaceholder() && "Expected non-zero VSTOffsetPlaceholder");
-  // Get the offset of the VST we are writing, and backpatch it into
-  // the VST forward declaration record.
-  uint64_t VSTOffset = Stream.GetCurrentBitNo();
-  assert((VSTOffset & 31) == 0 && "VST block not 32-bit aligned");
-  Stream.BackpatchWord(VSTOffsetPlaceholder, VSTOffset / 32);
-
-  Stream.EnterSubblock(bitc::VALUE_SYMTAB_BLOCK_ID, 4);
-
-  auto Abbv = std::make_shared<BitCodeAbbrev>();
-  Abbv->Add(BitCodeAbbrevOp(bitc::VST_CODE_COMBINED_ENTRY));
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // valueid
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // refguid
-  unsigned EntryAbbrev = Stream.EmitAbbrev(std::move(Abbv));
-
-  SmallVector<uint64_t, 64> NameVals;
-  for (const auto &GVI : valueIds()) {
-    // VST_CODE_COMBINED_ENTRY: [valueid, refguid]
-    NameVals.push_back(GVI.second);
-    NameVals.push_back(GVI.first);
 
-    // Emit the finished record.
-    Stream.EmitRecord(bitc::VST_CODE_COMBINED_ENTRY, NameVals, EntryAbbrev);
-    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;
for (BasicBlock::const_iterator I = BB->begin(), E = BB->end();
       Stream.EmitRecord(bitc::FUNC_CODE_DEBUG_LOC, Vals);
       Vals.clear();
 
       LastDL = DL;
     }
 
   // Emit names for all the instructions etc.
   if (auto *Symtab = F.getValueSymbolTable())
-    writeValueSymbolTable(*Symtab);
+    writeFunctionLevelValueSymbolTable(*Symtab);
 
   if (NeedsMetadataAttachment)
     writeFunctionMetadataAttachment(F);
   if (VE.shouldPreserveUseListOrder())
     writeUseListBlock(&F);
   VE.purgeFunction();
   Stream.ExitBlock();
 }
void ModuleBitcodeWriter::writePerModuleGlobalValueSummary() {
 
   Stream.EmitRecord(bitc::FS_VERSION, ArrayRef<uint64_t>{INDEX_VERSION});
 
   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});
+  }
+
   // Abbrev for FS_PERMODULE.
   auto Abbv = std::make_shared<BitCodeAbbrev>();
   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));   // numrefs
   // numrefs x valueid, n x (valueid)
void ModuleBitcodeWriter::writePerModuleGlobalValueSummary() {
   Stream.ExitBlock();
 }
 
 /// Emit the combined summary section into the combined index file.
 void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   Stream.EnterSubblock(bitc::GLOBALVAL_SUMMARY_BLOCK_ID, 3);
   Stream.EmitRecord(bitc::FS_VERSION, ArrayRef<uint64_t>{INDEX_VERSION});
 
+  // Create value IDs for undefined references.
+  for (const auto &I : *this) {
+    if (auto *VS = dyn_cast<GlobalVarSummary>(I.second)) {
+      for (auto &RI : VS->refs())
+        assignValueId(RI.getGUID());
+      continue;
+    }
+
+    auto *FS = dyn_cast<FunctionSummary>(I.second);
+    if (!FS)
+      continue;
+    for (auto &RI : FS->refs())
+      assignValueId(RI.getGUID());
+
+    for (auto &EI : FS->calls()) {
+      GlobalValue::GUID GUID = EI.first.getGUID();
+      if (!hasValueId(GUID)) {
+        // For SamplePGO, the indirect call targets for local functions will
+        // have its original name annotated in profile. We try to find the
+        // corresponding PGOFuncName as the GUID.
+        GUID = Index.getGUIDFromOriginalID(GUID);
+        if (GUID == 0 || !hasValueId(GUID))
+          continue;
+      }
+      assignValueId(GUID);
+    }
+  }
+
+  for (const auto &GVI : valueIds()) {
+    Stream.EmitRecord(bitc::FS_VALUE_GUID,
+                      ArrayRef<uint64_t>{GVI.second, GVI.first});
+  }
+
   // 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));   // numrefs

 }
 
 void ModuleBitcodeWriter::write() {
   writeIdentificationBlock(Stream);
 
   Stream.EnterSubblock(bitc::MODULE_BLOCK_ID, 3);
   size_t BlockStartPos = Buffer.size();
 
-  SmallVector<unsigned, 1> Vals;
-  unsigned CurVersion = 1;
-  Vals.push_back(CurVersion);
-  Stream.EmitRecord(bitc::MODULE_CODE_VERSION, Vals);
+  writeModuleVersion();
 
   // Emit blockinfo, which defines the standard abbreviations etc.
   writeBlockInfo();
 
   // Emit information about attribute groups.
   writeAttributeGroupTable();
 
   // Emit information about parameter attributes.
for (Module::const_iterator F = M.begin(), E = M.end(); F != E; ++F)
     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();
 
-  writeValueSymbolTable(M.getValueSymbolTable(),
-                        /* IsModuleLevel */ true, &FunctionToBitcodeIndex);
+  writeGlobalValueSymbolTable(FunctionToBitcodeIndex);
 
   writeModuleHash(BlockStartPos);
 
   Stream.ExitBlock();
 }
 
 static void writeInt32ToBuffer(uint32_t Value, SmallVectorImpl<char> &Buffer,
                                uint32_t &Position) {
static void writeBitcodeHeader(BitstreamWriter &Stream) {
   Stream.Emit(0xD, 4);
 }
 
 BitcodeWriter::BitcodeWriter(SmallVectorImpl<char> &Buffer)
     : Buffer(Buffer), Stream(new BitstreamWriter(Buffer)) {
   writeBitcodeHeader(*Stream);
 }
 
-BitcodeWriter::~BitcodeWriter() = default;
+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::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) {
-  ModuleBitcodeWriter ModuleWriter(M, Buffer, *Stream,
+  ModuleBitcodeWriter ModuleWriter(M, Buffer, StrtabBuilder, *Stream,
                                    ShouldPreserveUseListOrder, Index,
                                    GenerateHash, ModHash);
   ModuleWriter.write();
 }
 
 /// WriteBitcodeToFile - 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);
   Writer.writeModule(M, ShouldPreserveUseListOrder, Index, GenerateHash,
                      ModHash);
+  Writer.writeStrtab();
 
   if (TT.isOSDarwin() || TT.isOSBinFormatMachO())
     emitDarwinBCHeaderAndTrailer(Buffer, TT);
 
   // Write the generated bitstream to "Out".
   Out.write((char*)&Buffer.front(), Buffer.size());
 }
 
 void IndexBitcodeWriter::write() {
   Stream.EnterSubblock(bitc::MODULE_BLOCK_ID, 3);
 
-  SmallVector<unsigned, 1> Vals;
-  unsigned CurVersion = 1;
-  Vals.push_back(CurVersion);
-  Stream.EmitRecord(bitc::MODULE_CODE_VERSION, Vals);
-
-  // If we have a VST, write the VSTOFFSET record placeholder.
-  writeValueSymbolTableForwardDecl();
+  writeModuleVersion();
 
   // Write the module paths in the combined index.
   writeModStrings();
 
   // Write the summary combined index records.
   writeCombinedGlobalValueSummary();
 
-  // Need a special VST writer for the combined index (we don't have a
-  // real VST and real values when this is invoked).
-  writeCombinedValueSymbolTable();
-
   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(

llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp

void splitAndWriteThinLTOBitcode(
   BitcodeWriter W(Buffer);
   // Save the module hash produced for the full bitcode, which will
   // be used in the backends, and use that in the minimized bitcode
   // produced for the full link.
   ModuleHash ModHash = {{0}};
   W.writeModule(&M, /*ShouldPreserveUseListOrder=*/false, &Index,
                 /*GenerateHash=*/true, &ModHash);
   W.writeModule(MergedM.get());
+  W.writeStrtab();
   OS << Buffer;
 
   // If a minimized bitcode module was requested for the thin link,
   // strip the debug info (the merged module was already stripped above)
   // and write it to the given OS.
   if (ThinLinkOS) {
     Buffer.clear();
     BitcodeWriter W2(Buffer);
     StripDebugInfo(M);
     W2.writeModule(&M, /*ShouldPreserveUseListOrder=*/false, &Index,
                    /*GenerateHash=*/false, &ModHash);
     W2.writeModule(MergedM.get());
+    W2.writeStrtab();
     *ThinLinkOS << Buffer;
   }
 }
 
 // Returns whether this module needs to be split because it uses type metadata.
 bool requiresSplit(Module &M) {
   SmallVector<MDNode *, 1> MDs;
   for (auto &GO : M.global_objects()) {

llvm/test/Bitcode/thinlto-alias.ll

 ; Test to check the callgraph in summary
 ; RUN: opt -module-summary %s -o %t.o
 ; RUN: llvm-bcanalyzer -dump %t.o | FileCheck %s
 ; RUN: opt -module-summary %p/Inputs/thinlto-alias.ll -o %t2.o
 ; RUN: llvm-lto -thinlto -o %t3 %t.o %t2.o
 ; RUN: llvm-bcanalyzer -dump %t3.thinlto.bc | FileCheck %s --check-prefix=COMBINED
 
+; CHECK: <SOURCE_FILENAME
+; "main"
+; CHECK-NEXT: <FUNCTION op0=0 op1=4
+; "analias"
+; CHECK-NEXT: <FUNCTION op0=4 op1=7
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
 ; CHECK-NEXT:    <VERSION
-; See if the call to func is registered, using the expected callsite count
-; and value id matching the subsequent value symbol table.
-; CHECK-NEXT:    <PERMODULE {{.*}} op4=[[FUNCID:[0-9]+]]/>
+; See if the call to func is registered.
+; The value id 1 matches the second FUNCTION record above.
+; CHECK-NEXT:    <PERMODULE {{.*}} op4=1/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
-; CHECK-NEXT:  <VALUE_SYMTAB
-; CHECK-NEXT:    <FNENTRY {{.*}} record string = 'main'
-; External function analias should have entry with value id FUNCID
-; CHECK-NEXT:    <ENTRY {{.*}} op0=[[FUNCID]] {{.*}} record string = 'analias'
-; CHECK-NEXT:  </VALUE_SYMTAB>
+
+; CHECK: <STRTAB_BLOCK
+; CHECK-NEXT: blob data = 'mainanalias'
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
-; See if the call to analias is registered, using the expected callsite count
-; and value id matching the subsequent value symbol table.
-; COMBINED-NEXT:    <COMBINED {{.*}} op5=[[ALIASID:[0-9]+]]/>
-; Followed by the alias and aliasee
+; See if the call to analias is registered, using the expected value id.
+; COMBINED-NEXT:    <VALUE_GUID op0=[[ALIASID:[0-9]+]] op1=-5751648690987223394/>
+; COMBINED-NEXT:    <VALUE_GUID
+; COMBINED-NEXT:    <VALUE_GUID op0=[[ALIASEEID:[0-9]+]] op1=-1039159065113703048/>
+; COMBINED-NEXT:    <COMBINED {{.*}} op5=[[ALIASID]]/>
 ; COMBINED-NEXT:    <COMBINED {{.*}}
-; COMBINED-NEXT:    <COMBINED_ALIAS  {{.*}} op3=[[ALIASEEID:[0-9]+]]
+; COMBINED-NEXT:    <COMBINED_ALIAS  {{.*}} op3=[[ALIASEEID]]
 ; COMBINED-NEXT:  </GLOBALVAL_SUMMARY_BLOCK
-; COMBINED-NEXT:  <VALUE_SYMTAB
-; Entry for function func should have entry with value id ALIASID
-; COMBINED-NEXT:    <COMBINED_ENTRY {{.*}} op0=[[ALIASID]] op1=-5751648690987223394/>
-; COMBINED-NEXT:    <COMBINED
-; COMBINED-NEXT:    <COMBINED_ENTRY {{.*}} op0=[[ALIASEEID]] op1=-1039159065113703048/>
-; COMBINED-NEXT:  </VALUE_SYMTAB>
 
 ; ModuleID = 'thinlto-function-summary-callgraph.ll'
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 ; Function Attrs: nounwind uwtable
 define i32 @main() {
 entry:
     call void (...) @analias()
     ret i32 0
 }
 
 declare void @analias(...)

llvm/test/Bitcode/thinlto-function-summary-callgraph-pgo.ll

 ; Test to check the callgraph in summary when there is PGO
 ; RUN: opt -module-summary %s -o %t.o
 ; RUN: llvm-bcanalyzer -dump %t.o | FileCheck %s
 
 ; RUN: opt -module-summary %p/Inputs/thinlto-function-summary-callgraph.ll -o %t2.o
 ; RUN: llvm-lto -thinlto -o %t3 %t.o %t2.o
 ; RUN: llvm-bcanalyzer -dump %t3.thinlto.bc | FileCheck %s --check-prefix=COMBINED
 
 ; Check parsing for old summary versions generated from this file.
 ; RUN: llvm-lto -thinlto-index-stats %p/Inputs/thinlto-function-summary-callgraph-pgo.1.bc  | FileCheck %s --check-prefix=OLD
 ; RUN: llvm-lto -thinlto-index-stats %p/Inputs/thinlto-function-summary-callgraph-pgo-combined.1.bc  | FileCheck %s --check-prefix=OLD-COMBINED
 
+; CHECK: <SOURCE_FILENAME
+; CHECK-NEXT: <FUNCTION
+; "func"
+; CHECK-NEXT: <FUNCTION op0=4 op1=4
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
 ; CHECK-NEXT:    <VERSION
-; See if the call to func is registered, using the expected callsite count
-; and hotness type, with value id matching the subsequent value symbol table.
-; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op4=[[FUNCID:[0-9]+]] op5=2/>
+; See if the call to func is registered, using the expected hotness type.
+; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op4=1 op5=2/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
-; CHECK-NEXT:  <VALUE_SYMTAB
-; CHECK-NEXT:    <FNENTRY {{.*}} record string = 'main'
-; External function func should have entry with value id FUNCID
-; CHECK-NEXT:    <ENTRY {{.*}} op0=[[FUNCID]] {{.*}} record string = 'func'
-; CHECK-NEXT:  </VALUE_SYMTAB>
+; CHECK: <STRTAB_BLOCK
+; CHECK-NEXT: blob data = 'mainfunc'
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <VALUE_GUID op0=[[FUNCID:[0-9]+]] op1=7289175272376759421/>
+; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <COMBINED
-; See if the call to func is registered, using the expected callsite count
-; and hotness type, with value id matching the subsequent value symbol table.
+; See if the call to func is registered, using the expected hotness type.
 ; op6=2 which is hotnessType::None.
-; COMBINED-NEXT:    <COMBINED_PROFILE {{.*}} op5=[[FUNCID:[0-9]+]] op6=2/>
+; COMBINED-NEXT:    <COMBINED_PROFILE {{.*}} op5=[[FUNCID]] op6=2/>
 ; COMBINED-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
-; COMBINED-NEXT:  <VALUE_SYMTAB
-; Entry for function func should have entry with value id FUNCID
-; COMBINED-NEXT:    <COMBINED_ENTRY {{.*}} op0=[[FUNCID]] op1=7289175272376759421/>
-; COMBINED-NEXT:    <COMBINED
-; COMBINED-NEXT:  </VALUE_SYMTAB>
 
 ; ModuleID = 'thinlto-function-summary-callgraph.ll'
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 ; Function Attrs: nounwind uwtable
 define i32 @main() #0 !prof !2 {
 entry:

llvm/test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll

 ; Test to check the callgraph in summary when there is PGO
 ; RUN: opt -module-summary %s -o %t.o
 ; RUN: llvm-bcanalyzer -dump %t.o | FileCheck %s
 ; RUN: opt -module-summary %p/Inputs/thinlto-function-summary-callgraph-profile-summary.ll -o %t2.o
 ; RUN: llvm-lto -thinlto -o %t3 %t.o %t2.o
 ; RUN: llvm-bcanalyzer -dump %t3.thinlto.bc | FileCheck %s --check-prefix=COMBINED
 
 
+; CHECK: <SOURCE_FILENAME
+; "hot_function"
+; CHECK-NEXT: <FUNCTION op0=0 op1=12
+; "hot1"
+; CHECK-NEXT: <FUNCTION op0=12 op1=4
+; "hot2"
+; CHECK-NEXT: <FUNCTION op0=16 op1=4
+; "hot3"
+; CHECK-NEXT: <FUNCTION op0=20 op1=4
+; "hot4"
+; CHECK-NEXT: <FUNCTION op0=24 op1=4
+; "cold"
+; CHECK-NEXT: <FUNCTION op0=28 op1=4
+; "none1"
+; CHECK-NEXT: <FUNCTION op0=32 op1=5
+; "none2"
+; CHECK-NEXT: <FUNCTION op0=37 op1=5
+; "none3"
+; CHECK-NEXT: <FUNCTION op0=42 op1=5
 ; CHECK-LABEL:       <GLOBALVAL_SUMMARY_BLOCK
 ; CHECK-NEXT:    <VERSION
-; See if the call to func is registered, using the expected callsite count
-; and profile count, with value id matching the subsequent value symbol table.
-; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op4=[[HOT1:.*]] op5=3 op6=[[COLD:.*]] op7=1 op8=[[HOT2:.*]] op9=3 op10=[[HOT4:.*]] op11=3 op12=[[NONE1:.*]] op13=2 op14=[[HOT3:.*]] op15=3 op16=[[NONE2:.*]] op17=2 op18=[[NONE3:.*]] op19=2 op20=[[LEGACY:.*]] op21=3/>
+; CHECK-NEXT:    <VALUE_GUID op0=25 op1=123/>
+; op4=hot1 op6=cold op8=hot2 op10=hot4 op12=none1 op14=hot3 op16=none2 op18=none3 op20=123
+; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op4=1 op5=3 op6=5 op7=1 op8=2 op9=3 op10=4 op11=3 op12=6 op13=2 op14=3 op15=3 op16=7 op17=2 op18=8 op19=2 op20=25 op21=3/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
-; CHECK-LABEL:  <VALUE_SYMTAB
-; CHECK-NEXT:       <FNENTRY {{.*}} record string = 'hot_function
-; CHECK-DAG:        <ENTRY abbrevid=6 op0=[[NONE1]] {{.*}} record string = 'none1'
-; CHECK-DAG:        <ENTRY abbrevid=6 op0=[[COLD]] {{.*}} record string = 'cold'
-; CHECK-DAG:        <ENTRY abbrevid=6 op0=[[NONE2]] {{.*}} record string = 'none2'
-; CHECK-DAG:        <ENTRY abbrevid=6 op0=[[NONE3]] {{.*}} record string = 'none3'
-; CHECK-DAG:        <ENTRY abbrevid=6 op0=[[HOT1]] {{.*}} record string = 'hot1'
-; CHECK-DAG:        <ENTRY abbrevid=6 op0=[[HOT2]] {{.*}} record string = 'hot2'
-; CHECK-DAG:        <ENTRY abbrevid=6 op0=[[HOT3]] {{.*}} record string = 'hot3'
-; CHECK-DAG:        <ENTRY abbrevid=6 op0=[[HOT4]] {{.*}} record string = 'hot4'
-; CHECK-DAG:        <COMBINED_ENTRY abbrevid=11 op0=[[LEGACY]] op1=123/>
-; CHECK-LABEL:  </VALUE_SYMTAB>
+
+; CHECK: <STRTAB_BLOCK
+; CHECK-NEXT: blob data = 'hot_functionhot1hot2hot3hot4coldnone1none2none3'
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <VALUE_GUID
+; COMBINED-NEXT:    <VALUE_GUID
+; COMBINED-NEXT:    <VALUE_GUID
+; COMBINED-NEXT:    <VALUE_GUID
+; COMBINED-NEXT:    <VALUE_GUID
+; COMBINED-NEXT:    <VALUE_GUID
+; COMBINED-NEXT:    <VALUE_GUID
+; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED_PROFILE {{.*}} op5=[[HOT1:.*]] op6=3 op7=[[COLD:.*]] op8=1 op9=[[HOT2:.*]] op10=3 op11=[[NONE1:.*]] op12=2 op13=[[HOT3:.*]] op14=3 op15=[[NONE2:.*]] op16=2 op17=[[NONE3:.*]] op18=2/>
 ; COMBINED_NEXT:    <COMBINED abbrevid=

llvm/test/Bitcode/thinlto-function-summary-callgraph.ll

 ; Test to check the callgraph in summary
 ; RUN: opt -module-summary %s -o %t.o
 ; RUN: llvm-bcanalyzer -dump %t.o | FileCheck %s
 
 ; RUN: opt -module-summary %p/Inputs/thinlto-function-summary-callgraph.ll -o %t2.o
 ; RUN: llvm-lto -thinlto -o %t3 %t.o %t2.o
 ; RUN: llvm-bcanalyzer -dump %t3.thinlto.bc | FileCheck %s --check-prefix=COMBINED
 
 ; Check parsing for old summary versions generated from this file.
 ; RUN: llvm-lto -thinlto-index-stats %p/Inputs/thinlto-function-summary-callgraph.1.bc  | FileCheck %s --check-prefix=OLD
 ; RUN: llvm-lto -thinlto-index-stats %p/Inputs/thinlto-function-summary-callgraph-combined.1.bc  | FileCheck %s --check-prefix=OLD-COMBINED
 
+; CHECK: <SOURCE_FILENAME
+; CHECK-NEXT: <FUNCTION
+; "func"
+; CHECK-NEXT: <FUNCTION op0=4 op1=4
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
 ; CHECK-NEXT:    <VERSION
-; See if the call to func is registered, using the expected callsite count
-; and value id matching the subsequent value symbol table.
-; CHECK-NEXT:    <PERMODULE {{.*}} op4=[[FUNCID:[0-9]+]]/>
+; See if the call to func is registered.
+; CHECK-NEXT:    <PERMODULE {{.*}} op4=1/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
-; CHECK-NEXT:  <VALUE_SYMTAB
-; CHECK-NEXT:    <FNENTRY {{.*}} record string = 'main'
-; External function func should have entry with value id FUNCID
-; CHECK-NEXT:    <ENTRY {{.*}} op0=[[FUNCID]] {{.*}} record string = 'func'
-; CHECK-NEXT:  </VALUE_SYMTAB>
+; CHECK: <STRTAB_BLOCK
+; CHECK-NEXT: blob data = 'mainfunc'
+
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <VALUE_GUID op0=[[FUNCID:[0-9]+]] op1=7289175272376759421/>
+; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <COMBINED
-; See if the call to func is registered, using the expected callsite count
-; and value id matching the subsequent value symbol table.
-; COMBINED-NEXT:    <COMBINED {{.*}} op5=[[FUNCID:[0-9]+]]/>
+; See if the call to func is registered.
+; COMBINED-NEXT:    <COMBINED {{.*}} op5=[[FUNCID]]/>
 ; COMBINED-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
-; COMBINED-NEXT:  <VALUE_SYMTAB
-; Entry for function func should have entry with value id FUNCID
-; COMBINED-NEXT:    <COMBINED_ENTRY {{.*}} op0=[[FUNCID]] op1=7289175272376759421/>
-; COMBINED-NEXT:    <COMBINED
-; COMBINED-NEXT:  </VALUE_SYMTAB>
 
 ; ModuleID = 'thinlto-function-summary-callgraph.ll'
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 ; Function Attrs: nounwind uwtable
 define i32 @main() #0 {
 entry:
     call void (...) @func()
     ret i32 0
 }
 
 declare void @func(...) #1
 
 ; OLD: Index {{.*}} contains 1 nodes (1 functions, 0 alias, 0 globals) and 1 edges (0 refs and 1 calls)
-; OLD-COMBINED: Index {{.*}} contains 2 nodes (2 functions, 0 alias, 0 globals) and 1 edges (0 refs and 1 calls)
+; OLD-COMBINED: Index {{.*}} contains 2 nodes (2 functions, 0 alias, 0 globals) and 1 edges (0 refs and 1 calls)
 

llvm/test/Bitcode/thinlto-function-summary-originalnames.ll

 ; Test to check the callgraph in summary
 ; RUN: opt -module-summary %s -o %t.o
 ; RUN: llvm-lto -thinlto-action=thinlink -o %t.index.bc %t.o
 ; RUN: llvm-bcanalyzer -dump %t.index.bc | FileCheck %s --check-prefix=COMBINED
 
 ; COMBINED:       <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT:    <VERSION
+; COMBINED-NEXT:    <VALUE_GUID {{.*}} op1=4947176790635855146/>
+; COMBINED-NEXT:    <VALUE_GUID {{.*}} op1=-6591587165810580810/>
+; COMBINED-NEXT:    <VALUE_GUID {{.*}} op1=-4377693495213223786/>
 ; COMBINED-DAG:    <COMBINED
 ; COMBINED-DAG:    <COMBINED_ORIGINAL_NAME op0=6699318081062747564/>
 ; COMBINED-DAG:    <COMBINED_GLOBALVAR_INIT_REFS
 ; COMBINED-DAG:    <COMBINED_ORIGINAL_NAME op0=-2012135647395072713/>
 ; COMBINED-DAG:    <COMBINED_ALIAS
 ; COMBINED-DAG:    <COMBINED_ORIGINAL_NAME op0=-4170563161550796836/>
 ; COMBINED-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
-; COMBINED-NEXT:  <VALUE_SYMTAB
-; COMBINED-NEXT:   <COMBINED_ENTRY {{.*}} op1=4947176790635855146/>
-; COMBINED-NEXT:   <COMBINED_ENTRY {{.*}} op1=-6591587165810580810/>
-; COMBINED-NEXT:   <COMBINED_ENTRY {{.*}} op1=-4377693495213223786/>
-; COMBINED-NEXT:  </VALUE_SYMTAB>
 
 source_filename = "/path/to/source.c"
 
 ; ModuleID = 'thinlto-function-summary-callgraph.ll'
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 @bar = internal global i32 0
 @fooalias = internal alias void (...), bitcast (void ()* @foo to void (...)*)
 
 define internal void @foo() {
     ret void
 }

llvm/test/Bitcode/thinlto-function-summary-refgraph.ll

 ; Test to check both the callgraph and refgraph in summary
 ; RUN: opt -module-summary %s -o %t.o
 ; RUN: llvm-bcanalyzer -dump %t.o | FileCheck %s
 
+; CHECK: <SOURCE_FILENAME
+; "bar"
+; CHECK-NEXT: <GLOBALVAR {{.*}} op0=0 op1=3
+; "globalvar"
+; CHECK-NEXT: <GLOBALVAR {{.*}} op0=3 op1=9
+; "func"
+; CHECK-NEXT: <FUNCTION op0=12 op1=4
+; "func2"
+; CHECK-NEXT: <FUNCTION op0=16 op1=5
+; "foo"
+; CHECK-NEXT: <FUNCTION op0=21 op1=3
+; "func3"
+; CHECK-NEXT: <FUNCTION op0=24 op1=5
+; "W"
+; CHECK-NEXT: <FUNCTION op0=29 op1=1
+; "X"
+; CHECK-NEXT: <FUNCTION op0=30 op1=1
+; "Y"
+; CHECK-NEXT: <FUNCTION op0=31 op1=1
+; "Z"
+; CHECK-NEXT: <FUNCTION op0=32 op1=1
+; "llvm.ctpop.i8"
+; CHECK-NEXT: <FUNCTION op0=33 op1=13
+; "main"
+; CHECK-NEXT: <FUNCTION op0=46 op1=4
+
 ; See if the calls and other references are recorded properly using the
 ; expected value id and other information as appropriate (callsite cout
 ; for calls). Use different linkage types for the various test cases to
 ; distinguish the test cases here (op1 contains the linkage type).
 ; Note that op3 contains the # non-call references.
 ; This also ensures that we didn't include a call or reference to intrinsic
 ; llvm.ctpop.i8.
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
 ; Function main contains call to func, as well as address reference to func:
-; CHECK-DAG:    <PERMODULE {{.*}} op0=[[MAINID:[0-9]+]] op1=0 {{.*}} op3=1 op4=[[FUNCID:[0-9]+]] op5=[[FUNCID]]/>
+; op0=main op4=func op5=func
+; CHECK-DAG:    <PERMODULE {{.*}} op0=11 op1=0 {{.*}} op3=1 op4=2 op5=2/>
 ; Function W contains a call to func3 as well as a reference to globalvar:
-; CHECK-DAG:    <PERMODULE {{.*}} op0=[[WID:[0-9]+]] op1=5 {{.*}} op3=1 op4=[[GLOBALVARID:[0-9]+]] op5=[[FUNC3ID:[0-9]+]]/>
+; op0=W op4=globalvar op5=func3
+; CHECK-DAG:    <PERMODULE {{.*}} op0=6 op1=5 {{.*}} op3=1 op4=1 op5=5/>
 ; Function X contains call to foo, as well as address reference to foo
 ; which is in the same instruction as the call:
-; CHECK-DAG:    <PERMODULE {{.*}} op0=[[XID:[0-9]+]] op1=1 {{.*}} op3=1 op4=[[FOOID:[0-9]+]] op5=[[FOOID]]/>
+; op0=X op4=foo op5=foo
+; CHECK-DAG:    <PERMODULE {{.*}} op0=7 op1=1 {{.*}} op3=1 op4=4 op5=4/>
 ; Function Y contains call to func2, and ensures we don't incorrectly add
 ; a reference to it when reached while earlier analyzing the phi using its
 ; return value:
-; CHECK-DAG:    <PERMODULE {{.*}} op0=[[YID:[0-9]+]] op1=8 {{.*}} op3=0 op4=[[FUNC2ID:[0-9]+]]/>
+; op0=Y op4=func2
+; CHECK-DAG:    <PERMODULE {{.*}} op0=8 op1=8 {{.*}} op3=0 op4=3/>
 ; Function Z contains call to func2, and ensures we don't incorrectly add
 ; a reference to it when reached while analyzing subsequent use of its return
 ; value:
-; CHECK-DAG:    <PERMODULE {{.*}} op0=[[ZID:[0-9]+]] op1=3 {{.*}} op3=0 op4=[[FUNC2ID:[0-9]+]]/>
+; op0=Z op4=func2
+; CHECK-DAG:    <PERMODULE {{.*}} op0=9 op1=3 {{.*}} op3=0 op4=3/>
 ; Variable bar initialization contains address reference to func:
-; CHECK-DAG:    <PERMODULE_GLOBALVAR_INIT_REFS {{.*}} op0=[[BARID:[0-9]+]] op1=0 op2=[[FUNCID]]/>
+; op0=bar op2=func
+; CHECK-DAG:    <PERMODULE_GLOBALVAR_INIT_REFS {{.*}} op0=0 op1=0 op2=2/>
 ; CHECK:  </GLOBALVAL_SUMMARY_BLOCK>
 
-; CHECK-NEXT:  <VALUE_SYMTAB
-; CHECK-DAG:    <ENTRY {{.*}} op0=[[BARID]] {{.*}} record string = 'bar'
-; CHECK-DAG:    <ENTRY {{.*}} op0=[[FUNCID]] {{.*}} record string = 'func'
-; CHECK-DAG:    <ENTRY {{.*}} op0=[[FOOID]] {{.*}} record string = 'foo'
-; CHECK-DAG:    <FNENTRY {{.*}} op0=[[MAINID]] {{.*}} record string = 'main'
-; CHECK-DAG:    <FNENTRY {{.*}} op0=[[WID]] {{.*}} record string = 'W'
-; CHECK-DAG:    <FNENTRY {{.*}} op0=[[XID]] {{.*}} record string = 'X'
-; CHECK-DAG:    <FNENTRY {{.*}} op0=[[YID]] {{.*}} record string = 'Y'
-; CHECK-DAG:    <FNENTRY {{.*}} op0=[[ZID]] {{.*}} record string = 'Z'
-; CHECK-DAG:    <ENTRY {{.*}} op0=[[FUNC2ID]] {{.*}} record string = 'func2'
-; CHECK-DAG:    <ENTRY {{.*}} op0=[[FUNC3ID]] {{.*}} record string = 'func3'
-; CHECK-DAG:    <ENTRY {{.*}} op0=[[GLOBALVARID]] {{.*}} record string = 'globalvar'
-; CHECK:  </VALUE_SYMTAB>
+; CHECK: <STRTAB_BLOCK
+; CHECK-NEXT: blob data = 'barglobalvarfuncfunc2foofunc3WXYZllvm.ctpop.i8main'
 
 ; ModuleID = 'thinlto-function-summary-refgraph.ll'
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 @bar = global void (...)* bitcast (void ()* @func to void (...)*), align 8
 
 @globalvar = global i32 0, align 4

llvm/test/Bitcode/thinlto-function-summary.ll

 ; RUN: opt -name-anon-globals -module-summary < %s | llvm-bcanalyzer -dump | FileCheck %s -check-prefix=BC
 ; RUN: opt -passes=name-anon-globals -module-summary < %s | llvm-bcanalyzer -dump | FileCheck %s -check-prefix=BC
 ; Check for summary block/records.
 
-; Check the value ids in the summary entries against the
-; same in the ValueSumbolTable, to ensure the ordering is stable.
-; Also check the linkage field on the summary entries.
+; BC: <SOURCE_FILENAME
+; "h"
+; BC-NEXT: <GLOBALVAR {{.*}} op0=0 op1=1
+; "foo"
+; BC-NEXT: <FUNCTION op0=1 op1=3
+; "bar"
+; BC-NEXT: <FUNCTION op0=4 op1=3
+; "anon.[32 chars].0"
+; BC-NEXT: <FUNCTION op0=7 op1=39
+; "variadic"
+; BC-NEXT: <FUNCTION op0=46 op1=8
+; "f"
+; BC-NEXT: <ALIAS op0=54 op1=1
 ; BC: <GLOBALVAL_SUMMARY_BLOCK
 ; BC-NEXT: <VERSION
 ; BC-NEXT: <PERMODULE {{.*}} op0=1 op1=0
 ; BC-NEXT: <PERMODULE {{.*}} op0=2 op1=0
 ; BC-NEXT: <PERMODULE {{.*}} op0=3 op1=7
 ; BC-NEXT: <PERMODULE {{.*}} op0=4 op1=16
 ; BC-NEXT: <ALIAS {{.*}} op0=5 op1=0 op2=3
 ; BC-NEXT: </GLOBALVAL_SUMMARY_BLOCK
-; BC-NEXT: <VALUE_SYMTAB
-; BC-NEXT: <FNENTRY {{.*}} op0=4 {{.*}}> record string = 'variadic'
-; BC-NEXT: <FNENTRY {{.*}} op0=1 {{.*}}> record string = 'foo'
-; BC-NEXT: <FNENTRY {{.*}} op0=2 {{.*}}> record string = 'bar'
-; BC-NEXT: <ENTRY {{.*}} op0=5 {{.*}}> record string = 'f'
-; BC-NEXT: <ENTRY {{.*}} record string = 'h'
-; BC-NEXT: <FNENTRY {{.*}} op0=3 {{.*}}> record string = 'anon.
+; BC: <STRTAB_BLOCK
+; BC-NEXT: blob data = 'hfoobaranon.{{................................}}.0variadicf'
 
 
 ; RUN: opt -name-anon-globals -module-summary < %s | llvm-dis | FileCheck %s
 ; Check that this round-trips correctly.
 
 ; ModuleID = '<stdin>'
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"

llvm/test/ThinLTO/X86/autoupgrade.ll

 ; Verify that auto-upgrading intrinsics works with Lazy loaded bitcode
 ; Do setup work for all below tests: generate bitcode and combined index
 ; RUN: opt -module-summary %s -o %t.bc
 ; RUN: llvm-lto -thinlto-action=thinlink -o %t3.bc %t.bc %p/Inputs/autoupgrade.bc
 
 ; We can't use llvm-dis here, because it would do the autoupgrade itself.
 
 ; RUN: llvm-link  -summary-index=%t3.bc \
 ; RUN:            -import=globalfunc1:%p/Inputs/autoupgrade.bc %t.bc \
 ; RUN:     | llvm-bcanalyzer -dump | FileCheck %s
 
-
-; CHECK-NOT: 'llvm.invariant.start'
-; CHECK: record string = 'llvm.invariant.start.p0i8'
-; CHECK-NOT: 'llvm.invariant.start'
+; CHECK: <STRTAB_BLOCK
+; CHECK-NEXT: blob data = 'mainglobalfunc1llvm.invariant.start.p0i8'
 
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx10.11.0"
 
 define i32 @main() #0 {
 entry:
   call void (...) @globalfunc1()
   ret i32 0
 }
 
 declare void @globalfunc1(...) #1

llvm/test/ThinLTO/X86/distributed_indexes.ll

 ; RUN: opt -module-summary %s -o %t1.bc
 ; RUN: opt -module-summary %p/Inputs/distributed_indexes.ll -o %t2.bc
 ; RUN: llvm-lto -thinlto-action=thinlink -o %t.index.bc %t1.bc %t2.bc
 ; RUN: llvm-lto -thinlto-action=distributedindexes -thinlto-index %t.index.bc %t1.bc %t2.bc
 ; RUN: llvm-bcanalyzer -dump %t1.bc.thinlto.bc | FileCheck %s --check-prefix=BACKEND1
 ; RUN: llvm-bcanalyzer -dump %t2.bc.thinlto.bc | FileCheck %s --check-prefix=BACKEND2
 
 ; The backend index for this module contains summaries from itself and
 ; Inputs/distributed_indexes.ll, as it imports from the latter.
 ; BACKEND1: <MODULE_STRTAB_BLOCK
 ; BACKEND1-NEXT: <ENTRY {{.*}} record string = '{{.*}}distributed_indexes.ll.tmp{{.*}}.bc'
 ; BACKEND1-NEXT: <ENTRY {{.*}} record string = '{{.*}}distributed_indexes.ll.tmp{{.*}}.bc'
 ; BACKEND1-NEXT: </MODULE_STRTAB_BLOCK
 ; BACKEND1-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; BACKEND1-NEXT: <VERSION
+; BACKEND1-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
+; BACKEND1-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; BACKEND1-NEXT: <COMBINED
 ; BACKEND1-NEXT: <COMBINED
 ; BACKEND1-NEXT: </GLOBALVAL_SUMMARY_BLOCK
-; BACKEND1-NEXT: <VALUE_SYMTAB
-; Check that the format is: op0=valueid, op1=offset, op2=funcguid,
-; where funcguid is the lower 64 bits of the function name MD5.
-; BACKEND1-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
-; BACKEND1-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
-; BACKEND1-NEXT: </VALUE_SYMTAB
 
 ; The backend index for Input/distributed_indexes.ll contains summaries from
 ; itself only, as it does not import anything.
 ; BACKEND2: <MODULE_STRTAB_BLOCK
 ; BACKEND2-NEXT: <ENTRY {{.*}} record string = '{{.*}}distributed_indexes.ll.tmp2.bc'
 ; BACKEND2-NEXT: </MODULE_STRTAB_BLOCK
 ; BACKEND2-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; BACKEND2-NEXT: <VERSION
+; BACKEND2-NEXT: <VALUE_GUID op0=1 op1=-5300342847281564238
 ; BACKEND2-NEXT: <COMBINED
 ; BACKEND2-NEXT: </GLOBALVAL_SUMMARY_BLOCK
-; BACKEND2-NEXT: <VALUE_SYMTAB
-; Check that the format is: op0=valueid, op1=offset, op2=funcguid,
-; where funcguid is the lower 64 bits of the function name MD5.
-; BACKEND2-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0=1 op1=-5300342847281564238
-; BACKEND2-NEXT: </VALUE_SYMTAB
 
 declare void @g(...)
 
 define void @f() {
 entry:
   call void (...) @g()
   ret void
 }

llvm/test/tools/gold/X86/thinlto.ll

 ; The backend index for this module contains summaries from itself and
 ; Inputs/thinlto.ll, as it imports from the latter.
 ; BACKEND1: <MODULE_STRTAB_BLOCK
 ; BACKEND1-NEXT: <ENTRY {{.*}} record string = '{{.*}}/test/tools/gold/X86/Output/thinlto.ll.tmp{{.*}}.o'
 ; BACKEND1-NEXT: <ENTRY {{.*}} record string = '{{.*}}/test/tools/gold/X86/Output/thinlto.ll.tmp{{.*}}.o'
 ; BACKEND1-NEXT: </MODULE_STRTAB_BLOCK
 ; BACKEND1-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; BACKEND1-NEXT: <VERSION
+; BACKEND1-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
+; BACKEND1-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; BACKEND1-NEXT: <COMBINED
 ; BACKEND1-NEXT: <COMBINED
 ; BACKEND1-NEXT: </GLOBALVAL_SUMMARY_BLOCK
-; BACKEND1-NEXT: <VALUE_SYMTAB
-; Check that the format is: op0=valueid, op1=offset, op2=funcguid,
-; where funcguid is the lower 64 bits of the function name MD5.
-; BACKEND1-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
-; BACKEND1-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
-; BACKEND1-NEXT: </VALUE_SYMTAB
 
 ; The backend index for Input/thinlto.ll contains summaries from itself only,
 ; as it does not import anything.
 ; BACKEND2: <MODULE_STRTAB_BLOCK
 ; BACKEND2-NEXT: <ENTRY {{.*}} record string = '{{.*}}/test/tools/gold/X86/Output/thinlto.ll.tmp2.o'
 ; BACKEND2-NEXT: </MODULE_STRTAB_BLOCK
 ; BACKEND2-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; BACKEND2-NEXT: <VERSION
+; BACKEND2-NEXT: <VALUE_GUID op0=1 op1=-5300342847281564238
 ; BACKEND2-NEXT: <COMBINED
 ; BACKEND2-NEXT: </GLOBALVAL_SUMMARY_BLOCK
-; BACKEND2-NEXT: <VALUE_SYMTAB
-; Check that the format is: op0=valueid, op1=offset, op2=funcguid,
-; where funcguid is the lower 64 bits of the function name MD5.
-; BACKEND2-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0=1 op1=-5300342847281564238
-; BACKEND2-NEXT: </VALUE_SYMTAB
 
 ; COMBINED: <MODULE_STRTAB_BLOCK
 ; COMBINED-NEXT: <ENTRY {{.*}} record string = '{{.*}}/test/tools/gold/X86/Output/thinlto.ll.tmp{{.*}}.o'
 ; COMBINED-NEXT: <ENTRY {{.*}} record string = '{{.*}}/test/tools/gold/X86/Output/thinlto.ll.tmp{{.*}}.o'
 ; COMBINED-NEXT: </MODULE_STRTAB_BLOCK
 ; COMBINED-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT: <VERSION
+; COMBINED-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
+; COMBINED-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; COMBINED-NEXT: <COMBINED
 ; COMBINED-NEXT: <COMBINED
 ; COMBINED-NEXT: </GLOBALVAL_SUMMARY_BLOCK
-; COMBINED-NEXT: <VALUE_SYMTAB
-; Check that the format is: op0=valueid, op1=offset, op2=funcguid,
-; where funcguid is the lower 64 bits of the function name MD5.
-; COMBINED-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
-; COMBINED-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
-; COMBINED-NEXT: </VALUE_SYMTAB
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 declare void @g(...)
 
 define void @f() {
 entry:
   call void (...) @g()
   ret void
 }

llvm/test/tools/llvm-lto/thinlto.ll

 ; Test combined function index generation for ThinLTO via llvm-lto.
 ; RUN: opt -module-summary %s -o %t.o
 ; RUN: opt -module-summary %p/Inputs/thinlto.ll -o %t2.o
 ; RUN: llvm-lto -thinlto -o %t3 %t.o %t2.o
 ; RUN: llvm-bcanalyzer -dump %t3.thinlto.bc | FileCheck %s --check-prefix=COMBINED
 ; RUN: not test -e %t3
 
 ; COMBINED: <MODULE_STRTAB_BLOCK
 ; COMBINED-NEXT: <ENTRY {{.*}} record string = '{{.*}}thinlto.ll.tmp{{.*}}.o'
 ; COMBINED-NEXT: <ENTRY {{.*}} record string = '{{.*}}thinlto.ll.tmp{{.*}}.o'
 ; COMBINED-NEXT: </MODULE_STRTAB_BLOCK
 ; COMBINED-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT: <VERSION
+; COMBINED-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
+; COMBINED-NEXT: <VALUE_GUID op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
 ; COMBINED-NEXT: <COMBINED
 ; COMBINED-NEXT: <COMBINED
 ; COMBINED-NEXT: </GLOBALVAL_SUMMARY_BLOCK
-; COMBINED-NEXT: <VALUE_SYMTAB
-; Check that the format is: op0=valueid, op1=offset, op2=funcguid,
-; where funcguid is the lower 64 bits of the function name MD5.
-; COMBINED-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
-; COMBINED-NEXT: <COMBINED_ENTRY abbrevid={{[0-9]+}} op0={{1|2}} op1={{-3706093650706652785|-5300342847281564238}}
-; COMBINED-NEXT: </VALUE_SYMTAB
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 
 define void @f() {
 entry:
   ret void
 }

llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp

static const char *GetBlockName(unsigned BlockID,
   case bitc::VALUE_SYMTAB_BLOCK_ID:        return "VALUE_SYMTAB";
   case bitc::METADATA_BLOCK_ID:            return "METADATA_BLOCK";
   case bitc::METADATA_KIND_BLOCK_ID:       return "METADATA_KIND_BLOCK";
   case bitc::METADATA_ATTACHMENT_ID:       return "METADATA_ATTACHMENT_BLOCK";
   case bitc::USELIST_BLOCK_ID:             return "USELIST_BLOCK_ID";
   case bitc::GLOBALVAL_SUMMARY_BLOCK_ID:
                                            return "GLOBALVAL_SUMMARY_BLOCK";
   case bitc::MODULE_STRTAB_BLOCK_ID:       return "MODULE_STRTAB_BLOCK";
+  case bitc::STRTAB_BLOCK_ID:              return "STRTAB_BLOCK";
   }
 }
 
 /// GetCodeName - Return a symbolic code name if known, otherwise return
 /// null.
 static const char *GetCodeName(unsigned CodeID, unsigned BlockID,
                                const BitstreamBlockInfo &BlockInfo,
                                CurStreamTypeType CurStreamType) {
default:
       STRINGIFY_CODE(FS, COMBINED_ALIAS)
       STRINGIFY_CODE(FS, COMBINED_ORIGINAL_NAME)
       STRINGIFY_CODE(FS, VERSION)
       STRINGIFY_CODE(FS, TYPE_TESTS)
       STRINGIFY_CODE(FS, TYPE_TEST_ASSUME_VCALLS)
       STRINGIFY_CODE(FS, TYPE_CHECKED_LOAD_VCALLS)
       STRINGIFY_CODE(FS, TYPE_TEST_ASSUME_CONST_VCALL)
       STRINGIFY_CODE(FS, TYPE_CHECKED_LOAD_CONST_VCALL)
+      STRINGIFY_CODE(FS, VALUE_GUID)
     }
   case bitc::METADATA_ATTACHMENT_ID:
     switch(CodeID) {
     default:return nullptr;
       STRINGIFY_CODE(METADATA, ATTACHMENT)
     }
   case bitc::METADATA_BLOCK_ID:
     switch(CodeID) {
case bitc::USELIST_BLOCK_ID:
     case bitc::USELIST_CODE_BB:      return "USELIST_CODE_BB";
     }
 
   case bitc::OPERAND_BUNDLE_TAGS_BLOCK_ID:
     switch(CodeID) {
     default: return nullptr;
     case bitc::OPERAND_BUNDLE_TAG: return "OPERAND_BUNDLE_TAG";
     }
+  case bitc::STRTAB_BLOCK_ID:
+    switch(CodeID) {
+    default: return nullptr;
+    case bitc::STRTAB_BLOB: return "BLOB";
+    }
   }
 #undef STRINGIFY_CODE
 }
 
 struct PerRecordStats {
   unsigned NumInstances;
   unsigned NumAbbrev;
   uint64_t TotalBits;

llvm/tools/llvm-cat/llvm-cat.cpp

int main(int argc, char **argv) {
 
   SmallVector<char, 0> Buffer;
   BitcodeWriter Writer(Buffer);
   if (BinaryCat) {
     for (const auto &InputFilename : InputFilenames) {
       std::unique_ptr<MemoryBuffer> MB = ExitOnErr(
           errorOrToExpected(MemoryBuffer::getFileOrSTDIN(InputFilename)));
       std::vector<BitcodeModule> Mods = ExitOnErr(getBitcodeModuleList(*MB));
-      for (auto &BitcodeMod : Mods)
+      for (auto &BitcodeMod : Mods) {
         Buffer.insert(Buffer.end(), BitcodeMod.getBuffer().begin(),
                       BitcodeMod.getBuffer().end());
+        Writer.copyStrtab(BitcodeMod.getStrtab());
+      }
     }
   } else {
+    // The string table does not own strings added to it, some of which are
+    // owned by the modules; keep them alive until we write the string table.
+    std::vector<std::unique_ptr<Module>> OwnedMods;
     for (const auto &InputFilename : InputFilenames) {
       SMDiagnostic Err;
       std::unique_ptr<Module> M = parseIRFile(InputFilename, Err, Context);
       if (!M) {
         Err.print(argv[0], errs());
         return 1;
       }
       Writer.writeModule(M.get());
+      OwnedMods.push_back(std::move(M));
     }
+    Writer.writeStrtab();
   }
 
   std::error_code EC;
   raw_fd_ostream OS(OutputFilename, EC, sys::fs::OpenFlags::F_None);
   if (EC) {
     llvm::errs() << argv[0] << ": cannot open " << OutputFilename
                  << " for writing: " << EC.message();
     return 1;
   }
 
   OS.write(Buffer.data(), Buffer.size());
   return 0;
 }

llvm/tools/llvm-modextract/llvm-modextract.cpp

int main(int argc, char **argv) {
   }
 
   std::error_code EC;
   std::unique_ptr<tool_output_file> Out(
       new tool_output_file(OutputFilename, EC, sys::fs::F_None));
   ExitOnErr(errorCodeToError(EC));
 
   if (BinaryExtract) {
-    SmallVector<char, 0> Header;
-    BitcodeWriter Writer(Header);
-    Out->os() << Header << Ms[ModuleIndex].getBuffer();
+    SmallVector<char, 0> Result;
+    BitcodeWriter Writer(Result);
+    Result.append(Ms[ModuleIndex].getBuffer().begin(),
+                  Ms[ModuleIndex].getBuffer().end());
+    Writer.copyStrtab(Ms[ModuleIndex].getStrtab());
+    Out->os() << Result;
     Out->keep();
     return 0;
   }
 
   std::unique_ptr<Module> M = ExitOnErr(Ms[ModuleIndex].parseModule(Context));
   WriteBitcodeToFile(M.get(), Out->os());
 
   Out->keep();
   return 0;
 }