[LLD][COFF] Early dependency detection

[aganea]

Summary

This patch adds more fine grained information in ObjFile about PDB type server dependencies and precomp OBJ dependencies.
Dependencies are required to be loaded & merged first, before any dependent OBJ that relies on it.

Before, dependencies were discovered and loaded along the way, when the type stream for a given OBJ was being merged (in PDB.cpp).

This patch is part of ground work towards parallelizing the type merging. The objective is to split PDBLinker::addObjFile into several smaller parallelizable pieces. See D59226 for the overall intention.

[rnk]

COFF/InputFiles.h

168–182

I'm starting to feel like mergeDebugT should really be behind a virtual interface, something like this:

class TPISource { // TpiSource?
public:
  virtual CVIndexMap *mergeTPI(ObjFile *File, CVIndexMap *ObjectIndexMap) = 0;
};
...
class SectionTPISource { ... }; // ObjectTPISource? RegularTPISource? Z7TPISource? TpiSource?
class TypeServerTPISource { ... };
class PrecompTPISource { ... };
class UsePrecompTPISource { ... };

The class names I came up with are kind of crummy, though.

I feel like 4 public, optional members of ObjFile leaks a lot of PDB details into the rest of the linker. Instead, we could have a pointer to some interface. Do you think this, or something like it, is worth doing now, ever, or later?

The "regular" or .debug$T based type merger could just be some stateless global variable that all the regular objs point to, since we pass the object file in through the interface, and that's all the info it needs. Every file using a type server would point to the same TypeServerTPISource. I'm not sure how the PCH stuff would work, since I'm less familiar.

[aganea]

COFF/InputFiles.h

168–182

Yes you're completly right - somehow I started doing that at first, but there were too many changes, so I meant to do this incrementally. I'll lay out this new class hierarchy in this patch, and then I'll implement mergeTPI() in a subsequent patch.

[aganea]

Introduce TpiSource and derived types as suggested by @rnk.
Please see D59226 for more information as for where this is going.

[ruiu]

COFF/DebugTypes.cpp

47

What is this? You are not using this. (If you need it in another patch, move this to the another patch.)

66

nit: Please add a blank line between function definitions.

COFF/InputFiles.cpp

688

If you do know the first argument for all function calls of makeTpiSource, you can define one function for each value of the first argument, instead of calling the same function and then dispatch according to the first argument.

693

Avoid auto.

COFF/PDB.cpp

406

Please do not use auto unless its type is obvious from the right-hand side (e.g. cast or new).

[aganea]

Updated with changes as suggested by @ruiu

COFF/DebugTypes.cpp

47

Normally we should have std::unique_ptr<TpiSource> DebugTypesObj in COFF/InputFiles.h, L166, but I wanted to avoid #including DebugTypes.h just so we can use std::unique_ptr. I'm keeping hard references to TpiSource objects here instead.

COFF/InputFiles.cpp

688

I did like you said - however now there are details leaking out of DebugTypes.h, like TypeServer2Record parameter to makeUseTypeServerSource(), which now requires having #include "llvm/DebugInfo/CodeView/TypeRecord.h" directly in DebugTypes.h, which can slow down compilation - if DebugTypes.h is included elsewhere. It's a tradeoff between terseness and compilation speed, please let me know which you prefer.

693

The right side already specifies that it deserializes as a TypeServer2Record, but yes I made that explicit.

[aganea]

Remove reference to llvm/DebugInfo/CodeView/TypeRecord.h from DebugTypes.h

COFF/InputFiles.cpp

688

Forget what I said, it was late last night. Changed the parameters to pointers and forward declarations.

[ruiu]

COFF/InputFiles.cpp

662

Could you write a function comment as to what this function is supposed to do so that it can be easily understood for a first-time reader?

688

I was about to say that you probably could make use of forward declaration, but you already did. :)

[aganea]

Document ObjFile::initializeDependencies().

[aganea]

Ping! Any further comments?

[rnk]

Not from me. :)

COFF/CMakeLists.txt

 set(LLVM_TARGET_DEFINITIONS Options.td)
 tablegen(LLVM Options.inc -gen-opt-parser-defs)
 add_public_tablegen_target(COFFOptionsTableGen)
 
 if(NOT LLD_BUILT_STANDALONE)
   set(tablegen_deps intrinsics_gen)
 endif()
 
 add_lld_library(lldCOFF
   Chunks.cpp
+  DebugTypes.cpp
   DLL.cpp
   Driver.cpp
   DriverUtils.cpp
   ICF.cpp
   InputFiles.cpp
   LTO.cpp
   MapFile.cpp
   MarkLive.cpp

COFF/DebugTypes.h

+//===- DebugTypes.h ---------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_COFF_DEBUGTYPES_H
+#define LLD_COFF_DEBUGTYPES_H
+
+#include "llvm/Support/Error.h"
+
+namespace llvm {
+namespace codeview {
+class PrecompRecord;
+class TypeServer2Record;
+} // namespace codeview
+} // namespace llvm
+
+namespace lld {
+namespace coff {
+
+class ObjFile;
+
+class TpiSource {
+public:
+  enum TpiKind { Regular, PCH, UsingPCH, PDB, UsingPDB };
+
+  TpiSource(TpiKind K, ObjFile *F);
+  virtual ~TpiSource() {}
+
+  const TpiKind Kind;
+  ObjFile *File;
+};
+
+TpiSource *makeTpiSource(ObjFile *F);
+TpiSource *makeTypeServerSource(ObjFile *F);
+TpiSource *makeUseTypeServerSource(ObjFile *F,
+                                   llvm::codeview::TypeServer2Record *TS);
+TpiSource *makePrecompSource(ObjFile *F);
+TpiSource *makeUsePrecompSource(ObjFile *F,
+                                llvm::codeview::PrecompRecord *Precomp);
+
+// Temporary interface to get the dependency
+template <typename T> const T &retrieveDependencyInfo(TpiSource *Source);
+
+} // namespace coff
+} // namespace lld
+
+#endif
 No newline at end of file

COFF/DebugTypes.cpp

+//===- DebugTypes.cpp -----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "DebugTypes.h"
+#include "InputFiles.h"
+#include "llvm/DebugInfo/CodeView/TypeRecord.h"
+
+using namespace lld;
+using namespace lld::coff;
+using namespace llvm;
+using namespace llvm::codeview;
+
+namespace {
+class TypeServerSource : public TpiSource {
+public:
+  TypeServerSource(ObjFile *F) : TpiSource(PDB, F) {}
+};
+
+class UseTypeServerSource : public TpiSource {
+public:
+  UseTypeServerSource(ObjFile *F, TypeServer2Record *TS)
+      : TpiSource(UsingPDB, F), TypeServerDependency(*TS) {}
+
+  // Information about the PDB type server dependency, that needs to be loaded
+  // in before merging this OBJ.
+  TypeServer2Record TypeServerDependency;
+};
+
+class PrecompSource : public TpiSource {
+public:
+  PrecompSource(ObjFile *F) : TpiSource(PCH, F) {}
+};
+
+class UsePrecompSource : public TpiSource {
+public:
+  UsePrecompSource(ObjFile *F, PrecompRecord *Precomp)
+      : TpiSource(UsingPCH, F), PrecompDependency(*Precomp) {}
+
+  // Information about the Precomp OBJ dependency, that needs to be loaded in
+  // before merging this OBJ.
+  PrecompRecord PrecompDependency;
+};
+} // namespace
+
+static std::vector<std::unique_ptr<TpiSource>> GC;
+
+TpiSource::TpiSource(TpiKind K, ObjFile *F) : Kind(K), File(F) {
+  GC.push_back(std::unique_ptr<TpiSource>(this));
+}
+
+TpiSource *coff::makeTpiSource(ObjFile *F) {
+  return new TpiSource(TpiSource::Regular, F);
+}
+
+TpiSource *coff::makeTypeServerSource(ObjFile *F) {
+  return new TypeServerSource(F);
+}
+
+TpiSource *coff::makeUseTypeServerSource(ObjFile *F, TypeServer2Record *TS) {
+  return new UseTypeServerSource(F, TS);
+}
+
+TpiSource *coff::makePrecompSource(ObjFile *F) { return new PrecompSource(F); }
+
+TpiSource *coff::makeUsePrecompSource(ObjFile *F, PrecompRecord *Precomp) {
+  return new UsePrecompSource(F, Precomp);
+}
+
+template <>
+const PrecompRecord &coff::retrieveDependencyInfo(TpiSource *Source) {
+  assert(Source->Kind == TpiSource::UsingPCH);
+  return ((UsePrecompSource *)Source)->PrecompDependency;
+}
+
+template <>
+const TypeServer2Record &coff::retrieveDependencyInfo(TpiSource *Source) {
+  assert(Source->Kind == TpiSource::UsingPDB);
+  return ((UseTypeServerSource *)Source)->TypeServerDependency;
+}
 No newline at end of file

COFF/InputFiles.h

 class Defined;
 class DefinedImportData;
 class DefinedImportThunk;
 class DefinedRegular;
 class Lazy;
 class SectionChunk;
 class Symbol;
 class Undefined;
+class TpiSource;
 
 // The root class of input files.
 class InputFile {
 public:
   enum Kind { ArchiveKind, ObjectKind, ImportKind, BitcodeKind };
   Kind kind() const { return FileKind; }
   virtual ~InputFile() {}
 
public:
   // When using Microsoft precompiled headers, this is the PCH's key.
   // The same key is used by both the precompiled object, and objects using the
   // precompiled object. Any difference indicates out-of-date objects.
   llvm::Optional<uint32_t> PCHSignature;
 
   // Tells whether this file was compiled with /hotpatch
   bool HotPatchable = false;
 
   // Whether the object was already merged into the final PDB or not
   bool MergedIntoPDB = false;
 
+  // If the OBJ has a .debug$T stream, this tells how it will be handled.
+  TpiSource *DebugTypesObj = nullptr;
+
+  // The .debug$T stream if there's one.
+  llvm::Optional<llvm::codeview::CVTypeArray> DebugTypes;
+
 private:
   const coff_section* getSection(uint32_t I);
   const coff_section *getSection(COFFSymbolRef Sym) {
     return getSection(Sym.getSectionNumber());
   }
 
   void initializeChunks();
   void initializeSymbols();
   void initializeFlags();
+  void initializeDependencies();
 
   SectionChunk *
   readSection(uint32_t SectionNumber,
               const llvm::object::coff_aux_section_definition *Def,
               StringRef LeaderName);
 
   void readAssociativeDefinition(
       COFFSymbolRef COFFSym,

COFF/InputFiles.cpp

 //===- InputFiles.cpp -----------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "InputFiles.h"
 #include "Chunks.h"
 #include "Config.h"
+#include "DebugTypes.h"
 #include "Driver.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
 #include "llvm-c/lto.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/COFF.h"
 #include "llvm/DebugInfo/CodeView/DebugSubsectionRecord.h"
 #include "llvm/DebugInfo/CodeView/SymbolDeserializer.h"
 #include "llvm/DebugInfo/CodeView/SymbolRecord.h"
+#include "llvm/DebugInfo/CodeView/TypeDeserializer.h"
 #include "llvm/Object/Binary.h"
 #include "llvm/Object/COFF.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
void ObjFile::parse() {
   } else {
     fatal(toString(this) + " is not a COFF file");
   }
 
   // Read section and symbol tables.
   initializeChunks();
   initializeSymbols();
   initializeFlags();
+  initializeDependencies();
 }
 
 const coff_section* ObjFile::getSection(uint32_t I) {
   const coff_section *Sec;
   if (auto EC = COFFObj->getSection(I, Sec))
     fatal("getSection failed: #" + Twine(I) + ": " + EC.message());
   return Sec;
 }
for (unsigned I = 0; I < 2; ++I) {
             Sym.get()));
         PCHSignature = ObjName.Signature;
       }
       Offset += Sym->length();
     }
   }
 }
 
+// Depending on the compilation flags, OBJs can refer to external files,
+// necessary to merge this OBJ into the final PDB. We currently support two
+// types of external files: Precomp/PCH OBJs, when compiling with /Yc and /Yu.
+// And PDB type servers, when compiling with /Zi. This function extracts these
+// dependencies and makes them available as a TpiSource interface (see
+// DebugTypes.h).
+void ObjFile::initializeDependencies() {
+  if (!Config->Debug)
+    return;
+
+  bool IsPCH = false;
+
+  ArrayRef<uint8_t> Data = getDebugSection(".debug$P");
+  if (!Data.empty())
+    IsPCH = true;
+  else
+    Data = getDebugSection(".debug$T");
+
+  if (Data.empty())
+    return;
+
+  CVTypeArray Types;
+  BinaryStreamReader Reader(Data, support::little);
+  cantFail(Reader.readArray(Types, Reader.getLength()));
+
+  CVTypeArray::Iterator FirstType = Types.begin();
+  if (FirstType == Types.end())
+    return;
+
+  DebugTypes.emplace(Types);
+
+  if (IsPCH) {
+    DebugTypesObj = makePrecompSource(this);
+    return;
+  }
+
+  if (FirstType->kind() == LF_TYPESERVER2) {
+    TypeServer2Record TS = cantFail(
+        TypeDeserializer::deserializeAs<TypeServer2Record>(FirstType->data()));
+    DebugTypesObj = makeUseTypeServerSource(this, &TS);
+    return;
+  }
+
+  if (FirstType->kind() == LF_PRECOMP) {
+    PrecompRecord Precomp = cantFail(
+        TypeDeserializer::deserializeAs<PrecompRecord>(FirstType->data()));
+    DebugTypesObj = makeUsePrecompSource(this, &Precomp);
+    return;
+  }
+
+  DebugTypesObj = makeTpiSource(this);
+}
+
 StringRef ltrim1(StringRef S, const char *Chars) {
   if (!S.empty() && strchr(Chars, S[0]))
     return S.substr(1);
   return S;
 }
 
 void ImportFile::parse() {
   const char *Buf = MB.getBufferStart();

COFF/PDB.cpp

 //===- PDB.cpp ------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "PDB.h"
 #include "Chunks.h"
 #include "Config.h"
+#include "DebugTypes.h"
 #include "Driver.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
 #include "Writer.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Timer.h"
 #include "lld/Common/Threads.h"
 #include "llvm/DebugInfo/CodeView/DebugFrameDataSubsection.h"
public:
   ///
   /// If the object does not use a type server PDB (compiled with /Z7), we merge
   /// all the type and item records from the .debug$S stream and fill in the
   /// caller-provided ObjectIndexMap.
   Expected<const CVIndexMap &> mergeDebugT(ObjFile *File,
                                            CVIndexMap *ObjectIndexMap);
 
   /// Reads and makes available a PDB.
-  Expected<const CVIndexMap &> maybeMergeTypeServerPDB(ObjFile *File,
-                                                       const CVType &FirstType);
+  Expected<const CVIndexMap &> maybeMergeTypeServerPDB(ObjFile *File);
 
   /// Merges a precompiled headers TPI map into the current TPI map. The
   /// precompiled headers object will also be loaded and remapped in the
   /// process.
-  Expected<const CVIndexMap &>
-  mergeInPrecompHeaderObj(ObjFile *File, const CVType &FirstType,
-                          CVIndexMap *ObjectIndexMap);
+  Error mergeInPrecompHeaderObj(ObjFile *File, CVIndexMap *ObjectIndexMap);
 
   /// Reads and makes available a precompiled headers object.
   ///
   /// This is a requirement for objects compiled with cl.exe /Yu. In that
   /// case, the referenced object (which was compiled with /Yc) has to be loaded
   /// first. This is mainly because the current object's TPI stream has external
   /// references to the precompiled headers object.
   ///
   /// If the precompiled headers object was already loaded, this function will
   /// simply return its (remapped) TPI map.
-  Expected<const CVIndexMap &> aquirePrecompObj(ObjFile *File,
-                                                PrecompRecord Precomp);
+  Expected<const CVIndexMap &> aquirePrecompObj(ObjFile *File);
 
   /// Adds a precompiled headers object signature -> TPI mapping.
   std::pair<CVIndexMap &, bool /*already there*/>
   registerPrecompiledHeaders(uint32_t Signature);
 
   void mergeSymbolRecords(ObjFile *File, const CVIndexMap &IndexMap,
                           std::vector<ulittle32_t *> &StringTableRefs,
                           BinaryStreamRef SymData);
TypeTable.ForEachRecord([&](TypeIndex TI, const CVType &Type) {
     TpiBuilder.addTypeRecord(Type.RecordData, *Hash);
   });
 }
 
 Expected<const CVIndexMap &>
 PDBLinker::mergeDebugT(ObjFile *File, CVIndexMap *ObjectIndexMap) {
   ScopedTimer T(TypeMergingTimer);
 
-  bool IsPrecompiledHeader = false;
-
-  ArrayRef<uint8_t> Data = File->getDebugSection(".debug$T");
-  if (Data.empty()) {
-    // Try again, Microsoft precompiled headers use .debug$P instead of
-    // .debug$T
-    Data = File->getDebugSection(".debug$P");
-    IsPrecompiledHeader = true;
-  }
-  if (Data.empty())
-    return *ObjectIndexMap; // no debug info
+  if (!File->DebugTypesObj)
+      return *ObjectIndexMap; // no Types stream
 
   // Precompiled headers objects need to save the index map for further
   // reference by other objects which use the precompiled headers.
-  if (IsPrecompiledHeader) {
+  if (File->DebugTypesObj->Kind == TpiSource::PCH) {
     uint32_t PCHSignature = File->PCHSignature.getValueOr(0);
     if (PCHSignature == 0)
       fatal("No signature found for the precompiled headers OBJ (" +
             File->getName() + ")");
 
     // When a precompiled headers object comes first on the command-line, we
     // update the mapping here. Otherwise, if an object referencing the
     // precompiled headers object comes first, the mapping is created in
     // aquirePrecompObj(), thus we would skip this block.
     if (!ObjectIndexMap->IsPrecompiledTypeMap) {
       auto R = registerPrecompiledHeaders(PCHSignature);
       if (R.second)
         fatal(
             "A precompiled headers OBJ with the same signature was already "
             "provided! (" +
             File->getName() + ")");
 
       ObjectIndexMap = &R.first;
     }
   }
 
-  BinaryByteStream Stream(Data, support::little);
-  CVTypeArray Types;
-  BinaryStreamReader Reader(Stream);
-  if (auto EC = Reader.readArray(Types, Reader.getLength()))
-    fatal("Reader::readArray failed: " + toString(std::move(EC)));
-
-  auto FirstType = Types.begin();
-  if (FirstType == Types.end())
-    return *ObjectIndexMap;
-
-  if (FirstType->kind() == LF_TYPESERVER2) {
+  if (File->DebugTypesObj->Kind == TpiSource::UsingPDB) {
     // Look through type servers. If we've already seen this type server,
     // don't merge any type information.
-    return maybeMergeTypeServerPDB(File, *FirstType);
-  } else if (FirstType->kind() == LF_PRECOMP) {
+    return maybeMergeTypeServerPDB(File);
+  }
+  
+  CVTypeArray &Types = *File->DebugTypes;
+
+  if (File->DebugTypesObj->Kind == TpiSource::UsingPCH) {
     // This object was compiled with /Yu, so process the corresponding
     // precompiled headers object (/Yc) first. Some type indices in the current
     // object are referencing data in the precompiled headers object, so we need
     // both to be loaded.
-    auto E = mergeInPrecompHeaderObj(File, *FirstType, ObjectIndexMap);
-    if (!E)
-      return E.takeError();
-
-    // Drop LF_PRECOMP record from the input stream, as it needs to be replaced
-    // with the precompiled headers object type stream.
-    // Note that we can't just call Types.drop_front(), as we explicitly want to
-    // rebase the stream.
+    Error E = mergeInPrecompHeaderObj(File, ObjectIndexMap);
+    if (E)
+      return std::move(E);
+
+    // Drop LF_PRECOMP record from the input stream, as it has been replaced
+    // with the precompiled headers Type stream in the mergeInPrecompHeaderObj()
+    // call above. Note that we can't just call Types.drop_front(), as we
+    // explicitly want to rebase the stream.
+    CVTypeArray::Iterator FirstType = Types.begin();
     Types.setUnderlyingStream(
         Types.getUnderlyingStream().drop_front(FirstType->RecordData.size()));
   }
 
   // Fill in the temporary, caller-provided ObjectIndexMap.
   if (Config->DebugGHashes) {
     ArrayRef<GloballyHashedType> Hashes;
     std::vector<GloballyHashedType> OwnedHashes;
tryToLoadPDB(const codeview::GUID &GuidFromObj, StringRef TSPath) {
   // PDB file doesn't mean it matches.  For it to match the InfoStream's GUID
   // must match the GUID specified in the TypeServer2 record.
   if (ExpectedInfo->getGuid() != GuidFromObj)
     return make_error<pdb::PDBError>(pdb::pdb_error_code::signature_out_of_date);
 
   return std::move(NS);
 }
 
-Expected<const CVIndexMap &>
-PDBLinker::maybeMergeTypeServerPDB(ObjFile *File, const CVType &FirstType) {
-  TypeServer2Record TS;
-  if (auto EC =
-          TypeDeserializer::deserializeAs(const_cast<CVType &>(FirstType), TS))
-    fatal("error reading record: " + toString(std::move(EC)));
+Expected<const CVIndexMap &> PDBLinker::maybeMergeTypeServerPDB(ObjFile *File) {
+  const TypeServer2Record &TS =
+      retrieveDependencyInfo<TypeServer2Record>(File->DebugTypesObj);
 
   const codeview::GUID &TSId = TS.getGuid();
   StringRef TSPath = TS.getName();
 
   // First, check if the PDB has previously failed to load.
   auto PrevErr = MissingTypeServerPDBs.find(TSId);
   if (PrevErr != MissingTypeServerPDBs.end())
     return createFileError(
if (Config->DebugGHashes) {
     if (auto Err = mergeIdRecords(IDTable, IndexMap.TPIMap, IndexMap.IPIMap,
                                   ExpectedIpi->typeArray()))
       fatal("codeview::mergeIdRecords failed: " + toString(std::move(Err)));
   }
 
   return IndexMap;
 }
 
-Expected<const CVIndexMap &>
-PDBLinker::mergeInPrecompHeaderObj(ObjFile *File, const CVType &FirstType,
+Error PDBLinker::mergeInPrecompHeaderObj(ObjFile *File,
                                          CVIndexMap *ObjectIndexMap) {
-  PrecompRecord Precomp;
-  if (auto EC = TypeDeserializer::deserializeAs(const_cast<CVType &>(FirstType),
-                                                Precomp))
-    fatal("error reading record: " + toString(std::move(EC)));
+  const PrecompRecord &Precomp =
+      retrieveDependencyInfo<PrecompRecord>(File->DebugTypesObj);
 
-  auto E = aquirePrecompObj(File, Precomp);
+  Expected<const CVIndexMap &> E = aquirePrecompObj(File);
   if (!E)
     return E.takeError();
 
   const CVIndexMap &PrecompIndexMap = *E;
   assert(PrecompIndexMap.IsPrecompiledTypeMap);
 
   if (PrecompIndexMap.TPIMap.empty())
-    return PrecompIndexMap;
+    return Error::success();
 
   assert(Precomp.getStartTypeIndex() == TypeIndex::FirstNonSimpleIndex);
   assert(Precomp.getTypesCount() <= PrecompIndexMap.TPIMap.size());
   // Use the previously remapped index map from the precompiled headers.
   ObjectIndexMap->TPIMap.append(PrecompIndexMap.TPIMap.begin(),
                                 PrecompIndexMap.TPIMap.begin() +
                                     Precomp.getTypesCount());
-  return *ObjectIndexMap;
+  return Error::success();
 }
 
 static bool equals_path(StringRef path1, StringRef path2) {
 #if defined(_WIN32)
   return path1.equals_lower(path2);
 #else
   return path1.equals(path2);
 #endif
PDBLinker::registerPrecompiledHeaders(uint32_t Signature) {
   CVIndexMap &IndexMap = Insertion.first->second;
   if (!Insertion.second)
     return {IndexMap, true};
   // Mark this map as a precompiled types map.
   IndexMap.IsPrecompiledTypeMap = true;
   return {IndexMap, false};
 }
 
-Expected<const CVIndexMap &>
-PDBLinker::aquirePrecompObj(ObjFile *File, PrecompRecord Precomp) {
+Expected<const CVIndexMap &> PDBLinker::aquirePrecompObj(ObjFile *File) {
+  const PrecompRecord &Precomp =
+      retrieveDependencyInfo<PrecompRecord>(File->DebugTypesObj);
+
   // First, check if we already loaded the precompiled headers object with this
   // signature. Return the type index mapping if we've already seen it.
   auto R = registerPrecompiledHeaders(Precomp.getSignature());
   if (R.second)
     return R.first;
 
   CVIndexMap &IndexMap = R.first;