Modules: Rename MemoryBufferCache to InMemoryModuleCache

Change MemoryBufferCache to InMemoryModuleCache, moving it from Basic to
Serialization.  Another patch will start using it to manage module build
more explicitly, but this is split out because it's mostly mechanical.

Because of the move to Serialization we can no longer abuse the
Preprocessor to forward it to the ASTReader.  Besides the rename and
file move, that means Preprocessor::Preprocessor has one fewer parameter
and ASTReader::ASTReader has one more.

llvm-svn: 355777

33 files changed, 227 insertions, 217 deletions

diff --git a/clang/include/clang/Frontend/ASTUnit.h b/clang/include/clang/Frontend/ASTUnit.h
index cef638e2716..750f6c8577b 100644
--- a/clang/include/clang/Frontend/ASTUnit.h
+++ b/clang/include/clang/Frontend/ASTUnit.h
@@ -71,7 +71,7 @@ class FileManager;
 class FrontendAction;
 class HeaderSearch;
 class InputKind;
-class MemoryBufferCache;
+class InMemoryModuleCache;
 class PCHContainerOperations;
 class PCHContainerReader;
 class Preprocessor;
@@ -107,7 +107,7 @@ private:
   IntrusiveRefCntPtr<DiagnosticsEngine>   Diagnostics;
   IntrusiveRefCntPtr<FileManager>         FileMgr;
   IntrusiveRefCntPtr<SourceManager>       SourceMgr;
-  IntrusiveRefCntPtr<MemoryBufferCache>   PCMCache;
+  IntrusiveRefCntPtr<InMemoryModuleCache> ModuleCache;
   std::unique_ptr<HeaderSearch>           HeaderInfo;
   IntrusiveRefCntPtr<TargetInfo>          Target;
   std::shared_ptr<Preprocessor>           PP;
diff --git a/clang/include/clang/Frontend/CompilerInstance.h b/clang/include/clang/Frontend/CompilerInstance.h
index 002cc61eb47..2fc61574e30 100644
--- a/clang/include/clang/Frontend/CompilerInstance.h
+++ b/clang/include/clang/Frontend/CompilerInstance.h
@@ -44,7 +44,7 @@ class ExternalASTSource;
 class FileEntry;
 class FileManager;
 class FrontendAction;
-class MemoryBufferCache;
+class InMemoryModuleCache;
 class Module;
 class Preprocessor;
 class Sema;
@@ -92,7 +92,7 @@ class CompilerInstance : public ModuleLoader {
   IntrusiveRefCntPtr<SourceManager> SourceMgr;
 
   /// The cache of PCM files.
-  IntrusiveRefCntPtr<MemoryBufferCache> PCMCache;
+  IntrusiveRefCntPtr<InMemoryModuleCache> ModuleCache;
 
   /// The preprocessor.
   std::shared_ptr<Preprocessor> PP;
@@ -192,7 +192,7 @@ public:
   explicit CompilerInstance(
       std::shared_ptr<PCHContainerOperations> PCHContainerOps =
           std::make_shared<PCHContainerOperations>(),
-      MemoryBufferCache *SharedPCMCache = nullptr);
+      InMemoryModuleCache *SharedModuleCache = nullptr);
   ~CompilerInstance() override;
 
   /// @name High-Level Operations
@@ -671,7 +671,8 @@ public:
   /// \return - The new object on success, or null on failure.
   static IntrusiveRefCntPtr<ASTReader> createPCHExternalASTSource(
       StringRef Path, StringRef Sysroot, bool DisablePCHValidation,
-      bool AllowPCHWithCompilerErrors, Preprocessor &PP, ASTContext &Context,
+      bool AllowPCHWithCompilerErrors, Preprocessor &PP,
+      InMemoryModuleCache &ModuleCache, ASTContext &Context,
       const PCHContainerReader &PCHContainerRdr,
       ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
       DependencyFileGenerator *DependencyFile,
@@ -813,7 +814,7 @@ public:
 
   void setExternalSemaSource(IntrusiveRefCntPtr<ExternalSemaSource> ESS);
 
-  MemoryBufferCache &getPCMCache() const { return *PCMCache; }
+  InMemoryModuleCache &getModuleCache() const { return *ModuleCache; }
 };
 
 } // end namespace clang
diff --git a/clang/include/clang/Lex/Preprocessor.h b/clang/include/clang/Lex/Preprocessor.h
index 29d42504906..0292a33d603 100644
--- a/clang/include/clang/Lex/Preprocessor.h
+++ b/clang/include/clang/Lex/Preprocessor.h
@@ -71,7 +71,6 @@ class FileEntry;
 class FileManager;
 class HeaderSearch;
 class MacroArgs;
-class MemoryBufferCache;
 class PragmaHandler;
 class PragmaNamespace;
 class PreprocessingRecord;
@@ -132,7 +131,6 @@ class Preprocessor {
   const TargetInfo *AuxTarget = nullptr;
   FileManager       &FileMgr;
   SourceManager     &SourceMgr;
-  MemoryBufferCache &PCMCache;
   std::unique_ptr<ScratchBuffer> ScratchBuf;
   HeaderSearch      &HeaderInfo;
   ModuleLoader      &TheModuleLoader;
@@ -779,7 +777,6 @@ private:
 public:
   Preprocessor(std::shared_ptr<PreprocessorOptions> PPOpts,
                DiagnosticsEngine &diags, LangOptions &opts, SourceManager &SM,
-               MemoryBufferCache &PCMCache,
                HeaderSearch &Headers, ModuleLoader &TheModuleLoader,
                IdentifierInfoLookup *IILookup = nullptr,
                bool OwnsHeaderSearch = false,
@@ -819,7 +816,6 @@ public:
   const TargetInfo *getAuxTargetInfo() const { return AuxTarget; }
   FileManager &getFileManager() const { return FileMgr; }
   SourceManager &getSourceManager() const { return SourceMgr; }
-  MemoryBufferCache &getPCMCache() const { return PCMCache; }
   HeaderSearch &getHeaderSearchInfo() const { return HeaderInfo; }
 
   IdentifierTable &getIdentifierTable() { return Identifiers; }
diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
index 5b92b137224..58a3b6594c2 100644
--- a/clang/include/clang/Serialization/ASTReader.h
+++ b/clang/include/clang/Serialization/ASTReader.h
@@ -97,7 +97,7 @@ class HeaderSearchOptions;
 class LangOptions;
 class LazyASTUnresolvedSet;
 class MacroInfo;
-class MemoryBufferCache;
+class InMemoryModuleCache;
 class NamedDecl;
 class NamespaceDecl;
 class ObjCCategoryDecl;
@@ -440,9 +440,6 @@ private:
   /// The module manager which manages modules and their dependencies
   ModuleManager ModuleMgr;
 
-  /// The cache that manages memory buffers for PCM files.
-  MemoryBufferCache &PCMCache;
-
   /// A dummy identifier resolver used to merge TU-scope declarations in
   /// C, for the cases where we don't have a Sema object to provide a real
   /// identifier resolver.
@@ -1481,8 +1478,8 @@ public:
   ///
   /// \param ReadTimer If non-null, a timer used to track the time spent
   /// deserializing.
-  ASTReader(Preprocessor &PP, ASTContext *Context,
-            const PCHContainerReader &PCHContainerRdr,
+  ASTReader(Preprocessor &PP, InMemoryModuleCache &ModuleCache,
+            ASTContext *Context, const PCHContainerReader &PCHContainerRdr,
             ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
             StringRef isysroot = "", bool DisableValidation = false,
             bool AllowASTWithCompilerErrors = false,
diff --git a/clang/include/clang/Serialization/ASTWriter.h b/clang/include/clang/Serialization/ASTWriter.h
index ed512ef8f54..b0f72224700 100644
--- a/clang/include/clang/Serialization/ASTWriter.h
+++ b/clang/include/clang/Serialization/ASTWriter.h
@@ -74,8 +74,8 @@ class IdentifierResolver;
 class LangOptions;
 class MacroDefinitionRecord;
 class MacroInfo;
-class MemoryBufferCache;
 class Module;
+class InMemoryModuleCache;
 class ModuleFileExtension;
 class ModuleFileExtensionWriter;
 class NamedDecl;
@@ -132,7 +132,7 @@ private:
   const SmallVectorImpl<char> &Buffer;
 
   /// The PCM manager which manages memory buffers for pcm files.
-  MemoryBufferCache &PCMCache;
+  InMemoryModuleCache &ModuleCache;
 
   /// The ASTContext we're writing.
   ASTContext *Context = nullptr;
@@ -542,7 +542,7 @@ public:
   /// Create a new precompiled header writer that outputs to
   /// the given bitstream.
   ASTWriter(llvm::BitstreamWriter &Stream, SmallVectorImpl<char> &Buffer,
-            MemoryBufferCache &PCMCache,
+            InMemoryModuleCache &ModuleCache,
             ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
             bool IncludeTimestamps = true);
   ~ASTWriter() override;
@@ -981,7 +981,8 @@ protected:
   SmallVectorImpl<char> &getPCH() const { return Buffer->Data; }
 
 public:
-  PCHGenerator(const Preprocessor &PP, StringRef OutputFile, StringRef isysroot,
+  PCHGenerator(const Preprocessor &PP, InMemoryModuleCache &ModuleCache,
+               StringRef OutputFile, StringRef isysroot,
                std::shared_ptr<PCHBuffer> Buffer,
                ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
                bool AllowASTWithErrors = false, bool IncludeTimestamps = true);
diff --git a/clang/include/clang/Basic/MemoryBufferCache.h b/clang/include/clang/Serialization/InMemoryModuleCache.h
index 9a2b62e0d9a..aea4a8d60b9 100644
--- a/clang/include/clang/Basic/MemoryBufferCache.h
+++ b/clang/include/clang/Serialization/InMemoryModuleCache.h
@@ -1,4 +1,4 @@
-//===- MemoryBufferCache.h - Cache for loaded memory buffers ----*- C++ -*-===//
+//===- InMemoryModuleCache.h - In-memory cache for modules ------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,10 +6,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_CLANG_BASIC_MEMORYBUFFERCACHE_H
-#define LLVM_CLANG_BASIC_MEMORYBUFFERCACHE_H
+#ifndef LLVM_CLANG_SERIALIZATION_INMEMORYMODULECACHE_H
+#define LLVM_CLANG_SERIALIZATION_INMEMORYMODULECACHE_H
 
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringMap.h"
 #include <memory>
 
@@ -19,17 +20,22 @@ class MemoryBuffer;
 
 namespace clang {
 
-/// Manage memory buffers across multiple users.
+/// In-memory cache for modules.
 ///
-/// Ensures that multiple users have a consistent view of each buffer.  This is
-/// used by \a CompilerInstance when building PCMs to ensure that each \a
-/// ModuleManager sees the same files.
+/// This is a cache for modules for use across a compilation, sharing state
+/// between the CompilerInstances in an implicit modules build.  It must be
+/// shared by each CompilerInstance, ASTReader, ASTWriter, and ModuleManager
+/// that are coordinating.
+///
+/// Critically, it ensures that a single process has a consistent view of each
+/// PCM.  This is used by \a CompilerInstance when building PCMs to ensure that
+/// each \a ModuleManager sees the same files.
 ///
 /// \a finalizeCurrentBuffers() should be called before creating a new user.
-/// This locks in the current buffers, ensuring that no buffer that has already
-/// been accessed can be purged, preventing use-after-frees.
-class MemoryBufferCache : public llvm::RefCountedBase<MemoryBufferCache> {
-  struct BufferEntry {
+/// This locks in the current PCMs, ensuring that no PCM that has already been
+/// accessed can be purged, preventing use-after-frees.
+class InMemoryModuleCache : public llvm::RefCountedBase<InMemoryModuleCache> {
+  struct PCM {
     std::unique_ptr<llvm::MemoryBuffer> Buffer;
 
     /// Track the timeline of when this was added to the cache.
@@ -37,7 +43,7 @@ class MemoryBufferCache : public llvm::RefCountedBase<MemoryBufferCache> {
   };
 
   /// Cache of buffers.
-  llvm::StringMap<BufferEntry> Buffers;
+  llvm::StringMap<PCM> PCMs;
 
   /// Monotonically increasing index.
   unsigned NextIndex = 0;
@@ -76,4 +82,4 @@ public:
 
 } // end namespace clang
 
-#endif // LLVM_CLANG_BASIC_MEMORYBUFFERCACHE_H
+#endif // LLVM_CLANG_SERIALIZATION_INMEMORYMODULECACHE_H
diff --git a/clang/include/clang/Serialization/Module.h b/clang/include/clang/Serialization/Module.h
index 45f82d4764c..ebaaeea29a9 100644
--- a/clang/include/clang/Serialization/Module.h
+++ b/clang/include/clang/Serialization/Module.h
@@ -174,7 +174,7 @@ public:
   unsigned Generation;
 
   /// The memory buffer that stores the data associated with
-  /// this AST file, owned by the PCMCache in the ModuleManager.
+  /// this AST file, owned by the InMemoryModuleCache.
   llvm::MemoryBuffer *Buffer;
 
   /// The size of this file, in bits.
diff --git a/clang/include/clang/Serialization/ModuleManager.h b/clang/include/clang/Serialization/ModuleManager.h
index 7bd7dc290a7..5b3b22be759 100644
--- a/clang/include/clang/Serialization/ModuleManager.h
+++ b/clang/include/clang/Serialization/ModuleManager.h
@@ -38,7 +38,7 @@ class FileEntry;
 class FileManager;
 class GlobalModuleIndex;
 class HeaderSearch;
-class MemoryBufferCache;
+class InMemoryModuleCache;
 class ModuleMap;
 class PCHContainerReader;
 
@@ -67,7 +67,7 @@ class ModuleManager {
   FileManager &FileMgr;
 
   /// Cache of PCM files.
-  IntrusiveRefCntPtr<MemoryBufferCache> PCMCache;
+  IntrusiveRefCntPtr<InMemoryModuleCache> ModuleCache;
 
   /// Knows how to unwrap module containers.
   const PCHContainerReader &PCHContainerRdr;
@@ -139,7 +139,7 @@ public:
       SmallVectorImpl<std::unique_ptr<ModuleFile>>::reverse_iterator>;
   using ModuleOffset = std::pair<uint32_t, StringRef>;
 
-  explicit ModuleManager(FileManager &FileMgr, MemoryBufferCache &PCMCache,
+  explicit ModuleManager(FileManager &FileMgr, InMemoryModuleCache &ModuleCache,
                          const PCHContainerReader &PCHContainerRdr,
                          const HeaderSearch &HeaderSearchInfo);
   ~ModuleManager();
@@ -317,7 +317,7 @@ public:
   /// View the graphviz representation of the module graph.
   void viewGraph();
 
-  MemoryBufferCache &getPCMCache() const { return *PCMCache; }
+  InMemoryModuleCache &getModuleCache() const { return *ModuleCache; }
 };
 
 } // namespace serialization
diff --git a/clang/lib/Basic/CMakeLists.txt b/clang/lib/Basic/CMakeLists.txt
index 2770cd31c91..18dd7d61fbb 100644
--- a/clang/lib/Basic/CMakeLists.txt
+++ b/clang/lib/Basic/CMakeLists.txt
@@ -50,7 +50,6 @@ add_clang_library(clangBasic
   FixedPoint.cpp
   IdentifierTable.cpp
   LangOptions.cpp
-  MemoryBufferCache.cpp
   Module.cpp
   ObjCRuntime.cpp
   OpenMPKinds.cpp
diff --git a/clang/lib/Basic/MemoryBufferCache.cpp b/clang/lib/Basic/MemoryBufferCache.cpp
deleted file mode 100644
index d3ea99bc0c3..00000000000
--- a/clang/lib/Basic/MemoryBufferCache.cpp
+++ /dev/null
@@ -1,47 +0,0 @@
-//===- MemoryBufferCache.cpp - Cache for loaded memory buffers ------------===//
-//
-// 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 "clang/Basic/MemoryBufferCache.h"
-#include "llvm/Support/MemoryBuffer.h"
-
-using namespace clang;
-
-llvm::MemoryBuffer &
-MemoryBufferCache::addBuffer(llvm::StringRef Filename,
-                             std::unique_ptr<llvm::MemoryBuffer> Buffer) {
-  auto Insertion =
-      Buffers.insert({Filename, BufferEntry{std::move(Buffer), NextIndex++}});
-  assert(Insertion.second && "Already has a buffer");
-  return *Insertion.first->second.Buffer;
-}
-
-llvm::MemoryBuffer *MemoryBufferCache::lookupBuffer(llvm::StringRef Filename) {
-  auto I = Buffers.find(Filename);
-  if (I == Buffers.end())
-    return nullptr;
-  return I->second.Buffer.get();
-}
-
-bool MemoryBufferCache::isBufferFinal(llvm::StringRef Filename) {
-  auto I = Buffers.find(Filename);
-  if (I == Buffers.end())
-    return false;
-  return I->second.Index < FirstRemovableIndex;
-}
-
-bool MemoryBufferCache::tryToRemoveBuffer(llvm::StringRef Filename) {
-  auto I = Buffers.find(Filename);
-  assert(I != Buffers.end() && "No buffer to remove...");
-  if (I->second.Index < FirstRemovableIndex)
-    return true;
-
-  Buffers.erase(I);
-  return false;
-}
-
-void MemoryBufferCache::finalizeCurrentBuffers() { FirstRemovableIndex = NextIndex; }
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index c404f3232dc..0b2995b8eed 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -30,7 +30,6 @@
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/LangOptions.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
@@ -60,6 +59,7 @@
 #include "clang/Serialization/ASTReader.h"
 #include "clang/Serialization/ASTWriter.h"
 #include "clang/Serialization/ContinuousRangeMap.h"
+#include "clang/Serialization/InMemoryModuleCache.h"
 #include "clang/Serialization/Module.h"
 #include "clang/Serialization/PCHContainerOperations.h"
 #include "llvm/ADT/ArrayRef.h"
@@ -217,8 +217,8 @@ struct ASTUnit::ASTWriterData {
   llvm::BitstreamWriter Stream;
   ASTWriter Writer;
 
-  ASTWriterData(MemoryBufferCache &PCMCache)
-      : Stream(Buffer), Writer(Stream, Buffer, PCMCache, {}) {}
+  ASTWriterData(InMemoryModuleCache &ModuleCache)
+      : Stream(Buffer), Writer(Stream, Buffer, ModuleCache, {}) {}
 };
 
 void ASTUnit::clearFileLevelDecls() {
@@ -758,7 +758,7 @@ std::unique_ptr<ASTUnit> ASTUnit::LoadFromASTFile(
   AST->SourceMgr = new SourceManager(AST->getDiagnostics(),
                                      AST->getFileManager(),
                                      UserFilesAreVolatile);
-  AST->PCMCache = new MemoryBufferCache;
+  AST->ModuleCache = new InMemoryModuleCache;
   AST->HSOpts = std::make_shared<HeaderSearchOptions>();
   AST->HSOpts->ModuleFormat = PCHContainerRdr.getFormat();
   AST->HeaderInfo.reset(new HeaderSearch(AST->HSOpts,
@@ -778,7 +778,7 @@ std::unique_ptr<ASTUnit> ASTUnit::LoadFromASTFile(
 
   AST->PP = std::make_shared<Preprocessor>(
       AST->PPOpts, AST->getDiagnostics(), *AST->LangOpts,
-      AST->getSourceManager(), *AST->PCMCache, HeaderInfo, AST->ModuleLoader,
+      AST->getSourceManager(), HeaderInfo, AST->ModuleLoader,
       /*IILookup=*/nullptr,
       /*OwnsHeaderSearch=*/false);
   Preprocessor &PP = *AST->PP;
@@ -791,10 +791,10 @@ std::unique_ptr<ASTUnit> ASTUnit::LoadFromASTFile(
   bool disableValid = false;
   if (::getenv("LIBCLANG_DISABLE_PCH_VALIDATION"))
     disableValid = true;
-  AST->Reader = new ASTReader(PP, AST->Ctx.get(), PCHContainerRdr, {},
-                              /*isysroot=*/"",
-                              /*DisableValidation=*/disableValid,
-                              AllowPCHWithCompilerErrors);
+  AST->Reader = new ASTReader(
+      PP, *AST->ModuleCache, AST->Ctx.get(), PCHContainerRdr, {},
+      /*isysroot=*/"",
+      /*DisableValidation=*/disableValid, AllowPCHWithCompilerErrors);
 
   AST->Reader->setListener(llvm::make_unique<ASTInfoCollector>(
       *AST->PP, AST->Ctx.get(), *AST->HSOpts, *AST->PPOpts, *AST->LangOpts,
@@ -1477,7 +1477,7 @@ ASTUnit::create(std::shared_ptr<CompilerInvocation> CI,
   AST->UserFilesAreVolatile = UserFilesAreVolatile;
   AST->SourceMgr = new SourceManager(AST->getDiagnostics(), *AST->FileMgr,
                                      UserFilesAreVolatile);
-  AST->PCMCache = new MemoryBufferCache;
+  AST->ModuleCache = new InMemoryModuleCache;
 
   return AST;
 }
@@ -1757,7 +1757,7 @@ ASTUnit *ASTUnit::LoadFromCommandLine(
     VFS = llvm::vfs::getRealFileSystem();
   VFS = createVFSFromCompilerInvocation(*CI, *Diags, VFS);
   AST->FileMgr = new FileManager(AST->FileSystemOpts, VFS);
-  AST->PCMCache = new MemoryBufferCache;
+  AST->ModuleCache = new InMemoryModuleCache;
   AST->OnlyLocalDecls = OnlyLocalDecls;
   AST->CaptureDiagnostics = CaptureDiagnostics;
   AST->TUKind = TUKind;
@@ -1768,7 +1768,7 @@ ASTUnit *ASTUnit::LoadFromCommandLine(
   AST->Invocation = CI;
   AST->SkipFunctionBodies = SkipFunctionBodies;
   if (ForSerialization)
-    AST->WriterData.reset(new ASTWriterData(*AST->PCMCache));
+    AST->WriterData.reset(new ASTWriterData(*AST->ModuleCache));
   // Zero out now to ease cleanup during crash recovery.
   CI = nullptr;
   Diags = nullptr;
@@ -2317,8 +2317,8 @@ bool ASTUnit::serialize(raw_ostream &OS) {
 
   SmallString<128> Buffer;
   llvm::BitstreamWriter Stream(Buffer);
-  MemoryBufferCache PCMCache;
-  ASTWriter Writer(Stream, Buffer, PCMCache, {});
+  InMemoryModuleCache ModuleCache;
+  ASTWriter Writer(Stream, Buffer, ModuleCache, {});
   return serializeUnit(Writer, Buffer, getSema(), hasErrors, OS);
 }
 
diff --git a/clang/lib/Frontend/ChainedIncludesSource.cpp b/clang/lib/Frontend/ChainedIncludesSource.cpp
index 566c1d712cb..48154ecf474 100644
--- a/clang/lib/Frontend/ChainedIncludesSource.cpp
+++ b/clang/lib/Frontend/ChainedIncludesSource.cpp
@@ -82,9 +82,9 @@ createASTReader(CompilerInstance &CI, StringRef pchFile,
                 ASTDeserializationListener *deserialListener = nullptr) {
   Preprocessor &PP = CI.getPreprocessor();
   std::unique_ptr<ASTReader> Reader;
-  Reader.reset(new ASTReader(PP, &CI.getASTContext(),
+  Reader.reset(new ASTReader(PP, CI.getModuleCache(), &CI.getASTContext(),
                              CI.getPCHContainerReader(),
-                             /*Extensions=*/{ },
+                             /*Extensions=*/{},
                              /*isysroot=*/"", /*DisableValidation=*/true));
   for (unsigned ti = 0; ti < bufNames.size(); ++ti) {
     StringRef sr(bufNames[ti]);
@@ -159,8 +159,8 @@ IntrusiveRefCntPtr<ExternalSemaSource> clang::createChainedIncludesSource(
     auto Buffer = std::make_shared<PCHBuffer>();
     ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions;
     auto consumer = llvm::make_unique<PCHGenerator>(
-        Clang->getPreprocessor(), "-", /*isysroot=*/"", Buffer,
-        Extensions, /*AllowASTWithErrors=*/true);
+        Clang->getPreprocessor(), Clang->getModuleCache(), "-", /*isysroot=*/"",
+        Buffer, Extensions, /*AllowASTWithErrors=*/true);
     Clang->getASTContext().setASTMutationListener(
                                             consumer->GetASTMutationListener());
     Clang->setASTConsumer(std::move(consumer));
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index d9e3226e11d..8fa1393cef1 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -13,7 +13,6 @@
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/FileManager.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/Stack.h"
 #include "clang/Basic/TargetInfo.h"
@@ -35,6 +34,7 @@
 #include "clang/Sema/Sema.h"
 #include "clang/Serialization/ASTReader.h"
 #include "clang/Serialization/GlobalModuleIndex.h"
+#include "clang/Serialization/InMemoryModuleCache.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Support/BuryPointer.h"
 #include "llvm/Support/CrashRecoveryContext.h"
@@ -57,14 +57,15 @@ using namespace clang;
 
 CompilerInstance::CompilerInstance(
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
-    MemoryBufferCache *SharedPCMCache)
-    : ModuleLoader(/* BuildingModule = */ SharedPCMCache),
+    InMemoryModuleCache *SharedModuleCache)
+    : ModuleLoader(/* BuildingModule = */ SharedModuleCache),
       Invocation(new CompilerInvocation()),
-      PCMCache(SharedPCMCache ? SharedPCMCache : new MemoryBufferCache),
+      ModuleCache(SharedModuleCache ? SharedModuleCache
+                                    : new InMemoryModuleCache),
       ThePCHContainerOperations(std::move(PCHContainerOps)) {
   // Don't allow this to invalidate buffers in use by others.
-  if (SharedPCMCache)
-    getPCMCache().finalizeCurrentBuffers();
+  if (SharedModuleCache)
+    getModuleCache().finalizeCurrentBuffers();
 }
 
 CompilerInstance::~CompilerInstance() {
@@ -136,7 +137,7 @@ IntrusiveRefCntPtr<ASTReader> CompilerInstance::getModuleManager() const {
   return ModuleManager;
 }
 void CompilerInstance::setModuleManager(IntrusiveRefCntPtr<ASTReader> Reader) {
-  assert(PCMCache.get() == &Reader->getModuleManager().getPCMCache() &&
+  assert(ModuleCache.get() == &Reader->getModuleManager().getModuleCache() &&
          "Expected ASTReader to use the same PCM cache");
   ModuleManager = std::move(Reader);
 }
@@ -378,11 +379,11 @@ void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
   HeaderSearch *HeaderInfo =
       new HeaderSearch(getHeaderSearchOptsPtr(), getSourceManager(),
                        getDiagnostics(), getLangOpts(), &getTarget());
-  PP = std::make_shared<Preprocessor>(
-      Invocation->getPreprocessorOptsPtr(), getDiagnostics(), getLangOpts(),
-      getSourceManager(), getPCMCache(), *HeaderInfo, *this,
-      /*IdentifierInfoLookup=*/nullptr,
-      /*OwnsHeaderSearch=*/true, TUKind);
+  PP = std::make_shared<Preprocessor>(Invocation->getPreprocessorOptsPtr(),
+                                      getDiagnostics(), getLangOpts(),
+                                      getSourceManager(), *HeaderInfo, *this,
+                                      /*IdentifierInfoLookup=*/nullptr,
+                                      /*OwnsHeaderSearch=*/true, TUKind);
   getTarget().adjust(getLangOpts());
   PP->Initialize(getTarget(), getAuxTarget());
 
@@ -489,19 +490,17 @@ void CompilerInstance::createPCHExternalASTSource(
   bool Preamble = getPreprocessorOpts().PrecompiledPreambleBytes.first != 0;
   ModuleManager = createPCHExternalASTSource(
       Path, getHeaderSearchOpts().Sysroot, DisablePCHValidation,
-      AllowPCHWithCompilerErrors, getPreprocessor(), getASTContext(),
-      getPCHContainerReader(),
-      getFrontendOpts().ModuleFileExtensions,
-      TheDependencyFileGenerator.get(),
-      DependencyCollectors,
-      DeserializationListener,
-      OwnDeserializationListener, Preamble,
-      getFrontendOpts().UseGlobalModuleIndex);
+      AllowPCHWithCompilerErrors, getPreprocessor(), getModuleCache(),
+      getASTContext(), getPCHContainerReader(),
+      getFrontendOpts().ModuleFileExtensions, TheDependencyFileGenerator.get(),
+      DependencyCollectors, DeserializationListener, OwnDeserializationListener,
+      Preamble, getFrontendOpts().UseGlobalModuleIndex);
 }
 
 IntrusiveRefCntPtr<ASTReader> CompilerInstance::createPCHExternalASTSource(
     StringRef Path, StringRef Sysroot, bool DisablePCHValidation,
-    bool AllowPCHWithCompilerErrors, Preprocessor &PP, ASTContext &Context,
+    bool AllowPCHWithCompilerErrors, Preprocessor &PP,
+    InMemoryModuleCache &ModuleCache, ASTContext &Context,
     const PCHContainerReader &PCHContainerRdr,
     ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
     DependencyFileGenerator *DependencyFile,
@@ -511,7 +510,7 @@ IntrusiveRefCntPtr<ASTReader> CompilerInstance::createPCHExternalASTSource(
   HeaderSearchOptions &HSOpts = PP.getHeaderSearchInfo().getHeaderSearchOpts();
 
   IntrusiveRefCntPtr<ASTReader> Reader(new ASTReader(
-      PP, &Context, PCHContainerRdr, Extensions,
+      PP, ModuleCache, &Context, PCHContainerRdr, Extensions,
       Sysroot.empty() ? "" : Sysroot.data(), DisablePCHValidation,
       AllowPCHWithCompilerErrors, /*AllowConfigurationMismatch*/ false,
       HSOpts.ModulesValidateSystemHeaders, UseGlobalModuleIndex));
@@ -1094,11 +1093,11 @@ compileModuleImpl(CompilerInstance &ImportingInstance, SourceLocation ImportLoc,
          Invocation->getModuleHash() && "Module hash mismatch!");
 
   // Construct a compiler instance that will be used to actually create the
-  // module.  Since we're sharing a PCMCache,
+  // module.  Since we're sharing an in-memory module cache,
   // CompilerInstance::CompilerInstance is responsible for finalizing the
   // buffers to prevent use-after-frees.
   CompilerInstance Instance(ImportingInstance.getPCHContainerOperations(),
-                            &ImportingInstance.getPreprocessor().getPCMCache());
+                            &ImportingInstance.getModuleCache());
   auto &Inv = *Invocation;
   Instance.setInvocation(std::move(Invocation));
 
@@ -1255,7 +1254,7 @@ static bool compileAndLoadModule(CompilerInstance &ImportingInstance,
     llvm::LockFileManager Locked(ModuleFileName);
     switch (Locked) {
     case llvm::LockFileManager::LFS_Error:
-      // PCMCache takes care of correctness and locks are only necessary for
+      // ModuleCache takes care of correctness and locks are only necessary for
       // performance. Fallback to building the module in case of any lock
       // related errors.
       Diags.Report(ModuleNameLoc, diag::remark_module_lock_failure)
@@ -1282,9 +1281,9 @@ static bool compileAndLoadModule(CompilerInstance &ImportingInstance,
       case llvm::LockFileManager::Res_OwnerDied:
         continue; // try again to get the lock.
       case llvm::LockFileManager::Res_Timeout:
-        // Since PCMCache takes care of correctness, we try waiting for another
-        // process to complete the build so clang does not do it done twice. If
-        // case of timeout, build it ourselves.
+        // Since ModuleCache takes care of correctness, we try waiting for
+        // another process to complete the build so clang does not do it done
+        // twice. If case of timeout, build it ourselves.
         Diags.Report(ModuleNameLoc, diag::remark_module_lock_timeout)
             << Module->Name;
         // Clear the lock file so that future invocations can make progress.
@@ -1482,14 +1481,13 @@ void CompilerInstance::createModuleManager() {
                                                  "Reading modules",
                                                  *FrontendTimerGroup);
     ModuleManager = new ASTReader(
-        getPreprocessor(), &getASTContext(), getPCHContainerReader(),
-        getFrontendOpts().ModuleFileExtensions,
+        getPreprocessor(), getModuleCache(), &getASTContext(),
+        getPCHContainerReader(), getFrontendOpts().ModuleFileExtensions,
         Sysroot.empty() ? "" : Sysroot.c_str(), PPOpts.DisablePCHValidation,
         /*AllowASTWithCompilerErrors=*/false,
         /*AllowConfigurationMismatch=*/false,
         HSOpts.ModulesValidateSystemHeaders,
-        getFrontendOpts().UseGlobalModuleIndex,
-        std::move(ReadTimer));
+        getFrontendOpts().UseGlobalModuleIndex, std::move(ReadTimer));
     if (hasASTConsumer()) {
       ModuleManager->setDeserializationListener(
         getASTConsumer().GetASTDeserializationListener());
diff --git a/clang/lib/Frontend/FrontendActions.cpp b/clang/lib/Frontend/FrontendActions.cpp
index a71d74ec796..5ad9a1cc036 100644
--- a/clang/lib/Frontend/FrontendActions.cpp
+++ b/clang/lib/Frontend/FrontendActions.cpp
@@ -109,10 +109,10 @@ GeneratePCHAction::CreateASTConsumer(CompilerInstance &CI, StringRef InFile) {
   auto Buffer = std::make_shared<PCHBuffer>();
   std::vector<std::unique_ptr<ASTConsumer>> Consumers;
   Consumers.push_back(llvm::make_unique<PCHGenerator>(
-                        CI.getPreprocessor(), OutputFile, Sysroot,
-                        Buffer, FrontendOpts.ModuleFileExtensions,
-                        CI.getPreprocessorOpts().AllowPCHWithCompilerErrors,
-                        FrontendOpts.IncludeTimestamps));
+      CI.getPreprocessor(), CI.getModuleCache(), OutputFile, Sysroot, Buffer,
+      FrontendOpts.ModuleFileExtensions,
+      CI.getPreprocessorOpts().AllowPCHWithCompilerErrors,
+      FrontendOpts.IncludeTimestamps));
   Consumers.push_back(CI.getPCHContainerWriter().CreatePCHContainerGenerator(
       CI, InFile, OutputFile, std::move(OS), Buffer));
 
@@ -172,11 +172,11 @@ GenerateModuleAction::CreateASTConsumer(CompilerInstance &CI,
   std::vector<std::unique_ptr<ASTConsumer>> Consumers;
 
   Consumers.push_back(llvm::make_unique<PCHGenerator>(
-                        CI.getPreprocessor(), OutputFile, Sysroot,
-                        Buffer, CI.getFrontendOpts().ModuleFileExtensions,
-                        /*AllowASTWithErrors=*/false,
-                        /*IncludeTimestamps=*/
-                          +CI.getFrontendOpts().BuildingImplicitModule));
+      CI.getPreprocessor(), CI.getModuleCache(), OutputFile, Sysroot, Buffer,
+      CI.getFrontendOpts().ModuleFileExtensions,
+      /*AllowASTWithErrors=*/false,
+      /*IncludeTimestamps=*/
+      +CI.getFrontendOpts().BuildingImplicitModule));
   Consumers.push_back(CI.getPCHContainerWriter().CreatePCHContainerGenerator(
       CI, InFile, OutputFile, std::move(OS), Buffer));
   return llvm::make_unique<MultiplexConsumer>(std::move(Consumers));
@@ -329,8 +329,8 @@ void VerifyPCHAction::ExecuteAction() {
   bool Preamble = CI.getPreprocessorOpts().PrecompiledPreambleBytes.first != 0;
   const std::string &Sysroot = CI.getHeaderSearchOpts().Sysroot;
   std::unique_ptr<ASTReader> Reader(new ASTReader(
-      CI.getPreprocessor(), &CI.getASTContext(), CI.getPCHContainerReader(),
-      CI.getFrontendOpts().ModuleFileExtensions,
+      CI.getPreprocessor(), CI.getModuleCache(), &CI.getASTContext(),
+      CI.getPCHContainerReader(), CI.getFrontendOpts().ModuleFileExtensions,
       Sysroot.empty() ? "" : Sysroot.c_str(),
       /*DisableValidation*/ false,
       /*AllowPCHWithCompilerErrors*/ false,
diff --git a/clang/lib/Frontend/PrecompiledPreamble.cpp b/clang/lib/Frontend/PrecompiledPreamble.cpp
index 5d6cc840a8e..d6418645856 100644
--- a/clang/lib/Frontend/PrecompiledPreamble.cpp
+++ b/clang/lib/Frontend/PrecompiledPreamble.cpp
@@ -157,9 +157,12 @@ private:
 class PrecompilePreambleConsumer : public PCHGenerator {
 public:
   PrecompilePreambleConsumer(PrecompilePreambleAction &Action,
-                             const Preprocessor &PP, StringRef isysroot,
+                             const Preprocessor &PP,
+                             InMemoryModuleCache &ModuleCache,
+                             StringRef isysroot,
                              std::unique_ptr<raw_ostream> Out)
-      : PCHGenerator(PP, "", isysroot, std::make_shared<PCHBuffer>(),
+      : PCHGenerator(PP, ModuleCache, "", isysroot,
+                     std::make_shared<PCHBuffer>(),
                      ArrayRef<std::shared_ptr<ModuleFileExtension>>(),
                      /*AllowASTWithErrors=*/true),
         Action(Action), Out(std::move(Out)) {}
@@ -211,7 +214,7 @@ PrecompilePreambleAction::CreateASTConsumer(CompilerInstance &CI,
     Sysroot.clear();
 
   return llvm::make_unique<PrecompilePreambleConsumer>(
-      *this, CI.getPreprocessor(), Sysroot, std::move(OS));
+      *this, CI.getPreprocessor(), CI.getModuleCache(), Sysroot, std::move(OS));
 }
 
 template <class T> bool moveOnNoError(llvm::ErrorOr<T> Val, T &Output) {
diff --git a/clang/lib/Frontend/Rewrite/FrontendActions.cpp b/clang/lib/Frontend/Rewrite/FrontendActions.cpp
index 62ce9c26ce6..aaef44b79dc 100644
--- a/clang/lib/Frontend/Rewrite/FrontendActions.cpp
+++ b/clang/lib/Frontend/Rewrite/FrontendActions.cpp
@@ -237,7 +237,7 @@ public:
 
     // Rewrite the contents of the module in a separate compiler instance.
     CompilerInstance Instance(CI.getPCHContainerOperations(),
-                              &CI.getPreprocessor().getPCMCache());
+                              &CI.getModuleCache());
     Instance.setInvocation(
         std::make_shared<CompilerInvocation>(CI.getInvocation()));
     Instance.createDiagnostics(
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 0179668f131..7b4983dcfe4 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -77,12 +77,12 @@ ExternalPreprocessorSource::~ExternalPreprocessorSource() = default;
 
 Preprocessor::Preprocessor(std::shared_ptr<PreprocessorOptions> PPOpts,
                            DiagnosticsEngine &diags, LangOptions &opts,
-                           SourceManager &SM, MemoryBufferCache &PCMCache,
-                           HeaderSearch &Headers, ModuleLoader &TheModuleLoader,
+                           SourceManager &SM, HeaderSearch &Headers,
+                           ModuleLoader &TheModuleLoader,
                            IdentifierInfoLookup *IILookup, bool OwnsHeaders,
                            TranslationUnitKind TUKind)
     : PPOpts(std::move(PPOpts)), Diags(&diags), LangOpts(opts),
-      FileMgr(Headers.getFileMgr()), SourceMgr(SM), PCMCache(PCMCache),
+      FileMgr(Headers.getFileMgr()), SourceMgr(SM),
       ScratchBuf(new ScratchBuffer(SourceMgr)), HeaderInfo(Headers),
       TheModuleLoader(TheModuleLoader), ExternalSource(nullptr),
       // As the language options may have not been loaded yet (when
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 39df352cb77..b8b390afc42 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -46,7 +46,6 @@
 #include "clang/Basic/IdentifierTable.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/LangOptions.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/ObjCRuntime.h"
 #include "clang/Basic/OperatorKinds.h"
@@ -76,6 +75,7 @@
 #include "clang/Serialization/ASTDeserializationListener.h"
 #include "clang/Serialization/ContinuousRangeMap.h"
 #include "clang/Serialization/GlobalModuleIndex.h"
+#include "clang/Serialization/InMemoryModuleCache.h"
 #include "clang/Serialization/Module.h"
 #include "clang/Serialization/ModuleFileExtension.h"
 #include "clang/Serialization/ModuleManager.h"
@@ -4291,7 +4291,7 @@ ASTReader::readUnhashedControlBlock(ModuleFile &F, bool WasImportedBy,
   }
 
   if (Result == OutOfDate && F.Kind == MK_ImplicitModule) {
-    // If this module has already been finalized in the PCMCache, we're stuck
+    // If this module has already been finalized in the ModuleCache, we're stuck
     // with it; we can only load a single version of each module.
     //
     // This can happen when a module is imported in two contexts: in one, as a
@@ -4309,7 +4309,7 @@ ASTReader::readUnhashedControlBlock(ModuleFile &F, bool WasImportedBy,
     // validation will fail during the as-system import since the PCM on disk
     // doesn't guarantee that -Werror was respected.  However, the -Werror
     // flags were checked during the initial as-user import.
-    if (PCMCache.isBufferFinal(F.FileName)) {
+    if (getModuleManager().getModuleCache().isBufferFinal(F.FileName)) {
       Diag(diag::warn_module_system_bit_conflict) << F.FileName;
       return Success;
     }
@@ -11606,7 +11606,8 @@ void ASTReader::pushExternalDeclIntoScope(NamedDecl *D, DeclarationName Name) {
   }
 }
 
-ASTReader::ASTReader(Preprocessor &PP, ASTContext *Context,
+ASTReader::ASTReader(Preprocessor &PP, InMemoryModuleCache &ModuleCache,
+                     ASTContext *Context,
                      const PCHContainerReader &PCHContainerRdr,
                      ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
                      StringRef isysroot, bool DisableValidation,
@@ -11619,11 +11620,9 @@ ASTReader::ASTReader(Preprocessor &PP, ASTContext *Context,
                    : cast<ASTReaderListener>(new PCHValidator(PP, *this))),
       SourceMgr(PP.getSourceManager()), FileMgr(PP.getFileManager()),
       PCHContainerRdr(PCHContainerRdr), Diags(PP.getDiagnostics()), PP(PP),
-      ContextObj(Context),
-      ModuleMgr(PP.getFileManager(), PP.getPCMCache(), PCHContainerRdr,
-                PP.getHeaderSearchInfo()),
-      PCMCache(PP.getPCMCache()), DummyIdResolver(PP),
-      ReadTimer(std::move(ReadTimer)), isysroot(isysroot),
+      ContextObj(Context), ModuleMgr(PP.getFileManager(), ModuleCache,
+                                     PCHContainerRdr, PP.getHeaderSearchInfo()),
+      DummyIdResolver(PP), ReadTimer(std::move(ReadTimer)), isysroot(isysroot),
       DisableValidation(DisableValidation),
       AllowASTWithCompilerErrors(AllowASTWithCompilerErrors),
       AllowConfigurationMismatch(AllowConfigurationMismatch),
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 06c477e9487..a385eec2727 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -41,7 +41,6 @@
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/Lambda.h"
 #include "clang/Basic/LangOptions.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/ObjCRuntime.h"
 #include "clang/Basic/OpenCLOptions.h"
@@ -65,6 +64,7 @@
 #include "clang/Sema/Sema.h"
 #include "clang/Sema/Weak.h"
 #include "clang/Serialization/ASTReader.h"
+#include "clang/Serialization/InMemoryModuleCache.h"
 #include "clang/Serialization/Module.h"
 #include "clang/Serialization/ModuleFileExtension.h"
 #include "clang/Serialization/SerializationDiagnostic.h"
@@ -4568,10 +4568,11 @@ void ASTWriter::SetSelectorOffset(Selector Sel, uint32_t Offset) {
 }
 
 ASTWriter::ASTWriter(llvm::BitstreamWriter &Stream,
-                     SmallVectorImpl<char> &Buffer, MemoryBufferCache &PCMCache,
+                     SmallVectorImpl<char> &Buffer,
+                     InMemoryModuleCache &ModuleCache,
                      ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
                      bool IncludeTimestamps)
-    : Stream(Stream), Buffer(Buffer), PCMCache(PCMCache),
+    : Stream(Stream), Buffer(Buffer), ModuleCache(ModuleCache),
       IncludeTimestamps(IncludeTimestamps) {
   for (const auto &Ext : Extensions) {
     if (auto Writer = Ext->createExtensionWriter(*this))
@@ -4621,9 +4622,9 @@ ASTFileSignature ASTWriter::WriteAST(Sema &SemaRef,
   WritingAST = false;
   if (SemaRef.Context.getLangOpts().ImplicitModules && WritingModule) {
     // Construct MemoryBuffer and update buffer manager.
-    PCMCache.addBuffer(OutputFile,
-                       llvm::MemoryBuffer::getMemBufferCopy(
-                           StringRef(Buffer.begin(), Buffer.size())));
+    ModuleCache.addBuffer(OutputFile,
+                          llvm::MemoryBuffer::getMemBufferCopy(
+                              StringRef(Buffer.begin(), Buffer.size())));
   }
   return Signature;
 }
diff --git a/clang/lib/Serialization/CMakeLists.txt b/clang/lib/Serialization/CMakeLists.txt
index a312cb91eb0..3d24c571f31 100644
--- a/clang/lib/Serialization/CMakeLists.txt
+++ b/clang/lib/Serialization/CMakeLists.txt
@@ -14,6 +14,7 @@ add_clang_library(clangSerialization
   ASTWriterStmt.cpp
   GeneratePCH.cpp
   GlobalModuleIndex.cpp
+  InMemoryModuleCache.cpp
   Module.cpp
   ModuleFileExtension.cpp
   ModuleManager.cpp
diff --git a/clang/lib/Serialization/GeneratePCH.cpp b/clang/lib/Serialization/GeneratePCH.cpp
index 4860b54f83a..7c2ef5a13a1 100644
--- a/clang/lib/Serialization/GeneratePCH.cpp
+++ b/clang/lib/Serialization/GeneratePCH.cpp
@@ -21,13 +21,13 @@
 using namespace clang;
 
 PCHGenerator::PCHGenerator(
-    const Preprocessor &PP, StringRef OutputFile, StringRef isysroot,
-    std::shared_ptr<PCHBuffer> Buffer,
+    const Preprocessor &PP, InMemoryModuleCache &ModuleCache,
+    StringRef OutputFile, StringRef isysroot, std::shared_ptr<PCHBuffer> Buffer,
     ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
     bool AllowASTWithErrors, bool IncludeTimestamps)
     : PP(PP), OutputFile(OutputFile), isysroot(isysroot.str()),
       SemaPtr(nullptr), Buffer(std::move(Buffer)), Stream(this->Buffer->Data),
-      Writer(Stream, this->Buffer->Data, PP.getPCMCache(), Extensions,
+      Writer(Stream, this->Buffer->Data, ModuleCache, Extensions,
              IncludeTimestamps),
       AllowASTWithErrors(AllowASTWithErrors) {
   this->Buffer->IsComplete = false;
diff --git a/clang/lib/Serialization/InMemoryModuleCache.cpp b/clang/lib/Serialization/InMemoryModuleCache.cpp
new file mode 100644
index 00000000000..130ece01504
--- /dev/null
+++ b/clang/lib/Serialization/InMemoryModuleCache.cpp
@@ -0,0 +1,49 @@
+//===- InMemoryModuleCache.cpp - Cache for loaded memory buffers ----------===//
+//
+// 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 "clang/Serialization/InMemoryModuleCache.h"
+#include "llvm/Support/MemoryBuffer.h"
+
+using namespace clang;
+
+llvm::MemoryBuffer &
+InMemoryModuleCache::addBuffer(llvm::StringRef Filename,
+                               std::unique_ptr<llvm::MemoryBuffer> Buffer) {
+  auto Insertion = PCMs.insert({Filename, PCM{std::move(Buffer), NextIndex++}});
+  assert(Insertion.second && "Already has a buffer");
+  return *Insertion.first->second.Buffer;
+}
+
+llvm::MemoryBuffer *
+InMemoryModuleCache::lookupBuffer(llvm::StringRef Filename) {
+  auto I = PCMs.find(Filename);
+  if (I == PCMs.end())
+    return nullptr;
+  return I->second.Buffer.get();
+}
+
+bool InMemoryModuleCache::isBufferFinal(llvm::StringRef Filename) {
+  auto I = PCMs.find(Filename);
+  if (I == PCMs.end())
+    return false;
+  return I->second.Index < FirstRemovableIndex;
+}
+
+bool InMemoryModuleCache::tryToRemoveBuffer(llvm::StringRef Filename) {
+  auto I = PCMs.find(Filename);
+  assert(I != PCMs.end() && "No buffer to remove...");
+  if (I->second.Index < FirstRemovableIndex)
+    return true;
+
+  PCMs.erase(I);
+  return false;
+}
+
+void InMemoryModuleCache::finalizeCurrentBuffers() {
+  FirstRemovableIndex = NextIndex;
+}
diff --git a/clang/lib/Serialization/ModuleManager.cpp b/clang/lib/Serialization/ModuleManager.cpp
index 72b557f45b9..173fadcb76d 100644
--- a/clang/lib/Serialization/ModuleManager.cpp
+++ b/clang/lib/Serialization/ModuleManager.cpp
@@ -14,10 +14,10 @@
 #include "clang/Serialization/ModuleManager.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/LLVM.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/ModuleMap.h"
 #include "clang/Serialization/GlobalModuleIndex.h"
+#include "clang/Serialization/InMemoryModuleCache.h"
 #include "clang/Serialization/Module.h"
 #include "clang/Serialization/PCHContainerOperations.h"
 #include "llvm/ADT/STLExtras.h"
@@ -159,12 +159,13 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
   // Load the contents of the module
   if (std::unique_ptr<llvm::MemoryBuffer> Buffer = lookupBuffer(FileName)) {
     // The buffer was already provided for us.
-    NewModule->Buffer = &PCMCache->addBuffer(FileName, std::move(Buffer));
+    NewModule->Buffer = &ModuleCache->addBuffer(FileName, std::move(Buffer));
     // Since the cached buffer is reused, it is safe to close the file
     // descriptor that was opened while stat()ing the PCM in
     // lookupModuleFile() above, it won't be needed any longer.
     Entry->closeFile();
-  } else if (llvm::MemoryBuffer *Buffer = PCMCache->lookupBuffer(FileName)) {
+  } else if (llvm::MemoryBuffer *Buffer =
+                 getModuleCache().lookupBuffer(FileName)) {
     NewModule->Buffer = Buffer;
     // As above, the file descriptor is no longer needed.
     Entry->closeFile();
@@ -185,7 +186,7 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
       return Missing;
     }
 
-    NewModule->Buffer = &PCMCache->addBuffer(FileName, std::move(*Buf));
+    NewModule->Buffer = &getModuleCache().addBuffer(FileName, std::move(*Buf));
   }
 
   // Initialize the stream.
@@ -197,7 +198,7 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
                                           ExpectedSignature, ErrorStr)) {
     // Try to remove the buffer.  If it can't be removed, then it was already
     // validated by this process.
-    if (!PCMCache->tryToRemoveBuffer(NewModule->FileName))
+    if (!getModuleCache().tryToRemoveBuffer(NewModule->FileName))
       FileMgr.invalidateCache(NewModule->File);
     return OutOfDate;
   }
@@ -267,11 +268,11 @@ void ModuleManager::removeModules(
     // rebuilt (or there was an error). Invalidate them so that we can load the
     // new files that will be renamed over the old ones.
     //
-    // The PCMCache tracks whether the module was successfully loaded in another
-    // thread/context; in that case, it won't need to be rebuilt (and we can't
-    // safely invalidate it anyway).
+    // The ModuleCache tracks whether the module was successfully loaded in
+    // another thread/context; in that case, it won't need to be rebuilt (and
+    // we can't safely invalidate it anyway).
     if (LoadedSuccessfully.count(&*victim) == 0 &&
-        !PCMCache->tryToRemoveBuffer(victim->FileName))
+        !getModuleCache().tryToRemoveBuffer(victim->FileName))
       FileMgr.invalidateCache(victim->File);
   }
 
@@ -327,11 +328,12 @@ void ModuleManager::moduleFileAccepted(ModuleFile *MF) {
   ModulesInCommonWithGlobalIndex.push_back(MF);
 }
 
-ModuleManager::ModuleManager(FileManager &FileMgr, MemoryBufferCache &PCMCache,
+ModuleManager::ModuleManager(FileManager &FileMgr,
+                             InMemoryModuleCache &ModuleCache,
                              const PCHContainerReader &PCHContainerRdr,
-                             const HeaderSearch& HeaderSearchInfo)
-    : FileMgr(FileMgr), PCMCache(&PCMCache), PCHContainerRdr(PCHContainerRdr),
-      HeaderSearchInfo(HeaderSearchInfo) {}
+                             const HeaderSearch &HeaderSearchInfo)
+    : FileMgr(FileMgr), ModuleCache(&ModuleCache),
+      PCHContainerRdr(PCHContainerRdr), HeaderSearchInfo(HeaderSearchInfo) {}
 
 ModuleManager::~ModuleManager() { delete FirstVisitState; }
 
diff --git a/clang/test/Modules/outofdate-rebuild.m b/clang/test/Modules/outofdate-rebuild.m
index 510325f62dc..b18c94c54bd 100644
--- a/clang/test/Modules/outofdate-rebuild.m
+++ b/clang/test/Modules/outofdate-rebuild.m
@@ -11,5 +11,5 @@
 // RUN:   -fsyntax-only
 
 // This testcase reproduces a use-after-free in when ModuleManager removes an
-// entry from the PCMCache without notifying its parent ASTReader.
+// entry from the ModuleCache without notifying its parent ASTReader.
 @import Cocoa;
diff --git a/clang/unittests/Basic/CMakeLists.txt b/clang/unittests/Basic/CMakeLists.txt
index 537f3ba5fcc..d883c362e28 100644
--- a/clang/unittests/Basic/CMakeLists.txt
+++ b/clang/unittests/Basic/CMakeLists.txt
@@ -7,7 +7,6 @@ add_clang_unittest(BasicTests
   DiagnosticTest.cpp
   FileManagerTest.cpp
   FixedPointTest.cpp
-  MemoryBufferCacheTest.cpp
   SourceManagerTest.cpp
   )
 
diff --git a/clang/unittests/Basic/SourceManagerTest.cpp b/clang/unittests/Basic/SourceManagerTest.cpp
index 61451aed127..ff8a3647365 100644
--- a/clang/unittests/Basic/SourceManagerTest.cpp
+++ b/clang/unittests/Basic/SourceManagerTest.cpp
@@ -11,7 +11,6 @@
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/LangOptions.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/TargetOptions.h"
 #include "clang/Lex/HeaderSearch.h"
@@ -60,11 +59,10 @@ TEST_F(SourceManagerTest, isBeforeInTranslationUnit) {
   SourceMgr.setMainFileID(mainFileID);
 
   TrivialModuleLoader ModLoader;
-  MemoryBufferCache PCMCache;
   HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
                           Diags, LangOpts, &*Target);
   Preprocessor PP(std::make_shared<PreprocessorOptions>(), Diags, LangOpts,
-                  SourceMgr, PCMCache, HeaderInfo, ModLoader,
+                  SourceMgr, HeaderInfo, ModLoader,
                   /*IILookup =*/nullptr,
                   /*OwnsHeaderSearch =*/false);
   PP.Initialize(*Target);
@@ -229,11 +227,10 @@ TEST_F(SourceManagerTest, getMacroArgExpandedLocation) {
   SourceMgr.overrideFileContents(headerFile, std::move(HeaderBuf));
 
   TrivialModuleLoader ModLoader;
-  MemoryBufferCache PCMCache;
   HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
                           Diags, LangOpts, &*Target);
   Preprocessor PP(std::make_shared<PreprocessorOptions>(), Diags, LangOpts,
-                  SourceMgr, PCMCache, HeaderInfo, ModLoader,
+                  SourceMgr, HeaderInfo, ModLoader,
                   /*IILookup =*/nullptr,
                   /*OwnsHeaderSearch =*/false);
   PP.Initialize(*Target);
@@ -348,11 +345,10 @@ TEST_F(SourceManagerTest, isBeforeInTranslationUnitWithMacroInInclude) {
   SourceMgr.overrideFileContents(headerFile, std::move(HeaderBuf));
 
   TrivialModuleLoader ModLoader;
-  MemoryBufferCache PCMCache;
   HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
                           Diags, LangOpts, &*Target);
   Preprocessor PP(std::make_shared<PreprocessorOptions>(), Diags, LangOpts,
-                  SourceMgr, PCMCache, HeaderInfo, ModLoader,
+                  SourceMgr, HeaderInfo, ModLoader,
                   /*IILookup =*/nullptr,
                   /*OwnsHeaderSearch =*/false);
   PP.Initialize(*Target);
diff --git a/clang/unittests/CMakeLists.txt b/clang/unittests/CMakeLists.txt
index 6eff59986cb..4c8a3a840d5 100644
--- a/clang/unittests/CMakeLists.txt
+++ b/clang/unittests/CMakeLists.txt
@@ -32,3 +32,4 @@ if(NOT WIN32 AND CLANG_TOOL_LIBCLANG_BUILD)
 endif()
 add_subdirectory(Rename)
 add_subdirectory(Index)
+add_subdirectory(Serialization)
diff --git a/clang/unittests/Lex/HeaderSearchTest.cpp b/clang/unittests/Lex/HeaderSearchTest.cpp
index 42d12d76fa0..6365d3ed057 100644
--- a/clang/unittests/Lex/HeaderSearchTest.cpp
+++ b/clang/unittests/Lex/HeaderSearchTest.cpp
@@ -11,12 +11,12 @@
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/LangOptions.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/TargetOptions.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/HeaderSearchOptions.h"
+#include "clang/Serialization/InMemoryModuleCache.h"
 #include "gtest/gtest.h"
 
 namespace clang {
diff --git a/clang/unittests/Lex/LexerTest.cpp b/clang/unittests/Lex/LexerTest.cpp
index c12f0805dc5..320b60ea639 100644
--- a/clang/unittests/Lex/LexerTest.cpp
+++ b/clang/unittests/Lex/LexerTest.cpp
@@ -11,7 +11,6 @@
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/LangOptions.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/TargetOptions.h"
@@ -48,12 +47,11 @@ protected:
         llvm::MemoryBuffer::getMemBuffer(Source);
     SourceMgr.setMainFileID(SourceMgr.createFileID(std::move(Buf)));
 
-    MemoryBufferCache PCMCache;
     HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
                             Diags, LangOpts, Target.get());
     std::unique_ptr<Preprocessor> PP = llvm::make_unique<Preprocessor>(
         std::make_shared<PreprocessorOptions>(), Diags, LangOpts, SourceMgr,
-        PCMCache, HeaderInfo, ModLoader,
+        HeaderInfo, ModLoader,
         /*IILookup =*/nullptr,
         /*OwnsHeaderSearch =*/false);
     PP->Initialize(*Target);
diff --git a/clang/unittests/Lex/PPCallbacksTest.cpp b/clang/unittests/Lex/PPCallbacksTest.cpp
index 44edcb71fe8..91765960c3d 100644
--- a/clang/unittests/Lex/PPCallbacksTest.cpp
+++ b/clang/unittests/Lex/PPCallbacksTest.cpp
@@ -13,7 +13,6 @@
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/LangOptions.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/TargetOptions.h"
@@ -178,14 +177,13 @@ protected:
     SourceMgr.setMainFileID(SourceMgr.createFileID(std::move(Buf)));
 
     TrivialModuleLoader ModLoader;
-    MemoryBufferCache PCMCache;
 
     HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
                             Diags, LangOpts, Target.get());
     AddFakeHeader(HeaderInfo, HeaderPath, SystemHeader);
 
     Preprocessor PP(std::make_shared<PreprocessorOptions>(), Diags, LangOpts,
-                    SourceMgr, PCMCache, HeaderInfo, ModLoader,
+                    SourceMgr, HeaderInfo, ModLoader,
                     /*IILookup =*/nullptr,
                     /*OwnsHeaderSearch =*/false);
     return InclusionDirectiveCallback(PP)->FilenameRange;
@@ -198,14 +196,13 @@ protected:
     SourceMgr.setMainFileID(SourceMgr.createFileID(std::move(Buf)));
 
     TrivialModuleLoader ModLoader;
-    MemoryBufferCache PCMCache;
 
     HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
                             Diags, LangOpts, Target.get());
     AddFakeHeader(HeaderInfo, HeaderPath, SystemHeader);
 
     Preprocessor PP(std::make_shared<PreprocessorOptions>(), Diags, LangOpts,
-                    SourceMgr, PCMCache, HeaderInfo, ModLoader,
+                    SourceMgr, HeaderInfo, ModLoader,
                     /*IILookup =*/nullptr,
                     /*OwnsHeaderSearch =*/false);
     return InclusionDirectiveCallback(PP)->FileType;
@@ -233,14 +230,13 @@ protected:
   std::vector<CondDirectiveCallbacks::Result>
   DirectiveExprRange(StringRef SourceText) {
     TrivialModuleLoader ModLoader;
-    MemoryBufferCache PCMCache;
     std::unique_ptr<llvm::MemoryBuffer> Buf =
         llvm::MemoryBuffer::getMemBuffer(SourceText);
     SourceMgr.setMainFileID(SourceMgr.createFileID(std::move(Buf)));
     HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
                             Diags, LangOpts, Target.get());
     Preprocessor PP(std::make_shared<PreprocessorOptions>(), Diags, LangOpts,
-                    SourceMgr, PCMCache, HeaderInfo, ModLoader,
+                    SourceMgr, HeaderInfo, ModLoader,
                     /*IILookup =*/nullptr,
                     /*OwnsHeaderSearch =*/false);
     PP.Initialize(*Target);
@@ -270,12 +266,11 @@ protected:
     SourceMgr.setMainFileID(SourceMgr.createFileID(std::move(SourceBuf)));
 
     TrivialModuleLoader ModLoader;
-    MemoryBufferCache PCMCache;
     HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
                             Diags, OpenCLLangOpts, Target.get());
 
     Preprocessor PP(std::make_shared<PreprocessorOptions>(), Diags,
-                    OpenCLLangOpts, SourceMgr, PCMCache, HeaderInfo, ModLoader,
+                    OpenCLLangOpts, SourceMgr, HeaderInfo, ModLoader,
                     /*IILookup =*/nullptr,
                     /*OwnsHeaderSearch =*/false);
     PP.Initialize(*Target);
diff --git a/clang/unittests/Lex/PPConditionalDirectiveRecordTest.cpp b/clang/unittests/Lex/PPConditionalDirectiveRecordTest.cpp
index 54a131e16ff..ba756395786 100644
--- a/clang/unittests/Lex/PPConditionalDirectiveRecordTest.cpp
+++ b/clang/unittests/Lex/PPConditionalDirectiveRecordTest.cpp
@@ -11,7 +11,6 @@
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/LangOptions.h"
-#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/TargetOptions.h"
@@ -75,11 +74,10 @@ TEST_F(PPConditionalDirectiveRecordTest, PPRecAPI) {
   SourceMgr.setMainFileID(SourceMgr.createFileID(std::move(Buf)));
 
   TrivialModuleLoader ModLoader;
-  MemoryBufferCache PCMCache;
   HeaderSearch HeaderInfo(std::make_shared<HeaderSearchOptions>(), SourceMgr,
                           Diags, LangOpts, Target.get());
   Preprocessor PP(std::make_shared<PreprocessorOptions>(), Diags, LangOpts,
-                  SourceMgr, PCMCache, HeaderInfo, ModLoader,
+                  SourceMgr, HeaderInfo, ModLoader,
                   /*IILookup =*/nullptr,
                   /*OwnsHeaderSearch =*/false);
   PP.Initialize(*Target);
diff --git a/clang/unittests/Serialization/CMakeLists.txt b/clang/unittests/Serialization/CMakeLists.txt
new file mode 100644
index 00000000000..c7ec9a4f070
--- /dev/null
+++ b/clang/unittests/Serialization/CMakeLists.txt
@@ -0,0 +1,17 @@
+set(LLVM_LINK_COMPONENTS
+  BitReader
+  Support
+  )
+
+add_clang_unittest(SerializationTests
+  InMemoryModuleCacheTest.cpp
+  )
+
+target_link_libraries(SerializationTests
+  PRIVATE
+  clangAST
+  clangBasic
+  clangLex
+  clangSema
+  clangSerialization
+  )
diff --git a/clang/unittests/Basic/MemoryBufferCacheTest.cpp b/clang/unittests/Serialization/InMemoryModuleCacheTest.cpp
index 02e3fe25a17..356c9ed56f5 100644
--- a/clang/unittests/Basic/MemoryBufferCacheTest.cpp
+++ b/clang/unittests/Serialization/InMemoryModuleCacheTest.cpp
@@ -1,4 +1,4 @@
-//===- MemoryBufferCacheTest.cpp - MemoryBufferCache tests ----------------===//
+//===- InMemoryModuleCacheTest.cpp - InMemoryModuleCache tests ------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "clang/Basic/MemoryBufferCache.h"
+#include "clang/Serialization/InMemoryModuleCache.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "gtest/gtest.h"
 
@@ -22,7 +22,7 @@ std::unique_ptr<MemoryBuffer> getBuffer(int I) {
                                     /* RequiresNullTerminator = */ false);
 }
 
-TEST(MemoryBufferCacheTest, addBuffer) {
+TEST(InMemoryModuleCacheTest, addBuffer) {
   auto B1 = getBuffer(1);
   auto B2 = getBuffer(2);
   auto B3 = getBuffer(3);
@@ -31,7 +31,7 @@ TEST(MemoryBufferCacheTest, addBuffer) {
   auto *RawB3 = B3.get();
 
   // Add a few buffers.
-  MemoryBufferCache Cache;
+  InMemoryModuleCache Cache;
   EXPECT_EQ(RawB1, &Cache.addBuffer("1", std::move(B1)));
   EXPECT_EQ(RawB2, &Cache.addBuffer("2", std::move(B2)));
   EXPECT_EQ(RawB3, &Cache.addBuffer("3", std::move(B3)));
@@ -58,9 +58,9 @@ TEST(MemoryBufferCacheTest, addBuffer) {
   EXPECT_FALSE(Cache.isBufferFinal("3"));
 }
 
-TEST(MemoryBufferCacheTest, finalizeCurrentBuffers) {
+TEST(InMemoryModuleCacheTest, finalizeCurrentBuffers) {
   // Add a buffer.
-  MemoryBufferCache Cache;
+  InMemoryModuleCache Cache;
   auto B1 = getBuffer(1);
   auto *RawB1 = B1.get();
   Cache.addBuffer("1", std::move(B1));