[clang] Use InMemoryModuleCache for readASTFileControlBlock NFC

When a pcm has already been loaded from disk, reuse it from the
InMemoryModuleCache in readASTFileControlBlock. This avoids potentially
reading it again.

As noted in the FIXME, ideally we would also add the module to the cache
if it will be used again later, but that could modify its build state
and we do not have enough context currenlty to know if it's correct.

Differential Revision: https://reviews.llvm.org/D138160

clang/include/clang/Serialization/ASTReader.h

@@ -1731,8 +1731,8 @@ public:
   /// Read the control block for the named AST file.
   ///
   /// \returns true if an error occurred, false otherwise.
-  static bool
+  static bool readASTFileControlBlock(StringRef Filename, FileManager &FileMgr,
-  readASTFileControlBlock(StringRef Filename, FileManager &FileMgr,
+                                      const InMemoryModuleCache &ModuleCache,
                                       const PCHContainerReader &PCHContainerRdr,
                                       bool FindModuleFileExtensions,
                                       ASTReaderListener &Listener,
@@ -1741,6 +1741,7 @@ public:
   /// Determine whether the given AST file is acceptable to load into a
   /// translation unit with the given language and target options.
   static bool isAcceptableASTFile(StringRef Filename, FileManager &FileMgr,
+                                  const InMemoryModuleCache &ModuleCache,
                                   const PCHContainerReader &PCHContainerRdr,
                                   const LangOptions &LangOpts,
                                   const TargetOptions &TargetOpts,

clang/lib/Frontend/CompilerInstance.cpp

@@ -252,7 +252,8 @@ static void collectIncludePCH(CompilerInstance &CI,
     // used here since we're not interested in validating the PCH at this time,
     // but only to check whether this is a file containing an AST.
     if (!ASTReader::readASTFileControlBlock(
-            Dir->path(), FileMgr, CI.getPCHContainerReader(),
+            Dir->path(), FileMgr, CI.getModuleCache(),
+            CI.getPCHContainerReader(),
             /*FindModuleFileExtensions=*/false, Validator,
             /*ValidateDiagnosticOptions=*/false))
       MDC->addFile(Dir->path());

clang/lib/Frontend/FrontendAction.cpp

@@ -778,8 +778,9 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
            Dir != DirEnd && !EC; Dir.increment(EC)) {
         // Check whether this is an acceptable AST file.
         if (ASTReader::isAcceptableASTFile(
-                Dir->path(), FileMgr, CI.getPCHContainerReader(),
+                Dir->path(), FileMgr, CI.getModuleCache(),
-                CI.getLangOpts(), CI.getTargetOpts(), CI.getPreprocessorOpts(),
+                CI.getPCHContainerReader(), CI.getLangOpts(),
+                CI.getTargetOpts(), CI.getPreprocessorOpts(),
                 SpecificModuleCachePath, /*RequireStrictOptionMatches=*/true)) {
           PPOpts.ImplicitPCHInclude = std::string(Dir->path());
           Found = true;

clang/lib/Frontend/FrontendActions.cpp

@@ -851,7 +851,8 @@ void DumpModuleInfoAction::ExecuteAction() {
   assert(isCurrentFileAST() && "dumping non-AST?");
   // Set up the output file.
   std::unique_ptr<llvm::raw_fd_ostream> OutFile;
-  StringRef OutputFileName = getCompilerInstance().getFrontendOpts().OutputFile;
+  CompilerInstance &CI = getCompilerInstance();
+  StringRef OutputFileName = CI.getFrontendOpts().OutputFile;
   if (!OutputFileName.empty() && OutputFileName != "-") {
     std::error_code EC;
     OutFile.reset(new llvm::raw_fd_ostream(OutputFileName.str(), EC,
@@ -861,14 +862,14 @@ void DumpModuleInfoAction::ExecuteAction() {
   llvm::raw_ostream &Out = OutputStream ? *OutputStream : llvm::outs();
 
   Out << "Information for module file '" << getCurrentFile() << "':\n";
-  auto &FileMgr = getCompilerInstance().getFileManager();
+  auto &FileMgr = CI.getFileManager();
   auto Buffer = FileMgr.getBufferForFile(getCurrentFile());
   StringRef Magic = (*Buffer)->getMemBufferRef().getBuffer();
   bool IsRaw = (Magic.size() >= 4 && Magic[0] == 'C' && Magic[1] == 'P' &&
                 Magic[2] == 'C' && Magic[3] == 'H');
   Out << "  Module format: " << (IsRaw ? "raw" : "obj") << "\n";
 
-  Preprocessor &PP = getCompilerInstance().getPreprocessor();
+  Preprocessor &PP = CI.getPreprocessor();
   DumpModuleInfoListener Listener(Out);
   HeaderSearchOptions &HSOpts = PP.getHeaderSearchInfo().getHeaderSearchOpts();
 
@@ -966,7 +967,8 @@ void DumpModuleInfoAction::ExecuteAction() {
   // The reminder of the output is produced from the listener as the AST
   // FileCcontrolBlock is (re-)parsed.
   ASTReader::readASTFileControlBlock(
-      getCurrentFile(), FileMgr, getCompilerInstance().getPCHContainerReader(),
+      getCurrentFile(), FileMgr, CI.getModuleCache(),
+      CI.getPCHContainerReader(),
       /*FindModuleFileExtensions=*/true, Listener,
       HSOpts.ModulesValidateDiagnosticOptions);
 }

clang/lib/Serialization/ASTReader.cpp

@@ -5169,19 +5169,28 @@ namespace {
 
 bool ASTReader::readASTFileControlBlock(
     StringRef Filename, FileManager &FileMgr,
-    const PCHContainerReader &PCHContainerRdr,
+    const InMemoryModuleCache &ModuleCache,
-    bool FindModuleFileExtensions,
+    const PCHContainerReader &PCHContainerRdr, bool FindModuleFileExtensions,
     ASTReaderListener &Listener, bool ValidateDiagnosticOptions) {
   // Open the AST file.
+  std::unique_ptr<llvm::MemoryBuffer> OwnedBuffer;
+  llvm::MemoryBuffer *Buffer = ModuleCache.lookupPCM(Filename);
+  if (!Buffer) {
+    // FIXME: We should add the pcm to the InMemoryModuleCache if it could be
+    // read again later, but we do not have the context here to determine if it
+    // is safe to change the result of InMemoryModuleCache::getPCMState().
+
     // FIXME: This allows use of the VFS; we do not allow use of the
     // VFS when actually loading a module.
-  auto Buffer = FileMgr.getBufferForFile(Filename);
+    auto BufferOrErr = FileMgr.getBufferForFile(Filename);
-  if (!Buffer) {
+    if (!BufferOrErr)
       return true;
+    OwnedBuffer = std::move(*BufferOrErr);
+    Buffer = OwnedBuffer.get();
   }
 
   // Initialize the stream
-  StringRef Bytes = PCHContainerRdr.ExtractPCH(**Buffer);
+  StringRef Bytes = PCHContainerRdr.ExtractPCH(*Buffer);
   BitstreamCursor Stream(Bytes);
 
   // Sniff for the signature.
@@ -5434,6 +5443,7 @@ bool ASTReader::readASTFileControlBlock(
 }
 
 bool ASTReader::isAcceptableASTFile(StringRef Filename, FileManager &FileMgr,
+                                    const InMemoryModuleCache &ModuleCache,
                                     const PCHContainerReader &PCHContainerRdr,
                                     const LangOptions &LangOpts,
                                     const TargetOptions &TargetOpts,
@@ -5443,9 +5453,9 @@ bool ASTReader::isAcceptableASTFile(StringRef Filename, FileManager &FileMgr,
   SimplePCHValidator validator(LangOpts, TargetOpts, PPOpts,
                                ExistingModuleCachePath, FileMgr,
                                RequireStrictOptionMatches);
-  return !readASTFileControlBlock(Filename, FileMgr, PCHContainerRdr,
+  return !readASTFileControlBlock(Filename, FileMgr, ModuleCache,
-                                  /*FindModuleFileExtensions=*/false,
+                                  PCHContainerRdr,
-                                  validator,
+                                  /*FindModuleFileExtensions=*/false, validator,
                                   /*ValidateDiagnosticOptions=*/true);
 }
 

clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

@@ -103,7 +103,7 @@ static void visitPrebuiltModule(StringRef PrebuiltModuleFilename,
 
   while (!Worklist.empty())
     ASTReader::readASTFileControlBlock(
-        Worklist.pop_back_val(), CI.getFileManager(),
+        Worklist.pop_back_val(), CI.getFileManager(), CI.getModuleCache(),
         CI.getPCHContainerReader(),
         /*FindModuleFileExtensions=*/false, Listener,
         /*ValidateDiagnosticOptions=*/false);