clang/lib/Frontend/PrecompiledPreamble.cpp

   1 //===--- PrecompiledPreamble.cpp - Build precompiled preambles --*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // Helper class to build precompiled preamble.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "clang/Frontend/PrecompiledPreamble.h"
  14 #include "clang/Basic/FileManager.h"
  15 #include "clang/Basic/LangStandard.h"
  16 #include "clang/Frontend/CompilerInstance.h"
  17 #include "clang/Frontend/CompilerInvocation.h"
  18 #include "clang/Frontend/FrontendActions.h"
  19 #include "clang/Frontend/FrontendOptions.h"
  20 #include "clang/Lex/HeaderSearch.h"
  21 #include "clang/Lex/Lexer.h"
  22 #include "clang/Lex/Preprocessor.h"
  23 #include "clang/Lex/PreprocessorOptions.h"
  24 #include "clang/Serialization/ASTWriter.h"
  25 #include "llvm/ADT/SmallString.h"
  26 #include "llvm/ADT/StringSet.h"
  27 #include "llvm/ADT/iterator_range.h"
  28 #include "llvm/Config/llvm-config.h"
  29 #include "llvm/Support/CrashRecoveryContext.h"
  30 #include "llvm/Support/FileSystem.h"
  31 #include "llvm/Support/Path.h"
  32 #include "llvm/Support/Process.h"
  33 #include "llvm/Support/VirtualFileSystem.h"
  34 #include <limits>
  35 #include <mutex>
  36 #include <utility>
  37
  38 using namespace clang;
  39
  40 namespace {
  41
  42 StringRef getInMemoryPreamblePath() {
  43 #if defined(LLVM_ON_UNIX)
  44   return "/__clang_tmp/___clang_inmemory_preamble___";
  45 #elif defined(_WIN32)
  46   return "C:\\__clang_tmp\\___clang_inmemory_preamble___";
  47 #else
  48 #warning "Unknown platform. Defaulting to UNIX-style paths for in-memory PCHs"
  49   return "/__clang_tmp/___clang_inmemory_preamble___";
  50 #endif
  51 }
  52
  53 IntrusiveRefCntPtr<llvm::vfs::FileSystem>
  54 createVFSOverlayForPreamblePCH(StringRef PCHFilename,
  55                                std::unique_ptr<llvm::MemoryBuffer> PCHBuffer,
  56                                IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS) {
  57   // We want only the PCH file from the real filesystem to be available,
  58   // so we create an in-memory VFS with just that and overlay it on top.
  59   IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> PCHFS(
  60       new llvm::vfs::InMemoryFileSystem());
  61   PCHFS->addFile(PCHFilename, 0, std::move(PCHBuffer));
  62   IntrusiveRefCntPtr<llvm::vfs::OverlayFileSystem> Overlay(
  63       new llvm::vfs::OverlayFileSystem(VFS));
  64   Overlay->pushOverlay(PCHFS);
  65   return Overlay;
  66 }
  67
  68 class PreambleDependencyCollector : public DependencyCollector {
  69 public:
  70   // We want to collect all dependencies for correctness. Avoiding the real
  71   // system dependencies (e.g. stl from /usr/lib) would probably be a good idea,
  72   // but there is no way to distinguish between those and the ones that can be
  73   // spuriously added by '-isystem' (e.g. to suppress warnings from those
  74   // headers).
  75   bool needSystemDependencies() override { return true; }
  76 };
  77
  78 // Collects files whose existence would invalidate the preamble.
  79 // Collecting *all* of these would make validating it too slow though, so we
  80 // just find all the candidates for 'file not found' diagnostics.
  81 //
  82 // A caveat that may be significant for generated files: we'll omit files under
  83 // search path entries whose roots don't exist when the preamble is built.
  84 // These are pruned by InitHeaderSearch and so we don't see the search path.
  85 // It would be nice to include them but we don't want to duplicate all the rest
  86 // of the InitHeaderSearch logic to reconstruct them.
  87 class MissingFileCollector : public PPCallbacks {
  88   llvm::StringSet<> &Out;
  89   const HeaderSearch &Search;
  90   const SourceManager &SM;
  91
  92 public:
  93   MissingFileCollector(llvm::StringSet<> &Out, const HeaderSearch &Search,
  94                        const SourceManager &SM)
  95       : Out(Out), Search(Search), SM(SM) {}
  96
  97   void InclusionDirective(SourceLocation HashLoc, const Token &IncludeTok,
  98                           StringRef FileName, bool IsAngled,
  99                           CharSourceRange FilenameRange,
 100                           OptionalFileEntryRef File, StringRef SearchPath,
 101                           StringRef RelativePath, const Module *Imported,
 102                           SrcMgr::CharacteristicKind FileType) override {
 103     // File is std::nullopt if it wasn't found.
 104     // (We have some false negatives if PP recovered e.g. <foo> -> "foo")
 105     if (File)
 106       return;
 107
 108     // If it's a rare absolute include, we know the full path already.
 109     if (llvm::sys::path::is_absolute(FileName)) {
 110       Out.insert(FileName);
 111       return;
 112     }
 113
 114     // Reconstruct the filenames that would satisfy this directive...
 115     llvm::SmallString<256> Buf;
 116     auto NotFoundRelativeTo = [&](const DirectoryEntry *DE) {
 117       Buf = DE->getName();
 118       llvm::sys::path::append(Buf, FileName);
 119       llvm::sys::path::remove_dots(Buf, /*remove_dot_dot=*/true);
 120       Out.insert(Buf);
 121     };
 122     // ...relative to the including file.
 123     if (!IsAngled) {
 124       if (const FileEntry *IncludingFile =
 125               SM.getFileEntryForID(SM.getFileID(IncludeTok.getLocation())))
 126         if (IncludingFile->getDir())
 127           NotFoundRelativeTo(IncludingFile->getDir());
 128     }
 129     // ...relative to the search paths.
 130     for (const auto &Dir : llvm::make_range(
 131              IsAngled ? Search.angled_dir_begin() : Search.search_dir_begin(),
 132              Search.search_dir_end())) {
 133       // No support for frameworks or header maps yet.
 134       if (Dir.isNormalDir())
 135         NotFoundRelativeTo(Dir.getDir());
 136     }
 137   }
 138 };
 139
 140 /// Keeps a track of files to be deleted in destructor.
 141 class TemporaryFiles {
 142 public:
 143   // A static instance to be used by all clients.
 144   static TemporaryFiles &getInstance();
 145
 146 private:
 147   // Disallow constructing the class directly.
 148   TemporaryFiles() = default;
 149   // Disallow copy.
 150   TemporaryFiles(const TemporaryFiles &) = delete;
 151
 152 public:
 153   ~TemporaryFiles();
 154
 155   /// Adds \p File to a set of tracked files.
 156   void addFile(StringRef File);
 157
 158   /// Remove \p File from disk and from the set of tracked files.
 159   void removeFile(StringRef File);
 160
 161 private:
 162   std::mutex Mutex;
 163   llvm::StringSet<> Files;
 164 };
 165
 166 TemporaryFiles &TemporaryFiles::getInstance() {
 167   static TemporaryFiles Instance;
 168   return Instance;
 169 }
 170
 171 TemporaryFiles::~TemporaryFiles() {
 172   std::lock_guard<std::mutex> Guard(Mutex);
 173   for (const auto &File : Files)
 174     llvm::sys::fs::remove(File.getKey());
 175 }
 176
 177 void TemporaryFiles::addFile(StringRef File) {
 178   std::lock_guard<std::mutex> Guard(Mutex);
 179   auto IsInserted = Files.insert(File).second;
 180   (void)IsInserted;
 181   assert(IsInserted && "File has already been added");
 182 }
 183
 184 void TemporaryFiles::removeFile(StringRef File) {
 185   std::lock_guard<std::mutex> Guard(Mutex);
 186   auto WasPresent = Files.erase(File);
 187   (void)WasPresent;
 188   assert(WasPresent && "File was not tracked");
 189   llvm::sys::fs::remove(File);
 190 }
 191
 192 // A temp file that would be deleted on destructor call. If destructor is not
 193 // called for any reason, the file will be deleted at static objects'
 194 // destruction.
 195 // An assertion will fire if two TempPCHFiles are created with the same name,
 196 // so it's not intended to be used outside preamble-handling.
 197 class TempPCHFile {
 198 public:
 199   // A main method used to construct TempPCHFile.
 200   static std::unique_ptr<TempPCHFile> create() {
 201     // FIXME: This is a hack so that we can override the preamble file during
 202     // crash-recovery testing, which is the only case where the preamble files
 203     // are not necessarily cleaned up.
 204     if (const char *TmpFile = ::getenv("CINDEXTEST_PREAMBLE_FILE"))
 205       return std::unique_ptr<TempPCHFile>(new TempPCHFile(TmpFile));
 206
 207     llvm::SmallString<64> File;
 208     // Using a version of createTemporaryFile with a file descriptor guarantees
 209     // that we would never get a race condition in a multi-threaded setting
 210     // (i.e., multiple threads getting the same temporary path).
 211     int FD;
 212     if (auto EC =
 213             llvm::sys::fs::createTemporaryFile("preamble", "pch", FD, File))
 214       return nullptr;
 215     // We only needed to make sure the file exists, close the file right away.
 216     llvm::sys::Process::SafelyCloseFileDescriptor(FD);
 217     return std::unique_ptr<TempPCHFile>(new TempPCHFile(File.str().str()));
 218   }
 219
 220   TempPCHFile &operator=(const TempPCHFile &) = delete;
 221   TempPCHFile(const TempPCHFile &) = delete;
 222   ~TempPCHFile() { TemporaryFiles::getInstance().removeFile(FilePath); };
 223
 224   /// A path where temporary file is stored.
 225   llvm::StringRef getFilePath() const { return FilePath; };
 226
 227 private:
 228   TempPCHFile(std::string FilePath) : FilePath(std::move(FilePath)) {
 229     TemporaryFiles::getInstance().addFile(this->FilePath);
 230   }
 231
 232   std::string FilePath;
 233 };
 234
 235 class PrecompilePreambleAction : public ASTFrontendAction {
 236 public:
 237   PrecompilePreambleAction(std::shared_ptr<PCHBuffer> Buffer, bool WritePCHFile,
 238                            PreambleCallbacks &Callbacks)
 239       : Buffer(std::move(Buffer)), WritePCHFile(WritePCHFile),
 240         Callbacks(Callbacks) {}
 241
 242   std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,
 243                                                  StringRef InFile) override;
 244
 245   bool hasEmittedPreamblePCH() const { return HasEmittedPreamblePCH; }
 246
 247   void setEmittedPreamblePCH(ASTWriter &Writer) {
 248     if (FileOS) {
 249       *FileOS << Buffer->Data;
 250       // Make sure it hits disk now.
 251       FileOS.reset();
 252     }
 253
 254     this->HasEmittedPreamblePCH = true;
 255     Callbacks.AfterPCHEmitted(Writer);
 256   }
 257
 258   bool BeginSourceFileAction(CompilerInstance &CI) override {
 259     assert(CI.getLangOpts().CompilingPCH);
 260     return ASTFrontendAction::BeginSourceFileAction(CI);
 261   }
 262
 263   bool shouldEraseOutputFiles() override { return !hasEmittedPreamblePCH(); }
 264   bool hasCodeCompletionSupport() const override { return false; }
 265   bool hasASTFileSupport() const override { return false; }
 266   TranslationUnitKind getTranslationUnitKind() override { return TU_Prefix; }
 267
 268 private:
 269   friend class PrecompilePreambleConsumer;
 270
 271   bool HasEmittedPreamblePCH = false;
 272   std::shared_ptr<PCHBuffer> Buffer;
 273   bool WritePCHFile; // otherwise the PCH is written into the PCHBuffer only.
 274   std::unique_ptr<llvm::raw_pwrite_stream> FileOS; // null if in-memory
 275   PreambleCallbacks &Callbacks;
 276 };
 277
 278 class PrecompilePreambleConsumer : public PCHGenerator {
 279 public:
 280   PrecompilePreambleConsumer(PrecompilePreambleAction &Action,
 281                              const Preprocessor &PP,
 282                              InMemoryModuleCache &ModuleCache,
 283                              StringRef isysroot,
 284                              std::shared_ptr<PCHBuffer> Buffer)
 285       : PCHGenerator(PP, ModuleCache, "", isysroot, std::move(Buffer),
 286                      ArrayRef<std::shared_ptr<ModuleFileExtension>>(),
 287                      /*AllowASTWithErrors=*/true),
 288         Action(Action) {}
 289
 290   bool HandleTopLevelDecl(DeclGroupRef DG) override {
 291     Action.Callbacks.HandleTopLevelDecl(DG);
 292     return true;
 293   }
 294
 295   void HandleTranslationUnit(ASTContext &Ctx) override {
 296     PCHGenerator::HandleTranslationUnit(Ctx);
 297     if (!hasEmittedPCH())
 298       return;
 299     Action.setEmittedPreamblePCH(getWriter());
 300   }
 301
 302   bool shouldSkipFunctionBody(Decl *D) override {
 303     return Action.Callbacks.shouldSkipFunctionBody(D);
 304   }
 305
 306 private:
 307   PrecompilePreambleAction &Action;
 308 };
 309
 310 std::unique_ptr<ASTConsumer>
 311 PrecompilePreambleAction::CreateASTConsumer(CompilerInstance &CI,
 312                                             StringRef InFile) {
 313   std::string Sysroot;
 314   if (!GeneratePCHAction::ComputeASTConsumerArguments(CI, Sysroot))
 315     return nullptr;
 316
 317   if (WritePCHFile) {
 318     std::string OutputFile; // unused
 319     FileOS = GeneratePCHAction::CreateOutputFile(CI, InFile, OutputFile);
 320     if (!FileOS)
 321       return nullptr;
 322   }
 323
 324   if (!CI.getFrontendOpts().RelocatablePCH)
 325     Sysroot.clear();
 326
 327   return std::make_unique<PrecompilePreambleConsumer>(
 328       *this, CI.getPreprocessor(), CI.getModuleCache(), Sysroot, Buffer);
 329 }
 330
 331 template <class T> bool moveOnNoError(llvm::ErrorOr<T> Val, T &Output) {
 332   if (!Val)
 333     return false;
 334   Output = std::move(*Val);
 335   return true;
 336 }
 337
 338 } // namespace
 339
 340 PreambleBounds clang::ComputePreambleBounds(const LangOptions &LangOpts,
 341                                             const llvm::MemoryBufferRef &Buffer,
 342                                             unsigned MaxLines) {
 343   return Lexer::ComputePreamble(Buffer.getBuffer(), LangOpts, MaxLines);
 344 }
 345
 346 class PrecompiledPreamble::PCHStorage {
 347 public:
 348   static std::unique_ptr<PCHStorage> file(std::unique_ptr<TempPCHFile> File) {
 349     assert(File);
 350     std::unique_ptr<PCHStorage> S(new PCHStorage());
 351     S->File = std::move(File);
 352     return S;
 353   }
 354   static std::unique_ptr<PCHStorage> inMemory(std::shared_ptr<PCHBuffer> Buf) {
 355     std::unique_ptr<PCHStorage> S(new PCHStorage());
 356     S->Memory = std::move(Buf);
 357     return S;
 358   }
 359
 360   enum class Kind { InMemory, TempFile };
 361   Kind getKind() const {
 362     if (Memory)
 363       return Kind::InMemory;
 364     if (File)
 365       return Kind::TempFile;
 366     llvm_unreachable("Neither Memory nor File?");
 367   }
 368   llvm::StringRef filePath() const {
 369     assert(getKind() == Kind::TempFile);
 370     return File->getFilePath();
 371   }
 372   llvm::StringRef memoryContents() const {
 373     assert(getKind() == Kind::InMemory);
 374     return StringRef(Memory->Data.data(), Memory->Data.size());
 375   }
 376
 377   // Shrink in-memory buffers to fit.
 378   // This incurs a copy, but preambles tend to be long-lived.
 379   // Only safe to call once nothing can alias the buffer.
 380   void shrink() {
 381     if (!Memory)
 382       return;
 383     Memory->Data = decltype(Memory->Data)(Memory->Data);
 384   }
 385
 386 private:
 387   PCHStorage() = default;
 388   PCHStorage(const PCHStorage &) = delete;
 389   PCHStorage &operator=(const PCHStorage &) = delete;
 390
 391   std::shared_ptr<PCHBuffer> Memory;
 392   std::unique_ptr<TempPCHFile> File;
 393 };
 394
 395 PrecompiledPreamble::~PrecompiledPreamble() = default;
 396 PrecompiledPreamble::PrecompiledPreamble(PrecompiledPreamble &&) = default;
 397 PrecompiledPreamble &
 398 PrecompiledPreamble::operator=(PrecompiledPreamble &&) = default;
 399
 400 llvm::ErrorOr<PrecompiledPreamble> PrecompiledPreamble::Build(
 401     const CompilerInvocation &Invocation,
 402     const llvm::MemoryBuffer *MainFileBuffer, PreambleBounds Bounds,
 403     DiagnosticsEngine &Diagnostics,
 404     IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
 405     std::shared_ptr<PCHContainerOperations> PCHContainerOps, bool StoreInMemory,
 406     PreambleCallbacks &Callbacks) {
 407   assert(VFS && "VFS is null");
 408
 409   auto PreambleInvocation = std::make_shared<CompilerInvocation>(Invocation);
 410   FrontendOptions &FrontendOpts = PreambleInvocation->getFrontendOpts();
 411   PreprocessorOptions &PreprocessorOpts =
 412       PreambleInvocation->getPreprocessorOpts();
 413
 414   std::shared_ptr<PCHBuffer> Buffer = std::make_shared<PCHBuffer>();
 415   std::unique_ptr<PCHStorage> Storage;
 416   if (StoreInMemory) {
 417     Storage = PCHStorage::inMemory(Buffer);
 418   } else {
 419     // Create a temporary file for the precompiled preamble. In rare
 420     // circumstances, this can fail.
 421     std::unique_ptr<TempPCHFile> PreamblePCHFile = TempPCHFile::create();
 422     if (!PreamblePCHFile)
 423       return BuildPreambleError::CouldntCreateTempFile;
 424     Storage = PCHStorage::file(std::move(PreamblePCHFile));
 425   }
 426
 427   // Save the preamble text for later; we'll need to compare against it for
 428   // subsequent reparses.
 429   std::vector<char> PreambleBytes(MainFileBuffer->getBufferStart(),
 430                                   MainFileBuffer->getBufferStart() +
 431                                       Bounds.Size);
 432   bool PreambleEndsAtStartOfLine = Bounds.PreambleEndsAtStartOfLine;
 433
 434   // Tell the compiler invocation to generate a temporary precompiled header.
 435   FrontendOpts.ProgramAction = frontend::GeneratePCH;
 436   FrontendOpts.OutputFile = std::string(
 437       StoreInMemory ? getInMemoryPreamblePath() : Storage->filePath());
 438   PreprocessorOpts.PrecompiledPreambleBytes.first = 0;
 439   PreprocessorOpts.PrecompiledPreambleBytes.second = false;
 440   // Inform preprocessor to record conditional stack when building the preamble.
 441   PreprocessorOpts.GeneratePreamble = true;
 442
 443   // Create the compiler instance to use for building the precompiled preamble.
 444   std::unique_ptr<CompilerInstance> Clang(
 445       new CompilerInstance(std::move(PCHContainerOps)));
 446
 447   // Recover resources if we crash before exiting this method.
 448   llvm::CrashRecoveryContextCleanupRegistrar<CompilerInstance> CICleanup(
 449       Clang.get());
 450
 451   Clang->setInvocation(std::move(PreambleInvocation));
 452   Clang->setDiagnostics(&Diagnostics);
 453
 454   // Create the target instance.
 455   if (!Clang->createTarget())
 456     return BuildPreambleError::CouldntCreateTargetInfo;
 457
 458   if (Clang->getFrontendOpts().Inputs.size() != 1 ||
 459       Clang->getFrontendOpts().Inputs[0].getKind().getFormat() !=
 460           InputKind::Source ||
 461       Clang->getFrontendOpts().Inputs[0].getKind().getLanguage() ==
 462           Language::LLVM_IR) {
 463     return BuildPreambleError::BadInputs;
 464   }
 465
 466   // Clear out old caches and data.
 467   Diagnostics.Reset();
 468   ProcessWarningOptions(Diagnostics, Clang->getDiagnosticOpts());
 469
 470   VFS =
 471       createVFSFromCompilerInvocation(Clang->getInvocation(), Diagnostics, VFS);
 472
 473   // Create a file manager object to provide access to and cache the filesystem.
 474   Clang->setFileManager(new FileManager(Clang->getFileSystemOpts(), VFS));
 475
 476   // Create the source manager.
 477   Clang->setSourceManager(
 478       new SourceManager(Diagnostics, Clang->getFileManager()));
 479
 480   auto PreambleDepCollector = std::make_shared<PreambleDependencyCollector>();
 481   Clang->addDependencyCollector(PreambleDepCollector);
 482
 483   Clang->getLangOpts().CompilingPCH = true;
 484
 485   // Remap the main source file to the preamble buffer.
 486   StringRef MainFilePath = FrontendOpts.Inputs[0].getFile();
 487   auto PreambleInputBuffer = llvm::MemoryBuffer::getMemBufferCopy(
 488       MainFileBuffer->getBuffer().slice(0, Bounds.Size), MainFilePath);
 489   if (PreprocessorOpts.RetainRemappedFileBuffers) {
 490     // MainFileBuffer will be deleted by unique_ptr after leaving the method.
 491     PreprocessorOpts.addRemappedFile(MainFilePath, PreambleInputBuffer.get());
 492   } else {
 493     // In that case, remapped buffer will be deleted by CompilerInstance on
 494     // BeginSourceFile, so we call release() to avoid double deletion.
 495     PreprocessorOpts.addRemappedFile(MainFilePath,
 496                                      PreambleInputBuffer.release());
 497   }
 498
 499   auto Act = std::make_unique<PrecompilePreambleAction>(
 500       std::move(Buffer),
 501       /*WritePCHFile=*/Storage->getKind() == PCHStorage::Kind::TempFile,
 502       Callbacks);
 503   if (!Act->BeginSourceFile(*Clang.get(), Clang->getFrontendOpts().Inputs[0]))
 504     return BuildPreambleError::BeginSourceFileFailed;
 505
 506   // Performed after BeginSourceFile to ensure Clang->Preprocessor can be
 507   // referenced in the callback.
 508   Callbacks.BeforeExecute(*Clang);
 509
 510   std::unique_ptr<PPCallbacks> DelegatedPPCallbacks =
 511       Callbacks.createPPCallbacks();
 512   if (DelegatedPPCallbacks)
 513     Clang->getPreprocessor().addPPCallbacks(std::move(DelegatedPPCallbacks));
 514   if (auto CommentHandler = Callbacks.getCommentHandler())
 515     Clang->getPreprocessor().addCommentHandler(CommentHandler);
 516   llvm::StringSet<> MissingFiles;
 517   Clang->getPreprocessor().addPPCallbacks(
 518       std::make_unique<MissingFileCollector>(
 519           MissingFiles, Clang->getPreprocessor().getHeaderSearchInfo(),
 520           Clang->getSourceManager()));
 521
 522   if (llvm::Error Err = Act->Execute())
 523     return errorToErrorCode(std::move(Err));
 524
 525   // Run the callbacks.
 526   Callbacks.AfterExecute(*Clang);
 527
 528   Act->EndSourceFile();
 529
 530   if (!Act->hasEmittedPreamblePCH())
 531     return BuildPreambleError::CouldntEmitPCH;
 532   Act.reset(); // Frees the PCH buffer, unless Storage keeps it in memory.
 533
 534   // Keep track of all of the files that the source manager knows about,
 535   // so we can verify whether they have changed or not.
 536   llvm::StringMap<PrecompiledPreamble::PreambleFileHash> FilesInPreamble;
 537
 538   SourceManager &SourceMgr = Clang->getSourceManager();
 539   for (auto &Filename : PreambleDepCollector->getDependencies()) {
 540     auto FileOrErr = Clang->getFileManager().getFile(Filename);
 541     if (!FileOrErr ||
 542         *FileOrErr == SourceMgr.getFileEntryForID(SourceMgr.getMainFileID()))
 543       continue;
 544     auto File = *FileOrErr;
 545     if (time_t ModTime = File->getModificationTime()) {
 546       FilesInPreamble[File->getName()] =
 547           PrecompiledPreamble::PreambleFileHash::createForFile(File->getSize(),
 548                                                                ModTime);
 549     } else {
 550       llvm::MemoryBufferRef Buffer =
 551           SourceMgr.getMemoryBufferForFileOrFake(File);
 552       FilesInPreamble[File->getName()] =
 553           PrecompiledPreamble::PreambleFileHash::createForMemoryBuffer(Buffer);
 554     }
 555   }
 556
 557   // Shrinking the storage requires extra temporary memory.
 558   // Destroying clang first reduces peak memory usage.
 559   CICleanup.unregister();
 560   Clang.reset();
 561   Storage->shrink();
 562   return PrecompiledPreamble(
 563       std::move(Storage), std::move(PreambleBytes), PreambleEndsAtStartOfLine,
 564       std::move(FilesInPreamble), std::move(MissingFiles));
 565 }
 566
 567 PreambleBounds PrecompiledPreamble::getBounds() const {
 568   return PreambleBounds(PreambleBytes.size(), PreambleEndsAtStartOfLine);
 569 }
 570
 571 std::size_t PrecompiledPreamble::getSize() const {
 572   switch (Storage->getKind()) {
 573   case PCHStorage::Kind::InMemory:
 574     return Storage->memoryContents().size();
 575   case PCHStorage::Kind::TempFile: {
 576     uint64_t Result;
 577     if (llvm::sys::fs::file_size(Storage->filePath(), Result))
 578       return 0;
 579
 580     assert(Result <= std::numeric_limits<std::size_t>::max() &&
 581            "file size did not fit into size_t");
 582     return Result;
 583   }
 584   }
 585   llvm_unreachable("Unhandled storage kind");
 586 }
 587
 588 bool PrecompiledPreamble::CanReuse(const CompilerInvocation &Invocation,
 589                                    const llvm::MemoryBufferRef &MainFileBuffer,
 590                                    PreambleBounds Bounds,
 591                                    llvm::vfs::FileSystem &VFS) const {
 592
 593   assert(
 594       Bounds.Size <= MainFileBuffer.getBufferSize() &&
 595       "Buffer is too large. Bounds were calculated from a different buffer?");
 596
 597   auto PreambleInvocation = std::make_shared<CompilerInvocation>(Invocation);
 598   PreprocessorOptions &PreprocessorOpts =
 599       PreambleInvocation->getPreprocessorOpts();
 600
 601   // We've previously computed a preamble. Check whether we have the same
 602   // preamble now that we did before, and that there's enough space in
 603   // the main-file buffer within the precompiled preamble to fit the
 604   // new main file.
 605   if (PreambleBytes.size() != Bounds.Size ||
 606       PreambleEndsAtStartOfLine != Bounds.PreambleEndsAtStartOfLine ||
 607       !std::equal(PreambleBytes.begin(), PreambleBytes.end(),
 608                   MainFileBuffer.getBuffer().begin()))
 609     return false;
 610   // The preamble has not changed. We may be able to re-use the precompiled
 611   // preamble.
 612
 613   // Check that none of the files used by the preamble have changed.
 614   // First, make a record of those files that have been overridden via
 615   // remapping or unsaved_files.
 616   std::map<llvm::sys::fs::UniqueID, PreambleFileHash> OverriddenFiles;
 617   llvm::StringSet<> OverriddenAbsPaths; // Either by buffers or files.
 618   for (const auto &R : PreprocessorOpts.RemappedFiles) {
 619     llvm::vfs::Status Status;
 620     if (!moveOnNoError(VFS.status(R.second), Status)) {
 621       // If we can't stat the file we're remapping to, assume that something
 622       // horrible happened.
 623       return false;
 624     }
 625     // If a mapped file was previously missing, then it has changed.
 626     llvm::SmallString<128> MappedPath(R.first);
 627     if (!VFS.makeAbsolute(MappedPath))
 628       OverriddenAbsPaths.insert(MappedPath);
 629
 630     OverriddenFiles[Status.getUniqueID()] = PreambleFileHash::createForFile(
 631         Status.getSize(), llvm::sys::toTimeT(Status.getLastModificationTime()));
 632   }
 633
 634   // OverridenFileBuffers tracks only the files not found in VFS.
 635   llvm::StringMap<PreambleFileHash> OverridenFileBuffers;
 636   for (const auto &RB : PreprocessorOpts.RemappedFileBuffers) {
 637     const PrecompiledPreamble::PreambleFileHash PreambleHash =
 638         PreambleFileHash::createForMemoryBuffer(RB.second->getMemBufferRef());
 639     llvm::vfs::Status Status;
 640     if (moveOnNoError(VFS.status(RB.first), Status))
 641       OverriddenFiles[Status.getUniqueID()] = PreambleHash;
 642     else
 643       OverridenFileBuffers[RB.first] = PreambleHash;
 644
 645     llvm::SmallString<128> MappedPath(RB.first);
 646     if (!VFS.makeAbsolute(MappedPath))
 647       OverriddenAbsPaths.insert(MappedPath);
 648   }
 649
 650   // Check whether anything has changed.
 651   for (const auto &F : FilesInPreamble) {
 652     auto OverridenFileBuffer = OverridenFileBuffers.find(F.first());
 653     if (OverridenFileBuffer != OverridenFileBuffers.end()) {
 654       // The file's buffer was remapped and the file was not found in VFS.
 655       // Check whether it matches up with the previous mapping.
 656       if (OverridenFileBuffer->second != F.second)
 657         return false;
 658       continue;
 659     }
 660
 661     llvm::vfs::Status Status;
 662     if (!moveOnNoError(VFS.status(F.first()), Status)) {
 663       // If the file's buffer is not remapped and we can't stat it,
 664       // assume that something horrible happened.
 665       return false;
 666     }
 667
 668     std::map<llvm::sys::fs::UniqueID, PreambleFileHash>::iterator Overridden =
 669         OverriddenFiles.find(Status.getUniqueID());
 670     if (Overridden != OverriddenFiles.end()) {
 671       // This file was remapped; check whether the newly-mapped file
 672       // matches up with the previous mapping.
 673       if (Overridden->second != F.second)
 674         return false;
 675       continue;
 676     }
 677
 678     // Neither the file's buffer nor the file itself was remapped;
 679     // check whether it has changed on disk.
 680     if (Status.getSize() != uint64_t(F.second.Size) ||
 681         llvm::sys::toTimeT(Status.getLastModificationTime()) !=
 682             F.second.ModTime)
 683       return false;
 684   }
 685   for (const auto &F : MissingFiles) {
 686     // A missing file may be "provided" by an override buffer or file.
 687     if (OverriddenAbsPaths.count(F.getKey()))
 688       return false;
 689     // If a file previously recorded as missing exists as a regular file, then
 690     // consider the preamble out-of-date.
 691     if (auto Status = VFS.status(F.getKey())) {
 692       if (Status->isRegularFile())
 693         return false;
 694     }
 695   }
 696   return true;
 697 }
 698
 699 void PrecompiledPreamble::AddImplicitPreamble(
 700     CompilerInvocation &CI, IntrusiveRefCntPtr<llvm::vfs::FileSystem> &VFS,
 701     llvm::MemoryBuffer *MainFileBuffer) const {
 702   PreambleBounds Bounds(PreambleBytes.size(), PreambleEndsAtStartOfLine);
 703   configurePreamble(Bounds, CI, VFS, MainFileBuffer);
 704 }
 705
 706 void PrecompiledPreamble::OverridePreamble(
 707     CompilerInvocation &CI, IntrusiveRefCntPtr<llvm::vfs::FileSystem> &VFS,
 708     llvm::MemoryBuffer *MainFileBuffer) const {
 709   auto Bounds = ComputePreambleBounds(*CI.getLangOpts(), *MainFileBuffer, 0);
 710   configurePreamble(Bounds, CI, VFS, MainFileBuffer);
 711 }
 712
 713 PrecompiledPreamble::PrecompiledPreamble(
 714     std::unique_ptr<PCHStorage> Storage, std::vector<char> PreambleBytes,
 715     bool PreambleEndsAtStartOfLine,
 716     llvm::StringMap<PreambleFileHash> FilesInPreamble,
 717     llvm::StringSet<> MissingFiles)
 718     : Storage(std::move(Storage)), FilesInPreamble(std::move(FilesInPreamble)),
 719       MissingFiles(std::move(MissingFiles)),
 720       PreambleBytes(std::move(PreambleBytes)),
 721       PreambleEndsAtStartOfLine(PreambleEndsAtStartOfLine) {
 722   assert(this->Storage != nullptr);
 723 }
 724
 725 PrecompiledPreamble::PreambleFileHash
 726 PrecompiledPreamble::PreambleFileHash::createForFile(off_t Size,
 727                                                      time_t ModTime) {
 728   PreambleFileHash Result;
 729   Result.Size = Size;
 730   Result.ModTime = ModTime;
 731   Result.MD5 = {};
 732   return Result;
 733 }
 734
 735 PrecompiledPreamble::PreambleFileHash
 736 PrecompiledPreamble::PreambleFileHash::createForMemoryBuffer(
 737     const llvm::MemoryBufferRef &Buffer) {
 738   PreambleFileHash Result;
 739   Result.Size = Buffer.getBufferSize();
 740   Result.ModTime = 0;
 741
 742   llvm::MD5 MD5Ctx;
 743   MD5Ctx.update(Buffer.getBuffer().data());
 744   MD5Ctx.final(Result.MD5);
 745
 746   return Result;
 747 }
 748
 749 void PrecompiledPreamble::configurePreamble(
 750     PreambleBounds Bounds, CompilerInvocation &CI,
 751     IntrusiveRefCntPtr<llvm::vfs::FileSystem> &VFS,
 752     llvm::MemoryBuffer *MainFileBuffer) const {
 753   assert(VFS);
 754
 755   auto &PreprocessorOpts = CI.getPreprocessorOpts();
 756
 757   // Remap main file to point to MainFileBuffer.
 758   auto MainFilePath = CI.getFrontendOpts().Inputs[0].getFile();
 759   PreprocessorOpts.addRemappedFile(MainFilePath, MainFileBuffer);
 760
 761   // Configure ImpicitPCHInclude.
 762   PreprocessorOpts.PrecompiledPreambleBytes.first = Bounds.Size;
 763   PreprocessorOpts.PrecompiledPreambleBytes.second =
 764       Bounds.PreambleEndsAtStartOfLine;
 765   PreprocessorOpts.DisablePCHOrModuleValidation =
 766       DisableValidationForModuleKind::PCH;
 767
 768   // Don't bother generating the long version of the predefines buffer.
 769   // The preamble is going to overwrite it anyway.
 770   PreprocessorOpts.UsePredefines = false;
 771
 772   setupPreambleStorage(*Storage, PreprocessorOpts, VFS);
 773 }
 774
 775 void PrecompiledPreamble::setupPreambleStorage(
 776     const PCHStorage &Storage, PreprocessorOptions &PreprocessorOpts,
 777     IntrusiveRefCntPtr<llvm::vfs::FileSystem> &VFS) {
 778   if (Storage.getKind() == PCHStorage::Kind::TempFile) {
 779     llvm::StringRef PCHPath = Storage.filePath();
 780     PreprocessorOpts.ImplicitPCHInclude = PCHPath.str();
 781
 782     // Make sure we can access the PCH file even if we're using a VFS
 783     IntrusiveRefCntPtr<llvm::vfs::FileSystem> RealFS =
 784         llvm::vfs::getRealFileSystem();
 785     if (VFS == RealFS || VFS->exists(PCHPath))
 786       return;
 787     auto Buf = RealFS->getBufferForFile(PCHPath);
 788     if (!Buf) {
 789       // We can't read the file even from RealFS, this is clearly an error,
 790       // but we'll just leave the current VFS as is and let clang's code
 791       // figure out what to do with missing PCH.
 792       return;
 793     }
 794
 795     // We have a slight inconsistency here -- we're using the VFS to
 796     // read files, but the PCH was generated in the real file system.
 797     VFS = createVFSOverlayForPreamblePCH(PCHPath, std::move(*Buf), VFS);
 798   } else {
 799     assert(Storage.getKind() == PCHStorage::Kind::InMemory);
 800     // For in-memory preamble, we have to provide a VFS overlay that makes it
 801     // accessible.
 802     StringRef PCHPath = getInMemoryPreamblePath();
 803     PreprocessorOpts.ImplicitPCHInclude = std::string(PCHPath);
 804
 805     auto Buf = llvm::MemoryBuffer::getMemBuffer(
 806         Storage.memoryContents(), PCHPath, /*RequiresNullTerminator=*/false);
 807     VFS = createVFSOverlayForPreamblePCH(PCHPath, std::move(Buf), VFS);
 808   }
 809 }
 810
 811 void PreambleCallbacks::BeforeExecute(CompilerInstance &CI) {}
 812 void PreambleCallbacks::AfterExecute(CompilerInstance &CI) {}
 813 void PreambleCallbacks::AfterPCHEmitted(ASTWriter &Writer) {}
 814 void PreambleCallbacks::HandleTopLevelDecl(DeclGroupRef DG) {}
 815 std::unique_ptr<PPCallbacks> PreambleCallbacks::createPPCallbacks() {
 816   return nullptr;
 817 }
 818 CommentHandler *PreambleCallbacks::getCommentHandler() { return nullptr; }
 819
 820 static llvm::ManagedStatic<BuildPreambleErrorCategory> BuildPreambleErrCategory;
 821
 822 std::error_code clang::make_error_code(BuildPreambleError Error) {
 823   return std::error_code(static_cast<int>(Error), *BuildPreambleErrCategory);
 824 }
 825
 826 const char *BuildPreambleErrorCategory::name() const noexcept {
 827   return "build-preamble.error";
 828 }
 829
 830 std::string BuildPreambleErrorCategory::message(int condition) const {
 831   switch (static_cast<BuildPreambleError>(condition)) {
 832   case BuildPreambleError::CouldntCreateTempFile:
 833     return "Could not create temporary file for PCH";
 834   case BuildPreambleError::CouldntCreateTargetInfo:
 835     return "CreateTargetInfo() return null";
 836   case BuildPreambleError::BeginSourceFileFailed:
 837     return "BeginSourceFile() return an error";
 838   case BuildPreambleError::CouldntEmitPCH:
 839     return "Could not emit PCH";
 840   case BuildPreambleError::BadInputs:
 841     return "Command line arguments must contain exactly one source file";
 842   }
 843   llvm_unreachable("unexpected BuildPreambleError");
 844 }