ASTReader: Bypass overridden files when reading PCHs

If contents of a file that is part of a PCM are overridden when reading
it, but weren't overridden when the PCM was being built, the ASTReader
will emit an error.  Now it creates a separate FileEntry for recovery,
bypassing the overridden content instead of discarding it.  The
pre-existing testcase clang/test/PCH/remap-file-from-pch.cpp confirms
that the new recovery method works correctly.

This resolves a long-standing FIXME to avoid hypothetically invalidating
another precompiled module that's already using the overridden contents.

This also removes ContentCache-related API that would be unsafe to use
across `CompilerInstance`s in an implicit modules build.  This helps to
unblock us sinking it from SourceManager into FileManager in the future,
which would allow us to delete `InMemoryModuleCache`.

https://reviews.llvm.org/D66710

llvm-svn: 370546

2 files changed, 31 insertions, 16 deletions

diff --git a/clang/lib/Basic/FileManager.cpp b/clang/lib/Basic/FileManager.cpp
index 4330c7ac61c..cc6c2613fb3 100644
--- a/clang/lib/Basic/FileManager.cpp
+++ b/clang/lib/Basic/FileManager.cpp
@@ -390,6 +390,25 @@ FileManager::getVirtualFile(StringRef Filename, off_t Size,
   return UFE;
 }
 
+llvm::Optional<FileEntryRef> FileManager::getBypassFile(FileEntryRef VF) {
+  // Stat of the file and return nullptr if it doesn't exist.
+  llvm::vfs::Status Status;
+  if (getStatValue(VF.getName(), Status, /*isFile=*/true, /*F=*/nullptr))
+    return None;
+
+  // Fill it in from the stat.
+  BypassFileEntries.push_back(std::make_unique<FileEntry>());
+  const FileEntry &VFE = VF.getFileEntry();
+  FileEntry &BFE = *BypassFileEntries.back();
+  BFE.Name = VFE.getName();
+  BFE.Size = Status.getSize();
+  BFE.Dir = VFE.Dir;
+  BFE.ModTime = llvm::sys::toTimeT(Status.getLastModificationTime());
+  BFE.UID = NextFileUID++;
+  BFE.IsValid = true;
+  return FileEntryRef(VF.getName(), BFE);
+}
+
 bool FileManager::FixupRelativePath(SmallVectorImpl<char> &path) const {
   StringRef pathRef(path.data(), path.size());
 
@@ -515,12 +534,6 @@ void FileManager::GetUniqueIDMapping(
     UIDToFiles[VFE->getUID()] = VFE.get();
 }
 
-void FileManager::modifyFileEntry(FileEntry *File,
-                                  off_t Size, time_t ModificationTime) {
-  File->Size = Size;
-  File->ModTime = ModificationTime;
-}
-
 StringRef FileManager::getCanonicalName(const DirectoryEntry *Dir) {
   // FIXME: use llvm::sys::fs::canonical() when it gets implemented
   llvm::DenseMap<const DirectoryEntry *, llvm::StringRef>::iterator Known
diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index d49d594e290..58b95289eaf 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -669,17 +669,19 @@ void SourceManager::overrideFileContents(const FileEntry *SourceFile,
   getOverriddenFilesInfo().OverriddenFiles[SourceFile] = NewFile;
 }
 
-void SourceManager::disableFileContentsOverride(const FileEntry *File) {
-  if (!isFileOverridden(File))
-    return;
-
-  const SrcMgr::ContentCache *IR = getOrCreateContentCache(File);
-  const_cast<SrcMgr::ContentCache *>(IR)->replaceBuffer(nullptr);
-  const_cast<SrcMgr::ContentCache *>(IR)->ContentsEntry = IR->OrigEntry;
+const FileEntry *
+SourceManager::bypassFileContentsOverride(const FileEntry &File) {
+  assert(isFileOverridden(&File));
+  llvm::Optional<FileEntryRef> BypassFile =
+      FileMgr.getBypassFile(FileEntryRef(File.getName(), File));
+
+  // If the file can't be found in the FS, give up.
+  if (!BypassFile)
+    return nullptr;
 
-  assert(OverriddenFilesInfo);
-  OverriddenFilesInfo->OverriddenFiles.erase(File);
-  OverriddenFilesInfo->OverriddenFilesWithBuffer.erase(File);
+  const FileEntry *FE = &BypassFile->getFileEntry();
+  (void)getOrCreateContentCache(FE);
+  return FE;
 }
 
 void SourceManager::setFileIsTransient(const FileEntry *File) {