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

1 files changed, 8 insertions, 13 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index aaa59fcf506..10b2a5c4f9d 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -2315,19 +2315,14 @@ InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool Complain) {
   if ((!Overridden && !Transient) && SM.isFileOverridden(File)) {
     if (Complain)
       Error(diag::err_fe_pch_file_overridden, Filename);
-    // After emitting the diagnostic, recover by disabling the override so
-    // that the original file will be used.
-    //
-    // FIXME: This recovery is just as broken as the original state; there may
-    // be another precompiled module that's using the overridden contents, or
-    // we might be half way through parsing it. Instead, we should treat the
-    // overridden contents as belonging to a separate FileEntry.
-    SM.disableFileContentsOverride(File);
-    // The FileEntry is a virtual file entry with the size of the contents
-    // that would override the original contents. Set it to the original's
-    // size/time.
-    FileMgr.modifyFileEntry(const_cast<FileEntry*>(File),
-                            StoredSize, StoredTime);
+
+    // After emitting the diagnostic, bypass the overriding file to recover
+    // (this creates a separate FileEntry).
+    File = SM.bypassFileContentsOverride(*File);
+    if (!File) {
+      F.InputFilesLoaded[ID - 1] = InputFile::getNotFound();
+      return InputFile();
+    }
   }
 
   bool IsOutOfDate = false;