[ThinLTO] Update ThinLTO cache file atimes when on Windows

ThinLTO cache file access times are used for expiration based pruning
and since Vista, file access times are not updated by Windows by
default:

https://blogs.technet.microsoft.com/filecab/2006/11/07/disabling-last-access-time-in-windows-vista-to-improve-ntfs-performance

This means on Windows, cache files are currently being pruned from
creation time. This change manually updates cache files that are
accessed by ThinLTO, when on Windows.

Patch by Owen Reynolds.

Differential Revision: https://reviews.llvm.org/D47266

llvm-svn: 336276

1 files changed, 32 insertions, 0 deletions

diff --git a/llvm/unittests/Support/Path.cpp b/llvm/unittests/Support/Path.cpp
index ff301dc7d89..dcbe94c6715 100644
--- a/llvm/unittests/Support/Path.cpp
+++ b/llvm/unittests/Support/Path.cpp
@@ -26,6 +26,7 @@
 
 #ifdef _WIN32
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/Support/Chrono.h"
 #include <windows.h>
 #include <winerror.h>
 #endif
@@ -1251,8 +1252,39 @@ TEST_F(FileSystemTest, OpenFileForRead) {
     ASSERT_NO_ERROR(fs::getUniqueID(Twine(ResultPath), D2));
     ASSERT_EQ(D1, D2);
   }
+  ::close(FileDescriptor);
+  ::close(FileDescriptor2);
+
+#ifdef _WIN32
+  // Since Windows Vista, file access time is not updated by default.
+  // This is instead updated manually by openFileForRead.
+  // https://blogs.technet.microsoft.com/filecab/2006/11/07/disabling-last-access-time-in-windows-vista-to-improve-ntfs-performance/
+  // This part of the unit test is Windows specific as the updating of
+  // access times can be disabled on Linux using /etc/fstab.
+
+  // Set access time to UNIX epoch.
+  ASSERT_NO_ERROR(sys::fs::openFileForWrite(Twine(TempPath), FileDescriptor,
+                                            fs::CD_OpenExisting));
+  TimePoint<> Epoch(std::chrono::milliseconds(0));
+  ASSERT_NO_ERROR(fs::setLastModificationAndAccessTime(FileDescriptor, Epoch));
+  ::close(FileDescriptor);
 
+  // Open the file and ensure access time is updated, when forced.
+  bool ForceATime = true;
+  ASSERT_NO_ERROR(fs::openFileForRead(Twine(TempPath), FileDescriptor,
+                                      fs::OF_UpdateAtime, &ResultPath));
+
+  sys::fs::file_status Status;
+  ASSERT_NO_ERROR(sys::fs::status(FileDescriptor, Status));
+  auto FileAccessTime = Status.getLastAccessedTime();
+
+  ASSERT_NE(Epoch, FileAccessTime);
   ::close(FileDescriptor);
+
+  // Ideally this test would include a case when ATime is not forced to update,
+  // however the expected behaviour will differ depending on the configuration
+  // of the Windows file system.
+#endif
 }
 
 static void createFileWithData(const Twine &Path, bool ShouldExistBefore,