[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, 23 insertions, 8 deletions

diff --git a/llvm/lib/LTO/Caching.cpp b/llvm/lib/LTO/Caching.cpp
index bd6190d9961..089e77e742e 100644
--- a/llvm/lib/LTO/Caching.cpp
+++ b/llvm/lib/LTO/Caching.cpp
@@ -19,6 +19,12 @@
 #include "llvm/Support/Process.h"
 #include "llvm/Support/raw_ostream.h"
 
+#if !defined(_MSC_VER) && !defined(__MINGW32__)
+#include <unistd.h>
+#else
+#include <io.h>
+#endif
+
 using namespace llvm;
 using namespace llvm::lto;
 
@@ -33,11 +39,21 @@ Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
     SmallString<64> EntryPath;
     sys::path::append(EntryPath, CacheDirectoryPath, "llvmcache-" + Key);
     // First, see if we have a cache hit.
-    ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
-        MemoryBuffer::getFile(EntryPath);
-    if (MBOrErr) {
-      AddBuffer(Task, std::move(*MBOrErr));
-      return AddStreamFn();
+    int FD;
+    SmallString<64> ResultPath;
+    std::error_code EC = sys::fs::openFileForRead(
+        Twine(EntryPath), FD, sys::fs::OF_UpdateAtime, &ResultPath);
+    if (!EC) {
+      ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
+          MemoryBuffer::getOpenFile(FD, EntryPath,
+                                    /*FileSize*/ -1,
+                                    /*RequiresNullTerminator*/ false);
+      close(FD);
+      if (MBOrErr) {
+        AddBuffer(Task, std::move(*MBOrErr));
+        return AddStreamFn();
+      }
+      EC = MBOrErr.getError();
     }
 
     // On Windows we can fail to open a cache file with a permission denied
@@ -46,10 +62,9 @@ Expected<NativeObjectCache> lto::localCache(StringRef CacheDirectoryPath,
     // process has opened the file without the sharing permissions we need.
     // Since the file is probably being deleted we handle it in the same way as
     // if the file did not exist at all.
-    if (MBOrErr.getError() != errc::no_such_file_or_directory &&
-        MBOrErr.getError() != errc::permission_denied)
+    if (EC != errc::no_such_file_or_directory && EC != errc::permission_denied)
       report_fatal_error(Twine("Failed to open cache file ") + EntryPath +
-                         ": " + MBOrErr.getError().message() + "\n");
+                         ": " + EC.message() + "\n");
 
     // This native object stream is responsible for commiting the resulting
     // file to the cache and calling AddBuffer to add it to the link.