Index: llvm/lib/Support/raw_ostream.cpp
===================================================================
--- llvm/lib/Support/raw_ostream.cpp
+++ llvm/lib/Support/raw_ostream.cpp
@@ -551,6 +551,15 @@
   if (FD >= 0) {
     flush();
     if (ShouldClose) {
+#if defined(LLVM_ON_WIN32)
+      // On Windows, we have observed that programs that read a file after it
+      // was written will sometimes read bytes with value 0, when that isn't
+      // actually the value that was written. Calling FlushFileBuffers before
+      // closing the file seems to avoid the issue.
+      HANDLE FileHandle = reinterpret_cast<HANDLE>(_get_osfhandle(FD));
+      if (FileHandle != INVALID_HANDLE_VALUE)
+        ::FlushFileBuffers(FileHandle);
+#endif
       if (auto EC = sys::Process::SafelyCloseFileDescriptor(FD))
         error_detected(EC);
     }