Support: On Windows, use CreateFileW to delete files in sys::fs::remove().

[pcc]

Summary

This saves a call to stat().

[pcc]

• Use CreateFile

[zturner]

Can you add a comment indicating what the first two flags are used for? They aren't very common, so it might help someone in the future understand what's going on.

Also maybe a top-level comment indicating why we're doing things this way instead of the old way.

Don't need to re-upload, lgtm already.

[amccarth]

llvm/lib/Support/Windows/Path.inc

266

Zach's right that this is likely a tad faster, but it's also a little less clear. How about a comment to make it point out that we're using CreateFileW to mark the file/direction for deletion?

[pcc]

Thanks, I've added a big comment block explaining what's going on.

llvm/lib/Support/Windows/Path.inc

 
 std::error_code create_hard_link(const Twine &to, const Twine &from) {
   return create_link(to, from);
 }
 
 std::error_code remove(const Twine &path, bool IgnoreNonExisting) {
   SmallVector<wchar_t, 128> path_utf16;
 
-  file_status ST;
-  if (std::error_code EC = status(path, ST)) {
-    if (EC != errc::no_such_file_or_directory || !IgnoreNonExisting)
-      return EC;
-    return std::error_code();
-  }
-
   if (std::error_code ec = widenPath(path, path_utf16))
     return ec;
 
-  if (ST.type() == file_type::directory_file) {
+  // Speculate that the path is actually a file in order to save a stat() call.
+  if (!::DeleteFileW(c_str(path_utf16))) {
+    std::error_code EC = mapWindowsError(::GetLastError());
+    if (EC == errc::permission_denied) {
       if (!::RemoveDirectoryW(c_str(path_utf16))) {
         std::error_code EC = mapWindowsError(::GetLastError());
         if (EC != errc::no_such_file_or_directory || !IgnoreNonExisting)
           return EC;
       }
       return std::error_code();
     }
-  if (!::DeleteFileW(c_str(path_utf16))) {
-    std::error_code EC = mapWindowsError(::GetLastError());
+
     if (EC != errc::no_such_file_or_directory || !IgnoreNonExisting)
       return EC;
   }
   return std::error_code();
 }
 
 static std::error_code is_local_internal(SmallVectorImpl<wchar_t> &Path,
                                          bool &Result) {