<filesystem>: Improve symlink_status performance

[nikola-sh]

_Get_any_status(__Path, __std_fs_stats_flags::_Attributes | __std_fs_stats_flags::_Reparse_tag) calls to many WinAPI functions for regular files or directories. It calls GetFileAttributesEx + CreateFile + GetFileInformationByHandleEx(FileBasicInfo) but GetFileAttributesEx is enough to get all needed data if it is known that a file is not a reparse point.
This problem affects symlink_status performance.

Benchmark symlink_status results before changes:

---------------------------------------------------------
Benchmark               Time             CPU   Iterations
---------------------------------------------------------
symlink_status      15376 ns        15346 ns        44800

Benchmark symlink_status results after changes:

---------------------------------------------------------
Benchmark               Time             CPU   Iterations
---------------------------------------------------------
symlink_status       2219 ns         2148 ns       320000

[Stephan T. Lavavej (StephanTLavavej)]

Thanks! On my system (5950X, 24H2, Samsung SSD 980 PRO), I observe much less of a performance improvement, but still major: 21126 ns => 10098 ns, for a speedup of 2.1x.

[nikola-sh]

Thanks! On my system (5950X, 24H2, Samsung SSD 980 PRO), I observe much less of a performance improvement, but still major: 21126 ns => 10098 ns, for a speedup of 2.1x.

Thank you too!
Yes, performance improvement depends on filesystem minifilter drivers configuration.
For example, for paths on system drive GetFileAttributes works much slower than for paths from other drives.

[Stephan T. Lavavej (StephanTLavavej)]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[Stephan T. Lavavej (StephanTLavavej)]

Thanks again, and congratulations on your first microsoft/STL commit! 😻 🎉 💾

This change is expected to ship in VS 2022 17.13 Preview 3.