[llvm] Windows Filesystem fs::status Conditionally Call GetFileAttributes (PR #78118)

[Haydn Trigg via llvm-commits]

https://github.com/HaydnTrigg created https://github.com/llvm/llvm-project/pull/78118

Rather than conditionally using the output from GetFileAttributesW move the branch to avoid calling GetFileAttributesW entirely if not required. This avoids hitting IO an extra time for a small performance improvement.

>From 4fce203eec1918888a624547345948e1e3d6ac61 Mon Sep 17 00:00:00 2001
From: Haydn Trigg <me at haydntrigg.com>
Date: Mon, 15 Jan 2024 13:12:54 +1030
Subject: [PATCH] fs::status Conditionally call GetFileAttributes

Rather than conditionally using the output from GetFileAttributesW move the branch to avoid calling GetFileAttributesW entirely if not required. This avoids hitting IO an extra time for a small performance improvement.
---
 llvm/lib/Support/Windows/Path.inc | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Support/Windows/Path.inc b/llvm/lib/Support/Windows/Path.inc
index 2bf68b7972e746..6598586545ddd0 100644
--- a/llvm/lib/Support/Windows/Path.inc
+++ b/llvm/lib/Support/Windows/Path.inc
@@ -777,14 +777,15 @@ std::error_code status(const Twine &path, file_status &result, bool Follow) {
   if (std::error_code ec = widenPath(path8, path_utf16))
     return ec;
 
-  DWORD attr = ::GetFileAttributesW(path_utf16.begin());
-  if (attr == INVALID_FILE_ATTRIBUTES)
-    return getStatus(INVALID_HANDLE_VALUE, result);
-
-  DWORD Flags = FILE_FLAG_BACKUP_SEMANTICS;
-  // Handle reparse points.
-  if (!Follow && (attr & FILE_ATTRIBUTE_REPARSE_POINT))
-    Flags |= FILE_FLAG_OPEN_REPARSE_POINT;
+  if (!Follow) {
+    DWORD attr = ::GetFileAttributesW(path_utf16.begin());
+    if (attr == INVALID_FILE_ATTRIBUTES)
+      return getStatus(INVALID_HANDLE_VALUE, result);
+    
+    // Handle reparse points.
+    if (attr & FILE_ATTRIBUTE_REPARSE_POINT)
+      Flags |= FILE_FLAG_OPEN_REPARSE_POINT;
+  }
 
   ScopedFileHandle h(
       ::CreateFileW(path_utf16.begin(), 0, // Attributes only.