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

[Haydn Trigg via llvm-commits]

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

>From 5543af058a18b5deda18e3e5171eb6076f7132f7 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 | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Support/Windows/Path.inc b/llvm/lib/Support/Windows/Path.inc
index 2bf68b7972e746..80be44fbdd05c1 100644
--- a/llvm/lib/Support/Windows/Path.inc
+++ b/llvm/lib/Support/Windows/Path.inc
@@ -777,14 +777,16 @@ 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.