From d6c7725be042038003ab13588f0a44acdf356201 Mon Sep 17 00:00:00 2001
From: Denis Petukhov <dapetukhov@mail.ru>
Date: Wed, 26 Aug 2026 00:24:26 +0300
Subject: [PATCH] Add fast path for Overlaps when other is HashSet with same
 equality comparer and has more items

---
 .../src/System/Collections/Generic/HashSet.cs      | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/HashSet.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/HashSet.cs
index 34756784e28b91..43d19da2f9e785 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/HashSet.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/HashSet.cs
@@ -1114,6 +1114,20 @@ public bool Overlaps(IEnumerable<T> other)
                 return true;
             }
 
+            // Fast path for Overlaps when other is HashSet with same equality comparer and has more items
+            if (other is HashSet<T> otherAsSet && EqualityComparersAreEqual(this, otherAsSet) && otherAsSet.Count > Count)
+            {
+                foreach (T element in this)
+                {
+                    if (otherAsSet.Contains(element))
+                    {
+                        return true;
+                    }
+                }
+
+                return false;
+            }
+
             foreach (T element in other)
             {
                 if (Contains(element))