From 87bd1fa32502d94088bc7e227d5c28a92b2a3620 Mon Sep 17 00:00:00 2001
From: prozolic <42107886+prozolic@users.noreply.github.com>
Date: Thu, 4 Jun 2026 23:14:42 +0900
Subject: [PATCH] Reduce redundant lookup in OrderedDictionary.Remove

Reduce a redundant lookup in
`OrderedDictionary<TKey, TValue>.Remove(KeyValuePair<TKey, TValue>)`
by using the index obtained from `TryGetValue` to call `RemoveAt`.
Also remove a duplicated null check in `IDictionary.Add`.
---
 .../Collections/Generic/OrderedDictionary.cs  | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/src/libraries/System.Collections/src/System/Collections/Generic/OrderedDictionary.cs b/src/libraries/System.Collections/src/System/Collections/Generic/OrderedDictionary.cs
index 58d8f2e4fef46f..0bacc72b32f4d3 100644
--- a/src/libraries/System.Collections/src/System/Collections/Generic/OrderedDictionary.cs
+++ b/src/libraries/System.Collections/src/System/Collections/Generic/OrderedDictionary.cs
@@ -1218,10 +1218,16 @@ void ICollection<KeyValuePair<TKey, TValue>>.CopyTo(KeyValuePair<TKey, TValue>[]
         }
 
         /// <inheritdoc/>
-        bool ICollection<KeyValuePair<TKey, TValue>>.Remove(KeyValuePair<TKey, TValue> item) =>
-            TryGetValue(item.Key, out TValue? value) &&
-            EqualityComparer<TValue>.Default.Equals(value, item.Value) &&
-            Remove(item.Key);
+        bool ICollection<KeyValuePair<TKey, TValue>>.Remove(KeyValuePair<TKey, TValue> item)
+        {
+            if (TryGetValue(item.Key, out TValue? value, out int index) && EqualityComparer<TValue>.Default.Equals(value, item.Value))
+            {
+                RemoveAt(index);
+                return true;
+            }
+
+            return false;
+        }
 
         /// <inheritdoc/>
         void IDictionary.Add(object key, object? value)
@@ -1237,11 +1243,6 @@ void IDictionary.Add(object key, object? value)
                 throw new ArgumentException(SR.Format(SR.Arg_WrongType, key, typeof(TKey)), nameof(key));
             }
 
-            if (default(TValue) is not null)
-            {
-                ArgumentNullException.ThrowIfNull(value);
-            }
-
             TValue tvalue = default!;
             if (value is not null)
             {