From 828225cbc23682b376fd958d84f9ebfa6c575d77 Mon Sep 17 00:00:00 2001
From: Ben Adams <thundercat@illyriad.co.uk>
Date: Wed, 22 Feb 2017 00:51:08 +0000
Subject: [PATCH] Faster List Add

---
 .../src/System/Collections/Generic/List.cs    | 30 +++++++++++++++++--
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/mscorlib/src/System/Collections/Generic/List.cs b/src/mscorlib/src/System/Collections/Generic/List.cs
index 82f6e41c361e..6eeda8df078c 100644
--- a/src/mscorlib/src/System/Collections/Generic/List.cs
+++ b/src/mscorlib/src/System/Collections/Generic/List.cs
@@ -208,10 +208,34 @@ public class List<T> : IList<T>, System.Collections.IList, IReadOnlyList<T>
         // increased by one. If required, the capacity of the list is doubled
         // before adding the new element.
         //
-        public void Add(T item) {
-            if (_size == _items.Length) EnsureCapacity(_size + 1);
-            _items[_size++] = item;
+        public void Add(T item)
+        {
+            if (_size < _items.Length)
+            {
+                AddWithoutResize(item);
+            }
+            else
+            {
+                AddWithResize(item);
+            }
+        }
+
+        private void AddWithoutResize(T item)
+        {
+            var size = _size;
+            _version++;
+            _size = size + 1;
+            _items[size] = item;
+        }
+
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        private void AddWithResize(T item)
+        {
+            var size = _size;
             _version++;
+            _size = size + 1;
+            EnsureCapacity(size + 1);
+            _items[size] = item;
         }
 
         int System.Collections.IList.Add(Object item)