From 1f593d39c47fab0510dd015d0886f9ad0f831575 Mon Sep 17 00:00:00 2001
From: yesmey <jesper.meyr@gmail.com>
Date: Sun, 27 Mar 2022 22:51:06 +0200
Subject: [PATCH] Allow List to be unrolled/vectorized in IEnumerable
 SequenceEqual

---
 src/libraries/System.Linq/src/System/Linq/Enumerable.cs   | 8 +++++---
 .../System.Linq/src/System/Linq/SequenceEqual.cs          | 4 ++--
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/libraries/System.Linq/src/System/Linq/Enumerable.cs b/src/libraries/System.Linq/src/System/Linq/Enumerable.cs
index 6e3b2d772609dd..368794f747e7ea 100644
--- a/src/libraries/System.Linq/src/System/Linq/Enumerable.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Enumerable.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
@@ -14,12 +15,13 @@ public static partial class Enumerable
         /// <summary>Validates that source is not null and then tries to extract a span from the source.</summary>
         [MethodImpl(MethodImplOptions.AggressiveInlining)] // fast type checks that don't add a lot of overhead
         private static bool TryGetSpan<TSource>(this IEnumerable<TSource> source, out ReadOnlySpan<TSource> span)
+        {
             // This constraint isn't required, but the overheads involved here can be more substantial when TSource
-            // is a reference type and generic implementations are shared.  So for now we're protecting ourselves
+            // is a reference type and generic implementations are shared. So for now we're protecting ourselves
             // and forcing a conscious choice to remove this in the future, at which point it should be paired with
             // sufficient performance testing.
-            where TSource : struct
-        {
+            Debug.Assert(typeof(TSource).IsValueType);
+
             if (source is null)
             {
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
diff --git a/src/libraries/System.Linq/src/System/Linq/SequenceEqual.cs b/src/libraries/System.Linq/src/System/Linq/SequenceEqual.cs
index d1d6dc1586b0f5..5badacd1118c7d 100644
--- a/src/libraries/System.Linq/src/System/Linq/SequenceEqual.cs
+++ b/src/libraries/System.Linq/src/System/Linq/SequenceEqual.cs
@@ -24,9 +24,9 @@ public static bool SequenceEqual<TSource>(this IEnumerable<TSource> first, IEnum
 
             if (first is ICollection<TSource> firstCol && second is ICollection<TSource> secondCol)
             {
-                if (first is TSource[] firstArray && second is TSource[] secondArray)
+                if (typeof(TSource).IsValueType && first.TryGetSpan(out ReadOnlySpan<TSource> firstSpan) && second.TryGetSpan(out ReadOnlySpan<TSource> secondSpan))
                 {
-                    return ((ReadOnlySpan<TSource>)firstArray).SequenceEqual(secondArray, comparer);
+                    return firstSpan.SequenceEqual(secondSpan, comparer);
                 }
 
                 if (firstCol.Count != secondCol.Count)