From fbadbf137e24dd0e3ecfd93943b78e58ed4faff0 Mon Sep 17 00:00:00 2001
From: Stephen Toub <stoub@microsoft.com>
Date: Sat, 13 Feb 2021 21:38:29 -0500
Subject: [PATCH] Optimize Enumerable.Min/Max<T> with Comparer<T>.Default
 intrinsic

---
 src/libraries/System.Linq/src/System/Linq/Max.cs | 13 +++++--------
 src/libraries/System.Linq/src/System/Linq/Min.cs | 13 +++++--------
 2 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/src/libraries/System.Linq/src/System/Linq/Max.cs b/src/libraries/System.Linq/src/System/Linq/Max.cs
index 9dc4c92cd1f865..0e9c4c0476ae0c 100644
--- a/src/libraries/System.Linq/src/System/Linq/Max.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Max.cs
@@ -448,11 +448,10 @@ public static decimal Max(this IEnumerable<decimal> source)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
             }
 
-            Comparer<TSource> comparer = Comparer<TSource>.Default;
             TSource? value = default;
-            if (value == null)
+            using (IEnumerator<TSource> e = source.GetEnumerator())
             {
-                using (IEnumerator<TSource> e = source.GetEnumerator())
+                if (value == null)
                 {
                     do
                     {
@@ -465,6 +464,7 @@ public static decimal Max(this IEnumerable<decimal> source)
                     }
                     while (value == null);
 
+                    Comparer<TSource> comparer = Comparer<TSource>.Default;
                     while (e.MoveNext())
                     {
                         TSource x = e.Current;
@@ -474,10 +474,7 @@ public static decimal Max(this IEnumerable<decimal> source)
                         }
                     }
                 }
-            }
-            else
-            {
-                using (IEnumerator<TSource> e = source.GetEnumerator())
+                else
                 {
                     if (!e.MoveNext())
                     {
@@ -488,7 +485,7 @@ public static decimal Max(this IEnumerable<decimal> source)
                     while (e.MoveNext())
                     {
                         TSource x = e.Current;
-                        if (comparer.Compare(x, value) > 0)
+                        if (Comparer<TSource>.Default.Compare(x, value) > 0)
                         {
                             value = x;
                         }
diff --git a/src/libraries/System.Linq/src/System/Linq/Min.cs b/src/libraries/System.Linq/src/System/Linq/Min.cs
index 9958c8468bec44..f8c7f3bec469be 100644
--- a/src/libraries/System.Linq/src/System/Linq/Min.cs
+++ b/src/libraries/System.Linq/src/System/Linq/Min.cs
@@ -406,11 +406,10 @@ public static decimal Min(this IEnumerable<decimal> source)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
             }
 
-            Comparer<TSource> comparer = Comparer<TSource>.Default;
             TSource? value = default;
-            if (value == null)
+            using (IEnumerator<TSource> e = source.GetEnumerator())
             {
-                using (IEnumerator<TSource> e = source.GetEnumerator())
+                if (value == null)
                 {
                     do
                     {
@@ -423,6 +422,7 @@ public static decimal Min(this IEnumerable<decimal> source)
                     }
                     while (value == null);
 
+                    Comparer<TSource> comparer = Comparer<TSource>.Default;
                     while (e.MoveNext())
                     {
                         TSource x = e.Current;
@@ -432,10 +432,7 @@ public static decimal Min(this IEnumerable<decimal> source)
                         }
                     }
                 }
-            }
-            else
-            {
-                using (IEnumerator<TSource> e = source.GetEnumerator())
+                else
                 {
                     if (!e.MoveNext())
                     {
@@ -446,7 +443,7 @@ public static decimal Min(this IEnumerable<decimal> source)
                     while (e.MoveNext())
                     {
                         TSource x = e.Current;
-                        if (comparer.Compare(x, value) < 0)
+                        if (Comparer<TSource>.Default.Compare(x, value) < 0)
                         {
                             value = x;
                         }