From d018afa90151ee43078ffc617734ec198ea17aa6 Mon Sep 17 00:00:00 2001
From: Andy Ayers <andya@microsoft.com>
Date: Fri, 21 Jul 2023 08:31:28 -0700
Subject: [PATCH 1/2] Block inlining of IntroSort

With PGO and (via #88749) one level of recursive inlining enabled, the jit sees
the recursive call made by `IntroSort` as an attractive inline candidate,
but it isn't.

Fixes #89106.
---
 src/libraries/System.Private.CoreLib/src/System/Array.cs        | 2 ++
 .../src/System/Collections/Generic/ArraySortHelper.cs           | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Array.cs b/src/libraries/System.Private.CoreLib/src/System/Array.cs
index 313b064fc9e676..5ba66adf90c18b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Array.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Array.cs
@@ -2207,6 +2207,7 @@ private void IntrospectiveSort(int left, int length)
                 }
             }
 
+            [MethodImpl(MethodImplOptions.NoInlining)]
             private void IntroSort(int lo, int hi, int depthLimit)
             {
                 Debug.Assert(hi >= lo);
@@ -2421,6 +2422,7 @@ private void IntrospectiveSort(int left, int length)
                 }
             }
 
+            [MethodImpl(MethodImplOptions.NoInlining)]
             private void IntroSort(int lo, int hi, int depthLimit)
             {
                 Debug.Assert(hi >= lo);
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.cs
index cf481d8999649a..5a65f6e5a97245 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.cs
@@ -128,6 +128,7 @@ internal static void IntrospectiveSort(Span<T> keys, Comparison<T> comparer)
             }
         }
 
+        [MethodImpl(MethodImplOptions.NoInlining)]
         private static void IntroSort(Span<T> keys, int depthLimit, Comparison<T> comparer)
         {
             Debug.Assert(!keys.IsEmpty);
@@ -402,6 +403,7 @@ private static void Swap(ref T i, ref T j)
             j = t;
         }
 
+        [MethodImpl(MethodImplOptions.NoInlining)]
         private static void IntroSort(Span<T> keys, int depthLimit)
         {
             Debug.Assert(!keys.IsEmpty);

From e15846f347997698dc75c7fb6647784aa622ca74 Mon Sep 17 00:00:00 2001
From: Andy Ayers <andya@microsoft.com>
Date: Fri, 21 Jul 2023 09:39:52 -0700
Subject: [PATCH 2/2] add comment

---
 src/libraries/System.Private.CoreLib/src/System/Array.cs      | 4 ++++
 .../src/System/Collections/Generic/ArraySortHelper.cs         | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Array.cs b/src/libraries/System.Private.CoreLib/src/System/Array.cs
index 5ba66adf90c18b..cecfcf12ccf9aa 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Array.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Array.cs
@@ -2207,6 +2207,8 @@ private void IntrospectiveSort(int left, int length)
                 }
             }
 
+            // IntroSort is recursive; block it from being inlined into itself as
+            // this is currenly not profitable.
             [MethodImpl(MethodImplOptions.NoInlining)]
             private void IntroSort(int lo, int hi, int depthLimit)
             {
@@ -2422,6 +2424,8 @@ private void IntrospectiveSort(int left, int length)
                 }
             }
 
+            // IntroSort is recursive; block it from being inlined into itself as
+            // this is currenly not profitable.
             [MethodImpl(MethodImplOptions.NoInlining)]
             private void IntroSort(int lo, int hi, int depthLimit)
             {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.cs b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.cs
index 5a65f6e5a97245..1d937f4b853369 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Collections/Generic/ArraySortHelper.cs
@@ -128,6 +128,8 @@ internal static void IntrospectiveSort(Span<T> keys, Comparison<T> comparer)
             }
         }
 
+        // IntroSort is recursive; block it from being inlined into itself as
+        // this is currenly not profitable.
         [MethodImpl(MethodImplOptions.NoInlining)]
         private static void IntroSort(Span<T> keys, int depthLimit, Comparison<T> comparer)
         {
@@ -403,6 +405,8 @@ private static void Swap(ref T i, ref T j)
             j = t;
         }
 
+        // IntroSort is recursive; block it from being inlined into itself as
+        // this is currenly not profitable.
         [MethodImpl(MethodImplOptions.NoInlining)]
         private static void IntroSort(Span<T> keys, int depthLimit)
         {