From 492da020cf08e28cbbf6386bc6dcb244fb9fe665 Mon Sep 17 00:00:00 2001
From: Lucy Satheesan <lsatheesan@apple.com>
Date: Tue, 23 May 2023 10:50:00 -0700
Subject: [PATCH 1/2] [gardening] remove superfluous #if

---
 stdlib/public/core/ArraySlice.swift | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/stdlib/public/core/ArraySlice.swift b/stdlib/public/core/ArraySlice.swift
index be6363e3a9483..05eb45ea4ece1 100644
--- a/stdlib/public/core/ArraySlice.swift
+++ b/stdlib/public/core/ArraySlice.swift
@@ -195,11 +195,7 @@ extension ArraySlice {
   func _checkSubscript(
     _ index: Int, wasNativeTypeChecked: Bool
   ) -> _DependenceToken {
-#if _runtime(_ObjC)
     _buffer._checkValidSubscript(index)
-#else
-    _buffer._checkValidSubscript(index)
-#endif
     return _DependenceToken()
   }
 

From ff76106177df00aca1d11af8bdcef411117ecf01 Mon Sep 17 00:00:00 2001
From: Lucy Satheesan <lsatheesan@apple.com>
Date: Tue, 23 May 2023 10:51:49 -0700
Subject: [PATCH 2/2] [stdlib] don't copy array contents on
 `removeAll(keepingCapacity: true)`

---
 stdlib/public/core/Array.swift           | 9 ++++++++-
 stdlib/public/core/ArraySlice.swift      | 9 ++++++++-
 stdlib/public/core/ContiguousArray.swift | 5 ++++-
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/stdlib/public/core/Array.swift b/stdlib/public/core/Array.swift
index 667ccf932e51d..443d2227eeaa7 100644
--- a/stdlib/public/core/Array.swift
+++ b/stdlib/public/core/Array.swift
@@ -1378,9 +1378,16 @@ extension Array: RangeReplaceableCollection {
     if !keepCapacity {
       _buffer = _Buffer()
     }
-    else {
+    else if _buffer.isMutableAndUniquelyReferenced() {
       self.replaceSubrange(indices, with: EmptyCollection())
     }
+    else {
+      let buffer = _ContiguousArrayBuffer<Element>(
+        _uninitializedCount: 0,
+        minimumCapacity: capacity
+      )
+      _buffer = _Buffer(_buffer: buffer, shiftedToStartIndex: startIndex)
+    }
   }
 
   //===--- algorithms -----------------------------------------------------===//
diff --git a/stdlib/public/core/ArraySlice.swift b/stdlib/public/core/ArraySlice.swift
index 05eb45ea4ece1..369f42dd8301d 100644
--- a/stdlib/public/core/ArraySlice.swift
+++ b/stdlib/public/core/ArraySlice.swift
@@ -1067,9 +1067,16 @@ extension ArraySlice: RangeReplaceableCollection {
     if !keepCapacity {
       _buffer = _Buffer()
     }
-    else {
+    else if _buffer.isMutableAndUniquelyReferenced() {
       self.replaceSubrange(indices, with: EmptyCollection())
     }
+    else {
+      let buffer = _ContiguousArrayBuffer<Element>(
+        _uninitializedCount: 0,
+        minimumCapacity: capacity
+      )
+      _buffer = _Buffer(_buffer: buffer, shiftedToStartIndex: startIndex)
+    }
   }
 
   //===--- algorithms -----------------------------------------------------===//
diff --git a/stdlib/public/core/ContiguousArray.swift b/stdlib/public/core/ContiguousArray.swift
index 0d41e4b0f1592..c06d55c61ed7f 100644
--- a/stdlib/public/core/ContiguousArray.swift
+++ b/stdlib/public/core/ContiguousArray.swift
@@ -975,9 +975,12 @@ extension ContiguousArray: RangeReplaceableCollection {
     if !keepCapacity {
       _buffer = _Buffer()
     }
-    else {
+    else if _buffer.isMutableAndUniquelyReferenced() {
       self.replaceSubrange(indices, with: EmptyCollection())
     }
+    else {
+      _buffer = _Buffer(_uninitializedCount: 0, minimumCapacity: capacity)
+    }
   }
 
   //===--- algorithms -----------------------------------------------------===//