Revert "[stdlib] Add custom implementations of removeLast and remove(at:) to Array (#14212)"

This reverts commit 5ed4afe. It
doesn't appear to be correct when the client is compiled with
optimizations (as in, there's a failing bot).

Author: jrose-apple

stdlib/public/core/Arrays.swift.gyb

@@ -1493,6 +1493,17 @@ extension ${Self} : RangeReplaceableCollection, ArrayProtocol {
   }
 
 %if Self == 'ArraySlice':
+  /// Removes and returns the last element of the array.
+  ///
+  /// The array must not be empty. This example removes the last number from an
+  /// array of `Double` values.
+  ///
+  ///     var measurements: [Double] = [1.1, 1.5, 2.9, 1.2, 1.5, 1.3, 1.2]
+  ///     let removed = measurements.removeLast()
+  ///     print(measurements)
+  ///     // Prints "[1.1, 1.5, 2.9, 1.2, 1.5, 1.3]"
+  ///
+  /// - Returns: The element that was removed.
   @_inlineable
   public mutating func _customRemoveLast() -> Element? {
     _precondition(count > 0, "Can't removeLast from an empty ${Self}")
@@ -1508,54 +1519,33 @@ extension ${Self} : RangeReplaceableCollection, ArrayProtocol {
     self.replaceSubrange((i &- 1)..<i, with: EmptyCollection())
     return result
   }
-  
-  /// Removes and returns the element at the specified position.
-  ///
-  /// All the elements following the specified position are moved up to
-  /// close the gap.
+%end
+
+  /// Inserts a new element at the specified position.
   ///
-  ///     var measurements: [Double] = [1.1, 1.5, 2.9, 1.2, 1.5, 1.3, 1.2]
-  ///     let removed = measurements.remove(at: 2)
-  ///     print(measurements)
-  ///     // Prints "[1.1, 1.5, 1.2, 1.5, 1.3, 1.2]"
+  /// The new element is inserted before the element currently at the specified
+  /// index. If you pass the array's `endIndex` property as the `index`
+  /// parameter, the new element is appended to the array.
   ///
-  /// - Parameter index: The position of the element to remove. `index` must
-  ///   be a valid index of the array.
-  /// - Returns: The element at the specified index.
+  ///     var numbers = [1, 2, 3, 4, 5]
+  ///     numbers.insert(100, at: 3)
+  ///     numbers.insert(200, at: numbers.endIndex)
   ///
-  /// - Complexity: O(*n*), where *n* is the length of the array.
-  @_inlineable
-  @discardableResult
-  public mutating func remove(at index: Int) -> Element {
-    let result = self[index]
-    self.replaceSubrange(index..<(index + 1), with: EmptyCollection())
-    return result
-  }
-
-%else:
-  /// Removes and returns the last element of the array.
+  ///     print(numbers)
+  ///     // Prints "[1, 2, 3, 100, 4, 5, 200]"
   ///
-  /// - Returns: The last element of the array if the array is not empty;
-  ///   otherwise, `nil`.
+  /// - Parameter newElement: The new element to insert into the array.
+  /// - Parameter i: The position at which to insert the new element.
+  ///   `index` must be a valid index of the array or equal to its `endIndex`
+  ///   property.
   ///
-  /// - Complexity: O(*n*) if the array is bridged, where *n* is the length
-  ///   of the array; otherwise, O(1).
+  /// - Complexity: O(*n*), where *n* is the length of the array.
   @_inlineable
-  public mutating func popLast() -> Element? {
-    guard !isEmpty else { return nil }
-    return _customRemoveLast().unsafelyUnwrapped
+  public mutating func insert(_ newElement: Element, at i: Int) {
+    _checkIndex(i)
+    self.replaceSubrange(i..<i, with: CollectionOfOne(newElement))
   }
 
-  @_inlineable
-  public mutating func _customRemoveLast() -> Element? {
-    _precondition(!isEmpty, "Can't removeLast from an empty ${Self}")
-    _makeUniqueAndReserveCapacityIfNotUnique()
-    let newCount = _getCount() - 1
-    let pointer = (_buffer.firstElementAddress + newCount)
-    let element = pointer.move()
-    _buffer.count = newCount
-    return element
-  }
   /// Removes and returns the element at the specified position.
   ///
   /// All the elements following the specified position are moved up to
@@ -1574,42 +1564,10 @@ extension ${Self} : RangeReplaceableCollection, ArrayProtocol {
   @_inlineable
   @discardableResult
   public mutating func remove(at index: Int) -> Element {
-    _precondition(index < endIndex, "Index out of range")
-    _precondition(index >= startIndex, "Index out of range")
-    _makeUniqueAndReserveCapacityIfNotUnique()
-    let newCount = _getCount() - 1
-    let pointer = (_buffer.firstElementAddress + index)
-    let result = pointer.move()
-    pointer.moveInitialize(from: pointer + 1, count: newCount - index)
-    _buffer.count = newCount
+    let result = self[index]
+    self.replaceSubrange(index..<(index + 1), with: EmptyCollection())
     return result
   }
-%end
-
-  /// Inserts a new element at the specified position.
-  ///
-  /// The new element is inserted before the element currently at the specified
-  /// index. If you pass the array's `endIndex` property as the `index`
-  /// parameter, the new element is appended to the array.
-  ///
-  ///     var numbers = [1, 2, 3, 4, 5]
-  ///     numbers.insert(100, at: 3)
-  ///     numbers.insert(200, at: numbers.endIndex)
-  ///
-  ///     print(numbers)
-  ///     // Prints "[1, 2, 3, 100, 4, 5, 200]"
-  ///
-  /// - Parameter newElement: The new element to insert into the array.
-  /// - Parameter i: The position at which to insert the new element.
-  ///   `index` must be a valid index of the array or equal to its `endIndex`
-  ///   property.
-  ///
-  /// - Complexity: O(*n*), where *n* is the length of the array.
-  @_inlineable
-  public mutating func insert(_ newElement: Element, at i: Int) {
-    _checkIndex(i)
-    self.replaceSubrange(i..<i, with: CollectionOfOne(newElement))
-  }
 
   /// Removes all elements from the array.
   ///
@@ -2400,6 +2358,35 @@ extension Array {
 }
 #endif
 
+extension Array {
+  /// Removes and returns the last element of the array.
+  ///
+  /// - Returns: The last element of the array if the array is not empty;
+  ///   otherwise, `nil`.
+  ///
+  /// - Complexity: O(*n*) if the array is bridged, where *n* is the length
+  ///   of the array; otherwise, O(1).
+  @_inlineable
+  public mutating func popLast() -> Element? {
+    guard !isEmpty else { return nil }
+    return removeLast()
+  }
+}
+
+extension ContiguousArray {
+  /// Removes and returns the last element of the array.
+  ///
+  /// - Returns: The last element of the array if the array is not empty;
+  ///   otherwise, `nil`.
+  ///
+  /// - Complexity: O(1)
+  @_inlineable
+  public mutating func popLast() -> Element? {
+    guard !isEmpty else { return nil }
+    return removeLast()
+  }
+}
+
 extension ArraySlice {
   @_inlineable
   public // @testable