diff --git a/stdlib/public/core/Array.swift b/stdlib/public/core/Array.swift
index 2a03a8d64dc65..859e301e52867 100644
--- a/stdlib/public/core/Array.swift
+++ b/stdlib/public/core/Array.swift
@@ -1202,6 +1202,48 @@ extension Array: RangeReplaceableCollection {
     _appendElementAssumeUniqueAndCapacity(oldCount, newElement: newElement)
     _endMutation()
   }
+  
+  /// Adds the elements of a collection to the end of the array.
+  ///
+  /// Use this method to append the elements of a collection to the end of this
+  /// array. This example appends the elements of a `Range<Int>` instance
+  /// to an array of integers.
+  ///
+  ///     var numbers = [1, 2, 3, 4, 5]
+  ///     numbers.append(contentsOf: 10...15)
+  ///     print(numbers)
+  ///     // Prints "[1, 2, 3, 4, 5, 10, 11, 12, 13, 14, 15]"
+  ///
+  /// - Parameter newElements: The elements to append to the array.
+  ///
+  /// - Complexity: O(*m*) on average, where *m* is the length of
+  ///   `newElements`, over many calls to `append(contentsOf:)` on the same
+  ///   array.
+  @_alwaysEmitIntoClient
+  @_semantics("array.append_contentsOf")
+  @_effects(notEscaping self.value**)
+  public mutating func append(contentsOf newElements: __owned some Collection<Element>) {
+    let newElementsCount = newElements.count
+    // This check prevents a data race writing to _swiftEmptyArrayStorage
+    if newElementsCount == 0 {
+      return
+    }
+    defer {
+      _endMutation()
+    }
+    _reserveCapacityImpl(minimumCapacity: self.count + newElementsCount,
+                         growForAppend: true)
+
+    let oldCount = _buffer.mutableCount
+    let startNewElements = _buffer.mutableFirstElementAddress + oldCount
+    let buf = UnsafeMutableBufferPointer(
+                start: startNewElements,
+                count: newElementsCount)
+    _debugPrecondition(buf.endIndex <= _buffer.mutableCapacity)
+    let end = buf.initialize(fromContentsOf: newElements)
+    _precondition(end == buf.endIndex)
+    _buffer.mutableCount = _buffer.mutableCount + newElementsCount
+  }
 
   /// Adds the elements of a sequence to the end of the array.
   ///
@@ -1225,6 +1267,14 @@ extension Array: RangeReplaceableCollection {
   public mutating func append<S: Sequence>(contentsOf newElements: __owned S)
     where S.Element == Element {
 
+    let wasContiguous = newElements.withContiguousStorageIfAvailable {
+      append(contentsOf: $0)
+      return true
+    }
+    if wasContiguous != nil {
+      return
+    }
+      
     defer {
       _endMutation()
     }
diff --git a/stdlib/public/core/ArraySlice.swift b/stdlib/public/core/ArraySlice.swift
index 6c213c31c3a26..9b58f06464bbe 100644
--- a/stdlib/public/core/ArraySlice.swift
+++ b/stdlib/public/core/ArraySlice.swift
@@ -925,6 +925,47 @@ extension ArraySlice: RangeReplaceableCollection {
     _appendElementAssumeUniqueAndCapacity(oldCount, newElement: newElement)
     _endMutation()
   }
+  
+  /// Adds the elements of a collection to the end of the array.
+  ///
+  /// Use this method to append the elements of a collection to the end of this
+  /// array. This example appends the elements of a `Range<Int>` instance
+  /// to an array of integers.
+  ///
+  ///     var numbers = [1, 2, 3, 4, 5]
+  ///     numbers.append(contentsOf: 10...15)
+  ///     print(numbers)
+  ///     // Prints "[1, 2, 3, 4, 5, 10, 11, 12, 13, 14, 15]"
+  ///
+  /// - Parameter newElements: The elements to append to the array.
+  ///
+  /// - Complexity: O(*m*) on average, where *m* is the length of
+  ///   `newElements`, over many calls to `append(contentsOf:)` on the same
+  ///   array.
+  @_alwaysEmitIntoClient
+  @_semantics("array.append_contentsOf")
+  public mutating func append(contentsOf newElements: __owned some Collection<Element>) {
+    let newElementsCount = newElements.count
+    // This check prevents a data race writing to _swiftEmptyArrayStorage
+    if newElementsCount == 0 {
+      return
+    }
+    defer {
+      _endMutation()
+    }
+    reserveCapacityForAppend(newElementsCount: newElementsCount)
+    _ = _buffer.beginCOWMutation()
+
+    let oldCount = self.count
+    let startNewElements = _buffer.firstElementAddress + oldCount
+    let buf = UnsafeMutableBufferPointer(
+                start: startNewElements,
+                count: newElementsCount)
+    _debugPrecondition(buf.endIndex <= self.capacity)
+    let end = buf.initialize(fromContentsOf: newElements)
+    _precondition(end == buf.endIndex)
+    _buffer.count += newElementsCount
+  }
 
   /// Adds the elements of a sequence to the end of the array.
   ///
@@ -947,6 +988,17 @@ extension ArraySlice: RangeReplaceableCollection {
   public mutating func append<S: Sequence>(contentsOf newElements: __owned S)
     where S.Element == Element {
 
+    let wasContiguous = newElements.withContiguousStorageIfAvailable {
+      append(contentsOf: $0)
+      return true
+    }
+    if wasContiguous != nil {
+      return
+    }
+      
+    defer {
+      _endMutation()
+    }
     let newElementsCount = newElements.underestimatedCount
     reserveCapacityForAppend(newElementsCount: newElementsCount)
     _ = _buffer.beginCOWMutation()
@@ -975,7 +1027,6 @@ extension ArraySlice: RangeReplaceableCollection {
       // append them in slow sequence-only mode
       _buffer._arrayAppendSequence(IteratorSequence(remainder))
     }
-    _endMutation()
   }
 
   @inlinable
diff --git a/stdlib/public/core/ContiguousArray.swift b/stdlib/public/core/ContiguousArray.swift
index 3c7cf01fea388..0c5ca1ec4c300 100644
--- a/stdlib/public/core/ContiguousArray.swift
+++ b/stdlib/public/core/ContiguousArray.swift
@@ -815,6 +815,50 @@ extension ContiguousArray: RangeReplaceableCollection {
     _appendElementAssumeUniqueAndCapacity(oldCount, newElement: newElement)
     _endMutation()
   }
+  
+  /// Adds the elements of a sequence to the end of the array.
+  ///
+  /// Use this method to append the elements of a sequence to the end of this
+  /// array. This example appends the elements of a `Range<Int>` instance
+  /// to an array of integers.
+  ///
+  ///     var numbers = [1, 2, 3, 4, 5]
+  ///     numbers.append(contentsOf: 10...15)
+  ///     print(numbers)
+  ///     // Prints "[1, 2, 3, 4, 5, 10, 11, 12, 13, 14, 15]"
+  ///
+  /// - Parameter newElements: The elements to append to the array.
+  ///
+  /// - Complexity: O(*m*) on average, where *m* is the length of
+  ///   `newElements`, over many calls to `append(contentsOf:)` on the same
+  ///   array.
+  @_alwaysEmitIntoClient
+  @_semantics("array.append_contentsOf")
+  public mutating func append(
+    contentsOf newElements: __owned some Collection<Element>
+  ) {
+    let newElementsCount = newElements.count
+    // This check prevents a data race writing to _swiftEmptyArrayStorage
+    if newElementsCount == 0 {
+      return
+    }
+    defer {
+      _endMutation()
+    }
+
+    _reserveCapacityImpl(minimumCapacity: self.count + newElementsCount,
+                         growForAppend: true)
+
+    let oldCount = _buffer.mutableCount
+    let startNewElements = _buffer.mutableFirstElementAddress + oldCount
+    let buf = UnsafeMutableBufferPointer(
+                start: startNewElements,
+                count: newElementsCount)
+    _debugPrecondition(buf.endIndex <= _buffer.mutableCapacity)
+    let end = buf.initialize(fromContentsOf: newElements)
+    _precondition(end == buf.endIndex)
+    _buffer.count += newElementsCount
+  }
 
   /// Adds the elements of a sequence to the end of the array.
   ///
@@ -836,6 +880,14 @@ extension ContiguousArray: RangeReplaceableCollection {
   @_semantics("array.append_contentsOf")
   public mutating func append<S: Sequence>(contentsOf newElements: __owned S)
     where S.Element == Element {
+      
+    let wasContiguous = newElements.withContiguousStorageIfAvailable {
+      append(contentsOf: $0)
+      return true
+    }
+    if wasContiguous != nil {
+      return
+    }
 
     defer {
       _endMutation()
diff --git a/stdlib/public/core/ContiguousArrayBuffer.swift b/stdlib/public/core/ContiguousArrayBuffer.swift
index 0796d97668071..3fe4882ca39f4 100644
--- a/stdlib/public/core/ContiguousArrayBuffer.swift
+++ b/stdlib/public/core/ContiguousArrayBuffer.swift
@@ -1063,6 +1063,12 @@ extension Sequence {
 internal func _copySequenceToContiguousArray<
   S: Sequence
 >(_ source: S) -> ContiguousArray<S.Element> {
+  let contigArray = source.withContiguousStorageIfAvailable {
+    _copyCollectionToContiguousArray($0)
+  }
+  if let contigArray {
+    return contigArray
+  }
   let initialCapacity = source.underestimatedCount
   var builder =
     _UnsafePartiallyInitializedContiguousArrayBuffer<S.Element>(
diff --git a/test/SILOptimizer/array_contentof_opt.swift b/test/SILOptimizer/array_contentof_opt.swift
index 4671fd11631ad..48e26633cc773 100644
--- a/test/SILOptimizer/array_contentof_opt.swift
+++ b/test/SILOptimizer/array_contentof_opt.swift
@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -O -sil-verify-all -emit-sil -Xllvm '-sil-inline-never-functions=$sSa6appendyy' -Xllvm -sil-inline-never-function='$sSa6append10contentsOfyqd__n_t7ElementQyd__RszSTRd__lFSi_SaySiGTg5' %s | %FileCheck %s
+// RUN: %target-swift-frontend -O -sil-verify-all -emit-sil -Xllvm '-sil-inline-never-functions=$sSa6appendyy' -Xllvm -sil-inline-never-function='$sSa6append10contentsOfyqd__n_t7ElementQyd__RszSlRd__lFSi_SaySiGTg5' %s | %FileCheck %s
 // REQUIRES: swift_stdlib_no_asserts,optimized_stdlib
 
 // This is an end-to-end test of the Array.append(contentsOf:) ->
@@ -63,7 +63,7 @@ public func dontPropagateContiguousArray(_ a: inout ContiguousArray<UInt8>) {
 
 // Check if the specialized Array.append<A>(contentsOf:) is reasonably optimized for Array<Int>.
 
-// CHECK-LABEL: sil shared {{.*}}@$sSa6append10contentsOfyqd__n_t7ElementQyd__RszSTRd__lFSi_SaySiGTg5
+// CHECK-LABEL: sil shared {{.*}}@$sSa6append10contentsOfyqd__n_t7ElementQyd__RszSlRd__lFSi_SaySiGTg5
 
 // There should only be a single call to _createNewBuffer or reserveCapacityForAppend/reserveCapacityImpl.
 
@@ -72,5 +72,5 @@ public func dontPropagateContiguousArray(_ a: inout ContiguousArray<UInt8>) {
 // CHECK: apply [[F]]
 // CHECK-NOT: apply
 
-// CHECK-LABEL: } // end sil function '$sSa6append10contentsOfyqd__n_t7ElementQyd__RszSTRd__lFSi_SaySiGTg5
+// CHECK-LABEL: } // end sil function '$sSa6append10contentsOfyqd__n_t7ElementQyd__RszSlRd__lFSi_SaySiGTg5