Remove "illegal" UnsafePointer casts from the stdlib.

Update for SE-0107: UnsafeRawPointer This adds a "mutating" initialize to UnsafePointer to make Immutable -> Mutable conversions explicit. These are quick fixes to stdlib, overlays, and test cases that are necessary in order to remove arbitrary UnsafePointer conversions. Many cases can be expressed better up by reworking the surrounding code, but we first need a working starting point.
2025-12-14 20:36:38 +01:00 · 2016-07-26 22:39:58 -07:00
parent 178d194aa1
commit 0b75ee975e
41 changed files with 418 additions and 326 deletions
--- a/stdlib/private/SwiftPrivateLibcExtras/SwiftPrivateLibcExtras.swift
+++ b/stdlib/private/SwiftPrivateLibcExtras/SwiftPrivateLibcExtras.swift
@@ -97,11 +97,17 @@ public func _stdlib_select(
        let readAddr = readfds.baseAddress
        let writeAddr = writefds.baseAddress
        let errorAddr = errorfds.baseAddress
+        func asFdSetPtr(
+          _ p: UnsafeMutablePointer<UInt>?
+        ) -> UnsafeMutablePointer<fd_set>? {
+          return UnsafeMutableRawPointer(p)?
+            .assumingMemoryBound(to: fd_set.self)
+        }
        return select(
          _stdlib_FD_SETSIZE,
-          UnsafeMutablePointer(readAddr),
-          UnsafeMutablePointer(writeAddr),
-          UnsafeMutablePointer(errorAddr),
+          asFdSetPtr(readAddr),
+          asFdSetPtr(writeAddr),
+          asFdSetPtr(errorAddr),
          timeout)
      }
    }
--- a/stdlib/private/SwiftPrivatePthreadExtras/SwiftPrivatePthreadExtras.swift
+++ b/stdlib/private/SwiftPrivatePthreadExtras/SwiftPrivatePthreadExtras.swift
@@ -113,7 +113,8 @@ public class _stdlib_Barrier {
  var _pthreadBarrier: _stdlib_pthread_barrier_t

  var _pthreadBarrierPtr: UnsafeMutablePointer<_stdlib_pthread_barrier_t> {
-    return UnsafeMutablePointer(_getUnsafePointerToStoredProperties(self))
+    return _getUnsafePointerToStoredProperties(self)
+      .assumingMemoryBound(to: _stdlib_pthread_barrier_t.self)
  }

  public init(threadCount: Int) {
--- a/stdlib/public/SDK/Dispatch/Data.swift
+++ b/stdlib/public/SDK/Dispatch/Data.swift
@@ -114,10 +114,12 @@ public struct DispatchData : RandomAccessCollection, _ObjectiveCBridgeable {
 	///
 	/// - parameter buffer: The buffer of bytes to append. The size is calculated from `SourceType` and `buffer.count`.
 	public mutating func append<SourceType>(_ buffer : UnsafeBufferPointer<SourceType>) {
-		self.append(UnsafePointer(buffer.baseAddress!), count: buffer.count * sizeof(SourceType.self))
+		buffer.baseAddress!.withMemoryRebound(to: UInt8.self, capacity: buffer.count * strideof(SourceType.self)) {
+			self.append($0, count: buffer.count * sizeof(SourceType.self))
+		}
 	}

-	private func _copyBytesHelper(to pointer: UnsafeMutablePointer<UInt8>, from range: CountableRange<Index>) {
+	private func _copyBytesHelper(to pointer: UnsafeMutableRawPointer, from range: CountableRange<Index>) {
 		var copiedCount = 0
 		__dispatch_data_apply(__wrapped) { (data: __DispatchData, offset: Int, ptr: UnsafeRawPointer, size: Int) in
 			let limit = Swift.min((range.endIndex - range.startIndex) - copiedCount, size)
@@ -172,8 +174,7 @@ public struct DispatchData : RandomAccessCollection, _ObjectiveCBridgeable {
 		
 		guard !copyRange.isEmpty else { return 0 }
 		
-		let pointer : UnsafeMutablePointer<UInt8> = UnsafeMutablePointer<UInt8>(buffer.baseAddress!)
-		_copyBytesHelper(to: pointer, from: copyRange)
+		_copyBytesHelper(to: buffer.baseAddress!, from: copyRange)
 		return copyRange.count
 	}

--- a/stdlib/public/SDK/Foundation/Data.swift
+++ b/stdlib/public/SDK/Foundation/Data.swift
@@ -314,7 +314,7 @@ public struct Data : ReferenceConvertible, Equatable, Hashable, RandomAccessColl
        _mapUnmanaged { $0.getBytes(pointer, length: count) }
    }
    
-    private func _copyBytesHelper(to pointer: UnsafeMutablePointer<UInt8>, from range: NSRange) {
+    private func _copyBytesHelper(to pointer: UnsafeMutableRawPointer, from range: NSRange) {
        _mapUnmanaged { $0.getBytes(pointer, range: range) }
    }
    
@@ -355,8 +355,7 @@ public struct Data : ReferenceConvertible, Equatable, Hashable, RandomAccessColl
        guard !copyRange.isEmpty else { return 0 }
        
        let nsRange = NSMakeRange(copyRange.lowerBound, copyRange.upperBound - copyRange.lowerBound)
-        let pointer : UnsafeMutablePointer<UInt8> = UnsafeMutablePointer<UInt8>(buffer.baseAddress!)
-        _copyBytesHelper(to: pointer, from: nsRange)
+        _copyBytesHelper(to: buffer.baseAddress!, from: nsRange)
        return copyRange.count
    }
    
--- a/stdlib/public/SDK/Foundation/NSStringAPI.swift
+++ b/stdlib/public/SDK/Foundation/NSStringAPI.swift
@@ -387,12 +387,10 @@ extension String {
        outputArray in
        // FIXME: completePath(...) is incorrectly annotated as requiring
        // non-optional output parameters. rdar://problem/25494184
-        let outputNonOptionalName = AutoreleasingUnsafeMutablePointer<NSString?>(
-          UnsafeMutablePointer<NSString>(outputName)
-        )
-        let outputNonOptionalArray = AutoreleasingUnsafeMutablePointer<NSArray?>(
-          UnsafeMutablePointer<NSArray>(outputArray)
-        )
+        let outputNonOptionalName = unsafeBitCast(
+          outputName, to: AutoreleasingUnsafeMutablePointer<NSString?>.self)
+        let outputNonOptionalArray = unsafeBitCast(
+          outputArray, to: AutoreleasingUnsafeMutablePointer<NSArray?>.self)
        return self._ns.completePath(
          into: outputNonOptionalName,
          caseSensitive: caseSensitive,
@@ -505,7 +503,7 @@ extension String {
      var stop_ = false
      body(line: line, stop: &stop_)
      if stop_ {
-        UnsafeMutablePointer<ObjCBool>(stop).pointee = true
+        stop.pointee = true
      }
    }
  }
@@ -541,7 +539,7 @@ extension String {
      var stop_ = false
      body($0, self._range($1), self._range($2), &stop_)
      if stop_ {
-        UnsafeMutablePointer($3).pointee = true
+        $3.pointee = true
      }
    }
  }
@@ -823,7 +821,7 @@ extension String {
    freeWhenDone flag: Bool
  ) {
    self = NSString(
-      charactersNoCopy: UnsafeMutablePointer(utf16CodeUnitsNoCopy),
+      charactersNoCopy: UnsafeMutablePointer(mutating: utf16CodeUnitsNoCopy),
      length: count,
      freeWhenDone: flag) as String
  }
--- a/stdlib/public/SDK/SceneKit/SceneKit.swift
+++ b/stdlib/public/SDK/SceneKit/SceneKit.swift
@@ -170,7 +170,7 @@ extension SCNGeometryElement {
      fatalError("Expected constant number of indices per primitive")
    }
    self.init(
-      data: Data(bytes: UnsafePointer<UInt8>(indices), count: indexCount * sizeof(IndexType.self)),
+      data: Data(bytes: indices, count: indexCount * sizeof(IndexType.self)),
      primitiveType: primitiveType,
      primitiveCount: primitiveCount,
      bytesPerIndex: sizeof(IndexType.self))
--- a/stdlib/public/SwiftShims/RuntimeStubs.h
+++ b/stdlib/public/SwiftShims/RuntimeStubs.h
@@ -29,7 +29,7 @@ SWIFT_BEGIN_NULLABILITY_ANNOTATIONS

 SWIFT_RUNTIME_STDLIB_INTERFACE
 __swift_ssize_t
-swift_stdlib_readLine_stdin(char * _Nullable * _Nonnull LinePtr);
+swift_stdlib_readLine_stdin(unsigned char * _Nullable * _Nonnull LinePtr);

 SWIFT_RUNTIME_STDLIB_INTERFACE
 char * _Nullable * _Nonnull
--- a/stdlib/public/SwiftShims/UnicodeShims.h
+++ b/stdlib/public/SwiftShims/UnicodeShims.h
@@ -66,16 +66,16 @@ _swift_stdlib_unicode_compare_utf16_utf16(const __swift_uint16_t *Left,

 SWIFT_RUNTIME_STDLIB_INTERFACE
 __attribute__((__pure__)) __swift_int32_t
-_swift_stdlib_unicode_compare_utf8_utf16(const char *Left,
+_swift_stdlib_unicode_compare_utf8_utf16(const unsigned char *Left,
                                         __swift_int32_t LeftLength,
                                         const __swift_uint16_t *Right,
                                         __swift_int32_t RightLength);

 SWIFT_RUNTIME_STDLIB_INTERFACE
 __attribute__((__pure__)) __swift_int32_t
-_swift_stdlib_unicode_compare_utf8_utf8(const char *Left,
+_swift_stdlib_unicode_compare_utf8_utf8(const unsigned char *Left,
                                        __swift_int32_t LeftLength,
-                                        const char *Right,
+                                        const unsigned char *Right,
                                        __swift_int32_t RightLength);

 SWIFT_RUNTIME_STDLIB_INTERFACE
@@ -84,7 +84,8 @@ _swift_stdlib_unicode_hash(const __swift_uint16_t *Str, __swift_int32_t Length);

 SWIFT_RUNTIME_STDLIB_INTERFACE
 __attribute__((__pure__)) __swift_intptr_t
-_swift_stdlib_unicode_hash_ascii(const char *Str, __swift_int32_t Length);
+_swift_stdlib_unicode_hash_ascii(const unsigned char *Str,
+                                 __swift_int32_t Length);

 SWIFT_RUNTIME_STDLIB_INTERFACE
 __swift_int32_t _swift_stdlib_unicode_strToUpper(
--- a/stdlib/public/core/ArrayBuffer.swift
+++ b/stdlib/public/core/ArrayBuffer.swift
@@ -204,7 +204,8 @@ extension _ArrayBuffer {
      location: bounds.lowerBound,
      length: bounds.upperBound - bounds.lowerBound)

-    let buffer = UnsafeMutablePointer<AnyObject>(target)
+    let buffer = UnsafeMutableRawPointer(target).assumingMemoryBound(
+      to: AnyObject.self)
    
    // Copies the references out of the NSArray without retaining them
    nonNative.getObjects(buffer, range: nsSubRange)
@@ -242,9 +243,11 @@ extension _ArrayBuffer {
        cocoa.contiguousStorage(Range(self.indices))

      if let cocoaStorageBaseAddress = cocoaStorageBaseAddress {
+        let basePtr = UnsafeMutableRawPointer(cocoaStorageBaseAddress)
+          .assumingMemoryBound(to: Element.self)
        return _SliceBuffer(
          owner: nonNative,
-          subscriptBaseAddress: UnsafeMutablePointer(cocoaStorageBaseAddress),
+          subscriptBaseAddress: basePtr,
          indices: bounds,
          hasNativeBuffer: false)
      }
@@ -255,7 +258,8 @@ extension _ArrayBuffer {

      // Tell Cocoa to copy the objects into our storage
      cocoa.buffer.getObjects(
-        UnsafeMutablePointer(result.firstElementAddress),
+        UnsafeMutableRawPointer(result.firstElementAddress)
+          .assumingMemoryBound(to: AnyObject.self),
        range: _SwiftNSRange(location: bounds.lowerBound, length: boundsCount))

      return _SliceBuffer(result, shiftedToStartIndex: bounds.lowerBound)
--- a/stdlib/public/core/BridgeObjectiveC.swift
+++ b/stdlib/public/core/BridgeObjectiveC.swift
@@ -355,7 +355,7 @@ public struct AutoreleasingUnsafeMutablePointer<Pointee /* TODO : class */>
    /// Retrieve the value the pointer points to.
    @_transparent get {
      // We can do a strong load normally.
-      return UnsafeMutablePointer<Pointee>(self).pointee
+      return unsafeBitCast(self, to: UnsafeMutablePointer<Pointee>.self).pointee
    }
    /// Set the value the pointer points to, copying over the previous value.
    ///
@@ -402,6 +402,9 @@ public struct AutoreleasingUnsafeMutablePointer<Pointee /* TODO : class */>
  /// This is inherently unsafe; UnsafeMutablePointer assumes the
  /// referenced memory has +1 strong ownership semantics, whereas
  /// AutoreleasingUnsafeMutablePointer implies +0 semantics.
+  ///
+  /// - Warning: Accessing `pointee` as a type that is unrelated to
+  ///   the underlying memory's bound type is undefined.
  @_transparent public
  init<U>(_ from: UnsafeMutablePointer<U>) {
    self._rawValue = from._rawValue
@@ -414,6 +417,9 @@ public struct AutoreleasingUnsafeMutablePointer<Pointee /* TODO : class */>
  /// This is inherently unsafe; UnsafeMutablePointer assumes the
  /// referenced memory has +1 strong ownership semantics, whereas
  /// AutoreleasingUnsafeMutablePointer implies +0 semantics.
+  ///
+  /// - Warning: Accessing `pointee` as a type that is unrelated to
+  ///   the underlying memory's bound type is undefined.
  @_transparent public
  init?<U>(_ from: UnsafeMutablePointer<U>?) {
    guard let unwrapped = from else { return nil }
@@ -424,6 +430,9 @@ public struct AutoreleasingUnsafeMutablePointer<Pointee /* TODO : class */>
  ///
  /// This is inherently unsafe because UnsafePointers do not imply
  /// mutability.
+  ///
+  /// - Warning: Accessing `pointee` as a type that is unrelated to
+  ///   the underlying memory's bound type is undefined.
  @_transparent
  init<U>(_ from: UnsafePointer<U>) {
    self._rawValue = from._rawValue
@@ -435,6 +444,9 @@ public struct AutoreleasingUnsafeMutablePointer<Pointee /* TODO : class */>
  ///
  /// This is inherently unsafe because UnsafePointers do not imply
  /// mutability.
+  ///
+  /// - Warning: Accessing `pointee` as a type that is unrelated to
+  ///   the underlying memory's bound type is undefined.
  @_transparent
  init?<U>(_ from: UnsafePointer<U>?) {
    guard let unwrapped = from else { return nil }
@@ -442,6 +454,40 @@ public struct AutoreleasingUnsafeMutablePointer<Pointee /* TODO : class */>
  }
 }

+extension UnsafeMutableRawPointer {
+  /// Convert from `AutoreleasingUnsafeMutablePointer`.
+  @_transparent
+  public init<T>(_ other: AutoreleasingUnsafeMutablePointer<T>) {
+    _rawValue = other._rawValue
+  }
+
+  /// Convert other `AutoreleasingUnsafeMutablePointer`.
+  ///
+  /// Returns nil if `other` is nil.
+  @_transparent
+  public init?<T>(_ other: AutoreleasingUnsafeMutablePointer<T>?) {
+    guard let unwrapped = other else { return nil }
+    self.init(unwrapped)
+  }
+}
+
+extension UnsafeRawPointer {
+  /// Convert other `AutoreleasingUnsafeMutablePointer`.
+  @_transparent
+  public init<T>(_ other: AutoreleasingUnsafeMutablePointer<T>) {
+    _rawValue = other._rawValue
+  }
+
+  /// Convert other `AutoreleasingUnsafeMutablePointer`.
+  ///
+  /// Returns nil if `other` is nil.
+  @_transparent
+  public init?<T>(_ other: AutoreleasingUnsafeMutablePointer<T>?) {
+    guard let unwrapped = other else { return nil }
+    self.init(unwrapped)
+  }
+}
+
 extension AutoreleasingUnsafeMutablePointer : CustomDebugStringConvertible {
  /// A textual representation of `self`, suitable for debugging.
  public var debugDescription: String {
--- a/stdlib/public/core/Builtin.swift
+++ b/stdlib/public/core/Builtin.swift
@@ -88,9 +88,11 @@ internal func _roundUp(_ offset: Int, toAlignment alignment: Int) -> Int {
  return Int(_roundUpImpl(UInt(bitPattern: offset), toAlignment: alignment))
 }

+// This function takes a raw pointer and returns a typed pointer. It implicitly
+// assumes that memory at the returned pointer is bound to `Destination` type.
@_versioned
-internal func _roundUp<T, DestinationType>(
-  _ pointer: UnsafeMutablePointer<T>,
+internal func _roundUp<DestinationType>(
+  _ pointer: UnsafeMutableRawPointer,
  toAlignmentOf destinationType: DestinationType.Type
 ) -> UnsafeMutablePointer<DestinationType> {
  // Note: unsafe unwrap is safe because this operation can only increase the
@@ -245,11 +247,11 @@ public func unsafeDowncast<T : AnyObject>(_ x: AnyObject, to: T.Type) -> T {

@inline(__always)
 public func _getUnsafePointerToStoredProperties(_ x: AnyObject)
-  -> UnsafeMutablePointer<UInt8> {
+  -> UnsafeMutableRawPointer {
  let storedPropertyOffset = _roundUp(
    sizeof(_HeapObject.self),
    toAlignment: alignof(Optional<AnyObject>.self))
-  return UnsafeMutablePointer<UInt8>(Builtin.bridgeToRawPointer(x)) +
+  return UnsafeMutableRawPointer(Builtin.bridgeToRawPointer(x)) +
    storedPropertyOffset
 }

--- a/stdlib/public/core/CocoaArray.swift
+++ b/stdlib/public/core/CocoaArray.swift
@@ -66,7 +66,8 @@ internal struct _CocoaArrayWrapper : RandomAccessCollection {
    }
    
    return contiguousCount >= subRange.upperBound
-      ? UnsafeMutablePointer<AnyObject>(enumerationState.itemsPtr!)
+      ? UnsafeMutableRawPointer(enumerationState.itemsPtr!)
+          .assumingMemoryBound(to: AnyObject.self)
        + subRange.lowerBound
      : nil
  }
--- a/stdlib/public/core/ContiguousArrayBuffer.swift
+++ b/stdlib/public/core/ContiguousArrayBuffer.swift
@@ -115,7 +115,8 @@ final class _ContiguousArrayStorage<Element> : _ContiguousArrayStorage1 {
  ) rethrows {
    if _isBridgedVerbatimToObjectiveC(Element.self) {
      let count = __manager.header.count
-      let elements = UnsafePointer<AnyObject>(__manager._elementPointer)
+      let elements = UnsafeMutableRawPointer(__manager._elementPointer)
+        .assumingMemoryBound(to: AnyObject.self)
      defer { _fixLifetime(__manager) }
      try body(UnsafeBufferPointer(start: elements, count: count))
    }
--- a/stdlib/public/core/FloatingPointParsing.swift.gyb
+++ b/stdlib/public/core/FloatingPointParsing.swift.gyb
@@ -57,10 +57,9 @@ extension ${Self} : LosslessStringConvertible {
    func parseNTBS(_ chars: UnsafePointer<CChar>) -> (${Self}, Int) {
      var result: ${Self} = 0
      let endPtr = withUnsafeMutablePointer(to: &result) {
-        _swift_stdlib_strto${cFuncSuffix2[bits]}_clocale(
-          chars, UnsafeMutablePointer($0))
+        _swift_stdlib_strto${cFuncSuffix2[bits]}_clocale(chars, $0)
      }
-      return (result, endPtr == nil ? 0 : UnsafePointer(endPtr!) - chars)
+      return (result, endPtr == nil ? 0 : endPtr! - chars)
    }

    let (result, n) = text.withCString(parseNTBS)
--- a/stdlib/public/core/HashedCollections.swift.gyb
+++ b/stdlib/public/core/HashedCollections.swift.gyb
@@ -2584,7 +2584,7 @@ final internal class _Native${Self}StorageImpl<${TypeParameters}> :
        _UnsafeBitMap.sizeInWords(forSizeInBits: _body.capacity),
        strideof(UInt.self))
    let start =
-      UnsafeMutablePointer<UInt8>(_initializedHashtableEntriesBitMapStorage)
+      UnsafeMutableRawPointer(_initializedHashtableEntriesBitMapStorage)
      + bitMapSizeInBytes
    return _roundUp(start, toAlignmentOf: Key.self)
  }
@@ -2593,7 +2593,7 @@ final internal class _Native${Self}StorageImpl<${TypeParameters}> :
  // This API is unsafe and needs a `_fixLifetime` in the caller.
  internal var _values: UnsafeMutablePointer<Value> {
    let keysSizeInBytes = _unsafeMultiply(_body.capacity, strideof(Key.self))
-    let start = UnsafeMutablePointer<UInt8>(_keys) + keysSizeInBytes
+    let start = UnsafeMutableRawPointer(_keys) + keysSizeInBytes
    return _roundUp(start, toAlignmentOf: Value.self)
  }
 %end
@@ -3359,7 +3359,8 @@ final internal class _Native${Self}StorageOwner<${TypeParametersDecl}>
  /// Returns the pointer to the stored property, which contains bridged
  /// ${Self} elements.
  internal var _heapBufferBridgedPtr: UnsafeMutablePointer<AnyObject?> {
-    return UnsafeMutablePointer(_getUnsafePointerToStoredProperties(self))
+    return _getUnsafePointerToStoredProperties(self).assumingMemoryBound(
+      to: Optional<AnyObject>.self)
  }

  /// The storage for bridged ${Self} elements, if present.
@@ -4754,12 +4755,14 @@ final internal class _Cocoa${Self}Iterator : IteratorProtocol {

  internal var _fastEnumerationStatePtr:
    UnsafeMutablePointer<_SwiftNSFastEnumerationState> {
-    return UnsafeMutablePointer(_getUnsafePointerToStoredProperties(self))
+    return _getUnsafePointerToStoredProperties(self).assumingMemoryBound(
+      to: _SwiftNSFastEnumerationState.self)
  }

  internal var _fastEnumerationStackBufPtr:
    UnsafeMutablePointer<_CocoaFastEnumerationStackBuf> {
-    return UnsafeMutablePointer(_fastEnumerationStatePtr + 1)
+    return UnsafeMutableRawPointer(_fastEnumerationStatePtr + 1)
+      .assumingMemoryBound(to: _CocoaFastEnumerationStackBuf.self)
  }

  // These members have to be word-sized integers, they cannot be limited to
@@ -4788,7 +4791,8 @@ final internal class _Cocoa${Self}Iterator : IteratorProtocol {
      // state struct.
      itemCount = cocoa${Self}.countByEnumerating(
        with: _fastEnumerationStatePtr,
-        objects: UnsafeMutablePointer(_fastEnumerationStackBufPtr),
+        objects: UnsafeMutableRawPointer(_fastEnumerationStackBufPtr)
+          .assumingMemoryBound(to: AnyObject.self),
        count: stackBufCount)
      if itemCount == 0 {
        itemIndex = -1
@@ -4796,8 +4800,9 @@ final internal class _Cocoa${Self}Iterator : IteratorProtocol {
      }
      itemIndex = 0
    }
-    let itemsPtrUP: UnsafeMutablePointer<AnyObject> =
-      UnsafeMutablePointer(_fastEnumerationState.itemsPtr!)
+    let itemsPtrUP =
+    UnsafeMutableRawPointer(_fastEnumerationState.itemsPtr!)
+      .assumingMemoryBound(to: AnyObject.self)
    let itemsPtr = _UnmanagedAnyObjectArray(itemsPtrUP)
    let key: AnyObject = itemsPtr[itemIndex]
    itemIndex += 1
--- a/stdlib/public/core/HeapBuffer.swift
+++ b/stdlib/public/core/HeapBuffer.swift
@@ -92,19 +92,20 @@ struct _HeapBuffer<Value, Element> : Equatable {
            : (heapAlign < elementAlign ? elementAlign : heapAlign))
  }

-  internal var _address: UnsafeMutablePointer<Int8> {
-    return UnsafeMutablePointer(
+  internal var _address: UnsafeMutableRawPointer {
+    return UnsafeMutableRawPointer(
      Builtin.bridgeToRawPointer(self._nativeObject))
  }

  internal var _value: UnsafeMutablePointer<Value> {
-    return UnsafeMutablePointer(
-      _HeapBuffer._valueOffset() + _address)
+    return (_HeapBuffer._valueOffset() + _address).assumingMemoryBound(
+      to: Value.self)
  }

  public // @testable
  var baseAddress: UnsafeMutablePointer<Element> {
-    return UnsafeMutablePointer(_HeapBuffer._elementOffset() + _address)
+    return (_HeapBuffer._elementOffset() + _address).assumingMemoryBound(
+      to: Element.self)
  }

  internal func _allocatedSize() -> Int {
--- a/stdlib/public/core/InputStream.swift
+++ b/stdlib/public/core/InputStream.swift
@@ -22,7 +22,7 @@ import SwiftShims
 /// Standard input is interpreted as `UTF-8`.  Invalid bytes
 /// will be replaced by Unicode [replacement characters](http://en.wikipedia.org/wiki/Specials_(Unicode_block)#Replacement_character).
 public func readLine(strippingNewline: Bool = true) -> String? {
-  var linePtrVar: UnsafeMutablePointer<CChar>? = nil
+  var linePtrVar: UnsafeMutablePointer<UInt8>? = nil
  var readBytes = swift_stdlib_readLine_stdin(&linePtrVar)
  if readBytes == -1 {
    return nil
@@ -41,8 +41,8 @@ public func readLine(strippingNewline: Bool = true) -> String? {
    // <rdar://problem/20013999> Recognize Unicode newlines in readLine()
    //
    // Recognize only LF and CR+LF combinations for now.
-    let cr = CChar(UInt8(ascii: "\r"))
-    let lf = CChar(UInt8(ascii: "\n"))
+    let cr = UInt8(ascii: "\r")
+    let lf = UInt8(ascii: "\n")
    if readBytes == 1 && linePtr[0] == lf {
      return ""
    }
@@ -61,7 +61,7 @@ public func readLine(strippingNewline: Bool = true) -> String? {
  }
  let result = String._fromCodeUnitSequenceWithRepair(UTF8.self,
    input: UnsafeMutableBufferPointer(
-      start: UnsafeMutablePointer<UTF8.CodeUnit>(linePtr),
+      start: linePtr,
      count: readBytes)).0
  _swift_stdlib_free(linePtr)
  return result
--- a/stdlib/public/core/ManagedBuffer.swift
+++ b/stdlib/public/core/ManagedBuffer.swift
@@ -395,8 +395,8 @@ public struct ManagedBufferPointer<Header, Element> : Equatable {
  }

  /// The address of this instance in a convenient pointer-to-bytes form
-  internal var _address: UnsafePointer<UInt8> {
-    return UnsafePointer(Builtin.bridgeToRawPointer(_nativeBuffer))
+  internal var _address: UnsafeMutableRawPointer {
+    return UnsafeMutableRawPointer(Builtin.bridgeToRawPointer(_nativeBuffer))
  }

  /// Offset from the allocated storage for `self` to the stored `Header`
@@ -412,7 +412,8 @@ public struct ManagedBufferPointer<Header, Element> : Equatable {
  /// guarantee it doesn't dangle
  internal var _headerPointer: UnsafeMutablePointer<Header> {
    _onFastPath()
-    return UnsafeMutablePointer(_address + _My._headerOffset)
+    return (_address + _My._headerOffset).assumingMemoryBound(
+      to: Header.self)
  }

  /// An **unmanaged** pointer to the storage for `Element`s.  Not
@@ -420,7 +421,8 @@ public struct ManagedBufferPointer<Header, Element> : Equatable {
  /// dangle.
  internal var _elementPointer: UnsafeMutablePointer<Element> {
    _onFastPath()
-    return UnsafeMutablePointer(_address + _My._elementOffset)
+    return (_address + _My._elementOffset).assumingMemoryBound(
+      to: Element.self)
  }

  /// Offset from the allocated storage for `self` to the `Element` storage
--- a/stdlib/public/core/Runtime.swift.gyb
+++ b/stdlib/public/core/Runtime.swift.gyb
@@ -120,10 +120,11 @@ func _stdlib_atomicCompareExchangeStrongInt${bits}(
  object target: UnsafeMutablePointer<Int${bits}>,
  expected: UnsafeMutablePointer<Int${bits}>,
  desired: Int${bits}) -> Bool {
-  return _stdlib_atomicCompareExchangeStrongUInt${bits}(
-    object: UnsafeMutablePointer(target),
-    expected: UnsafeMutablePointer(expected),
-    desired: UInt${bits}(bitPattern: desired))
+
+  let (oldValue, won) = Builtin.cmpxchg_seqcst_seqcst_Int${bits}(
+    target._rawValue, expected.pointee._value, desired._value)
+  expected.pointee._value = oldValue
+  return Bool(won)
 }

@_transparent
@@ -138,9 +139,8 @@ func _swift_stdlib_atomicStoreUInt${bits}(
 func _swift_stdlib_atomicStoreInt${bits}(
  object target: UnsafeMutablePointer<Int${bits}>,
  desired: Int${bits}) {
-  return _swift_stdlib_atomicStoreUInt${bits}(
-    object: UnsafeMutablePointer(target),
-    desired: UInt${bits}(bitPattern: desired))
+
+  Builtin.atomicstore_seqcst_Int${bits}(target._rawValue, desired._value)
 }

 public // @testable
@@ -153,9 +153,9 @@ func _swift_stdlib_atomicLoadUInt${bits}(

 func _swift_stdlib_atomicLoadInt${bits}(
  object target: UnsafeMutablePointer<Int${bits}>) -> Int${bits} {
-  return Int${bits}(bitPattern:
-    _swift_stdlib_atomicLoadUInt${bits}(
-      object: UnsafeMutablePointer(target)))
+
+  let value = Builtin.atomicload_seqcst_Int${bits}(target._rawValue)
+  return Int${bits}(value)
 }

 %   for operation in ['Add', 'And', 'Or', 'Xor']:
@@ -176,10 +176,11 @@ func _swift_stdlib_atomicFetch${operation}UInt${bits}(
 func _swift_stdlib_atomicFetch${operation}Int${bits}(
  object target: UnsafeMutablePointer<Int${bits}>,
  operand: Int${bits}) -> Int${bits} {
-  return Int${bits}(bitPattern:
-    _swift_stdlib_atomicFetch${operation}UInt${bits}(
-      object: UnsafeMutablePointer(target),
-      operand: UInt${bits}(bitPattern: operand)))
+
+  let value = Builtin.atomicrmw_${operation.lower()}_seqcst_Int${bits}(
+    target._rawValue, operand._value)
+
+  return Int${bits}(value)
 }
 %   end

@@ -190,29 +191,23 @@ func _stdlib_atomicCompareExchangeStrongInt(
  expected: UnsafeMutablePointer<Int>,
  desired: Int) -> Bool {
 #if arch(i386) || arch(arm)
-  return _stdlib_atomicCompareExchangeStrongUInt32(
-    object: UnsafeMutablePointer(target),
-    expected: UnsafeMutablePointer(expected),
-    desired: UInt32(bitPattern: Int32(desired)))
+  let (oldValue, won) = Builtin.cmpxchg_seqcst_seqcst_Int32(
+    target._rawValue, expected.pointee._value, desired._value)
 #elseif arch(x86_64) || arch(arm64) || arch(powerpc64) || arch(powerpc64le) || arch(s390x)
-  return _stdlib_atomicCompareExchangeStrongUInt64(
-    object: UnsafeMutablePointer(target),
-    expected: UnsafeMutablePointer(expected),
-    desired: UInt64(bitPattern: Int64(desired)))
+  let (oldValue, won) = Builtin.cmpxchg_seqcst_seqcst_Int64(
+    target._rawValue, expected.pointee._value, desired._value)
 #endif
+  expected.pointee._value = oldValue
+  return Bool(won)
 }

 func _swift_stdlib_atomicStoreInt(
  object target: UnsafeMutablePointer<Int>,
  desired: Int) {
 #if arch(i386) || arch(arm)
-  return _swift_stdlib_atomicStoreUInt32(
-    object: UnsafeMutablePointer(target),
-    desired: UInt32(bitPattern: Int32(desired)))
+  Builtin.atomicstore_seqcst_Int32(target._rawValue, desired._value)
 #elseif arch(x86_64) || arch(arm64) || arch(powerpc64) || arch(powerpc64le) || arch(s390x)
-  return _swift_stdlib_atomicStoreUInt64(
-    object: UnsafeMutablePointer(target),
-    desired: UInt64(bitPattern: Int64(desired)))
+  Builtin.atomicstore_seqcst_Int64(target._rawValue, desired._value)
 #endif
 }

@@ -220,13 +215,11 @@ func _swift_stdlib_atomicStoreInt(
 public func _swift_stdlib_atomicLoadInt(
  object target: UnsafeMutablePointer<Int>) -> Int {
 #if arch(i386) || arch(arm)
-  return Int(Int32(bitPattern:
-    _swift_stdlib_atomicLoadUInt32(
-      object: UnsafeMutablePointer(target))))
+  let value = Builtin.atomicload_seqcst_Int32(target._rawValue)
+  return Int(value)
 #elseif arch(x86_64) || arch(arm64) || arch(powerpc64) || arch(powerpc64le) || arch(s390x)
-  return Int(Int64(bitPattern:
-    _swift_stdlib_atomicLoadUInt64(
-      object: UnsafeMutablePointer(target))))
+  let value = Builtin.atomicload_seqcst_Int64(target._rawValue)
+  return Int(value)
 #endif
 }

@@ -245,7 +238,7 @@ func _stdlib_atomicLoadARCRef(
  object target: UnsafeMutablePointer<AnyObject?>
 ) -> AnyObject? {
  let result = _swift_stdlib_atomicLoadPtrImpl(
-    object: UnsafeMutablePointer(target))
+    object: unsafeBitCast(target, to: UnsafeMutablePointer<OpaquePointer>.self))
  if let unwrapped = result {
    return Unmanaged<AnyObject>.fromOpaque(
      UnsafePointer(unwrapped)).takeUnretainedValue()
@@ -261,12 +254,12 @@ public func _swift_stdlib_atomicFetch${operation}Int(
 #if arch(i386) || arch(arm)
  return Int(Int32(bitPattern:
    _swift_stdlib_atomicFetch${operation}UInt32(
-      object: UnsafeMutablePointer(target),
+      object: unsafeBitCast(target, to: UnsafeMutablePointer<UInt32>.self),
      operand: UInt32(bitPattern: Int32(operand)))))
 #elseif arch(x86_64) || arch(arm64) || arch(powerpc64) || arch(powerpc64le) || arch(s390x)
  return Int(Int64(bitPattern:
    _swift_stdlib_atomicFetch${operation}UInt64(
-      object: UnsafeMutablePointer(target),
+      object: unsafeBitCast(target, to: UnsafeMutablePointer<UInt64>.self),
      operand: UInt64(bitPattern: Int64(operand)))))
 #endif
 }
@@ -276,7 +269,8 @@ public final class _stdlib_AtomicInt {
  var _value: Int

  var _valuePtr: UnsafeMutablePointer<Int> {
-    return UnsafeMutablePointer(_getUnsafePointerToStoredProperties(self))
+    return _getUnsafePointerToStoredProperties(self).assumingMemoryBound(
+      to: Int.self)
  }

  public init(_ value: Int = 0) {
@@ -321,23 +315,34 @@ public final class _stdlib_AtomicInt {

 /// A 32 byte buffer.
 internal struct _Buffer32 {
-  internal var _x0: UInt64 = 0
-  internal var _x1: UInt64 = 0
-  internal var _x2: UInt64 = 0
-  internal var _x3: UInt64 = 0
+% for i in range(32):
+  internal var _x${i}: UInt8 = 0
+% end
+
+  mutating func withBytes<Result>(
+    _ body: @noescape (UnsafeMutablePointer<UInt8>) throws -> Result
+  ) rethrows -> Result
+  {
+    return try withUnsafeMutablePointer(to: &self) {
+      try body(UnsafeMutableRawPointer($0).assumingMemoryBound(to: UInt8.self))
+    }
+  }
 }

 /// A 72 byte buffer.
 internal struct _Buffer72 {
-  internal var _x0: UInt64 = 0
-  internal var _x1: UInt64 = 0
-  internal var _x2: UInt64 = 0
-  internal var _x3: UInt64 = 0
-  internal var _x4: UInt64 = 0
-  internal var _x5: UInt64 = 0
-  internal var _x6: UInt64 = 0
-  internal var _x7: UInt64 = 0
-  internal var _x8: UInt64 = 0
+% for i in range(72):
+  internal var _x${i}: UInt8 = 0
+% end
+
+  mutating func withBytes<Result>(
+    _ body: @noescape (UnsafeMutablePointer<UInt8>) throws -> Result
+  ) rethrows -> Result
+  {
+    return try withUnsafeMutablePointer(to: &self) {
+      try body(UnsafeMutableRawPointer($0).assumingMemoryBound(to: UInt8.self))
+    }
+  }
 }

 % for bits in [ 32, 64, 80 ]:
@@ -381,14 +386,11 @@ func _float${bits}ToString(_ value: Float${bits}, debug: Bool) -> String {
  _sanityCheck(sizeof(_Buffer72.self) == 72)

  var buffer = _Buffer32()
-  return withUnsafeMutablePointer(to: &buffer) {
-    (bufferPtr) in
-    let bufferUTF8Ptr = UnsafeMutablePointer<UTF8.CodeUnit>(bufferPtr)
-    let actualLength = _float${bits}ToStringImpl(bufferUTF8Ptr, 32, value, debug)
+  return buffer.withBytes { (bufferPtr) in
+    let actualLength = _float${bits}ToStringImpl(bufferPtr, 32, value, debug)
    return String._fromWellFormedCodeUnitSequence(
      UTF8.self,
-      input: UnsafeBufferPointer(
-        start: bufferUTF8Ptr, count: Int(actualLength)))
+      input: UnsafeBufferPointer(start: bufferPtr, count: Int(actualLength)))
  }
 }

@@ -410,27 +412,21 @@ func _int64ToString(
 ) -> String {
  if radix >= 10 {
    var buffer = _Buffer32()
-    return withUnsafeMutablePointer(to: &buffer) {
-      (bufferPtr) in
-      let bufferUTF8Ptr = UnsafeMutablePointer<UTF8.CodeUnit>(bufferPtr)
-      let actualLength =
-        _int64ToStringImpl(bufferUTF8Ptr, 32, value, radix, uppercase)
+    return buffer.withBytes { (bufferPtr) in
+      let actualLength
+      = _int64ToStringImpl(bufferPtr, 32, value, radix, uppercase)
      return String._fromWellFormedCodeUnitSequence(
        UTF8.self,
-        input: UnsafeBufferPointer(
-          start: bufferUTF8Ptr, count: Int(actualLength)))
+        input: UnsafeBufferPointer(start: bufferPtr, count: Int(actualLength)))
    }
  } else {
    var buffer = _Buffer72()
-    return withUnsafeMutablePointer(to: &buffer) {
-      (bufferPtr) in
-      let bufferUTF8Ptr = UnsafeMutablePointer<UTF8.CodeUnit>(bufferPtr)
-      let actualLength =
-        _int64ToStringImpl(bufferUTF8Ptr, 72, value, radix, uppercase)
+    return buffer.withBytes { (bufferPtr) in
+      let actualLength
+      = _int64ToStringImpl(bufferPtr, 72, value, radix, uppercase)
      return String._fromWellFormedCodeUnitSequence(
        UTF8.self,
-        input: UnsafeBufferPointer(
-          start: bufferUTF8Ptr, count: Int(actualLength)))
+        input: UnsafeBufferPointer(start: bufferPtr, count: Int(actualLength)))
    }
  }
 }
@@ -447,27 +443,21 @@ func _uint64ToString(
 ) -> String {
  if radix >= 10 {
    var buffer = _Buffer32()
-    return withUnsafeMutablePointer(to: &buffer) {
-      (bufferPtr) in
-      let bufferUTF8Ptr = UnsafeMutablePointer<UTF8.CodeUnit>(bufferPtr)
-      let actualLength =
-        _uint64ToStringImpl(bufferUTF8Ptr, 32, value, radix, uppercase)
+    return buffer.withBytes { (bufferPtr) in
+      let actualLength
+      = _uint64ToStringImpl(bufferPtr, 32, value, radix, uppercase)
      return String._fromWellFormedCodeUnitSequence(
        UTF8.self,
-        input: UnsafeBufferPointer(
-          start: bufferUTF8Ptr, count: Int(actualLength)))
+        input: UnsafeBufferPointer(start: bufferPtr, count: Int(actualLength)))
    }
  } else {
    var buffer = _Buffer72()
-    return withUnsafeMutablePointer(to: &buffer) {
-      (bufferPtr) in
-      let bufferUTF8Ptr = UnsafeMutablePointer<UTF8.CodeUnit>(bufferPtr)
-      let actualLength =
-        _uint64ToStringImpl(bufferUTF8Ptr, 72, value, radix, uppercase)
+    return buffer.withBytes { (bufferPtr) in
+      let actualLength
+      = _uint64ToStringImpl(bufferPtr, 72, value, radix, uppercase)
      return String._fromWellFormedCodeUnitSequence(
        UTF8.self,
-        input: UnsafeBufferPointer(
-          start: bufferUTF8Ptr, count: Int(actualLength)))
+        input: UnsafeBufferPointer(start: bufferPtr, count: Int(actualLength)))
    }
  }
 }
--- a/stdlib/public/core/String.swift
+++ b/stdlib/public/core/String.swift
@@ -584,28 +584,20 @@ extension String {
 #else
    switch (_core.isASCII, rhs._core.isASCII) {
    case (true, false):
-      let lhsPtr = UnsafePointer<Int8>(_core.startASCII)
-      let rhsPtr = UnsafePointer<UTF16.CodeUnit>(rhs._core.startUTF16)
-
      return Int(_swift_stdlib_unicode_compare_utf8_utf16(
-        lhsPtr, Int32(_core.count), rhsPtr, Int32(rhs._core.count)))
+          _core.startASCII, Int32(_core.count),
+          rhs._core.startUTF16, Int32(rhs._core.count)))
    case (false, true):
      // Just invert it and recurse for this case.
      return -rhs._compareDeterministicUnicodeCollation(self)
    case (false, false):
-      let lhsPtr = UnsafePointer<UTF16.CodeUnit>(_core.startUTF16)
-      let rhsPtr = UnsafePointer<UTF16.CodeUnit>(rhs._core.startUTF16)
-
      return Int(_swift_stdlib_unicode_compare_utf16_utf16(
-        lhsPtr, Int32(_core.count),
-        rhsPtr, Int32(rhs._core.count)))
+        _core.startUTF16, Int32(_core.count),
+        rhs._core.startUTF16, Int32(rhs._core.count)))
    case (true, true):
-      let lhsPtr = UnsafePointer<Int8>(_core.startASCII)
-      let rhsPtr = UnsafePointer<Int8>(rhs._core.startASCII)
-
      return Int(_swift_stdlib_unicode_compare_utf8_utf8(
-        lhsPtr, Int32(_core.count),
-        rhsPtr, Int32(rhs._core.count)))
+        _core.startASCII, Int32(_core.count),
+        rhs._core.startASCII, Int32(rhs._core.count)))
    }
 #endif
  }
@@ -699,15 +691,10 @@ extension String : Hashable {
    }
 #else
    if self._core.isASCII {
-      return _core.startASCII.withMemoryRebound(
-        to: CChar.self, capacity: _core.count) {
-        _swift_stdlib_unicode_hash_ascii($0, Int32(_core.count))
-      }
+      return _swift_stdlib_unicode_hash_ascii(
+        _core.startASCII, Int32(_core.count))
    } else {
-      return _core.startUTF16.withMemoryRebound(
-        to: UInt16.self, capacity: _core.count) {
-        _swift_stdlib_unicode_hash($0, Int32(_core.count))
-      }
+      return _swift_stdlib_unicode_hash(_core.startUTF16, Int32(_core.count))
    }
 #endif
  }
@@ -822,9 +809,12 @@ internal func _nativeUnicodeLowercaseString(_ str: String) -> String {
  var buffer = _StringBuffer(
    capacity: str._core.count, initialSize: str._core.count, elementWidth: 2)

-  // Try to write it out to the same length.
+  // Allocation of a StringBuffer requires binding the memory to the correct
+  // encoding type.
  let dest = buffer.start.bindMemory(
    to: UTF16.CodeUnit.self, capacity: str._core.count)
+
+  // Try to write it out to the same length.
  let z = _swift_stdlib_unicode_strToLower(
    dest, Int32(str._core.count),
    str._core.startUTF16, Int32(str._core.count))
@@ -847,9 +837,12 @@ internal func _nativeUnicodeUppercaseString(_ str: String) -> String {
  var buffer = _StringBuffer(
    capacity: str._core.count, initialSize: str._core.count, elementWidth: 2)

-  // Try to write it out to the same length.
+  // Allocation of a StringBuffer requires binding the memory to the correct
+  // encoding type.
  let dest = buffer.start.bindMemory(
    to: UTF16.CodeUnit.self, capacity: str._core.count)
+
+  // Try to write it out to the same length.
  let z = _swift_stdlib_unicode_strToUpper(
    dest, Int32(str._core.count),
    str._core.startUTF16, Int32(str._core.count))
--- a/stdlib/public/core/StringBridge.swift
+++ b/stdlib/public/core/StringBridge.swift
@@ -40,7 +40,7 @@ public // @testable
 func _stdlib_binary_CFStringGetCharactersPtr(
  _ source: _CocoaString
 ) -> UnsafeMutablePointer<UTF16.CodeUnit>? {
-  return UnsafeMutablePointer(_swift_stdlib_CFStringGetCharactersPtr(source))
+  return UnsafeMutablePointer(mutating: _swift_stdlib_CFStringGetCharactersPtr(source))
 }

 /// Bridges `source` to `Swift.String`, assuming that `source` has non-ASCII
--- a/stdlib/public/core/StringBuffer.swift
+++ b/stdlib/public/core/StringBuffer.swift
@@ -241,7 +241,8 @@ public struct _StringBuffer {
    // }

    // &StringBufferIVars.usedEnd
-    let usedEndPhysicalPtr = _PointerToPointer(_storage._value)
+    let usedEndPhysicalPtr = UnsafeMutableRawPointer(_storage._value)
+      .assumingMemoryBound(to: Optional<UnsafeRawPointer>.self)
    // Create a temp var to hold the exchanged `expected` value.
    var expected : UnsafeRawPointer? = bounds.upperBound
    if _stdlib_atomicCompareExchangeStrongPtr(
--- a/stdlib/public/core/SwiftNativeNSArray.swift
+++ b/stdlib/public/core/SwiftNativeNSArray.swift
@@ -138,7 +138,8 @@ extension _SwiftNativeNSArrayWithContiguousStorage : _NSArrayCore {
  internal let _nativeStorage: _ContiguousArrayStorageBase

  internal var _heapBufferBridgedPtr: UnsafeMutablePointer<AnyObject?> {
-    return UnsafeMutablePointer(_getUnsafePointerToStoredProperties(self))
+    return _getUnsafePointerToStoredProperties(self).assumingMemoryBound(
+      to: Optional<AnyObject>.self)
  }

  internal typealias HeapBufferStorage = _HeapBufferStorage<Int, AnyObject>
--- a/stdlib/public/core/Unicode.swift
+++ b/stdlib/public/core/Unicode.swift
@@ -427,7 +427,9 @@ public struct UTF8 : UnicodeCodec {
  }

  public static func _nullCodeUnitOffset(in input: UnsafePointer<CodeUnit>) -> Int {
-    return Int(_swift_stdlib_strlen(UnsafePointer(input)))
+    // Relying on a permissive memory model in C.
+    let cstr = unsafeBitCast(input, to: UnsafePointer<CChar>.self)
+    return Int(_swift_stdlib_strlen(cstr))
  }
  // Support parsing C strings as-if they are UTF8 strings.
  public static func _nullCodeUnitOffset(in input: UnsafePointer<CChar>) -> Int {
--- a/stdlib/public/core/UnsafePointer.swift.gyb
+++ b/stdlib/public/core/UnsafePointer.swift.gyb
@@ -69,6 +69,8 @@ public struct ${Self}<Pointee>
  }

  /// Construct ${a_Self} with a given pattern of bits.
+  ///
+  /// Returns nil if `bitPattern` is zero.
  @_transparent
  public init?(bitPattern: UInt) {
    if bitPattern == 0 { return nil }
@@ -121,6 +123,25 @@ public struct ${Self}<Pointee>
    self.init(unwrapped)
  }

+%  if mutable:
+  /// Convert from `UnsafePointer` to `UnsafeMutablePointer` of the same
+  /// `Pointee`.
+  @_transparent
+  public init(mutating other: UnsafePointer<Pointee>) {
+    self._rawValue = other._rawValue
+  }
+
+  /// Convert from `UnsafePointer` to `UnsafeMutablePointer` of the same
+  /// `Pointee`.
+  ///
+  /// Returns nil if `bitPattern` is zero.
+  @_transparent
+  public init?(mutating other: UnsafePointer<Pointee>?) {
+    guard let unwrapped = other else { return nil }
+    self.init(mutating: unwrapped)
+  }
+%  end
+
 %  if mutable:
  /// Allocate and point at uninitialized aligned memory for `count`
  /// instances of `Pointee`.
--- a/stdlib/public/core/UnsafeRawPointer.swift.gyb
+++ b/stdlib/public/core/UnsafeRawPointer.swift.gyb
@@ -27,13 +27,21 @@ public struct Unsafe${Mutable}RawPointer : Strideable, Hashable, _Pointer {
  /// Implements conformance to the public protocol `_Pointer`.
  public let _rawValue: Builtin.RawPointer

-  // Construct ${a_Self} from another ${a_Self}.
-  // FIXME: Why is this necessary?
+  /// Construct ${a_Self} from another ${a_Self}.
  @_transparent
  public init(_ other: Unsafe${Mutable}RawPointer) {
    self = other
  }

+  /// Construct ${a_Self} from another ${a_Self}.
+  ///
+  /// Returns nil if `other` is nil.
+  @_transparent
+  public init?(_ other: Unsafe${Mutable}RawPointer?) {
+    guard let unwrapped = other else { return nil }
+    self = unwrapped
+  }
+
  /// Convert a builtin raw pointer to ${a_Self}.
  @_transparent
  public init(_ _rawValue: Builtin.RawPointer) {
--- a/stdlib/public/stubs/Stubs.cpp
+++ b/stdlib/public/stubs/Stubs.cpp
@@ -261,14 +261,14 @@ extern "C" uint64_t swift_float80ToString(char *Buffer, size_t BufferLength,
 ///
 /// \returns Size of character data returned in \c LinePtr, or -1
 /// if an error occurred, or EOF was reached.
-ssize_t swift::swift_stdlib_readLine_stdin(char **LinePtr) {
+ssize_t swift::swift_stdlib_readLine_stdin(unsigned char **LinePtr) {
 #if defined(_MSC_VER)
  if (LinePtr == nullptr)
    return -1;

  ssize_t Capacity = 0;
  ssize_t Pos = 0;
-  char *ReadBuf = nullptr;
+  unsigned char *ReadBuf = nullptr;

  _lock_file(stdin);

@@ -285,7 +285,8 @@ ssize_t swift::swift_stdlib_readLine_stdin(char **LinePtr) {
    if (Capacity - Pos <= 1) {
      // Capacity changes to 128, 128*2, 128*4, 128*8, ...
      Capacity = Capacity ? Capacity * 2 : 128;
-      char *NextReadBuf = static_cast<char *>(realloc(ReadBuf, Capacity));
+      char *NextReadBuf =
+        static_cast<unsigned char *>(realloc(ReadBuf, Capacity));
      if (NextReadBuf == nullptr) {
        if (ReadBuf)
          free(ReadBuf);
@@ -308,7 +309,7 @@ ssize_t swift::swift_stdlib_readLine_stdin(char **LinePtr) {
  return Pos;
 #else
  size_t Capacity = 0;
-  return getline(LinePtr, &Capacity, stdin);
+  return getline((char **)LinePtr, &Capacity, stdin);
 #endif
 }

--- a/stdlib/public/stubs/UnicodeNormalization.cpp
+++ b/stdlib/public/stubs/UnicodeNormalization.cpp
@@ -153,7 +153,7 @@ swift::_swift_stdlib_unicode_compare_utf16_utf16(const uint16_t *LeftString,
 /// ==0 the strings are equal according to their collation.
 ///  >0 the left string is greater than the right string.
 int32_t
-swift::_swift_stdlib_unicode_compare_utf8_utf16(const char *LeftString,
+swift::_swift_stdlib_unicode_compare_utf8_utf16(const unsigned char *LeftString,
                                                int32_t LeftLength,
                                                const uint16_t *RightString,
                                                int32_t RightLength) {
@@ -183,9 +183,9 @@ swift::_swift_stdlib_unicode_compare_utf8_utf16(const char *LeftString,
 /// ==0 the strings are equal according to their collation.
 ///  >0 the left string is greater than the right string.
 int32_t
-swift::_swift_stdlib_unicode_compare_utf8_utf8(const char *LeftString,
+swift::_swift_stdlib_unicode_compare_utf8_utf8(const unsigned char *LeftString,
                                               int32_t LeftLength,
-                                               const char *RightString,
+                                               const unsigned char *RightString,
                                               int32_t RightLength) {
  UCharIterator LeftIterator;
  UCharIterator RightIterator;
@@ -266,7 +266,7 @@ swift::_swift_stdlib_unicode_hash(const uint16_t *Str, int32_t Length) {
  return hashFinish(HashState);
 }

-intptr_t swift::_swift_stdlib_unicode_hash_ascii(const char *Str,
+intptr_t swift::_swift_stdlib_unicode_hash_ascii(const unsigned char *Str,
                                                 int32_t Length) {
  const ASCIICollation *Table = ASCIICollation::getTable();
  intptr_t HashState = HASH_SEED;
--- a/test/1_stdlib/BridgeNonVerbatim.swift
+++ b/test/1_stdlib/BridgeNonVerbatim.swift
@@ -88,9 +88,9 @@ func testScope() {
  objects.withUnsafeMutableBufferPointer {
    // FIXME: Can't elide signature and use $0 here <rdar://problem/17770732> 
    (buf: inout UnsafeMutableBufferPointer<Int>) -> () in
-    nsx.getObjects(
-      UnsafeMutablePointer<AnyObject>(buf.baseAddress!),
-      range: _SwiftNSRange(location: 1, length: 2))
+    let objPtr = UnsafeMutableRawPointer(buf.baseAddress!).bindMemory(
+      to: AnyObject.self, capacity: 2)
+    nsx.getObjects(objPtr, range: _SwiftNSRange(location: 1, length: 2))
  }

  // CHECK-NEXT: getObjects yields them at +0: true
--- a/test/1_stdlib/NSStringAPI.swift
+++ b/test/1_stdlib/NSStringAPI.swift
@@ -204,7 +204,9 @@ NSStringAPIs.test("init(utf8String:)") {
    i += 1
  }
  up[i] = 0
-  expectOptionalEqual(s, String(utf8String: UnsafePointer(up)))
+  let cstr = UnsafeMutableRawPointer(up)
+    .bindMemory(to: CChar.self, capacity: 100)
+  expectOptionalEqual(s, String(utf8String: cstr))
  up.deallocate(capacity: 100)
 }

--- a/test/1_stdlib/StringAPI.swift
+++ b/test/1_stdlib/StringAPI.swift
@@ -325,19 +325,19 @@ StringTests.test("CompareStringsWithUnpairedSurrogates")

 var CStringTests = TestSuite("CStringTests")

-func getNullCString() -> UnsafeMutablePointer<CChar>? {
+func getNullUTF8() -> UnsafeMutablePointer<UInt8>? {
  return nil
 }

-func getASCIICString() -> (UnsafeMutablePointer<CChar>, dealloc: () -> ()) {
-  let up = UnsafeMutablePointer<CChar>.allocate(capacity: 100)
+func getASCIIUTF8() -> (UnsafeMutablePointer<UInt8>, dealloc: () -> ()) {
+  let up = UnsafeMutablePointer<UInt8>.allocate(capacity: 100)
  up[0] = 0x61
  up[1] = 0x62
  up[2] = 0
  return (up, { up.deallocate(capacity: 100) })
 }

-func getNonASCIICString() -> (UnsafeMutablePointer<CChar>, dealloc: () -> ()) {
+func getNonASCIIUTF8() -> (UnsafeMutablePointer<UInt8>, dealloc: () -> ()) {
  let up = UnsafeMutablePointer<UInt8>.allocate(capacity: 100)
  up[0] = 0xd0
  up[1] = 0xb0
@@ -348,7 +348,7 @@ func getNonASCIICString() -> (UnsafeMutablePointer<CChar>, dealloc: () -> ()) {
 }

 func getIllFormedUTF8String1(
-) -> (UnsafeMutablePointer<CChar>, dealloc: () -> ()) {
+) -> (UnsafeMutablePointer<UInt8>, dealloc: () -> ()) {
  let up = UnsafeMutablePointer<UInt8>.allocate(capacity: 100)
  up[0] = 0x41
  up[1] = 0xed
@@ -360,7 +360,7 @@ func getIllFormedUTF8String1(
 }

 func getIllFormedUTF8String2(
-) -> (UnsafeMutablePointer<CChar>, dealloc: () -> ()) {
+) -> (UnsafeMutablePointer<UInt8>, dealloc: () -> ()) {
  let up = UnsafeMutablePointer<UInt8>.allocate(capacity: 100)
  up[0] = 0x41
  up[0] = 0x41
@@ -376,7 +376,7 @@ func asCCharArray(_ a: [UInt8]) -> [CChar] {
  return a.map { CChar(bitPattern: $0) }
 }

-func getCStringLength(_ cString: UnsafePointer<CChar>) -> Int {
+func getUTF8Length(_ cString: UnsafePointer<UInt8>) -> Int {
  var length = 0
  while cString[length] != 0 {
    length += 1
@@ -384,13 +384,13 @@ func getCStringLength(_ cString: UnsafePointer<CChar>) -> Int {
  return length
 }

-func bindAsUTF8(_ cString: UnsafePointer<CChar>) -> UnsafePointer<UInt8> {
-  return UnsafeRawPointer(cString).bindMemory(to: UInt8.self,
-    capacity: getCStringLength(cString))
+func bindAsCChar(_ utf8: UnsafePointer<UInt8>) -> UnsafePointer<CChar> {
+  return UnsafeRawPointer(utf8).bindMemory(to: CChar.self,
+    capacity: getUTF8Length(utf8))
 }

-func expectEqualCString(_ lhs: UnsafePointer<CChar>,
-  _ rhs: UnsafePointer<CChar>) {
+func expectEqualCString(_ lhs: UnsafePointer<UInt8>,
+  _ rhs: UnsafePointer<UInt8>) {

  var index = 0
  while lhs[index] != 0 {
@@ -400,18 +400,18 @@ func expectEqualCString(_ lhs: UnsafePointer<CChar>,
  expectEqual(0, rhs[index])
 }

-func expectEqualCString(_ lhs: UnsafePointer<CChar>,
-  _ rhs: ContiguousArray<CChar>) {
+func expectEqualCString(_ lhs: UnsafePointer<UInt8>,
+  _ rhs: ContiguousArray<UInt8>) {
  rhs.withUnsafeBufferPointer {
    expectEqualCString(lhs, $0.baseAddress!)
  }
 }

-func expectEqualCString(_ lhs: UnsafePointer<CChar>,
-  _ rhs: ContiguousArray<UInt8>) {
+func expectEqualCString(_ lhs: UnsafePointer<UInt8>,
+  _ rhs: ContiguousArray<CChar>) {
  rhs.withUnsafeBufferPointer {
    $0.baseAddress!.withMemoryRebound(
-      to: CChar.self, capacity: rhs.count) {
+      to: UInt8.self, capacity: rhs.count) {
      expectEqualCString(lhs, $0)
    }
  }
@@ -419,36 +419,36 @@ func expectEqualCString(_ lhs: UnsafePointer<CChar>,

 CStringTests.test("String.init(validatingUTF8:)") {
  do {
-    let (s, dealloc) = getASCIICString()
-    expectOptionalEqual("ab", String(validatingUTF8: s))
+    let (s, dealloc) = getASCIIUTF8()
+    expectOptionalEqual("ab", String(validatingUTF8: bindAsCChar(s)))
    dealloc()
  }
  do {
-    let (s, dealloc) = getNonASCIICString()
-    expectOptionalEqual("аб", String(validatingUTF8: s))
+    let (s, dealloc) = getNonASCIIUTF8()
+    expectOptionalEqual("аб", String(validatingUTF8: bindAsCChar(s)))
    dealloc()
  }
  do {
    let (s, dealloc) = getIllFormedUTF8String1()
-    expectEmpty(String(validatingUTF8: s))
+    expectEmpty(String(validatingUTF8: bindAsCChar(s)))
    dealloc()
  }
 }

 CStringTests.test("String(cString:)") {
  do {
-    let (s, dealloc) = getASCIICString()
+    let (s, dealloc) = getASCIIUTF8()
    let result = String(cString: s)
    expectEqual("ab", result)
-    let su = bindAsUTF8(s)
+    let su = bindAsCChar(s)
    expectEqual("ab", String(cString: su))
    dealloc()
  }
  do {
-    let (s, dealloc) = getNonASCIICString()
+    let (s, dealloc) = getNonASCIIUTF8()
    let result = String(cString: s)
    expectEqual("аб", result)
-    let su = bindAsUTF8(s)
+    let su = bindAsCChar(s)
    expectEqual("аб", String(cString: su))
    dealloc()
  }
@@ -456,7 +456,7 @@ CStringTests.test("String(cString:)") {
    let (s, dealloc) = getIllFormedUTF8String1()
    let result = String(cString: s)
    expectEqual("\u{41}\u{fffd}\u{fffd}\u{fffd}\u{41}", result)
-    let su = bindAsUTF8(s)
+    let su = bindAsCChar(s)
    expectEqual("\u{41}\u{fffd}\u{fffd}\u{fffd}\u{41}", String(cString: su))
    dealloc()
  }
@@ -464,14 +464,14 @@ CStringTests.test("String(cString:)") {

 CStringTests.test("String.decodeCString") {
  do {
-    let s = getNullCString()
-    let result = String.decodeCString(UnsafePointer(s), as: UTF8.self)
+    let s = getNullUTF8()
+    let result = String.decodeCString(s, as: UTF8.self)
    expectEmpty(result)
  }
  do { // repairing
    let (s, dealloc) = getIllFormedUTF8String1()
    if let (result, repairsMade) = String.decodeCString(
-      UnsafePointer(s), as: UTF8.self, repairingInvalidCodeUnits: true) {
+      s, as: UTF8.self, repairingInvalidCodeUnits: true) {
      expectOptionalEqual("\u{41}\u{fffd}\u{fffd}\u{fffd}\u{41}", result)
      expectTrue(repairsMade)
    } else {
@@ -482,7 +482,7 @@ CStringTests.test("String.decodeCString") {
  do { // non repairing
    let (s, dealloc) = getIllFormedUTF8String1()
    let result = String.decodeCString(
-      UnsafePointer(s), as: UTF8.self, repairingInvalidCodeUnits: false)
+      s, as: UTF8.self, repairingInvalidCodeUnits: false)
    expectEmpty(result)
    dealloc()
  }
@@ -490,13 +490,13 @@ CStringTests.test("String.decodeCString") {

 CStringTests.test("String.utf8CString") {
  do {
-    let (cstr, dealloc) = getASCIICString()
+    let (cstr, dealloc) = getASCIIUTF8()
    let str = String(cString: cstr)
    expectEqualCString(cstr, str.utf8CString)
    dealloc()
  }
  do {
-    let (cstr, dealloc) = getNonASCIICString()
+    let (cstr, dealloc) = getNonASCIIUTF8()
    let str = String(cString: cstr)
    expectEqualCString(cstr, str.utf8CString)
    dealloc()
--- a/test/1_stdlib/TestUUID.swift
+++ b/test/1_stdlib/TestUUID.swift
@@ -75,7 +75,7 @@ class TestUUID : TestUUIDSuper {
        var bytes: [UInt8] = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
        let valFromBytes = bytes.withUnsafeMutableBufferPointer { buffer -> UUID in
            ref.getBytes(buffer.baseAddress)
-            return UUID(uuid: UnsafePointer<uuid_t>(buffer.baseAddress!).pointee)
+            return UUID(uuid: UnsafeRawPointer(buffer.baseAddress!).load(as: uuid_t.self))
        }
        let valFromStr = UUID(uuidString: ref.uuidString)
        expectEqual(ref.uuidString, valFromRef.uuidString)
--- a/test/Constraints/lvalues.swift
+++ b/test/Constraints/lvalues.swift
@@ -179,7 +179,7 @@ func rdar19835413() {
    f1(&a[i])
    f1(&a[0])
    f1(pi)
-    f1(UnsafeMutablePointer(pi))
+    f1(pi)
  }
 }

--- a/test/Interpreter/SDK/archiving_generic_swift_class.swift
+++ b/test/Interpreter/SDK/archiving_generic_swift_class.swift
@@ -70,10 +70,11 @@ func driver() {
    }

    // Spawn the archiver process.
+    let str: StaticString = "-archive"
+    let optStr = UnsafeMutableRawPointer(mutating: str.utf8Start).bindMemory(
+      to: CChar.self, capacity: str.utf8CodeUnitCount)
    let archiverArgv: [UnsafeMutablePointer<Int8>?] = [
-      CommandLine.unsafeArgv[0],
-      UnsafeMutablePointer(("-archive" as StaticString).utf8Start),
-      nil
+      CommandLine.unsafeArgv[0], optStr, nil
    ]
    guard posix_spawn(&archiver, CommandLine.unsafeArgv[0],
                      &archiverActions, nil,
@@ -99,11 +100,12 @@ func driver() {
    }

    // Spawn the unarchiver process.
+    let str = "-unarchive" as StaticString
+    let optStr = UnsafeMutableRawPointer(mutating: str.utf8Start).bindMemory(
+      to: CChar.self, capacity: str.utf8CodeUnitCount)
    var unarchiver: pid_t = 0
    let unarchiverArgv: [UnsafeMutablePointer<Int8>?] = [
-      CommandLine.unsafeArgv[0],
-      UnsafeMutablePointer(("-unarchive" as StaticString).utf8Start),
-      nil
+      CommandLine.unsafeArgv[0], optStr, nil
    ]
    guard posix_spawn(&unarchiver, CommandLine.unsafeArgv[0],
                      &unarchiverActions, nil,
--- a/test/Interpreter/SDK/objc_inner_pointer.swift
+++ b/test/Interpreter/SDK/objc_inner_pointer.swift
@@ -28,7 +28,7 @@ autoreleasepool {
  repeat {
    let data = NSData(bytes: [2, 3, 5, 7] as [UInt8], length: 4)
    hangCanary(data)
-    bytes = UnsafeMutablePointer<UInt8>(data.bytes.assumingMemoryBound(to: UInt8.self))
+    bytes = UnsafeMutablePointer<UInt8>(mutating: data.bytes.assumingMemoryBound(to: UInt8.self))
  } while false // CHECK-NOT: died
  print(bytes[0]) // CHECK:      2
  print(bytes[1]) // CHECK-NEXT: 3
@@ -44,7 +44,7 @@ autoreleasepool {
    let data = NSData(bytes: [11, 13, 17, 19] as [UInt8], length: 4)
    hangCanary(data)
    let dataAsAny: AnyObject = data
-    bytes = UnsafeMutablePointer<UInt8>(dataAsAny.bytes!.assumingMemoryBound(to: UInt8.self))
+    bytes = UnsafeMutablePointer<UInt8>(mutating: dataAsAny.bytes!.assumingMemoryBound(to: UInt8.self))
  } while false // CHECK-NOT: died
  print(bytes[0]) // CHECK:      11
  print(bytes[1]) // CHECK-NEXT: 13
--- a/test/Parse/pointer_conversion.swift.gyb
+++ b/test/Parse/pointer_conversion.swift.gyb
@@ -259,10 +259,6 @@ func stringArguments(_ s: String) {
 }


-func pointerConstructor(_ x: UnsafeMutablePointer<Int>) -> UnsafeMutablePointer<Float> {
-  return UnsafeMutablePointer(x)
-}
-
 func optionality(_ op: UnsafeMutablePointer<Float>?) {
  takesMutableVoidPointer(op)
 % if not suffix:
@@ -286,10 +282,10 @@ func genericPointerArithmetic<T>(_ x: UnsafeMutablePointer<T>, i: Int, t: T) ->
  p.initialize(to: t)
 }

-func passPointerToClosure(_ f: (UnsafeMutablePointer<Float>) -> Int) -> Int { }
+func passPointerToClosure(_ f: (UnsafeMutablePointer<Int>) -> Int) -> Int { }

-func pointerInClosure(_ f: (UnsafeMutablePointer<Int>) -> Int) -> Int {
-  return passPointerToClosure { f(UnsafeMutablePointer($0)) }
+func pointerInClosure(_ f: (UnsafePointer<Int>) -> Int) -> Int {
+  return passPointerToClosure { f($0) }
 }

 struct NotEquatable {}
--- a/test/decl/subscript/addressors.swift
+++ b/test/decl/subscript/addressors.swift
@@ -72,7 +72,7 @@ struct AddressorAndGet {

  subscript(index: Int) -> Int {
    unsafeAddress { // expected-error {{subscript cannot provide both 'address' and a getter}}
-      return UnsafePointer(base)
+      return base
    }
    get {
      return base.get()
@@ -85,7 +85,7 @@ struct AddressorAndSet {

  subscript(index: Int) -> Int {
    unsafeAddress {
-      return UnsafePointer(base)
+      return base
    }
    set { // expected-error {{subscript cannot provide both 'address' and a setter; use an ordinary getter instead}}
    }
--- a/validation-test/stdlib/AtomicInt.swift
+++ b/validation-test/stdlib/AtomicInt.swift
@@ -704,7 +704,8 @@ struct AtomicInitializeARCRefRaceTest : RaceTestWithPerTrialData {
    var _atomicReference: AnyObject? = nil

    var atomicReferencePtr: UnsafeMutablePointer<AnyObject?> {
-      return UnsafeMutablePointer(_getUnsafePointerToStoredProperties(self))
+      return _getUnsafePointerToStoredProperties(self).assumingMemoryBound(
+        to: Optional<AnyObject>.self)
    }

    init() {}
--- a/validation-test/stdlib/CoreAudio.swift
+++ b/validation-test/stdlib/CoreAudio.swift
@@ -106,25 +106,25 @@ CoreAudioTestSuite.test(
 }

 CoreAudioTestSuite.test("AudioBufferList.sizeInBytes(maximumBuffers: Int)") {
-  expectEqual(ablHeaderSize + strideof(AudioBuffer),
+  expectEqual(ablHeaderSize + strideof(AudioBuffer.self),
    AudioBufferList.sizeInBytes(maximumBuffers: 1))
-  expectEqual(ablHeaderSize + 16 * strideof(AudioBuffer),
+  expectEqual(ablHeaderSize + 16 * strideof(AudioBuffer.self),
    AudioBufferList.sizeInBytes(maximumBuffers: 16))
 }

 CoreAudioTestSuite.test("AudioBufferList.sizeInBytes(maximumBuffers: Int)/trap/count<0") {
  expectCrashLater()
-  AudioBufferList.sizeInBytes(maximumBuffers: -1)
+  _ = AudioBufferList.sizeInBytes(maximumBuffers: -1)
 }

 CoreAudioTestSuite.test("AudioBufferList.sizeInBytes(maximumBuffers: Int)/trap/count==0") {
  expectCrashLater()
-  AudioBufferList.sizeInBytes(maximumBuffers: -1)
+  _ = AudioBufferList.sizeInBytes(maximumBuffers: -1)
 }

 CoreAudioTestSuite.test("AudioBufferList.sizeInBytes(maximumBuffers: Int)/trap/overflow") {
  expectCrashLater()
-  AudioBufferList.sizeInBytes(maximumBuffers: Int.max)
+  _ = AudioBufferList.sizeInBytes(maximumBuffers: Int.max)
 }

 CoreAudioTestSuite.test("AudioBufferList.allocate(maximumBuffers: Int)") {
@@ -142,17 +142,17 @@ CoreAudioTestSuite.test("AudioBufferList.allocate(maximumBuffers: Int)") {

 CoreAudioTestSuite.test("AudioBufferList.allocate(maximumBuffers: Int)/trap/count==0") {
  expectCrashLater()
-  AudioBufferList.allocate(maximumBuffers: 0)
+  _ = AudioBufferList.allocate(maximumBuffers: 0)
 }

 CoreAudioTestSuite.test("AudioBufferList.allocate(maximumBuffers: Int)/trap/count<0") {
  expectCrashLater()
-  AudioBufferList.allocate(maximumBuffers: -1)
+  _ = AudioBufferList.allocate(maximumBuffers: -1)
 }

 CoreAudioTestSuite.test("AudioBufferList.allocate(maximumBuffers: Int)/trap/overflow") {
  expectCrashLater()
-  AudioBufferList.allocate(maximumBuffers: Int.max)
+  _ = AudioBufferList.allocate(maximumBuffers: Int.max)
 }

 CoreAudioTestSuite.test("UnsafeMutableAudioBufferListPointer/AssociatedTypes") {
@@ -201,28 +201,36 @@ CoreAudioTestSuite.test(

 CoreAudioTestSuite.test("UnsafeMutableAudioBufferListPointer.count") {
  let sizeInBytes = AudioBufferList.sizeInBytes(maximumBuffers: 16)
-  let ablPtr = UnsafeMutablePointer<AudioBufferList>(
-    UnsafeMutablePointer<UInt8>.allocate(capacity: sizeInBytes))
+  let rawPtr = UnsafeMutableRawPointer.allocate(
+    bytes: sizeInBytes, alignedTo: alignof(AudioBufferList.self))
+  let ablPtr = rawPtr.bindMemory(to: AudioBufferList.self,
+    capacity: sizeInBytes / strideof(AudioBufferList.self))

  // It is important that 'ablPtrWrapper' is a 'let'.  We are verifying that
  // the 'count' property has a nonmutating setter.
  let ablPtrWrapper = UnsafeMutableAudioBufferListPointer(ablPtr)

  // Test getter.
-  UnsafeMutablePointer<UInt32>(ablPtr).pointee = 0x1234_5678
+  rawPtr.storeBytes(of: 0x1234_5678, as: UInt32.self)
  expectEqual(0x1234_5678, ablPtrWrapper.count)

  // Test setter.
  ablPtrWrapper.count = 0x7765_4321
-  expectEqual(0x7765_4321, UnsafeMutablePointer<UInt32>(ablPtr).pointee)
+  expectEqual(0x7765_4321, rawPtr.load(as: UInt32.self))

-  ablPtr.deallocate(capacity: sizeInBytes)
+  rawPtr.deallocate(
+    bytes: sizeInBytes, alignedTo: alignof(AudioBufferList.self))
 }

 CoreAudioTestSuite.test("UnsafeMutableAudioBufferListPointer.subscript(_: Int)") {
  let sizeInBytes = AudioBufferList.sizeInBytes(maximumBuffers: 16)
-  let ablPtr = UnsafeMutablePointer<AudioBufferList>(
-    UnsafeMutablePointer<UInt8>.allocate(capacity: sizeInBytes))
+
+  let rawPtr = UnsafeMutableRawPointer.allocate(
+    bytes: sizeInBytes, alignedTo: 1)
+
+  let ablPtr = rawPtr.bindMemory(
+    to: AudioBufferList.self,
+    capacity: sizeInBytes / sizeof(AudioBufferList.self))

  // It is important that 'ablPtrWrapper' is a 'let'.  We are verifying that
  // the subscript has a nonmutating setter.
@@ -234,9 +242,9 @@ CoreAudioTestSuite.test("UnsafeMutableAudioBufferListPointer.subscript(_: Int)")
      mNumberChannels: 2, mDataByteSize: 1024,
      mData: UnsafeMutableRawPointer(bitPattern: 0x1234_5678))

-    UnsafeMutablePointer<AudioBuffer>(
-        UnsafeMutablePointer<UInt8>(ablPtr) + ablHeaderSize
-      ).pointee = audioBuffer
+    let bufPtr = (rawPtr + ablHeaderSize).assumingMemoryBound(
+      to: AudioBuffer.self)
+    bufPtr.pointee = audioBuffer
    ablPtrWrapper.count = 1

    expectEqual(2, ablPtrWrapper[0].mNumberChannels)
@@ -253,8 +261,8 @@ CoreAudioTestSuite.test("UnsafeMutableAudioBufferListPointer.subscript(_: Int)")
    ablPtrWrapper.count = 2
    ablPtrWrapper[1] = audioBuffer

-    let audioBufferPtr = UnsafeMutablePointer<AudioBuffer>(
-      UnsafeMutablePointer<UInt8>(ablPtr) + ablHeaderSize) + 1
+    let audioBufferPtr = (rawPtr + ablHeaderSize).assumingMemoryBound(
+      to: AudioBuffer.self) + 1
    expectEqual(5, audioBufferPtr.pointee.mNumberChannels)
    expectEqual(256, audioBufferPtr.pointee.mDataByteSize)
    expectEqual(audioBuffer.mData, audioBufferPtr.pointee.mData)
--- a/validation-test/stdlib/NewArray.swift.gyb
+++ b/validation-test/stdlib/NewArray.swift.gyb
@@ -190,7 +190,10 @@ func nsArrayOfStrings() -> Array<NSString> {
  let src: ContiguousArray<NSString> = ["foo", "bar", "baz"]

  return src.withUnsafeBufferPointer {
-    let ns =  NSArray(objects: UnsafePointer($0.baseAddress!), count: $0.count)
+    let ns =  NSArray(
+      objects: unsafeBitCast($0.baseAddress!,
+        to: UnsafeMutablePointer<AnyObject>.self),
+      count: $0.count)
    return ns as! [NSString]
  }
 }
--- a/validation-test/stdlib/Prototypes/PersistentVector.swift.gyb
+++ b/validation-test/stdlib/Prototypes/PersistentVector.swift.gyb
@@ -104,20 +104,16 @@ import SwiftShims
 //

 func allocBytes(count: Int, alignment: Int)
-  -> UnsafeMutablePointer<UInt8> {
-  return UnsafeMutablePointer(
-    Builtin.allocRaw(count._builtinWordValue, alignment._builtinWordValue))
+  -> UnsafeMutableRawPointer {
+  return UnsafeMutableRawPointer.allocate(bytes: count, alignedTo: alignment)
 }

 func deallocBytes(
-  _ pointer: UnsafeMutablePointer<UInt8>,
+  _ pointer: UnsafeMutableRawPointer,
  byteCount: Int,
  alignment: Int
 ) {
-  Builtin.deallocRaw(
-    pointer._rawValue,
-    byteCount._builtinWordValue,
-    alignment._builtinWordValue)
+  pointer.deallocate(bytes: byteCount, alignedTo: alignment)
 }

 func _swift_stdlib_atomicStoreInt(
@@ -125,7 +121,7 @@ func _swift_stdlib_atomicStoreInt(
  desired: Int) {
 #if arch(x86_64)
  return _swift_stdlib_atomicStoreUInt64(
-    object: UnsafeMutablePointer(target),
+    object: unsafeBitCast(target, to: UnsafeMutablePointer<UInt64>.self),
    desired: UInt64(UInt(bitPattern: desired)))
 #endif
 }
@@ -357,10 +353,10 @@ struct _PVSparseVectorNodePointer<Key : Hashable, Value>
    return _valueVectorOffset(layout: layout) + _valueVectorSize(layout: layout)
  }

-  var _nodePointer: UnsafeMutablePointer<UInt8>
+  var _nodePointer: UnsafeMutableRawPointer

  var _referenceCountPointer: UnsafeMutablePointer<Int> {
-    return UnsafeMutablePointer(_nodePointer)
+    return _nodePointer.assumingMemoryBound(to: Int.self)
  }

  var layoutParameters: _PVSparseVectorNodeLayoutParameters {
@@ -403,23 +399,23 @@ struct _PVSparseVectorNodePointer<Key : Hashable, Value>

  var childNodePopulationBitmap: _Int32Bitmap {
    unsafeAddress {
-      return UnsafePointer(
-        _nodePointer + _Self._childNodePopulationBitmapOffset)
+      return UnsafePointer((_nodePointer + _Self._childNodePopulationBitmapOffset)
+        .assumingMemoryBound(to: _Int32Bitmap.self))
    }
    nonmutating unsafeMutableAddress {
-      return UnsafeMutablePointer(
-        _nodePointer + _Self._childNodePopulationBitmapOffset)
+      return (_nodePointer + _Self._childNodePopulationBitmapOffset)
+        .assumingMemoryBound(to: _Int32Bitmap.self)
    }
  }

  var keyPopulationBitmap: _Int32Bitmap {
    unsafeAddress {
-      return UnsafePointer(
-        _nodePointer + _Self._keyPopulationBitmapOffset)
+      return UnsafePointer((_nodePointer + _Self._keyPopulationBitmapOffset)
+        .assumingMemoryBound(to: _Int32Bitmap.self))
    }
    nonmutating unsafeMutableAddress {
-      return UnsafeMutablePointer(
-        _nodePointer + _Self._keyPopulationBitmapOffset)
+      return (_nodePointer + _Self._keyPopulationBitmapOffset)
+        .assumingMemoryBound(to: _Int32Bitmap.self)
    }
  }

@@ -432,8 +428,8 @@ struct _PVSparseVectorNodePointer<Key : Hashable, Value>
  }

  var _childNodeVector: UnsafeMutablePointer<_PVAnyNodePointer<Key, Value>?> {
-    return UnsafeMutablePointer(
-      _nodePointer + _Self._childNodeVectorOffset)
+    return (_nodePointer + _Self._childNodeVectorOffset)
+      .assumingMemoryBound(to: Optional<_PVAnyNodePointer<Key, Value>>.self)
  }

  var childNodes: UnsafeMutableBufferPointer<_PVAnyNodePointer<Key, Value>?> {
@@ -444,17 +440,17 @@ struct _PVSparseVectorNodePointer<Key : Hashable, Value>

  func _keyVector(layout: _PVSparseVectorNodeLayoutParameters)
    -> UnsafeMutablePointer<Key> {
-    return UnsafeMutablePointer(
-      _nodePointer + _Self._keyVectorOffset(layout: layout))
+    return (_nodePointer + _Self._keyVectorOffset(layout: layout))
+      .assumingMemoryBound(to: Key.self)
  }

  func _valueVector(layout: _PVSparseVectorNodeLayoutParameters)
    -> UnsafeMutablePointer<Value> {
-    return UnsafeMutablePointer(
-      _nodePointer + _Self._valueVectorOffset(layout: layout))
+    return (_nodePointer + _Self._valueVectorOffset(layout: layout))
+      .assumingMemoryBound(to: Value.self)
  }

-  init(_nodePointer: UnsafeMutablePointer<UInt8>) {
+  init(_nodePointer: UnsafeMutableRawPointer) {
    self._nodePointer = _nodePointer
  }

@@ -1025,10 +1021,10 @@ struct _PVArrayNodePointer<Key : Hashable, Value>
    return _valueArrayOffset + _valueArraySize
  }

-  var _nodePointer: UnsafeMutablePointer<UInt8>
+  var _nodePointer: UnsafeMutableRawPointer

  var _referenceCountPointer: UnsafeMutablePointer<Int> {
-    return UnsafeMutablePointer(_nodePointer)
+    return _nodePointer.assumingMemoryBound(to: Int.self)
  }

  func retain() {
@@ -1049,14 +1045,14 @@ struct _PVArrayNodePointer<Key : Hashable, Value>

  func dealloc() {
    for i in childNodePopulationBitmap.setBitIndices {
-      UnsafeMutablePointer<_PVAnyNodePointer<Key, Value>>(
-        _childNodeOrKeyArray + _Self._childNodeOrKeyStride * i)
+      (_childNodeOrKeyArray + _Self._childNodeOrKeyStride * i)
+        .assumingMemoryBound(to: _PVAnyNodePointer<Key, Value>.self)
        .pointee.release()
    }
    if !_isPOD(Key.self) {
      for i in keyPopulationBitmap.setBitIndices {
-        UnsafeMutablePointer<Key>(
-          _childNodeOrKeyArray + _Self._childNodeOrKeyStride * i)
+        (_childNodeOrKeyArray + _Self._childNodeOrKeyStride * i)
+          .assumingMemoryBound(to: Key.self)
          .deinitialize()
      }
    }
@@ -1076,23 +1072,23 @@ struct _PVArrayNodePointer<Key : Hashable, Value>

  var childNodePopulationBitmap: _Int32Bitmap {
    unsafeAddress {
-      return UnsafePointer(
-        _nodePointer + _Self._childNodePopulationBitmapOffset)
+      return UnsafePointer((_nodePointer + _Self._childNodePopulationBitmapOffset)
+        .assumingMemoryBound(to: _Int32Bitmap.self))
    }
    nonmutating unsafeMutableAddress {
-      return UnsafeMutablePointer(
-        _nodePointer + _Self._childNodePopulationBitmapOffset)
+      return (_nodePointer + _Self._childNodePopulationBitmapOffset)
+        .assumingMemoryBound(to: _Int32Bitmap.self)
    }
  }

  var keyPopulationBitmap: _Int32Bitmap {
    unsafeAddress {
-      return UnsafePointer(
-        _nodePointer + _Self._keyPopulationBitmapOffset)
+      return UnsafePointer((_nodePointer + _Self._keyPopulationBitmapOffset)
+        .assumingMemoryBound(to: _Int32Bitmap.self))
    }
    nonmutating unsafeMutableAddress {
-      return UnsafeMutablePointer(
-        _nodePointer + _Self._keyPopulationBitmapOffset)
+      return (_nodePointer + _Self._keyPopulationBitmapOffset)
+        .assumingMemoryBound(to: _Int32Bitmap.self)
    }
  }

@@ -1104,17 +1100,16 @@ struct _PVArrayNodePointer<Key : Hashable, Value>
    return keyPopulationBitmap.setBitCount
  }

-  var _childNodeOrKeyArray: UnsafeMutablePointer<UInt8> {
-    return UnsafeMutablePointer(
-      _nodePointer + _Self._childNodeOrKeyArrayOffset)
+  var _childNodeOrKeyArray: UnsafeMutableRawPointer {
+    return _nodePointer + _Self._childNodeOrKeyArrayOffset
  }

  var _valueArray: UnsafeMutablePointer<Value> {
-    return UnsafeMutablePointer(
-      _nodePointer + _Self._valueArrayOffset)
+    return (_nodePointer + _Self._valueArrayOffset)
+      .assumingMemoryBound(to: Value.self)
  }

-  init(_nodePointer: UnsafeMutablePointer<UInt8>) {
+  init(_nodePointer: UnsafeMutableRawPointer) {
    self._nodePointer = _nodePointer
  }

@@ -1138,9 +1133,8 @@ struct _PVArrayNodePointer<Key : Hashable, Value>
    precondition(!childNodePopulationBitmap[i]) // sanity check
    precondition(!keyPopulationBitmap[i]) // sanity check

-    UnsafeMutablePointer<Key>(
-      _childNodeOrKeyArray + _Self._childNodeOrKeyStride * i)
-      .initialize(to: key)
+    (_childNodeOrKeyArray + _Self._childNodeOrKeyStride * i)
+      .initializeMemory(as: Key.self, to: key)
    (_valueArray + i).initialize(to: value)

    keyPopulationBitmap[i] = true
@@ -1242,10 +1236,10 @@ struct _PVCollisionNodePointer<Key : Hashable, Value>
    return _valueArrayOffset(layout: layout) + _valueArraySize(layout: layout)
  }

-  var _nodePointer: UnsafeMutablePointer<UInt8>
+  var _nodePointer: UnsafeMutableRawPointer

  var _referenceCountPointer: UnsafeMutablePointer<Int> {
-    return UnsafeMutablePointer(_nodePointer)
+    return _nodePointer.assumingMemoryBound(to: Int.self)
  }

  var layoutParameters: _PVCollisionNodePointerLayoutParameters {
@@ -1284,25 +1278,27 @@ struct _PVCollisionNodePointer<Key : Hashable, Value>

  var keyCount: Int {
    unsafeAddress {
-      return UnsafePointer(_nodePointer + _Self._countOffset)
+      return UnsafePointer((_nodePointer + _Self._countOffset)
+        .assumingMemoryBound(to: Int.self))
    }
    nonmutating unsafeMutableAddress {
-      return UnsafeMutablePointer(_nodePointer + _Self._countOffset)
+      return (_nodePointer + _Self._countOffset)
+        .assumingMemoryBound(to: Int.self)
    }
  }

  var _keyArray: UnsafeMutablePointer<Key> {
-    return UnsafeMutablePointer(
-      _nodePointer + _Self._keyArrayOffset)
+    return (_nodePointer + _Self._keyArrayOffset)
+      .assumingMemoryBound(to: Key.self)
  }

  func _valueArray(layout: _PVCollisionNodePointerLayoutParameters)
    -> UnsafeMutablePointer<Value> {
-    return UnsafeMutablePointer(
-      _nodePointer + _Self._valueArrayOffset(layout: layout))
+    return (_nodePointer + _Self._valueArrayOffset(layout: layout))
+      .assumingMemoryBound(to: Value.self)
  }

-  init(_nodePointer: UnsafeMutablePointer<UInt8>) {
+  init(_nodePointer: UnsafeMutableRawPointer) {
    self._nodePointer = _nodePointer
  }

@@ -1486,9 +1482,9 @@ struct _PVCollisionNodePointer<Key : Hashable, Value>
 struct _PVAnyNodePointer<Key : Hashable, Value>
  : CustomReflectable, Equatable {

-  let taggedPointer: UnsafeMutablePointer<UInt8>
+  let taggedPointer: UnsafeMutableRawPointer

-  init(taggedPointer: UnsafeMutablePointer<UInt8>) {
+  init(taggedPointer: UnsafeMutableRawPointer) {
    self.taggedPointer = taggedPointer
  }

@@ -1501,14 +1497,14 @@ struct _PVAnyNodePointer<Key : Hashable, Value>
  init(_ arrayNode: _PVArrayNodePointer<Key, Value>) {
    precondition(
      Int(bitPattern: arrayNode._nodePointer) & 0x3 == 0) // sanity check
-    self.taggedPointer = UnsafeMutablePointer(bitPattern:
+    self.taggedPointer = UnsafeMutableRawPointer(bitPattern:
      Int(bitPattern: arrayNode._nodePointer) | 1)!
  }

  init(_ collisionNode: _PVCollisionNodePointer<Key, Value>) {
    precondition(
      Int(bitPattern: collisionNode._nodePointer) & 0x3 == 0) // sanity check
-    self.taggedPointer = UnsafeMutablePointer(bitPattern:
+    self.taggedPointer = UnsafeMutableRawPointer(bitPattern:
      Int(bitPattern: collisionNode._nodePointer) | 2)!
  }

@@ -1516,13 +1512,13 @@ struct _PVAnyNodePointer<Key : Hashable, Value>
    return Int(bitPattern: taggedPointer) & 0x3
  }

-  var _untaggedPointer: UnsafeMutablePointer<UInt8> {
-    return UnsafeMutablePointer(bitPattern:
+  var _untaggedPointer: UnsafeMutableRawPointer {
+    return UnsafeMutableRawPointer(bitPattern:
      Int(bitPattern: taggedPointer) & ~0x3)!
  }

  var _referenceCountPointer: UnsafeMutablePointer<Int> {
-    return UnsafeMutablePointer(_untaggedPointer)
+    return _untaggedPointer.assumingMemoryBound(to: Int.self)
  }

  var asSparseVectorNode: _PVSparseVectorNodePointer<Key, Value> {