[stdlib] MemoryLayout: Add support for non-copyable type arguments

Author: lorentey

stdlib/public/core/MemoryLayout.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -40,7 +40,9 @@
 ///             byteCount: count * MemoryLayout<Point>.stride,
 ///             alignment: MemoryLayout<Point>.alignment)
 @frozen // namespace
-public enum MemoryLayout<T> {
+public enum MemoryLayout<T: ~Copyable> {}
+
+extension MemoryLayout where T: ~Copyable {
   /// The contiguous memory footprint of `T`, in bytes.
   ///
   /// A type's size does not include any dynamically allocated or out of line
@@ -50,6 +52,7 @@ public enum MemoryLayout<T> {
   /// When allocating memory for multiple instances of `T` using an unsafe
   /// pointer, use a multiple of the type's stride instead of its size.
   @_transparent
+  @_alwaysEmitIntoClient
   public static var size: Int {
     return Int(Builtin.sizeof(T.self))
   }
@@ -62,6 +65,7 @@ public enum MemoryLayout<T> {
   /// trades runtime performance for space efficiency. This value is always
   /// positive.
   @_transparent
+  @_alwaysEmitIntoClient
   public static var stride: Int {
     return Int(Builtin.strideof(T.self))
   }
@@ -71,12 +75,36 @@ public enum MemoryLayout<T> {
   /// Use the `alignment` property for a type when allocating memory using an
   /// unsafe pointer. This value is always positive.
   @_transparent
+  @_alwaysEmitIntoClient
   public static var alignment: Int {
     return Int(Builtin.alignof(T.self))
   }
 }
 
 extension MemoryLayout {
+  // TODO: Merge this back into the noncopyable variant once we have @_preInverseGenerics
+  @available(swift, obsoleted: 5.11) // Legacy ABI compatibility
+  @usableFromInline
+  internal static var size: Int {
+    return Int(Builtin.sizeof(T.self))
+  }
+
+  // TODO: Merge this back into the noncopyable variant once we have @_preInverseGenerics
+  @available(swift, obsoleted: 5.11) // Legacy ABI compatibility
+  @usableFromInline
+  internal static var stride: Int {
+    return Int(Builtin.strideof(T.self))
+  }
+
+  // TODO: Merge this back into the noncopyable variant once we have @_preInverseGenerics
+  @available(swift, obsoleted: 5.11) // Legacy ABI compatibility
+  @usableFromInline
+  internal static var alignment: Int {
+    return Int(Builtin.alignof(T.self))
+  }
+}
+
+extension MemoryLayout where T: ~Copyable {
   /// Returns the contiguous memory footprint of the given instance.
   ///
   /// The result does not include any dynamically allocated or out of line
@@ -100,7 +128,8 @@ extension MemoryLayout {
   /// - Parameter value: A value representative of the type to describe.
   /// - Returns: The size, in bytes, of the given value's type.
   @_transparent
-  public static func size(ofValue value: T) -> Int {
+  @_alwaysEmitIntoClient
+  public static func size(ofValue value: borrowing T) -> Int {
     return MemoryLayout.size
   }
 
@@ -128,7 +157,8 @@ extension MemoryLayout {
   /// - Parameter value: A value representative of the type to describe.
   /// - Returns: The stride, in bytes, of the given value's type.
   @_transparent
-  public static func stride(ofValue value: T) -> Int {
+  @_alwaysEmitIntoClient
+  public static func stride(ofValue value: borrowing T) -> Int {
     return MemoryLayout.stride
   }
 
@@ -153,10 +183,36 @@ extension MemoryLayout {
   /// - Returns: The default memory alignment, in bytes, of the given value's
   ///   type. This value is always positive.
   @_transparent
-  public static func alignment(ofValue value: T) -> Int {
+  @_alwaysEmitIntoClient
+  public static func alignment(ofValue value: borrowing T) -> Int {
     return MemoryLayout.alignment
   }
+}
 
+extension MemoryLayout {
+  // TODO: Merge this back into the noncopyable variant once we have @_preInverseGenerics
+  @available(swift, obsoleted: 5.11) // Legacy ABI compatibility
+  @usableFromInline
+  internal static func size(ofValue value: borrowing T) -> Int {
+    return MemoryLayout.size
+  }
+
+  // TODO: Merge this back into the noncopyable variant once we have @_preInverseGenerics
+  @available(swift, obsoleted: 5.11) // Legacy ABI compatibility
+  @usableFromInline
+  internal static func stride(ofValue value: borrowing T) -> Int {
+    return MemoryLayout.stride
+  }
+
+  // TODO: Merge this back into the noncopyable variant once we have @_preInverseGenerics
+  @available(swift, obsoleted: 5.11) // Legacy ABI compatibility
+  @usableFromInline
+  internal static func alignment(ofValue value: borrowing T) -> Int {
+    return MemoryLayout.alignment
+  }
+}
+
+extension MemoryLayout {
   /// Returns the offset of an inline stored property within a type's in-memory
   /// representation.
   ///
@@ -226,12 +282,15 @@ extension MemoryLayout {
   @_transparent
   @_unavailableInEmbedded
   public static func offset(of key: PartialKeyPath<T>) -> Int? {
+    // FIXME(noncopyableGenerics): The new (implicit) `where T: Copyable`
+    // extension constraint currently changes the mangling of this from a
+    // standalone function to an extension method.
     return key._storedInlineOffset
   }
 }
 
 // Not-yet-public alignment conveniences
-extension MemoryLayout {
+extension MemoryLayout where T: ~Copyable {
   internal static var _alignmentMask: Int { return alignment - 1 }
 
   internal static func _roundingUpToAlignment(_ value: Int) -> Int {

test/stdlib/Noncopyables/MemoryLayout.swift

@@ -0,0 +1,40 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-run-simple-swift(-enable-experimental-feature NoncopyableGenerics) | %FileCheck %s
+// REQUIRES: executable_test, noncopyable_generics
+
+struct A: ~Copyable {
+  let value: Int
+
+  init(_ value: Int) { self.value = value }
+}
+
+let expectedSize = MemoryLayout<Int>.size
+let expectedStride = MemoryLayout<Int>.stride
+let expectedAlignment = MemoryLayout<Int>.alignment
+
+
+let actualSize1 = MemoryLayout<A>.size
+// CHECK: size: true
+print("size: \(actualSize1 == expectedSize)")
+
+let actualStride1 = MemoryLayout<A>.stride
+// CHECK: stride: true
+print("stride: \(actualStride1 == expectedStride)")
+
+let actualAlignment1 = MemoryLayout<A>.alignment
+// CHECK: alignment: true
+print("alignment: \(actualAlignment1 == expectedAlignment)")
+
+let a = A(42)
+
+let actualSize2 = MemoryLayout.size(ofValue: a)
+// CHECK: size(ofValue:): true
+print("size(ofValue:): \(actualSize2 == expectedSize)")
+
+let actualStride2 = MemoryLayout.stride(ofValue: a)
+// CHECK: stride(ofValue:): true
+print("stride(ofValue:): \(actualStride2 == expectedStride)")
+
+let actualAlignment2 = MemoryLayout.alignment(ofValue: a)
+// CHECK: alignment(ofValue:): true
+print("alignment(ofValue:): \(actualAlignment2 == expectedAlignment)")