Deep Dive into "any" and "some"

At SwiftHeroes 2023

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1. Deep Dive into “any” and “some” Yuki ‘freddi’ Aki, LINE SwiftHeroes 2023 Secrets from deep side of Swift
2. ‘any’ and ‘some’ evolution ‘any’ Mechanism with Existential Container Optimization of ‘any’ and ‘some’
3. ‘any’ and ‘some’ evolution Optimization of ‘any’ and ‘some’ ‘any’ Mechanism with Existential Container
4. ‘any’ and ‘some’ evolution ‘any’ Mechanism with Existential Container Optimization of ‘any’ and ‘some’
5. ‘any’ and ‘some’ evolution ‘any’ Mechanism with Existential Container Optimization of ‘any’ and ‘some’
6. ‘any’ and ‘some’ evolution ‘any’ Mechanism with Existential Container Optimization of ‘any’ and ‘some’
7. some any
8. any some Existential Type Opaque Type
9. any some Existential Type Opaque Type
10. Example of Existential Type
11. protocol Shape { . . . } Example of Existential Type
12. protocol Shape { . . . } struct Rectangle: Shape {} struct Triangle: Shape {} Example of Existential Type
13. protocol Shape { . . . } = /* make assignable any object conform to Shape */ Example of Existential Type var shape
14. protocol Shape { . . . } : Shape = Rectangle() Example of Existential Type var shape
15. protocol Shape { . . . } var shape: Shape = Rectangle() shape = Triangle() Example of Existential Type
16. protocol Shape { . . . } var shape: shape = Triangle() ‘Shape’ is Existential Type Example of Existential Type Shape = Rectangle() Shape
17. protocol Shape { . . . } SE-0335 Introduce existential ‘any’ ‘any Shape’ is Existential Type // SE-0355, any is forced from Swift 6 var shape: shape = Triangle() Shape = Rectangle() any any
18. var shape: shape = Triangle() Existential Type’s cost Existential Container any Shape Shape = Rectangle() any
19. Existential Type’s cost Existential Container any Shape Read value Call Functions Performance Cost var shape: shape = Triangle() Shape = Rectangle() any
20. var shape: Shape Existential Type? Class? Structure?
21. Existential Type? Class? Structure? // Does Shape have existential container’s cost? var shape: Shape
22. any Existential Type? Class? Structure? // It is more clear that ‘Shape’ is existential type var shape: Shape
23. SE-0309 Unlock existentials for all protocols protocol P { associatedtype A }
24. let x: SE-0309 Unlock existentials for all protocols protocol P { associatedtype A } ~ Swift 5.6 P = /* ... */
25. SE-0309 Unlock existentials for all protocols protocol P { associatedtype A } Swift 5.7 ~ let x: P = /* ... */ any
26. protocol P { associatedtype A }
27. protocol P<A> { associatedtype A } P<A> Introduced by SE-0346 “Lightweight same-type requirements for primary associated types”
28. public protocol Clock<Duration>: Sendable public protocol BidirectionalCollection<Element>: Collection public protocol Collection<Element>: Sequence public protocol RawRepresentable<RawValue> public protocol Identifiable<ID> public protocol InstantProtocol<Duration> public protocol MutableCollection<Element> public protocol RandomAccessCollection<Element> public protocol RangeExpression<Bound> public protocol RangeReplaceableCollection<Element> public protocol SIMD<Scalar> public protocol IteratorProtocol<Element> public protocol Sequence<Element> public protocol SetAlgebra<Element> public protocol Strideable<Stride> Introduced by SE-0358 “Primary Associated Types in the Standard Library” Collection
29. func <C: >(_ collection: C) where C.Element == Int { . . . } Collection apply
30. func apply(_ collection: AnyCollection<Int>) { . . . }
31. func apply(_ collection: any Collection<Int>) { . . . } Introduced by SE-0353 “Constrained Existential Types”
32. protocol P<A> { associatedtype A } func method(_ p: any P<Int> ) { . . . } extension P<Int> { . . . } P<A> P<Int> Don’t need to write “P where A == Int” P<Int>
33. protocol P<A> { associatedtype A } func method(_ p: any P<Int> ) { . . . } extension P<Int> { . . . } let p: any P<Int> P<A> P<Int> Don’t need to prepare hand-made type erasure P<Int>
34. any some Existential Type Opaque Type
35. any some Existential Type Opaque Type
36. Existential Type’s cost func method(_ p: . . . } ‘any’ uses Existential Container P<Int>) { any
37. Existential Type’s cost Opaque Type (‘some’) doesn’t require Existential Container (SE-341 Opaque Parameter Declarations) some func method(_ p: . . . } P<Int>) {
38. Generics and Opaque Type in argument func method<T: P>(_ p: T) { . . . }
39. Generics and Opaque Type in argument • Generics doesn’t use Existential Container because “Keeps type information" func method<T: P>(_ p: T) { . . . }
40. Generics and Opaque Type in argument func method(_ p: some P) { . . . } ← • Generics doesn’t use Existential Container because “Keeps type information" • Opaque Type argument is syntax sugar of Generics func method<T: P>(_ p: T) { . . . } swiftc
41. func method() -> some P { // Opaque result type?? . . . }
42. Type-level abstraction Value-level abstraction Argument Return Protocol abstraction
43. Type-level abstraction protocol Shape { . . . } func draw<T: Shape>(shape: T) { . . . } • Example: Generics (argument), Opaque Type (argument and return) • Abstract by using concrete type information (Type variable)
44. Value-level abstraction protocol Shape { . . . } var shape: any Shape = Rectangle() shape = Triangle() • Example: Existential Type (argument and return) • Abstract by erasing type information of value and use underlying (protocol) type
45. Return Argument Existential type Type-level abstraction Value-level abstraction Generics ~ Swift 4 Protocol abstraction
46. Return Argument Existential type Type-level abstraction Value-level abstraction Generics Existential type ~ Swift 4 Protocol abstraction
47. ??? P func method PImpl() } () -> {
48. <PType: P> PType func method PImpl() } () -> {
49. Cannot convert return expression of type ‘P‘ to return type ‘PImpl' <PType: P> PType func method PImpl() } () -> {
50. Paying cost of Existential Container any P func method PImpl() } () -> {
51. PImpl func method PImpl() } () -> {
52. PImpl Too opened implementation Detail func method PImpl() } () -> {
53. let p = method() p.pImplFunc() No room for the developer to change the return type of the API Too opened implementation Detail PImpl func method PImpl() } () -> {
54. PImpl func method PImpl() } () -> {
55. -> <PType: P> PType “Reverse Generics” (not implemented) func method PImpl() } () () -> {
56. var p = method() “Reverse Generics” (not implemented) Treat type as “some type conforms P” -> <PType: P> PType func method PImpl() } () -> {
57. var p = method() Introduced by SE-0244 “Opaque Result Type” some P func method PImpl() } some () -> {
58. Return Argument Existential type Existential type Type-level abstraction Value-level abstraction Generics Opaque Type (5.7) Opaque Type (5.1) Swift 5 (5.1 and 5.7) ~ Protocol abstraction
59. ‘any’ and ‘some’ evolution ‘any’ Mechanism with Existential Container Optimization of ‘any’ and ‘some’
60. ‘any’ and ‘some’ evolution ‘any’ Mechanism with Existential Container Optimization of ‘any’ and ‘some’
61. How Existential Type works? var shape: any Shape = Rectangle() shape = Triangle()
62. How Existential Type works? var shape: any Shape = Rectangle() shape = Triangle() Existential Container any Shape
63. How Existential Type works? var shape: any Shape = Rectangle() shape = Triangle() Existential Container any Shape
64. How Existential Type works? var shape: any Shape = Rectangle() shape = Triangle() Existential Container any Shape
65. struct Triangle: Shape { var vertex = 3 } struct BigColoredRectangle: Shape { var color = UIColor.green var vertex = 4 }
66. struct Triangle: Shape { var vertex = 3 } struct BigColoredRectangle: Shape { var color = UIColor.green var vertex = 4 } print(MemoryLayout.size(ofValue: Triangle())) print(MemoryLayout.size(ofValue: BigColoredRectangle())) 8 16
67. struct Triangle: Shape { var vertex = 3 } struct BigColoredRectangle: Shape { var color = UIColor.green var vertex = 4 } print(MemoryLayout.size(ofValue: Triangle())) print(MemoryLayout.size(ofValue: BigColoredRectangle())) let shape1: any Shape = Triangle() let shape2: any Shape = BigColoredRectangle() 8 16
68. struct Triangle: Shape { var vertex = 3 } struct BigColoredRectangle: Shape { var color = UIColor.green var vertex = 4 } print(MemoryLayout.size(ofValue: Triangle())) print(MemoryLayout.size(ofValue: BigColoredRectangle())) let shape1: any Shape = Triangle() let shape2: any Shape = BigColoredRectangle() print(MemoryLayout.size(ofValue: shape1)) print(MemoryLayout.size(ofValue: shape2)) 8 16 40 40
69. struct VeryBigRectangle: Shape { . . . } print(MemoryLayout.size(ofValue: VeryBigRectangle())) 48
70. struct VeryBigRectangle: Shape { . . . } print(MemoryLayout.size(ofValue: VeryBigRectangle())) let shape: any Shape = VeryBigRectangle() print(MemoryLayout.size(ofValue: shape)) 48 40
71. Existential Container (struct) Existential Container
72. any Shape Object in Existential Container (struct) small struct var x: Int64 var y: Int64 Existential Container let shape: = Triangle()
73. Object in Existential Container (struct) small struct var x: Int64 var y: Int64 Existential Container = 40byte any Shape let shape: Triangle()
74. Object in Existential Container (struct) Buffer(64bit) Buffer(64bit) Buffer(64bit) small struct var x: Int64 var y: Int64 Existential Container = any Shape let shape: Triangle()
75. Object in Existential Container (struct) x: Int64 y: Int64 Buffer(64bit) small struct var x: Int64 var y: Int64 Existential Container = any Shape let shape: Triangle()
76. VeryBigRectangle() Object in Existential Container (struct) Buffer(64bit) Buffer(64bit) Buffer(64bit) large struct var x: Int64 var y: Int64 var z: Int64 var w: Int64 Existential Container = any Shape let shape:
77. Object in Existential Container (struct) Buffer(64bit) Buffer(64bit) Heap large struct var x: Int64 var y: Int64 var z: Int64 var w: Int64 Existential Container = VeryBigRectangle() any Shape let shape: Reference
78. Object in Existential Container (struct) Buffer(64bit) Buffer(64bit) Heap large struct var x: Int64 var y: Int64 var z: Int64 var w: Int64 Existential Container = Copy VeryBigRectangle() any Shape let shape: Reference x: Int y: Int z: Int w: Int
79. Object in Existential Container (struct) Reference Buffer(64bit) Buffer(64bit) Heap large struct var x: Int64 var y: Int64 var z: Int64 var w: Int64 Existential Container = Copy VeryBigRectangle() any Shape let shape: x: Int y: Int z: Int w: Int
80. struct VeryBigRectangle: Shape { . . . } print(MemoryLayout.size(ofValue: VeryBigRectangle())) let shape: any Shape = VeryBigRectangle() print(MemoryLayout.size(ofValue: shape)) 40 (without Heap area size)
81. Method Dispatch of Existential Container Buffer(64bit) Buffer(64bit) Buffer(64bit) Existential Container
82. Method Dispatch of Existential Container Buffer(64bit) Buffer(64bit) Buffer(64bit) Existential Container Protocol Witness Table
83. Witness Table Value Witness Table Protocol Witness Table
84. Witness Table Value Witness Table Protocol Witness Table Information of Type Allocation, Deinitialization, size, stride …
85. Witness Table Value Witness Table Protocol Witness Table Information for Method Dispatch (Method Table) Used when selecting the function of protocol Information of Type Allocation, Deinitialization, size, stride …
86. Method Dispatch of Existential Container x: Int64 y: Int64 Buffer(64bit) small struct var x: Int64 var y: Int64 Existential Container = Protocol Witness Table any Shape let shape: Triangle()
87. Method Dispatch of Existential Container x: Int64 y: Int64 Buffer(64bit) small struct var x: Int64 var y: Int64 func draw() Existential Container = Shape protocol func draw() Protocol Witness Table any Shape let shape: Triangle()
88. x: Int64 y: Int64 Buffer(64bit) small struct var x: Int64 var y: Int64 func draw() Existential Container = Shape protocol func draw() Name Which func needs call? draw() Triangle.draw() Protocol Witness Table Method Dispatch of Existential Container any Shape let shape: Triangle() Triangle’s Protocol Witness Table
89. x: Int64 y: Int64 Buffer(64bit) small struct var x: Int64 var y: Int64 func draw() Existential Container = Shape protocol func draw() Name Which func needs call? draw() Triangle.draw() Protocol Witness Table Method Dispatch of Existential Container any Shape let : Triangle() Triangle’s Protocol Witness Table shape
90. x: Int64 y: Int64 Buffer(64bit) Existential Container .draw() Protocol Witness Table Method Dispatch of Existential Container shape
91. x: Int64 y: Int64 Buffer(64bit) Existential Container Name Which func needs call? draw() Triangle.draw() combine() Triangle.combine() … … Protocol Witness Table Method Dispatch of Existential Container shape .draw()
92. x: Int64 y: Int64 Buffer(64bit) Existential Container Protocol Witness Table Method Dispatch of Existential Container shape .draw() Name Which func needs call? draw() Triangle.draw() combine() Triangle.combine() … …
93. Method Dispatch of Existential Type Dynamic Dispatch Static Dispatch
94. Method Dispatch of Existential Type Dynamic Dispatch Static Dispatch Method is selected on runtime Existential Container (Witness Table), Class (Virtual Table), Objective-C Runtime (Message Dispatch) … Method is selected on compile time struct, global function call, extension … Runtime Cost
95. Existential Container (struct) Buffer(64bit) Buffer(64bit) Buffer(64bit) Existential Container Protocol Witness Table
96. Existential Container (struct) Buffer(64bit) Buffer(64bit) Buffer(64bit) Existential Container Metadata Protocol Witness Table Record of type information with Value Witness Table
97. Existential Container (struct) Buffer(64bit) Buffer(64bit) Buffer(64bit) Existential Container Metadata Protocol Witness Table 64bit + 64bit + 64bit = 192bit (24byte) 64bit (8byte) 8byte 40byte
98. Summary: Existential Container
99. Summary: Existential Container • Existential Container size is fixed regardless of type (struct: 40Byte in 64bit CPU)
100. Summary: Existential Container • Existential Container allocates heap if the object exceeds its buffer • Existential Container size is fixed regardless of type (struct: 40Byte in 64bit CPU)
101. Summary: Existential Container • Existential Container size is fixed regardless of type (struct: 40Byte in 64bit CPU) • Existential Container allocates heap if the object exceeds its buffer • Existential Container method dispatch: Dynamic Dispatch
102. How Existential Container actually works?
103. How Existential Container actually works? • We can see how Existential type is initialized via Swift Intermediate Language(SIL)
104. How Existential Container actually works? • We can see how Existential type is initialized via Swift Intermediate Language(SIL) AST AST (Typed) SIL IR (LLVM) 📱 App
105. How Existential Container actually works? • We can see how Existential type is initialized via Swift Intermediate Language(SIL) AST AST (Typed) SIL IR (LLVM) 📱 App • SIL shows many codes which is hidden in normal Swift code • Reference Count • Witness Table …
106. protocol Shape { func draw() } struct Triangle: Shape { func draw() {} } let shape: any Shape = Triangle() shape.draw()
107. protocol Shape { func draw() } struct Triangle: Shape { func draw() {} } let shape: any Shape = Triangle() shape.draw() $ swiftc heroes.swift -emit-sil -o heroes.sil
108. sil_stage canonical import Builtin import Swift import SwiftShims protocol Shape { func draw() } struct Triangle : Shape { func draw() init() } @_hasStorage @_hasInitialValue let shape: Shape { get } // shape sil_global hidden [let] @$s6heroes5shapeAA5Shape_pvp : $Shape // main sil @main : $@convention(c) (Int32, UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>) -> Int32 { bb0(%0 : $Int32, %1 : $UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>): alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to $*@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape // users: %9, %9, %8 %8 = witness_method $@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $*@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@in_guaranteed τ_0_0) -> () // type-defs: %7; user: %9 %9 = apply %8<@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@in_guaranteed τ_0_0) -> () // type-defs: %7 %10 = integer_literal $Builtin.Int32, 0 // user: %11 %11 = struct $Int32 (%10 : $Builtin.Int32) // user: %12 return %11 : $Int32 // id: %12 } // end sil function 'main' // Triangle.draw() sil hidden @$s6heroes8TriangleV4drawyyF : $@convention(method) (Triangle) -> () { // %0 "self" // user: %1 bb0(%0 : $Triangle): debug_value %0 : $Triangle, let, name "self", argno 1, implicit // id: %1 %2 = tuple () // user: %3 return %2 : $() // id: %3 } // end sil function '$s6heroes8TriangleV4drawyyF' // Triangle.init() sil hidden @$s6heroes8TriangleVACycfC : $@convention(method) (@thin Triangle.Type) -> Triangle { // %0 "$metatype" bb0(%0 : $@thin Triangle.Type): %1 = struct $Triangle () // user: %2 return %1 : $Triangle // id: %2 } // end sil function '$s6heroes8TriangleVACycfC' // protocol witness for Shape.draw() in conformance Triangle sil private [transparent] [thunk] @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW : $@convention(witness_method: Shape) (@in_guaranteed Triangle) -> () { // %0 // user: %1 bb0(%0 : $*Triangle): %1 = load %0 : $*Triangle // user: %3 // function_ref Triangle.draw() %2 = function_ref @$s6heroes8TriangleV4drawyyF : $@convention(method) (Triangle) -> () // user: %3 %3 = apply %2(%1) : $@convention(method) (Triangle) -> () %4 = tuple () // user: %5 return %4 : $() // id: %5 } // end sil function ‘$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW’ // Mappings from '#fileID' to '#filePath': // 'heroes/heroes.swift' => 'heroes.swift' sil_witness_table hidden Triangle: Shape module heroes { method #Shape.draw: <Self where Self : Shape> (Self) -> () -> () : @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW // protocol witness for Shape.draw() in conformance Triangle }
109. sil_witness_table hidden Triangle: Shape module heroes { method #Shape.draw: <Self where Self : Shape> (Self) -> () -> () : @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW } Protocol Witness Table of ‘Triangle’
110. sil_witness_table hidden Triangle: Shape module heroes { method #Shape.draw: <Self where Self : Shape> (Self) -> () -> () : @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW } Protocol Function (‘Shape.draw’) Protocol Witness Table of ‘Triangle’
111. sil_witness_table hidden Triangle: Shape module heroes { method #Shape.draw: <Self where Self : Shape> (Self) -> () -> () : @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW } Protocol Function (‘Shape.draw’) Symbol of ‘Triangle.draw’ Protocol Witness Table of ‘Triangle’
112. sil_stage canonical import Builtin import Swift import SwiftShims protocol Shape { func draw() } struct Triangle : Shape { func draw() init() } @_hasStorage @_hasInitialValue let shape: Shape { get } // shape sil_global hidden [let] @$s6heroes5shapeAA5Shape_pvp : $Shape // main sil @main : $@convention(c) (Int32, UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>) -> Int32 { bb0(%0 : $Int32, %1 : $UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>): %10 = integer_literal $Builtin.Int32, 0 // user: %11 %11 = struct $Int32 (%10 : $Builtin.Int32) // user: %12 return %11 : $Int32 // id: %12 } // end sil function 'main' // Triangle.draw() sil hidden @$s6heroes8TriangleV4drawyyF : $@convention(method) (Triangle) -> () { // %0 "self" // user: %1 bb0(%0 : $Triangle): debug_value %0 : $Triangle, let, name "self", argno 1, implicit // id: %1 %2 = tuple () // user: %3 return %2 : $() // id: %3 } // end sil function '$s6heroes8TriangleV4drawyyF' // Triangle.init() sil hidden @$s6heroes8TriangleVACycfC : $@convention(method) (@thin Triangle.Type) -> Triangle { // %0 "$metatype" bb0(%0 : $@thin Triangle.Type): %1 = struct $Triangle () // user: %2 return %1 : $Triangle // id: %2 } // end sil function '$s6heroes8TriangleVACycfC' // protocol witness for Shape.draw() in conformance Triangle sil private [transparent] [thunk] @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW : $@convention(witness_method: Shape) (@in_guaranteed Triangle) -> () { // %0 // user: %1 bb0(%0 : $*Triangle): %1 = load %0 : $*Triangle // user: %3 // function_ref Triangle.draw() %2 = function_ref @$s6heroes8TriangleV4drawyyF : $@convention(method) (Triangle) -> () // user: %3 %3 = apply %2(%1) : $@convention(method) (Triangle) -> () %4 = tuple () // user: %5 return %4 : $() // id: %5 } // end sil function ‘$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW’ // Mappings from '#fileID' to '#filePath': // 'heroes/heroes.swift' => 'heroes.swift' sil_witness_table hidden Triangle: Shape module heroes { method #Shape.draw: <Self where Self : Shape> (Self) -> () -> () : @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW // protocol witness for Shape.draw() in conformance Triangle } alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to $*@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape // users: %9, %9, %8 %8 = witness_method $@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $*@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@in_guaranteed τ_0_0) -> () // type-defs: %7; user %9 = apply %8<@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@in_guaranteed τ_0_0) -> () // type-defs: %7
113. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to $*@opened("CA01F70C-D958-11ED-8F40- %8 = witness_method $@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape, #Shape.draw : <Self %9 = apply %8<@opened("CA01F70C-D958-11ED-8F40-9E59F6EF2BA0") Shape>(%7) : $@convention(witness let shape: any Shape = Triangle() shape.draw() %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@
114. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw()
115. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw() Allocating memory area for shape
116. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw() Call ‘Triangle’s initializer to create object Allocating memory area for shape
117. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw() Create Existential Container and assign ‘Triangle’ object Call ‘Triangle’s initializer to create object Allocating memory area for shape
118. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw()
119. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw()
120. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw() Load Existential Container
121. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw() Load Existential Container Get function symbol of Shape.draw from Protocol Witness Table in Existential Container
122. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, #Shape.draw : <Self where Self : Shape> (Self) -> () -> (), %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw() #Shape.draw : <Self where Self : Shape> (Self) -> () -> () Load Existential Container Get function symbol of Shape.draw from Protocol Witness Table in Existential Container
123. sil_witness_table hidden Triangle: Shape module heroes { method : @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW } Protocol Function (‘Shape.draw’) Symbol of ‘Triangle.draw’ #Shape.draw : <Self where Self : Shape> (Self) -> () -> () @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW Protocol Witness Table of ‘Triangle’
124. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, , %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw() #Shape.draw : <Self where Self : Shape> (Self) -> () -> () Obtained: @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW Load Existential Container Get function symbol of Shape.draw from Protocol Witness Table in Existential Container
125. alloc_global @$s6heroes5shapeAA5Shape_pvp // id: %2 %3 = global_addr @$s6heroes5shapeAA5Shape_pvp : $*Shape // users: %7, %5 %4 = struct $Triangle () // user: %6 %5 = init_existential_addr %3 : $*Shape, $Triangle // user: %6 store %4 to %5 : $*Triangle // id: %6 %7 = open_existential_addr immutable_access %3 : $*Shape to … Shape // users: %9, %9, %8 %8 = witness_method … Shape, , %7 : $ %9 = apply %8<… Shape>(%7) : $@convention(witness_method: Shape) <τ_0_0 where τ_0_0 : Shape> (@ let shape: any Shape = Triangle() shape.draw() #Shape.draw : <Self where Self : Shape> (Self) -> () -> () The function is called with selected information (Dynamic Dispatch) Load Existential Container Get function symbol of Shape.draw from Protocol Witness Table in Existential Container Obtained: @$s6heroes8TriangleVAA5ShapeA2aDP4drawyyFTW
126. let shape = Triangle() shape.draw()
127. %8 = load %3 : $*Triangle // user: %10 // function_ref Triangle.draw() %9 = function_ref @$s6heroes8TriangleV4drawyyF : $@convention(method) (Triangle) -> () // user: %10 = apply %9(%8) : $@convention(method) (Triangle) -> () let shape = Triangle() shape.draw()
128. %8 = load %3 : $*Triangle // user: %10 // function_ref Triangle.draw() %9 = function_ref @$s6heroes8TriangleV4drawyyF : $@convention(method) (Triangle) -> () // user: %10 = apply %9(%8) : $@convention(method) (Triangle) -> () Function symbol ($s6heroes8TriangleV4drawyyF) is selected (Static Dispatch) let shape = Triangle() shape.draw()
129. let shape: some Shape = Triangle() shape.draw()
130. let shape: some Shape = Triangle() shape.draw() ??? Please try:$ swiftc heroes.swift -emit-sil -o heroes.sil
131. ‘any’ and ‘some’ evolution ‘any’ Mechanism with Existential Container Optimization of ‘any’ and ‘some’
132. ‘any’ and ‘some’ evolution ‘any’ Mechanism with Existential Container Optimization of ‘any’ and ‘some’
133. func draw<T: Shape>(shape: T) // draw is called inside of function
134. // draw<A>(shape:) sil hidden @$s6heroes4draw5shapeyx_tAA5ShapeRzlF : . . . { . . . %11 = witness_method $T . . . 
 . . . } func draw<T: Shape>(shape: T) // draw is called inside of function Compile to SIL code
135. // draw<A>(shape:) sil hidden @$s6heroes4draw5shapeyx_tAA5ShapeRzlF : . . . { . . . %11 = witness_method $T . . . 
 . . . } Try to check Witness Table of ‘shape’ from type variable ’T’ func draw<T: Shape>(shape: T) // draw is called inside of function Compile to SIL code
136. • Generics also uses Witness Table if Swift compiler doesn’t optimize function code Specialization of function argument with Generics
137. • Generics also uses Witness Table if Swift compiler doesn’t optimize function code • Optimizer in Swift compiler generates “function with specialized argument“ Specialization of function argument with Generics
138. func draw<T: Shape>(shape: T) draw(shape: Triangle())
139. func draw<T: Shape>(shape: T) draw(shape: Triangle()) Compile code with optimization (‘-O’ flag) // specialized draw<A>(shape:) sil hidden @$s6heroes4draw5shapeyx_tAA5ShapeRzlFAA8TriangleC_Tg5
140. func draw<T: Shape>(shape: T) draw(shape: Triangle()) Compile code with optimization (‘-O’ flag) // specialized draw<A>(shape:) sil hidden @$s6heroes4draw5shapeyx_tAA5ShapeRzlFAA8TriangleC_Tg5 ‘draw(shape: Triangle)’
141. • Specialized function has concrete type information, and witness_table isn’t needed • Generics also uses Witness Table if Swift compiler doesn’t optimize code • Swift compiler’s optimizer generates “function with specialized argument“ Specialization of function argument with Generics
142. public func draw<T: Shape>(shape: T) draw(shape: Triangle()) Module A Module B class OriginalShape: ModuleA.Shape draw(shape: OriginalShape())
143. public func draw<T: Shape>(shape: T) draw(shape: Triangle()) Module A Module B class OriginalShape: ModuleA.Shape draw(shape: OriginalShape()) Specialized
144. public func draw<T: Shape>(shape: T) draw(shape: Triangle()) Module A Module B class OriginalShape: ModuleA.Shape draw(shape: OriginalShape()) Specialized Not-Specialized
145. • Function’s argument is not specialized in some cases Limitation of argument Specialization
146. • Different module, complex type … etc • Function’s argument is not specialized in some cases Limitation of argument Specialization
147. • Use ‘@inlinable’ attribute to make specializable in outside of modules (or @_specialize) public func draw<T: Shape>(shape: T) draw(shape: Triangle()) @inlinable • Different module, complex type … etc • Function’s argument is not specialized in some cases Limitation of argument Specialization
148. Specialization of ‘any’ and ‘some’ argument
149. Specialization of ‘any’ and ‘some’ argument • ‘some’ argument still uses Witness Table as default
150. • ‘some’ argument still uses Witness Table as default • ‘any’ and ‘some’ argument are also specialized if possible Specialization of ‘any’ and ‘some’ argument
151. func draw(shape: any Shape) draw(shape: Triangle())
152. // specialized draw(shape:) sil hidden @$s6heroes4draw5shapeyAA5Shape_p_..._nAA8TriangleC_Tg5 func draw(shape: any Shape) draw(shape: Triangle()) Compile code with optimization (‘-O’ flag) ‘draw(shape: Triangle)’
153. • ‘some’ still uses Witness Table as default • ‘any’ and ‘some’ argument are also specialized if possible Specialization of ‘some’ and ‘any’ argument
154. • ‘some’ still uses Witness Table as default • ‘any’ and ‘some’ argument are also specialized if possible Specialization of ‘some’ and ‘any’ argument • Use appropriate ‘some’ and ‘any’ regardless of specialization any some YES YES NO (inline only) YES Same module Different module(inlinable) Specialization of some an any
155. Summary: Optimization
156. Summary: Optimization • Existential Type, Opaque Type and Generics are “specialized” by compiler as possible
157. Summary: Optimization • Existential Type, Opaque Type and Generics are “specialized” by compiler as possible • Use appropriate ‘some’ and ‘any’ as possible regardless of specialization
158. Recap
159. Recap • Existential type and Opaque type evolution
160. Recap • Existential type and Opaque type evolution • Existential Container and Performance
161. Recap • Existential type and Opaque type evolution • Existential Container and Performance • Specialization for Generics, Existential type and Opaque type
162. Learn more evolution SE-0360 Opaque result types with limited availability apple/swift-evolution SE-0375 Opening existential arguments to optional parameters SE-0352 Implicitly Opened Existentials SE-0328 Structural opaque result types apple/swift-evolution apple/swift-evolution apple/swift-evolution
163. Learn API Design with ‘any’ and ‘some’ Embrace Swift generics WWDC 22 Design protocol interfaces in Swift WWDC 22
164. Other Talks Generic Protocols and Associated types - POWER TOOLS FOR UNIT TESTING SwiftHeroes 2023 Swift Optimizing (at Compiler World) NSSpain 2020
165. Thank you! Yuki ‘freddi’ Aki - iOS Engineer at LINE • Github @ freddi-kit • Twitter @ _ _ _freddi_ _ _ Special Thanks @koher (Author of “Heart of Swift” https://heart-of-swift.github.io/) @kateinoigakukun (Swift Compiler specialist) Engineers and Interpreters in LINE Corp SwiftHeroes Team