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Swift KeyPath Internals

Yuta Saito
October 04, 2022

Swift KeyPath Internals

Yuta Saito

October 04, 2022
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  1. Swift KeyPath Internals
    Θ͍Θ͍swiftc #38
    @kateinoigakukun
    1

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  2. ۙگ
    • ݚڀ: αΠζ࠷దԽؤுͬͯΔ
    • ϚΠΫϩϕϯνͰ͔͠ޮ͔ͳ͍࠷దԽ
    • Ruby: VenturaͰಈ͘Α͏ʹؤுͬͨ
    • SwiftWasm: ϓϩμΫγϣϯࣄྫग़͖ͯͯ͏Ε͍͠
    2

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  3. KeyPathͷಛ௃
    3

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  4. KeyPath ศར
    ཚ๫ʹݴ͏ͱ getter ͱ setter ΛऔΓճ͢දݱ
    ৭ΜͳॴͰ࢖ΘΕͯΔ
    • subscript(dynamicMember: KeyPath) -> Z
    • func map(_ keyPath: KeyPath) ->
    Publishers.MapKeyPath
    • Key Paths Expressions as Functions
    4

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  5. KeyPath Ή͔͍ͣ͠
    ҙຯ͸ಉ͕ͩ͡ɺಈ࡞͸શ͘ҧ͏ɻ
    foo[\.bar]
    foo.bar
    5

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  6. KeyPath ͓͍ͦ
    struct Foo {
    let bar: Int
    }
    let foo = Foo(bar: 42)
    @_optimize(none)
    func getter() { _ = foo.bar }
    @_optimize(none)
    func keyPathGetter() { _ = foo[keyPath: \.bar] }
    print("Simple Getter =>", ContinuousClock().measure {
    for _ in 1...10000000 { getter() }
    })
    print("KeyPath Getter =>", ContinuousClock().measure {
    for _ in 1...10000000 { keyPathGetter() }
    })
    $ swiftc main.swift
    $ ./main
    Simple Getter => 0.046666295 seconds
    KeyPath Getter => 1.590084352 seconds
    ʢ࠷దԽ͠ͳ͍ͱʣ
    34ഒ ͓͍ͦ
    !
    6

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  7. KeyPath ࢖ͬͯΔ…ʁ
    ࢖ΘΕͯແͦ͞͏ͳϚΠφʔػೳ
    • \[String: Int].["foo"]
    • \[Int].last?.littleEndian
    • class KeyPath: Hashable, Equatable
    • PartialKeyPath.appending(path:)
    let arrayDescription: PartialKeyPath> = \.description
    let stringLength: PartialKeyPath = \.count
    let arrayDescriptionLength = arrayDescription.appending(path: stringLength)
    7

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  8. ҉໧ʹ subscript indexΩϟϓνϟͯ͠Δέʔ
    ε
    KeyPath͕SendableʹͳΕͳ͍࿩ by iceman
    @dynamicMemberLookup struct Box {
    var value: Value
    subscript(dynamicMember keyPath: KeyPath) -> T {
    get { value[keyPath: keyPath] }
    }
    }
    struct ContentView: View {
    @State private var state = Box(value: Dog())
    var body: some View {
    TextField("", text: $state.name)
    // TextField("", text: _state.projectedValue[dynamicMember: \Box.[dynamicMember: \Dog.name]])
    }
    }
    8

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  9. KeyPath࣮૷ͷ֓ཁ
    9

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  10. ͔ͳΓ୯७Խͨ͠KeyPathͷ࣮૷
    let kp0 = \Foo.bar
    // -> let kp0 = KeyPath(getter: { $0.bar })
    let kp1 = \Foo.[42]
    // -> let kp1 = KeyPath(getter: { $0[42] })
    ࣮ࡍ͸΋ͬͱෳࡶ
    10

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  11. KeyPath࣮૷ͷา͖ํʢίϯύΠϥ෦෼ʣ
    ࣮ߦॱɻҙຯղੳ·Ͱলུ
    File Description
    lib/SILGen/SILGenExpr.cpp KeyPathInst SIL໋ྩͱΞΫηαΛੜ੒
    lib/SILOptimizer/SILCombiner/
    SILCombinerApplyVisitors.cpp
    getter/setterΞΫηε΁࠷దԽ
    lib/IRGen/GenKeyPath.cpp ϥϯλΠϜ͕ಡΉͨΊͷKeyPathσʔλͱα
    ϯΫΛੜ੒
    11

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  12. KeyPath࣮૷ͷา͖ํʢϥϯλΠϜ෦෼ʣ
    stdlib/public/core/KeyPath.swift
    • ίΞͷϩδοΫ͢΂͕ͯهड़͞ΕͯΔ
    • ΠϯελϯεԽ
    • ΞΫηε
    • ൺֱͳͲ
    • SwiftͰॻ͔Ε͍ͯΔ
    12

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  13. KeyPathͷ࣮૷ৄࡉ
    13

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  14. ΋͘͡
    1. SIL্ͷKeyPathදݱ
    2. LLVM IR্ͷKeyPathදݱ
    3. KeyPathͷϥϯλΠϜ࣮૷
    4. ίϯύΠϥ࠷దԽ
    14

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  15. SIL্ͷKeyPathදݱ
    15

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  16. SIL্ͷදݱ
    // keyPathGetter()
    sil hidden [Onone] @$s4main13keyPathGetteryyF : $@convention(thin) () -> () {
    bb0:
    // 1. άϩʔόϧม਺ `foo` Λϩʔυ
    %0 = global_addr @$s4main3fooAA3FooVvp : $*Foo // user: %1
    %1 = load %0 : $*Foo // user: %4
    // 2. `\Foo.bar` ͷKeyPathΛੜ੒
    %2 = keypath $KeyPath, (root $Foo; stored_property #Foo.bar : $Int) // users: %10, %7
    // 3. `foo` ΛελοΫʹΞϩέʔτ
    %3 = alloc_stack $Foo // users: %4, %9, %7
    store %1 to %3 : $*Foo // id: %4
    // 4. `foo` ͔ΒKeyPathܦ༝Ͱ `bar` Λऔಘ
    %5 = function_ref @swift_getAtKeyPath
    : $@convention(thin) <τ_0_0, τ_0_1> (@in_guaranteed τ_0_0, @guaranteed KeyPath<τ_0_0, τ_0_1>) -> @out τ_0_1 // user: %7
    %6 = alloc_stack $Int // users: %8, %7
    %7 = apply %5(%6, %3, %2)
    : $@convention(thin) <τ_0_0, τ_0_1> (@in_guaranteed τ_0_0, @guaranteed KeyPath<τ_0_0, τ_0_1>) -> @out τ_0_1
    dealloc_stack %6 : $*Int // id: %8
    dealloc_stack %3 : $*Foo // id: %9
    strong_release %2 : $KeyPath // id: %10
    %11 = tuple () // user: %12
    return %11 : $() // id: %12
    } // end sil function '$s4main13keyPathGetteryyF'
    16

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  17. KeyPathInstͷߏ଄
    keypath /* ಘΒΕΔKeyPathܕ */, (
    root /* ϧʔτͷܕ */;
    /* ύεͷཁૉ1 ʢKeyPathPatternComponentʣ */
    /* ύεͷཁૉ2 ʢKeyPathPatternComponentʣ */
    /* ύεͷཁૉN ʢKeyPathPatternComponentʣ */
    )
    17

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  18. KeyPathPatternComponent ͷछྨ
    class KeyPathPatternComponent {
    ...
    enum class Kind: unsigned {
    StoredProperty, // \Foo.bar (stored)
    GettableProperty, // \Foo.bar (getter), \Foo.[42] (subscript)
    SettableProperty, // GettableProperty + setter
    TupleElement, // \(Int, String).1
    OptionalChain, // \Foo.bar?.baz
    OptionalForce, // \Foo.bar!
    OptionalWrap, // \Foo.bar?.baz
    };
    };
    18

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  19. StoredProperty
    struct Foo {
    let bar: Int
    }
    // `\Foo.bar` =>
    %2 = keypath $KeyPath, (
    root $Foo;
    stored_property #Foo.bar : $Int
    )
    19

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  20. StoredProperty
    struct Foo {
    var bar: Int
    }
    // `\Foo.bar` =>
    %2 = keypath $WritableKeyPath, (
    root $Foo;
    stored_property #Foo.bar : $Int
    )
    20

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  21. TupleElement
    typealias Foo = (
    bar: Int,
    baz: String
    )
    // `\Foo.bar` =>
    %2 = keypath $WritableKeyPath<(bar: Int, baz: String), Int>, (
    root $(bar: Int, String);
    tuple_element #0 : $Int
    )
    21

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  22. GettableProperty
    struct Foo {
    var bar: Int { 42 }
    }
    // `\Foo.bar` =>
    %2 = keypath $KeyPath, (
    root $Foo;
    gettable_property $Int,
    id @$s4main3FooV3barSivg : $@convention(method) (Foo) -> Int,
    getter @$s4main3FooV3barSivpACTK : $@convention(thin) (@in_guaranteed Foo) -> @out Int
    )
    22

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  23. GettableProperty (Subscript)
    struct Foo {
    subscript(x: Int) -> Int { 0xbadbabe }
    }
    // `\Foo.[42]` =>
    %2 = integer_literal $Builtin.Int64, 0xdeadbeef
    %3 = struct $Int (%2 : $Builtin.Int64)
    %4 = keypath $KeyPath, (
    root $Foo;
    gettable_property $Int,
    id @$s4main3FooVyS2icig : $@convention(method) (Int, Foo) -> Int,
    getter @$s4main3FooVyS2icipACTK : $@convention(thin) (@in_guaranteed Foo, UnsafeRawPointer) -> @out Int,
    indices [%$0 : $Int : $Int],
    indices_equals @$sSiTH : $@convention(thin) (UnsafeRawPointer, UnsafeRawPointer) -> Bool,
    indices_hash @$sSiTh : $@convention(thin) (UnsafeRawPointer) -> Int
    ) (%3)
    ஋ʢindicesʣɺൺֱɺϋογϡͷͨΊͷؔ਺ΛΩϟϓνϟ
    23

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  24. GettableProperty (Subscript)
    • ϥϯλΠϜ͔Βݺ͹ΕΔ༻ͷαϯΫ
    • ͢΂ͯͷcomputed subscriptΛ୯ҰͷγάωνϟͰݺͼग़ͨ͢Ίʹඞཁ
    // key path getter for Foo.subscript(_:) : Foo
    sil shared [thunk] @$s4main3FooVyS2icipACTK : $@convention(thin) (@in_guaranteed Foo, UnsafeRawPointer) -> @out Int {
    // %0 // user: %8
    // %1 // user: %3
    // %2 // user: %4
    bb0(%0 : $*Int, %1 : $*Foo, %2 : $UnsafeRawPointer):
    %3 = load %1 : $*Foo // user: %7
    %4 = pointer_to_address %2 : $UnsafeRawPointer to $*Int // user: %5
    %5 = load %4 : $*Int // user: %7
    // function_ref Foo.subscript.getter
    %6 = function_ref @$s4main3FooVyS2icig : $@convention(method) (Int, Foo) -> Int // user: %7
    %7 = apply %6(%5, %3) : $@convention(method) (Int, Foo) -> Int // user: %8
    store %7 to %0 : $*Int // id: %8
    %9 = tuple () // user: %10
    return %9 : $() // id: %10
    } // end sil function '$s4main3FooVyS2icipACTK'
    24

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  25. SettableProperty
    struct Foo {
    var bar: Int { get { 42 } set { } }
    }
    // `\Foo.bar` =>
    %2 = keypath $WritableKeyPath, (
    root $Foo;
    settable_property $Int,
    id @$s4main3FooV3barSivg : $@convention(method) (Foo) -> Int,
    getter @$s4main3FooV3barSivpACTK : $@convention(thin) (@in_guaranteed Foo) -> @out Int,
    setter @$s4main3FooV3barSivpACTk : $@convention(thin) (@in_guaranteed Int, @inout Foo) -> ()
    )
    25

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  26. GettableProperty + GettableProperty
    struct Foo {
    struct Bar { var baz: Int { 42 } }
    var bar: Bar { Bar() }
    }
    // `\Foo.bar.baz` =>
    %2 = keypath $KeyPath, (
    root $Foo;
    gettable_property $Foo.Bar,
    id @$s4main3FooV3barAC3BarVvg : $@convention(method) (Foo) -> Foo.Bar,
    getter @$s4main3FooV3barAC3BarVvpACTK : $@convention(thin) (@in_guaranteed Foo) -> @out Foo.Bar;
    gettable_property $Int,
    id @$s4main3FooV3BarV3bazSivg : $@convention(method) (Foo.Bar) -> Int,
    getter @$s4main3FooV3BarV3bazSivpAETK : $@convention(thin) (@in_guaranteed Foo.Bar) -> @out Int
    )
    26

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  27. OptionalChain + OptionalWrap
    struct Foo {
    struct Bar { var baz: Int { 42 } }
    var bar: Bar? { Bar() }
    }
    // `\Foo.bar.baz` =>
    %2 = keypath $KeyPath>, (
    root $Foo;
    gettable_property $Optional,
    id @$s4main3FooV3barAC3BarVSgvg : $@convention(method) (Foo) -> Optional,
    getter @$s4main3FooV3barAC3BarVSgvpACTK : $@convention(thin) (@in_guaranteed Foo) -> @out Optional;
    optional_chain : $Foo.Bar;
    gettable_property $Int,
    id @$s4main3FooV3BarV3bazSivg : $@convention(method) (Foo.Bar) -> Int,
    getter @$s4main3FooV3BarV3bazSivpAETK : $@convention(thin) (@in_guaranteed Foo.Bar) -> @out Int;
    optional_wrap : $Optional
    )
    27

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  28. LLVM IR্ͷKeyPathදݱ
    28

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  29. ͔͜͜Βઌɺ͜ͷίʔυΛର৅ʹ࿩ΛਐΊΔɻ
    struct Foo {
    subscript(x: Int) -> Int { 0xbadbabe }
    }
    let foo = Foo()
    @_optimize(none)
    func keyPathGetter() { _ = foo[keyPath: \Foo.[0xdeadbeef]] }
    29

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  30. LLVM IR্ͷදݱ
    • KeyPath Object (Not ABI)
    • KeyPathΠϯελϯε͕อ࣋͢Δ৘ใ
    • ͍ͭ΋Ϣʔβ͕औΓճͯ͠Δͷ͸͜Ε
    • KeyPath Pattern (ABI)
    • PropertyͷಛੑͱKeyPathͱͯ͠ͷ஋ͷಛੑΛදݱ
    • ϥϯλΠϜ͕Pattern͔ΒKeyPath ObjectΛੜ੒͢Δ
    30

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  31. KeyPath Pattern -> KeyPath Object (ΠϯελϯεԽ)
    ΠϯελϯεԽʹ͸Ҿ਺ΛऔΔ৔߹͕͋Δ
    • Ҿ਺: IndicesɺGeneric Params
    • Ҿ਺͕ඞཁͳ͍৔߹͸Πϯελϯε͕Ωϟογϡ͞ΕΔ
    func withIndices(_ x: Int, y: String) -> AnyKeyPath {
    return \Foo.[x, y]
    }
    func withGenericContext(_ x: X.Type) -> AnyKeyPath {
    return \Blah.[x]
    }
    31

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  32. KeyPath Pattern in LLVM IR (Gettable Subscript)
    \Foo.[0xdeadbeef]
    @keypath = private global <{ i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32 }> <{
    ; oncePtr (0 if not cacheable, otherwise a relative pointer to the cache space)
    i32 0,
    ; --- KeyPathComponentHeader ---
    ; genericEnvironment
    i32 0,
    ; rootMetadataRef
    i32 cast_relptr (i64 symbolic_ref @$s4main3FooVMn), ; nominal type descriptor for main.Foo
    ; leafMetadataRef
    i32 cast_relptr (i64 symbolic_ref @$sSi), ; mangled name for Swift.Int ("Si\0")
    ; kvcString
    i32 0,
    ; KeyPathBuffer.Header
    i32 0b00000000000000000000000000011000, ; (size: 24, hasReferencePrefix: false, trivial: false)
    ; --- RawKeyPathComponent ---
    ; RawKeyPathComponent.Header
    i32 0b00000010000010000000000000000000, ; (hasComputedArguments: true, discriminator: computedTag(2))
    ; RawKeyPathComponent.idValue
    i32 cast_relptr (i64 (i64)* @"$s4main3FooVyS2icig" to i64), ; main.Foo.subscript.getter : (Swift.Int) -> Swift.Int
    ; RawKeyPathComponent.getter
    i32 cast_relptr (i64 (i64)* @"$s4main3FooVyS2icipACTK" to i64), ; key path getter for main.Foo.subscript(Swift.Int) -> Swift.Int : main.Foo
    ; --- KeyPathPatternComputedArguments ---
    ; KeyPathPatternComputedArguments.getLayout
    i32 cast_relptr ({ i64, i64 } (i8*)* @keypath_get_arg_layout to i64),
    ; KeyPathPatternComputedArguments.witnesses
    i32 cast_relptr ({ i8*, void (i8*, i8*, i64)*, i1 (i8*, i8*)*, i64 (i8*)* }* @keypath_witnesses to i64),
    ; KeyPathPatternComputedArguments.initializer
    i32 cast_relptr (void (i8*, i8*)* @keypath_arg_init to i64),
    }>, section ".rodata", align 8
    32

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  33. KeyPathੜ੒ in LLVM IR
    ; 1. Argument Bufferͷ૊Έཱͯ
    %1 = alloca i8, i64 8, align 16
    %2 = getelementptr inbounds i8, i8* %1, i64 0
    %3 = bitcast i8* %2 to %TSi*
    %._value = getelementptr inbounds %TSi, %TSi* %3, i32 0, i32 0
    store i64 0xdeadbeef, i64* %._value, align 8
    ; 2. KeyPath Objectͷੜ੒
    %4 = call %swift.refcounted* @swift_getKeyPath(i8* @keypath_pattern, i8* %1)
    33

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  34. KeyPathͷϥϯλΠϜ࣮૷
    34

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  35. swift_getKeyPath
    KeyPath patternΛarguments͔ΒKeyPath objectΛੜ੒͢ΔϥϯλΠϜؔ਺
    @_cdecl("swift_getKeyPathImpl")
    public func _swift_getKeyPath(pattern: UnsafeMutableRawPointer,
    arguments: UnsafeRawPointer)
    -> UnsafeRawPointer
    35

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  36. swift_getKeyPath
    1. oncePtrͷΩϟογϡνΣοΫʢεϨουηʔϑʣ
    2. KeyPathΠϯελϯεͷੜ੒
    1. Pattern͔ΒKeyPathαϒΫϥεͱΦϒδΣΫταΠζΛܭࢉ
    2. Patternͱarguments͔ΒΦϒδΣΫτΛ૊Έཱͯ
    3. Ωϟογϡʹอଘ
    36

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  37. 1. oncePtrͷΩϟογϡνΣοΫ
    let oncePtrPtr = pattern
    let oncePtrOffset = oncePtrPtr.load(as: Int32.self)
    let oncePtr: UnsafeRawPointer?
    if oncePtrOffset != 0 {
    let theOncePtr = _resolveRelativeAddress(oncePtrPtr, oncePtrOffset)
    oncePtr = theOncePtr
    // See whether we already instantiated this key path.
    // This is a non-atomic load because the instantiated pointer will be
    // written with a release barrier, and loads of the instantiated key path
    // ought to carry a dependency through this loaded pointer.
    let existingInstance = theOncePtr.load(as: UnsafeRawPointer?.self)
    if let existingInstance = existingInstance {
    // Return the instantiated object at +1.
    let object = Unmanaged.fromOpaque(existingInstance)
    // TODO: This retain will be unnecessary once we support global objects
    // with inert refcounting.
    _ = object.retain()
    return existingInstance
    }
    } else {
    oncePtr = nil
    }
    37

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  38. 2. KeyPathΠϯελϯεͷੜ੒
    // Instantiate a new key path object modeled on the pattern.
    // Do a pass to determine the class of the key path we'll be instantiating
    // and how much space we'll need for it.
    let (keyPathClass, rootType, size, _)
    = _getKeyPathClassAndInstanceSizeFromPattern(patternPtr, arguments)
    // Allocate the instance.
    let instance = keyPathClass._create(capacityInBytes: size) { instanceData in
    // Instantiate the pattern into the instance.
    _instantiateKeyPathBuffer(patternPtr, instanceData, rootType, arguments)
    }
    38

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  39. 2. KeyPathΠϯελϯεͷੜ੒
    Tail-alloc͞ΕͨόοϑΝ͸KeyPathBufferͱͯ͠࢖ΘΕΔ
    public class AnyKeyPath: Hashable, _AppendKeyPath {
    ...
    internal static func _create(
    capacityInBytes bytes: Int,
    initializedBy body: (UnsafeMutableRawBufferPointer) -> Void
    ) -> Self {
    _internalInvariant(bytes > 0 && bytes % 4 == 0,
    "capacity must be multiple of 4 bytes")
    let result = Builtin.allocWithTailElems_1(self, (bytes/4)._builtinWordValue,
    Int32.self)
    result._kvcKeyPathStringPtr = nil
    let base = UnsafeMutableRawPointer(Builtin.projectTailElems(result,
    Int32.self))
    body(UnsafeMutableRawBufferPointer(start: base, count: bytes))
    return result
    }
    ...
    }
    39

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  40. 3. Ωϟογϡʹอଘ
    • CAS (Compared-and-Swap)ͰΞτ
    ϛοΫʹΩϟογϡྖҬʹॻ͖ࠐΈ
    • ΋͠ଞͷεϨου͕Ωϟογϡॻ͖
    ࠐΈʹ੒ޭͨ͠ΒͦΕΛ࠾༻ͯ͠ɺ
    ࡞ͬͨΦϒδΣΫτΛഇغ
    // Try to replace a null pointer in the cache variable with the instance
    // pointer.
    let instancePtr = Unmanaged.passRetained(instance)
    while true {
    let (oldValue, won) = Builtin.cmpxchg_seqcst_seqcst_Word(
    oncePtr._rawValue,
    0._builtinWordValue,
    UInt(bitPattern: instancePtr.toOpaque())._builtinWordValue)
    // If the exchange succeeds, then the instance we formed is the canonical
    // one.
    if Bool(won) {
    break
    }
    // Otherwise, someone raced with us to instantiate the key path pattern
    // and won. Their instance should be just as good as ours, so we can take
    // that one and let ours get deallocated.
    if let existingInstance = UnsafeRawPointer(bitPattern: Int(oldValue)) {
    // Return the instantiated object at +1.
    let object = Unmanaged.fromOpaque(existingInstance)
    // TODO: This retain will be unnecessary once we support global objects
    // with inert refcounting.
    _ = object.retain()
    // Release the instance we created.
    instancePtr.release()
    return existingInstance
    } else {
    // Try the cmpxchg again if it spuriously failed.
    continue
    }
    }
    40

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  41. swift_getAtKeyPath
    KeyPath objectͱRootͷ஋͔ΒValueΛऔΓग़͢ϥϯλΠϜؔ਺
    @_silgen_name("swift_getAtKeyPath")
    public // COMPILER_INTRINSIC
    func _getAtKeyPath(
    root: Root,
    keyPath: KeyPath
    ) -> Value {
    return keyPath._projectReadOnly(from: root)
    }
    41

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  42. • ίϯϙʔωϯτ͝ͱʹ۩ମܕ
    ΛऔΓग़ͯ͠౤Өʢprojectʣͯ͠
    ͍͘
    • δΣωϦοΫλΠϓͳͷͰOpaque
    Pointer
    @usableFromInline
    internal final func _projectReadOnly(from root: Root) -> Value {
    // TODO: For perf, we could use a local growable buffer instead of Any
    var curBase: Any = root
    return withBuffer {
    var buffer = $0
    if buffer.data.isEmpty {
    return unsafeBitCast(root, to: Value.self)
    }
    while true {
    let (rawComponent, optNextType) = buffer.next()
    let valueType = optNextType ?? Value.self
    let isLast = optNextType == nil
    func project(_ base: CurValue) -> Value? {
    func project2(_: NewValue.Type) -> Value? {
    switch rawComponent._projectReadOnly(base,
    to: NewValue.self, endingWith: Value.self) {
    case .continue(let newBase):
    if isLast {
    _internalInvariant(NewValue.self == Value.self,
    "key path does not terminate in correct type")
    return unsafeBitCast(newBase, to: Value.self)
    } else {
    curBase = newBase
    return nil
    }
    case .break(let result):
    return result
    }
    }
    return _openExistential(valueType, do: project2)
    }
    if let result = _openExistential(curBase, do: project) {
    return result
    }
    }
    }
    }
    42

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  43. internal struct RawKeyPathComponent {
    ...
    internal func _projectReadOnly(
    _ base: CurValue,
    to: NewValue.Type,
    endingWith: LeafValue.Type
    ) -> ProjectionResult {
    switch value {
    ...
    case .get(id: _, accessors: let accessors, argument: let argument),
    .mutatingGetSet(id: _, accessors: let accessors, argument: let argument),
    .nonmutatingGetSet(id: _, accessors: let accessors, argument: let argument):
    return .continue(accessors.getter()(
    base,
    argument?.data.baseAddress ?? accessors._value,
    argument?.data.count ?? 0)
    )
    ...
    }
    ...
    }
    getterΛݺΜͩΓɺstoredPropertyΛऔΓग़ͨ͠Γ͢Δ
    43

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  44. getterݺͼग़͠
    internal typealias Getter = @convention(thin)
    (CurValue, UnsafeRawPointer, Int) -> NewValue
    accessors.getter()(
    base,
    argument?.data.baseAddress ?? accessors._value,
    argument?.data.count ?? 0
    )
    ݺͼग़͞ΕΔؔ਺
    // key path getter for Foo.subscript(_:) : Foo
    sil shared [thunk] @$s4main3FooVyS2icipACTK : $@convention(thin) (@in_guaranteed Foo, UnsafeRawPointer) -> @out Int
    44

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  45. ༨ஊ: getterఆٛʹόϑΝαΠζͷύϥϝʔλ͕଍Γͯͳ͍
    • ଍Γͯͳ͍
    • αΠζ΍Argument Buffer͕ඞཁͳ
    ͍έʔεͰ͸লུ͞Εͯ͠·͏
    • γάωνϟෆҰக͸WasmͰ͸
    Τϥʔ
    • ৗʹ3ύϥϝʔλు͘Α͏ʹύον
    ౰ͯͯΔ
    ఆٛ
    sil shared [thunk] @$s4main3FooVyS2icipACTK : $@convention(thin) (
    @in_guaranteed Foo, // base
    UnsafeRawPointer // KeyPath Argument Buffer
    ) -> @out Int
    ݺͼग़͠ଆ
    let ret = accessors.getter()(
    base,
    argument?.data.baseAddress ?? accessors._value,
    argument?.data.count ?? 0
    )
    45

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  46. KeyPath Argument BufferͷϨΠΞ΢τ
    ྫ1. subscript(x: Int) -> Int
    Offset Type
    0
    Int
    46

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  47. KeyPath Argument BufferͷϨΠΞ΢τ
    ྫ2. subscript(x: T, y: Int) -> Int
    Offset Type
    0
    T = Int
    8
    Int
    47

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  48. KeyPath Argument BufferͷϨΠΞ΢τ
    ྫ3. subscript(x: T, y: Int) -> Int
    Offset Type
    0
    T
    sizeof(T) Int
    sizeof(T) + 8 %swift.type* T
    sizeof(T) + 16 witness table for T: Hashable
    48

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  49. ೋॏαϯΫ໰୊
    49

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  50. ೋॏαϯΫ໰୊
    key path getter͕δΣωϦοΫύϥϝʔλΛ࣋ͭ৔߹ɺLLVM IRͰ͸Ҿ਺ʹϝλλΠ
    ϓͱWitness Table͕౉͞ΕΔɻ
    // key path getter for Bar.subscript(_:_:) : BarA
    sil [thunk] @$s4main3BarVySix_SitcluipSHRzlACxTK : $@convention(thin) (
    @in_guaranteed Bar,
    UnsafeRawPointer
    ) -> @out Int

    define swiftcc void @"$s4main3BarVySix_SitcluipSHRzlACxTK"(
    %TSi* noalias nocapture sret(%TSi) %0,
    %T4main3BarV* noalias nocapture dereferenceable(24) %1,
    i8* %2,
    %swift.type* %T,
    i8** %T.Hashable
    )
    50

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  51. ೋॏαϯΫ໰୊
    ϥϯλΠϜ͸୯ҰͷγάωνϟͰkey path getterΛݺͼग़͍ͨ͠ͷͰɺ
    δΣωϦοΫύϥϝʔλΛArgument Buffer͔ΒऔΓग़ͯ͠key path getterΛݺͼग़
    ͢αϯΫΛߋʹੜ੒͢Δɻ
    define private swiftcc void @keypath_get(%TSi* noalias nocapture sret(%TSi) %0, %T4main3BarV* noalias nocapture %1, i8* %2, i64 %3) {
    entry:
    %4 = sub i64 %3, 16
    %5 = getelementptr inbounds i8, i8* %2, i64 %4
    %6 = bitcast i8* %5 to %swift.type**
    %"\CF\84_0_0" = load %swift.type*, %swift.type** %6, align 8
    %7 = getelementptr inbounds %swift.type*, %swift.type** %6, i32 1
    %8 = bitcast %swift.type** %7 to i8***
    %"\CF\84_0_0.Hashable" = load i8**, i8*** %8, align 8
    ; key path getter for Bar.subscript(_:_:) : BarA
    call swiftcc void @"$s4main3BarVySix_SitcluipSHRzlACxTK"(
    %TSi* noalias nocapture sret(%TSi) %0, ; return value
    %T4main3BarV* noalias nocapture dereferenceable(24) %1, ; base
    i8* %2, ; KeyPath Argument Buffer
    %swift.type* %"\CF\84_0_0", ; generic parameter
    i8** %"\CF\84_0_0.Hashable" ; Hashable witness table
    )
    ret void
    }
    51

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  52. ೋॏαϯΫ໰୊
    • KeyPath getter͸SILϨϕϧͰ࡞ΒΕΔ΍ͭͱɺIRGenͰ࡞ΒΕΔαϯΫ͕͋Δɻ
    • IRGenϨϕϧͷαϯΫ͸ɺΩϟϓνϟ͞ΕͨδΣωϦοΫύϥϝʔλ͕͋Δͱ
    ͖ɺ
    όοϑΝ͔ΒϝλλΠϓΛऔΓग़ͯ͠SILϨϕϧͰ࡞ΒΕͨgetterʹ
    ϑΥϫʔυ͢Δɻ
    • ݺͼग़͠ن໿ͷ࣮૷͕IRGenͱSILGenʹඈͼࢄͬͯΔ
    52

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  53. KeyPath଎͍ͨ͘͠
    53

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  54. Flame Graph Search ic
    [[stack]]
    _..
    __sw..
    _swi..
    $s5benchyyXEfU0_
    swift_getAtKeyPath
    __swift_instantiateCanonicalPrespecializedGen..
    _swift_getGen..
    swift_getAtKeyPath
    bench
    _swift_getGe..
    swift..
    getCache
    $s5bench13keyPathGetteryyF
    s..
    s..
    $s..
    $..
    main
    s..
    _start
    _swift_getGenericMetadata
    s..
    getCache
    $sypSgMf
    swift::C..
    swift_g..
    $..
    $ss7KeyPathC16_projectReadOnly4fromq_x_tFq_s0aB6BufferVXEfU_
    __libc_start_main
    getC..
    swift_getAtK..
    __swift_instantia..
    $ss19RawKeyPa..
    $ss5ClockPsE7measurey8DurationQzyyKXEKF
    _..
    __swift_inst..
    swift_..
    sw..
    _sw..
    https://gist.github.com/kateinoigakukun/d540dfdabe1948258d0860c7c6f462ee 54

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  55. KeyPath଎͍ͨ͘͠ ʢίϯύΠϥͰͰ͖Δ͜ͱʣ
    ϥϯλΠϜؔ਺ͷݺͼग़͠Λফ͢ʢSILCombiner in SIL Optimizerʣ
    %kp = keypath $KeyPath, (
    root $Foo;
    gettable_property $Int,
    id @$s4main3FooV3barSivg : $@convention(method) (Foo) -> Int,
    getter @$s4main3FooV3barSivpACTK : $@convention(thin) (@in_guaranteed Foo) -> @out Int
    )
    %fn = function_ref @swift_getAtKeyPath
    %ret = alloc_stack $Int
    apply %fn(%ret, %base, %kp)

    // function_ref key path getter for Foo.bar : Foo
    %getter = function_ref @$s4main3FooV3barSivpACTK
    %ret = alloc_stack $Int
    apply %getter(%ret, %base) : $@convention(thin) (@in_guaranteed Foo) -> @out Int
    55

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  56. SILCombiner ͷ੍໿
    • Argument BufferΛҾ਺ʹऔΔ৔߹͸࠷దԽͰ͖ͳ͍ɻ
    • Argument BufferͷϝϞϦϨΠΞ΢τ͸IRGenͰ૊·ΕΔͷͰɺ
    SIL Optimizerͷஈ֊ͰҾ਺Λ૊ΈཱͯΒΕͳ͍ͨΊɻ
    // key path getter for Bar.subscript(_:_:) : BarA
    sil [thunk] @$s4main3BarVySix_SitcluipSHRzlACxTK : $@convention(thin) (
    @in_guaranteed Bar,
    UnsafeRawPointer
    ) -> @out Int
    56

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  57. KeyPath଎͍ͨ͘͠ ʢϢʔβίʔυͰͰ͖Δ͜ͱʣ
    • ଎౓͕ඞཁͳΒgetter/setterΛ࢖͏
    • Argument Bufferਚ͖ͷKeyPathͳΒͰ͖Δ͚ͩΩϟογϡ͢Δ
    57

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  58. ల๬
    • Wasm༻ͷϋοΫ͸ྲྀੴʹͦͷ··ΞοϓετϦʔϜͰ͖ͳ͍ͷͰɺ
    ઌʹϦϑΝΫλϦϯά͍ͨ͠ɻ
    • ϦϑΝΫλϦϯάͷ෭࣍ޮՌͰɺArgument Buffer෇͖ͷKeyPathΞΫηε࠷దԽ
    Ͱ͖ΔΑ͏ʹͳΔ͔΋ɻ
    58

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