意外と知られてないXcode13の新しい参照カウンタ最適化オプションの挙動

Transcript

1. Θ͍Θ͍swiftc Vol 31
   ARC in Swift: So, what’s new?
   freddi, iOS Engineer
   

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2. Auto Reference Counting (ARC) ͱ͸
   

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3. ARCͱ͸?
   ΦϒδΣΫτͷϥΠϑαΠΫϧ؅ཧ
   • ϦϑΝϨϯεΧ΢ϯτʹΑΔΦϒδΣΫτͷ؅ཧ
   
   
   • ΦϒδΣΫτ͕ࢀর → “retain͢Δ” ʢΧ΢ϯτΛ૿΍͢ʣ
   
   
   • “Retain Cycle” ͕͍ΘΏΔϝϞϦϦʔΫΛى͜͢
   
   
   • “Reference Cycle”, “॥؀ࢀর” ͱ΋
   

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4. ARC ͷ঺հ at WWDC21
   

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5. https://developer.apple.com/videos/play/wwdc2021/10216/
   

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6. https://developer.apple.com/videos/play/wwdc2021/10216/
   ARCؔ࿈ͷΦϓγϣϯ૿͑ͨ from Xcode 13
   

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7. OPTIMIZE_OBJECT_LIFETIME in Xcode
   Xcode 13͔Βͷ৽͍͠Φϓγϣϯ
   • ʮΦϒδΣΫτण໋ͷ࠷దԽʯͱ͍͏ײ͡Ͱ঺հ
   
   
   • ୹ॖARC࠷దԽͱ͔ݺ͹Εͯͨ
   
   
   • ࣮ݧతͳΦϓγϣϯ
   
   
   • 20ඵ͘Β͍͔͠঺հ͞Εͯͳ͍ṖͷΦϓγϣϯ
   

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8. ARCͷ୹ॖͱ͸?
   

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9. Swift Compiler ίϚϯυΛݟΔ
   • Ϗϧυ࣌ʹͲΜͳswiftcίϚϯυ͕ݺ͹Ε͔ͨ
   
   
   • ͭ͡͸↓ͷͱ͜Ζ͔ΒݟΕͨΓ͢Δ
   ΞϓϦΛϏϧυ͢Δࡍʹݺ͹ΕΔίϚϯυΛݟΔ
   

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10. Swift Compiler ίϚϯυΛݟΔ
    Swiftc ͷ௥ՃΦϓγϣϯ
    /../swiftc ... -enforce-exclusivity\=checked -Xfrontend -enable-copy-propagation ...
    
    
    # Without OPTIMIZE_OBJECT_LIFETIME
    

    /../swiftc ... -enforce-exclusivity\=checked ...
    

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11. -enable-copy-propagation
    swift ίϯύΠϥͷίʔυ͔ΒΦϓγϣϯΛಡΈղ͘
    https://github.com/apple/swift/blob/main/include/swift/Option/FrontendOptions.td#L202
    

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12. -enable-copy-propagation
    swift ίϯύΠϥͷίʔυ͔ΒΦϓγϣϯΛಡΈղ͘
    • Run SIL propagation to shorten object lifetime
    
    
    • SIL఻೻Λ૸ΒͤɺΦϒδΣΫτͷϥΠϑλΠϜΛ୹ॖ
    
    
    • Α͘Θ͔ΒΜ
    

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13. ࠷దԽςΫχοΫ
    • ίϐʔ఻೻ɺෳࣸͷ఻೻ʢ೔ຊޠ༁ʣ
    
    
    • a = b; c = a + d ͱ͍͏ίʔυΛ c = b + d ʹ͢Δ࠷దԽ
    Copy Propagation
    http://www.hpcs.cs.tsukuba.ac.jp/~msato/lecture-note/comp-lecture/note11.html
    

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14. Θ͔Γқ͍ྫ
    Copy Propagation
    http://itdoc.hitachi.co.jp/manuals/3000/30003D0800/GD080480.HTM
    

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15. ARCͷཁ఺
    ͳͥ࠷దԽ͕ඞཁͳͷʁ
    • ARCʹ͸ARCͳΓʹΦʔόʔϔου͕͋Δ
    
    
    • ҰํɺARCͷ৔߹ɺม਺ʹΠϯελϯεΛ୅ೖͨ͠Γ ….ɺͦͷม਺͕είʔϓ
    Λൈ͚ͨΓ͢Δ౓ʹࢀরΧ΢ϯλͷνΣοΫॲཧ͕ೖΔͷͰɺͦͷ෼ɺΦʔ
    όʔϔου͕͔͔Δͱ͍͏σϝϦοτ͕͋Γ·͢ɻ
    https://rakusui.org/swift_arc/
    

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16. ARCͷཁ఺
    ͳͥ࠷దԽ͕ඞཁͳͷʁ
    • SwiftͷதؒݴޠͰ͋ΔSwift Intermediate Language Ͱ͸
    ARC͕ͲͷΑ͏ʹॲཧ͞Ε͍ͯΔͷ͔͕໨ʹݟ͑ͯΘ͔Δ
    
    
    • தؒݴޠ͕ੜ੒͞ΕΔͱ͖ʹΧ΢ϯτͷॲཧ͕ૠೖ͞ΕΔ
    
    
    • ௨ৗͷSwiftͷίʔυͩͱݟ͑ͳ͍
    

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17. Swift Intermedia Language
    ๻ͷొஃͩͱ਌ͷإΑΓ΋ݟΔ͜ͱʹͳΔ SILʹ͍ͭͯ
    • Swift͕ίϯύΠϧ͞ΕΔͱ͖ͷϑϩʔதͷதؒݴޠ
    
    
    • Swiftಛ༗ͷ࠷దԽ΍਍அ͕ߦΘΕΔ
    
    
    • Լͷਤ֮͑ͯؼ͍ͬͯͩ͘͞
    AST AS
    T

    (Typed)
    SIL I
    R

    (LLVM)
    📱
    App
    

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18. SIL Ͱͷ ARC ͷදݱʹ͍ͭͯ
    Reference Count ΛݮΒ͢ɾ૿΍͢ίʔυ
    • strong_retain
    
    
    • Χ΢ϯτΛʴ̍͢Δ
    
    
    • strong_release
    
    
    • Χ΢ϯτΛʔ̍͢Δ
    
    
    • ͋ͱΧ΢ϯτ͕0ҎԼʹͳͬͨΦϒδΣΫτΛഁغ
    

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19. ࣮ࡍͷSILͰͷARCΧ΢ϯτΛݟΔ
    ҎԼͷίʔυΛม׵
    class Cat {
    
    
    func meow(){}
    
    
    }
    
    
    do {
    
    
    let mike = Cat()
    
    
    let tama = mike
    
    
    tama.meow()
    
    
    }
    

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20. ࣮ࡍͷSILͰͷARCΧ΢ϯτΛݟΔ
    ࣮ࡍͷίʔυʹ͍ͭͯ(Ұ෦ൈਮ)
    …
    
    
    %4 = apply %3(%2) : $@convention(method) ...
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    strong_retain %4 : $Cat // id: %6
    
    
    debug_value %4 : $Cat, let, name "tama" // id: %7
    
    
    %8 = class_method %4 : $Cat, ...
    
    
    %9 = apply %8(%4) : $@convention(method) (@guaranteed Cat) -> ()
    
    
    strong_release %4 : $Cat // id: %10
    
    
    strong_release %4 : $Cat // id: %11
    
    
    …
    Reference Count͕͋Δ࠷దԽࡁΈ(canonical SIL)SIL
    

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21. copy-propagation ΛΦϯʹͯ͠ΈΔ
    ࠶ͼ͜ͷίʔυ
    class Cat {
    
    
    func meow(){}
    
    
    }
    
    
    do {
    
    
    let mike = Cat()
    
    
    let tama = mike
    
    
    tama.meow()
    
    
    }
    

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22. copy-propagation ΛΦϯʹͯ͠ΈΔ
    Φϯʹ͢Δલͷίʔυ
    …
    
    
    %4 = apply %3(%2) : $@convention(method) ...
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    strong_retain %4 : $Cat // id: %6
    
    
    debug_value %4 : $Cat, let, name "tama" // id: %7
    
    
    %8 = class_method %4 : $Cat, ...
    
    
    %9 = apply %8(%4) : $@convention(method) (@guaranteed Cat) -> ()
    
    
    strong_release %4 : $Cat // id: %10
    
    
    strong_release %4 : $Cat // id: %11
    
    
    …
    copy-propagation ൈ͖
    

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23. …
    
    
    %4 = apply %3(%2) : $@convention(method) ...
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    strong_retain %4 : $Cat // id: %6
    
    
    debug_value %4 : $Cat, let, name "tama" // id: %7
    
    
    %8 = class_method %4 : $Cat, ...
    
    
    %9 = apply %8(%4) : $@convention(method) (@guaranteed Cat) -> ()
    
    
    strong_release %4 : $Cat // id: %10
    
    
    strong_release %4 : $Cat // id: %11
    
    
    …
    Retain count (mike’s object to tama)
    copy-propagation ΛΦϯʹͯ͠ΈΔ
    Φϯʹ͢Δલͷίʔυ
    copy-propagation ൈ͖
    

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24. …
    
    
    %4 = apply %3(%2) : $@convention(method) ...
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    strong_retain %4 : $Cat // id: %6
    
    
    debug_value %4 : $Cat, let, name "tama" // id: %7
    
    
    %8 = class_method %4 : $Cat, ...
    
    
    %9 = apply %8(%4) : $@convention(method) (@guaranteed Cat) -> ()
    
    
    strong_release %4 : $Cat // id: %10
    
    
    strong_release %4 : $Cat // id: %11
    
    
    …
    Retain count (mike’s object to tama)
    Decrease count (mike’s object to tama)
    Decrease count (mike)
    copy-propagation ΛΦϯʹͯ͠ΈΔ
    Φϯʹ͢Δલͷίʔυ
    copy-propagation ൈ͖
    

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25. …
    
    
    %4 = apply %3(%2) : $@convention(method) …
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    debug_value %4 : $Cat, let, name "tama" // id: %6
    
    
    %7 = class_method %4 : $Cat, #Cat.meow : (Cat) -> () -> () …
    
    
    %8 = apply %7(%4) : $@convention(method) (@guaranteed Cat) -> ()
    
    
    strong_release %4 : $Cat // id: %9
    
    
    …
    copy-propagation ΛΦϯʹͯ͠ΈΔ
    Φϯʹͨ͠ޙͷίʔυ
    copy-propagation Ϛγ
    

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26. …
    
    
    %4 = apply %3(%2) : $@convention(method) …
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    debug_value %4 : $Cat, let, name "tama" // id: %6
    
    
    %7 = class_method %4 : $Cat, #Cat.meow : (Cat) -> () -> () …
    
    
    %8 = apply %7(%4) : $@convention(method) (@guaranteed Cat) -> ()
    
    
    strong_release %4 : $Cat // id: %9
    
    
    …
    Decrease count (mike)
    No retain count for tama
    copy-propagation ΛΦϯʹͯ͠ΈΔ
    Φϯʹͨ͠ޙͷίʔυ
    copy-propagation Ϛγ
    

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27. // main
    
    
    sil @main : $@convention(c) (Int32, UnsafeMutablePointer>>) -> Int32 {
    
    
    bb0(%0 : $Int32, %1 : $UnsafeMutablePointer>>):
    
    
    %2 = metatype $@thick Cat.Type // user: %4
    
    
    // function_ref Cat.__allocating_init()
    
    
    %3 = function_ref @$s4test3CatCACycfC : $@convention(method) (@thick Cat.Type) -> @owned Cat // user: %4
    
    
    %4 = apply %3(%2) : $@convention(method) (@thick Cat.Type) -> @owned Cat // users: %11, %10, %7, %9, %8, %6, %5
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    strong_retain %4 : $Cat // id: %6
    
    
    debug_value %4 : $Cat, let, name "tama" // id: %7
    
    
    %8 = class_method %4 : $Cat, #Cat.meow : (Cat) -> () -> (), $@convention(method) (@guaranteed Cat) -> () // user: %9
    
    
    %9 = apply %8(%4) : $@convention(method) (@guaranteed Cat) -> ()
    
    
    strong_release %4 : $Cat // id: %10
    
    
    strong_release %4 : $Cat // id: %11
    
    
    %12 = integer_literal $Builtin.Int32, 0 // user: %13
    
    
    %13 = struct $Int32 (%12 : $Builtin.Int32) // user: %14
    
    
    return %13 : $Int32 // id: %14
    
    
    } // end sil function 'main'
    
    
    copy-propagation ͋Γ/ͳ͠ൺֱ
    Φϯʹ͢Δલͷίʔυ
    

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28. // main
    
    
    sil @main : $@convention(c) (Int32, UnsafeMutablePointer>>) -> Int32 {
    
    
    bb0(%0 : $Int32, %1 : $UnsafeMutablePointer>>):
    
    
    %2 = metatype $@thick Cat.Type // user: %4
    
    
    // function_ref Cat.__allocating_init()
    
    
    %3 = function_ref @$s5test23CatCACycfC : $@convention(method) (@thick Cat.Type) -> @owned Cat // user: %4
    
    
    %4 = apply %3(%2) : $@convention(method) (@thick Cat.Type) -> @owned Cat // users: %9, %6, %8, %7, %5
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    debug_value %4 : $Cat, let, name "tama" // id: %6
    
    
    %7 = class_method %4 : $Cat, #Cat.meow : (Cat) -> () -> (), $@convention(method) (@guaranteed Cat) -> () // user: %8
    
    
    %8 = apply %7(%4) : $@convention(method) (@guaranteed Cat) -> ()
    
    
    strong_release %4 : $Cat // id: %9
    
    
    %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'
    
    
    copy-propagation ͋Γ/ͳ͠ൺֱ
    Φϯʹͨ͠ޙͷίʔυ
    

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29. ࢀরΧ΢ϯλফඅ͠ͳ͍ͷͰಉ͡ͳͷͰ͸
    • weak ʹΑΔࢀর (ऑࢀর) ΋ಉ͡Α͏ʹಇ͘આ
    class Cat {
    
    
    func meow(){}
    
    
    }
    
    
    do {
    
    
    let mike = Cat()
    
    
    weak var tama = mike
    
    
    tama?.meow()
    
    
    }
    weak/unownedͱͷൺֱʁ
    

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30. ࢀরΧ΢ϯλফඅ͠ͳ͍ͷͰಉ͡ͳͷͰ͸
    ࣮͸ weak ͸ΊͬͪΌ௕͘ͳΔ
    …
    
    
    %4 = apply %3(%2) : $@convention(method) (@thick Cat.Type) -> @owned Cat // users: %39, %8, %7, %5
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    %6 = alloc_stack $@sil_weak Optional, var, name "tama" // users: %38, %37, %9, %11
    
    
    strong_retain %4 : $Cat // id: %7
    
    
    %8 = enum $Optional, #Optional.some!enumelt, %4 : $Cat // users: %10, %9
    
    
    store_weak %8 to [initialization] %6 : $*@sil_weak Optional // id: %9
    
    
    release_value %8 : $Optional // id: %10
    
    
    %11 = begin_access [read] [static] %6 : $*@sil_weak Optional // users: %28, %21, %13
    
    
    %12 = alloc_stack $Optional // users: %14, %32, %27, %24, %20, %19, %17
    
    
    %13 = load_weak %11 : $*@sil_weak Optional // user: %14
    
    
    store %13 to %12 : $*Optional // id: %14
    
    
    %15 = integer_literal $Builtin.Int1, -1 // user: %17
    
    
    %16 = integer_literal $Builtin.Int1, 0 // user: %17
    
    
    %17 = select_enum_addr %12 : $*Optional, case #Optional.some!enumelt: %15, default %16 : $Builtin.Int1 // user: %18
    
    
    cond_br %17, bb2, bb1 // id: %18
    
    
    bb1: // Preds: bb0
    
    
    destroy_addr %12 : $*Optional // id: %19
    
    
    dealloc_stack %12 : $*Optional // id: %20
    
    
    end_access %11 : $*@sil_weak Optional // id: %21
    
    
    %22 = enum $Optional, #Optional.none!enumelt // user: %23
    
    
    br bb3(%22 : $Optional) // id: %23
    
    
    …
    weak/unownedͱͷൺֱʁ
    

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31. weak/unownedͱͷൺֱʁ
    weak ͱ Optional ʹ͍ͭͯ
    • Optional ͷ ? ͸ SIL ্ͩͱ nil ͡Όͳ͍͔ΛνΣοΫ͢Δ
    ৚݅෼ذ͕ൃੜ͢Δ
    
    
    • ͳͷͰͦͷ෼ͷ৚݅෼ذ͕૿͍͑ͯΔͱ͍͏͜ͱ
    

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32. weak/unownedͱͷൺֱʁ
    • unowned ʹॻ͖׵͑ͯࢼͯ͠ΈΔ
    class Cat {
    
    
    func meow(){}
    
    
    }
    
    
    do {
    
    
    let mike = Cat()
    
    
    unowned let tama = mike
    
    
    tama.meow()
    
    
    }
    ͡Ό͋ unowned ͸Ͳ͏Α
    

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33. unowned ͷ΄͏͕ copy-propagation ༗ΓΑΓ௕͍
    ͡Ό͋ unowned ͸Ͳ͏Α
    …
    
    
    %4 = apply %3(%2) : $@convention(method) (@thick Cat.Type) -> @owned Cat // users: %20, %12, %8, %7, %5
    
    
    debug_value %4 : $Cat, let, name "mike" // id: %5
    
    
    %6 = alloc_stack $@sil_unowned Cat, let, name "tama" // users: %11, %19, %18
    
    
    strong_retain %4 : $Cat // id: %7
    
    
    %8 = ref_to_unowned %4 : $Cat to $@sil_unowned Cat // users: %14, %11, %13, %10, %9
    
    
    unowned_retain %8 : $@sil_unowned Cat // id: %9
    
    
    unowned_retain %8 : $@sil_unowned Cat // id: %10
    
    
    store %8 to %6 : $*@sil_unowned Cat // id: %11
    
    
    strong_release %4 : $Cat // id: %12
    
    
    %13 = strong_copy_unowned_value %8 : $@sil_unowned Cat // users: %17, %16, %15
    
    
    unowned_release %8 : $@sil_unowned Cat // id: %14
    
    
    %15 = class_method %13 : $Cat, #Cat.meow : (Cat) -> () -> (), $@convention(method) (@guaranteed Cat) -> () // user: %16
    
    
    %16 = apply %15(%13) : $@convention(method) (@guaranteed Cat) -> ()
    
    
    strong_release %13 : $Cat // id: %17
    
    
    destroy_addr %6 : $*@sil_unowned Cat // id: %18
    
    
    dealloc_stack %6 : $*@sil_unowned Cat // id: %19
    
    
    strong_release %4 : $Cat // id: %20
    
    
    …
    weak/unownedͱͷൺֱʁ
    

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34. weak/unownedͱͷൺֱʁ
    unowned ʹ͍ͭͯ
    • unowned ΋ unowned Ͱಛ༗ͷॲཧ͕͋ΔͷͰ݁ہ௕͍
    
    
    • unowned_retain ͱ͔
    

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35. LLVMIRίʔυͷൺֱ
    Կ΋ͳ͠ vs copy-propagation vs unowned vs weak vs μʔΫϥΠ
    • ҎԼͷॱ൪Ͱ୹͍
    
    
    • copy-propagation
    
    
    • Կ΋ͳ͠
    
    
    • unowned
    
    
    • weak
    

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36. Conclusion
    

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37. Points of this talk
    Why we need to optimize it
    • OPTIMIZE_OBJECT_LIFETIME from Xcode 13
    
    
    • -Xfrontend -enable-copy-propagation for swiftc
    
    
    • copy-propagation Ͱίʔυ΍ARCͷΦʔόʔϔουݮΒͤΔ
    
    
    • unowned ΍ weak ΑΓ΋୹͍
    

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38. ࣍ճ༧ࠂ
    

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39. ࣍ճ͸͕࣌ؒ͋Ε͹࣮૷ΛಡΜͰ͍͘
    ָ͓͠Έʹ
    • https://github.com/apple/swift/blob/
    6bafc8498dd727f05ba14bf573e3f3d78de93a4e/lib/
    SILOptimizer/Transforms/CopyPropagation.cpp
    

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