Swiftのリンク時最適化プロジェクト

わいわいswiftc #21 https://iosdiscord.connpass.com/event/177407/

Transcript

1. SwiftͷϦϯΫ࣌࠷దԽϓϩδΣΫτ
   Θ͍Θ͍swiftc #21
   @kateinoigakukun
   1
   

   View Slide

2. Swiftͷ࠷దԽϨϕϧ
   • ϑΝΠϧ୯Ґ ( -O )
   • Ϟδϡʔϧ୯Ґ ( -whole-module-optimization )
   http://llvm.org/devmtg/2016-10/slides/GroffLattner-SILHighLevelIR.pdf 2
   

   View Slide

3. Swiftͷ࠷దԽϨϕϧ
   • ϑΝΠϧ୯Ґ ( -O )
   • Ϟδϡʔϧ୯Ґ ( -whole-module-optimization )
   • (New
   ➕
   ) ϓϩάϥϜશମ at LLVMϨϕϧ
   • (New
   ➕
   ) ϓϩάϥϜશମ at SILϨϕϧ
   3
   

   View Slide

4. LTO (Link Time Optimization)
   ίϯύΠϥͰ͸ͳ͘ɼϦϯΧ͕࣮ߦ͢Δ࠷దԽɽϓϩάϥϜશ
   ମΛҰͭͷ୯Ґͱͯ͠࠷దԽ͢Δɽ
   4
   

   View Slide

5. LTO (Link Time Optimization)
   ϝϦοτ
   • όΠφϦͷґଘ෺͢΂ͯͷ৘ใΛ࢖͑Δ
   • ϦϯΧ಺෦ͷγϯϘϧςʔϒϧΛ࠶ར༻Ͱ͖Δ
   5
   

   View Slide

6. LLVM Ϩϕϧ LTO
   ΦϒδΣΫτϑΝΠϧͰ͸ͳ͘ɼLLVMϏοτίʔυΛೖྗϑΝ
   Πϧͱͯ͠ड͚෇͚Δɽ
   6
   

   View Slide

7. LLVM Ϩϕϧ LTO
   ಛ௃
   • ந৅౓ͷߴ͍࠷దԽ
   • LLVMͷ࠷దԽύεΛ࠶ར༻
   7
   

   View Slide

8. ྫ͑͹
   // LibX.swift
   public func unusedPublicFunc() {}
   public func publicFunc() {}
   // main.swift
   import LibX
   publicFunc()
   8
   

   View Slide

9. // LibX.ll
   define swiftcc void @"$s4LibX16unusedPublicFuncyyF"() #0 {
   entry:
   ret void
   }
   define swiftcc void @"$s4LibX10publicFuncyyF"() #0 {
   entry:
   ret void
   }
   // main.ll
   define i32 @main(i32 %0, i8** %1) #0 {
   entry:
   %2 = bitcast i8** %1 to i8*
   call swiftcc void @"$s4LibX10publicFuncyyF"()
   ret i32 0
   }
   9
   

   View Slide

10. // LibX.ll
    define swiftcc void @"$s4LibX16unusedPublicFuncyyF"() #0 {
    entry:
    ret void
    }
    define swiftcc void @"$s4LibX10publicFuncyyF"() #0 {
    entry:
    ret void
    }
    // main.ll
    define i32 @main(i32 %0, i8** %1) #0 {
    entry:
    %2 = bitcast i8** %1 to i8*
    call swiftcc void @"$s4LibX10publicFuncyyF"()
    ret i32 0
    }
    9
    

    View Slide

11. LLVM Ϩϕϧͩͱ೉͍͠࠷దԽ
    • ݴޠʹґଘͨ͠ϝλσʔλͷऔΓѻ͍
    • ܕύϥϝʔλͷεϖγϟϥΠζ
    • ؔ਺ςʔϒϧʹࡌͬͨؔ਺ͷDFE (Dead Function
    Elimination)
    10
    

    View Slide

12. ྫ͑͹
    // LibX.swift
    public protocol P {
    func foo()
    func unusedMethod()
    }
    public struct S: P {
    public func foo() {}
    public func unusedMethod() {}
    }
    // main.swift
    import LibX
    func useP(_ value: T) {
    value.foo()
    }
    useP(S())
    11
    

    View Slide

13. // LibX.ll
    @"$s4LibX1SVAA1PAAWP" = constant [3 x i8*] [
    ...,
    i8* bitcast (void (%T4LibX1SV*, %swift.type*, i8**)* @"$s4LibX1SVAA1PA2aDP3fooyyFTW" to i8*),
    i8* bitcast (void (%T4LibX1SV*, %swift.type*, i8**)* @"$s4LibX1SVAA1PA2aDP12unusedMethodyyFTW" to i8*)
    ], align 8
    define linkonce_odr hidden swiftcc void @"$s4LibX1SVAA1PA2aDP3fooyyFTW"(...) { ... }
    define linkonce_odr hidden swiftcc void @"$s4LibX1SVAA1PA2aDP12unusedMethodyyFTW"(...) { ... }
    // main.ll
    define i32 @main(i32 %0, i8** %1) #0 {
    entry:
    ...
    call swiftcc void @"$s4main4usePyyx4LibX1PRzlF"(
    %swift.opaque* noalias nocapture undef,
    %swift.type* @"$s4LibX1SVN", i8** @"$s4LibX1SVAA1PAAWP"
    )
    ret i32 0
    }
    define hidden swiftcc void @"$s4main4usePyyx4LibX1PRzlF"(%swift.opaque* noalias nocapture %0, %swift.type* %T, i8** %T.P) {
    entry:
    %1 = getelementptr inbounds i8*, i8** %T.P, i32 1
    %2 = load i8*, i8** %1, align 8, !invariant.load !14
    %3 = bitcast i8* %2 to void (%swift.opaque*, %swift.type*, i8**)*
    call swiftcc void %3(%swift.opaque* noalias nocapture swiftself %0, %swift.type* %T, i8** %T.P)
    ret void
    }
    12
    

    View Slide

14. // LibX.ll
    @"$s4LibX1SVAA1PAAWP" = constant [3 x i8*] [
    ...,
    i8* bitcast (void (%T4LibX1SV*, %swift.type*, i8**)* @"$s4LibX1SVAA1PA2aDP3fooyyFTW" to i8*),
    i8* bitcast (void (%T4LibX1SV*, %swift.type*, i8**)* @"$s4LibX1SVAA1PA2aDP12unusedMethodyyFTW" to i8*)
    ], align 8
    define linkonce_odr hidden swiftcc void @"$s4LibX1SVAA1PA2aDP3fooyyFTW"(...) { ... }
    define linkonce_odr hidden swiftcc void @"$s4LibX1SVAA1PA2aDP12unusedMethodyyFTW"(...) { ... }
    // main.ll
    define i32 @main(i32 %0, i8** %1) #0 {
    entry:
    ...
    call swiftcc void @"$s4main4usePyyx4LibX1PRzlF"(
    %swift.opaque* noalias nocapture undef,
    %swift.type* @"$s4LibX1SVN", i8** @"$s4LibX1SVAA1PAAWP"
    )
    ret i32 0
    }
    define hidden swiftcc void @"$s4main4usePyyx4LibX1PRzlF"(%swift.opaque* noalias nocapture %0, %swift.type* %T, i8** %T.P) {
    entry:
    %1 = getelementptr inbounds i8*, i8** %T.P, i32 1
    %2 = load i8*, i8** %1, align 8, !invariant.load !14
    %3 = bitcast i8* %2 to void (%swift.opaque*, %swift.type*, i8**)*
    call swiftcc void %3(%swift.opaque* noalias nocapture swiftself %0, %swift.type* %T, i8** %T.P)
    ret void
    }
    12
    

    View Slide

15. // LibX.ll
    @"$s4LibX1SVAA1PAAWP" = constant [3 x i8*] [
    ...,
    i8* bitcast (void (%T4LibX1SV*, %swift.type*, i8**)* @"$s4LibX1SVAA1PA2aDP3fooyyFTW" to i8*),
    i8* bitcast (void (%T4LibX1SV*, %swift.type*, i8**)* @"$s4LibX1SVAA1PA2aDP12unusedMethodyyFTW" to i8*)
    ], align 8
    define linkonce_odr hidden swiftcc void @"$s4LibX1SVAA1PA2aDP3fooyyFTW"(...) { ... }
    define linkonce_odr hidden swiftcc void @"$s4LibX1SVAA1PA2aDP12unusedMethodyyFTW"(...) { ... }
    // main.ll
    define i32 @main(i32 %0, i8** %1) #0 {
    entry:
    ...
    call swiftcc void @"$s4main4usePyyx4LibX1PRzlF"(
    %swift.opaque* noalias nocapture undef,
    %swift.type* @"$s4LibX1SVN", i8** @"$s4LibX1SVAA1PAAWP"
    )
    ret i32 0
    }
    define hidden swiftcc void @"$s4main4usePyyx4LibX1PRzlF"(%swift.opaque* noalias nocapture %0, %swift.type* %T, i8** %T.P) {
    entry:
    %1 = getelementptr inbounds i8*, i8** %T.P, i32 1
    %2 = load i8*, i8** %1, align 8, !invariant.load !14
    %3 = bitcast i8* %2 to void (%swift.opaque*, %swift.type*, i8**)*
    call swiftcc void %3(%swift.opaque* noalias nocapture swiftself %0, %swift.type* %T, i8** %T.P)
    ret void
    }
    12
    

    View Slide

16. SIL Ϩϕϧ LTO
    13
    

    View Slide

17. SIL Ϩϕϧ LTO
    14
    

    View Slide

18. SIL Ϩϕϧ LTO ͷ Ϟνϕʔγϣϯ
    • LLVM IRΑΓந৅౓ͷߴ͍࠷దԽ
    • SwiftͷηϚϯςΟΫεΛҡ࣋ͨ͠··LTO͍ͨ͠
    • Ͳ͏ͤ੩తϦϯΫ͢ΔͳΒɺABI resiliencyΛແࢹͨ͠࠷దԽ
    Λ͍ͨ͠ɻ
    • ࣮ߦ࣌ύϑΥʔϚϯεͷվળͱόΠφϦαΠζͷॖখΛظ଴
    15
    

    View Slide

19. ࠷దԽϙΠϯτ (ະ࣮૷)
    16
    

    View Slide

20. 1. Cross Module Devirtualization
    17
    

    View Slide

21. https://speakerdeck.com/kateinoigakukun/konpairakaraniu-jie-kuswift-method-dispatch-1?slide=39 18
    

    View Slide

22. https://speakerdeck.com/kateinoigakukun/konpairakaraniu-jie-kuswift-method-dispatch-1?slide=55 19
    

    View Slide

23. View Slide

24. Cross Module Devirtualization
    • ͢΂ͯͷϞδϡʔϧ͕LTOର৅ͳΒɺϝιου͕Φʔόʔϥ
    Πυ͞Ε͍ͯΔ͔ඞͣ෼͔Δ
    • ࣮࣭finalೝఆͰ͖Δݺͼग़͕͠૿͑Δ
    • ABI resiliencyͷͨΊͷςʔϒϧܦ༝ݺͼग़͠Λ੩తݺͼग़͠
    ʹͰ͖Δɻ
    21
    

    View Slide

25. // LibX.swift
    open class A {
    public func foo1() {}
    open func foo2() {}
    }
    public func invokeFoo1InModule(_ a: A) {
    // ͜Ε͸ݱঢ়ͷ࠷దԽύεͰdevirtͰ͖Δ
    a.foo1()
    }
    // main.swift
    import LibX
    func invokeFoo1(_ a: A) {
    // [LTO] ֎෦Ϟδϡʔϧͷؔ਺͕ͩɺABI resiliencyແࢹͰdevirtͰ͖Δɻ
    a.foo1()
    // [LTO] ֎෦Ϟδϡʔϧͷؔ਺͕ͩɺ୭΋override͍ͯ͠ͳ͍ͷͰdevirtͰ͖Δɻ
    a.foo2()
    }
    22
    

    View Slide

26. 2. Cross Module Specialization
    23
    

    View Slide

27. Cross Module Specialization
    • ϞδϡʔϧΛ·͍ͨͩεϖγϟϥΠζ
    • ABI resiliencyΛແࢹͯ͠ɺશͯʹ@inlinable ͕͍͍ͭͯΔ
    Πϝʔδ
    • όΠφϦαΠζͷංେԽ͕৺഑
    24
    

    View Slide

28. // LibX.swift
    public protocol Animal {
    func bark()
    }
    public struct Cat: Animal {
    func bark() { }
    }
    // main.swift
    import LibX
    public callBark(_ animal: T) {
    animal.bark()
    }
    25
    

    View Slide

29. 3. Dead Table Elimination
    26
    

    View Slide

30. Dead Table Elimination
    • ௨ৗɺpublicͳVTable΍Protocol Witness Table͸ৗʹग़ྗ͞
    ΕΔ
    • LTOͷ৔߹ɺΫϩεϞδϡʔϧͰ࢖ΘΕ͍ͯΔ৔߹͚ͩग़ྗ
    ͢Ε͹͍͍ɻ
    • devirtͱεϖγϟϥΠζͰςʔϒϧ΁ͷࢀর͕ফ͑Δͱɺ͜ͷ
    ύε͕ΑΓޮՌతʹͳΔ
    27
    

    View Slide

31. 4. Dead public Function
    Elimination
    28
    

    View Slide

32. Dead public Function Elimination
    • ௨ৗͷDFE͸internalͳؔ਺͕ର৅
    • LTOͷ৔߹ɺpublicؔ਺΋ফͤΔ
    • ࣮ࡍʹ͸Dead Table Eliminationͱಉ࣌ʹ΍Δ
    • mainؔ਺͔Βґଘ͢Δؔ਺Λ෯༏ઌ୳ࡧͰϚʔΫ͍ͯ͘͠
    29
    

    View Slide

33. ࡞ۀਐḿ
    िใΛϑΥʔϥϜʹॻ͍ͯΔ
    https://forums.swift.org/t/gsoc-lto-support-progress-report/
    37149
    30
    

    View Slide

34. LTO͕ಛʹخ͍͠৔໘
    31
    

    View Slide

35. stdlibΛؙ͝ͱ੩తϦϯΫ͢ΔͨΊɺ࢖͍ͬͯͳ͍ػೳ΋όΠφ
    Ϧʹೖͬͯ͠·͏ɻ
    Hello, worldͰ͢Β10MBɻ·͞ʹLTOͷग़൪
    32
    

    View Slide