コンパイラから紐解くSwift method dispatch

https://www.youtube.com/watch?v=lOY0YkH_5cA
https://fortee.jp/iosdc-japan-2018/proposal/1056b7c9-d1ab-4c66-b6a7-e37254b969ee

Transcript

1. ίϯύΠϥ͔Βඥղ͘
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2. ࣗݾ঺հ w !LBUFJOPJHBLVLVO
   w ૣҴాେֶߴ౳ֶӃ̏೥
3. ͍͖ͳΓͰ͕͢
4. ΫΠζͰ͢
   
5. class Cat { func bark() -> String { return "ʹΌΜ" } } class Dog { func bark() -> String { return "ΘΜ" } } let cat = Cat() let dog = unsafeBitCast(cat, to: Dog.self) print(dog.bark()) 2
   Կ͕ग़ྗ͞ΕΔͰ͠ΐ͏ʁ ʹΌΜ
   PS
   ΘΜ
6. class Cat { func bark() -> String { return "ʹΌΜ" } } class Dog { func bark() -> String { return "ΘΜ" } } let cat = Cat() let dog = unsafeBitCast(cat, to: Dog.self) print(dog.bark()) 2
   Կ͕ग़ྗ͞ΕΔͰ͠ΐ͏ʁ "
   ΘΜ
7. ʮΘΜʯ
8. ࠓ೔࿩͢͜ͱ w .FUIPE
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9. 2
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10. 2
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    ϝιου͕ݺͼग़͞ΕΔ࣌ʹɺ
 ࣮ࡍʹͲͷϝιουΛ࣮ߦ͢Δ͔ΛܾΊΔػߏ
12. class Animal { func bark() { print("ΞχϚϧͰ͢") } } class Cat: Animal { override func bark() { print("ʹΌΜ") } } func callAnimalBark(_ animal: Animal) { animal.bark() }
13. class Animal { func bark() { print("ΞχϚϧͰ͢") } } class Cat: Animal { override func bark() { print("ʹΌΜ") } } func callAnimalBark(_ animal: Animal) { animal.bark() // ΞχϚϧͰ͢ or ʹΌΜ }
14. class Animal { func bark() { print("ΞχϚϧͰ͢") } } class Cat: Animal { override func bark() { print("ʹΌΜ") } } func callAnimalBark(_ animal: Animal) { animal.bark() // ΞχϚϧͰ͢ or ʹΌΜ } ࣮ߦ͞ΕΔϝιου͸Ͳͬͪʁʁ
15. .FUIPE
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16. 4UBUJD
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    w ஋ܕͷϝιου
    w FYUFOTJPOʹॻ͍ͨϝιου
    w pOBMͳϝιου struct S { func foo() {} } let s = S() s.foo()
17. 4UBUJD
    %JTQBUDI struct S { func foo() {} } let s = S() s.foo() ಉ͡γάωνϟͷϝιου͕ଘࡏ͠ͳ͍ w ؔ਺
    w ஋ܕͷϝιου
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18. %ZOBNJD
    %JTQBUDI w $MBTTͷϝιου
    w 1SPUPDPMͷϝιου protocol Animal { func foo() } struct Cat: Animal { func foo() {} } func callFoo<T: Animal>(_ animal: T) { animal.foo() }
19. w $MBTTͷϝιου
    
    
    
    
    
    
    
    
    
    
    
    
    
    
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    ෳ਺ͷܕ͕४ڌ %ZOBNJD
    %JTQBUDI protocol Animal { func foo() } struct Cat: Animal { func foo() {} } func callFoo<T: Animal>(_ animal: T) { animal.foo() } ಉ͡γάωνϟͷϝιου͕ෳ਺ଘࡏ͢Δ
20. .FUIPE
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21. .FUIPE
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    w 75BCMF
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22. 75BCMF w Ծ૝ؔ਺ςʔϒϧ͔ΒϝιουΛ୳ࡧ͢Δ%JTQBUDIํࣜ
    w ΫϥεͷϝιουΛݺͼग़࣌͢ʹ࢖͏
    w ΠϯελϯεͷϝλσʔλʹຒΊࠐ·ΕΔ
23. func Animal.bark() *Animal.bark 75BCMF
    GPS
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24. func Animal.bark() *Animal.bark 75BCMF
    GPS
    $BU *Animal.bark 75BCMF
    GPS
    "OJNBM class Animal { func bark() {} } class Cat: Animal { }
25. func Cat.foo() func Animal.bark() *Animal.bark *Animal.bark *Cat.foo 75BCMF
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    "OJNBM 75BCMF
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    $BU class Animal { func bark() {} } class Cat: Animal { func foo() {} }
26. class Animal { func bark() {} } class Cat: Animal { override func bark() {} func foo() {} } 75BCMF
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    $BU func Animal.bark() 75BCMF
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    "OJNBM *Animal.bark *Animal.bark *Cat.foo func Cat.bark() func Cat.foo()
27. 8JUOFTT
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28. protocol Animal { func bark() }
29. protocol Animal { func bark() } struct Dog: Animal { func bark() {} } 8JUOFTT
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30. ʮΘΜʯ໰୊
31. class Cat { func bark() -> String { return "ʹΌΜ" } } class Dog { func bark() -> String { return “ΘΜ" } } let cat = Cat() let dog = unsafeBitCast(cat, to: Dog.self) print(dog.bark()) ϝϞϦϨΠΞ΢τ͸มߋ͞Εͳ͍ ࢀর͢ΔVTable΋มΘΒͳ͍ Catͷςʔϒϧ͕ࢀর͞ΕΔ ʮʹΌΜʯ͕ग़ྗ͞ΕΔ͸ͣʂ
32. ͔͠͠ɺ
33. class Cat { func bark() -> String { return "ʹΌΜ" } } class Dog { func bark() -> String { return "ΘΜ" } } let cat = Cat() let dog = unsafeBitCast(cat, to: Dog.self) print(dog.bark()) // ΘΜ ʮΘΜʯ
35. ࠷దԽΛΦϑʹͯ͠ΈΔ
36. $ swiftc -frontend -c -primary-file animal.swift $ swiftc animal.o $ ./animal ʹΌΜ ʮʹΌΜʯ
37. ࠷దԽͷաఔʹԿ͔͋Γͦ͏
38. %FWJSUVBMJ[F
39. %FWJSUVBMJ[F w 4*-0QUJNJ[FSͷ࠷దԽύε
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    w ίϯύΠϧ࣌ͷܕ৘ใ͔ΒϝιουΛ̍ͭʹܾΊΔ
40. 75BCMFͷ࠷దԽ
41. USZ%FWJSUVBMJ[F"QQMZ auto &M = FAS.getModule(); auto Instance = stripUpCasts(CMI->getOperand()); auto ClassType = Instance->getType(); ... if (isEffectivelyFinalMethod(FAS, ClassType, CD, CHA)) return tryDevirtualizeClassMethod(FAS, Instance, ORE, true /*isEffectivelyFinalMethod*/); if (auto Instance = getInstanceWithExactDynamicType(CMI->getOperand(), CMI->getModule(), CHA)) return tryDevirtualizeClassMethod(FAS, Instance, ORE); if (auto ExactTy = getExactDynamicType(CMI->getOperand(), CMI->getModule(), CHA)) { if (ExactTy == CMI->getOperand()->getType()) return tryDevirtualizeClassMethod(FAS, CMI->getOperand(), ORE); } MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
42. USZ%FWJSUVBMJ[F"QQMZ auto &M = FAS.getModule(); auto Instance = stripUpCasts(CMI->getOperand()); auto ClassType = Instance->getType(); ... if (isEffectivelyFinalMethod(FAS, ClassType, CD, CHA)) return tryDevirtualizeClassMethod(FAS, Instance, ORE, true /*isEffectivelyFinalMethod*/); if (auto Instance = getInstanceWithExactDynamicType(CMI->getOperand(), CMI->getModule(), CHA)) return tryDevirtualizeClassMethod(FAS, Instance, ORE); if (auto ExactTy = getExactDynamicType(CMI->getOperand(), CMI->getModule(), CHA)) { if (ExactTy == CMI->getOperand()->getType()) return tryDevirtualizeClassMethod(FAS, CMI->getOperand(), ORE); } Πϯελϯεͷ࣮ߦ࣌ͷܕ͕੩తʹܾఆͰ͖Δύλʔϯ MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
43. %FWJSUVBMJ[F
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    75BCMF class Animal { func bark() {} } class Cat: Animal { override func bark() {} } let animal: Animal = Cat() // ΠχγϟϥΠβ͔Β࡞ͬͯΔͷͰCatܕ animal.bark() Πϯελϯεͷ࣮ߦ࣌ͷܕ͕੩తʹܾఆͰ͖Δύλʔϯ
44. USZ%FWJSUVBMJ[F"QQMZ auto &M = FAS.getModule(); auto Instance = stripUpCasts(CMI->getOperand()); auto ClassType = Instance->getType(); ... if (isEffectivelyFinalMethod(FAS, ClassType, CD, CHA)) return tryDevirtualizeClassMethod(FAS, Instance, ORE, true /*isEffectivelyFinalMethod*/); if (auto Instance = getInstanceWithExactDynamicType(CMI->getOperand(), CMI->getModule(), CHA)) return tryDevirtualizeClassMethod(FAS, Instance, ORE); if (auto ExactTy = getExactDynamicType(CMI->getOperand(), CMI->getModule(), CHA)) { if (ExactTy == CMI->getOperand()->getType()) return tryDevirtualizeClassMethod(FAS, CMI->getOperand(), ORE); } ϝιου͕
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45. JT&⒎FDUJWFMZ'JOBM.FUIPE static bool isEffectivelyFinalMethod(FullApplySite AI, SILType ClassType, ClassDecl *CD, ClassHierarchyAnalysis *CHA) { if (CD && CD->isFinal()) return true; const DeclContext *DC = AI.getModule().getAssociatedContext(); auto *CMI = cast<MethodInst>(AI.getCallee()); if (!calleesAreStaticallyKnowable(AI.getModule(), CMI->getMember())) return false; auto *Method = CMI->getMember().getAbstractFunctionDecl(); if (!Method->isOverridden()) return true; ... return true; } ϝιου͕
    z࣮࣭pOBMzͳύλʔϯ MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
46. JT&⒎FDUJWFMZ'JOBM.FUIPE static bool isEffectivelyFinalMethod(FullApplySite AI, SILType ClassType, ClassDecl *CD, ClassHierarchyAnalysis *CHA) { if (CD && CD->isFinal()) return true; const DeclContext *DC = AI.getModule().getAssociatedContext(); auto *CMI = cast<MethodInst>(AI.getCallee()); if (!calleesAreStaticallyKnowable(AI.getModule(), CMI->getMember())) return false; auto *Method = CMI->getMember().getAbstractFunctionDecl(); if (!Method->isOverridden()) return true; ... return true; } ϝιου͕
    z࣮࣭pOBMzͳύλʔϯ MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
47. JT&⒎FDUJWFMZ'JOBM.FUIPE static bool isEffectivelyFinalMethod(FullApplySite AI, SILType ClassType, ClassDecl *CD, ClassHierarchyAnalysis *CHA) { if (CD && CD->isFinal()) return true; const DeclContext *DC = AI.getModule().getAssociatedContext(); auto *CMI = cast<MethodInst>(AI.getCallee()); if (!calleesAreStaticallyKnowable(AI.getModule(), CMI->getMember())) return false; auto *Method = CMI->getMember().getAbstractFunctionDecl(); if (!Method->isOverridden()) return true; ... return true; } ϝιου͕
    z࣮࣭pOBMzͳύλʔϯ MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
48. DBMMFFT"SF4UBUJDBMMZ,OPXBCMF bool swift::calleesAreStaticallyKnowable(SILModule &M, SILDeclRef Decl) { ... switch (AFD->getEffectiveAccess()) { case AccessLevel::Open: return false; case AccessLevel::Public: if (isa<ConstructorDecl>(AFD)) { auto *ND = AFD->getDeclContext()->getSelfNominalTypeDecl(); if (ND->getEffectiveAccess() == AccessLevel::Open) return false; } case AccessLevel::Internal: return M.isWholeModule(); case AccessLevel::FilePrivate: case AccessLevel::Private: return true; } } ϝιουΛ੩తʹܾఆͰ͖Δύλʔϯ MJC4*-0QUJNJ[FS6UJMT-PDBMDQQ
49. JT&⒎FDUJWFMZ'JOBM.FUIPE static bool isEffectivelyFinalMethod(FullApplySite AI, SILType ClassType, ClassDecl *CD, ClassHierarchyAnalysis *CHA) { if (CD && CD->isFinal()) return true; const DeclContext *DC = AI.getModule().getAssociatedContext(); auto *CMI = cast<MethodInst>(AI.getCallee()); if (!calleesAreStaticallyKnowable(AI.getModule(), CMI->getMember())) return false; auto *Method = CMI->getMember().getAbstractFunctionDecl(); if (!Method->isOverridden()) return true; ... return true; } ϝιου͕
    z࣮࣭pOBMzͳύλʔϯ MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
50. JT&⒎FDUJWFMZ'JOBM.FUIPE static bool isEffectivelyFinalMethod(FullApplySite AI, SILType ClassType, ClassDecl *CD, ClassHierarchyAnalysis *CHA) { ... if (!Method->isOverridden()) return true; ClassHierarchyAnalysis::ClassList Subs; getAllSubclasses(CHA, CD, ClassType, AI.getModule(), Subs); auto *ImplMethod = CD->findImplementingMethod(Method); for (auto S : Subs) { auto *ImplFD = S->findImplementingMethod(Method); if (ImplFD != ImplMethod) return false; } return true; } ϝιου͕
    z࣮࣭pOBMzͳύλʔϯ MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
51. JT&⒎FDUJWFMZ'JOBM.FUIPE static bool isEffectivelyFinalMethod(FullApplySite AI, SILType ClassType, ClassDecl *CD, ClassHierarchyAnalysis *CHA) { ... if (!Method->isOverridden()) return true; ClassHierarchyAnalysis::ClassList Subs; getAllSubclasses(CHA, CD, ClassType, AI.getModule(), Subs); auto *ImplMethod = CD->findImplementingMethod(Method); for (auto S : Subs) { auto *ImplFD = S->findImplementingMethod(Method); if (ImplFD != ImplMethod) return false; } return true; } ϝιου͕
    z࣮࣭pOBMzͳύλʔϯ MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
52. JT&⒎FDUJWFMZ'JOBM.FUIPE static bool isEffectivelyFinalMethod(FullApplySite AI, SILType ClassType, ClassDecl *CD, ClassHierarchyAnalysis *CHA) { ... if (!Method->isOverridden()) return true; ClassHierarchyAnalysis::ClassList Subs; getAllSubclasses(CHA, CD, ClassType, AI.getModule(), Subs); auto *ImplMethod = CD->findImplementingMethod(Method); for (auto S : Subs) { auto *ImplFD = S->findImplementingMethod(Method); if (ImplFD != ImplMethod) return false; } return true; } ϝιου͕
    z࣮࣭pOBMzͳύλʔϯ MJC4*-0QUJNJ[FS6UJMT%FWJSUVBMJ[FDQQ
53. 0WFSSJEF͞ΕͭͭΠϯελϯε͕
    ͦͷαϒΫϥεʹͳΓಘͳ͍৔߹ class Cat<Name> { func bark() {} } enum Tama {} enum Kuro {} class TamaCat: Cat<Tama> { override func bark() {} } func callBark(cat: Cat<Kuro>) { cat.bark() }
54. class Cat<Name> { func bark() {} } enum Tama {} enum Kuro {} // Cat<Kuro>ͷαϒλΠϓͰ͸ͳ͍ class TamaCat: Cat<Tama> { override func bark() {} } func callBark(cat: Cat<Kuro>) { cat.bark() } 0WFSSJEF͞ΕͭͭΠϯελϯε͕
    ͦͷαϒΫϥεʹͳΓಘͳ͍৔߹
55. JT&⒎FDUJWFMZ'JOBM.FUIPE ϝιου͕
    z࣮࣭pOBMzͳύλʔϯ
56. ʮΘΜʯ໰୊
57. class Cat { func bark() -> String { return “ʹΌΜ" } } class Dog { func bark() -> String { return "ΘΜ" } } let cat = Cat() let dog = unsafeBitCast(cat, to: Dog.self) print(dog.bark()) // ΘΜ ࠷దԽ͋Γͷ৔߹ Dog.barkϝιου͸non-final ΦʔόʔϥΠυ͞Ε͍ͯͳ͍ͷͰ”࣮࣭final” dog.bark()͕Static Dispatchʹ࠷దԽ͞ΕΔ
58. ࠷దԽͳ͠ͷ৔߹ class Cat { func bark() -> String { return “ʹΌΜ" } } class Dog { func bark() -> String { return "ΘΜ" } } let cat = Cat() let dog = unsafeBitCast(cat, to: Dog.self) print(dog.bark()) // ʹΌΜ Whole Module࠷దԽ͕Φϑ Ϟδϡʔϧ಺ͰΦʔόʔϥΠυ͞ΕΔՄೳੑ͕͋Δ ΠϯελϯεͷϝλσʔλͷVTable͔Β Dynamic Dispatch͢Δ
59. %JTQBUDI
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60. LBUFJOPJHBLVLVO%JTQBUDI#FODINBSL
61. 3VOUJNF
    1FSGPSNBODF /VNCFS
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    5JNF
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63. w IUUQTHJUIVCDPNBQQMFTXJGUCMPCNBTUFSEPDT4*-STU
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