SwiftのThin Cross Module Optimization (WIP)

https://iosdiscord.connpass.com/event/188624/

Transcript

1. SwiftͷThin Cross Module
   Optimization (WIP)
   Θ͍Θ͍swiftc #22
   @kateinoigakukun
   1
   

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2. GSoC (Google Summer of Code)
   https://summerofcode.withgoogle.com
   • Google͕ೝఆͨ͠ΦʔϓϯιʔεͷϓϩδΣΫτʹࢀՃ͢Δ
   ͱGoogle͔ΒใुΛ΋Β͑Δɺֶੜ޲͚Πϕϯτ
   • Swift΋ࢀՃ͍ͯ͠Δ
   2
   

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3. https://summerofcode.withgoogle.com/projects/#6691362033893376 3
   

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4. ݱࡏͷεςʔλε
   • GSoCظ͕ؒऴΘͬͨ
   • ࣗ෼ͷϒϥϯνͰͷ࡞ۀ͸େମऴΘ͍ͬͯΔ
   • Ϛʔδ͞Ε͍ͯͳ͍PR͕ͨ͘͞Μ࢒͍ͬͯΔͷͰϨϏϡΞʔ
   Λ୳ͯ͠ఆظతʹಥ෇͍ͯΔ
   4
   

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5. ౰ॳͷܭը
   libLTO.dylibతͳϦϯΧϓϥάΠϯΛ࡞Δ༧ఆͩͬͨɻ
   $ clang -flto file1.c file2.c -c
   $ ls
   file1.c file1.o file2.c file2.o
   $ file file1.o
   file1.o: LLVM bitcode, wrapper x86_64
   $ ld file1.o file2.o -lto_library path/to/libLTO.dylib
   5
   

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8. ͜ͷΞʔΩςΫνϟͷ໰୊఺
   ϦϯΧ͕SIBશମΛಡΜͰղੳ͢Δ͜ͱʹͳΔͷͰɺ࠷దԽ࣌ؒ
   తʹεέʔϥϒϧͰͳ͍
   -> LLVM ͷLTOͰ΋Ҏલಉ༷ͷ໰୊͕͋ͬͨɻ
   8
   

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9. http://llvm.org/devmtg/2016-11/Slides/Amini-Johnson-ThinLTO.pdf 9
   

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10. http://llvm.org/devmtg/2016-11/Slides/Amini-Johnson-ThinLTO.pdf 10
    

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11. LLVM Thin LTO
    • Bitcode͔Βͷίʔυੜ੒ΛฒྻԽͰ͖Δ
    • αϚϦʔΛૢ࡞͢ΔThin Link͸௚ྻʹͳΔ͕ɺLLVM໋ྩΛ
    ղੳ͠ͳ͍ͷͰ͍ܰ
    11
    

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12. LLVM Thin LTOϞσϧΛࢀߟʹ৽͍͠ύΠϓϥΠϯΛ࣮૷ͯ͠Έ
    ͨɻ
    • SwiftϞδϡʔϧͷαϚϦΛग़ྗ
    • ΫϩεϞδϡʔϧͰղੳ͢Δͱ͖SIBΛશͯύʔε͢Δඞཁ͕
    ແ͘ͳΔ
    12
    

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15. ࣮ࡍͷίϚϯυ
    15
    

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16. Compile Module A
    $ swift-frontend A1.swift A2.swift \
    -whole-module-optimization \
    -emit-module -emit-module-summary -emit-sib \
    -o A.swiftmodule
    ग़ྗ: A.swiftmodule, A.swiftmodulesummary, A.sib
    16
    

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17. Compile Module B
    $ swift-frontend B1.swift B2.swift \
    -whole-module-optimization \
    -emit-module -emit-module-summary -emit-sib \
    -I. \
    -o B.swiftmodule
    ग़ྗ: B.swiftmodule, B.swiftmodulesummary, B.sib
    17
    

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18. Merge Module Summary
    ௚ྻϙΠϯτ
    $ swift-frontend -merge-module-summary \
    A.swiftmodulesummary B.swiftmodulesummary \
    -o merged-module.swiftmodulesummary
    18
    

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19. CodeGen
    ͜͜͸ฒྻʹͰ͖Δ
    $ swift-frontend -emit-object A.sib -o A.o \
    -module-summary-path merged-module.swiftmodulesummary
    $ swift-frontend -emit-object B.sib -o B.o \
    -module-summary-path merged-module.swiftmodulesummary
    19
    

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20. Swift Module Summary
    SILModuleΛཁ໿ͨ͠ΦϒδΣΫτɻ
    • ؔ਺ͷίʔϧάϥϑ
    • ؔ਺ςʔϒϧͷந৅ͱ࣮૷ͷରԠؔ܎
    Λ࣋ͭ
    20
    

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21. ྫ
    func myPrint(_ text: String) { ... }
    public protocol Animal {
    func bark()
    }
    public struct Cat: Animal {
    public func bark() { myPrint("mew") }
    }
    public struct Dog: Animal {
    public func bark() { myPrint("bow")}
    }
    public func callBark(_ animal: T) {
    animal.bark()
    }
    21
    

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22. ϚʔδͷλΠϛϯάͰ΍͍ͬͯΔ͜ͱ
    1. swiftmodulesummaryΛҰͭͷαϚϦʔΦϒδΣΫτʹϩʔ
    υͯ͠ϦϯΫ
    2. PreservedͳγϯϘϧΛऩू
    3. PreservedͳγϯϘϧ͔Βḷ࣮ͬͯߦ࣌ࢀরՄೳͳܕΛϚʔΫ
    4. PreservedͳγϯϘϧ͔Β౸ୡՄೳͳؔ਺Λliveͱͯ͠ϚʔΫ
    ͯ͠౸ୡෆೳͳؔ਺Λચ͍ग़͢
    22
    

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23. ౸ୡෆೳͳؔ਺Λચ͍ग़͢
    void markDeadSymbols(ModuleSummaryIndex &summary, llvm::DenseSet &PreservedGUIDs) {
    SmallVector Worklist;
    for (auto GUID : PreservedGUIDs) {
    Worklist.push_back(GUID);
    }
    while (!Worklist.empty()) {
    auto GUID = Worklist.pop_back_val();
    auto Func = summary.getFunction(GUID);
    if (Func->isLive()) continue;
    Func->setLive(true);
    for (auto Call : Func->calls()) {
    switch (Call.getKind()) {
    case EdgeTy::Kind::Static: {
    Worklist.push_back(Call.getCallee());
    continue;
    }
    case EdgeTy::Kind::Witness:
    case EdgeTy::Kind::VTable: {
    auto Impls = summary.getImplementations(Call);
    for (auto Impl : Impls) {
    Worklist.push_back(Impl);
    }
    break;
    }
    }
    }
    }
    23
    

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24. ౸ୡෆೳͳؔ਺Λચ͍ग़͢
    void markDeadSymbols(ModuleSummaryIndex &summary, llvm::DenseSet &PreservedGUIDs) {
    SmallVector Worklist;
    for (auto GUID : PreservedGUIDs) {
    Worklist.push_back(GUID);
    }
    while (!Worklist.empty()) {
    auto GUID = Worklist.pop_back_val();
    auto Func = summary.getFunction(GUID);
    if (Func->isLive()) continue;
    Func->setLive(true);
    for (auto Call : Func->calls()) {
    switch (Call.getKind()) {
    case EdgeTy::Kind::Static: {
    Worklist.push_back(Call.getCallee());
    continue;
    }
    case EdgeTy::Kind::Witness:
    case EdgeTy::Kind::VTable: {
    auto Impls = summary.getImplementations(Call);
    for (auto Impl : Impls) {
    Worklist.push_back(Impl);
    }
    break;
    }
    }
    }
    }
    23
    

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25. ౸ୡෆೳͳؔ਺Λચ͍ग़͢
    void markDeadSymbols(ModuleSummaryIndex &summary, llvm::DenseSet &PreservedGUIDs) {
    SmallVector Worklist;
    for (auto GUID : PreservedGUIDs) {
    Worklist.push_back(GUID);
    }
    while (!Worklist.empty()) {
    auto GUID = Worklist.pop_back_val();
    auto Func = summary.getFunction(GUID);
    if (Func->isLive()) continue;
    Func->setLive(true);
    for (auto Call : Func->calls()) {
    switch (Call.getKind()) {
    case EdgeTy::Kind::Static: {
    Worklist.push_back(Call.getCallee());
    continue;
    }
    case EdgeTy::Kind::Witness:
    case EdgeTy::Kind::VTable: {
    auto Impls = summary.getImplementations(Call);
    for (auto Impl : Impls) {
    Worklist.push_back(Impl);
    }
    break;
    }
    }
    }
    }
    23
    

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26. ౸ୡෆೳͳؔ਺Λચ͍ग़͢
    void markDeadSymbols(ModuleSummaryIndex &summary, llvm::DenseSet &PreservedGUIDs) {
    SmallVector Worklist;
    for (auto GUID : PreservedGUIDs) {
    Worklist.push_back(GUID);
    }
    while (!Worklist.empty()) {
    auto GUID = Worklist.pop_back_val();
    auto Func = summary.getFunction(GUID);
    if (Func->isLive()) continue;
    Func->setLive(true);
    for (auto Call : Func->calls()) {
    switch (Call.getKind()) {
    case EdgeTy::Kind::Static: {
    Worklist.push_back(Call.getCallee());
    continue;
    }
    case EdgeTy::Kind::Witness:
    case EdgeTy::Kind::VTable: {
    auto Impls = summary.getImplementations(Call);
    for (auto Impl : Impls) {
    Worklist.push_back(Impl);
    }
    break;
    }
    }
    }
    }
    23
    

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27. ౸ୡෆೳͳؔ਺Λચ͍ग़͢
    void markDeadSymbols(ModuleSummaryIndex &summary, llvm::DenseSet &PreservedGUIDs) {
    SmallVector Worklist;
    for (auto GUID : PreservedGUIDs) {
    Worklist.push_back(GUID);
    }
    while (!Worklist.empty()) {
    auto GUID = Worklist.pop_back_val();
    auto Func = summary.getFunction(GUID);
    if (Func->isLive()) continue;
    Func->setLive(true);
    for (auto Call : Func->calls()) {
    switch (Call.getKind()) {
    case EdgeTy::Kind::Static: {
    Worklist.push_back(Call.getCallee());
    continue;
    }
    case EdgeTy::Kind::Witness:
    case EdgeTy::Kind::VTable: {
    auto Impls = summary.getImplementations(Call);
    for (auto Impl : Impls) {
    Worklist.push_back(Impl);
    }
    break;
    }
    }
    }
    }
    23
    

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28. ౸ୡෆೳͳؔ਺Λચ͍ग़͢
    void markDeadSymbols(ModuleSummaryIndex &summary, llvm::DenseSet &PreservedGUIDs) {
    SmallVector Worklist;
    for (auto GUID : PreservedGUIDs) {
    Worklist.push_back(GUID);
    }
    while (!Worklist.empty()) {
    auto GUID = Worklist.pop_back_val();
    auto Func = summary.getFunction(GUID);
    if (Func->isLive()) continue;
    Func->setLive(true);
    for (auto Call : Func->calls()) {
    switch (Call.getKind()) {
    case EdgeTy::Kind::Static: {
    Worklist.push_back(Call.getCallee());
    continue;
    }
    case EdgeTy::Kind::Witness:
    case EdgeTy::Kind::VTable: {
    auto Impls = summary.getImplementations(Call);
    for (auto Impl : Impls) {
    Worklist.push_back(Impl);
    }
    break;
    }
    }
    }
    }
    23
    

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29. void markDeadSymbols(ModuleSummaryIndex &summary, llvm::DenseSet &PreservedGUIDs) {
    ...
    for (auto Call : Func->calls()) {
    switch (Call.getKind()) {
    case EdgeTy::Kind::Static: {
    Worklist.push_back(Call.getCallee());
    continue;
    }
    case EdgeTy::Kind::Witness:
    case EdgeTy::Kind::VTable: {
    auto Impls = summary.getImplementations(Call);
    for (auto Impl : Impls) {
    Worklist.push_back(Impl);
    }
    break;
    }
    }
    ...
    }
    24
    

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30. void markDeadSymbols(ModuleSummaryIndex &summary, llvm::DenseSet &PreservedGUIDs) {
    ...
    for (auto Call : Func->calls()) {
    switch (Call.getKind()) {
    case EdgeTy::Kind::Static: {
    Worklist.push_back(Call.getCallee());
    continue;
    }
    case EdgeTy::Kind::Witness:
    case EdgeTy::Kind::VTable: {
    auto Impls = summary.getImplementations(Call);
    for (auto Impl : Impls) {
    Worklist.push_back(Impl);
    }
    break;
    }
    }
    ...
    }
    24
    

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31. ܕ͕࢖ΘΕ͍ͯͳ͚Ε͹ςʔϒϧܦ༝Ͱϝιου͕ݺ͹ΕΔ͜
    ͱ΋ͳ͍ͷͰফͤΔ
    void markDeadSymbols(ModuleSummaryIndex &summary, llvm::DenseSet &PreservedGUIDs) {
    ...
    for (auto Call : Func->calls()) {
    switch (Call.getKind()) {
    case EdgeTy::Kind::Static: {
    Worklist.push_back(Call.getCallee());
    continue;
    }
    case EdgeTy::Kind::Witness:
    case EdgeTy::Kind::VTable: {
    auto Impls = summary.getImplementations(Call);
    for (auto Impl : Impls) {
    if (UsedTypes.find(Impl.Type) == UsedTypes.end()) {
    continue;
    }
    Worklist.push_back(Impl);
    }
    break;
    }
    }
    ...
    }
    25
    

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32. ϕϯνϚʔΫ
    https://github.com/kateinoigakukun/swift-lto-benchmark
    26
    

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33. Stdlib
    ର৅ίʔυ: https://
    github.com/kateinoigakukun/
    swift-lto-benchmark/blob/
    master/Example/
    SwiftStdlibExample.swift
    let alphabet = "abcdefghijklmnopqrstuvwxyz"
    /// All edits that are one edit away from `word`
    func edits(_ word: String) -> Set {
    let splits = word.indices.map {
    (String(word[..<$0]), String(word[$0...]))
    }
    var result: Array = []
    for (left, right) in splits {
    // drop a character
    result.append(left + right.dropFirst())
    // transpose two characters
    if let fst = right.first {
    let drop1 = right.dropFirst()
    if let snd = drop1.first {
    result.append(left + [snd,fst] + drop1.dropFirst())
    }
    }
    // replace each character with another
    for letter in alphabet {
    result.append(left + [letter] + right.dropFirst())
    }
    // insert rogue characters
    for letter in alphabet {
    result.append(left + [letter] + right)
    }
    }
    // have to map back to strings right at the end
    return Set(result)
    }
    27
    

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34. όΠφϦαΠζ
    28
    

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35. Ϗϧυ࣌ؒ
    29
    

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36. • 60%ऑͷόΠφϦαΠζ࡟ݮ
    • SIL -> IRͷม׵ύε͕ߴίετͳͷͰɺ߱Լͤ͞Δؔ਺͕
    ݮͬͨ͜ͱʹΑͬͯίϯύΠϧ࣌ؒ΋ݮগ͍ͯ͠Δɻ
    30
    

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37. Ϗϧυ࣌ؒͷ಺༁
    ninjatracing ͱ͍͏πʔϧͰninjaͷϏϧυϩά͔ΒϏϧυ࣌
    ؒΛChromeͰϏδϡΞϥΠζͰ͖ΔϑΥʔϚοτʹม׵Ͱ͖
    Δ
    https://github.com/nico/ninjatracing
    31
    

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38. View Slide

39. ফͤͳ͍ؔ਺ͷղੳ
    ཧ૝తʹ͸ফ͍͕ͨ͠liveϚʔΫ͕෇͍ͯ͠·͍ͬͯΔؔ਺͕
    ࢒͍ͬͯΔͷͰղੳ͍ͨ͠ɻ
    ղੳͷΞΠσΟΞ
    • ίʔϧάϥϑΛϏδϡΞϥΠζͯ͠ΈΔ
    • ίʔϧάϥϑ͔Βࢧ഑໦(Dominator Tree)Λߏஙͯ͠େ͖ͳ
    ؔ਺ΛҾ͖࿈Εͯ͘ΔݪҼΛݟ͚ͭΔ
    33
    

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40. ίʔϧάϥϑΛϏδϡΞϥΠζͯ͠ΈΔ
    ΍ͬͯΈͨɻ
    34
    

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41. View Slide

42. ਓ͕ؒݟΒΕΔάϥϑ͡Όͳ͔ͬͨ
    36
    

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43. Dominator Tree (ࢧ഑໦)
    • ίϯύΠϥͷϑϩʔղੳʹΑ͘࢖ΘΕΔ
    • ༗޲άϥϑʹରͯ͠ߏஙͰ͖Δ໦ߏ଄
    • ͋Δϊʔυʹ౸ୡ͢ΔͨΊʹඞͣ௨ΔҰ൪͍ۙϊʔυΛ਌ʹ
    ͱΔߏ଄
    37
    

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44. ྫ
    ݩͷ༗޲άϥϑ ࢧ഑໦
    1
    2
    3 4 5 6
    https://en.wikipedia.org/wiki/Dominator(graphtheory) 38
    

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45. Dominator TreeΛ࢖͏ͱͲͷؔ਺͕୔ࢁ໋ྩΛҾ͖࿈Ε͍ͯΔ
    ͔ղੳ͠΍͘͢ͳΔɻ
    39
    

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46. ղੳͨ݁͠Ռ
    • RxSwiftͷ৔߹͸ɺdeinit ͕৭ʑҾ͖࿈Ε͖͍ͯͯͨɻ
    • disposeΛεέδϡʔϥʹࡌ͍ͤͯΔॲཧ͕ॏ͍
    • deinit͸ϥϯλΠϜ͕ಈతʹݺͿͷͰpreserve͍ͯͨ͠ɻ
    • Stdlibͷ৔߹͸ɺΫϥογϡ࣌ʹϥϯλΠϜ͔Βݺ͹ΕΔ
    debugPrint͕ॏ͔ͬͨɻ
    40
    

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47. ରԠͷߏ૝
    • deinit
    • ʮalloc ͞Εͳ͚Ε͹deinit΋ݺ͹Εͳ͍ʯΛ࢖ͬͯফ͠
    ͯΈΔ
    • debugPrint
    • Ϋϥογϡ࣌ʹԿ΋ग़ྗ͠ͳ͍Ͱࢮ͵ϞʔυΛ௥Ճͯ͠Έ
    Δʁ
    41
    

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48. ײ૝
    • λΠϜκʔϯͷҧ͍͕େม
    • ίϯύΠϥΤϯδχΞͬΆ͍࢓ࣄ͕Ͱָ͖͔ͯͬͨ͠
    • ํ਑స׵͸͠ΜͲ͔͕ͬͨɺσΟεΧογϣϯͯ͠ྑ͍Ξϓ
    ϩʔνʹͳͬͨͷ͸ྑ͔ͬͨ
    42
    

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49. ֤छϦϯΫ
    ϓϩϙʔβϧ: https://docs.google.com/document/d/
    1qT77pc7rJaisuds4msSMfGPYCjy4uiJ-J1U7-nEW2Y0
    ϑΥʔϥϜ:
    • https://forums.swift.org/t/refactoring-plan-of-silvisitor-for-
    lto/37678
    • https://forums.swift.org/t/gsoc-lto-support-progress-report/
    37149
    43
    

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