iOS エンジニアのための LLVM Optimiazation

by Toshihiro Morimoto

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iOS ΤϯδχΞͷͨΊͷ LLVM Optimiazation 2014/11/29 ԣ඿΁ͳͪΐ͜iOSษڧձ#34.1 @dealforest Toshihro Morimoto

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ࣗݾ঺հ http://about.me/dealforest ! ! iOS App / Web Application(perl, ruby) @dealforest Toshihro Morimoto

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Έͳ͞Μ ͜Μͳܦݧ͋Γ·ͤΜ͔ʁ

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Debug ϏϧυͰ͔֬͠ೝͤͣ ৹ࠪʹͩͯ͠͠·ͬͨ͜ͱ

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͍͟ϦϦʔε͞ΕΔͱ...

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ʊਓਓਓਓਓਓਓਓʊ ʼɹಥવͷ Crashɹʻ ʉY^Y^Y^Y^Y^Y^Yʉ

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ͳͥͦΜͳ͜ͱ͕͓͖Δͷ͔ʁ

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LLVM ͷ࠷దԽʹΑΓ ͜ͷΑ͏ͳ͜ͱ͕ ى͖ͯ͠·͏έʔε͕͋Γ·͢

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LLVM ͷ࠷దԽ͸ԿΛ͍ͯ͠Δͷ͔ʁ

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όΠφϦαΠζΛখͨ͘͞͠Γ ॲཧΛߴ଎Խͨ͠Γ͠·͢ (಺༰͸ઃఆʹΑͬͯมΘΓ·͢)

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ͪΌΜͱ Release ϏϧυͰ ςετ͠Ζͬͯݴ͑͹ ͦ͏ͳΜͰ͚͢ͲͶɻɻɻɻ

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Ͳ͏ͯ͠࠷దԽͰ Crash ͢ΔΑ͏ʹ ͳͬͯ͠·ͬͨͷ͔

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࠷దԽͰԿ͕ߦΘΕ͍ͯΔͷ͔

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ࠓճ͸ͦΕΛௐ΂ͯΈ·ͨ͠

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஫ҙࣄ߲ ༻ޠ / ༻๏ڞʹؒҧ͍͕͋ΔՄೳੑ͕ ͋Γ·͢ͷͰ͔͋͠Βͣ

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ͦ΋ͦ΋Ͳ͜Ͱઃఆ͢Δͷʁ

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Build Settings

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࠷దԽͷछྨ • O0 : ࠷΋଎͘ίϯύΠϧग़དྷɺ࠷΋σόοΨϒϧͳίʔυΛ ੜ੒͢Δɻ࠷దԽͳ͠ • O1 : جຊతͳ࠷దԽΛ࣮ߦ͢Δ • O2 : ΄ͱΜͲ͢΂ͯͷ࠷దԽΛ࣮ߦ͢Δ • O3 : O2 ͱࣅ͍ͯΔ͕ίϯύΠϧʹΑΓ͕͔͔࣌ؒΓ αΠζ͕େ͖͘ͳΔɻ͔͠͠ੑೳͷྑ͍ίʔυΛੜ੒͢Δ • Os : O2ͷ࠷దԽʹՃ͑ͯίʔυαΠζΛ཈͑Δ • Ofast : ن໿ΛҰ෦ແࢹͨ͠࠷దԽΛߦ͏Α͏ͳͷͰ࢖Θͳ͍΄͏ ͕͍͍Ͱ͢ɻ by Compiler-Level Optimizations

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͍·͍ͪϐϯͱ͖·ͤΜͶ

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Ξό΢τ͗͢Δ…

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͜ΕΛ஌ΔͨΊʹ͸ LLVM ͷਂ෵Λ ೷͔ͳ͍ͱ͍͚·ͤΜͰͨ͠

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ͱ͍ͬͯ΋ LLVM ͷ֓೦ࣗମ͕ γϯϓϧͰͱͯ΋෼͔Γ΍͍͢ʂ

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ͦ΋ͦ΋ LLVM ͬͯԿʁ

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LLVM

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LLVM LLVM ͱ͸ɺίϯύΠϧ࣌ɺϦϯΫ࣌ɺ࣮ߦ࣌ͳͲ ͋ΒΏΔ࣌఺ͰϓϩάϥϜΛ࠷దԽ͢ΔΑ͏ઃܭ ͞Εͨɺ೚ҙͷϓϩάϥϛϯάݴޠʹରԠՄೳͳ ίϯύΠϥج൫Ͱ͋Δɻ౰ॳ͸ɺLLVM ͷ໊শͷ༝ དྷ͸ɺLow Level Virtual Machine (௿ਫ४Ծ૝ػց) ͷུͰ͋Δͱ͍͕ͯͨ͠ɺݱࡏ͸ɺԿͷ಄จࣈͰ ΋ͳ͍ͱ͍ͯ͠Δɻ by Wikipekia

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LLVM - Phase- by LLVM and NVVM

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LLVM - Phase- • Front-end • Middle-end • Back-end

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LLVM - Phase Front-end - • ࣈ۟ղੳ • ߏจղੳ • தؒίʔυ(LLVM IR)࡞੒

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LLVM - Phase Middle-end - தؒίʔυͷ࠷దԽΛ͠ɺ ࠷దԽ͞ΕͨதؒίʔυΛग़ྗ͢Δ

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LLVM - Phase Back-end - ࠷దԽ͞Εͨதؒίʔυ͔Βλʔήοτʹ ߹ΘͤͨίʔυΛग़ྗ͢Δ ಛఆͷ CPU ͷωΠςΟϒίʔυͱ͔ Javascript ͱ͔

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;Ή;Ή

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ࠓճ͸࠷దԽͷ͜ͱΛ஌Γ͍ͨͷͰ Middle-end Λௐ΂Ε͹Αͦ͞͏Ͱ͢Ͷ

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Middle-end(LLVM optimiser) Λ ௐ΂͍ͯ͘ͱ Pass ͱ͍͏࢓૊Έʹ ͍͖͖ͭ·͢

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Pass Middle-end Ͱ࠷దԽ͢ΔॲཧΛ͍ͯ͠Δ LLVM IR ͷίʔυΛର৅ʹɺͦͷ಺༰Λղ ੳ͠ɺ࠷దԽ΍ɺ໋ྩͷஔ׵ͳͲΛߦ͏ͨ ΊͷϑϨʔϜϫʔΫ

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ͭ·Γ͸ͲΜͳ Pass ͕࣮ߦ͞Ε͍ͯΔ͔Λ ௐ΂Ε͹ͲΜͳ࠷దԽ͕ߦΘΕ͍ͯΔ͔͕ ෼͔Δͱ͍͏Θ͚Ͱ͢Ͷ

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؀ڥߏங $ brew install llvm ! `/usr/local/Cellar/llvm/3.5.0/bin/opt` ͱ࣮ߦ͢ Δͷ͕ΊΜͲ͍͘͞৔߹͸ `brew link llvm` Λ࣮ߦ͢Δ

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ௐࠪϑϩʔ 1. ࠷దԽͳ͠ͷ .o ϑΝΠϧΛ࡞੒͢Δઃ ఆΛௐ΂Δ 2. ͦͷઃఆΛ༻͍ͯதؒίʔυ(LLVM IR)Λ ࡞੒ 3. ֤࠷దԽΛ࣮ߦͯ͠ϑΝΠϧʹग़ྗ 4. diff ΛͱΓ Pass ͷࠩ෼Λௐ΂Δ

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࠷దԽͳ͠ͷ .o ϑΝΠϧΛ ࡞੒͢ΔઃఆΛௐ΂Δ xcodebuild build -conﬁguration Debug

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தؒίʔυ(LLVM IR)Λ࡞੒ • ઌ΄Ͳௐ΂ͨઃఆΛར༻ • `-S -emit-llvm` ΦϓγϣϯΛ௥Ճͯ͠த ؒίʔυΛग़ྗ • `-o` ͷ஋Λมߋͯ͠தؒίʔυͷग़ྗઌ Λมߋ(.o -> .ll)

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֤࠷దԽΛ࣮ߦͯ͠ϑΝΠϧʹग़ྗ $ /usr/local/Cellar/llvm/3.5.0/bin/opt \ -debug-pass=Structure \ -O1 [தؒίʔυ].ll > /dev/null ! ඞཁͳ৘ใ͸ඪ४Τϥʔग़ྗʹදࣔ͞ΕΔ

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֤࠷దԽΛ࣮ߦͯ͠ϑΝΠϧʹग़ྗ

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ݟʹ͍͘ͷͰ gist ʹ·ͱΊ·ͨ͠ https://gist.github.com/dealforest/ 718df40a09d8e27758c7

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ͦ΋ͦ΋ Debug ࣌΋ Os ΍Ε͹͍͍Μ͡Ό...

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! ͱࢥ͚ͬͨͲɺίϯύΠϧ͕͔͔࣌ؒΔͷͱɺC, C++ ͷίʔυͰ BreakPoint Λ࢓ֻ͚ͨΓ͢Δͱશ͘ ݟ౰ҧ͍ͳߦͰఀࢭͨ͠Γ͠·͢ ͳͷͰ։ൃαΠΫϧʹӨڹ͕Ͱͯ͠·͏ͷͰ O0 ͕ ࠾༻͞Ε͍ͯΔͱΘ͚Ͱ͢Ͷɻೲಘ @niwatako ͞Μᐌ͘ɺObjective-C Ͱ΋ͣΕΔΒ͍͠ Ͱ͢

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·ͱΊ ࠷దԽ͸ࢥͬͯΔҎ্ʹ৭ʑ͍ͬͯ͡ΔͷͰͪΌ Μͱ֬ೝ͠·͠ΐ͏ Ή͠Ζ֬ೝ͔ͯ͠Β͡Όͳ͍ͱɺ৹ࠪʹͩͤͳ͍ εΩʔϜΛͭ͘Δ͜ͱ͕େࣄ

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http://www.amazon.co.jp/dp/4883379310/

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͓·͚ Xcode6 ͔Β௥Ճ͞Εͨ Proﬁle Guided Optimization(PGO) ͱ͍͏࠷దԽ͕͋Δ ؆୯ʹ͍͏ͱɺ࢖༻ස౓ͷߴ͍ॱʹίʔυϨΠΞ ΢τΛ࠷దԽ͢ΔΒ͍͠ ͸΍͘ͳΔΑʂ

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͓·͚ Xcode6 ͔Β௥Ճ͞Εͨ࠷దԽ Proﬁle Guided Optimization(PGO) ͕͋Δ ؆୯ʹ͍͏ͱΑ͘࢖͏ॱ൪ʹίʔυϨΠΞ΢τΛ ࠷దԽ͢ΔΒ͍͠ ͸΍͘ͳΔΑʂ