Introduction to Swift Performance - Try! Swift 2016

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An Introduction to Swift Performance Danielle Tomlinson - @dantoml

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What makes code slow?

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Allocation

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Stack

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Heap

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Reference Counting

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func perform(with object: Object) { object.doAThing() }

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func perform(with object: Object) { __swift_retain(object) object.doAThing() __swift_release(object) }

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Dispatch

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Inline (0ns)

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Static (~1ns)

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Dynamic (~5ns)

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Objects

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Classes

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p: Index* Stack class Index { let section: Int let item: Int } let i = Index(section: 1, item: 1) Heap section: Int item: Int

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i: Index* Stack class Index { let section: Int let item: Int } let i = Index(section: 1, item: 1) let i2 = i Heap section: Int item: Int i2: Index*

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i: Index* Stack class Index { let section: Int let item: Int } let i = Index(section: 1, item: 1) __swift_retain(i) let i2 = i Heap section: Int item: Int i2: Index*

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Structs

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Stack

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section: 1 item: 1 Stack struct Index { let section: Int let item: Int } let i = Index(section: 1, item: 1)

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Stack struct Index { let section: Int let item: Int } let i = Index(section: 1, item: 1) let i2 = i section: 1 item: 1 section: 1 item: 1

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name: StringA* id: StringB* Stack struct User { let name: String let id: String } let u = User(name: "Joe", id: "1234")

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name: StringA* id: StringB* Stack name: StringA* id: StringB* struct User { let name: String let id: String } let u = User(name: "Joe", id: "1234") __swift_retain(u.name._textStorage) __swift_retain(u.id._textStorage) let u2 = u

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Abstractions

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Example (0.3s) : struct Circle { let radius: Double let center: Point func draw() {} } var circles = (1..<100_000_000).map { _ in Circle(...) } for circle in circles { circle.draw() }

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Requirements Change

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Protocols

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Example (4s) : protocol Drawable { func draw() } struct Circle: Drawable { let radius: Double let center: Point func draw() {} } let drawables: [Drawable] = (1..<100_000_000).map { _ in Circle(...) } for drawable in drawables { drawable.draw() }

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Why?

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struct Circle { let radius: Double let center: Point func draw() {} } var circles = (1..<100_000_000).map { _ in Circle(...) } for circle in circles { circle.draw() }

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protocol Drawable { func draw() } struct Circle: Drawable { let radius: Double let center: Point func draw() {} } var drawables: [Drawable] = (1..<100_000_000).map { _ in return Circle(...) } for drawable in drawables { drawable.draw() }

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ProtocolWitnessTable draw() CircleDrawable ... draw() LineDrawable ...

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ExistentialContainer ValueBuffer ProtocolWitnessTable

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ExistentialContainer radius struct Circle: Drawable { let radius: Double let center: Point func draw() {} } center

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ExistentialContainer struct Line: Drawable { let origin: Point let end: Point func draw() {} } Origin End

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Example (45s) : protocol Drawable { func draw() } struct Line: Drawable { let origin: Point let end: Point func draw() {} } let drawables: [Drawable] = (1..<100_000_000).map { _ in Line(...) } for drawable in drawables { drawable.draw() }

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No content

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ValueWitnessTable ValueBuffer allocate: copy: destruct: deallocate:

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In Practice Stack origin Line vwt pwt end LineDrawable copy: ... Heap drawable: func draw(drawable: Drawable) { drawable.draw() } let value: Drawable = Line() draw(local: value) // Generates func draw(value: ECTDrawable) { var drawable: ECTDrawable = ECTDrawable() let vwt = value.vwt let pwt = value.pwt drawable.vwt = value.vwt drawable.pwt = value.pwt vwt.allocateBuffAndCopyValue(&drawable, value) pwt.draw(vwt.projectBuffer(&drawable) }

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Modelling Your Data

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Generics

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struct Stack { ... }

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Enumerations

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enum AccountStatus: String, RawRepresentable { case .banned, .verified, incomplete }