Swift internals

let swift(16)
Internals
LLVM, Type system, Swift Foundation
OSXDEV.orgj

Agenda
Swift Compiler
Swift Type System
Swift Type Internals
Swift Foundation
Summary

let swift(16)
Swift Compiler
LLVM, Clang, Swiftc

A LoNG Time AGo,
in a galaxy
far, far away...

LLVM
Low-Level Virtual Machine
An Infrastructure for Multi-stage Optimization
− by Chris Arthur Lattner @2002
Design and Implementation of a compiler infrastructure
− support a unique multi-stage optimization system
− support inter-procedural and profile-driven optimizations
LLVM virtual instruction (IR)
− with high-level type information
Sponsored by APPLE

Chris Lattner
The Father of LLVM

LLVM Compiler
GCC#4.2#
프론트엔드#
C"
Tree*SSA#
최적화기#
코드 생성기#C++"
Objec)ve+C"
실행파일"
GCC"4.2"
GCC#4.2#
프론트엔드#
C"
LLVM#
최적화기#
LLVM#
코드 생성기#
C++"
Objec)ve+C"
실행파일"
LLVM+GCC"4.2"
Clang#
프론트엔드#
C"
LLVM#
최적화기#
LLVM#
코드 생성기#
C++"
Objec)ve+C"
실행파일"
LLVM"

Swift Compiler
yp RVHES
− 9 RHMF DL MSH M RHR
− % < OD GD D
p
− d S MREN L % -: % DMD H
> : c
k ib p ib y AHM
.swift 기계코드

let swift(16)
Swift Type System
Duck Type vs. HM Type Inference

Objective-C Type System
Static Type + Duck Type System
− C-style static type
− Smalltalk-style duck type
Duck Type History
− a message to comp.lang.python Newsgroup (2000)
Don't check whether it IS-a duck: check whether it QUACKS-like-a
duck, WALKS-like-a duck, etc, etc, depending on exactly what subset
of duck-like behaviour you need to play your language-games with.
“
”

Swift Type System
Bi-directional type inference
Constraint-based type checker
− Based classical Hindley-Milner type system
− Include polymorphic types & function overloading
− Step : Generate ➔ Solve ➔ Solution Application
func foo(x: Double) -> Int { … }

var doubleValue : Double = 3.141592

var unknown = foo(doubleValue)

func bar<T>(x: T) -> T { return x }

var ﬂoatValue: Float = -bar(1.414)

“The Principal Type-Scheme of an Object in
Combinatory Logic” Hindley, J. Roger (1969)
− Describe what types an expression can have
− Present an algorithm actually computing a type.
Deductive System
First implemented as part of the system of ML.
Hindley-Milner Type System
A, A ➔ B
B
(rule)

Hindley-Milner Algorithm W
[Var]
[App]
[Abs]
[Let]

Type Checker - Constraints
0PT HS x
TAS OD r
NMUD RHNM r q DPT HS RTAS OD
NMRS T SHNM s r q
DLAD c% h
NMEN L M D p
GD DC RS R q
-OO H A D ETM SHNM d
UD N C AHMCHMF y
RR
NMITMSHNM /HRITM SHNM a i p i

Constraint Solving
Take a given set of constraints
Determine the most specific type binding for each of the type
variables
The Design of the solver
− Simplification : Relational, Member constraints
− Strategies : solver scope, overload selection
− Comparing solutions : choose solution with smaller scores
“more specific” type
the super-type of overload binds

let swift(16)
Swift Type Internals
class, enumeration, struct, protocol

Native class type
class NativePen {
let id = 512
var sequence = 1024
}
// class.NativePen.__deallocating_deinit
@_TFC5class9NativePenD : $@convention(method) (@owned NativePen) -> () {
%0 : $NativePen, let, name "self", argno 1
%3 = class.NativePen.deinit(%0)
%4 = unchecked_ref_cast(%3) // $Builtin.NativeObject to $NativePen
dealloc_ref(%4)
}
// class.NativePen.deinit
@_TFC5class9NativePend : $@convention(method) (@guaranteed NativePen) -> @owned
Builtin.NativeObject {
%0 : $NativePen, let, name "self", argno 1
%2 = unchecked_ref_cast(%0) // $NativePen to $Builtin.NativeObject
return %2 // $Builtin.NativeObject
}
deinit

Native class type
// class.NativePen.init () -> class.NativePen
@_TFC5class9NativePencfT_S0_ : $@convention(method) (@owned NativePen) -> @owned
NativePen {
%0 : $NativePen, let, name "self"
%2 = mark_uninitialized([rootself], %0)
%4 = metatype(Int.Type)
%5 = integer_literal($Builtin.Int2048, 512)
%6 = Swift.Int.init(%5, %4)
%7 = ref_element_addr(%2 : $NativePen, #NativePen.id)
assign(%6 to %7)
%10 = metatype(Int.Type)
%12 = Swift.Int.init(%11, %10)
%13 = ref_element_addr(%2 : $NativePen, #NativePen.sequence)
assign (%12 to %13)
return %2 // $NativePen
}
// class.NativePen.__allocating_init () -> class.NativePen
@_TFC5class9NativePenCfT_S0_ : $@convention(thin) (@thick NativePen.Type) -> @owned
NativePen {
%1 = alloc_ref($NativePen)
%3 = class.NativePen.init(%1)
return %3 : $NativePen
}
init

enumeration type
_ p r q
− _l u q p
RG A D O NSN N
0PT S A D O NSN N
public protocol Hashable : Equatable {
var hashValue: Int { get }
}
public protocol Equatable {
@warn_unused_result
func == (lhs: Self, rhs: Self) -> Bool
}

enum type example
enum PenModels {
case BallPen
case NamePen
}
// enum.PenModels.hashValue.getter : Swift.Int
@_TFO4enum9PenModelsg9hashValueSi : $@convention(method) (PenModels) -> Int {
%2 = alloc_box($Int, var, name "index")
%3 = mark_uninitialized([var] %2#1 : $*Int)
switch_enum %0 : $PenModels,
case #PenModels.BallPen!enumelt: bb1,
case #PenModels.NamePen!enumelt: bb2
bb1:
%6 = metatype($@thin Int.Type)
%8 = Swift.Int.init(%7, %6) // (Builtin.Int2048, @thin Int.Type) -> Int
assign(%8 to %3)
br bb3
bb2:
%12 = metatype($@thin Int.Type)
%14 = Swift.Int.init(%13, %12) // (Builtin.Int2048, @thin Int.Type) -> Int
assign(%14 to %3)
br bb3
bb3:
%17 = load(%3 : $*Int)
%19 = Swift.Int.hashValue.getter(%17) // $@convention(method) (Int) -> Int
strong_release(%2#0) // $@box Int
return %19
}
getter

enum type example
// protocol witness for static Swift.Equatable.== infix (A, A) -> Swift.Bool
@_TTWO4enum9PenModelss9EquatableS_ZFS1_oi2eefTxx_Sb :
$@convention(witness_method) (@in PenModels, @in PenModels, @thick
PenModels.Type) -> Bool {
%3 = load(%0 : $*PenModels)
%6 = enum.== infix(%3, %4)
return %6 // $Bool
}
// protocol witness for Swift.Hashable.hashValue.getter : Swift.Int
@_TTWO4enum9PenModelss8HashableS_FS1_g9hashValueSi :
$@convention(witness_method) (@in_guaranteed PenModels) -> Int {
%1 = alloc_stack($PenModels)
copy_addr(%0 to [initialization] %1 : $*PenModels)
%5 = enum.PenModels.hashValue.getter(%3)
dealloc_stack(%1 : $*PenModels)
return %5 // $Int
}
sil_witness_table PenModels: Equatable module enum {
method #Equatable."=="!1:
@_TTWO4enum9PenModelss9EquatableS_ZFS1_oi2eefTxx_Sb
}
sil_witness_table PenModels: Hashable module enum {
base_protocol Equatable: PenModels: Equatable module enum
method #Hashable.hashValue!getter.1:
@_TTWO4enum9PenModelss8HashableS_FS1_g9hashValueSi
}
Protocol Witness Table

struct type
i wp p
− MS - % DS% /H SHNM t )(
f
i HED D c
− r
n g b r
− DS HM D D RD

struct type - let example
struct Car {
let model = "apple"
}
// struct.Car.init () -> struct.Car
@_TFV6struct3CarCfT_S0_ : $@convention(thin) (@thin Car.Type) -> @owned Car {
%1 = alloc_box($Car, var, name "self", argno 1)
%2 = mark_uninitialized([rootself] %1#1 : $*Car)
%4 = metatype($@thin String.Type)
%5 = string_literal(utf8 "apple")
%6 = integer_literal($Builtin.Word, 5)
%7 = integer_literal($Builtin.Int1, -1)
%8 = Swift.String.init(%5, %6, %7, %4)
%9 = struct_element_addr(%2 : $*Car, #Car.model)
assign(%8 to %9 : $*String)
%11 = load(%2 : $*Car)
retain_value(%11 : $Car)
strong_release(%1#0 : $@box Car)
return %11
}
// struct.Car.model.getter : Swift.String
@_TFV6struct3Carg5modelSS : $@convention(method) (@guaranteed Car) -> @owned String {
%2 = struct_extract(%0 : $Car, #Car.model)
retain_value(%2 : $String)
return %2
}

struct type - var example
struct Car {
var driver = "tim"
}
// struct.Car.init (driver : Swift.String) -> struct.Car
@_TFV6struct3CarCfT6driverSS_S0_ : $@convention(thin) (@owned String, @thin Car.Type)
-> @owned Car {
%2 = struct.$Car(%0 : $String)
return %2
}
// struct.Car.init () -> struct.Car
@_TFV6struct3CarCfT_S0_ : $@convention(thin) (@thin Car.Type) -> @owned Car {
%2 = mark_uninitialized([rootself] %1#1 : $*Car)
%4 = metatype($@thin String.Type)
%5 = string_literal(utf8 "tim")
%6 = integer_literal($Builtin.Word, 3)
%7 = integer_literal($Builtin.Int1, -1)
%8 = Swift.String.init(%5, %6, %7, %4)
%9 = struct_element_addr(%2 : $*Car, #Car.driver)
%11 = load(%2 : $*Car)
retain_value(%11 : $Car)
return %11
}
init

struct type - var example
// struct.Car.driver.getter : Swift.String
@_TFV6struct3Carg6driverSS : $@convention(method) (@guaranteed Car) -> @owned String {
%2 = struct_extract(%0 : $Car, #Car.driver)
return %2
}
// struct.Car.driver.setter : Swift.String
@_TFV6struct3Cars6driverSS : $@convention(method) (@owned String, @inout Car) -> () {
copy_addr(%1 to [initialization] %3#1 : $*Car)
%6 = struct_element_addr(%3#1 : $*Car, #Car.driver)
copy_addr(%3#1 to %1 : $*Car)
release_value(%0 : $String)
%11 = tuple ()
return %11
}
// struct.Car.driver.materializeForSet : Swift.String
@_TFV6struct3Carm6driverSS : $@convention(method) (Builtin.RawPointer, @inout
Builtin.UnsafeValueBuffer, @inout Car) -> (Builtin.RawPointer, Optional<@convention(thin)
(Builtin.RawPointer, inout Builtin.UnsafeValueBuffer, inout Car, @thick Car.Type) -> ()>) {
%3 = struct_element_addr(%2 : $*Car, #Car.driver)
%4 = address_to_pointer(%3 : $*String to $Builtin.RawPointer)
%5 = enum $Optional<@convention(thin) (Builtin.RawPointer, inout
Builtin.UnsafeValueBuffer, inout Car, @thick Car.Type) -> ()>, #Optional.None!enumelt
%6 = tuple (%4 : $Builtin.RawPointer, %5 : $Optional<@convention(thin)
(Builtin.RawPointer, inout Builtin.UnsafeValueBuffer, inout Car, @thick Car.Type) -> ()>)
return %6 : $(Builtin.RawPointer, Optional<@convention(thin) (Builtin.RawPointer, inout
Builtin.UnsafeValueBuffer, inout Car, @thick Car.Type) -> ()>)
}
getter/setter

let swift(16)
Swift 3 Foundation

Foundation SDK
source : WWDC 2016. Session207. Whats new in foundation for swift

파일 구분 관련 타입들 설명
AffineTransform OTA H RS T S -EEHMD< MREN L -EEHMD< MREN L v p f
CharacterSet
HMSD M EHM RR
VHES G SD DS
G SD DS d TS A D G SD DS p n
Data HMSD M EHM RR VHES / S / S TS A D/ S p n
Date OTA H RS T S / SD <HLD MSD U SHLD m b p
DateComponents OTA H RS T S / SD NLONMDMSR / SD NLONMDMSR p m
DateInterval OTA H RS T S / SD MSD U / SD MSD U p m i o
Decimal D SDMRHNM /D HL
t % e % /D HL TLAD
a p
FileManager OTA H RR H D M FD H D M FD
IndexPath OTA H RS T S MCD 9 SG MCD 9 SG v p o f
IndexSet OTA H RS T S MCD DS MCD DS v p o f
Measurement
OTA H RS T S D RT DLDMS+ MHS< OD
MHS,
D RT DLDMS v p o f
Notification OTA H RS T S NSHEH SHNM NSHEH SHNM v p o f
NSError D SDMRHNM 0 N 0 N 9 NSN N 0 N o u
URL OTA H RS T S : : p f
URLComponents OTA H RS T S : NLONMDMSR : NLONMDMSR p f
URLRequest OTA H RS T S : :DPTDRS TS A D : :DPTDRS p f

Summary
Swift Compiler
− LLVM + Chris Lattner, Talyer swift
Type System
− HM Type System + W Algorithm
Type Internals
− class, enumeration, struct, protocol Types
Swift Foundation
− IndexPath, IndexSet, Measurement, Notification

References
llvm.org
swift.org
https://github.com/apple/swift-evolution
https://github.com/apple/swift/tree/swift-3.0-preview-2-branch
https://en.wikipedia.org/wiki/Duck_typing
https://en.wikipedia.org/wiki/
Hindley%E2%80%93Milner_type_system
http://akgupta.ca/blog/2013/05/14/so-you-still-dont-understand-
hindley-milner/
https://developer.apple.com/videos/wwdc2016/

Swift internals

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