class Teacher {
var age : Int = 3
var name : String = "張三"
}
var t = Teacher()
swiftc -emit-sil main.swift ｜ xcrun swift-demangle
如果編譯有問題可以添加：
swiftc -emit-sil main.swift -target x86_64-apple-ios14.0-simulator -sdk $(xcrun --show-sdk-path --sdk iphonesimulator)| xcrun swift-demangle
class Teacher {
@_hasStorage @_hasInitialValue var age: Int { get set }
@_hasStorage @_hasInitialValue var name: String { get set }
@objc deinit
init()
}
%0 %1: 寄存器
bb0 bb1: 代碼快
$String: SIL中的String 類型
$*String: SIL里的 String 類型的值地址
sil_global: 全局變量
apply: 調(diào)用函數(shù)跺撼，并傳入函數(shù)
function_ref: 直接函數(shù)引用調(diào)用
class_method: 通過函數(shù)表來查找實(shí)現(xiàn)調(diào)用
sil_vtable: 類的函數(shù)表
thin: 靜態(tài)的
thick: 動(dòng)態(tài)的，運(yùn)行時(shí)的
cond_br: 三目運(yùn)算 判斷寄存器上的值進(jìn)行跳轉(zhuǎn)
Builtin將 LLVM IR 的類型和方法直接暴露給 Swift 標(biāo)準(zhǔn)庫扒怖，使用時(shí)沒有額外的運(yùn)行時(shí)負(fù)擔(dān)。
@_hasStorage @_hasInitialValue var t: Teacher { get set }
// t
sil_global hidden @$s4main1tAA7TeacherCvp : $Teacher
// main
sil @main : $@convention(c) (Int32, UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>) -> Int32 {
bb0(%0 : $Int32, %1 : $UnsafeMutablePointer<Optional<UnsafeMutablePointer<Int8>>>):
alloc_global @$s4main1tAA7TeacherCvp // id: %2
%3 = global_addr @$s4main1tAA7TeacherCvp : $*Teacher // user: %7 ：拿到全局變量的地址給%3
%4 = metatype $@thick Teacher.Type // user: %6 ：獲取Teacher.Type的元類型給%4
// function_ref Teacher.__allocating_init()
%5 = function_ref @$s4main7TeacherCACycfC : $@convention(method) (@thick Teacher.Type) -> @owned Teacher // user: %6 ：初始化函數(shù)地址引用
%6 = apply %5(%4) : $@convention(method) (@thick Teacher.Type) -> @owned Teacher // user: %7
store %6 to %3 : $*Teacher // id: %7
%8 = integer_literal $Builtin.Int32, 0 // user: %9
%9 = struct $Int32 (%8 : $Builtin.Int32) // user: %10
return %9 : $Int32 // id: %10
} // end sil function 'main'
- %0 -- %9 在sil中被稱為寄存器(虛擬寄存器)
-
s4main1tAA7TeacherCvp ： 是經(jīng)過重整修改的（包含碱璃，項(xiàng)目名稱菩鲜、類名淋样、方法名、參數(shù)名稱唆垃、參數(shù)類型）可以通過 xcrun swift-demangle 還原
image.png
// Teacher.__allocating_init()
sil hidden [exact_self_class] @$s4main7TeacherCACycfC : $@convention(method) (@thick Teacher.Type) -> @owned Teacher {
// %0 "$metatype"
bb0(%0 : $@thick Teacher.Type):
%1 = alloc_ref $Teacher // user: %3
// function_ref Teacher.init()
%2 = function_ref @$s4main7TeacherCACycfc : $@convention(method) (@owned Teacher) -> @owned Teacher // user: %3
%3 = apply %2(%1) : $@convention(method) (@owned Teacher) -> @owned Teacher // user: %4
return %3 : $Teacher // id: %4
} // end sil function '$s4main7TeacherCACycfC'
讓我們看一下函數(shù)調(diào)用的過程：
-
Teacher()
image.png
image.png
-
__allocating_init()
image.png -
swift_allocObject
image.png -
swift_slowAlloc
image.png
對(duì)Teacher進(jìn)行修改
class Teacher : NSObject{
var age : Int = 3
var name : String = "張三"
}
var t = Teacher()
-
Teacher()
image.png -
__allocating_init()
image.png
從源碼中分析swift_allocObject
image.png
image.png
image.png
該函數(shù)有三個(gè)參數(shù)：
- HdapMetadata const *metadata：元數(shù)據(jù)類型五芝；
- requiredSize：所需要的大小辕万；
- requiredAlignmentMask：對(duì)齊所需要的掩碼与柑，可以從objc的源碼中得知谤辜，其為7，因?yàn)槭?字節(jié)對(duì)齊价捧；
將requiredSize和requiredAlignmentMask傳遞給函數(shù)swift_slowAlloc丑念，該函數(shù)返回了一個(gè)HeapObject類型的指針； reinterpret_cast用來做指針類型的轉(zhuǎn)換结蟋；
- new (object) HeapObject(metadata)：HeapObject初始化脯倚；
那么swift_slowAlloc是用來干什么的呢？
image.png
- 如果alignMask<=15則直接使用malloc 在堆上申請(qǐng)內(nèi)存嵌屎，否則內(nèi)存對(duì)其后(例如：alignMask = 17推正，對(duì)其后 alignMask = 32)然后分配內(nèi)存。
swift類的初始化流程
- 首先會(huì)調(diào)用_allocating_init()：該函數(shù)有編譯器生成宝惰；
- 對(duì)于純Swift類將會(huì)再調(diào)用swift_allocObject()函數(shù)植榕；
- 然后在swift_allocObjec()總會(huì)調(diào)用私有函數(shù)_swift_allocObject；
- 然后通過函數(shù)swift_slowAlloc調(diào)用malloc來申請(qǐng)堆區(qū)的內(nèi)存空間尼夺；
getter/setter方法
// Teacher.age.getter
sil hidden [transparent] @$s4main7TeacherC3ageSivg : $@convention(method) (@guaranteed Teacher) -> Int {
// %0 "self" // users: %2, %1
bb0(%0 : $Teacher):
debug_value %0 : $Teacher, let, name "self", argno 1, implicit // id: %1
%2 = ref_element_addr %0 : $Teacher, #Teacher.age // user: %3
%3 = begin_access [read] [dynamic] %2 : $*Int // users: %4, %5
%4 = load %3 : $*Int // user: %6
end_access %3 : $*Int // id: %5
return %4 : $Int // id: %6
} // end sil function '$s4main7TeacherC3ageSivg'
// Teacher.age.setter
sil hidden [transparent] @$s4main7TeacherC3ageSivs : $@convention(method) (Int, @guaranteed Teacher) -> () {
// %0 "value" // users: %6, %2
// %1 "self" // users: %4, %3
bb0(%0 : $Int, %1 : $Teacher):
debug_value %0 : $Int, let, name "value", argno 1, implicit // id: %2
debug_value %1 : $Teacher, let, name "self", argno 2, implicit // id: %3
%4 = ref_element_addr %1 : $Teacher, #Teacher.age // user: %5
%5 = begin_access [modify] [dynamic] %4 : $*Int // users: %6, %7
store %0 to %5 : $*Int // id: %6
end_access %5 : $*Int // id: %7
%8 = tuple () // user: %9
return %8 : $() // id: %9
} // end sil function '$s4main7TeacherC3ageSivs'
// Teacher.name.getter
sil hidden [transparent] @$s4main7TeacherC4nameSSvg : $@convention(method) (@guaranteed Teacher) -> @owned String {
// %0 "self" // users: %2, %1
bb0(%0 : $Teacher):
debug_value %0 : $Teacher, let, name "self", argno 1, implicit // id: %1
%2 = ref_element_addr %0 : $Teacher, #Teacher.name // user: %3
%3 = begin_access [read] [dynamic] %2 : $*String // users: %4, %6
%4 = load %3 : $*String // users: %7, %5
retain_value %4 : $String // id: %5
end_access %3 : $*String // id: %6
return %4 : $String // id: %7
} // end sil function '$s4main7TeacherC4nameSSvg'
// Teacher.name.setter
sil hidden [transparent] @$s4main7TeacherC4nameSSvs : $@convention(method) (@owned String, @guaranteed Teacher) -> () {
// %0 "value" // users: %11, %8, %4, %2
// %1 "self" // users: %5, %3
bb0(%0 : $String, %1 : $Teacher):
debug_value %0 : $String, let, name "value", argno 1, implicit // id: %2
debug_value %1 : $Teacher, let, name "self", argno 2, implicit // id: %3
retain_value %0 : $String // id: %4
%5 = ref_element_addr %1 : $Teacher, #Teacher.name // user: %6
%6 = begin_access [modify] [dynamic] %5 : $*String // users: %8, %7, %10
%7 = load %6 : $*String // user: %9
store %0 to %6 : $*String // id: %8
release_value %7 : $String // id: %9
end_access %6 : $*String // id: %10
release_value %0 : $String // id: %11
%12 = tuple () // user: %13
return %12 : $() // id: %13
} // end sil function '$s4main7TeacherC4nameSSvs'
- 析構(gòu)方法
// Teacher.deinit
sil hidden @$s4main7TeacherCfd : $@convention(method) (@guaranteed Teacher) -> @owned Builtin.NativeObject {
// %0 "self" // users: %6, %2, %1
bb0(%0 : $Teacher):
debug_value %0 : $Teacher, let, name "self", argno 1, implicit // id: %1
%2 = ref_element_addr %0 : $Teacher, #Teacher.name // user: %3
%3 = begin_access [deinit] [static] %2 : $*String // users: %5, %4
destroy_addr %3 : $*String // id: %4
end_access %3 : $*String // id: %5
%6 = unchecked_ref_cast %0 : $Teacher to $Builtin.NativeObject // user: %7
return %6 : $Builtin.NativeObject // id: %7
} // end sil function '$s4main7TeacherCfd'
// Teacher.__deallocating_deinit
sil hidden @$s4main7TeacherCfD : $@convention(method) (@owned Teacher) -> () {
// %0 "self" // users: %3, %1
bb0(%0 : $Teacher):
debug_value %0 : $Teacher, let, name "self", argno 1, implicit // id: %1
// function_ref Teacher.deinit
%2 = function_ref @$s4main7TeacherCfd : $@convention(method) (@guaranteed Teacher) -> @owned Builtin.NativeObject // user: %3
%3 = apply %2(%0) : $@convention(method) (@guaranteed Teacher) -> @owned Builtin.NativeObject // user: %4
%4 = unchecked_ref_cast %3 : $Builtin.NativeObject to $Teacher // user: %5
dealloc_ref %4 : $Teacher // id: %5
%6 = tuple () // user: %7
return %6 : $() // id: %7
} // end sil function '$s4main7TeacherCfD'
