LLVM

摘要： LLVM: 模組化,可重用的編譯器以及工具鏈技術集合. 創始人: Chris Lattner LLVM不是Low Level Virtual Machine(低階虛擬機器)的縮寫,LLVM就是他的專案全名. 傳統編譯器: GCC Clang 傳統編譯器架構: ...

LLVM:

模組化,可重用的編譯器以及工具鏈技術集合.

創始人: Chris Lattner

LLVM不是Low Level Virtual Machine(低階虛擬機器)的縮寫,LLVM就是他的專案全名.

傳統編譯器:

GCC

Clang

傳統編譯器架構:

• Frontend: 前端

詞法分析,語法分析,語義分析,生成中間程式碼

• Opotimizer: 優化器

中間程式碼優化

• Backend: 後端

生成機器碼

LLVM架構

• 不同的前端後端使用統一的中間程式碼 LLVM Intermediate Representation(LLVM IR).
• 如果需要支援一種新的程式語言,只需要實現一個新的前端.
• 如果需要支援一種新的硬體裝置,只需要增加一個新的後端.
• 優化階段是一個通用階段,它針對的是統一的LLVM IR,無論是支援新的程式語言,還是支援新的硬體裝置,都不需要對優化階段做修改.
• 相比之下,GCC的前端和後端沒分的泰開,前端後端耦合在一起.所以GCC為了來支援一門新的語言或者新的硬體裝置,就變得很困難.
• LLVM現在被用作為實現各種靜態和執行時變易語言的通用基礎結構.(GCC家族,Java,.net,Python等)

Clang

• LLVM一個子專案
• 基於LVVM架構的C/C++/Objective-C編譯器前端

優點:

• 編譯速度快,在某些平臺上Clang的便以速度顯著地快過GCC
• 佔用記憶體小,Clang生成的AST所佔用的內訓師CGG的五分之一左右
• 模組化設計,基於庫的模組化設計,易於IDE整合以及其他用途的重用
• 診斷資訊可讀性強: 在編譯過程中,Clang建立並保留了大量詳細的元資料(metadata),有利於除錯和錯誤解讀.
• 設計清晰簡單,容易理解,易於擴充套件增強

Clang與LLVM

• 廣義LLVM

整個LLVM架構

• 狹義LLVM

LLVM後端(程式碼優化,目的碼生成等)

OC原始檔編譯過程

命令列檢視編譯過程

clang -ccc-print-phases main.m

➜TestSwift clang -ccc-print-phases main.swift
0: input, "main.swift", object
1: linker, {0}, image
2: bind-arch, "x86_64", {1}, image

➜TestOC clang -ccc-print-phases main.m
0: input, "main.m", objective-c
1: preprocessor, {0}, objective-c-cpp-output
2: compiler, {1}, ir
3: backend, {2}, assembler
4: assembler, {3}, object
5: linker, {4}, image
6: bind-arch, "x86_64", {5}, image

Swift比OC少了4個編譯階段吶,有木有...

檢視preprocessor(預處理)的結果

clang -E main.m

//原始檔
print("Hello World")
//預處理輸出
➜TestSwift clang -E main.swift
clang: warning: main.swift: 'linker' input unused [-Wunused-command-line-argument]

//原始檔
#define AGE 10

int main(int argc, const char * argv[]) {

int a = 10;
int b = 20;
int c = a + b + AGE;

return 0;
}
//預處理輸出
➜TestOC clang -E main.m
# 1 "main.m"
# 1 "<built-in>" 1
# 1 "<built-in>" 3
# 373 "<built-in>" 3
# 1 "<command line>" 1
# 1 "<built-in>" 2
# 1 "main.m" 2
# 11 "main.m"
int main(int argc, const char * argv[]) {

int a = 10;
int b = 20;
int c = a + b + 10;

return 0;
}

詞法分析

• 詞法分析,生成Token(類似英語中主語,謂語,賓語,賓補...)

clang -fmodules -E -Xclang -dump-tokens main.m

➜TestSwift clang -fmodules -E -Xclang -dump-tokens main.swift

clang: warning: main.swift: 'linker' input unused [-Wunused-command-line-argument]

clang: warning: argument unused during compilation: '-fmodules' [-Wunused-command-line-argument]

clang: warning: argument unused during compilation: '-Xclang -dump-tokens' [-Wunused-command-line-argument]

➜TestOC clang -fmodules -E -Xclang -dump-tokens main.m
int 'int' [StartOfLine]Loc=<main.m:11:1>
identifier 'main' [LeadingSpace]Loc=<main.m:11:5>
l_paren '('Loc=<main.m:11:9>
int 'int'Loc=<main.m:11:10>
identifier 'argc' [LeadingSpace]Loc=<main.m:11:14>
comma ','Loc=<main.m:11:18>
const 'const' [LeadingSpace]Loc=<main.m:11:20>
char 'char' [LeadingSpace]Loc=<main.m:11:26>
star '*' [LeadingSpace]Loc=<main.m:11:31>
identifier 'argv' [LeadingSpace]Loc=<main.m:11:33>
l_square '['Loc=<main.m:11:37>
r_square ']'Loc=<main.m:11:38>
r_paren ')'Loc=<main.m:11:39>
l_brace '{' [LeadingSpace]Loc=<main.m:11:41>
int 'int' [StartOfLine] [LeadingSpace]Loc=<main.m:13:5>
identifier 'a' [LeadingSpace]Loc=<main.m:13:9>
equal '=' [LeadingSpace]Loc=<main.m:13:11>
numeric_constant '10' [LeadingSpace]Loc=<main.m:13:13>
semi ';'Loc=<main.m:13:15>
int 'int' [StartOfLine] [LeadingSpace]Loc=<main.m:14:5>
identifier 'b' [LeadingSpace]Loc=<main.m:14:9>
equal '=' [LeadingSpace]Loc=<main.m:14:11>
numeric_constant '20' [LeadingSpace]Loc=<main.m:14:13>
semi ';'Loc=<main.m:14:15>
int 'int' [StartOfLine] [LeadingSpace]Loc=<main.m:15:5>
identifier 'c' [LeadingSpace]Loc=<main.m:15:9>
equal '=' [LeadingSpace]Loc=<main.m:15:11>
identifier 'a' [LeadingSpace]Loc=<main.m:15:13>
plus '+' [LeadingSpace]Loc=<main.m:15:15>
identifier 'b' [LeadingSpace]Loc=<main.m:15:17>
plus '+' [LeadingSpace]Loc=<main.m:15:19>
numeric_constant '10' [LeadingSpace]Loc=<main.m:15:21 <Spelling=main.m:9:13>>
semi ';'Loc=<main.m:15:24>
return 'return' [StartOfLine] [LeadingSpace]Loc=<main.m:17:5>
numeric_constant '0' [LeadingSpace]Loc=<main.m:17:12>
semi ';'Loc=<main.m:17:13>
r_brace '}' [StartOfLine]Loc=<main.m:18:1>
eof ''Loc=<main.m:18:2>

語法分析

• 語法分析,生成語法樹(AST, Abstract Syntax Tree)

clang -fmodules -fsyntax-only -Xclang -ast-dump main.m

➜Test clang -fmodules -fsyntax-only -Xclang -ast-dump main.swift
clang: warning: main.swift: 'linker' input unused [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-fmodules' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-Xclang -ast-dump' [-Wunused-command-line-argument]

➜TestOC clang -fmodules -fsyntax-only -Xclang -ast-dump main.m
TranslationUnitDecl 0x7ff3730298e8 <<invalid sloc>> <invalid sloc>
|-TypedefDecl 0x7ff373029e60 <<invalid sloc>> <invalid sloc> implicit __int128_t '__int128'
| `-BuiltinType 0x7ff373029b80 '__int128'
|-TypedefDecl 0x7ff373029ed0 <<invalid sloc>> <invalid sloc> implicit __uint128_t 'unsigned __int128'
| `-BuiltinType 0x7ff373029ba0 'unsigned __int128'
|-TypedefDecl 0x7ff373029f70 <<invalid sloc>> <invalid sloc> implicit SEL 'SEL *'
| `-PointerType 0x7ff373029f30 'SEL *'
|`-BuiltinType 0x7ff373029dc0 'SEL'
|-TypedefDecl 0x7ff37302a058 <<invalid sloc>> <invalid sloc> implicit id 'id'
| `-ObjCObjectPointerType 0x7ff37302a000 'id'
|`-ObjCObjectType 0x7ff373029fd0 'id'
|-TypedefDecl 0x7ff37302a138 <<invalid sloc>> <invalid sloc> implicit Class 'Class'
| `-ObjCObjectPointerType 0x7ff37302a0e0 'Class'
|`-ObjCObjectType 0x7ff37302a0b0 'Class'
|-ObjCInterfaceDecl 0x7ff37302a190 <<invalid sloc>> <invalid sloc> implicit Protocol
|-TypedefDecl 0x7ff37302a4f8 <<invalid sloc>> <invalid sloc> implicit __NSConstantString 'struct __NSConstantString_tag'
| `-RecordType 0x7ff37302a300 'struct __NSConstantString_tag'
|`-Record 0x7ff37302a260 '__NSConstantString_tag'
|-TypedefDecl 0x7ff37302a590 <<invalid sloc>> <invalid sloc> implicit __builtin_ms_va_list 'char *'
| `-PointerType 0x7ff37302a550 'char *'
|`-BuiltinType 0x7ff373029980 'char'
|-TypedefDecl 0x7ff373062488 <<invalid sloc>> <invalid sloc> implicit __builtin_va_list 'struct __va_list_tag [1]'
| `-ConstantArrayType 0x7ff373062430 'struct __va_list_tag [1]' 1
|`-RecordType 0x7ff3730622a0 'struct __va_list_tag'
|`-Record 0x7ff373062200 '__va_list_tag'
`-FunctionDecl 0x7ff373062758 <main.m:11:1, line:18:1> line:11:5 main 'int (int, const char **)'
|-ParmVarDecl 0x7ff3730624f8 <col:10, col:14> col:14 argc 'int'
|-ParmVarDecl 0x7ff373062610 <col:20, col:38> col:33 argv 'const char **':'const char **'
`-CompoundStmt 0x7ff373062bd8 <col:41, line:18:1>
|-DeclStmt 0x7ff373062928 <line:13:5, col:15>
| `-VarDecl 0x7ff3730628a8 <col:5, col:13> col:9 used a 'int' cinit
|`-IntegerLiteral 0x7ff373062908 <col:13> 'int' 10
|-DeclStmt 0x7ff3730629d8 <line:14:5, col:15>
| `-VarDecl 0x7ff373062958 <col:5, col:13> col:9 used b 'int' cinit
|`-IntegerLiteral 0x7ff3730629b8 <col:13> 'int' 20
|-DeclStmt 0x7ff373062b88 <line:15:5, col:24>
| `-VarDecl 0x7ff373062a08 <col:5, line:9:13> line:15:9 c 'int' cinit
|`-BinaryOperator 0x7ff373062b60 <col:13, line:9:13> 'int' '+'
||-BinaryOperator 0x7ff373062b18 <line:15:13, col:17> 'int' '+'
|| |-ImplicitCastExpr 0x7ff373062ae8 <col:13> 'int' <LValueToRValue>
|| | `-DeclRefExpr 0x7ff373062a68 <col:13> 'int' lvalue Var 0x7ff3730628a8 'a' 'int'
|| `-ImplicitCastExpr 0x7ff373062b00 <col:17> 'int' <LValueToRValue>
||`-DeclRefExpr 0x7ff373062aa8 <col:17> 'int' lvalue Var 0x7ff373062958 'b' 'int'
|`-IntegerLiteral 0x7ff373062b40 <line:9:13> 'int' 10
`-ReturnStmt 0x7ff373062bc0 <line:17:5, col:12>
`-IntegerLiteral 0x7ff373062ba0 <col:12> 'int' 0

LLVM IR

LLVM IR有三種表示形式(本質等價,好比水的氣態,液態,固態)

1.text: 便於閱讀的文字格式,類似於組合語言,副檔名 .ll

> clang -S -emit-llvm main.m

; ModuleID = 'main.m'
source_filename = "main.m"
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.14.0"

; Function Attrs: noinline nounwind optnone ssp uwtable
define i32 @main(i32, i8**) #0 {
%3 = alloca i32, align 4
%4 = alloca i32, align 4
%5 = alloca i8**, align 8
%6 = alloca i32, align 4
%7 = alloca i32, align 4
%8 = alloca i32, align 4
store i32 0, i32* %3, align 4
store i32 %0, i32* %4, align 4
store i8** %1, i8*** %5, align 8
store i32 10, i32* %6, align 4
store i32 20, i32* %7, align 4
%9 = load i32, i32* %6, align 4
%10 = load i32, i32* %7, align 4
%11 = add nsw i32 %9, %10
%12 = add nsw i32 %11, 10
store i32 %12, i32* %8, align 4
ret i32 0
}

attributes #0 = { noinline nounwind optnone ssp uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+fxsr,+mmx,+sahf,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.module.flags = !{!0, !1, !2, !3, !4, !5, !6}
!llvm.ident = !{!7}

!0 = !{i32 1, !"Objective-C Version", i32 2}
!1 = !{i32 1, !"Objective-C Image Info Version", i32 0}
!2 = !{i32 1, !"Objective-C Image Info Section", !"__DATA,__objc_imageinfo,regular,no_dead_strip"}
!3 = !{i32 4, !"Objective-C Garbage Collection", i32 0}
!4 = !{i32 1, !"Objective-C Class Properties", i32 64}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{i32 7, !"PIC Level", i32 2}
!7 = !{!"Apple LLVM version 10.0.0 (clang-1000.11.45.2)"}
//什麼鬼東西

2.memory: 記憶體格式

3.bitcode: 二進位制格式,副檔名 .bc

clang -c -emit-llvm main.m

IR基本語法

• 註釋以分號 ; 開頭
• 全域性識別符號以 @ 開頭,區域性識別符號以 % 開頭
• alloca 在當前函式棧幀中分配記憶體
• i32 ,32bit,4個位元組的意思
• align ,記憶體對齊
• store ,寫入資料
• load ,讀取資料