前面一個章節(jié)已經(jīng)簡單介紹了LLVM。該章節(jié)主要介紹LLVM的編譯過程。
1. OC源文件
// Command Line Tool
#include <stdio.h>
#define AGE 30
int main(int argc, const char * argv[]) {
int a = 10;
int b = 20;
int c = a + b + AGE;
return 0;
}
2. 編譯過程
-
命令行查看編譯過程：
clang -ccc-print-phases main.m
0: input, "main.m", objective-c
//找到原代碼main.m
1: preprocessor, {0}, objective-c-cpp-output//預處理器 導入include import 及換掉宏定義
2: compiler, {1}, ir//編譯器 中間代碼生成ir
3: backend, {2}, assembler// 后端，{2}，匯編程序
4: assembler, {3}, object// 匯編程序 生成目標代碼
5: linker, {4}, image// 鏈接器 --- 動態(tài)庫、靜態(tài)庫
6: bind-arch, "x86_64", {5}, image//生成適合某個架構(gòu)的代碼
-
查看preprocessor（預處理）的結(jié)果：
clang -E main.m
...
...
...
extern int __vsnprintf_chk (char * restrict, size_t, int, size_t,
const char * restrict, va_list);
412 "/usr/include/stdio.h" 2 3 4
10 "main.m" 2
上面的一大段為：導入include <stdio.h>里的內(nèi)容
int main(int argc, const char * argv[]) {
int a = 10;
int b = 20;
int c = a + b + 30; //這里宏定義的AGE已經(jīng)被替換掉了
return 0;
}
-
詞法分析，生成Token：
clang -fmodules -E -Xclang -dump-tokens main.m
annot_module_include '#include <stdio.h>
.#define AGE 30
int main(int argc, const char * argv[]) {
int a = 10;
int b = 20;
int c = a + b + A' Loc=<main.m:9:1>
int'int'[StartOfLine] Loc=<main.m:11:1>//m:11:14 第11行第14個字符
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:12:5>
identifier'a'[LeadingSpace] Loc=<main.m:12:9>
equal'='[LeadingSpace] Loc=<main.m:12:11>
numeric_constant'10'[LeadingSpace] Loc=<main.m:12:13>
semi';'Loc=<main.m:12:15>
int'int'[StartOfLine] [LeadingSpace] Loc=<main.m:13:5>
identifier'b'[LeadingSpace] Loc=<main.m:13:9>
equal'='[LeadingSpace] Loc=<main.m:13:11>
numeric_constant'20'[LeadingSpace] Loc=<main.m:13:13>
semi';'Loc=<main.m:13:15>
int'int'[StartOfLine] [LeadingSpace] Loc=<main.m:14:5>
identifier'c'[LeadingSpace] Loc=<main.m:14:9>
equal'='[LeadingSpace] Loc=<main.m:14:11>
identifier'a'[LeadingSpace] Loc=<main.m:14:13>
plus'+'[LeadingSpace] Loc=<main.m:14:15>
identifier'b'[LeadingSpace] Loc=<main.m:14:17>
plus'+' [LeadingSpace] Loc=<main.m:14:19>
numeric_constant'30'[LeadingSpace] Loc=<main.m:14:21 <Spelling=main.m:10:13>>
semi';'Loc=<main.m:14:24>
return'return'[StartOfLine] [LeadingSpace] Loc=<main.m:16:5>
numeric_constant'0'[LeadingSpace] Loc=<main.m:16:12>
semi';'Loc=<main.m:16:13>
r_brace'}'[StartOfLine] Loc=<main.m:17:1>
eof '' Loc=<main.m:17:2>
- 詞法分析，生成語法樹（AST，Abstract Syntax Tree）：
- 主要看FunctionDecl之后。main函數(shù)語法樹
3. LLVM IR（中間代碼）
LLVM IR 有三種表現(xiàn)形式（但本質(zhì)是等價的，就好比水有氣態(tài)、液態(tài)、固態(tài)三種形式）
- text：便于閱讀的文本格式，類似于匯編語言，拓展名
.ll,$clang -S -emit-llvm main.m - memory：內(nèi)存格式
- bitcode：二進制格式，拓展名
.bc,$clang -c -emit-llvm main.m
//$clang -S -emit-llvm main.m
; 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, 30
store i32 %12, i32* %8, align 4
ret i32 0
}
IR基本語法
- 注釋以分號；開頭
- 全局標識以@開頭，局部標識以%開頭
-
alloca在當前函數(shù)棧幀中分配內(nèi)存 -
i3232bit 4個字節(jié)的意思 -
align內(nèi)存對齊 -
store寫入數(shù)據(jù) -
load讀取數(shù)據(jù)
