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Compilation process

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Alex Denisov
Alex Denisov

This document summarizes the different stages of the compilation process from source code to executable program. It begins by showing sample C code for a simple function. It then walks through each step of compiling this code, including lexical analysis, parsing, semantic analysis, code generation, optimization, assembly, and linking. Key aspects like the abstract syntax tree and intermediate representations used at different stages are also outlined.

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Compilation process How a program is born CocoaHeads Berlin, 2015
> whoami Twitter: @1101_debian Freenode: AlexDenisov Github: @AlexDenisov
Outline ? Compilation process ? LLVM/Clang ? Q & A
Compilation Process
int main(){ return 0; } 0000000 cf fa ed fe 07 00 00 01 03 00 00 80 02 00 00 00 0000010 0f 00 00 00 38 03 00 00 85 00 20 00 00 00 00 00 0000020 19 00 00 00 48 00 00 00 5f 5f 50 41 47 45 5a 45 0000030 52 4f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000040 00 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 0000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000060 00 00 00 00 00 00 00 00 19 00 00 00 38 01 00 00 0000070 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000080 00 00 00 00 01 00 00 00 00 10 00 00 00 00 00 00 0000090 00 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00000a0 07 00 00 00 05 00 00 00 03 00 00 00 00 00 00 00 00000b0 5f 5f 74 65 78 74 00 00 00 00 00 00 00 00 00 00 00000c0 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 00000d0 98 0f 00 00 01 00 00 00 08 00 00 00 00 00 00 00 00000e0 98 0f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00000f0 00 04 00 80 00 00 00 00 00 00 00 00 00 00 00 00 0000100 5f 5f 75 6e 77 69 6e 64 5f 69 6e 66 6f 00 00 00 0000110 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000120 a0 0f 00 00 01 00 00 00 48 00 00 00 00 00 00 00 0000130 a0 0f 00 00 02 00 00 00 00 00 00 00 00 00 00 00 0000140 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000150 5f 5f 65 68 5f 66 72 61 6d 65 00 00 00 00 00 00 0000160 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000170 e8 0f 00 00 01 00 00 00 18 00 00 00 00 00 00 00 0000180 e8 0f 00 00 03 00 00 00 00 00 00 00 00 00 00 00 0000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00001a0 19 00 00 00 48 00 00 00 5f 5f 4c 49 4e 4b 45 44 00001b0 49 54 00 00 00 00 00 00 00 10 00 00 01 00 00 00 00001c0 00 10 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00001d0 d8 00 00 00 00 00 00 00 07 00 00 00 01 00 00 00 00001e0 00 00 00 00 00 00 00 00 22 00 00 80 30 00 00 00 00001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
int main(){ return 0; } 0000000 cf fa ed fe 07 00 00 01 03 00 00 80 02 00 00 00 0000010 0f 00 00 00 38 03 00 00 85 00 20 00 00 00 00 00 0000020 19 00 00 00 48 00 00 00 5f 5f 50 41 47 45 5a 45 0000030 52 4f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000040 00 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 0000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000060 00 00 00 00 00 00 00 00 19 00 00 00 38 01 00 00 0000070 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000080 00 00 00 00 01 00 00 00 00 10 00 00 00 00 00 00 0000090 00 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00000a0 07 00 00 00 05 00 00 00 03 00 00 00 00 00 00 00 00000b0 5f 5f 74 65 78 74 00 00 00 00 00 00 00 00 00 00 00000c0 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 00000d0 98 0f 00 00 01 00 00 00 08 00 00 00 00 00 00 00 00000e0 98 0f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00000f0 00 04 00 80 00 00 00 00 00 00 00 00 00 00 00 00 0000100 5f 5f 75 6e 77 69 6e 64 5f 69 6e 66 6f 00 00 00 0000110 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000120 a0 0f 00 00 01 00 00 00 48 00 00 00 00 00 00 00 0000130 a0 0f 00 00 02 00 00 00 00 00 00 00 00 00 00 00 0000140 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000150 5f 5f 65 68 5f 66 72 61 6d 65 00 00 00 00 00 00 0000160 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000170 e8 0f 00 00 01 00 00 00 18 00 00 00 00 00 00 00 0000180 e8 0f 00 00 03 00 00 00 00 00 00 00 00 00 00 00 0000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00001a0 19 00 00 00 48 00 00 00 5f 5f 4c 49 4e 4b 45 44 00001b0 49 54 00 00 00 00 00 00 00 10 00 00 01 00 00 00 00001c0 00 10 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00001d0 d8 00 00 00 00 00 00 00 07 00 00 00 01 00 00 00 00001e0 00 00 00 00 00 00 00 00 22 00 00 80 30 00 00 00 00001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Lexer Parser Semantic ? Analysis Code Generation Optimization Assembler Linker
const float factor = 42.f; int calc(float x) { return factor * x; }
Lexer
const float factor = 42.f; int calc(float x) { return factor * x; }
const float factor = 42.f; int calc(float x) { return factor * x; } (KW ¡®const¡¯)
const float factor = 42.f; int calc(float x) { return factor * x; } (KW ¡®const¡¯), (TYPE ¡®float¡¯)
const float factor = 42.f; int calc(float x) { return factor * x; } (KW ¡®const¡¯), (TYPE ¡®float¡¯), (ID ¡®factor'), (EQ ¡®=¡®), (NUM ¡¯42.f¡¯), (SEMI ¡®;¡¯)
const float factor = 42.f; int calc(float x) { return factor * x; } (KW ¡®const¡¯), (TYPE ¡®float¡¯), (ID ¡®factor'), (EQ ¡®=¡®), (NUM ¡¯42.f¡¯), (SEMI ¡®;¡¯), (TYPE ¡®int¡¯), (ID ¡®calc¡¯), (L_PAREN ¡®(¡®), (TYPE ¡®float¡¯), (ID 'x') (R_PAREN ¡®)¡¯), (L_BRACE ¡®{¡®), (KW ¡®return¡¯), (ID ¡®factor¡¯), (STAR ¡®*¡¯), (ID ¡®x¡¯), (SEMI ¡®;¡¯), (R_BRACE ¡®}¡¯), (EOF '')
Parser
(KW ¡®return¡¯) (ID ¡®factor¡¯) (STAR ¡®*¡¯) (ID ¡®x¡¯)
ReturnStmt return BinaryOperator? * ReferenceDecl? x ReferenceDecl? factor (KW ¡®return¡¯) (ID ¡®factor¡¯) (STAR ¡®*¡¯) (ID ¡®x¡¯)
AST VariableDecl? factor : float FloatLiteral? 42.f FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return BinaryOperator? * ReferenceDecl? x ReferenceDecl? factor
Semantic Analysis
AST VariableDecl? factor : float FloatLiteral? 42.f FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return BinaryOperator? * ReferenceDecl? x ReferenceDecl? factor
AST VariableDecl? factor : float FloatLiteral? 42.f : ??? FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : ??? BinaryOperator? * : ??? ReferenceDecl? x : ??? ReferenceDecl? factor : ???
AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : ??? BinaryOperator? * : ??? ReferenceDecl? x : float ReferenceDecl? factor : float
AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : int BinaryOperator? * : ??? ReferenceDecl? x : float ReferenceDecl? factor : float
AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : int BinaryOperator? * : float ReferenceDecl? x : float ReferenceDecl? factor : float
AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : int BinaryOperator? * : float ReferenceDecl? x : float ReferenceDecl? factor : float ???
AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : int BinaryOperator? * : float ReferenceDecl? x : float ReferenceDecl? factor : float ImplicitCast ftoi : int
Code Generation
@factor = constant float 42.0 define calc(float %x) { entry: movf %x, %r1 movf @factor, %r2 %r3 = fmul %r1, %r2 movf %r3, %r0 ret }
Optimization
@factor = constant float 42.0 define calc(float %x) { entry: movf %x, %r1 movf @factor, %r2 %r3 = fmul %r1, %r2 movf %r3, %r0 ret }
@factor = constant float 42.0 define calc(float %x) { entry: %r0 = fmul @factor, %x ret }
Assembler
_calc: push {r7, lr} mov r7, sp mov r1, #36175872 orr r1, r1, #1073741824 bl ___mulsf3 bl ___fixsfsi pop {r7, lr} mov pc, lr .section __TEXT,__const .globl _factor @ @factor .align 2 _factor: .long 1109917696 @ float 42
Linker
> clang -c calc.c -o calc.o const float factor = 42.f; int calc(float x) { return factor * x; }
extern int calc(float); int main() { printf(¡°%dn¡±, calc(2.f)); return 0; } > clang -c main.c -o main.o
> nm main.o U _calc 0000000000000000 T _main U _printf
> nm main.o U _calc 0000000000000000 T _main U _printf > ld -lc calc.o main.o -o main > nm main 0000000000001f30 T _calc 0000000000001fc8 S _factor 0000000000001f60 T _main U _printf
LLVM & Clang
Lexer Parser Semantic ? Analysis Code Generation Optimization Assembler Linker
Optimization Assembler Linker Optimization Assembler Linker Code Generation Semantic ? Analysis ParserLexer Code Generation Semantic ? Analysis ParserLexer
Optimization Assembler Linker Code Generation Semantic ? Analysis ParserLexer Code Generation Semantic ? Analysis ParserLexer
Lexer Parser Semantic ? Analysis Code Generation Clang Optimization AssemblerLLVM LinkerOS
libclangLex
const float factor = 42.f; int calc(float x) { return factor * x; } > clang -cc1 -dump-tokens calc.c
const 'const' [StartOfLine] Loc=<calc.c:1:1> float 'float' [LeadingSpace] Loc=<calc.c:1:7> identifier 'factor' [LeadingSpace] Loc=<calc.c:1:13> equal '=' [LeadingSpace] Loc=<calc.c:1:20> numeric_constant '42.f' [LeadingSpace] Loc=<calc.c:1:22> semi ';' Loc=<calc.c:1:26> int 'int' [StartOfLine] Loc=<calc.c:3:1> identifier 'calc' [LeadingSpace] Loc=<calc.c:3:5> l_paren '(' Loc=<calc.c:3:9> float 'float' Loc=<calc.c:3:10> identifier 'x' [LeadingSpace] Loc=<calc.c:3:16> r_paren ')' Loc=<calc.c:3:17> l_brace '{' [LeadingSpace] Loc=<calc.c:3:19> return 'return' [StartOfLine] [LeadingSpace] Loc=<calc.c:4:3> identifier 'factor' [LeadingSpace] Loc=<calc.c:4:10> star '*' [LeadingSpace] Loc=<calc.c:4:17> identifier 'x' [LeadingSpace] Loc=<calc.c:4:19> semi ';' Loc=<calc.c:4:20> r_brace '}' [StartOfLine] Loc=<calc.c:5:1> eof '' Loc=<calc.c:6:1>
libclangParse/ libclangSema
const float factor = 42.f; int calc(float x) { return factor * x; } > clang -cc1 -ast-dump calc.c
TranslationUnitDecl <<invalid sloc>> <invalid sloc> |-VarDecl <calc.c:1:1, col:22> col:13 used factor 'const ?oat' cinit | `-FloatingLiteral <col:22> '?oat' 4.200000e+01 `-FunctionDecl <line:3:1, line:5:1> line:3:5 calc 'int (?oat)' |-ParmVarDecl <col:10, col:16> col:16 used x '?oat' `-CompoundStmt <col:19, line:5:1> `-ReturnStmt <line:4:3, col:19> `-ImplicitCastExpr <col:10, col:19> 'int' <FloatingToIntegral> `-BinaryOperator <col:10, col:19> '?oat' '*' |-ImplicitCastExpr <col:10> '?oat' <LValueToRValue> | `-DeclRefExpr <col:10> 'const ?oat' lvalue Var 'factor' 'const ?oat' `-ImplicitCastExpr <col:19> '?oat' <LValueToRValue> `-DeclRefExpr <col:19> '?oat' lvalue ParmVar 'x' '?oat'
libclangCodeGen
const float factor = 42.f; int calc(float x) { return factor * x; } > clang -S -emit-llvm calc.c
@factor = constant float 4.200000e+01, align 4 define i32 @calc(float %x) #0 { entry: %x.addr = alloca float, align 4 store float %x, float* %x.addr, align 4 %0 = load float* %x.addr, align 4 %mul = fmul float 4.200000e+01, %0 %conv = fptosi float %mul to i32 ret i32 %conv }
libclangCodeGen + opt
const float factor = 42.f; int calc(float x) { return factor * x; } > clang -S -emit-llvm -O1 calc.c
@factor = constant float 4.200000e+01, align 4 define i32 @calc(float %x) #0 { entry: %mul = fmul float %x, 4.200000e+01 %conv = fptosi float %mul to i32 ret i32 %conv }
libLLVMAsmPrinter
const float factor = 42.f; int calc(float x) { return factor * x; } > clang -S -arch arm -O0 calc.c
_calc: push {r7, lr} mov r7, sp mov r1, #36175872 orr r1, r1, #1073741824 bl ___mulsf3 bl ___fixsfsi pop {r7, lr} mov pc, lr .section __TEXT,__const .globl _factor @ @factor .align 2 _factor: .long 1109917696 @ float 42
Summary
Summary ? Learn your tools
Summary ? Learn your tools ? Provide feedback, don¡¯t make complaints
Summary ? Learn your tools ? Provide feedback, don¡¯t make complaints ? Give back to community
https://speakerdeck.com/alexdenisov/compilation-process ºÝºÝߣs: Twitter: @1101_debian Questions?

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Compilation process

  • 1. Compilation process How a program is born CocoaHeads Berlin, 2015
  • 3. Outline ? Compilation process ? LLVM/Clang ? Q & A
  • 5. int main(){ return 0; } 0000000 cf fa ed fe 07 00 00 01 03 00 00 80 02 00 00 00 0000010 0f 00 00 00 38 03 00 00 85 00 20 00 00 00 00 00 0000020 19 00 00 00 48 00 00 00 5f 5f 50 41 47 45 5a 45 0000030 52 4f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000040 00 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 0000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000060 00 00 00 00 00 00 00 00 19 00 00 00 38 01 00 00 0000070 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000080 00 00 00 00 01 00 00 00 00 10 00 00 00 00 00 00 0000090 00 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00000a0 07 00 00 00 05 00 00 00 03 00 00 00 00 00 00 00 00000b0 5f 5f 74 65 78 74 00 00 00 00 00 00 00 00 00 00 00000c0 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 00000d0 98 0f 00 00 01 00 00 00 08 00 00 00 00 00 00 00 00000e0 98 0f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00000f0 00 04 00 80 00 00 00 00 00 00 00 00 00 00 00 00 0000100 5f 5f 75 6e 77 69 6e 64 5f 69 6e 66 6f 00 00 00 0000110 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000120 a0 0f 00 00 01 00 00 00 48 00 00 00 00 00 00 00 0000130 a0 0f 00 00 02 00 00 00 00 00 00 00 00 00 00 00 0000140 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000150 5f 5f 65 68 5f 66 72 61 6d 65 00 00 00 00 00 00 0000160 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000170 e8 0f 00 00 01 00 00 00 18 00 00 00 00 00 00 00 0000180 e8 0f 00 00 03 00 00 00 00 00 00 00 00 00 00 00 0000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00001a0 19 00 00 00 48 00 00 00 5f 5f 4c 49 4e 4b 45 44 00001b0 49 54 00 00 00 00 00 00 00 10 00 00 01 00 00 00 00001c0 00 10 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00001d0 d8 00 00 00 00 00 00 00 07 00 00 00 01 00 00 00 00001e0 00 00 00 00 00 00 00 00 22 00 00 80 30 00 00 00 00001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  • 6. int main(){ return 0; } 0000000 cf fa ed fe 07 00 00 01 03 00 00 80 02 00 00 00 0000010 0f 00 00 00 38 03 00 00 85 00 20 00 00 00 00 00 0000020 19 00 00 00 48 00 00 00 5f 5f 50 41 47 45 5a 45 0000030 52 4f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000040 00 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 0000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000060 00 00 00 00 00 00 00 00 19 00 00 00 38 01 00 00 0000070 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000080 00 00 00 00 01 00 00 00 00 10 00 00 00 00 00 00 0000090 00 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00000a0 07 00 00 00 05 00 00 00 03 00 00 00 00 00 00 00 00000b0 5f 5f 74 65 78 74 00 00 00 00 00 00 00 00 00 00 00000c0 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 00000d0 98 0f 00 00 01 00 00 00 08 00 00 00 00 00 00 00 00000e0 98 0f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00000f0 00 04 00 80 00 00 00 00 00 00 00 00 00 00 00 00 0000100 5f 5f 75 6e 77 69 6e 64 5f 69 6e 66 6f 00 00 00 0000110 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000120 a0 0f 00 00 01 00 00 00 48 00 00 00 00 00 00 00 0000130 a0 0f 00 00 02 00 00 00 00 00 00 00 00 00 00 00 0000140 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0000150 5f 5f 65 68 5f 66 72 61 6d 65 00 00 00 00 00 00 0000160 5f 5f 54 45 58 54 00 00 00 00 00 00 00 00 00 00 0000170 e8 0f 00 00 01 00 00 00 18 00 00 00 00 00 00 00 0000180 e8 0f 00 00 03 00 00 00 00 00 00 00 00 00 00 00 0000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00001a0 19 00 00 00 48 00 00 00 5f 5f 4c 49 4e 4b 45 44 00001b0 49 54 00 00 00 00 00 00 00 10 00 00 01 00 00 00 00001c0 00 10 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00001d0 d8 00 00 00 00 00 00 00 07 00 00 00 01 00 00 00 00001e0 00 00 00 00 00 00 00 00 22 00 00 80 30 00 00 00 00001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  • 8. const float factor = 42.f; int calc(float x) { return factor * x; }
  • 10. const float factor = 42.f; int calc(float x) { return factor * x; }
  • 11. const float factor = 42.f; int calc(float x) { return factor * x; } (KW ¡®const¡¯)
  • 12. const float factor = 42.f; int calc(float x) { return factor * x; } (KW ¡®const¡¯), (TYPE ¡®float¡¯)
  • 13. const float factor = 42.f; int calc(float x) { return factor * x; } (KW ¡®const¡¯), (TYPE ¡®float¡¯), (ID ¡®factor'), (EQ ¡®=¡®), (NUM ¡¯42.f¡¯), (SEMI ¡®;¡¯)
  • 14. const float factor = 42.f; int calc(float x) { return factor * x; } (KW ¡®const¡¯), (TYPE ¡®float¡¯), (ID ¡®factor'), (EQ ¡®=¡®), (NUM ¡¯42.f¡¯), (SEMI ¡®;¡¯), (TYPE ¡®int¡¯), (ID ¡®calc¡¯), (L_PAREN ¡®(¡®), (TYPE ¡®float¡¯), (ID 'x') (R_PAREN ¡®)¡¯), (L_BRACE ¡®{¡®), (KW ¡®return¡¯), (ID ¡®factor¡¯), (STAR ¡®*¡¯), (ID ¡®x¡¯), (SEMI ¡®;¡¯), (R_BRACE ¡®}¡¯), (EOF '')
  • 16. (KW ¡®return¡¯) (ID ¡®factor¡¯) (STAR ¡®*¡¯) (ID ¡®x¡¯)
  • 18. AST VariableDecl? factor : float FloatLiteral? 42.f FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return BinaryOperator? * ReferenceDecl? x ReferenceDecl? factor
  • 20. AST VariableDecl? factor : float FloatLiteral? 42.f FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return BinaryOperator? * ReferenceDecl? x ReferenceDecl? factor
  • 21. AST VariableDecl? factor : float FloatLiteral? 42.f : ??? FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : ??? BinaryOperator? * : ??? ReferenceDecl? x : ??? ReferenceDecl? factor : ???
  • 22. AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : ??? BinaryOperator? * : ??? ReferenceDecl? x : float ReferenceDecl? factor : float
  • 23. AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : int BinaryOperator? * : ??? ReferenceDecl? x : float ReferenceDecl? factor : float
  • 24. AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : int BinaryOperator? * : float ReferenceDecl? x : float ReferenceDecl? factor : float
  • 25. AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : int BinaryOperator? * : float ReferenceDecl? x : float ReferenceDecl? factor : float ???
  • 26. AST VariableDecl? factor : float FloatLiteral? 42.f : float FunctionDecl? calc : int ParameterDecl? x : float ReturnStmt return : int BinaryOperator? * : float ReferenceDecl? x : float ReferenceDecl? factor : float ImplicitCast ftoi : int
  • 28. @factor = constant float 42.0 define calc(float %x) { entry: movf %x, %r1 movf @factor, %r2 %r3 = fmul %r1, %r2 movf %r3, %r0 ret }
  • 30. @factor = constant float 42.0 define calc(float %x) { entry: movf %x, %r1 movf @factor, %r2 %r3 = fmul %r1, %r2 movf %r3, %r0 ret }
  • 31. @factor = constant float 42.0 define calc(float %x) { entry: %r0 = fmul @factor, %x ret }
  • 33. _calc: push {r7, lr} mov r7, sp mov r1, #36175872 orr r1, r1, #1073741824 bl ___mulsf3 bl ___fixsfsi pop {r7, lr} mov pc, lr .section __TEXT,__const .globl _factor @ @factor .align 2 _factor: .long 1109917696 @ float 42
  • 35. > clang -c calc.c -o calc.o const float factor = 42.f; int calc(float x) { return factor * x; }
  • 36. extern int calc(float); int main() { printf(¡°%dn¡±, calc(2.f)); return 0; } > clang -c main.c -o main.o
  • 37. > nm main.o U _calc 0000000000000000 T _main U _printf
  • 38. > nm main.o U _calc 0000000000000000 T _main U _printf > ld -lc calc.o main.o -o main > nm main 0000000000001f30 T _calc 0000000000001fc8 S _factor 0000000000001f60 T _main U _printf
  • 41. Optimization Assembler Linker Optimization Assembler Linker Code Generation Semantic ? Analysis ParserLexer Code Generation Semantic ? Analysis ParserLexer
  • 45. const float factor = 42.f; int calc(float x) { return factor * x; } > clang -cc1 -dump-tokens calc.c
  • 46. const 'const' [StartOfLine] Loc=<calc.c:1:1> float 'float' [LeadingSpace] Loc=<calc.c:1:7> identifier 'factor' [LeadingSpace] Loc=<calc.c:1:13> equal '=' [LeadingSpace] Loc=<calc.c:1:20> numeric_constant '42.f' [LeadingSpace] Loc=<calc.c:1:22> semi ';' Loc=<calc.c:1:26> int 'int' [StartOfLine] Loc=<calc.c:3:1> identifier 'calc' [LeadingSpace] Loc=<calc.c:3:5> l_paren '(' Loc=<calc.c:3:9> float 'float' Loc=<calc.c:3:10> identifier 'x' [LeadingSpace] Loc=<calc.c:3:16> r_paren ')' Loc=<calc.c:3:17> l_brace '{' [LeadingSpace] Loc=<calc.c:3:19> return 'return' [StartOfLine] [LeadingSpace] Loc=<calc.c:4:3> identifier 'factor' [LeadingSpace] Loc=<calc.c:4:10> star '*' [LeadingSpace] Loc=<calc.c:4:17> identifier 'x' [LeadingSpace] Loc=<calc.c:4:19> semi ';' Loc=<calc.c:4:20> r_brace '}' [StartOfLine] Loc=<calc.c:5:1> eof '' Loc=<calc.c:6:1>
  • 48. const float factor = 42.f; int calc(float x) { return factor * x; } > clang -cc1 -ast-dump calc.c
  • 49. TranslationUnitDecl <<invalid sloc>> <invalid sloc> |-VarDecl <calc.c:1:1, col:22> col:13 used factor 'const ?oat' cinit | `-FloatingLiteral <col:22> '?oat' 4.200000e+01 `-FunctionDecl <line:3:1, line:5:1> line:3:5 calc 'int (?oat)' |-ParmVarDecl <col:10, col:16> col:16 used x '?oat' `-CompoundStmt <col:19, line:5:1> `-ReturnStmt <line:4:3, col:19> `-ImplicitCastExpr <col:10, col:19> 'int' <FloatingToIntegral> `-BinaryOperator <col:10, col:19> '?oat' '*' |-ImplicitCastExpr <col:10> '?oat' <LValueToRValue> | `-DeclRefExpr <col:10> 'const ?oat' lvalue Var 'factor' 'const ?oat' `-ImplicitCastExpr <col:19> '?oat' <LValueToRValue> `-DeclRefExpr <col:19> '?oat' lvalue ParmVar 'x' '?oat'
  • 51. const float factor = 42.f; int calc(float x) { return factor * x; } > clang -S -emit-llvm calc.c
  • 52. @factor = constant float 4.200000e+01, align 4 define i32 @calc(float %x) #0 { entry: %x.addr = alloca float, align 4 store float %x, float* %x.addr, align 4 %0 = load float* %x.addr, align 4 %mul = fmul float 4.200000e+01, %0 %conv = fptosi float %mul to i32 ret i32 %conv }
  • 54. const float factor = 42.f; int calc(float x) { return factor * x; } > clang -S -emit-llvm -O1 calc.c
  • 55. @factor = constant float 4.200000e+01, align 4 define i32 @calc(float %x) #0 { entry: %mul = fmul float %x, 4.200000e+01 %conv = fptosi float %mul to i32 ret i32 %conv }
  • 57. const float factor = 42.f; int calc(float x) { return factor * x; } > clang -S -arch arm -O0 calc.c
  • 58. _calc: push {r7, lr} mov r7, sp mov r1, #36175872 orr r1, r1, #1073741824 bl ___mulsf3 bl ___fixsfsi pop {r7, lr} mov pc, lr .section __TEXT,__const .globl _factor @ @factor .align 2 _factor: .long 1109917696 @ float 42
  • 61. Summary ? Learn your tools ? Provide feedback, don¡¯t make complaints
  • 62. Summary ? Learn your tools ? Provide feedback, don¡¯t make complaints ? Give back to community