From V8 Javascript Engine to Modern Compilers SITCON2017

1. 從V8 Javascript 引擎淺談現代編譯技術
FromV8 to Modern Compilers
Bekket McClane@SITCON2017

2. Who am I?
Bekket McClane
Computer Science @NTHU
LinkedIn: bekketmcclane
LLVM x OpenCL x JIT Compilers

3. Preface

4. 從V8 Javascript 引擎淺談現代編譯技術
FromV8 to Modern Compilers

5. Talking Compilers with Students…

6. Talking Compilers with Students…

7. It’s Not So Boring!
COMPILERS
COMPILERS EVERYWHERE!

8. Compilers are EVERYWHERE !

9. PerformanceCompilers
Good Compilers, Better Performance

10. Syllabus

11. Syllabus
• Execute Javascript in Old Days

12. Syllabus
• Execute Javascript in Old Days
• Compiler ✭Magic✭ inV8

13. Syllabus
• Execute Javascript in Old Days
• Compiler ✭Magic✭ inV8
• FromV8 to Modern Compilers

14. Execute Javascript in Old Days

15. Javascript
• Fast Prototyping
• Dynamic
• Well-Accepted Standard

16. Javascript
• Fast Prototyping
• Dynamic
• Well-Accepted Standard

17. INTERPRETER!

18. Simple Interpreter
switch(op){
case OpAdd: {…}
case OpStore: {…}
case …
}

19. Slow Execution Speed…

20. Flaw: CPU Pipeline Stalling
• CPU would “pre-fetch” instructions on branch
EXE MEM WBID
Instructions of branch AInstructions of branch B
CPU Pipeline Stages

21. Flaw: CPU Pipeline Stalling
switch(op){
case OpAdd: {…}
case OpStore: {…}
case …
}
• CPU would also try to “predict” next branch

22. Flaw: CPU Pipeline Stalling
switch(op){
case OpAdd: {…}
case OpStore: {…}
case …
}
• CPU would also try to “predict” next branch
Hard to Predict!

23. Flaw: CPU Pipeline Stalling
EXE MEM WBID
Instructions of branch A? Which Branch?
CPU Pipeline Stages
Stalling

24. Flaw: Lack of Aggressive Optimization
$a = fmul $x, $y
$b = fadd $a, $z
$b = fmadd $x, $y, $z
Example:

25. JIT(Just-in-Time) Compilation
Introducing…

26. What is JIT Compilation?
• Compile Code On-The-Fly
• Compile a small region of code once a time
and execute it.
• Can Apply More Optimizations
• Compilations are All Happening in Runtime
• Need FAST compilation speed

27. Compile Code On-The-Fly
JIT Compiler
Native
Code
Execute
Native Code
Source
Code

28. Compile Code On-The-Fly
JIT Compiler
Native
Code
Execute
Native Code
Source
Code

29. Classical Compilation Flow
First, Let’s Go BackTo…

30. Classical Compilation Flow
Source
Code
Front
End
IR Optimizer
Code
Gen
Native
Code
Back End
(Intermediate Representation)

31. Classical Compilation Flow
Source
Code
Front
End
IR Optimizer
Code
Gen
Native
Code
Back End
(Intermediate Representation)

32. Classical Compilation Flow
Source
Code
Front
End
IR Optimizer
Code
Gen
Native
Code
Back End
(Intermediate Representation)

33. Instruction Selection
foo %v1, %v2
bar %v3, %v1
IR

34. Instruction Selection
foo %v1, %v2
bar %v3, %v1
IR
MOV $eax, $ebx
ADD $ecx, $eax
x86 Assembly

35. Instruction Selection
foo %v1, %v2
bar %v3, %v1
IR
mov $r1, $r3
add $r4, $r4, $r1
ARM Assembly
MOV $eax, $ebx
ADD $ecx, $eax
x86 Assembly

36. Instruction Selection
bar %v1, %v2
foo %v3, %v1
yooo %v3

37. Instruction Selection
bar %v1, %v2
foo %v3, %v1
yooo %v3
mov $r1, $r3
add $r4, $r4

38. Instruction Selection
bar %v1, %v2
foo %v3, %v1
yooo %v3
shr $r1, $r3
ld $r4, $r1
mov $r1, $r3
add $r4, $r4

39. Instruction Selection
bar %v1, %v2
foo %v3, %v1
yooo %v3
shr $r1, $r3
ld $r4, $r1
mov $r1, $r3
add $r4, $r4
?Which One?

40. (Brief) Categories Of IR
Linear DAG Graph

41. Multi-Levels IR (Ex: LLVM)
Linear DAG (Another) Linear
Target-Independent
Optimizations • Instruction Selection
• Instruction Scheduling
Target-Specific
Optimizations

42. Control Flow Graph
x < 4
(Loop Body)
x++
TrueFalse
(Next)

43. V8: Unified Graph IR
• Use the same graph structure through
the entire compilation process
• Nodes represent operation (Data and
Control). Edges represent their
dependencies
• Without implicit ordering, it has more
freedom than CFG.

44. IR Graph inV8
IfTrue IfFalse
Branch
Start
Control is also Expressed By Node!

45. IR Graph inV8
IfTrue IfFalse
Branch
Start
Two Types of Dependencies: Data and Control
+
y 2
z
(z = y + 2)

46. IR Graph Example inV8
+
y 2
z
return
Start
function(){
z = y + 2;
return z;
}
Control Dependency
Data Dependency

47. Dependencies Only:
Good for Instruction Scheduling

48. IR Nodes Lowering / Reducing
High Level
Low Level

49. Instruction Selection? Graph Reducing
Target-Independent
Machine Code

50. Optimization? Still Graph Reducing !

51. Optimization? Still Graph Reducing !
C = (true)? x : y

52. Extensive Studying

53. Extensive Studying
• HowV8 Handles DynamicTypes?
(Hint: Inline Cache)

54. Extensive Studying
• HowV8 Handles DynamicTypes?
(Hint: Inline Cache)
• Ignition,The New INTERPRETER of V8
• Garbage Collection inV8

55. FromV8 to Modern Compilers

56. What I’d Learn in Compiler Class

57. What I’d Learn in Compiler Class
and…

58. What I’d Learn in Compiler Class
and…
Nothing More

59. What I’d Learn
in Real-World Compiler Projects
Front End
Back End
Optimization,
Instruction Selection,
Register Allocation…
The Real Battle Field!

60. What I’d Learn
inTraditional Compiler Research

61. What I’d Learn
inTraditional Compiler Research
• Optimization Algorithms

62. What I’d Learn
inTraditional Compiler Research
• Optimization Algorithms
• Optimization Algorithms

63. What I’d Learn
inTraditional Compiler Research
• Optimization Algorithms
• Optimization Algorithms
• Register Allocation Problems

64. What I’d Learn
inTraditional Compiler Research
• Optimization Algorithms
• Optimization Algorithms
• Register Allocation Problems
• …Still Optimization Algorithms

65. What I’d Learn
in Modern Compiler Research
• How to Boost Compilation Speed
• How to Reduce Compilers’ Memory Footprint
• How to Choose Proper Optimizations
• Dynamic-Profiled Optimizations

66. Yes, This Book is OUT-DATED

67. Basic

68. Basic
Modern Compiler Skills:
Just Read the F**king Code!

69. COMPILERS
COMPILERS EVERYWHERE!

70. Embrace Compilers,
Embrace Performance
PerformanceCompilers

71. Appendix
• V8 Source Code(Github Mirror):
https://github.com/v8/v8
• TurboFan: src/compiler
• Ignition: src/interpreter
• Inline Cache: src/ic

72. Cites
• Meurer, Benedikt.“An overview of theTurboFan compiler”.
28 October 2016. Google Presentation file
• Titzer, Ben.“TurboFan JIT Design”. 6 May 2016. Google
Presentation file
• Sevcik, Jaroslav.“TurboFan IR”. 11 November 2016. Google
Presentation file

73. ThankYou All !
Q & A