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From V8 to Modern Compilers
This document summarizes a talk about modern compiler techniques using Google's V8 JavaScript engine as an example. It discusses how early JavaScript interpreters led to slow execution speeds due to CPU pipeline stalling and lack of optimizations. Just-in-time (JIT) compilation was introduced to compile code on the fly and apply more optimizations. V8 uses a unified graph-based intermediate representation (IR) that allows optimizations and instruction selection by reducing the graph. The document contrasts traditional compiler courses with skills needed for real-world compiler projects, like those used at V8, which involve extensive optimizations, instruction selection, and dealing with dynamic types.
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From V8 to Modern Compilers
- 1. 從V8 Javascript 引擎淺談現代編譯技術 FromV8to Modern Compilers Bekket McClane@SITCON2017
- 2. Who am I? BekketMcClane Computer Science @NTHU LinkedIn: bekketmcclane LLVM x OpenCL x JIT Compilers
- 3.
- 4. 從V8 Javascript 引擎淺談現代編譯技術 FromV8to Modern Compilers
- 5. Talking Compilers withStudents…
- 6. Talking Compilers withStudents…
- 7. It’s Not SoBoring! COMPILERS COMPILERS EVERYWHERE!
- 8.
- 9. PerformanceCompilers Good Compilers, BetterPerformance
- 10.
- 11. Syllabus • Execute Javascriptin Old Days
- 12. Syllabus • Execute Javascriptin Old Days • Compiler ✭Magic✭ inV8
- 13. Syllabus • Execute Javascriptin Old Days • Compiler ✭Magic✭ inV8 • FromV8 to Modern Compilers
- 14. Execute Javascript inOld Days
- 15. Javascript • Fast Prototyping •Dynamic • Well-Accepted Standard
- 16. Javascript • Fast Prototyping •Dynamic • Well-Accepted Standard
- 17.
- 18. Simple Interpreter switch(op){ case OpAdd:{…} case OpStore: {…} case … }
- 19.
- 20. Flaw: CPU PipelineStalling • CPU would “pre-fetch” instructions on branch EXE MEM WBID Instructions of branch AInstructions of branch B CPU Pipeline Stages
- 21. Flaw: CPU PipelineStalling switch(op){ case OpAdd: {…} case OpStore: {…} case … } • CPU would also try to “predict” next branch
- 22. Flaw: CPU PipelineStalling switch(op){ case OpAdd: {…} case OpStore: {…} case … } • CPU would also try to “predict” next branch Hard to Predict!
- 23. Flaw: CPU PipelineStalling EXE MEM WBID Instructions of branch A? Which Branch? CPU Pipeline Stages Stalling
- 24. Flaw: Lack ofAggressive Optimization $a = fmul $x, $y $b = fadd $a, $z $b = fmadd $x, $y, $z Example:
- 25.
- 26. What is JITCompilation? • 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 JITCompiler Native Code Execute Native Code Source Code
- 28. Compile Code On-The-Fly JITCompiler Native Code Execute Native Code Source Code
- 29. Classical Compilation Flow First,Let’s Go BackTo…
- 30. Classical Compilation Flow Source Code Front End IROptimizer Code Gen Native Code Back End (Intermediate Representation)
- 31. Classical Compilation Flow Source Code Front End IROptimizer Code Gen Native Code Back End (Intermediate Representation)
- 32. Classical Compilation Flow Source Code Front End IROptimizer 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 OfIR 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 GraphIR • 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 IfTrueIfFalse Branch Start Control is also Expressed By Node!
- 45. IR Graph inV8 IfTrueIfFalse Branch Start Two Types of Dependencies: Data and Control + y 2 z (z = y + 2)
- 46. IR Graph ExampleinV8 + y 2 z return Start function(){ z = y + 2; return z; } Control Dependency Data Dependency
- 47. Dependencies Only: Good forInstruction Scheduling
- 48. IR Nodes Lowering/ Reducing High Level Low Level
- 49. Instruction Selection? GraphReducing Target-Independent Machine Code
- 50. Optimization? Still GraphReducing !
- 51. Optimization? Still GraphReducing ! C = (true)? x : y
- 52.
- 53. Extensive Studying • HowV8Handles DynamicTypes? (Hint: Inline Cache)
- 54. Extensive Studying • HowV8Handles DynamicTypes? (Hint: Inline Cache) • Ignition,The New INTERPRETER of V8 • Garbage Collection inV8
- 55. FromV8 to ModernCompilers
- 56. What I’d Learnin Compiler Class
- 57. What I’d Learnin Compiler Class and…
- 58. What I’d Learnin Compiler Class and… Nothing More
- 59. What I’d Learn inReal-World Compiler Projects Front End Back End Optimization, Instruction Selection, Register Allocation… The Real Battle Field!
- 60. What I’d Learn inTraditionalCompiler Research
- 61. What I’d Learn inTraditionalCompiler Research • Optimization Algorithms
- 62. What I’d Learn inTraditionalCompiler Research • Optimization Algorithms • Optimization Algorithms
- 63. What I’d Learn inTraditionalCompiler Research • Optimization Algorithms • Optimization Algorithms • Register Allocation Problems
- 64. What I’d Learn inTraditionalCompiler Research • Optimization Algorithms • Optimization Algorithms • Register Allocation Problems • …Still Optimization Algorithms
- 65. What I’d Learn inModern Compiler Research • How to Boost Compilation Speed • How to Reduce Compilers’ Memory Footprint • How to Choose Proper Optimizations • Dynamic-Profiled Optimizations
- 66. Yes, This Bookis OUT-DATED
- 67.
- 68. Basic Modern Compiler Skills: JustRead the F**king Code!
- 69.
- 70.
- 71. Appendix • V8 SourceCode(Github Mirror): https://github.com/v8/v8 • TurboFan: src/compiler • Ignition: src/interpreter • Inline Cache: src/ic
- 72. Cites • Meurer, Benedikt.“Anoverview 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.