ZJIT: The Ruby 4 JIT Compiler / Ruby Release 30th Anniversary Party

https://rubyassociation.doorkeeper.jp/events/190436

Transcript

1. Ruby Release 30th Anniversary Party 2025 ZJIT: The Ruby 4 JIT Compiler Takashi Kokubun / @k0kubun
2. self • Takashi Kokubun (@k0kubun) • Shopify: Ruby JIT team • Ruby committer: MJIT, RJIT, YJIT, ZJIT
3. YJIT
4. YJIT • Ruby 3.1+: ruby --yjit • Rust 1.58.0+ • Production-ready JIT compiler • Enabled by default on Rails 7.2+
5. https://speed.ruby-lang.org/
6. https://railsatscale.com/2025-01-10-yjit-3-4-even-faster-and-more-memory-e ff i cient/
7. ZJIT
8. ZJIT • Ruby 4.0+: ruby --zjit • Rust 1.85.0+ (2024 Edition) • Experimental JIT compiler • To be productionized at Ruby 4.1
13. Why ZJIT? • Unblock cross-instruction optimizations • Less incremental, larger comiplation units • No memory overhead for adding optimizations
14. How YJIT works
15. How YJIT works putobject 1 getconst TWO send + leave Bytecode
16. How YJIT works putobject 1 getconst TWO send + leave Bytecode YJIT block1 Mov Reg(0), 1
17. How YJIT works putobject 1 getconst TWO send + leave Bytecode YJIT block1 Mov Reg(0), 1 Context Reg(0): Integer YJIT block2 Mov Reg(1), 2 PatchPoint Constant TWO
18. How YJIT works putobject 1 getconst TWO send + leave Bytecode YJIT block1 Mov Reg(0), 1 Context Reg(0): Integer YJIT block2 YJIT block3 Mov Reg(1), 2 PatchPoint Constant TWO Context Reg(0): Integer Reg(1): Integer PatchPoint Integer#+ Add Reg(0), Reg(1) Ret Reg(0)
19. How ZJIT works putobject 1 getconst TWO send + leave Bytecode
20. How ZJIT works putobject 1 getconst TWO zjit_send + leave Bytecode
21. How ZJIT works putobject 1 getconst TWO zjit_send + leave Bytecode ZJIT HIR v1 = 1 PatchPoint TWO v2 = 2 PatchPoint Integer#+ v3 = 3 Return v3
22. How ZJIT works putobject 1 getconst TWO zjit_send + leave Bytecode ZJIT HIR v1 = 1 PatchPoint TWO v2 = 2 PatchPoint Integer#+ v3 = 3 Return v3 ZJIT LIR Ret 3 PatchPoint Const TWO PatchPoint Integer#+
23. ZJIT IR
24. ZJIT IR • ZJIT IR (Intermediate Representation): • HIR: High-level IR, new in ZJIT • LIR: Ligh-level IR, same as YJIT
25. HIR
26. HIR Optimization Passes
27. LIR
28. LIR Lowering Passes
29. How ZJIT compiles Ruby code
30. How ZJIT compiles Ruby code one: putobject 1 leave two: putobject 2 leave three: putself send :one putself send :two send :+ leave Parse & Compile
31. How ZJIT compiles Ruby code one: putobject 1 leave two: putobject 2 leave three: putself send :one putself send :two send :+ leave one: putobject 1 leave two: putobject 2 leave three: putself zjit_send :one putself zjit_send :two zjit_send :+ leave Parse & Compile Pro fi le
32. How ZJIT compiles Ruby code Initial HIR: fn three@/Users/k0kubun/tmp/a.rb:11: bb0(): EntryPoint interpreter v1:BasicObject = LoadSelf Jump bb2(v1) bb1(v4:BasicObject): EntryPoint JIT(0) Jump bb2(v4) bb2(v6:BasicObject): v11:BasicObject = SendWithoutBlock v6, :one v14:BasicObject = SendWithoutBlock v6, :two v17:BasicObject = SendWithoutBlock v11, :+, v14 CheckInterrupts Return v17 one: putobject 1 leave two: putobject 2 leave three: putself send :one putself send :two send :+ leave Compile
33. How ZJIT compiles Ruby code Optimized HIR: fn three@/Users/k0kubun/tmp/a.rb:11: bb0(): … bb2(v6:BasicObject): PatchPoint MethodRede fi ned(one) PatchPoint NoSingletonClass(Object) v24:HeapObject[Object] = GuardType v6, HeapObject[Object] v31:Fixnum[1] = Const Value(1) PatchPoint MethodRede fi ned(two) PatchPoint NoSingletonClass(Object) v28:HeapObject[Object] = GuardType v6, HeapObject[Object] v33:Fixnum[2] = Const Value(2) PatchPoint MethodRede fi ned(Integer, +) v38:Fixnum[3] = Const Value(3) CheckInterrupts Return v38 one: putobject 1 leave two: putobject 2 leave three: putself send :one putself send :two send :+ leave Inline
34. How ZJIT compiles Ruby code Optimized HIR: fn three@/Users/k0kubun/tmp/a.rb:11: bb0(): … bb2(v6:BasicObject): PatchPoint MethodRede fi ned(one) PatchPoint NoSingletonClass(Object) v24:HeapObject[Object] = GuardType v6, HeapObject[Object] v31:Fixnum[1] = Const Value(1) PatchPoint MethodRede fi ned(two) PatchPoint NoSingletonClass(Object) v28:HeapObject[Object] = GuardType v6, HeapObject[Object] v33:Fixnum[2] = Const Value(2) PatchPoint MethodRede fi ned(Integer, +) v38:Fixnum[3] = Const Value(3) CheckInterrupts Return v38 one: putobject 1 leave two: putobject 2 leave three: putself send :one putself send :two send :+ leave
35. Hacking on ZJIT HIR
36. How to dump ZJIT IR • HIR: ruby --zjit-dump-hir • LIR: ruby --zjit-dump-lir
38. tryzjit. fl y.dev
39. tryzjit. fl y.dev
40. tryzjit. fl y.dev
41. tryzjit. fl y.dev
42. tryzjit. fl y.dev
46. Future of Ruby Performance
47. Future of Ruby Performance • We want less C extensions • In particular, less C → Ruby callbacks
48. C functions dominate execution time Only 10% of execution time is spent in JIT code https://gist.github.com/k0kubun/5e0b3bb894e9fed9b01e25fd25e8bea5
49. C functions dominate execution time Some interpreter implementations are used for reasons https://gist.github.com/k0kubun/5e0b3bb894e9fed9b01e25fd25e8bea5 Complicated argument setup, C → Ruby calls, megamorphic callsite Instance variables: megamorphic callsite
50. C functions dominate execution time 15% is spent on DB queries https://gist.github.com/k0kubun/5e0b3bb894e9fed9b01e25fd25e8bea5
51. C functions dominate execution time 15% is spent on allocation and garbage collection https://gist.github.com/k0kubun/5e0b3bb894e9fed9b01e25fd25e8bea5
52. C functions dominate execution time Many methods are implemented in C https://gist.github.com/k0kubun/5e0b3bb894e9fed9b01e25fd25e8bea5
53. C functions dominate execution time • Methods written in C • C → Ruby calls • Megamorphic callsites Reasons why that happens
54. https://github.com/ruby/ruby/pull/3281
55. Conclusion • ZJIR unblocks cross-instructions optimizations • Enjoy hacking on ZJIT HIR • Stay tuned for Ruby 4.1 ZJIT