Deoptimization: How YJIT Speeds Up Ruby by Slowing Down / RubyKaigi 2025

https://rubykaigi.org/2025

1. Deoptimization: How YJIT Speeds Up Ruby by Slowing Down @k0kubun / RubyKaigi 2025
2. @k0kubun
3. @k0kubun Z
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7. YJIT
9. https://railsatscale.com/2025-01-10-yjit-3-4-even-faster-and-more-memory-ef fi cient/
12. Deoptimization
14. Deoptimization What if you can “slow down” Ruby at any time? You can speculatively optimize Ruby and invalidate it later
15. Playing with Deoptimization Build Ruby with: ./con fi gure --enable-yjit=dev Run Ruby with: ruby --yjit-call-threshold=1 --yjit-dump-disasm
16. Playing with Deoptimization
18. YJIT Deoptimization
19. Code Patching
24. Rewrite
25. Rewrite Jump
26. Global Invalidation
30. Ruby 3.4’s New YJIT Deoptimization
31. Invalidation on Escaped Locals
32. ?
35. Invalidation on Singleton Classes
40. Singleton Class Invalidation
41. Lazy Frame Push
45. Lazy Frame Push
50. YJIT-only Ruby Methods
51. Array#each
59. Primitive.attr! :c_trace
60. Conclusion Deoptimization enables speculative optimizations with lazy invalidation Ruby 3.4 YJIT optimizes method calls and local variables using deoptimization