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Deoptimization: How YJIT Speeds Up Ruby by Slow...
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Takashi Kokubun
April 16, 2025
Programming
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Deoptimization: How YJIT Speeds Up Ruby by Slowing Down / RubyKaigi 2025
https://rubykaigi.org/2025
Takashi Kokubun
April 16, 2025
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Transcript
Deoptimization: How YJIT Speeds Up Ruby by Slowing Down @k0kubun
/ RubyKaigi 2025
@k0kubun
@k0kubun Z
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We’re hiring https://candidate.shopify.com/form/ruby-kaigi-2025
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YJIT
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https://railsatscale.com/2025-01-10-yjit-3-4-even-faster-and-more-memory-ef fi cient/
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Deoptimization
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Deoptimization What if you can “slow down” Ruby at any
time? You can speculatively optimize Ruby and invalidate it later
Playing with Deoptimization Build Ruby with: ./con fi gure --enable-yjit=dev
Run Ruby with: ruby --yjit-call-threshold=1 --yjit-dump-disasm
Playing with Deoptimization
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YJIT Deoptimization
Code Patching
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Rewrite
Rewrite Jump
Global Invalidation
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Ruby 3.4’s New YJIT Deoptimization
Invalidation on Escaped Locals
?
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Invalidation on Singleton Classes
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Singleton Class Invalidation
Lazy Frame Push
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Lazy Frame Push
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YJIT-only Ruby Methods
Array#each
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Primitive.attr! :c_trace
Conclusion Deoptimization enables speculative optimizations with lazy invalidation Ruby 3.4
YJIT optimizes method calls and local variables using deoptimization