See YJIT: a basic block versioning JIT compiler for CRuby for a detailed introduction. With Lazy Basic Block Versioning (LBBV) it first compiles the beginning of a method, and incrementally compiles the rest when the type of arguments and variables are dynamically determined. While MJIT is a method-based JIT compiler and uses an external C compiler, YJIT uses Basic Block Versioning and includes a JIT compiler inside it. YJIT is an important contribution, and aims to improve the performance of Rails applications.

Recently Shopify contributed many Ruby improvements to speed up their Rails application. But even though the Optcarrot benchmark has shown impressive speedups, the JIT has not benefited real world business applications. Since Ruby 2.6 introduced MJIT in 2018, its performance greatly improved, and finally we achieved Rub圓x3 last year. Ruby 3.1 merges YJIT, a new in-process JIT compiler developed by Shopify. YJIT: New experimental in-process JIT compiler Ruby 3.1 keeps compatibility with Ruby 3.0 and also adds many features. We are pleased to announce the release of Ruby 3.1.0.

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