Why does V8 use a two-tier compilation strategy (Ignition + TurboFan)?
Ignition provides fast startup (bytecode is quick to generate). TurboFan provides high performance (optimized machine code for hot code). This balances startup speed and peak performance. Deoptimization provides a graceful fallback.
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More FAQs in V8's Ignition and TurboFan Explained
V8's interpreter. It compiles the AST into bytecode and executes it directly. Fast to generate (quick startup) but slower to execute than machine code. It collects type feedback for TurboFan.
V8's optimizing compiler. It takes hot (frequently executed) bytecode and compiles it to optimized machine code using type feedback from Ignition. Much faster execution. Deoptimizes if assumptions break.
When TurboFan's optimized assumptions break (e.g., a function receives a different type than expected), V8 discards the optimized machine code and falls back to Ignition bytecode. Performance drops until the function is re-optimized.
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