SpiderMonkey's Inline Caches: Beyond Simple Caching

This post delves into the implementation of inline caching (IC) within the SpiderMonkey JavaScript engine. Unlike traditional caching, SpiderMonkey's IC is a self-modifying code technique. It inserts a series of stubs at call sites, dynamically selecting efficient execution paths based on input types. The first call executes a fallback path and generates corresponding stubs based on the result. Subsequent calls of the same type hit the cache, significantly improving efficiency. The article uses JavaScript addition as an example to explain how IC works, and mentions SpiderMonkey's latest CacheIR architecture, which abstracts the details of ICs to enable sharing between different compilers.