Polymorphic inline caching (PIC) is a classic optimization for dynamic languages. JavaScriptCore (JSC) is a production JavaScript virtual machine with a mature polymorphic inline cache implementation. In the best case, JSC is able to use its PIC-based JIT optimizations to turn a JavaScript object lookup into single memory access instruction, or some cases, can even allow the JIT to constant-fold heap accesses. This talk describes in detail how JSC uses PIC optimizations, including: how PIC works in our interpreter, how PIC works in our JIT compilers, and most importantly, how PIC is used to drive type inference in our optimizing JIT compilers.

I work on compilers and language runtime systems at Apple. Most of my work there involves the WebKit open source project.