Google Chrome’s V8 engine is synonymous with the modern browser JavaScript engine, but Apple is looking to enter the conversation with upgrades to its JavaScriptCore engine.

The upgraded JavaScriptCore, codenamed FTLJIT (Fourth Tier LLVM Just-In-Time), has not yet been enabled, but Apple is making it available by default in the OS X port of the WebKit open-source browser engine and system framework for Safari. It can be enabled using command-line flags. FTLJIT uses the LLVM compiler to enhance JavaScript code performance, specifically the asm.js subset developed by Mozilla.

(Related: Google speeds up Chrome performance with concurrent JavaScript compilation)

The upgrades are integrated into JavaScriptCore as an alternative back end. FTLJIT works by invoking the LLVM compiler infrastructure to generate JavaScript code, instead of the current method of generating code directly from JavaScriptCore’s Data-Flow Graph Intermediate Representation. The code, which doesn’t act any differently, then runs markedly faster at speeds comparable to native C code, according to independent AreWeFastYet JavaScript benchmarks.

As of yet, FTLJIT is only available for OS X, so it remains to be seen how the integrated LLVM compiler technology performs across platforms.