Apple Implements LLVM JIT Back-End For WebKit JavaScript
Written by Michael Larabel in Compiler on 14 May 2014 at 12:46 AM EDT. 13 Comments
For speeding up the JavaScript performance within upstream WebKit, Apple developers have implemented a new just-in-time (JIT) back-end that's based upon LLVM.

WebKit's newly-enabled JavaScript JIT support is based on LLVM. The new LLVM-based JIT compiler is called FTL, for the Fourth Tier LLVM. For right now this new high-performance JavaScript back-end is enabled for the Mac OS X and iOS versions of the open-source web-browser rendering engine.

Apple developers have been working on this LLVM FTL support for the past year and have now finally been able to turn it on. By basing it on LLVM, they are taking advantage of new optimization approaches previously not applicable to WebKit's JavaScript.

Early performance figures by Apple show the FTL JIT support being much faster than their earlier DFG JIT back-end along with other comparison pipelines. While these early results are good, developers still have more performance optimizations planned for the LLVM FTL JIT support.

This WebKit LLVM support was brought up Tuesday on the LLVM developers' list and you can learn a lot more in detail via the blog.

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Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter or contacted via

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