[llvm-dev] Details on JavaScriptCore's new B3 JIT, replacing their LLVM JIT

Philip Reames via llvm-dev llvm-dev at lists.llvm.org
Wed Feb 17 15:46:52 PST 2016

FYI, Sanjoy just started a discussion on what a "check"-like construct 
might look like in LLVM over in the thread "RFC: Add guard intrinsics to 
LLVM".  To avoid confusion, it's worth calling out that the predicate is 
reversed in Sanjoy's proposal from how it's described in the b3 post.


On 02/15/2016 08:02 AM, Alex Bradbury via llvm-dev wrote:
> A great blog post has just gone up about JavascriptCore's new B3 JIT.
> https://webkit.org/blog/5852/introducing-the-b3-jit-compiler/
> This replaces LLVM as the low-level optimisation layer of the FTL JIT.
> They currently achieve roughly 5x faster compile time than LLVM while
> achieving roughly the same generated code quality for their workloads.
> I'm sharing as I thought some parts of the design may be interesting
> to other LLVM devs, including the use of Check opcodes ("like a
> marriage between a Branch and a Patchpoint")  and the backwards greedy
> pattern matching for lowering from B3 to Air.
> Alex
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