[Ecco]

I'm really wondering about the politics behind all this. I mean both LLVM and WebKit are Apple projects (even though they're Open Source). So it would have been reasonable to expect an improvement of LLVM instead of ditching it altogether.

[pcwalton]

I highly doubt there are any politics behind it. LLVM is an AOT C/C++ compiler at its core, and the tradeoffs it makes don't always make sense for dynamic, JIT compiled languages with extreme emphasis on compilation speed like JS. Personally, I expected this to happen.

[gsg]

Specialising LLVM for dynamic compilation might well come at the expense of LLVM's strengths as an AoT compiler, and it would probably not be easy in any case.

In addition to that, dedicated implementations can take various shortcuts to make their job easier - there are some nice examples given in the link. LuaJIT is example of a compiler project that benefits from being heavily specialised to a particular job, to remarkable effect.

[zepto]

If you read the technical explanation you will see that there are zero politics behind this.