[webkit-dev] Drop x86 (32bit) JIT backend

[Yusuke Suzuki]

Hello all,

Now, Xcode no longer has ability to build 32bit binary.
Fedora starts dropping x86 32bit kernel shipping.
Our x86/x86_64 JIT requires SSE2, so such CPUs can use JIT if they want by switching x86 to x86_64.
And these CPUs are modern enough to run CLoop at high speed.

x86 32bit JIT backend is very complicated and is being a major maintenance burden.
This is due to very few # of registers. Which scatters a lot of isX86 / CPU(X86) in Baseline, DFG, and Yarr.
I’m now planning to optimize some part of Yarr, but x86 YarrJIT is being a major barrier of such cleanups / optimizations.

So, I would like to propose dropping X86 32bit JIT support.

-Yusuke