They answer this on the github: > Unstable interfaces. An LLVM JIT is already used by Rubicon. A lot of efforts in preparation of code used by RTL insns (an en

They answer this on the github: > Unstable interfaces. An LLVM JIT is already used by Rubicon. A lot of efforts in preparation of code used by RTL insns (an environment) https://github.com/vnmakarov/ruby/tree/rtl_mjit_branch#a-few-possible-approaches-in-jit-implementation https://github.com/vnmakarov/ruby/tree/rtl_mjit_branch#a-few...