> And thinking about it some more, a register-based bytecode is less flexible and future proof. The flow analysis that modern JITs use to extract an SSA form f

> And thinking about it some more, a register-based bytecode is less flexible and future proof. The flow analysis that modern JITs use to extract an SSA form from stack-based bytecode is just as easy to perform on register-based bytecode. This SSA form is then optimized, instructions selected, and CPU registers allocated. From one perspective, you have a continuum from (essentially) infinite register machines with SSA (LLVM bitcode, SafeTSA) or memory machines (such as Inferno's Dis VM) to 256-register VMs (LuaJIT, Lua, others) to 16-register VMs (Dalvik, maybe others) to stack machines (JVM, p-code, FCode, etc.). From one perspective, stack machine bytecode is a compact representation of code for a register machine with 2 registers. Register machines aren't any less flexible than stack machines.