Ludicrous on YARV

Last night I was tinkering with Ludicrous and I decided to see how hard it would be to get it to run on YARV. After modifying the extension to compile against ruby 1.9, it turned out to be only a handful of lines of code to compile a simple method in YARV:

class Foo
  def foo
    return 42
  end

  go_plaid
end

puts Foo.new.foo #=> 42

The primary difference between methods on 1.8 and methods on YARV is that methods in 1.8 are represented by SCOPE nodes that hold a reference to that method’s AST, while YARV methods are represented by a METHOD node that holds a reference to that method’s instruction sequence. The code for compiling METHOD nodes and SCOPE nodes is remarkably similar, the primary difference lying in the code that compiles the instruction sequence:

class VM
  class Instruction
    class PUTOBJECT
      def ludicrous_compile(function, env)
        value = function.const(JIT::Type::OBJECT, self.operands[0])
        env.push(value)
      end
    end

    class LEAVE
      def ludicrous_compile(function, env)
        retval = env.pop
        function.insn_return(retval)
      end
    end
  end
end

Currently the stack is a simple Ruby array, which is probably going to run slower than YARV bytecode, but it shouldn’t be difficult to use a more highly optimized stack (perhaps the system stack).