benchmark:
  vm1_attr_ivar_set: |
    class C
      attr_accessor :a, :b
      def initialize
        @a = nil
        @b = nil
      end
    end
    obj = C.new
    i = 0
    while i<30_000_000 # while loop 1
      i += 1
      obj.a = 1
      obj.b = 2
    end
loop_count: 1