benchmark:
  vm1_gc_wb_obj_promoted: |
    class C
      attr_accessor :foo
    end
    long_lived = C.new

    if RUBY_VERSION >= "2.2.0"
      3.times{ GC.start(full_mark: false, immediate_mark: true, immediate_sweep: true) }
    elsif
      GC.start
    end

    i = 0
    short_lived = ''
    while i<30_000_000 # while loop 1
      long_lived.foo = short_lived # write barrier
      i+=1
    end
loop_count: 1