Iterative fib() using Rubinius register bytecode

gistfile1.txt

$ bin/rbx
irb(main):001:0> load './fib_r.rb'
=> true
irb(main):002:0> cc = A.instance_method(:fibi).executable
=> #<Rubinius::CompiledCode:0x3680 name=fibi file=(dynamic) line=1>
irb(main):003:0> cc.iseq
=> #<Rubinius::InstructionSequence:0x3840>
irb(main):004:0> iseq = _
=> #<Rubinius::InstructionSequence:0x3840>
irb(main):005:0> iseq.opcodes
=> #<Rubinius::Tuple: 184, 1, 127, 0, 0, 134, 2, 0, 148, 3, 2, 1, 126, 3, 49, 184, 0, 184, 3, 137, 4, 0, 0, 150, 5, 4, 2, 126, 5, 46, 136, 6, 0, 137, 0, 0, 3, 136, 3, 6, 137, 4, 4, 1, 181, 23, 135, 0, 0, 132, 0, 70, 0>
irb(main):006:0> puts cc.decode
0000:  r_load_1                   1
0002:  r_load_local               0, 0
0005:  r_load_int                 2, 0
0008:  n_ile                      3, 2, 1
0012:  b_if                       3, 49
0015:  r_load_1                   0
0017:  r_load_1                   3
0019:  n_iadd                     4, 0, 0
0023:  n_ige                      5, 4, 2
0027:  b_if                       5, 46
0030:  r_copy                     6, 0
0033:  n_iadd                     0, 0, 3
0037:  r_copy                     3, 6
0040:  n_iadd                     4, 4, 1
0044:  goto_past                  0023:
0046:  r_store_int                0, 0
0049:  r_store_stack              0
0051:  ret                        0
=> nil