Consider optimizing trivial case statements

[yorickpeterse]

Original issue: rubinius/rubinius#3620

Copied here for ease of reading:

---

Hello,

MRI adopts "jump table"-like optimization for case-when statement if all clauses have trivial immediate values such as Integer and Symbol. How about implementing this optimization in Rubinius?

100000.times do
  case 1000
  when 0
  when 1
  when 2
  ...
  when 999
  end
end

$ time ruby -v t.rb
ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-linux]

real    0m0.082s
user    0m0.068s
sys     0m0.012s

# time ruby -v t.rb
rubinius 3.14 (2.2.2 a7ba16db 2016-01-28 3.4.2 JI) [x86_64-linux-gnu]

real    0m2.311s
user    0m2.240s
sys     0m0.064s

(I'm using rubinius/docker.)

Thank you for your consideration,