[Yarv-devel] case/when optimization

[SASADA Koichi]

Hi,

I implemented optimization for case/when statement.

  * Order of case/when statement is O(n) (n: number of when conditons)
  * If when condtions are all special literals (Numeric, Symbol, String),
    when dispatch can be done with hash.

example:

case x
when :a
  Abody
when :b
  Bbody
when :c
  Cbody
else
  ElseBody
end

In this situation, we don't need compare with each conditions.
Following pseudo code is more fast.

  pos = hash.fetch(x, elsePos)
  goto pos
posA:
  Abody
  goto endPos
posB:
  Bbody
  goto endPos
posC:
  Cbody
  goto endPos
elsePos:
  Elsebody
endPos:


 * Note that if '===' method of these classes is redefined, we can't
   use above method.  In current, YARV doesn't check it (must check
   it).


Benchmark:

i=0
while i<1000000
  i+=1
  case :a
  when :x
  when :y
  when :z
  end
end

ruby  3.815000   0.010000   3.825000 (  3.893000)
yarv  1.231000   0.000000   1.231000 (  1.247000) old
yarv  0.370000   0.010000   0.380000 (  0.385000) new




Regards,
SASADA Koichi