Re: Int vs Word performance?

27 Feb 2009

      marlowsd:
...
Claus Reinke wrote:
...
...
...
Here is a trivial example with drastic difference between
T = Int and T = Word (~2.5x here):
main = print $ foldl' (+) 0 [1..100000000::T]
..
...
A quick grep shows almost no specialization at all for Word, or for
IntXX/WordXX (see below). Still, none of that seems to explain the
example repeated at the top of this message.
The Enum instance for Int uses specialised implementations of enumFromTo  
and friends, whereas the Word version uses the generic 
integralEnumFromTo.
Another good reason to use uvector,

    import Data.Array.Vector
    import Data.Word

    main = print $ foldlU (+) (0::T) (enumFromToU 1 (100000000::T))

type T = Word

    $wfold :: Word# -> Word# -> Word#

    $wfold =
      \ (ww_s1cg :: Word#) (ww1_s1ck :: Word#) ->
        case gtWord# ww1_s1ck __word 100000000 of wild_a19p {
          False ->
            $wfold
              (plusWord# ww_s1cg ww1_s1ck)
              (plusWord# ww1_s1ck __word 1);
          True -> ww_s1cg

Yields:

    Main_zdwfold_info:
    .Lc1e1:
      cmpq $100000000,%rdi
      ja .Lc1e4
      leaq 1(%rdi),%rax
      addq %rdi,%rsi
      movq %rax,%rdi
      jmp Main_zdwfold_info

While at 

    type T = Int

We get:

    $wfold :: Int# -> Int# -> Int#

    $wfold =
      \ (ww_s144 :: Int#) (ww1_s148 :: Int#) ->
        case ># ww1_s148 100000000 of wild_a11q {
          False ->
            $wfold
              (+# ww_s144 ww1_s148) (+# ww1_s148 1);
          True -> ww_s144

And *identical assembly*

    Main_zdwfold_info:
    .Lc15E:
      cmpq $100000000,%rdi
      jg .Lc15H
      leaq 1(%rdi),%rax
      addq %rdi,%rsi
      movq %rax,%rdi
      jmp Main_zdwfold_info

-- Don

Re: Int vs Word performance?

Don Stewart