haskell array access

[Lex Stein]

Great, thanks. Those suggestions narrow the gap from GHC -O being 330x
slower than GCC -O3 to it being 20x slower. Here are the new results:

gcc -O3      0.54s
ocamlopt     1.11s
ghc -O      10.76s
ocamlc      14.10s

GHC is still pretty slow for native x86 instruction code. Is there any way
to further explain the performance gap ? (new code below)

Thanks!
Lex

Haskell (GHC) source:

import Array
k :: Array Int Int
k = Array.array (0,15) [(i, i+1) | i <- [0 .. 15] ]
acc :: Int -> Int
acc 0 = 0
acc n = seq (k Array.! (n `mod` 16)) (acc (n-1))
main = do
    print (acc 100000000)

Caml test source:

let a = Array.make 16 0;;
let rec do1 i z =
    if (i>100000000) then z else
        do1 (i+1) (z + a.(i mod 16));;
do1 0 0;;

C (gcc) test source:

int main () {
    int i, k = 0;
    int a [16];
    for (i=0; i<100000000; i++) {
        k += a [i % 16];
    }
    return (k);
}


On Fri, 27 Jun 2003, Sven Panne wrote:

> Well, part of the answer is definitely that the Haskell program is the
> *only* one which really uses the array elements. :-) I guess that the
> compilers for the other languages simply remove the array access from
> the generated code (gcc definitely does, only an empty loop remains).
>
> Another reason is that the type signatures are missing, so Integer is
> used instead of Int, which is a bit unfair. Adding
>
>     k :: Array Int Int
>     acc :: Int -> Int
>
> cuts down the time by more than factor 5 on my machine.
>
> Cheers,
>     S.
>
>
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