[Haskell-cafe] Re: speed: ghc vs gcc

[Peter Verswyvelen]

When I change the C++ program into:
int n;
scanf("%d", &n);

for(i=0; i<n;i++)
{
sum += i;
}

GCC need 100 milliseconds on my 3.0GHz new Xeon with loop unrolling
enabled.

Without loop unrolling GCC needs about 635ms

Visual C++ does it in 577 ms, generating the following code:

loop: add        rbx,rax
        inc         rax
       cmp       rax,rcx
       jl          loop

GHC with -O2 -fvia-c (the fastest I could make it) needs

13075 for the naive sum
2100 ms with sum0
2018 ms using the stream-fusion

Interesting to see that the stream-fusion was slower when not doing -fvia-c
(more than twice as slow with -O)

So GHC is about 3 to 4 times slower as Visual C++ / GCC without loop
unrolling, which is not too bad since GHC does not perform register
optimization and loop unrolling yet no?

On Fri, Feb 20, 2009 at 3:44 PM, Achim Schneider <barsoap at web.de> wrote:

> Bulat Ziganshin <bulat.ziganshin at gmail.com> wrote:
>
>
> > execution times:
> >  sum:
> >    ghc 6.6.1 -O2               : 12.433 secs
> >    ghc 6.10.1 -O2              : 12.792 secs
> >  sum-fast:
> >    ghc 6.6.1 -O2               :  1.919 secs
> >    ghc 6.10.1 -O2              :  1.856 secs
> >    ghc 6.10.1 -O2 -fvia-C      :  1.966 secs
> >  C++:
> >    gcc 3.4.5 -O3 -funroll-loops:  0.062 secs
> >
> Nice! Now we know that gcc can calculate faster than Haskell can
> calculate and print. Next time, use exitWith, please.
>
>
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