[Haskell-cafe] GHC vs GCC

Rafael Almeida almeidaraf at gmail.com
Sat Mar 27 00:43:34 EDT 2010

On Fri, Mar 26, 2010 at 6:49 PM, Jason Dagit <dagit at codersbase.com> wrote:
> On Fri, Mar 26, 2010 at 2:33 PM, Bryan O'Sullivan <bos at serpentine.com>
> wrote:
>> On Fri, Mar 26, 2010 at 10:46 AM, Rafael Cunha de Almeida
>> <almeidaraf at gmail.com> wrote:
>>> During a talk with a friend I came up with two programs, one written in
>>> C and another in haskell.
>> Your Haskell code builds a huge thunked accumulator value, so of course
>> it's slow (put bang patterns on all arguments). Also, you should use rem
>> instead of mod. Make those tiny changes and you'll get a 5x speedup, to half
>> the performance of the C code.
> Interesting.  I had to add -fvia-C to get within half the performance of C.
> Just bang patterns and rem and I'm 1/5th of C.  I'm on a x86_64 machine.  I
> wonder if that plays in.
> Jason

Using bang patterns didn't help almost anything here. Using rem
instead of mod made the time go from 45s to 40s. Now, using -fvia-C
really helped (when I used rem but not using mod). It went down to

What's going on here? Doesn't ghc do tail recursion optimization?

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