Re: [Haskell-cafe] GHC vs GCC

On Fri, Mar 26, 2010 at 6:49 PM, Jason Dagit wrote:

On Fri, Mar 26, 2010 at 2:33 PM, Bryan O'Sullivan wrote:

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On Fri, Mar 26, 2010 at 10:46 AM, Rafael Cunha de Almeida wrote:

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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 10s. What's going on here? Doesn't ghc do tail recursion optimization?