Need C optimization help

[Mark Rose]

I accidentally forgot to save the reduced file before attaching it. Here is the 
proper attchment.

-Mark

On Saturday 15 May 2010 3:59:30 pm Mark Rose wrote:
> Hi All,
> 
> I have a line that gets called approxmiately 2 trillion times according to
> valgrind, and I love any suggestions for speeding it up. I have taken over
>  the project from someone else and my C abilities are only intermediate.
>  I've attached a trimmed down version of the function.
> 
> Here are some notes about the code:
> * tsMemAlloc and tsMemFree are basically wrappers to malloc/free.
> * dsfmt_genrand_close_open() generates a number in the range [0,1)
> 
> And notes about the data:
> * n_topics is 35 (loaded from a configuration file; changeable)
> * n_tokens is about 7M (and increases as the data set grows)
> * params->iter is 500
> * topics->wcount size is about 190k items
> * topics->dcount size is about 275k items
> * topics->tcount size is 35 items
> 
> I'm compling on an Opteron, with options: -03 -std=gnu99 -march=native
>  -ffast- math -ftree-loop-distribution -ftree-loop-linear
>  -ftree-interchange -floop- block -ftree-vectorizer-verbose=8
> 
> I'm using GCC 4.4.3.
> 
> The tree vectorizer spits out this note about the loop I'm particularly
> interested in:
> 
> for (int k = 1; k < n_topics; k++)
> 	cdf[k] = cdf[k-1] + (dcount[k+d_offset] + alpha)*(wcount[k+w_offset +
> beta)/(tcount[k] + wbeta);
> note: not vectorized: data ref analysis failed D.8597_92 = *D.8596_91;
> 
> I've done hours of googling, playing with restrict keywords, splitting the
> cdf[k-1] addition into another loop, and nothing will help. The error
>  message itself is very poor, as I can't find a decent explanation anywhere
>  online as to what it means nor how to fix it.
> 
> Thanks for whatever insight you can give!
> 
> -Mark
> 
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