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Re: [gomp] Fix degenerate omp for loops (PR libgomp/29949)


Hello,

> On Sat, Dec 02, 2006 at 12:23:06AM +0100, Zdenek Dvorak wrote:
> > > >Lastly, the compiler expanded loops (static without chunk size, static with
> > > >chunk size) failed because the arithmetics to compute range given to the
> > > >current thread was mostly done in unsigned long and thus when N2 - N1
> > > >was negative (for positive STEP resp. positive for negative STEP), we ended
> > > >up with a huge range.  I tried to figure out why this was cast to utype,
> > > >but haven't found why it has been written that way.
> > 
> > I think that not casting to unsigned type might give wrong results for
> > loops like
> > 
> > for (i = -many; i < many; i++)
> > 
> > ie. in cases the number of iterations does not fit in the signed type.
> > 
> > (sorry if I understand the situation wrong, I did not really check the
> > code whether this is the case or not, it just seems to be one possible
> > reason why we want to compute these things in unsigned type).
> 
> Guess you are right, in which case I'm afraid I need to revokethe omp-low.c
> part of my patch and instead add an additional comparison and conditional
> jump to the code I'm afraid.

could you please check whether the problem by chance is not fixed in
parloop branch?  I have rewritten most of the omp loop expansion code
there, and I would like to avoid conflicts if possible.

Zdenek


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