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Re: [RFC] Fix PR19401: always completely peel loops


On Thu, 13 Jan 2005, Zdenek Dvorak wrote:

> I am not persuaded that enabling complete loop unrolling unconditionally
> as done by this patch is a good idea.
>
> I would prefer:
>
> 1) Unrolling loops completely whenever this does not cause a code
>    growth.

It's hard to prove - especially for the std::pow issue, which is
the first case in the PR19401 audit trail.

> 2) Making all possible loops to be completely unrolled at -O3.

Yes, that makes sense - we already limit code size growth anyway.
Of course this would be done also with the patch to enable
-funroll-loops at -O3.

> 3) Possibly having a separate flag controlling complete loop unrolling.

I'd very much like this at least, if 1) does not work for the testcases.
As I said - previously I used -fpeel-loops for this, but that doesn't
work for the tree unroller -- so simply changing the cunroll guard
to contain flag_unroll_loops || flag_peel_loops would work also.

Richard.

--
Richard Guenther <richard dot guenther at uni-tuebingen dot de>
WWW: http://www.tat.physik.uni-tuebingen.de/~rguenth/


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