Duplicating loops and virtual phis

Steve Ellcey sellcey@cavium.com
Wed May 17 15:58:00 GMT 2017

On Wed, 2017-05-17 at 10:41 +0100, Bin.Cheng wrote:

> I happen to be working on loop distribution now (If guess correctly,
> to get hmmer fixed).  So far my idea is to fuse the finest
> distributed
> loop in two passes, in the first pass, we merge all SCCs due to
> "true"
> data dependence; in the second one we identify all SCCs and breaks
> them on dependent edges due to possible alias.  Breaking SCCs with
> minimal edge set can be modeled as Feedback arc set problem which is
> NP-hard. Fortunately the problem is small in our case and there are
> approximation algorithms.  OTOH, we should also improve loop
> distribution/fusion to maximize parallelism / minimize
> synchronization, as well as maximize data locality, but I think this
> is not needed to get hmmer vectorized.

Vectorizing hmmer is what I am interested in so I am glad to hear you
are looking into that.  You are obviously more knowledgable about the
GCC loop infrastructure then I am so I look forward to what you come up

Steve Ellcey

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