Re: [PATCH, vec-tails 05/10] Check if loop can be masked

[Jeff Law <law@redhat.com>]

On 06/15/2016 05:22 AM, Richard Biener wrote:
>
> You look at TREE_TYPE of LOOP_VINFO_NITERS (loop_vinfo) - I don't think
> this is meaningful (if then only by accident).  I think you should look at the
> control IV itself, possibly it's value-range, to determine the smallest possible
> type to use.
Can we get an IV that's created after VRP?  If so, then we have to be 
prepared for the case where there's no range information on the IV.  At 
which point I think using type min/max of the IV is probably the right 
fallback.  But I do think we should be looking at range info much more 
systematically.

I can't see how TREE_TYPE of the NITERS makes sense either.

> Finally we have a related missed optimization opportunity, namely avoiding
> peeling for gaps if we mask the last load of the group (profitability depends
> on the overhead of such masking of course as it would be done in the main
> vectorized loop).
I think that's a specific instance of a more general question -- what 
transformations can be avoided by masking and can we generate costs to 
select between those transformations and masking.  Seems like a 
follow-up item rather than a requirement for this work to go forward to me.

Jeff