[PATCH, vec-tails 07/10] Support loop epilogue combining

[Jeff Law]

On 07/22/2016 05:36 AM, Richard Biener wrote:
> The thing that needs work I think is re-running of if-conversion.
I wonder if we could revamp if-conversion to work on a subset of the 
CFG?   I can see that potentially being useful in other contexts.  Would 
that work for you Richi?

We've already got Bin doing that for DOM...


> Also I don't like at
> all that we have many variants of vectorizing but somehow the decision which one
> to choose is rather unclear.  The way the epilogue vectorization code
> is hooked in
> is rather awkward and bound to be a maintainance burden (well, maybe a
> small one).
I think it's going to be a small one.  I suspect that we really need 
another architecture with masking capabilities to really be able to see 
how the costing models ought to work and bring sanity to that decision.

>
> And last, I double there is a case for a masked vectorized loop - I can bet that
> doing a non-masked vectorized loop plus a masked epilogue (with no iteration
> then!) will be always faster unless you hit the window of very few iterations
> (or optimizing for size - in which case vectorizing is questionable on
> its own and
> disabled IIRC).
Ilya, does this case make a noticeable difference with the ICC 
implementation?

Jeff