On Tue, Jul 26, 2016 at 3:03 PM, Ilya Enkovich <enkovich....@gmail.com> wrote: > 2016-07-26 14:51 GMT+03:00 Richard Biener <richard.guent...@gmail.com>: >> On Tue, Jul 26, 2016 at 11:57 AM, Ilya Enkovich <enkovich....@gmail.com> >> wrote: >>> 2016-07-26 0:08 GMT+03:00 Jeff Law <l...@redhat.com>: >>>> On 07/25/2016 12:32 PM, Richard Biener wrote: >>>>> >>>>> On July 25, 2016 8:01:17 PM GMT+02:00, Jeff Law <l...@redhat.com> wrote: >>>>>> >>>>>> 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? >>>>> >>>>> >>>>> Well, you need to make it not need post-dominators or preserve them (or >>>>> compute "post-dominators" on SESE regions). >>>> >>>> Oh, but it'd be so nice to have DOMs and/or PDOMs on regions. But that's >>>> probably out of scope for gcc-7. >>>> >>>> >>>>> >>>>> What doesn't work with the idea to clone the epilogue using >>>>> __built-in_vectorized() >>>>> For the if- vs. Not if-converted loop? >>>> >>>> I must be missing something. I don't see how builtin_vectorized_function >>>> helps, but maybe I've got the wrong built-in or don't understand what >>>> you're >>>> suggesting. >>>> >>>> It sounds like this is the biggest impediment to moving forward. So let's >>>> reset and make sure we're all on the same page here. >>>> >>>> Ilya, what's the fundamental reason why we need to run if-conversion again? >>>> Yes, I know you want to if-convert the epilogue, but why? >>>> >>>> What are the consequences of not doing if-conversion on the epilogue? >>>> Presumably we miss a vectorization opportunity on the tail. But that may >>>> be >>>> a reasonable limitation to allow the existing work to move forward while >>>> you >>>> go back and revamp things a little. >>> >>> If we have some control-flow in a loop then we have to if-convert it >>> for vectorizer. >>> We need to preserve both versions: if-converted one for vectorizer and >>> the original >>> one to be used if vectorization fails. For epilogues we have similar >>> situation and >>> need two versions. I do it by running if-conversion on a copy of original >>> loop. >>> Note that it doesn't run full if-conversion pass. If-conversion is >>> called for epilogue >>> loop only. >> >> But it will still compute post-dominators for the full function for example. >> >> You have the if-converted loop available already - it's the loop we are going >> to vectorize. If if-conversion generated if (__builtin_vectorized_p ()) >> style >> loop copies then you can simply create the epilogue in the same way. >> If it didn't then the loop is already if-converted anyway. >> > > Agree. Calling if-conversion is just much simpler in implementation.
Agreed, but it's also quadratic in the number of vectorized loops in a function. Not sure if it is really very much simpler either. Richard. > Thanks, > Ilya > >> I see no need to re-run if-conversion here. >> >> Richard. >> >>> Thanks, >>> Ilya >>> >>>> >>>> Jeff
