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. Thanks, Ilya > I see no need to re-run if-conversion here. > > Richard. > >> Thanks, >> Ilya >> >>> >>> Jeff
