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