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. Thanks, Ilya > > Jeff
