https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109499
--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> --- On Thu, 13 Apr 2023, rsandifo at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109499 > > --- Comment #2 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> > --- > (In reply to Richard Biener from comment #1) > > Is there not enough info to catch this on the RTL level with a peephole? > That works for simple cases like the first loop. But in general, I think we > want the full power of gimple to push the information down. The second loop > is > one example of that, but in general, there could be a chain of operations that > naturally do the right thing for inactive lanes. AVX512 masking allows merge and zero modes, zero being cheaper (obviously). I think "zero" is what all targets support so we could define GIMPLE to be that way - inactive lanes become zero. That's then also less of a "partial definition" and "undefined" should be avoided at best?
