On Tue, 1 Oct 2019, Jeff Law wrote: > On 10/1/19 12:40 AM, Richard Biener wrote: > > On Mon, 30 Sep 2019, Prathamesh Kulkarni wrote: > > > >> On Wed, 25 Sep 2019 at 23:44, Richard Biener <rguent...@suse.de> wrote: > >>> > >>> On Wed, 25 Sep 2019, Prathamesh Kulkarni wrote: > >>> > >>>> On Fri, 20 Sep 2019 at 15:20, Jeff Law <l...@redhat.com> wrote: > >>>>> > >>>>> On 9/19/19 10:19 AM, Prathamesh Kulkarni wrote: > >>>>>> Hi, > >>>>>> For PR91532, the dead store is trivially deleted if we place dse pass > >>>>>> between ifcvt and vect. Would it be OK to add another instance of dse > >>>>>> there ? > >>>>>> Or should we add an ad-hoc "basic-block dse" sub-pass to ifcvt that > >>>>>> will clean up the dead store ? > >>>>> I'd hesitate to add another DSE pass. If there's one nearby could we > >>>>> move the existing pass? > >>>> Well I think the nearest one is just after pass_warn_restrict. Not > >>>> sure if it's a good > >>>> idea to move it up from there ? > >>> > >>> You'll need it inbetween ifcvt and vect so it would be disabled > >>> w/o vectorization, so no, that doesn't work. > >>> > >>> ifcvt already invokes SEME region value-numbering so if we had > >>> MESE region DSE it could use that. Not sure if you feel like > >>> refactoring DSE to work on regions - it currently uses a DOM > >>> walk which isn't suited for that. > >>> > >>> if-conversion has a little "local" dead predicate compute removal > >>> thingy (not that I like that), eventually it can be enhanced to > >>> do the DSE you want? Eventually it should be moved after the local > >>> CSE invocation though. > >> Hi, > >> Thanks for the suggestions. > >> For now, would it be OK to do "dse" on loop header in > >> tree_if_conversion, as in the attached patch ? > >> The patch does local dse in a new function ifcvt_local_dse instead of > >> ifcvt_local_dce, because it needed to be done after RPO VN which > >> eliminates: > >> Removing dead stmt _ifc__62 = *_55; > >> and makes the following store dead: > >> *_55 = _ifc__61; > > > > I suggested trying to move ifcvt_local_dce after RPO VN, you could > > try that as independent patch (pre-approved). > > > > I don't mind the extra walk though. > > > > What I see as possible issue is that dse_classify_store walks virtual > > uses and I'm not sure if the loop exit is a natural boundary for > > such walk (eventually the loop header virtual PHI is reached but > > there may also be a loop-closed PHI for the virtual operand, > > but not necessarily). So the question is whether to add a > > "stop at" argument to dse_classify_store specifying the virtual > > use the walk should stop at? > I think we want to stop at the block boundary -- aren't the cases we > care about here local to a block?
Sure, but I see no reason to not make it trivially work for SESE regions as well by instead specifying the "exit" virtual-operand. Richard.
