https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82604
--- Comment #15 from rguenther at suse dot de <rguenther at suse dot de> --- On Thu, 18 Jan 2018, amker at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82604 > > --- Comment #14 from amker at gcc dot gnu.org --- > (In reply to rguent...@suse.de from comment #13) > > On Thu, 18 Jan 2018, amker at gcc dot gnu.org wrote: > > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82604 > > > > > > --- Comment #12 from amker at gcc dot gnu.org --- > > > (In reply to rguent...@suse.de from comment #11) > > > > > > > Yes, this can be done. For now, it's disabled because without classifying > > > zeroing stmt as a builtin partition, it's fused because of shared memory > > > reference to y(l,i,j,k). This step can be made by cost model changes. > > > The > > > on;y problem is the cost model change doesn't make sense here (without > > > considering builtin partition stuff, it should be fused, right?) > > > > It might be profitable to distribute away stores that have no dependent > > stmts (thus stores from invariants). > > > > Another heuristic would be to never merge builtin partitions with > > other partitions because loop optimizations do not handle memory > > Together with last sentence of your comment. IIUC, so what we want to do is > still a builtin partition distribution from the original loop. The only > difference is now the loop nest of zeroing stmt is distributed into a > loop(outer) of memset call, rather than a single memset call. Of course if it > would be even better if it can be distributed into a single memset. > Currently such loop nest in this case is not classified as builtin partition. > > > builtins (the data dependence limitation). Which might also be a reason > > not to handle those as builtins but revert to a non-builtin > > classification. > But I don't quite follow this sentence, why not handle it as builtins? it is > special, but eventually we want to distribute it into memset (in a loop nest), > right? Do not handle it as builtins because we cannot handle builtins in data dependence and we do not want to distribute it into a separate nest because of data locality. Needs to be measured ;)
