On Thu, Sep 14, 2017 at 12:42 PM, Martin Liška <mli...@suse.cz> wrote: > On 09/14/2017 12:37 PM, Bin.Cheng wrote: >> On Thu, Sep 14, 2017 at 11:24 AM, Richard Biener >> <richard.guent...@gmail.com> wrote: >>> On Thu, Sep 14, 2017 at 12:18 PM, Martin Liška <mli...@suse.cz> wrote: >>>> On 09/14/2017 12:07 PM, Markus Trippelsdorf wrote: >>>>> On 2017.09.14 at 11:57 +0200, Richard Biener wrote: >>>>>> On Wed, Sep 13, 2017 at 6:11 PM, Nikos Chantziaras <rea...@gmail.com> >>>>>> wrote: >>>>>>> On 12/09/17 16:57, Wilco Dijkstra wrote: >>>>>>>> >>>>>>>> [...] As a result users are >>>>>>>> required to enable several additional optimizations by hand to get good >>>>>>>> code. >>>>>>>> Other compilers enable more optimizations at -O2 (loop unrolling in >>>>>>>> LLVM >>>>>>>> was >>>>>>>> mentioned repeatedly) which GCC could/should do as well. >>>>>>>> [...] >>>>>>>> >>>>>>>> I'd welcome discussion and other proposals for similar improvements. >>>>>>> >>>>>>> >>>>>>> What's the status of graphite? It's been around for years. Isn't it >>>>>>> mature >>>>>>> enough to enable these: >>>>>>> >>>>>>> -floop-interchange -ftree-loop-distribution -floop-strip-mine >>>>>>> -floop-block >>>>>>> >>>>>>> by default for -O2? (And I'm not even sure those are the complete set of >>>>>>> graphite optimization flags, or just the "useful" ones.) >>>>>> >>>>>> It's not on by default at any optimization level. The main issue is the >>>>>> lack of maintainance and a set of known common internal compiler errors >>>>>> we hit. The other issue is that there's no benefit of turning those on >>>>>> for >>>>>> SPEC CPU benchmarking as far as I remember but quite a bit of extra >>>>>> compile-time cost. >>>>> >>>>> Not to mention the numerous wrong-code bugs. IMHO graphite should >>>>> deprecated as soon as possible. >>>>> >>>> >>>> For wrong-code bugs we've got and I recently went through, I fully agree >>>> with this >>>> approach and I would do it for GCC 8. There are PRs where order of simple >>>> 2 loops >>>> is changed, causing wrong-code as there's a data dependence. >>>> >>>> Moreover, I know that Bin was thinking about selection whether to use >>>> classical loop >>>> optimizations or Graphite (depending on options provided). This would >>>> simplify it ;) >>> >>> I don't think removing graphite is warranted, I still think it is the >>> approach to use when >>> handling non-perfect nests. >> Hi, >> IMHO, we should not be in a hurry to remove graphite, though we are >> introducing some traditional transformations. It's a quite standalone >> part in GCC and supports more transformations. Also as it gets more >> attention, never know if somebody will find time to work on it. > > Ok. I just wanted to express that from user's perspective I would not > recommend it to use. > Even if it improves some interesting (and for classical loop optimization > hard) loop nests, > it can still blow up on a quite simple data dependence in between loops. That > said, it's quite > risky to use it.
We only have a single wrong-code bug in bugzilla with a testcase and I just fixed it (well, patch in testing). We do have plenty of ICEs, yes. Richard. > Thanks, > Martin > >> >> Thanks, >> bin >>> >>> Richard. >>> >>>> Martin >