> On May 4, 2023, at 9:05 AM, Martin Liška <mli...@suse.cz> wrote: > > On 5/4/23 14:54, Qing Zhao wrote: >> >> >>> On May 4, 2023, at 4:30 AM, Martin Liška <mli...@suse.cz> wrote: >>> >>> On 5/3/23 21:10, Qing Zhao via Gcc-patches wrote: >>>> Hi, Jan, >>>> >>>> You added the following patch into gcc10: >>>> >>>> From 34fbe3f0946f88828765184ed6581bda62cdf49f Mon Sep 17 00:00:00 2001 >>>> From: Jan Hubicka <hubi...@ucw.cz> >>>> Date: Thu, 5 Dec 2019 19:12:51 +0100 >>>> Subject: [PATCH] cgraphclones.c (localize_profile): New function. >>>> >>>> * cgraphclones.c (localize_profile): New function. >>>> (cgraph_node::create_clone): Use it for partial profiles. >>>> * common.opt (fprofile-partial-training): New flag. >>>> * doc/invoke.texi (-fprofile-partial-training): Document. >>>> * ipa-cp.c (update_profiling_info): For partial profiles do not >>>> set function profile to zero. >>>> * profile.c (compute_branch_probabilities): With partial profile >>>> watch if edge count is zero and turn all probabilities to guessed. >>>> (compute_branch_probabilities): For partial profiles do not apply >>>> profile when entry count is zero. >>>> * tree-profile.c (tree_profiling): Only do >>>> value_profile_transformations >>>> when profile is read. >>>> >>>> My question is: >>> >>> Hello. >>> >>> Why would anybody backport such change to unsupported code-stream of GCC 8? >>> Generally speaking, I discourage from doing that. >> >> Yes, I agree. >> However, many users still use GCC8 right now, and some of them are asking >> for more performance >> from PGO recently. That’s the reason I am studying this right now. > > I understand there are products that are based on GCC8, but as the branch is > officially unsupported, I don't > see a reason to backport a new feature from newer release. It's just asking > for troubles. If your clients are > interested in more performance, then they should use a recent supported > release. We are trying to persuade them to use newer GCC, but it’s quite hard... > >> >> From my understanding, -fprofile-partial-training is one important option >> for PGO performance. > > I don't think so, speed benefit would be rather small I guess. I saw some articles online to introduce this option for gcc10, https://documentation.suse.com/sbp/all/html/SBP-GCC-10/index.html#sec-gcc10-pgo And also based on my previous experience in Studio compiler, I guess that this one might have Some good performance impact on PGO. Is there any old performance data on this option? (I cannot find online)
thanks. Qing > >> I’d like >> to see any big technique difficult to prevent it from being back ported to >> GCC8. > > There might be of course some patch dependencies and I don't see a point why > should we waste > time with that. > > Cheers, > Martin > >> >> Thanks. >> >> Qing >> >>> >>> Martin >>> >>>> >>>> Can this patch be back ported to GCC8 easily? I am wondering any >>>> significant >>>> Change between GCC8 and GCC10 that might make the backporting very hard> >>>> Thanks a lot for your help. >>>> >>>> Qing
