On Fri, Aug 1, 2014 at 10:10 PM, Teresa Johnson <tejohn...@google.com> wrote: > On Wed, Jul 23, 2014 at 2:08 PM, Teresa Johnson <tejohn...@google.com> wrote: >> On Tue, Jul 22, 2014 at 7:29 PM, Jeff Law <l...@redhat.com> wrote: >>> On 03/26/14 17:44, Teresa Johnson wrote: >>>> >>>> Recently I discovered that the profile updates being performed by jump >>>> threading were incorrect in many cases, particularly in the case where >>>> the threading path contains a joiner. Some of the duplicated >>>> blocks/edges were not getting any counts, leading to incorrect >>>> function splitting and other downstream optimizations, and there were >>>> other insanities as well. After making a few attempts to fix the >>>> handling I ended up completely redesigning the profile update code, >>>> removing a few places throughout the code where it was attempting to >>>> do some updates. >>>> >>>> The biggest complication (see the large comment and example above the >>>> new routine compute_path_counts) is that we duplicate a conditional >>>> jump in the joiner case, possibly multiple times for multiple jump >>>> thread paths through that joiner, and it isn't trivial to figure out >>>> what probability to assign each of the duplicated successor edges (and >>>> the original after threading). Each jump thread path may need to have >>>> a different probability of staying on path through the joiner in order >>>> to keep the counts going out of the threading path sane. >>>> >>>> The patch below was bootstrapped and tested on >>>> x86_64-unknown-linux-gnu, and also tested with a profiledbootstrap. I >>>> additionally tested with cpu2006, confirming that the amount of >>>> resulting cycle samples in the split cold sections reduced, and >>>> through manual inspection that many different cases were now correct. >>>> I also measured performance with cpu2006, running each benchmark >>>> multiple times on a Westmere and see some speedups (453.povray 1-2%, >>>> 403.gcc 1-1.5%, and noisy but positive speedups in 471.omnetpp and >>>> 483.xalancbmk). >>>> >>>> Looks like my mailer is corrupting the spacing, which makes it harder >>>> to look at the CFG examples in the big header comment block I added. >>>> So I have also included the patch as an attachment. >>>> >>>> Ok for stage 1? >>>> >>>> Thanks, >>>> Teresa >>>> >>>> 2014-03-26 Teresa Johnson <tejohn...@google.com> >>>> >>>> * tree-ssa-threadupdate.c (struct ssa_local_info_t): New >>>> duplicate_blocks bitmap. >>>> (remove_ctrl_stmt_and_useless_edges): Ditto. >>>> (create_block_for_threading): Ditto. >>>> (compute_path_counts): New function. >>>> (update_profile): Ditto. >>>> (deduce_freq): Ditto. >>>> (recompute_probabilities): Ditto. >>>> (update_joiner_offpath_counts): Ditto. >>>> (ssa_fix_duplicate_block_edges): Update profile info. >>>> (ssa_create_duplicates): Pass new parameter. >>>> (ssa_redirect_edges): Remove old profile update. >>>> (thread_block_1): New duplicate_blocks bitmap, >>>> remove old profile update. >>>> (thread_single_edge): Pass new parameter. >>> >>> First off, sorry this took so long to get reviewed. >>> >>> Most of what's going on in here is similar to something I sketched out, but >>> never coded up a while back -- with the significant difference that you're >>> handling joiner blocks as well. >>> >>> Everything looks to be well thought through and documented in the code at a >>> level I wish existed throughout GCC. >>> >>> The only thing I see missing is regression tests. I don't think you need to >>> do anything huge here, but it ought to be possible to set up relatively >>> simple cases which show the probabilities/counts being updated properly. >>> >>> Otherwise it looks excellent. It's pre-approved once you've added some kind >>> of testing and fixed the nits noted below. >> >> Thanks! I will fix the issues you note below and create some test >> cases before I commit. > > Just an update - I found some good test cases by compiling the > c-torture tests with profile feedback with and without my patch. But > in the cases I pulled out I saw that there were still a couple profile > or probability insanities introduced by jump threading (albeit far > less than before), so I wanted to investigate before I commit. I ran > out of time this week and will not get to this until I get back from > vacation the week after next.
Another one to try is https://gcc.gnu.org/bugzilla/show_bug.cgi?id=22401 . Jeff and I are hoping your changes fix this one too. Thanks, Andrew Pinski > > Teresa > >> Teresa >> >>> >>> >>> >>>> + In the aboe example, after all jump threading is complete, we will >>> >>> s/aboe/above/ >>> >>> >>> >>>> + struct el *next, *el; >>>> + bitmap in_edge_srcs = BITMAP_ALLOC (NULL); >>>> + for (el = rd->incoming_edges; el; el = next) >>>> + { >>>> + next = el->next; >>>> + bitmap_set_bit (in_edge_srcs, el->e->src->index); >>>> + } >>> >>> Please add vertical whitespace after this loop, but before declaring >>> variables for the next loop. >>> >>> Jeff >>> >> >> >> >> -- >> Teresa Johnson | Software Engineer | tejohn...@google.com | 408-460-2413 > > > > -- > Teresa Johnson | Software Engineer | tejohn...@google.com | 408-460-2413
