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List:       gcc-patches
Subject:    Re: [RFA] Minor improvement to coremark, avoid unconditional jump to return
From:       Franz Sirl <Franz.Sirl-kernel () lauterbach ! com>
Date:       2022-10-07 15:11:21
Message-ID: 858efa95-95be-7143-0c9e-cbc6673fa03c () lauterbach ! com
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Am 2022-10-07 um 16:13 schrieb Jeff Law:
> 
> On 10/7/22 04:51, Franz Sirl wrote:
> > Am 2022-09-25 um 18:28 schrieb Jeff Law:
> > > This is a minor improvement for the core_list_find routine in coremark.
> > > 
> > > 
> > > Basically for riscv, and likely other targets, we can end up with an 
> > > unconditional jump to a return statement.    This is a result of 
> > > compensation code created by bb-reorder, and no jump optimization 
> > > pass runs after bb-reorder to clean this stuff up.
> > > 
> > > This patch utilizes preexisting code to identify suitable branch 
> > > targets as well as preexisting code to emit a suitable return, so 
> > > it's pretty simple.  Note that when we arrange to do this 
> > > optimization, the original return block may become unreachable. So we 
> > > conditionally call delete_unreachable_blocks to fix that up.
> > > 
> > > This triggers ~160 times during an x86_64 bootstrap.  Naturally it 
> > > bootstraps and regression tests on x86_64.
> > > 
> > > I've also bootstrapped this on riscv64, regression testing with qemu 
> > > shows some regressions, but AFAICT they're actually qemu bugs with 
> > > signal handling/delivery -- qemu user mode emulation is not 
> > > consistently calling user defined signal handlers.  Given the same 
> > > binary, sometimes they'll get called and the test passes, other times 
> > > the handler isn't called and the test (of course) fails. I'll 
> > > probably spend some time to try and chase this down for the sake of 
> > > making testing easier.
> > > 
> > > 
> > > OK for the trunk?
> > 
> > Hello Jeff,
> > 
> > I've bisected this change to break a "profiledbootstrap" on x86_64 
> > like that:
> > 
> > make[3]: Entering directory 
> > '/home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/obj-x86_64-suse-linux/gcc'
> > /home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/obj-x86_64-suse-linux/./prev-gcc/xg++ \
> > -B/home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/obj-x86_64-suse-linux/./prev-gcc/ \
> > -B/usr/x86_64-suse-linux/ bin/ -nostdinc++ 
> > -B/home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/obj-x86_64-suse-linux/prev-x86_64-suse-linux/libstdc++-v3/src/.libs \
> >                 -B/home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/obj-x86_64
> > -suse-linux/prev-x86_64-suse-linux/libstdc++-v3/libsupc++/.libs 
> > -I/home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/obj-x86_64-suse-linux/prev-x86_64-suse-linux/libstdc++-v3/include/x86_64-suse-linu
> >  x 
> > -I/home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/obj-x86_64-suse-linux/prev-x86_64-suse-linux/libstdc++-v3/include
> >                 
> > -I/home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/libstdc++-v3/libsupc++ -L
> > /home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/obj-x86_64-suse-linux/prev-x86_64-suse-linux/libstdc++-v3/src/.libs \
> > -L/home/fsirl/rpmbuild/BUILD/gcc-13.0.0+gitr13+2871/obj-x86_64-suse-linux/prev-x8 \
> >                 6_64-suse-linux/libstdc++-v3/libsupc++/.libs  -fno-PIE -c   -O2 \
> >                 -g 
> > -fmessage-length=0 -D_FORTIFY_SOURCE=2 -funwind-tables 
> > -fasynchronous-unwind-tables -U_FORTIFY_SOURCE -fprofile-use 
> > -fprofile-reprod
> > ucible=parallel-runs -DIN_GCC     -fno-exceptions -fno-rtti 
> > -fasynchronous-unwind-tables -W -Wall -Wno-narrowing -Wwrite-strings 
> > -Wcast-qual -Wmissing-format-attribute -Woverloaded-virtual -pedantic
> > -Wno-long-long -Wno-variadic-macros -Wno-overlength-strings 
> > -fno-common -DHAVE_CONFIG_H -I. -I. -I../../gcc -I../../gcc/. 
> > -I../../gcc/../include -I../../gcc/../libcpp/include 
> > -I../../gcc/../libcody
> > -I../../gcc/../libdecnumber -I../../gcc/../libdecnumber/bid 
> > -I../libdecnumber -I../../gcc/../libbacktrace   -o cgraph.o -MT 
> > cgraph.o -MMD -MP -MF ./.deps/cgraph.TPo ../../gcc/cgraph.cc
> > ../../gcc/cgraph.cc: In member function 'cgraph_edge* 
> > cgraph_edge::first_speculative_call_target()':
> > ../../gcc/cgraph.cc:1166:1: error: EDGE_CROSSING incorrectly set 
> > across same section
> > 1166 | }
> > > ^
> > ../../gcc/cgraph.cc:1166:1: error: No region crossing jump at section 
> > boundary in bb 19
> > during RTL pass: bbro
> > ../../gcc/cgraph.cc:1166:1: internal compiler error: verify_flow_info 
> > failed
> > 0xa7116e verify_flow_info()
> > ../../gcc/cfghooks.cc:284
> > 0x1c64958 execute
> > ../../gcc/bb-reorder.cc:2663
> > 
> > In such a case, what do you need to reproduce it? I'm a mere user of 
> > the Suse RPM builds here, no idea if profiling needs any extra data to 
> > reproduce to bug.
> 
> Franz, it's been a long time.  Good to hear from you.
> 
> 
> I'll take a look.  I'll start with a profiledbootstrap and if that 
> doesn't reproduce I'll get in contact

Yes, long time... Things happened :-) But I'm still following GCC and 
report bugs as time permits.

I've opened 107182 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107182 
with the -freport-bug file and cgraph.gcda. I hope this is enough to 
reproduce.

Franz.


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