Re: [RFA] Minor improvement to coremark, avoid unconditional jump to return

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Oct 7, 2022 at 12:51 PM Franz Sirl
<Franz.Sirl-kernel@lauterbach.com> 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:

Can you open a bugreport please?

> 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.
>