[Bug middle-end/116330] New: -fcompare-debug -gno-statement-frontiers failure with -O3 -march=znver3 -mshstk when building qtbase-6.7.2

[Bug middle-end/116330] New: -fcompare-debug -gno-statement-frontiers failure with -O3 -march=znver3 -mshstk when building qtbase-6.7.2

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116330

            Bug ID: 116330
           Summary: -fcompare-debug -gno-statement-frontiers failure with
                    -O3 -march=znver3 -mshstk when building qtbase-6.7.2
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sjames at gcc dot gnu.org
  Target Milestone: ---

Note that this is from a unity/jumbo build. Unfortunately, disabling it made
the bug go away.

Need `-march=znver3 -mshstk`, see PR116045 for that.

```
$ g++
../qtbase-everywhere-src-6.7.2_build/src/network/CMakeFiles/Network.dir/Unity/unity_1_cxx.cxx.ii
-march=znver3 -mshstk -O3 -fcompare-debug -gno-statement-frontiers -c
g++: error:
../qtbase-everywhere-src-6.7.2_build/src/network/CMakeFiles/Network.dir/Unity/unity_1_cxx.cxx.ii:
‘-fcompare-debug’ failure
```

```
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/15/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with:
/var/tmp/portage/sys-devel/gcc-15.0.9999/work/gcc-15.0.9999/configure
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr
--bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/15
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/15/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/15
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/15/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/15/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/15/include/g++-v15
--disable-silent-rules --disable-dependency-tracking
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/15/python
--enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt
--disable-werror --with-system-zlib --enable-nls --without-included-gettext
--disable-libunwind-exceptions --enable-checking=yes,extra,rtl,df
--with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 15.0.9999 p,
commit ecc3ba06c22edee6b22d2e8e5e05031d18fa372a' --with-gcc-major-version-only
--enable-libstdcxx-time --enable-lto --disable-libstdcxx-pch --enable-shared
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
--enable-multilib --with-multilib-list=m32,m64 --disable-fixed-point
--enable-targets=all --enable-libgomp --disable-libssp --disable-libada
--disable-cet --disable-systemtap --disable-valgrind-annotations
--disable-vtable-verify --disable-libvtv --with-zstd --without-isl
--enable-default-pie --enable-host-pie --disable-host-bind-now
--enable-default-ssp --disable-fixincludes --with-build-config='bootstrap-O3
bootstrap-lto'
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 15.0.0 20240810 (experimental)
8035619b7313d9503852e1c7c8c06cfddca4d648 (Gentoo 15.0.9999 p, commit
ecc3ba06c22edee6b22d2e8e5e05031d18fa372a)
```

[Bug middle-end/116330] -fcompare-debug -gno-statement-frontiers failure with -O3 -march=znver3 -mshstk when building qtbase-6.7.2

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116330

--- Comment #1 from Sam James <sjames at gcc dot gnu.org> ---
Created attachment 58900
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58900&action=edit
unity_1_cxx.cxx.ii.xz

[Bug middle-end/116330] -fcompare-debug -gno-statement-frontiers failure with -O3 -march=znver3 -mshstk when building qtbase-6.7.2

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116330

--- Comment #2 from Sam James <sjames at gcc dot gnu.org> ---
I'll kick off a reduction.

[Bug middle-end/116330] -fcompare-debug -gno-statement-frontiers failure with -O3 -march=znver3 -mshstk when building qtbase-6.7.2

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116330

--- Comment #3 from Sam James <sjames at gcc dot gnu.org> ---
Created attachment 58906
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58906&action=edit
unity_1_cxx-partial.cxx.ii.xz

Reducing this is painful so far.

Partial reduction (not cancelled it) attached.