[Bug rtl-optimization/121757] [15/16 Regression] ICE in rtl_ssa::clobber_info::recompute_group

[sjames at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121757

--- Comment #4 from Sam James <sjames at gcc dot gnu.org> ---
Created attachment 62295
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=62295&action=edit
unity_0_cxx.cxx.ii

```
$ g++ -O2 unity_0_cxx.cxx.ii -shared -flto
during RTL pass: late_combine
unity_0_cxx.cxx.ii: In member function ‘seek’:
unity_0_cxx.cxx.ii:58:1: internal compiler error: in recompute_group, at
rtl-ssa/accesses.cc:53
   58 | }
      | ^
0x15a23c7 diagnostics::context::diagnostic_impl(rich_location*,
diagnostics::metadata const*, diagnostics::option_id, char const*,
std::__va_list*, diagnostics::kind)
        ???:0
0x1481c67 internal_error(char const*, ...)
        ???:0
0x1481f23 fancy_abort(char const*, int, char const*)
        ???:0
0x2c33edb rtl_ssa::clobber_info::recompute_group()
        ???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://bugs.gentoo.org/> for instructions.
lto-wrapper: fatal error: g++ returned 1 exit status
compilation terminated.
/usr/lib/gcc/armv7a-unknown-linux-gnueabihf/16/../../../../armv7a-unknown-linux-gnueabihf/bin/ld:
error: lto-wrapper failed
collect2: error: ld returned 1 exit status
```

```

Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/armv7a-unknown-linux-gnueabihf/16/lto-wrapper
Target: armv7a-unknown-linux-gnueabihf
Configured with:
/var/tmp/portage/sys-devel/gcc-16.0.9999/work/gcc-16.0.9999/configure
--host=armv7a-unknown-linux-gnueabihf --build=armv7a-unknown-linux-gnueabihf
--prefix=/usr --bindir=/usr/armv7a-unknown-linux-gnueabihf/gcc-bin/16
--includedir=/usr/lib/gcc/armv7a-unknown-linux-gnueabihf/16/include
--datadir=/usr/share/gcc-data/armv7a-unknown-linux-gnueabihf/16
--mandir=/usr/share/gcc-data/armv7a-unknown-linux-gnueabihf/16/man
--infodir=/usr/share/gcc-data/armv7a-unknown-linux-gnueabihf/16/info
--with-gxx-include-dir=/usr/lib/gcc/armv7a-unknown-linux-gnueabihf/16/include/g++-v16
--disable-silent-rules --disable-dependency-tracking
--with-python-dir=/share/gcc-data/armv7a-unknown-linux-gnueabihf/16/python
--enable-libphobos --enable-objc-gc
--enable-languages=c,c++,d,objc,obj-c++,fortran,ada,rust --enable-obsolete
--enable-secureplt --disable-werror --with-system-zlib --enable-nls
--without-included-gettext --disable-libunwind-exceptions
--enable-checking=yes,extra,rtl --with-bugurl=https://bugs.gentoo.org/
--with-pkgversion='Gentoo 16.0.9999 p, commit
b40afae619f7e54eebfaccd612ca27b0c2c8eb8a' --with-gcc-major-version-only
--enable-libstdcxx-time --enable-lto --disable-libstdcxx-pch --enable-shared
--enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu
--disable-multilib --disable-fixed-point --with-float=hard --with-arch=armv7-a
--with-float=hard --with-fpu=vfpv3-d16 --enable-libgomp --disable-libssp
--enable-libada --disable-systemtap --disable-valgrind-annotations
--disable-vtable-verify --disable-libvtv --with-zstd --with-isl
--disable-isl-version-check --enable-default-pie --enable-host-pie
--enable-host-bind-now --enable-default-ssp --disable-fixincludes
--with-gxx-libcxx-include-dir=/usr/include/c++/v1
--with-build-config='bootstrap-O3 bootstrap-lto'
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 16.0.0 20250831 (experimental)
af979624128b24303c2e29b3f2535445877056ec (Gentoo 16.0.9999 p, commit
b40afae619f7e54eebfaccd612ca27b0c2c8eb8a)
```