https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121791
--- Comment #2 from Sam James <sjames at gcc dot gnu.org> ---
```
make[3]: Entering directory '/mnt/ramdisk/bld/gcc-15to16/gcc'
/mnt/ramdisk/bld/gcc-15to16/./prev-gcc/xg++
-B/mnt/ramdisk/bld/gcc-15to16/./prev-gcc/
-B/opt/gcc-16/x86_64-pc-linux-gnu/bin/ -nostdinc++
-B/mnt/ramdisk/bld/gcc-15to16/prev-x86_64-pc-linux-gnu/libstdc++-v3/src/.libs
-B/mnt/ramdisk/bld/gcc-15to16/prev-x86_64-pc-linux-gnu/libstdc++-v3/libsupc++/.libs
-I/mnt/ramdisk/bld/gcc-15to16/prev-x86_64-pc-linux-gnu/libstdc++-v3/include/x86_64-pc-linux-gnu
-I/mnt/ramdisk/bld/gcc-15to16/prev-x86_64-pc-linux-gnu/libstdc++-v3/include
-I/mnt/ramdisk/src/gcc/libstdc++-v3/libsupc++
-L/mnt/ramdisk/bld/gcc-15to16/prev-x86_64-pc-linux-gnu/libstdc++-v3/src/.libs
-L/mnt/ramdisk/bld/gcc-15to16/prev-x86_64-pc-linux-gnu/libstdc++-v3/libsupc++/.libs
-fno-PIE -c -g -O2 -fno-checking -gtoggle -fprofile-generate -DIN_GCC
-fno-exceptions -fno-rtti -fasynchronous-unwind-tables -W -Wall
-Wno-error=narrowing -Wwrite-strings -Wcast-qual -Wmissing-format-attribute
-Wconditionally-supported -Woverloaded-virtual -pedantic -Wno-long-long
-Wno-variadic-macros -Wno-overlength-strings -Werror -DHAVE_CONFIG_H -fno-PIE
-I. -I. -I../../../src/gcc/gcc -I../../../src/gcc/gcc/.
-I../../../src/gcc/gcc/../include -I../../../src/gcc/gcc/../libcpp/include
-I../../../src/gcc/gcc/../libcody -I/mnt/ramdisk/bld/gcc-15to16/./gmp
-I/mnt/ramdisk/src/gcc/gmp -I/mnt/ramdisk/bld/gcc-15to16/./mpfr/src
-I/mnt/ramdisk/src/gcc/mpfr/src -I/mnt/ramdisk/src/gcc/mpc/src
-I../../../src/gcc/gcc/../libdecnumber
-I../../../src/gcc/gcc/../libdecnumber/bid -I../libdecnumber
-I../../../src/gcc/gcc/../libbacktrace
-I/mnt/ramdisk/bld/gcc-15to16/./isl/include -I/mnt/ramdisk/src/gcc/isl/include
-o simplify-rtx.o -MT simplify-rtx.o -MMD -MP -MF ./.deps/simplify-rtx.TPo
../../../src/gcc/gcc/simplify-rtx.cc
In file included from ../../../src/gcc/gcc/coretypes.h:500,
from ../../../src/gcc/gcc/simplify-rtx.cc:23:
../../../src/gcc/gcc/simplify-rtx.cc: In member function ‘rtx_def*
simplify_context::simplify_subreg(machine_mode, rtx, machine_mode,
poly_uint64)’:
../../../src/gcc/gcc/simplify-rtx.cc:8388:48: error: ‘*(unsigned
int*)((char*)&int_outermode + offsetof(scalar_int_mode,
scalar_int_mode::m_mode))’ may be used uninitialized
[-Werror=maybe-uninitialized]
8388 | && known_eq (byte, subreg_lowpart_offset (int_outermode,
int_innermode)))
|
~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../src/gcc/gcc/poly-int.h:1248:39: note: in definition of macro
‘known_eq’
1248 | #define known_eq(A, B) (!maybe_ne (A, B))
| ^
../../../src/gcc/gcc/simplify-rtx.cc:8359:19: note: ‘*(unsigned
int*)((char*)&int_outermode + offsetof(scalar_int_mode,
scalar_int_mode::m_mode))’ was declared here
8359 | scalar_int_mode int_outermode, int_innermode;
| ^~~~~~~~~~~~~
cc1plus: all warnings being treated as errors
``
With profiledbootstrap, we recommend --disable-werror.
