https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105400
Bug ID: 105400
Summary: g++-11 regression produces -Warray-bounds false
positive warning with -O2
Product: gcc
Version: 11.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: laurent.pinchart at ideasonboard dot com
Target Milestone: ---
Created attachment 52887
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52887&action=edit
Test case
Starting with g++ 11, we noticed a -Warray-bounds warning when compiling the
libcamera project. I've narrowed it down to the attached standalone test case
(without any #include).
The warning is produced with the following g++ options:
$ g++-11.2.1 -v -save-temps -W -Wall -std=c++17 -O2 -c -o cast2.o cast2.cpp
Using built-in specs.
COLLECT_GCC=g++-11.2.1
Target: x86_64-pc-linux-gnu
Configured with:
/var/tmp/portage/sys-devel/gcc-11.2.1_p20220115/work/gcc-11-20220115/configure
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr
--bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/11.2.1
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/11.2.1
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/11.2.1/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/11.2.1/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/include/g++-v11
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/11.2.1/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
--with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo
11.2.1_p20220115 p4' --disable-esp --enable-libstdcxx-time
--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 --without-zstd --enable-lto --with-isl
--disable-isl-version-check --enable-default-pie --enable-default-ssp
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 11.2.1 20220115 (Gentoo 11.2.1_p20220115 p4)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wextra' '-Wall' '-std=c++17' '-O2'
'-c' '-o' 'cast2.o' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/libexec/gcc/x86_64-pc-linux-gnu/11.2.1/cc1plus -E -quiet -v -D_GNU_SOURCE
cast2.cpp -mtune=generic -march=x86-64 -std=c++17 -Wextra -Wall -O2
-fpch-preprocess -o cast2.ii
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/include/g++-v11
/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/include/g++-v11/x86_64-pc-linux-gnu
/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/include/g++-v11/backward
/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/include
/usr/local/include
/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wextra' '-Wall' '-std=c++17' '-O2'
'-c' '-o' 'cast2.o' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/libexec/gcc/x86_64-pc-linux-gnu/11.2.1/cc1plus -fpreprocessed cast2.ii
-quiet -dumpbase cast2.cpp -dumpbase-ext .cpp -mtune=generic -march=x86-64 -O2
-Wextra -Wall -std=c++17 -version -o cast2.s
GNU C++17 (Gentoo 11.2.1_p20220115 p4) version 11.2.1 20220115
(x86_64-pc-linux-gnu)
compiled by GNU C version 11.2.1 20220115, GMP version 6.2.1, MPFR
version 4.1.0-p13, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
GNU C++17 (Gentoo 11.2.1_p20220115 p4) version 11.2.1 20220115
(x86_64-pc-linux-gnu)
compiled by GNU C version 11.2.1 20220115, GMP version 6.2.1, MPFR
version 4.1.0-p13, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=30 --param ggc-min-heapsize=4096
Compiler executable checksum: 8c115abe653dbf0f6d87498ebb5d37f4
cast2.cpp: In function ‘void func()’:
cast2.cpp:25:26: warning: array subscript ‘Derived[0]’ is partly outside array
bounds of ‘Base [1]’ [-Warray-bounds]
25 | d->count = 0;
| ~~~~~~~~~^~~
cast2.cpp:36:14: note: while referencing ‘b’
36 | Base b(Base::Type2);
| ^
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wextra' '-Wall' '-std=c++17' '-O2'
'-c' '-o' 'cast2.o' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/../../../../x86_64-pc-linux-gnu/bin/as
-v --64 -o cast2.o cast2.s
GNU assembler version 2.37 (x86_64-pc-linux-gnu) using BFD version (Gentoo
2.37_p1 p2) 2.37
COMPILER_PATH=/usr/libexec/gcc/x86_64-pc-linux-gnu/11.2.1/:/usr/libexec/gcc/x86_64-pc-linux-gnu/11.2.1/:/usr/libexec/gcc/x86_64-pc-linux-gnu/:/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/:/usr/lib/gcc/x86_64-pc-linux-gnu/:/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/../../../../x86_64-pc-linux-gnu/bin/
LIBRARY_PATH=/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/:/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/../../../../x86_64-pc-linux-gnu/lib/:/usr/lib/gcc/x86_64-pc-linux-gnu/11.2.1/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wextra' '-Wall' '-std=c++17' '-O2'
'-c' '-o' 'cast2.o' '-shared-libgcc' '-mtune=generic' '-march=x86-64'
'-dumpdir' 'cast2.'
The out of bounds access is prevented by the type() check. The compiler can't
predict the outcome of the check as it doesn't know that type() will return the
type passed to the Base constructor.
