https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99580
Bug ID: 99580
Summary: False positive -Warray-bounds with -O2
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: sventeam at yandex dot ru
Target Milestone: ---
Created attachment 50383
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50383&action=edit
Source to reproduce the issue
Using default GCC from Ubuntu 20.10.
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/10/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
10.2.0-13ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-10/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-10
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --enable-libphobos-checking=release
--with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
--disable-werror --with-arch-32=i686 --with-abi=m64
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-10-JvwpWM/gcc-10-10.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-10-JvwpWM/gcc-10-10.2.0/debian/tmp-gcn/usr,hsa
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.2.0 (Ubuntu 10.2.0-13ubuntu1)
$ g++ -Warray-bounds -Werror -O2 qef_solver.cpp
qef_solver.cpp: In function ‘glm::mat3 jacobi(glm::mat3)’:
qef_solver.cpp:43:19: error: array subscript 3 is above array bounds of
‘glm::mat<3, 3, float>::col_type [3]’ {aka ‘glm::vec<3, float> [3]’}
[-Werror=array-bounds]
43 | return col[i];
| ~~~^
qef_solver.cpp:52:14: note: while referencing ‘glm::mat<3, 3, float>::col’
52 | col_type col[3];
| ^~~
qef_solver.cpp:43:19: error: array subscript 3 is above array bounds of
‘glm::mat<3, 3, float>::col_type [3]’ {aka ‘glm::vec<3, float> [3]’}
[-Werror=array-bounds]
43 | return col[i];
| ~~~^
qef_solver.cpp:52:14: note: while referencing ‘glm::mat<3, 3, float>::col’
52 | col_type col[3];
| ^~~
cc1plus: all warnings being treated as errors
This warning disappears if we change -O2 to -O1, or change `int j = i + 1` in
line 77 to `int j = i`, or comment out line 82 `max_j = j`.
