[Bug c++/126617] New: std::map<std::vector<unsigned char>, int> stringop-overread false positive at -O1/2/3

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D126617

            Bug ID: 126617
           Summary: std::map<std::vector<unsigned char>, int>
                    stringop-overread false positive at -O1/2/3
           Product: gcc
           Version: 14.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: o.putaans at gmail dot com
  Target Milestone: ---

Created attachment 65221
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D65221&action=3Dedit
preprocessed temporary file of the minimum example

gcc -v
Using built-in specs.
COLLECT_GCC=3Dg++
COLLECT_LTO_WRAPPER=3D/usr/libexec/gcc/x86_64-linux-gnu/14/lto-wrapper
OFFLOAD_TARGET_NAMES=3Dnvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=3D1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion=3D'Ubuntu
14.2.0-4ubuntu2~24.04.1' --with-bugurl=3Dfile:///usr/share/doc/gcc-14/READM=
E.Bugs
--enable-languages=3Dc,ada,c++,go,d,fortran,objc,obj-c++,m2,rust --prefix=
=3D/usr
--with-gcc-major-version-only --program-suffix=3D-14
--program-prefix=3Dx86_64-linux-gnu- --enable-shared --enable-linker-build-=
id
--libexecdir=3D/usr/libexec --without-included-gettext --enable-threads=3Dp=
osix
--libdir=3D/usr/lib --enable-nls --enable-bootstrap --enable-clocale=3Dgnu
--enable-libstdcxx-debug --enable-libstdcxx-time=3Dyes
--with-default-libstdcxx-abi=3Dnew --enable-libstdcxx-backtrace
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --enable-libphobos-checking=3Drelea=
se
--with-target-system-zlib=3Dauto --enable-objc-gc=3Dauto --enable-multiarch
--disable-werror --enable-cet --with-arch-32=3Di686 --with-abi=3Dm64
--with-multilib-list=3Dm32,m64,mx32 --enable-multilib --with-tune=3Dgeneric
--enable-offload-targets=3Dnvptx-none=3D/build/gcc-14-FpLBWZ/gcc-14-14.2.0/=
debian/tmp-nvptx/usr,amdgcn-amdhsa=3D/build/gcc-14-FpLBWZ/gcc-14-14.2.0/deb=
ian/tmp-gcn/usr
--enable-offload-defaulted --without-cuda-driver --enable-checking=3Drelease
--build=3Dx86_64-linux-gnu --host=3Dx86_64-linux-gnu --target=3Dx86_64-linu=
x-gnu
--with-build-config=3Dbootstrap-lto-lean --enable-link-serialization=3D2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.2.0 (Ubuntu 14.2.0-4ubuntu2~24.04.1)=20

Minimum reproducible example:
```
#include <map>
#include <vector>

std::map<std::vector<unsigned char>, int> m;

int main()
{
    m[{}] =3D 1;
}

```
Compile command:
g++-14 -save-temps -O1 -std=3Dc++23 -Werror=3Dstringop-overread ../test.cpp

In file included from /usr/include/c++/14/bits/stl_tree.h:63,
                 from /usr/include/c++/14/map:62,
                 from ../test.cpp:1:
In function =E2=80=98constexpr decltype (__comp((* __first1), (* __first2)))
std::lexicographical_compare_three_way(_InputIter1, _InputIter1, _InputIter=
2,
_InputIter2, _Comp) [with _InputIter1 =3D __gnu_cxx::__normal_iterator<const
unsigned char*, vector<unsigned char> >; _InputIter2 =3D
__gnu_cxx::__normal_iterator<const unsigned char*, vector<unsigned char> >;
_Comp =3D __detail::_Synth3way]=E2=80=99,
    inlined from =E2=80=98constexpr std::__detail::__synth3way_t<_Iterator>
std::operator<=3D>(const vector<_Tp, _Alloc>&, const vector<_Tp, _Alloc>&) =
[with
_Tp =3D unsigned char; _Alloc =3D allocator<unsigned char>]=E2=80=99 at
/usr/include/c++/14/bits/stl_vector.h:2071:52,
    inlined from =E2=80=98constexpr bool std::less<_Tp>::operator()(const _=
Tp&, const
_Tp&) const [with _Tp =3D std::vector<unsigned char>]=E2=80=99 at
/usr/include/c++/14/bits/stl_function.h:405:20,
    inlined from =E2=80=98std::map<_Key, _Tp, _Compare, _Alloc>::mapped_typ=
e&
std::map<_Key, _Tp, _Compare, _Alloc>::operator[](key_type&&) [with _Key =3D
std::vector<unsigned char>; _Tp =3D int; _Compare =3D
std::less<std::vector<unsigned char> >; _Alloc =3D std::allocator<std::pair=
<const
std::vector<unsigned char>, int> >]=E2=80=99 at
/usr/include/c++/14/bits/stl_map.h:531:32,
    inlined from =E2=80=98int main()=E2=80=99 at ../test.cpp:8:9:
/usr/include/c++/14/bits/stl_algobase.h:1874:39: error: =E2=80=98int
__builtin_memcmp(const void*, const void*, long unsigned int)=E2=80=99 spec=
ified bound
[9223372036854775808, 18446744073709551615] exceeds maximum object size
9223372036854775807 [-Werror=3Dstringop-overread]
 1874 |                     =3D __builtin_memcmp(&*__first1, &*__first2, __=
blen)
<=3D> 0;
      |                       ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~=
~~~
In function =E2=80=98constexpr decltype (__comp((* __first1), (* __first2)))
std::lexicographical_compare_three_way(_InputIter1, _InputIter1, _InputIter=
2,
_InputIter2, _Comp) [with _InputIter1 =3D __gnu_cxx::__normal_iterator<const
unsigned char*, vector<unsigned char> >; _InputIter2 =3D
__gnu_cxx::__normal_iterator<const unsigned char*, vector<unsigned char> >;
_Comp =3D __detail::_Synth3way]=E2=80=99,
    inlined from =E2=80=98constexpr std::__detail::__synth3way_t<_Iterator>
std::operator<=3D>(const vector<_Tp, _Alloc>&, const vector<_Tp, _Alloc>&) =
[with
_Tp =3D unsigned char; _Alloc =3D allocator<unsigned char>]=E2=80=99 at
/usr/include/c++/14/bits/stl_vector.h:2071:52,
    inlined from =E2=80=98constexpr bool std::less<_Tp>::operator()(const _=
Tp&, const
_Tp&) const [with _Tp =3D std::vector<unsigned char>]=E2=80=99 at
/usr/include/c++/14/bits/stl_function.h:405:20,
    inlined from =E2=80=98std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_lower_bound(_Link_type, _Base_ptr, const _Key&) [with _Key =3D
std::vector<unsigned char>; _Val =3D std::pair<const std::vector<unsigned c=
har>,
int>; _KeyOfValue =3D std::_Select1st<std::pair<const std::vector<unsigned =
char>,
int> >; _Compare =3D std::less<std::vector<unsigned char> >; _Alloc =3D
std::allocator<std::pair<const std::vector<unsigned char>, int> >]=E2=80=99=
 at
/usr/include/c++/14/bits/stl_tree.h:1948:29,
    inlined from =E2=80=98std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::lower_bound(const key_type&) [with _Key =3D std::vector<unsigned c=
har>;
_Val =3D std::pair<const std::vector<unsigned char>, int>; _KeyOfValue =3D
std::_Select1st<std::pair<const std::vector<unsigned char>, int> >; _Compar=
e =3D
std::less<std::vector<unsigned char> >; _Alloc =3D std::allocator<std::pair=
<const
std::vector<unsigned char>, int> >]=E2=80=99 at
/usr/include/c++/14/bits/stl_tree.h:1267:30,
    inlined from =E2=80=98std::map<_Key, _Tp, _Compare, _Alloc>::iterator
std::map<_Key, _Tp, _Compare, _Alloc>::lower_bound(const key_type&) [with _=
Key
=3D std::vector<unsigned char>; _Tp =3D int; _Compare =3D
std::less<std::vector<unsigned char> >; _Alloc =3D std::allocator<std::pair=
<const
std::vector<unsigned char>, int> >]=E2=80=99 at
/usr/include/c++/14/bits/stl_map.h:1308:32,
    inlined from =E2=80=98std::map<_Key, _Tp, _Compare, _Alloc>::mapped_typ=
e&
std::map<_Key, _Tp, _Compare, _Alloc>::operator[](key_type&&) [with _Key =3D
std::vector<unsigned char>; _Tp =3D int; _Compare =3D
std::less<std::vector<unsigned char> >; _Alloc =3D std::allocator<std::pair=
<const
std::vector<unsigned char>, int> >]=E2=80=99 at
/usr/include/c++/14/bits/stl_map.h:529:28,
    inlined from =E2=80=98int main()=E2=80=99 at ../test.cpp:8:9:
/usr/include/c++/14/bits/stl_algobase.h:1874:39: error: =E2=80=98int
__builtin_memcmp(const void*, const void*, long unsigned int)=E2=80=99 spec=
ified bound
[9223372036854775808, 18446744073709551615] exceeds maximum object size
9223372036854775807 [-Werror=3Dstringop-overread]
 1874 |                     =3D __builtin_memcmp(&*__first1, &*__first2, __=
blen)
<=3D> 0;
      |                       ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~=
~~~
cc1plus: some warnings being treated as errors



This same code compiles if instead -O0 is specified or unsigned char is
replaced with char or unsigned int, or int.

Using Godbolt I managed to replicate this behaviour in GCC 14.4 and GCC 13.=
4=