https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113239
Bug ID: 113239
Summary: [13 regression] After 822a11a1e64, bogus
-Warray-bounds warnings in std::vector
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dimi...@unified-streaming.com
Target Milestone: ---
We noticed spurious warnings in some C++17 code compiled with g++ 13.2.0, and I
bisected it to commit 822a11a1e642e0abe92a996e7033a5066905a447 ("libstdc++: Do
not use memmove for 1-element ranges [PR108846]") for bug 108846 ("std::copy,
std::copy_n and std::copy_backward on potentially overlapping subobjects").
Reduced test case:
// g++ -std=c++17 -Wall -O2 -c testcase.cpp
#include <cstdint>
#include <vector>
struct frame_t
{
uint64_t pts_;
uint32_t timescale_;
std::vector<uint8_t> data_;
};
struct frame_source_t
{
virtual frame_t get() = 0;
};
struct frame_filter_t : frame_source_t
{
frame_t get() override
{
if(current_frame_.data_.empty())
{
return current_frame_;
}
else
{
return frame_t();
}
}
frame_t current_frame_;
};
frame_filter_t create_frame_filter()
{
return frame_filter_t();
}
// EOT
With gcc-13-6371-ga41a56dee5c, this compiles without any warning. With
gcc-13-6372-g822a11a1e64 and later, up to gcc-14-6924-g00dea7e8c41 (master as
of 2024-01-04), you get:
In file included from
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/vector:62,
from testcase.cpp:5:
In static member function 'static void std::__copy_move<false, false,
std::random_access_iterator_tag>::__assign_one(_Tp*, _Up*) [with _Tp = unsigned
char; _Up = const unsigned char]',
inlined from 'static _Up* std::__copy_move<_IsMove, true,
std::random_access_iterator_tag>::__copy_m(_Tp*, _Tp*, _Up*) [with _Tp = const
unsigned char; _Up = unsigned char; bool _IsMove = false]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_algobase.h:441:20,
inlined from '_OI std::__copy_move_a2(_II, _II, _OI) [with bool _IsMove =
false; _II = const unsigned char*; _OI = unsigned char*]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_algobase.h:507:30,
inlined from '_OI std::__copy_move_a1(_II, _II, _OI) [with bool _IsMove =
false; _II = const unsigned char*; _OI = unsigned char*]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_algobase.h:534:42,
inlined from '_OI std::__copy_move_a(_II, _II, _OI) [with bool _IsMove =
false; _II = __gnu_cxx::__normal_iterator<const unsigned char*, vector<unsigned
char> >; _OI = unsigned char*]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_algobase.h:541:31,
inlined from '_OI std::copy(_II, _II, _OI) [with _II =
__gnu_cxx::__normal_iterator<const unsigned char*, vector<unsigned char> >; _OI
= unsigned char*]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_algobase.h:637:7,
inlined from 'static _ForwardIterator
std::__uninitialized_copy<true>::__uninit_copy(_InputIterator, _InputIterator,
_ForwardIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<const
unsigned char*, std::vector<unsigned char> >; _ForwardIterator = unsigned
char*]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_uninitialized.h:147:27,
inlined from '_ForwardIterator std::uninitialized_copy(_InputIterator,
_InputIterator, _ForwardIterator) [with _InputIterator =
__gnu_cxx::__normal_iterator<const unsigned char*, vector<unsigned char> >;
_ForwardIterator = unsigned char*]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_uninitialized.h:185:15,
inlined from '_ForwardIterator std::__uninitialized_copy_a(_InputIterator,
_InputIterator, _ForwardIterator, allocator<_Tp>&) [with _InputIterator =
__gnu_cxx::__normal_iterator<const unsigned char*, vector<unsigned char> >;
_ForwardIterator = unsigned char*; _Tp = unsigned char]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_uninitialized.h:373:37,
inlined from 'std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp,
_Alloc>&) [with _Tp = unsigned char; _Alloc = std::allocator<unsigned char>]'
at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_vector.h:603:31,
inlined from 'frame_t::frame_t(const frame_t&)' at testcase.cpp:7:8,
inlined from 'virtual frame_t frame_filter_t::get()' at testcase.cpp:25:14:
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_algobase.h:399:17:
warning: array subscript 0 is outside array bounds of 'unsigned char [0]'
[-Warray-bounds=]
399 | { *__to = *__from; }
| ~~~~~~^~~~~~~~~
In file included from
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/x86_64-pc-linux-gnu/bits/c++allocator.h:33,
from
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/allocator.h:46,
from
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/vector:63:
In member function '_Tp* std::__new_allocator<_Tp>::allocate(size_type, const
void*) [with _Tp = unsigned char]',
inlined from 'static _Tp* std::allocator_traits<std::allocator<_Tp1>
>::allocate(allocator_type&, size_type) [with _Tp = unsigned char]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/alloc_traits.h:475:28,
inlined from 'std::_Vector_base<_Tp, _Alloc>::pointer
std::_Vector_base<_Tp, _Alloc>::_M_allocate(std::size_t) [with _Tp = unsigned
char; _Alloc = std::allocator<unsigned char>]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_vector.h:377:33,
inlined from 'void std::_Vector_base<_Tp,
_Alloc>::_M_create_storage(std::size_t) [with _Tp = unsigned char; _Alloc =
std::allocator<unsigned char>]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_vector.h:395:44,
inlined from 'std::_Vector_base<_Tp, _Alloc>::_Vector_base(std::size_t,
const allocator_type&) [with _Tp = unsigned char; _Alloc =
std::allocator<unsigned char>]' at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_vector.h:331:26,
inlined from 'std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp,
_Alloc>&) [with _Tp = unsigned char; _Alloc = std::allocator<unsigned char>]'
at
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/stl_vector.h:600:61,
inlined from 'frame_t::frame_t(const frame_t&)' at testcase.cpp:7:8,
inlined from 'virtual frame_t frame_filter_t::get()' at testcase.cpp:25:14:
/home/dim/ins/gcc-14-6924-g00dea7e8c41/include/c++/14.0.0/bits/new_allocator.h:151:55:
note: object of size 0 allocated by 'operator new'
151 | return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n *
sizeof(_Tp)));
| ^
I think these warnings might be bogus, since it seems to be complaining about
copying an empty std::vector<uint8_t> here?
It might also get confused due to the padding inserted between the
frame_t::pts_ and frame_t::timescale_ members, since if you remove either of
these members, the warning goes away.
