https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110620
--- Comment #3 from Chris Uzdavinis <cuzdav at gmail dot com> --- Starting with Gcc12.1 (at least on x86) and through all versions up to the trunk (post 13.1) This warning hits with optimization -O2 or higher. https://godbolt.org/z/q3T39Wf8c #include <vector> void foo(std::vector<std::pair<int,int>>& vec) { if (vec.size() > 5) { vec[3].first = 0; } } int main() { auto v1 = std::vector{std::pair(1, 2)}; foo(v1); } What is interesting to me is that the analyzer is missing the fact that size is explicitly tested, and the index is a constant expression that is lower. There are a lot of array-bounds bugs reported, and all have similarities and I'm not sure if this is a dupe or not, though I went through the open ones in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56456 And did not see an example quite like this. In function 'void foo(std::vector<std::pair<int, int> >&)', inlined from 'int main()' at <source>:11:8: <source>:5:22: error: array subscript 3 is outside array bounds of 'std::pair<int, int> [1]' [-Werror=array-bounds=] 5 | vec[3].first = 0; In file included from /opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/x86_64-linux-gnu/bits/c++allocator.h:33, from /opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/bits/allocator.h:46, from /opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/vector:63, from <source>:1: In member function '_Tp* std::__new_allocator<_Tp>::allocate(size_type, const void*) [with _Tp = std::pair<int, int>]', inlined from 'constexpr _Tp* std::allocator< <template-parameter-1-1> >::allocate(std::size_t) [with _Tp = std::pair<int, int>]' at /opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/bits/allocator.h:198:40, inlined from 'static constexpr _Tp* std::allocator_traits<std::allocator<_Up> >::allocate(allocator_type&, size_type) [with _Tp = std::pair<int, int>]' at /opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/bits/alloc_traits.h:482:28, inlined from 'constexpr std::_Vector_base<_Tp, _Alloc>::pointer std::_Vector_base<_Tp, _Alloc>::_M_allocate(std::size_t) [with _Tp = std::pair<int, int>; _Alloc = std::allocator<std::pair<int, int> >]' at /opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/bits/stl_vector.h:378:33, inlined from 'constexpr void std::vector<_Tp, _Alloc>::_M_range_initialize(_ForwardIterator, _ForwardIterator, std::forward_iterator_tag) [with _ForwardIterator = const std::pair<int, int>*; _Tp = std::pair<int, int>; _Alloc = std::allocator<std::pair<int, int> >]' at /opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/bits/stl_vector.h:1687:25, inlined from 'constexpr std::vector<_Tp, _Alloc>::vector(std::initializer_list<_Tp>, const allocator_type&) [with _Tp = std::pair<int, int>; _Alloc = std::allocator<std::pair<int, int> >]' at /opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/bits/stl_vector.h:677:21, inlined from 'int main()' at <source>:10:42: /opt/compiler-explorer/gcc-13.1.0/include/c++/13.1.0/bits/new_allocator.h:147:55: note: at offset 24 into object of size 8 allocated by 'operator new' 147 | return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(__n * sizeof(_Tp))); | ^ cc1plus: all warnings being treated as errors Compiler returned: 1
