https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98465
Bug ID: 98465 Summary: Bogus warning stringop-overread wuth -std=gnu++20 -O2 and std::string::insert Product: gcc Version: 11.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: romain.geissler at amadeus dot com Target Milestone: --- Hi, The following C++ code compiled with -std=gnu++20 -O2 -Werror=stringop-overread emits a bogus warning/error with gcc trunk, while it works without problem when using gnu++17 instead. Tested on compiler explorer on x64 Linux: #include <string> const char constantString[] = {42, 53}; void f(std::string& s) { s.insert(0, static_cast<const char*>(constantString), 2); } In file included from /opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/string:40, from <source>:1: In static member function 'static constexpr std::char_traits<char>::char_type* std::char_traits<char>::copy(std::char_traits<char>::char_type*, const char_type*, std::size_t)', inlined from 'static void std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_S_copy(_CharT*, const _CharT*, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.h:351:21, inlined from 'static void std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_S_copy(_CharT*, const _CharT*, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.h:346:7, inlined from 'std::__cxx11::basic_string<_CharT, _Traits, _Allocator>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_M_replace(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, const _CharT*, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.tcc:481:20, inlined from 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::replace(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, const _CharT*, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.h:1946:19, inlined from 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::insert(std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type, const _CharT*, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]' at /opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/basic_string.h:1693:29, inlined from 'void f(std::string&)' at <source>:7:60: /opt/compiler-explorer/gcc-trunk-20201228/include/c++/11.0.0/bits/char_traits.h:402:56: error: 'void* __builtin_memcpy(void*, const void*, long unsigned int)' reading 2 bytes from a region of size 0 [-Werror=stringop-overread] 402 | return static_cast<char_type*>(__builtin_memcpy(__s1, __s2, __n)); | ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~ <source>: In function 'void f(std::string&)': <source>:3:12: note: at offset 2 into source object 'constantString' of size 2 3 | const char constantString[] = {42, 53}; | ^~~~~~~~~~~~~~ cc1plus: some warnings being treated as errors Compiler returned: 1 Note that gcc 10 doesn't issue any warning even with -Wall -Wextra with gnu++20. Cheers, Romain