[Bug c++/109563] New: accessing 9223372036854775810 or more bytes at offsets [2, 9223372036854775807] and 1 may overlap up to 9223372036854775813 bytes at offset -3 [-Wrestrict]

["f.heckenbach@fh-soft.de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109563

            Bug ID: 109563
           Summary: accessing 9223372036854775810 or more bytes at offsets
                    [2, 9223372036854775807] and 1 may overlap up to
                    9223372036854775813 bytes at offset -3 [-Wrestrict]
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: f.heckenbach@fh-soft.de
  Target Milestone: ---

I'd like to know if the warning is bogus or the library actually accesses
invalid memory.

% cat test.cpp
#include <string>

void f (const std::string &s)
{
  "x" + std::string (s);
}
% g++ --std=c++20 -O3 -Wall -c test.cpp
In file included from /usr/include/c++/12/string:40,
                 from test.cpp:1:
In static member function ‘static constexpr std::char_traits<char>::char_type*
std::char_traits<char>::copy(char_type*, const char_type*, std::size_t)’,
    inlined from ‘static constexpr void std::__cxx11::basic_string<_CharT,
_Traits, _Alloc>::_S_copy(_CharT*, const _CharT*, size_type) [with _CharT =
char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/usr/include/c++/12/bits/basic_string.h:423:21,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Allocator>& std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::_M_replace(size_type, size_type, const _CharT*, size_type) [with
_CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.tcc:532:22,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>& std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>::replace(size_type, size_type, const _CharT*, size_type) [with _CharT =
char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at
/usr/include/c++/12/bits/basic_string.h:2171:19,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::insert(size_type,
const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:1928:22,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Allocator> std::operator+(const _CharT*, __cxx11::basic_string<_CharT,
_Traits, _Allocator>&&) [with _CharT = char; _Traits = char_traits<char>;
_Alloc = allocator<char>]’ at /usr/include/c++/12/bits/basic_string.h:3541:36,
    inlined from ‘void f(const std::string&)’ at test.cpp:5:7:
/usr/include/c++/12/bits/char_traits.h:431:56: warning: ‘void*
__builtin_memcpy(void*, const void*, long unsigned int)’ accessing
9223372036854775810 or more bytes at offsets [2, 9223372036854775807] and 1 may
overlap up to 9223372036854775813 bytes at offset -3 [-Wrestrict]
  431 |         return static_cast<char_type*>(__builtin_memcpy(__s1, __s2,
__n));
      |