[Bug c++/105329] New: Bogus restrict warning when assigning 1-char string literal to std::string

["boris at kolpackov dot net" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105329

            Bug ID: 105329
           Summary: Bogus restrict warning when assigning 1-char string
                    literal to std::string
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: boris at kolpackov dot net
  Target Milestone: ---

When compiling my codebase (build2) with GCC 12 (12.0.1 20220421) the output is
littered with new bogus (AFAICS) -Wrestrict warnings that seems to be triggered
by any attempt to assign or append a 1-char string literal to std::string:

$ cat <<EOF >bogus-restrict.cxx
#include <string>

void f (std::string& s)
{
  s = "5";
}
EOF

$ g++ -Wall -Wextra -O3 -c -std=c++23 bogus-restrict.cxx
In file included from
/home/boris/work/build2/tests/modules/gcc2/gcc-install/include/c++/12.0.1/string:40,
                 from bogus-restrict.cxx: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
/home/boris/work/build2/tests/modules/gcc2/gcc-install/include/c++/12.0.1/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
/home/boris/work/build2/tests/modules/gcc2/gcc-install/include/c++/12.0.1/bits/basic_string.tcc:532:22,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::assign(const
_CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at
/home/boris/work/build2/tests/modules/gcc2/gcc-install/include/c++/12.0.1/bits/basic_string.h:1647:19,
    inlined from ‘constexpr std::__cxx11::basic_string<_CharT, _Traits,
_Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator=(const
_CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc =
std::allocator<char>]’ at
/home/boris/work/build2/tests/modules/gcc2/gcc-install/include/c++/12.0.1/bits/basic_string.h:815:28,
    inlined from ‘void f(std::string&)’ at bogus-restrict.cxx:5:7:
/home/boris/work/build2/tests/modules/gcc2/gcc-install/include/c++/12.0.1/bits/char_traits.h:431:56:
warning: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’
accessing 9223372036854775810 or more bytes at offsets -4611686018427387902 and
[-4611686018427387903, 4611686018427387904] may overlap up to
9223372036854775813 bytes at offset -3 [-Wrestrict]
  431 |         return static_cast<char_type*>(__builtin_memcpy(__s1, __s2,
__n));
      |