https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114385
Bug ID: 114385 Summary: -Wrestrict false positive creating std::string from iterators Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: wsf at fultondesigns dot co.uk Target Milestone: --- Observed in gcc-13.1.0, 13.2.0, gcc-14 (gcc-trunk-20240318). Minimal testcase: #include <string> template< class String_type > String_type substitute_esc_chars( typename String_type::const_iterator begin, typename String_type::const_iterator end ) { if( end - begin < 2 ) return String_type( begin, end ); // if( end - begin < 2 ) return String_type(1, *begin); // workaround 1 // if( end - begin == 0 || end - begin == 1 ) return String_type( begin, end ); // workaround 2 String_type result; result.resize( end - begin ); std::copy(begin, end, result.begin()); return result; } int main() { std::string ss[] = {"hi", "a"}; for (const std::string& s : ss) substitute_esc_chars<std::string>(s.begin(), s.end()); return 0; } gcc-13.1 version info... $ g++-13 -Wall -O1 -D_GLIBCXX_ASSERTIONS runme.cxx -o runme In file included from /usr/include/c++/13/string:42, from runme.cxx:1: In static member function ‘static std::char_traits<char>::char_type* std::char_traits<char>::copy(char_type*, const char_type*, std::size_t)’, inlined from ‘static 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++/13/bits/basic_string.h:420:21, inlined from ‘static void std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_S_copy_chars(_CharT*, const _CharT*, const _CharT*) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/13/bits/basic_string.h:474:16, inlined from ‘static void std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_S_copy_chars(_CharT*, const_iterator, const_iterator) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/13/bits/basic_string.h:463:22, inlined from ‘void std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_M_construct(_InIterator, _InIterator, std::forward_iterator_tag) [with _FwdIterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >; _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/13/bits/basic_string.tcc:243:21, inlined from ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::basic_string(_InputIterator, _InputIterator, const _Alloc&) [with _InputIterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >; <template-parameter-2-2> = void; _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]’ at /usr/include/c++/13/bits/basic_string.h:753:16, inlined from ‘String_type substitute_esc_chars(typename String_type::const_iterator, typename String_type::const_iterator) [with String_type = std::__cxx11::basic_string<char>]’ at runme.cxx:8:62: /usr/include/c++/13/bits/char_traits.h:445:56: warning: ‘void* __builtin_memcpy(void*, const void*, long unsigned int)’ accessing 9223372036854775808 or more bytes at offsets 0 and 0 may overlap up to 9223372036854775809 bytes at offset -1 [-Wrestrict] 445 | return static_cast<char_type*>(__builtin_memcpy(__s1, __s2, __n)); | ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~ $ g++-13 -v Using built-in specs. COLLECT_GCC=g++-13 COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/13/lto-wrapper Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 13.1.0-8ubuntu1~18.04' --with-bugurl=file:///usr/share/doc/gcc-13/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2,rust --prefix=/usr --with-gcc-major-version-only --program-suffix=-13 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --disable-cet --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 13.1.0 (Ubuntu 13.1.0-8ubuntu1~18.04)