https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113200
Bug ID: 113200
Summary: std::char_traits<char>::move is not constexpr when the
argument is a string literal
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: pdimov at gmail dot com
Target Milestone: ---
```
#include <string>
#include <cassert>
template<std::size_t N> struct S
{
char data_[ N ];
using traits_type = std::char_traits<char>;
constexpr S( char const* p ): data_{}
{
std::size_t n = traits_type::length( p );
assert( n < N );
traits_type::move( data_, p, n + 1 );
}
};
template<std::size_t N> S( char const(&)[N] ) -> S<N>;
constexpr S s( "test" );
```
(https://godbolt.org/z/PofY8MP6G)
fails with
```
In file included from
/opt/compiler-explorer/gcc-trunk-20240102/include/c++/14.0.0/string:42,
from <source>:1:
<source>:22:23: in 'constexpr' expansion of 'S<5>(((const char*)"test"))'
<source>:16:26: in 'constexpr' expansion of
'std::char_traits<char>::move(((char*)(&((S<5>*)this)->S<5>::data_)), p, (n +
1))'
/opt/compiler-explorer/gcc-trunk-20240102/include/c++/14.0.0/bits/char_traits.h:423:50:
in 'constexpr' expansion of '__gnu_cxx::char_traits<char>::move(__s1, __s2,
__n)'
/opt/compiler-explorer/gcc-trunk-20240102/include/c++/14.0.0/bits/char_traits.h:230:20:
error: '(((const __gnu_cxx::char_traits<char>::char_type*)(& s.S<5>::data_)) ==
((const char*)"test"))' is not a constant expression
230 | if (__s1 == __s2) // unlikely, but saves a lot of work
| ~~~~~^~~~~~~
```
(Reduced from a similar failure in Boost.StaticString.)
