https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93978
Bug ID: 93978
Summary: A snippet using views::join fails to compile with -O1,
but succeeds with -O0
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: ppalka at gcc dot gnu.org
Target Milestone: ---
$ cat join.cc
#include <ranges>
#include <vector>
namespace ranges = std::ranges;
namespace views = std::views;
void
test()
{
std::vector<std::string> x = {""};
auto i = std::counted_iterator(x.begin(), 1);
auto r = ranges::subrange{i, std::default_sentinel};
auto v = r | views::join;
}
$ g++ -std=c++2a -O0 join.cc
$ g++ -std=c++2a -O1 join.c
...
/home/patrick/code/gcc/libstdc++-v3/include/std/ranges:112:16: error: static
assertion failed
112 | static_assert(view<_Derived>);
| ^~~~~~~~~~~~~~
/home/patrick/code/gcc/libstdc++-v3/include/std/ranges:112:16: note:
constraints not satisfied
In file included from
/home/patrick/code/gcc/libstdc++-v3/include/std/string:54,
from
/home/patrick/code/gcc/libstdc++-v3/include/bits/locale_classes.h:40,
from
/home/patrick/code/gcc/libstdc++-v3/include/bits/ios_base.h:41,
from
/home/patrick/code/gcc/libstdc++-v3/include/std/streambuf:41,
from
/home/patrick/code/gcc/libstdc++-v3/include/bits/streambuf_iterator.h:35,
from
/home/patrick/code/gcc/libstdc++-v3/include/std/iterator:66,
from
/home/patrick/code/gcc/libstdc++-v3/include/std/ranges:44,
from join.cc:1:
/home/patrick/code/gcc/libstdc++-v3/include/bits/range_access.h:880:13:
required for the satisfaction of
‘range<std::ranges::join_view<std::ranges::subrange<std::counted_iterator<__gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> >*,
std::vector<std::__cxx11::basic_string<char, std::char_traits<char>,
std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char,
std::char_traits<char>, std::allocator<char> > > > > >,
std::default_sentinel_t, std::ranges::subrange_kind::sized> > >’
/home/patrick/code/gcc/libstdc++-v3/include/bits/range_access.h:880:21: in
requirements with
‘std::ranges::join_view<std::ranges::subrange<std::counted_iterator<__gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*,
std::vector<std::__cxx11::basic_string<char> > > >, std::default_sentinel_t,
std::ranges::subrange_kind::sized> >& __t’
/home/patrick/code/gcc/libstdc++-v3/include/bits/range_access.h:883:13: note:
the required expression ‘std::ranges::__cust::end(__t)’ is invalid
883 | ranges::end(__t);
| ~~~~~~~~~~~^~~~~
If we uncomment the code in constraint.cc that replays constraint satisfication
failures during diagnostics, it turns out that ranges::end(__t); is invalid
ultimately because
/home/patrick/code/gcc/libstdc++-v3/include/bits/range_access.h:437:26: error:
use of ‘constexpr auto std::ranges::join_view<_Vp>::end() [with _Vp =
std::ranges::subrange<std::counted_iterator<__gnu_cxx::__normal_iterator<std::__cxx11::basic_string<char>*,
std::vector<std::__cxx11::basic_string<char> > > >, std::default_sentinel_t,
std::ranges::subrange_kind::sized>]’ before deduction of ‘auto’
437 | { __decay_copy(__t.end()) }
| ~~~~~~~^~
Removing the static_assert(view<_Derived>); from view_interface::_M_derived()
fixes the compilation failure, but I'm not sure why.
