The standard says that <coroutine> should be present for freestanding.
That was intentionally left out of the initial implementation, but can
be done without much trouble. The header should be moved to libsupc++ at
some point in stage 1.
The standard also says that <coroutine> defines a std::hash
specialization, which was missing from our implementation. That's a
problem for freestanding (see LWG 3653) so only do that for hosted.
We can use concepts to constrain the __coroutine_traits_impl base class
when compiled with concepts enabled. In a pure C++20 implementation we
would not need that base class at all and could just use a constrained
partial specialization of coroutine_traits. But the absence of the
__coroutine_traits_impl<R, void> base would create an ABI difference
between the non-standard C++14/C++17 support for coroutines and the same
code compiled as C++20. If we drop support for <coroutine> pre-C++20 we
should revisit this.
libstdc++-v3/ChangeLog:
PR libstdc++/103726
* include/Makefile.am: Install <coroutine> for freestanding.
* include/Makefile.in: Regenerate.
* include/std/coroutine: Adjust headers and preprocessor
conditions.
(__coroutine_traits_impl): Use concepts when available.
[_GLIBCXX_HOSTED] (hash<coroutine_handle>): Define.
On the libsdc++ mailing list Lewis Hyatt pointed out the performance
overhead of using sputn in stream inserters, rather than writing
directly to the streambuf's put area:
https://gcc.gnu.org/pipermail/libstdc++/2021-July/052877.html
As Lewis noted, the standard explicitly requires a call to sputn for
inserting a std::basic_string_view or std::basic_string. But for
inserting single characters or null-terminated strings it is more vague,
and so we can improve performance by not using the __ostream_insert
function.
This is a minimal change that avoids __ostream_insert for single
characters. We can use the unformatted basic_ostream::put(charT)
function when we don't need the additional effects of a formatted output
function (i.e. padding and resetting the width). The put function will
insert into the buffer if possible, and only make a virtual call (to
overflow) if the buffer is full.
We could also avoid sputn when inserting null-terminated character
strings, but that would require using a new function for inserting
null-terminated strings, so the existing code using sputn is still used
for basic_string and basic_string_view. My preference is to leave that
for now, and try to improve the standard. We could either remove the
requirement to call sputn, or allow sputn to write directly to the
buffer instead of calling xsputn.
libstdc++-v3/ChangeLog:
* include/std/ostream (operator<<(basic_ostream&, charT)):
Use unformatted input if no padding is needed.
(operator<<(basic_ostream<char>&, char)): Likewise.
Clang has some bugs with destructors that use constraints to be
conditionally trivial, so disable the P2231R1 constexpr changes to
std::variant unless the compiler is GCC 12 or later.
If/when P2493R0 gets accepted and implemented by G++ we can remove the
__GNUC__ check and use __cpp_concepts >= 202002 instead.
libstdc++-v3/ChangeLog:
PR libstdc++/103891
* include/bits/c++config (_GLIBCXX_HAVE_COND_TRIVIAL_SPECIAL_MEMBERS):
Define.
* include/std/variant (__cpp_lib_variant): Only define C++20
value when the compiler is known to support conditionally
trivial destructors.
* include/std/version (__cpp_lib_variant): Likewise.
This avoids a potential race condition if std::setlocale is used
concurrently with std::from_chars.
libstdc++-v3/ChangeLog:
PR libstdc++/103911
* include/std/charconv (__from_chars_alpha_to_num): Return
char instead of unsigned char. Change invalid return value to
127 instead of using numeric trait.
(__from_chars_alnum): Fix comment. Do not use std::isdigit.
Change type of variable to char.
This feature is present in the C++23 draft.
With Jakub's recent front-end changes we can implement constexpr
equality by comparing the addresses of std::type_info objects. We do not
need string comparisons, because for constant evaluation cases we know
we aren't dealing with std::type_info objects defined in other
translation units.
The ARM EABI requires that the type_info::operator== function can be
defined out-of-line (and suggests that should be the default), but to be
a constexpr function it must be defined inline (at least for C++23
mode). To meet these conflicting requirements we make the inline version
of operator== call a new __equal function when called at runtime. That
is an alias for the non-inline definition of operator== defined in
libsupc++.
libstdc++-v3/ChangeLog:
* config/abi/pre/gnu.ver (GLIBCXX_3.4.30): Export new symbol for
ARM EABI.
* include/bits/c++config (_GLIBCXX23_CONSTEXPR): Define.
* include/std/version (__cpp_lib_constexpr_typeinfo): Define.
* libsupc++/tinfo.cc: Add #error to ensure non-inline definition
is emitted.
(type_info::__equal): Define alias symbol.
* libsupc++/typeinfo (type_info::before): Combine different
implementations into one.
(type_info::operator==): Likewise. Use address equality for
constant evaluation. Call __equal for targets that require the
definition to be non-inline.
* testsuite/18_support/type_info/constexpr.cc: New test.
This was an oversight in the original commit adding wait/notify
to atomic<T>.
libstdc++-v3/ChangeLog:
PR libstdc++/102994
* include/bits/atomic_base.h (__atomic_base<_PTp*>::wait()):
Add const qualifier.
* include/std/atomic (atomic<_Tp*>::wait(), atomic_wait()):
Likewise.
* testsuite/29_atomics/atomic/wait_notify/102994.cc:
New test.
This implements my P2467R0 proposal to support opening an fstream in
exclusive mode. The new constant is also supported pre-C++23 as
std::ios_base::__noreplace.
This proposal hasn't been approved for C++23 yet, but I am confident it
will be, as this is restoring a feture found in pre-ISO C++ iostreams
implementations (and still present in the MSVC library as _Noreplace).
If the proposal fails for C++23 we can remove the ios::noreplace
name and just keep ios::__noreplace as an extension.
libstdc++-v3/ChangeLog:
PR libstdc++/59769
* config/io/basic_file_stdio.cc (fopen_mode): Add support for
exclusive mode.
* include/bits/ios_base.h (_S_noreplace): Define new enumerator.
(ios_base::__noreplace): Define.
(ios_base::noreplace): Define for C++23.
* include/std/version (__cpp_lib_ios_noreplace): Define.
* testsuite/27_io/basic_ofstream/open/char/noreplace.cc: New test.
* testsuite/27_io/basic_ofstream/open/wchar_t/noreplace.cc: New test.
std::condition_variable::wait(unique_lock<mutex>&) is incorrectly marked
noexcept, which means that the __forced_unwind exception used by NPTL
cancellation will terminate the process. It should allow exceptions to
pass through, so that a thread can be cleanly cancelled when waiting on
a condition variable.
The new behaviour is exported as a new version of the symbol, to avoid
an ABI break for existing code linked to the non-throwing definition of
the function. Code linked against older releases will have a reference
to the @GLIBCXX_3.4.11 version, andcode compiled against the new
libstdc++ will get a reference to the @@GLIBCXX_3.4.30 version.
libstdc++-v3/ChangeLog:
PR libstdc++/103382
* config/abi/pre/gnu.ver (GLIBCXX_3.4.11): Do not export old
symbol if .symver renaming is supported.
(GLIBCXX_3.4.30): Export new symbol if .symver renaming is
supported.
* doc/xml/manual/evolution.xml: Document change.
* doc/html/manual/api.html: Regenerate.
* include/bits/std_mutex.h (__condvar::wait, __condvar::wait_until):
Remove noexcept.
* include/std/condition_variable (condition_variable::wait):
Likewise.
* src/c++11/condition_variable.cc (condition_variable::wait):
Likewise.
* src/c++11/compatibility-condvar.cc (__nothrow_wait_cv::wait):
Define nothrow wrapper around std::condition_variable::wait and
export the old symbol as an alias to it.
* testsuite/30_threads/condition_variable/members/103382.cc: New test.
This adds std::__is_constant_evaluated() as a C++11 wrapper for
__builtin_is_constant_evaluated, but just returning false if the
built-in isn't supported by the compiler. This allows us to use it
throughout the library without checking __has_builtin every time.
Some uses in std::vector and std::string can only be constexpr when the
std::is_constant_evaluated() function actually works, so we might as
well guard them with a relevant macro and call that function directly,
rather than the built-in or std::__is_constant_evaluated().
The remaining checks of the __cpp_lib_is_constant_evaluated macro could
now be replaced by checking __cplusplus >= 202002 instead, but there's
no practical difference. We still need some kind of preprocessor check
there anyway.
libstdc++-v3/ChangeLog:
* doc/doxygen/user.cfg.in (PREDEFINED): Change macro name.
* include/bits/allocator.h (allocate, deallocate): Use
std::__is_constant_evaluated() unconditionally, instead of
checking whether std::is_constant_evaluated() (or the built-in)
can be used.
* include/bits/basic_string.h: Check new macro. call
std::is_constant_evaluated() directly in C++20-only code that is
guarded by a suitable macro.
* include/bits/basic_string.tcc: Likewise.
* include/bits/c++config (__is_constant_evaluated): Define.
(_GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED): Replace with ...
(_GLIBCXX_HAVE_IS_CONSTANT_EVALUATED): New macro.
* include/bits/char_traits.h (char_traits): Replace conditional
calls to std::is_constant_evaluated with unconditional calls to
std::__is_constant_evaluated.
* include/bits/cow_string.h: Use new macro.
* include/bits/ranges_algobase.h (__copy_or_move): Replace
conditional calls to std::is_constant_evaluated with unconditional
calls to std::__is_constant_evaluated.
(__copy_or_move_backward, __fill_n_fn): Likewise.
* include/bits/ranges_cmp.h (ranges::less): Likewise.
* include/bits/stl_algobase.h (lexicographical_compare_three_way):
Likewise.
* include/bits/stl_bvector.h: Call std::is_constant_evaluated
directly in C++20-only code that is guarded by a suitable macro.
* include/bits/stl_construct.h (_Construct, _Destroy, _Destroy_n):
Replace is_constant_evaluated with __is_constant_evaluated.
* include/bits/stl_function.h (greater, less, greater_equal)
(less_equal): Replace __builtin_is_constant_evaluated and
__builtin_constant_p with __is_constant_evaluated.
* include/bits/stl_vector.h: Call std::is_constant_evaluated()
in C++20-only code.
* include/debug/helper_functions.h (__check_singular): Use
__is_constant_evaluated instead of built-in, or remove check
entirely.
* include/std/array (operator<=>): Use __is_constant_evaluated
unconditionally.
* include/std/bit (__bit_ceil): Likewise.
* include/std/type_traits (is_constant_evaluated): Define using
'if consteval' if possible.
* include/std/version: Use new macro.
* libsupc++/compare: Use __is_constant_evaluated instead of
__builtin_is_constant_evaluated.
* testsuite/23_containers/array/tuple_interface/get_neg.cc:
Adjust dg-error lines.
This patch adds [[nodiscard]] to std::byteswap, because the function
template doesn't do anything useful if the result isn't used.
2021-11-30 Jakub Jelinek <jakub@redhat.com>
* include/std/bit (byteswap): Add [[nodiscard]].
This patch attempts to implement P1272R4 (except for the std::bit_cast
changes in there which seem quite unrelated to this and will need to be
fixed on the compiler side).
While at least for GCC __builtin_bswap{16,32,64,128} should work fine
in constant expressions, I wonder about other compilers, so I'm using
a fallback implementation for constexpr evaluation always.
If you think that is unnecessary, I can drop the
__cpp_if_consteval >= 202106L &&
if !consteval
{
and
}
and reformat.
The fallback implementation is an attempt to make it work even for integral
types that don't have number of bytes divisible by 2 or when __CHAR_BIT__
is e.g. 16.
2021-11-28 Jakub Jelinek <jakub@redhat.com>
* include/std/bit (__cpp_lib_byteswap, byteswap): Define.
* include/std/version (__cpp_lib_byteswap): Define.
* testsuite/26_numerics/bit/bit.byteswap/byteswap.cc: New test.
* testsuite/26_numerics/bit/bit.byteswap/version.cc: New test.
The FE bug was fixed, so we don't need this workaround now.
libstdc++-v3/ChangeLog:
PR libstdc++/96592
* include/std/tuple (tuple::is_constructible): Remove.
Clang gives errors for constexpr std::string because the memory returned
by std::allocator<T>::allocate does not contain any objects yet, and
attempting to set them using char_traits::assign or char_traits::copy
fails with:
assignment to object outside its lifetime is not allowed in a constant expression
*__result = *__first;
^
This adds code to std::char_traits to use std::construct_at to begin
lifetimes when called during constant evaluation. To support
specializations of std::basic_string that don't use std::char_traits
there is now another layer of wrapper around the allocator_traits, so
that the lifetime of characters is begun as soon as the memory is
allocated. By doing it in the char traits and allocator traits, the rest
of basic_string can ignore the problem.
While modifying char_traits::copy and char_traits::assign to begin
lifetimes for the constexpr cases, I also replaced their uses of
std::copy and std::fill_n respectively. That means we don't need
<bits/stl_algobase.h> for char_traits.
libstdc++-v3/ChangeLog:
PR libstdc++/103295
* include/bits/basic_string.h (_Alloc_traits): Replace typedef
with struct for C++20 mode.
* include/bits/basic_string.tcc (_M_replace): Use _Alloc_traits
for allocation.
* include/bits/char_traits.h (__gnu_cxx::char_traits::assign):
Use std::_Construct during constant evaluation.
(__gnu_cxx::char_traits::assign(CharT*, const CharT*, size_t)):
Likewise. Replace std::fill_n with memset or manual loop.
(__gnu_cxx::char_traits::copy): Likewise, replacing std::copy
with memcpy.
* include/ext/vstring.h: Include <bits/stl_algobase.h> for
std::min.
* include/std/string_view: Likewise.
* testsuite/21_strings/basic_string/capacity/char/resize_and_overwrite.cc:
Add constexpr test.
This is only supported for the cxx11 ABI, not for COW strings.
libstdc++-v3/ChangeLog:
* include/bits/basic_string.h (basic_string, operator""s): Add
constexpr for C++20.
(basic_string::basic_string(basic_string&&)): Only copy
initialized portion of the buffer.
(basic_string::basic_string(basic_string&&, const Alloc&)):
Likewise.
* include/bits/basic_string.tcc (basic_string): Add constexpr
for C++20.
(basic_string::swap(basic_string&)): Only copy initialized
portions of the buffers.
(basic_string::_M_replace): Add constexpr implementation that
doesn't depend on pointer comparisons.
* include/bits/cow_string.h: Adjust comment.
* include/ext/type_traits.h (__is_null_pointer): Add constexpr.
* include/std/string (erase, erase_if): Add constexpr.
* include/std/version (__cpp_lib_constexpr_string): Update
value.
* testsuite/21_strings/basic_string/cons/char/constexpr.cc:
New test.
* testsuite/21_strings/basic_string/cons/wchar_t/constexpr.cc:
New test.
* testsuite/21_strings/basic_string/literals/constexpr.cc:
New test.
* testsuite/21_strings/basic_string/modifiers/constexpr.cc: New test.
* testsuite/21_strings/basic_string/modifiers/swap/char/constexpr.cc:
New test.
* testsuite/21_strings/basic_string/modifiers/swap/wchar_t/constexpr.cc:
New test.
* testsuite/21_strings/basic_string/version.cc: New test.
This implements P1004R2 ("Making std::vector constexpr") for C++20.
For now, debug mode vectors are not supported in constant expressions.
To make that work we might need to disable all attaching/detaching of
safe iterators. That can be fixed later.
Co-authored-by: Josh Marshall <joshua.r.marshall.1991@gmail.com>
libstdc++-v3/ChangeLog:
* include/bits/alloc_traits.h (_Destroy): Make constexpr for
C++20 mode.
* include/bits/allocator.h (__shrink_to_fit::_S_do_it):
Likewise.
* include/bits/stl_algobase.h (__fill_a1): Declare _Bit_iterator
overload constexpr for C++20.
* include/bits/stl_bvector.h (_Bit_type, _S_word_bit): Move out
of inline namespace.
(_Bit_reference, _Bit_iterator_base, _Bit_iterator)
(_Bit_const_iterator, _Bvector_impl_data, _Bvector_base)
(vector<bool, A>>): Add constexpr to every member function.
(_Bvector_base::_M_allocate): Initialize storage during constant
evaluation.
(vector<bool, A>::_M_initialize_value): Use __fill_bvector_n
instead of memset.
(__fill_bvector_n): New helper function to replace memset during
constant evaluation.
* include/bits/stl_uninitialized.h (__uninitialized_copy<false>):
Move logic to ...
(__do_uninit_copy): New function.
(__uninitialized_fill<false>): Move logic to ...
(__do_uninit_fill): New function.
(__uninitialized_fill_n<false>): Move logic to ...
(__do_uninit_fill_n): New function.
(__uninitialized_copy_a): Add constexpr. Use __do_uninit_copy.
(__uninitialized_move_a, __uninitialized_move_if_noexcept_a):
Add constexpr.
(__uninitialized_fill_a): Add constexpr. Use __do_uninit_fill.
(__uninitialized_fill_n_a): Add constexpr. Use
__do_uninit_fill_n.
(__uninitialized_default_n, __uninitialized_default_n_a)
(__relocate_a_1, __relocate_a): Add constexpr.
* include/bits/stl_vector.h (_Vector_impl_data, _Vector_impl)
(_Vector_base, vector): Add constexpr to every member function.
(_Vector_impl::_S_adjust): Disable ASan annotation during
constant evaluation.
(_Vector_base::_S_use_relocate): Disable bitwise-relocation
during constant evaluation.
(vector::_Temporary_value): Use a union for storage.
* include/bits/vector.tcc (vector, vector<bool>): Add constexpr
to every member function.
* include/std/vector (erase_if, erase): Add constexpr.
* testsuite/23_containers/headers/vector/synopsis.cc: Add
constexpr for C++20 mode.
* testsuite/23_containers/vector/bool/cmp_c++20.cc: Change to
compile-only test using constant expressions.
* testsuite/23_containers/vector/bool/capacity/29134.cc: Adjust
namespace for _S_word_bit.
* testsuite/23_containers/vector/bool/modifiers/insert/31370.cc:
Likewise.
* testsuite/23_containers/vector/cmp_c++20.cc: Likewise.
* testsuite/23_containers/vector/cons/89164.cc: Adjust errors
for C++20 and move C++17 test to ...
* testsuite/23_containers/vector/cons/89164_c++17.cc: ... here.
* testsuite/23_containers/vector/bool/capacity/constexpr.cc: New test.
* testsuite/23_containers/vector/bool/cons/constexpr.cc: New test.
* testsuite/23_containers/vector/bool/element_access/constexpr.cc: New test.
* testsuite/23_containers/vector/bool/modifiers/assign/constexpr.cc: New test.
* testsuite/23_containers/vector/bool/modifiers/constexpr.cc: New test.
* testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc: New test.
* testsuite/23_containers/vector/capacity/constexpr.cc: New test.
* testsuite/23_containers/vector/cons/constexpr.cc: New test.
* testsuite/23_containers/vector/data_access/constexpr.cc: New test.
* testsuite/23_containers/vector/element_access/constexpr.cc: New test.
* testsuite/23_containers/vector/modifiers/assign/constexpr.cc: New test.
* testsuite/23_containers/vector/modifiers/constexpr.cc: New test.
* testsuite/23_containers/vector/modifiers/swap/constexpr.cc: New test.
Calling the placement version of ::operator new "implicitly creates
objects in the returned region of storage" as per [intro.object]. This
allows the returned memory to be used as storage for implicit-lifetime
types (including arrays) without additional action by the caller. This
is required by the proposed resolution of LWG 3147.
libstdc++-v3/ChangeLog:
* include/std/memory_resource (memory_resource::allocate):
Implicitly create objects in the returned storage.
Currently std::variant uses __index_of<T, Types...> to find the first
occurence of a type in a pack, and __exactly_once<T, Types...> to check
that there is no other occurrence.
We can reuse the __find_uniq_type_in_pack<T, Types...>() function for
both tasks, and remove the recursive templates used to implement
__index_of and __exactly_once.
libstdc++-v3/ChangeLog:
* include/bits/utility.h (__find_uniq_type_in_pack): Move
definition to here, ...
* include/std/tuple (__find_uniq_type_in_pack): ... from here.
* include/std/variant (__detail__variant::__index_of): Remove.
(__detail::__variant::__exactly_once): Define using
__find_uniq_type_in_pack instead of __index_of.
(get<T>, get_if<T>, variant::__index_of): Likewise.
This reduces the number of class template instantiations needed for code
using tuples, by reusing _Nth_type in tuple_element and specializing
tuple_size_v for tuple, pair and array (and const-qualified versions of
them).
Also define the _Nth_type primary template as a complete type (but with
no nested 'type' member). This avoids "invalid use of incomplete type"
errors for out-of-range specializations of tuple_element. Those errors
would probably be confusing and unhelpful for users. We already have
a user-friendly static assert in tuple_element itself.
Also ensure that tuple_size_v is available whenever tuple_size is (as
proposed by LWG 3387). We already do that for tuple_element_t.
libstdc++-v3/ChangeLog:
* include/bits/stl_pair.h (tuple_size_v): Define partial
specializations for std::pair.
* include/bits/utility.h (_Nth_type): Move definition here
and define primary template.
(tuple_size_v): Move definition here.
* include/std/array (tuple_size_v): Define partial
specializations for std::array.
* include/std/tuple (tuple_size_v): Move primary template to
<bits/utility.h>. Define partial specializations for
std::tuple.
(tuple_element): Change definition to use _Nth_type.
* include/std/variant (_Nth_type): Move to <bits/utility.h>.
(variant_alternative, variant): Adjust qualification of
_Nth_type.
* testsuite/20_util/tuple/element_access/get_neg.cc: Prune
additional errors from _Nth_type.
libstdc++-v3/ChangeLog:
* include/std/variant (__detail::__variant::__emplace): New
function template.
(_Copy_assign_base::operator=): Reorder conditions to match
bulleted list of effects in the standard. Use __emplace instead
of _M_reset followed by _Construct.
(_Move_assign_base::operator=): Likewise.
(__construct_by_index): Remove.
(variant::emplace): Use __emplace instead of _M_reset followed
by __construct_by_index.
(variant::swap): Hoist valueless cases out of visitor. Use
__emplace to replace _M_reset followed by _Construct.
By defining additional partial specializations of _Nth_type we can
reduce the number of recursive instantiations needed to get from N to 0.
We can also use _Nth_type in variant_alternative, to take advantage of
that new optimization.
By adding a static_assert to variant_alternative we get a nicer error
than 'invalid use of incomplete type'.
By defining partial specializations of std::variant_size_v for the
common case we can avoid instantiating the std::variant_size class
template.
The __tuple_count class template and __tuple_count_v variable template
can be simplified to a single variable template, __count.
By adding a deleted constructor to the _Variant_union primary template
we can (very slightly) improve diagnostics for invalid attempts to
construct a std::variant with an out-of-range index. Instead of a
confusing error about "too many initializers for ..." we get a call to a
deleted function.
By using _Nth_type instead of variant_alternative (for cv-unqualified
variant types) we avoid instantiating variant_alternative.
By adding deleted overloads of variant::emplace we get better
diagnostics for emplace<invalid-index> or emplace<invalid-type>. Instead
of getting errors explaining why each of the four overloads wasn't
valid, we just get one error about calling a deleted function.
libstdc++-v3/ChangeLog:
* include/std/variant (_Nth_type): Define partial
specializations to reduce number of instantiations.
(variant_size_v): Define partial specializations to avoid
instantiations.
(variant_alternative): Use _Nth_type. Add static assert.
(__tuple_count, __tuple_count_v): Replace with ...
(__count): New variable template.
(_Variant_union): Add deleted constructor.
(variant::__to_type): Use _Nth_type.
(variant::emplace): Use _Nth_type. Add deleted overloads for
invalid types and indices.
Prior to r12-4447 (implementing P2231R1 constexpr changes) we didn't
construct the correct member of the union in __variant_construct_single,
we just plopped an object in the memory occupied by the union:
void* __storage = std::addressof(__lhs._M_u);
using _Type = remove_reference_t<decltype(__rhs_mem)>;
::new (__storage) _Type(std::forward<decltype(__rhs_mem)>(__rhs_mem));
We didn't care whether we had variant<int, const int>, we would just
place an int (or const int) into the storage, and then set the _M_index
to say which one it was.
In the new constexpr-friendly code we use std::construct_at to construct
the union object, which constructs the active member of the right type.
But now we need to know exactly the right type. We have to distinguish
between alternatives of type int and const int, and we have to be able
to find a const int (or const std::string, as in the OP) among the
alternatives. So my change from remove_reference_t<decltype(__rhs_mem)>
to remove_cvref_t<_Up> was wrong. It strips the const from const int,
and then we can't find the index of the const int alternative.
But just using remove_reference_t doesn't work either. When the copy
assignment operator of std::variant<int> uses __variant_construct_single
it passes a const int& as __rhs_mem, but if we don't strip the const
then we try to find const int among the alternatives, and *that* fails.
Similarly for the copy constructor, which also uses a const int& as the
initializer for a non-const int alternative.
The root cause of the problem is that __variant_construct_single doesn't
know the index of the type it's supposed to construct, and the new
_Variant_storage::__index_of<_Type> helper doesn't work if __rhs_mem and
the alternative being constructed have different const-qualification. We
need to replace __variant_construct_single with something that knows the
index of the alternative being constructed. All uses of that function do
actually know the index, but that context is lost by the time we call
__variant_construct_single. This patch replaces that function and
__variant_construct, inlining their effects directly into the callers.
libstdc++-v3/ChangeLog:
PR libstdc++/102912
* include/std/variant (_Variant_storage::__index_of): Remove.
(__variant_construct_single): Remove.
(__variant_construct): Remove.
(_Copy_ctor_base::_Copy_ctor_base(const _Copy_ctor_base&)): Do
construction directly instead of using __variant_construct.
(_Move_ctor_base::_Move_ctor_base(_Move_ctor_base&&)): Likewise.
(_Move_ctor_base::_M_destructive_move()): Remove.
(_Move_ctor_base::_M_destructive_copy()): Remove.
(_Copy_assign_base::operator=(const _Copy_assign_base&)): Do
construction directly instead of using _M_destructive_copy.
(variant::swap): Do construction directly instead of using
_M_destructive_move.
* testsuite/20_util/variant/102912.cc: New test.
In PR libstdc++/103013 Tim Song pointed out that we could reorder the
constraints of this constructor. That's worth doing just to reduce the
work the compiler has to do during overload resolution, even if it isn't
needed to make the code in the PR work.
libstdc++-v3/ChangeLog:
* include/std/span (span(Range&&)): Reorder constraints.
The std::begin and std::end overloads for std::valarray are defined in
terms of std::addressof(v[0]) which is undefined for an empty valarray.
libstdc++-v3/ChangeLog:
PR libstdc++/103022
* include/std/valarray (begin, end): Do not dereference an empty
valarray. Add noexcept and [[nodiscard]].
* testsuite/26_numerics/valarray/range_access.cc: Check empty
valarray. Check iterator properties. Run as well as compiling.
* testsuite/26_numerics/valarray/range_access2.cc: Likewise.
* testsuite/26_numerics/valarray/103022.cc: New test.
std::make_any should be constrained so it can only be called if the
construction of the return value would be valid.
libstdc++-v3/ChangeLog:
PR libstdc++/102894
* include/std/any (make_any): Add SFINAE constraint.
* testsuite/20_util/any/102894.cc: New test.
libstdc++-v3/ChangeLog:
* include/std/ranges (istream_view): Replace this function
template with an alias template as per P2432R1.
(wistream_view): Define as per P2432R1.
(views::_Istream, views::istream): Likewise.
* testsuite/std/ranges/istream_view.cc (test07): New test.
This implements P1739R4 along with the resolution for LWG 3407 which
corrects the paper's wording.
libstdc++-v3/ChangeLog:
* include/bits/ranges_util.h (views::_Drop): Forward declare.
(subrange): Befriend views::_Drop.
(subrange::_S_store_size): Declare constexpr instead of just
const, remove obsolete comment.
* include/std/ranges (views::__detail::__is_empty_view): Define.
(views::__detail::__is_basic_string_view): Likewise.
(views::__detail::__is_subrange): Likewise.
(views::__detail::__is_iota_view): Likewise.
(views::__detail::__can_take_view): Rename template parm _Tp to _Dp.
(views::_Take): Rename template parm _Tp to _Dp, make it non-deducible
and fix it to range_difference_t<_Range>. Implement P1739R4 and
LWG 3407 changes.
(views::__detail::__can_drop_view): Rename template parm _Tp to _Dp.
(views::_Drop): As with views::_Take.
(views::_Counted): Implement P1739R4 changes.
* include/std/span (__detail::__is_std_span): Rename to ...
(__detail::__is_span): ... this and turn it into a variable
template.
(__detail::__is_std_array): Turn it into a variable template.
(span::span): Adjust uses of __is_std_span and __is_std_array
accordingly.
* testsuite/std/ranges/adaptors/p1739.cc: New test.
libstdc++-v3/ChangeLog:
* include/std/ranges (lazy_split_view::base): Add forward_range
constraint as per LWG 3591.
(lazy_split_view::begin, lazy_split_view::end): Also check
simpleness of _Pattern as per LWG 3592.
(split_view::base): Relax copyable constraint as per LWG 3590.
libstdc++-v3/ChangeLog:
* include/std/ranges (join_view::__iter_cat::_S_iter_cat): Adjust
criteria for returning bidirectional_iterator_tag as per LWG 3535.
(join_view::_Iterator::_S_iter_concept): Likewise.
The constraints on transform and and_then can cause errors when checking
satisfaction. The constraints that were present in R6 of the paper were
moved for he final F8 revision, and so should have been included in the
implementation.
libstdc++-v3/ChangeLog:
PR libstdc++/102863
* include/std/optional (optional::and_then, optional::transform):
Remove requires-clause.
* testsuite/20_util/optional/monadic/and_then.cc: Check
overload resolution doesn't cause errors.
* testsuite/20_util/optional/monadic/transform.cc: Likewise.
libstdc++-v3/ChangeLog:
* include/std/ranges (iota_view::_Iterator): Befriend iota_view.
(iota_view::_Sentinel): Likewise.
(iota_view::iota_view): Add three overloads, each taking an
iterator/sentinel pair as per LWG 3523.
* testsuite/std/ranges/iota/iota_view.cc (test06): New test.
This patch also reverts r11-3504 since that workaround is now obsolete
after this resolution.
libstdc++-v3/ChangeLog:
* include/bits/ranges_base.h (view_interface): Forward declare.
(__detail::__is_derived_from_view_interface_fn): Declare.
(__detail::__is_derived_from_view_interface): Define as per LWG 3549.
(enable_view): Adjust as per LWG 3549.
* include/bits/ranges_util.h (view_interface): Don't derive from
view_base.
* include/std/ranges (filter_view): Revert r11-3504 change.
(transform_view): Likewise.
(take_view): Likewise.
(take_while_view): Likewise.
(drop_view): Likewise.
(drop_while_view): Likewise.
(join_view): Likewise.
(lazy_split_view): Likewise.
(split_view): Likewise.
(reverse_view): Likewise.
* testsuite/std/ranges/adaptors/sizeof.cc: Update expected sizes.
* testsuite/std/ranges/view.cc (test_view::test_view): Remove
this default ctor since views no longer need to be default initable.
(test01): New test.
This more clearly expresses the intent (a completely unused, trivial
type) than using char. It's also consistent with the unions in
std::optional.
libstdc++-v3/ChangeLog:
* include/std/variant (_Uninitialized): Use an empty struct
for the unused union member, instead of char.
Another new addition to the C++23 working draft.
The new member functions of std::optional are only defined for C++23,
but the new members of _Optional_payload_base are defined for C++20 so
that they can be used in non-propagating-cache in <ranges>. The
_Optional_payload_base::_M_construct member can also be used in
non-propagating-cache now, because it's constexpr since r12-4389.
There will be an LWG issue about the feature test macro, suggesting that
we should just bump the value of __cpp_lib_optional instead. I haven't
done that here, but it can be changed once consensus is reached on the
change.
libstdc++-v3/ChangeLog:
* include/std/optional (_Optional_payload_base::_Storage): Add
constructor taking a callable function to invoke.
(_Optional_payload_base::_M_apply): New function.
(__cpp_lib_monadic_optional): Define for C++23.
(optional::and_then, optional::transform, optional::or_else):
Define for C++23.
* include/std/ranges (__detail::__cached): Remove.
(__detail::__non_propagating_cache): Remove use of __cached for
contained value. Use _Optional_payload_base::_M_construct and
_Optional_payload_base::_M_apply to set the contained value.
* include/std/version (__cpp_lib_monadic_optional): Define.
* testsuite/20_util/optional/monadic/and_then.cc: New test.
* testsuite/20_util/optional/monadic/or_else.cc: New test.
* testsuite/20_util/optional/monadic/or_else_neg.cc: New test.
* testsuite/20_util/optional/monadic/transform.cc: New test.
* testsuite/20_util/optional/monadic/version.cc: New test.
A recently approved change for the C++23 working draft.
libstdc++-v3/ChangeLog:
* include/bits/basic_string.h (__cpp_lib_string_resize_and_overwrite):
Define for C++23.
(basic_string::resize_and_overwrite): Declare.
* include/bits/basic_string.tcc (basic_string::resize_and_overwrite):
Define.
* include/std/version (__cpp_lib_resize_and_overwrite): Define
for C++23.
* testsuite/21_strings/basic_string/capacity/char/resize_and_overwrite.cc:
New test.
This implements the changes in P2231R1 which make std::variant fully
constexpr in C++20.
We need to replace placement new with std::construct_at, but that isn't
defined for C++17. Use std::_Construct instead, which forwards to
std::construct_at in C++20 mode (since the related changes to make
std::optional fully constexpr, in r12-4389).
We also need to replace the untyped char buffer in _Uninitialized with a
union, which can be accessed in constexpr functions. But the union needs
to have a non-trivial destructor if its variant type is non-trivial,
which means that the _Variadic_union also needs a non-trivial
destructor. This adds a constrained partial specialization of
_Variadic_union for the C++20-only case where a non-trivial destructor
is needed.
We can't use concepts to constrain the specialization (or the primary
template's destructor) in C++17, so retain the untyped char buffer
solution for C++17 mode.
libstdc++-v3/ChangeLog:
* include/std/variant (__cpp_lib_variant): Update value for
C++20.
(__variant_cast, __variant_construct): Add constexpr for C++20.
(__variant_construct_single, __construct_by_index) Likewise. Use
std::_Construct instead of placement new.
(_Uninitialized<T, false>) [__cplusplus >= 202002]: Replace
buffer with a union and define a destructor.
(_Variadic_union) [__cplusplus >= 202002]: Add a specialization
for non-trivial destruction.
(_Variant_storage::__index_of): New helper variable template.
(_Variant_storage::~_Variant_storage()): Add constexpr.
(_Variant_storage::_M_reset()): Likewise.
(_Copy_ctor_base, _Move_ctor_base): Likewise.
(_Copy_assign_base, _Move_assign_base): Likewise.
(variant, swap): Likewise.
* include/std/version (__cpp_lib_variant): Update value for
C++20.
* testsuite/20_util/optional/version.cc: Check for exact value
in C++17.
* testsuite/20_util/variant/87619.cc: Increase timeout for
C++20 mode.
* testsuite/20_util/variant/constexpr.cc: New test.
* testsuite/20_util/variant/version.cc: New test.
The __variant_construct_by_index helper function sets the new index
before constructing the new object. This means that if the construction
throws then the exception needs to be caught, so the index can be reset
to variant_npos, and then the exception rethrown. This means callers are
responsible for restoring the variant's invariants and they need the
overhead of a catch handler and a rethrow.
If we don't set the index until after construction completes then the
invariant is never broken, and callers can ignore the exception and let
it propagate. The callers all call _M_reset() first, which sets index to
variant_npos as required while the variant is valueless.
We need to be slightly careful here, because changing the order of
operations in __variant_construct_by_index and removing the try-block
from variant::emplace<I> changes an implicit ABI contract between those
two functions. If the linker were to create an executable containing an
instantiation of the old __variant_construct_by_index and an
instantiation of the new variant::emplace<I> code then we would have a
combination that breaks the invariant and doesn't have the exception
handling to restore it. To avoid this problem, we can rename the
__variant_construct_by_index function so that the new emplace<I> code
calls a new symbol, and is unaffected by the behaviour of the old
symbol.
libstdc++-v3/ChangeLog:
* include/std/variant (__detail::__variant::__get_storage):
Remove unused function.
(__variant_construct_by_index): Set index after construction is
complete. Rename to ...
(__detail::__variant::__construct_by_index): ... this.
(variant): Use new name for __variant_construct_by_index friend
declaration. Remove __get_storage friend declaration.
(variant::emplace): Use new name and remove try-blocks.
These functions aren't used, and accessing the storage as a void* isn't
compatible with C++20 constexpr requirements anyway, so we're unlikely
to ever start using them in future.
libstdc++-v3/ChangeLog:
* include/std/variant (_Variant_storage::_M_storage()): Remove.
(__detail::__variant::__get_storage): Remove.
(variant): Remove friend declaration of __get_storage.
libstdc++-v3/ChangeLog:
* include/std/variant (__variant::__get(in_place_index_t<N>, U&&)):
Rename to __get_n and remove first argument. Replace pair of
overloads with a single function using 'if constexpr'.
(__variant::__get(Variant&&)): Adjust to use __get_n.
This implements the changes in P2231R1 which make std::optional fully
constexpr in C++20.
libstdc++-v3/ChangeLog:
* include/bits/stl_construct.h (_Construct): Use
std::construct_at when constant evaluated.
* include/std/optional (_Storage, _Optional_payload, optional):
Add constexpr as specified by P2231R1.
* include/std/version (__cpp_lib_optional): Update value for
C++20.
* testsuite/20_util/optional/requirements.cc: Check feature test
macro.
* testsuite/20_util/optional/constexpr/assign.cc: New test.
* testsuite/20_util/optional/constexpr/cons/conv.cc: New test.
* testsuite/20_util/optional/constexpr/modifiers.cc: New test.
* testsuite/20_util/optional/constexpr/swap.cc: New test.
* testsuite/20_util/optional/version.cc: New test.