the following testcase:

  bool f(const std::vector<bool>& v, std::size_t x) {
    return v[x];
  }

is compiled as:

f(std::vector<bool, std::allocator<bool> > const&, unsigned long):
        testq   %rsi, %rsi
        leaq    63(%rsi), %rax
        movq    (%rdi), %rdx
        cmovns  %rsi, %rax
        sarq    $6, %rax
        leaq    (%rdx,%rax,8), %rdx
        movq    %rsi, %rax
        sarq    $63, %rax
        shrq    $58, %rax
        addq    %rax, %rsi
        andl    $63, %esi
        subq    %rax, %rsi
        jns     .L2
        addq    $64, %rsi
        subq    $8, %rdx
.L2:
        movl    $1, %eax
        shlx    %rsi, %rax, %rax
        andq    (%rdx), %rax
        setne   %al
        ret

which is quite expensive for simple bit access in a bitmap.  The reason is that
the bit access is implemented using iterators
	return begin()[__n];
Which in turn cares about situation where __n is negative yielding the extra
conditional.

    _GLIBCXX20_CONSTEXPR
    void
    _M_incr(ptrdiff_t __i)
    {
      _M_assume_normalized();
      difference_type __n = __i + _M_offset;
      _M_p += __n / int(_S_word_bit);
      __n = __n % int(_S_word_bit);
      if (__n < 0)
        {
          __n += int(_S_word_bit);
          --_M_p;
        }
      _M_offset = static_cast<unsigned int>(__n);
    }

While we can use __builtin_unreachable to declare that __n is in range
0...max_size () but I think it is better to implement it directly, since
resulting code is shorter and much easier to optimize.

We now porduce:
.LFB1248:
        .cfi_startproc
        movq    (%rdi), %rax
        movq    %rsi, %rdx
        shrq    $6, %rdx
        andq    (%rax,%rdx,8), %rsi
        andl    $63, %esi
        setne   %al
        ret

Testcase suggests
        movq    (%rdi), %rax
        movl    %esi, %ecx
        shrq    $5, %rsi        # does still need to be 64-bit
        movl    (%rax,%rsi,4), %eax
        btl     %ecx, %eax
        setb    %al
        retq
Which is still one instruction shorter.

libstdc++-v3/ChangeLog:

	PR target/80813
	* include/bits/stl_bvector.h (vector<bool, _Alloc>::operator []): Do
	not use iterators.

gcc/testsuite/ChangeLog:

	PR target/80813
	* g++.dg/tree-ssa/bvector-3.C: New test.

As reported in PR118185, std::ranges::clamp does not correctly forward
the projected value to the comparator. Add the missing forward.

libstdc++-v3/ChangeLog:

	PR libstdc++/118185
	PR libstdc++/100249
	* include/bits/ranges_algo.h (__clamp_fn): Correctly forward the
	projected value to the comparator.
	* testsuite/25_algorithms/clamp/118185.cc: New test.

Signed-off-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Patrick Palka <ppalka@redhat.com>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

This adds <bits/ostream.h> so that other headers don't need to include
all of <ostream>, which pulls in all of <format> since C++23 (for the
std::print and std::println overloads in <ostream>). This new header
allows the constrained operator<< in <bits/unique_ptr.h> to be defined
without all of std::format being compiled.

We could also replace <ostream> with <bits/ostream.h> in all of
<istream>, <fstream>, <sstream>, and <spanstream>. That seems more
likely to cause problems for users who might be expecting <sstream> to
define std::endl, for example. Although the standard doesn't guarantee
that, it is more reasonable than expecting <memory> to define it! We can
look into making those changes for GCC 16.

libstdc++-v3/ChangeLog:

	PR libstdc++/99995
	* include/Makefile.am: Add new header.
	* include/Makefile.in: Regenerate.
	* include/bits/unique_ptr.h: Include bits/ostream.h instead of
	ostream.
	* include/std/ostream: Include new header.
	* include/bits/ostream.h: New file.

Do not report an error for (is_other(s1) && is_other(s2)) as the
standard originally said, nor for (is_other(s1) || is_other(s2)) as
libstdc++ was doing. We can compare inode numbers for special files and
so give sensible answers.

libstdc++-v3/ChangeLog:

	PR libstdc++/118158
	* src/c++17/fs_ops.cc (fs::equivalent): Remove error reporting
	for is_other(s1) && is_other(s2) case, as per LWG 2937.
	* testsuite/27_io/filesystem/operations/pr118158.cc: New test.

Replace some `__cplusplus > 201402L` preprocessor checks with more
expressive checks for the appropriate feature test macro.

libstdc++-v3/ChangeLog:

	* include/bits/stl_map.h: Check __glibcxx_node_extract instead
	of __cplusplus.
	* include/bits/stl_multimap.h: Likewise.
	* include/bits/stl_multiset.h: Likewise.
	* include/bits/stl_set.h: Likewise.
	* include/bits/stl_tree.h: Likewise.

This test should use __cpp_lib_ios_noreplace rather than the internal
__glibcxx_ios_noreplace macro.

libstdc++-v3/ChangeLog:

	* testsuite/27_io/ios_base/types/openmode/case_label.cc: Use
	standard feature test macro not internal one.

The alloc_ptr.cc test for std::set tries to use C++17 features
unconditionally, and tries to use the C++23 range members which haven't
been implemented for std::set yet.

Some of the range checks are left in place but commented out, so they
can be added after the ranges members are implemented. Others (such as
prepend_range) are not valid for std::set at all.

Also fix uses of internal feature test macros in two other tests, which
should use the standard __cpp_lib_xxx macros.

libstdc++-v3/ChangeLog:

	* testsuite/23_containers/set/requirements/explicit_instantiation/alloc_ptr.cc:
	Guard node extraction checks with feature test macro. Remove
	calls to non-existent range members.
	* testsuite/23_containers/forward_list/requirements/explicit_instantiation/alloc_ptr.cc:
	Use standard macro not internal one.
	* testsuite/23_containers/list/requirements/explicit_instantiation/alloc_ptr.cc:
	Likewise.

libstdc++-v3/ChangeLog:

	PR libstdc++/109849
	* include/bits/vector.tcc (vector::_M_range_insert): Fix
	reversed args in length calculation.

libstdc++-v3/ChangeLog:

	* testsuite/28_regex/traits/char/transform_primary.cc: Fix
	subclause numbering in references to the standard.

c++: Delete defaulted operator <=> if std::strong_ordering::equal doesn't convert to its rettype [PR118387]

Note, the PR raises another problem.
If on the same testcase the B b; line is removed, we silently synthetize
operator<=> which will crash at runtime due to returning without a return
statement.  That is because the standard says that in that case
it should return static_cast<int>(std::strong_ordering::equal);
but I can't find anywhere wording which would say that if that isn't
valid, the function is deleted.
https://eel.is/c++draft/class.compare#class.spaceship-2.2
seems to talk just about cases where there are some members and their
comparison is invalid it is deleted, but here there are none and it
follows
https://eel.is/c++draft/class.compare#class.spaceship-3.sentence-2
So, we synthetize with tf_none, see the static_cast is invalid, don't
add error_mark_node statement silently, but as the function isn't deleted,
we just silently emit it.
Should the standard be amended to say that the operator should be deleted
even if it has no elements and the static cast from
https://eel.is/c++draft/class.compare#class.spaceship-3.sentence-2

On Fri, Jan 10, 2025 at 12:04:53PM -0500, Jason Merrill wrote:
> That seems pretty obviously what we want, and is what the other compilers
> implement.

This patch implements it then.

2025-01-15  Jakub Jelinek  <jakub@redhat.com>

	PR c++/118387
	* method.cc (build_comparison_op): Set bad if
	std::strong_ordering::equal doesn't convert to rettype.

	* g++.dg/cpp2a/spaceship-err6.C: Expect another error.
	* g++.dg/cpp2a/spaceship-synth17.C: Likewise.
	* g++.dg/cpp2a/spaceship-synth-neg6.C: Likewise.
	* g++.dg/cpp2a/spaceship-synth-neg7.C: New test.

	* testsuite/25_algorithms/default_template_value.cc
	(Input::operator<=>): Use auto as return type rather than bool.

When running tests using the "sim" config, the command is launched in
non-readonly mode and the text retrieved from the expect command will
then replace all LF with CRLF. (The problem can be found in sim_load
where it calls remote_spawn without an input file).

libstdc++-v3/ChangeLog:

	* testsuite/27_io/print/1.cc: Allow both LF and CRLF in test.
	* testsuite/27_io/print/3.cc: Likewise.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>

Test assumes libatomic.a is always available, but for some embedded
targets, there is no libatomic.a and the test thus fail.

libstdc++-v3/ChangeLog:

	* testsuite/29_atomics/atomic_float/compare_exchange_padding.cc:
	Use effective-target libatomic_available.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>

This fixes warnings like the following during bootstrap:

sparc-sun-solaris2.11/libstdc++-v3/include/bits/atomic_futex.h:324:53: warning: unused parameter ‘__mo’ [-Wunused-parameter]
  324 |     _M_load_when_equal(unsigned __val, memory_order __mo)
      |                                        ~~~~~~~~~~~~~^~~~

libstdc++-v3/ChangeLog:

	* include/bits/atomic_futex.h (__atomic_futex_unsigned): Remove
	names of unused parameters in non-futex implementation.

libstdc++-v3/ChangeLog:

	* include/bits/move.h (__addressof, forward, forward_like, move)
	(move_if_noexcept, addressof): Add always_inline attribute.
	Replace _GLIBCXX_NODISCARD with [[__nodiscard__]].

libstdc++-v3/ChangeLog:

	PR libstdc++/118260
	* python/hook.in: Run 'skip' commands for some simple accessor
	functions.

std::to_underlying was missing from the std module introduced in
r15-5366-g7db55c0ba1baaf. This patch adds the missing export for this
utility.

libstdc++-v3/ChangeLog:

	PR libstdc++/106852
	* src/c++23/std.cc.in (to_underlying): Add.

Signed-off-by: Nicolas Werner <nicolas.werner@hotmail.de>

The std-clib.cc module definition file assumes that all names are
available unconditionally, but that's not true for all targets. Use the
same preprocessor conditions as are present in the <cxxx> headers.

A similar change is needed in std.cc.in for the <chrono> features that
depend on the SSO std::string, guarded with a __cpp_lib_chrono value
indicating full C++20 support.

The conditions for <cmath> are omitted from this change, as there are a
large number of them. That probably needs to be fixed.

libstdc++-v3/ChangeLog:

	PR libstdc++/118177
	* src/c++23/std-clib.cc.in: Use preprocessor conditions for
	names which are not always defined.
	* src/c++23/std.cc.in: Likewise.

libstdc++-v3/ChangeLog:

	* include/std/span: Fix indentation.

This commit implements P2447R6. The code is straightforward (just one
extra constructor, with constraints and conditional explicit).

I decided to suppress -Winit-list-lifetime because otherwise it would
give too many false positives. The new constructor is meant to be used
as a parameter-passing interface (this is a design choice, see
P2447R6/§2) and, as such, the initializer_list won't dangle despite
GCC's warnings.

The new constructor isn't 100% backwards compatible. A couple of
examples are included in Annex C, but I have also lifted some more
from R4. A new test checks for the old and the new behaviors.

libstdc++-v3/ChangeLog:

	* include/bits/version.def: Add the new feature-testing macro.
	* include/bits/version.h: Regenerate.
	* include/std/span: Add constructor from initializer_list.
	* testsuite/23_containers/span/init_list_cons.cc: New test.
	* testsuite/23_containers/span/init_list_cons_neg.cc: New test.

Signed-off-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

Any std::span<T, N> constructor with a runtime length has a precondition
that the length is equal to N (except when N == std::dynamic_extent).

Currently every constructor with a runtime length does:

if constexpr (extent != dynamic_extent)
  __glibcxx_assert(n == extent);

We can move those assertions into the __detail::__extent_storage<N>
constructor so they are only done in one place. To avoid checking the
assertions when we have a constant length we can add a second
constructor which is consteval and takes a integral_constant<size_t, N>
argument. The std::span constructors can pass a size_t for runtime
lengths and a std::integral_constant<size_t, N> for constant lengths
that don't need to be checked.

The __detail::__extent_storage<dynamic_extent> specialization only needs
one constructor, as a std::integral_constant<size_t, N> argument can
implicitly convert to size_t.

For the member functions that return a subspan with a constant extent we
return std::span<T,C>(ptr, C) which is redundant in two ways. Repeating
the constant length C when it's already a template argument is
redundant, and using the std::span(T*, size_t) constructor implies a
runtime length which will do a redundant assertion check.  Even though
that assertion won't fail and should be optimized away, it's still
unnecessary code that doesn't need to be instantiated and then optimized
away again. We can avoid that by adding a new private constructor that
only takes a pointer (wrapped in a custom tag struct to avoid
accidentally using that constructor) and automatically sets _M_extent to
the correct value.

libstdc++-v3/ChangeLog:

	* include/std/span (__detail::__extent_storage): Check
	precondition in constructor. Add consteval constructor for valid
	lengths and deleted constructor for invalid constant lengths.
	Make member functions always_inline.
	(__detail::__span_ptr): New class template.
	(span): Adjust constructors to use a std::integral_constant
	value for constant lengths. Declare all specializations of
	std::span as friends.
	(span::first<C>, span::last<C>, span::subspan<O,C>): Use new
	private constructor.
	(span(__span_ptr<T>)): New private constructor for constant
	lengths.

std::regex builds a cache of equivalence classes by calling
std::regex_traits<char>::transform_primary(c) for every char, which then
calls std::collate<char>::transform which calls strxfrm. On several
targets strxfrm fails for non-ASCII characters. Because strxfrm has no
return value reserved to indicate an error, some implementations return
INT_MAX or SIZE_MAX. This causes std::collate::transform to try to
allocate a huge buffer, which is either very slow or throws
std::bad_alloc. We should check errno after calling strxfrm to detect
errors and then throw a more appropriate exception instead of trying to
allocate a huge buffer.

Unfortunately the std::collate<C>::_M_transform function has a
non-throwing exception specifier, so we can't do the error handling
there.

As well as checking errno, this patch changes std::collate::do_transform
to use __builtin_alloca for small inputs, and to use RAII to deallocate
the buffers used for large inputs.

This change isn't sufficient to fix the three std::regex bugs caused by
the lack of error handling in std::collate::do_transform, we also need
to make std::regex_traits::transform_primary handle exceptions. This
change also attempts to make transform_primary closer to the effects
described in the standard, by not even attempting to use std::collate if
the locale's std::collate facet has been replaced (see PR 118105).
Implementing the correct effects for transform_primary requires RTTI, so
that we don't use some user-defined std::collate facet with unknown
semantics. When -fno-rtti is used transform_primary just returns an
empty string, making equivalence classes unusable in std::basic_regex.
That's not ideal, but I don't have any better ideas.

I'm unsure if std::regex_traits<C>::transform_primary is supposed to
convert the string to lower case or not.  The general regex traits
requirements ([re.req] p20) do say "when character case is not
considered" but the specification for the std::regex_traits<char> and
std::regex_traits<wchar_t> specializations ([re.traits] p7) don't say
anything about that.

With the r15-6317-geb339c29ee42aa change, transform_primary is not
called unless the regex actually uses an equivalence class. But using an
equivalence class would still fail (or be incredibly slow) on some
targets. With this commit, equivalence classes should be usable on all
targets, without excessive memory allocations.

Arguably, we should not even try to call transform_primary for any char
values over 127, since they're never valid in locales that use UTF-8 or
7-bit ASCII, and probably for other charsets too. Handling 128
exceptions for every std::regex compilation is very inefficient, but at
least it now works instead of failing with std::bad_alloc, and no longer
allocates 128 x 2GB. Maybe for C++26 we could check the locale's
std::text_encoding and use that to decide whether to cache equivalence
classes for char values over 127.

libstdc++-v3/ChangeLog:

	PR libstdc++/85824
	PR libstdc++/94409
	PR libstdc++/98723
	PR libstdc++/118105
	* include/bits/locale_classes.tcc (collate::do_transform): Check
	errno after calling _M_transform. Use RAII type to manage the
	buffer and to restore errno.
	* include/bits/regex.h (regex_traits::transform_primary): Handle
	exceptions from std::collate::transform and do not try to use
	std::collate for user-defined facets.

The current check for negative times (i.e. before the epoch) only checks
for a negative number of seconds. For a time 1ms before the epoch the
seconds part will be zero, but the futex syscall will still fail with an
EINVAL error. Extend the check to handle this case.

This change adds a redundant check in the headers too, so that we avoid
even calling into the library for negative times. Both checks can be
marked [[unlikely]]. The check in the headers avoids the cost of
splitting the time into seconds and nanoseconds and then making a PLT
call. The check inside the library matches where we were checking
already, and fixes existing binaries that were compiled against older
headers but use a newer libstdc++.so.6 at runtime.

libstdc++-v3/ChangeLog:

	PR libstdc++/118093
	* include/bits/atomic_futex.h (_M_load_and_test_until_impl):
	Return false for times before the epoch.
	* src/c++11/futex.cc (_M_futex_wait_until): Extend check for
	negative times to check for subsecond times. Add unlikely
	attribute.
	(_M_futex_wait_until_steady): Likewise.
	* testsuite/30_threads/future/members/118093.cc: New test.

We have several overloads of std::deque::_M_insert_aux, one of which is
variadic and called by std::deque::emplace. With a suitable set of
arguments to emplace, it's possible for one of the non-variadic
_M_insert_aux overloads to be selected by overload resolution, making
emplace ill-formed.

Rename the variadic _M_insert_aux to _M_emplace_aux so that calls to
emplace never select an _M_insert_aux overload. Also add an inline
_M_insert_aux for the const lvalue overload that is called from
insert(const_iterator, const value_type&).

libstdc++-v3/ChangeLog:

	PR libstdc++/90389
	* include/bits/deque.tcc (_M_insert_aux): Rename variadic
	overload to _M_emplace_aux.
	* include/bits/stl_deque.h (_M_insert_aux): Define inline.
	(_M_emplace_aux): Declare.
	* testsuite/23_containers/deque/modifiers/emplace/90389.cc: New
	test.

Also add "@since C++11" to std::move, std::forward etc.

libstdc++-v3/ChangeLog:

	* include/bits/move.h (forward, move, move_if_noexcept, addressof):
	Add @since to Doxygen comments.
	(forward_like): Add Doxygen comment.

libstdc++-v3/ChangeLog:

	* doc/xml/manual/evolution.xml: Replace invalid <variable>
	elements with <varname>.
	* doc/html/*: Regenerate.

Rotate ChangeLog files for ChangeLogs with yearly cadence.
Also remove empty lines before Form Feed line.

Commit 544be2be in 2019 remove Profile Mode and associated docs.
Now also remove generated HTML files.

libstdc++-v3:
	* doc/html/manual/profile_mode.html: Delete.
	* doc/html/manual/profile_mode_api.html: Ditto.
	* doc/html/manual/profile_mode_cost_model.html: Ditto.
	* doc/html/manual/profile_mode_design.html: Ditto.
	* doc/html/manual/profile_mode_devel.html: Ditto.
	* doc/html/manual/profile_mode_impl.html: Ditto.

Commit 544be2be in 2019 remove Profile Mode and associated docs
including the XML version of profile_mode_diagnostics.html. Somehow
the latter survived until now. Simply delete it as well.

libstdc++-v3:
	* doc/html/manual/profile_mode_diagnostics.html: Delete.

These two long-running tests happened to fail for me when
run in parallel (nprocs - 1) compared to a serial run, for
target mmix on my laptop.  The runtime is 3m40s for 3.cc
before this change, and 0.9s afterwards.

	* testsuite/std/time/year_month_day/3.cc (test01): Add ifdeffery to
	limit the tested dates.  For simulators, pass start and end dates
	limiting the tested range to 100000 days, centered on days (0).
	* testsuite/std/time/year_month_day/4.cc: Ditto.