The internal API is a lot more complicated than it actually needs to be.
This refactors the internal API to match the features and names of the
public one.
This patch addresses several implementation issues in `bitset`'s
conversion functions `to_ullong` and `to_ulong`, and refactors its
converting constructor `__bitset(unsigned long long __v)` to a more
generic and elegant implementation.
Unconditional evaluation of `char_traits<_CharT>::length(__str)` is problematic, because it causes
UB when `__str` points to a non-null-terminated array. We should only call `length` (currently, in
`basic_string_view`'s constructor) when `__n == npos` per [bitset.cons]/8.
Drive-by change: Reduction of conditional compilation, given that
- both `basic_string_view<_CharT>::size_type` and `basic_string<_CharT>::size_type` must be
`size_t`, and thus
- both `basic_string_view<_CharT>::npos` and `basic_string<_CharT>::npos` must be `size_t(-1)`.
For the type sameness in the standard wording, see:
- [string.view.template.general]
- [basic.string.general]
- [allocator.traits.types]/6
- [default.allocator.general]/1
Fixes#143684
This patch refactors the `all()` and `any()` methods in `bitset` to
eliminate redundant code while preserving the performance. Code
generation remains unchanged, as verified on Compiler
Explorer: https://godbolt.org/z/xx8hb4sPM.
This PR simplifies `__bitset::__init` into a more compact and readable
form, which avoids redundant computations of a `size_t` value and
eliminates the overhead of a local array.
This patch optimizes `bitset::to_string` by replacing the existing bit-by-bit processing with a more efficient
bit traversal strategy. Instead of checking each bit sequentially, we leverage `std::__countr_zero` to efficiently
locate the next set bit, skipping over consecutive zero bits. This greatly accelerates the conversion process,
especially for sparse `bitset`s where zero bits dominate. To ensure similar improvements for dense `bitset`s, we
exploit symmetry by inverting the bit pattern, allowing us to apply the same optimized traversal technique. Even
for uniformly distributed `bitset`s, the proposed approach offers measurable performance gains over the existing
implementation.
Benchmarks demonstrate substantial improvements, achieving up to 13.5x speedup for sparse `bitset`s with
`Pr(true bit) = 0.1`, 16.1x for dense `bitset`s with `Pr(true bit) = 0.9`, and 8.3x for uniformly distributed
`bitset`s with `Pr(true bit) = 0.5)`.
Previously, the segmented iterator optimization for `std::for_each` was restricted to C++23 and later due to its dependency on `__movable_box`, which is not available in earlier standards. This patch eliminates that restriction, enabling consistent optimizations starting from C++11.
By backporting this enhancement, we improve performance across older standards and create opportunities to extend similar optimizations to other algorithms by forwarding their calls to `std::for_each`.
The PR removes the unnecessary division and modulo operations in the
one-word specialization `__bitset<1, _Size>`. The reason is that for the
one-word specialization, we have `__pos < __bits_per_word` (as
`__bitset<1, _Size>` is an implementation detail only used by the public
`bitset`). So `__pos / __bits_per_word == 0` and `__pos / __pos %
__bits_per_word == __pos`.
The following three string-like constructors for `std::bitset`
- `bitset(const CharT* str, std::size_t n, CharT zero, CharT one)`;
- `bitset(const std::basic_string<CharT, Traits, Alloc>& str, typename
std::basic_string<CharT, Traits, Alloc>::size_type pos, CharT zero,
CharT one)`;
- `bitset(std::basic_string_view<CharT, Traits> str, std::size_t pos,
std::size_t n, CharT zero, CharT one)`
already initialize the underlying storage array to all zeroes via
default-constructor of the base class `__bitset`. Therefore,
re-assigning the storage array to zeroes via `std::fill_n` in the
string-like constructors is truly redundant.
This PR optimizes the performance of `std::ranges::equal` for
`vector<bool>::iterator`, addressing a subtask outlined in issue #64038.
The optimizations yield performance improvements of up to 188x for
aligned equality comparison and 82x for unaligned equality
comparison. Moreover, comprehensive tests covering up to 4 storage words
(256 bytes) with odd and even bit sizes are provided, which validate the
proposed optimizations in this patch.
This is technically not necessary in most cases to prevent issues with ADL,
but let's be consistent. This allows us to remove the libcpp-qualify-declval
clang-tidy check, which is now enforced by the robust-against-adl clang-tidy check.
As a follow-up to #121013 (which focused on `std::ranges::copy`), this
PR optimizes the performance of `std::ranges::copy_backward` for
`vector<bool>::iterator`, addressing a subtask outlined in issue #64038.
The optimizations yield performance improvements of up to 2000x for
aligned copies and 60x for unaligned copies.
This PR fixes the ambiguities in name lookup caused by non-standard
member typedefs `size_type` and `difference_type` in `std::bitset`.
Follows up #121620.
Closes#121618.
According to
[[template.bitset.general]](https://eel.is/c++draft/template.bitset.general),
`std::bitset` is supposed to have only
one (public) member typedef, `reference`. However, libc++'s
implementation of `std::bitset` offers more that that. Specifically, it
offers a public typedef `const_reference` and two private typedefs
`size_type` and `difference_type`. These non-standard member typedefs,
despite being private, can cause potential ambiguities in name lookup in
user-defined classes, as demonstrated in issue #121618.
Fixing the public member typedef `const_reference` is straightforward:
we can simply replace it with an `__ugly_name` such as
`__const_reference`. However, fixing the private member typedefs
`size_type` and `difference_type` is not so straightforward as they are
required by the `__bit_iterator` class and the corresponding algorithms
optimized for `__bit_iterator`s (e.g., `ranges::fill`).
This PR fixes the member typedef `const_reference` by using uglified
name for it. Further work will be undertaken to address `size_type` and
`difference_type`.
Follows up #80706, #111127, and #112843,
This patch implements the forwarding to frozen C++03 headers as
discussed in
https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc. In the
RFC, we initially proposed selecting the right headers from the Clang
driver, however consensus seemed to steer towards handling this in the
library itself. This patch implements that direction.
At a high level, the changes basically amount to making each public
header look like this:
```
// inside <vector>
#ifdef _LIBCPP_CXX03_LANG
# include <__cxx03/vector>
#else
// normal <vector> content
#endif
```
In most cases, public headers are simple umbrella headers so there isn't
much code in the #else branch. In other cases, the #else branch contains
the actual implementation of the header.
Currently, libc++'s `bitset`, `forward_list`, and `list` have
non-conforming member typedef name `base`. The typedef is private, but
can cause ambiguity in name lookup.
Some other classes in libc++ that are either implementation details or
not precisely specified by the standard also have member typdef `base`.
I think this can still be conforming.
Follows up #80706 and #111127.
[template.bitset.general] indicates that `bitset` shouldn't have member
typedef-names `iterator` and `const_iterator`. Currently libc++'s
typedef-names are causing ambiguity in name lookup, which isn't
conforming.
As these iterator types are themselves useful, I think we should just
use __uglified member typedef-names for them.
Fixes#111125
This patch adds a large number of missing includes in the libc++ headers
and the test suite. Those were found as part of the effort to move
towards a mostly monolithic top-level std module.
Originally, we used __libcpp_verbose_abort to handle assertion failures.
That function was declared from all public headers. Since we don't use
that mechanism anymore, we don't need to declare __libcpp_verbose_abort
from all public headers, and we can clean up a lot of unnecessary
includes.
This patch also moves the definition of the various assertion categories
to the <__assert> header, since we now rely on regular IWYU for these
assertion macros.
rdar://105510916
This patch runs clang-format on all of libcxx/include and libcxx/src, in
accordance with the RFC discussed at [1]. Follow-up patches will format
the benchmarks, the test suite and remaining parts of the code. I'm
splitting this one into its own patch so the diff is a bit easier to
review.
This patch was generated with:
find libcxx/include libcxx/src -type f \
| grep -v 'module.modulemap.in' \
| grep -v 'CMakeLists.txt' \
| grep -v 'README.txt' \
| grep -v 'libcxx.imp' \
| grep -v '__config_site.in' \
| xargs clang-format -i
A Git merge driver is available in libcxx/utils/clang-format-merge-driver.sh
to help resolve merge and rebase issues across these formatting changes.
[1]: https://discourse.llvm.org/t/rfc-clang-formatting-all-of-libc-once-and-for-all
This is in preparation for clang-formatting the whole code base. These
annotations are required either to avoid clang-format bugs or because
the manually formatted code is significantly more readable than the
clang-formatted alternative. All in all, it seems like very few
annotations are required, which means that clang-format is doing a very
good job in most cases.
In preparation for running clang-format on the whole code base, we are
also removing mentions of the legacy _LIBCPP_INLINE_VISIBILITY macro in
favor of the newer _LIBCPP_HIDE_FROM_ABI.
We're still leaving the definition of _LIBCPP_INLINE_VISIBILITY to avoid
creating needless breakage in case some older patches are checked-in
with mentions of the old macro. After we branch for LLVM 18, we can do
another pass to clean up remaining uses of the macro that might have
gotten introduced by mistake (if any) and remove the macro itself at the
same time. This is just a minor convenience to smooth out the transition
as much as possible.
See
https://discourse.llvm.org/t/rfc-clang-formatting-all-of-libc-once-and-for-all
for the clang-format proposal.
The single-iterator algorithms have an implementation for `false` and `true`, which are almost identical. Instead of writing two functions, this refactors the code to take the value searched for as a template parameter. This avoids a lot of code duplication and makes it easier to reason about the algorithm and their difference.
Reviewed By: #libc, Mordante
Spies: Mordante, libcxx-commits
Differential Revision: https://reviews.llvm.org/D156033
Based on the review comments in D153201 this combines the string and
c-string constructors. The common constructor is using a string_view:
- it allows propagating the _Traits, which are required to be used for
comparison.
- it avoids allocating
- libc++ supports it in C++03
Reviewed By: philnik, #libc, ldionne
Differential Revision: https://reviews.llvm.org/D154860
We changed the `abort` calls when trying to throw exceptions in `-fno-exceptions` mode to `__verbose_abort` calls, which removes the dependency in most files.
Reviewed By: ldionne, #libc
Spies: dim, emaste, mikhail.ramalho, smeenai, libcxx-commits
Differential Revision: https://reviews.llvm.org/D146076
This was discussed on Discord with the consensus that we should rename the macros.
Reviewed By: ldionne, Mordante, var-const, avogelsgesang, jloser, #libc
Spies: libcxx-commits
Differential Revision: https://reviews.llvm.org/D131498
