[libc++][C++03] Use `__cxx03/` headers in C++03 mode (#109002)

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++][C++03] Use `__cxx03/` headers in C++03 mode (#109002)

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.

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[libc++] Add #if 0 block to all the top-level headers (#119234)

Including The frozen C++03 headers results in a lot of formatting
changes in the main headers, so this splits these changes into a
sep

[libc++] Add #if 0 block to all the top-level headers (#119234)

Including The frozen C++03 headers results in a lot of formatting
changes in the main headers, so this splits these changes into a
separate commit instead.

This is part of
https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc.

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[libc++][NFC] Use [[__nodiscard__]] unconditionally (#80454)

`__has_cpp_attribute(__nodiscard__)` is always true now, so we might as
well replace `_LIBCPP_NODISCARD`. It's one less macro that can r

[libc++][NFC] Use [[__nodiscard__]] unconditionally (#80454)

`__has_cpp_attribute(__nodiscard__)` is always true now, so we might as
well replace `_LIBCPP_NODISCARD`. It's one less macro that can result in
bad diagnostics.

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[libc++] Remove _LIBCPP_DISABLE_NODISCARD_EXTENSIONS and refactor the tests (#87094)

This also adds a few tests that were missing.

[libc++] Format the code base (#74334)

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 benchmar

[libc++] Format the code base (#74334)

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

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[libc++] Add std::fpclassify overloads for floating-point. (#67913)

Standard says that implementation of math functions that have
floating-point-type parameter should provide an "overload for each

[libc++] Add std::fpclassify overloads for floating-point. (#67913)

Standard says that implementation of math functions that have
floating-point-type parameter should provide an "overload for each
cv-unqualified floating-point type".

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[libc++] Granulaize math.h and move the functions to std::__math

Reviewed By: #libc, Mordante

Spies: Mordante, arichardson, libcxx-commits

Differential Revision: https://reviews.llvm.org/D155258

[libc++] Remove Solaris related code

This was contributed ~10 years ago, but we don't officially support it
and I am not aware of any bot testing it, so this has likely rotten to
the point where it

[libc++] Remove Solaris related code

This was contributed ~10 years ago, but we don't officially support it
and I am not aware of any bot testing it, so this has likely rotten to
the point where it is unusable.

Differential Revision: https://reviews.llvm.org/D138680

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[libc++] Add [[nodiscard]] extensions in <math.h>

There are quite a few functions marked `[[gnu::const]]` inside the compiler. This patch adds `[[nodiscard]]` to libc++-provided overloads of these f

[libc++] Add [[nodiscard]] extensions in <math.h>

There are quite a few functions marked `[[gnu::const]]` inside the compiler. This patch adds `[[nodiscard]]` to libc++-provided overloads of these functions to match the diagnostics produced.

Reviewed By: ldionne, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D140855

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[libc++] [C++20] [P0415] Constexpr for std::complex.

This patch adds constexpr to <complex> header: operators, member operators, and member functions (real, imag, norm, conj).

https://eel.is/c++dra

[libc++] [C++20] [P0415] Constexpr for std::complex.

This patch adds constexpr to <complex> header: operators, member operators, and member functions (real, imag, norm, conj).

https://eel.is/c++draft/complex.numbers
https://wg21.link/p0415

Reviewed By: ldionne, #libc

Spies: philnik, danilaml, Quuxplusone, wmaxey, arichardson, libcxx-commits

Differential Revision: https://reviews.llvm.org/D79555

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[libc++] Implement constexpr {isfinite, isinf, isnan, isnormal}

This starts implementing P0533

Reviewed By: Mordante, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D

[libc++] Implement constexpr {isfinite, isinf, isnan, isnormal}

This starts implementing P0533

Reviewed By: Mordante, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D140277

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[libc++] Granularize <type_traits> includes in <compare>

Reviewed By: Mordante, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D140480

[libc++][math.h] Add double overloads

This allows libc++ to work with libcs that don't provide a proper math.h implementation.

Reviewed By: ldionne, #libc

Spies: aaron.ballman, fhahn, bcain, Izaro

[libc++][math.h] Add double overloads

This allows libc++ to work with libcs that don't provide a proper math.h implementation.

Reviewed By: ldionne, #libc

Spies: aaron.ballman, fhahn, bcain, Izaron, libcxx-commits

Differential Revision: https://reviews.llvm.org/D138629

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[libc++][math.h] move #undefs to the top and guard explicitly against MSVCRT instead

Reviewed By: ldionne, #libc

Spies: #libc_vendors, EricWF, libcxx-commits

Differential Revision: https://reviews

[libc++][math.h] move #undefs to the top and guard explicitly against MSVCRT instead

Reviewed By: ldionne, #libc

Spies: #libc_vendors, EricWF, libcxx-commits

Differential Revision: https://reviews.llvm.org/D137502

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[libc++][math.h] Use builtins for all the functions

This allows compiling libc++, even when the C library doesn't support floating point math.

Reviewed By: ldionne, #libc

Spies: daltenty, xingxue,

[libc++][math.h] Use builtins for all the functions

This allows compiling libc++, even when the C library doesn't support floating point math.

Reviewed By: ldionne, #libc

Spies: daltenty, xingxue, libcxx-commits, michaelplatings

Differential Revision: https://reviews.llvm.org/D136393

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[libc++][math.h][NFC] Refactor enable_ifs

Reviewed By: ldionne, Mordante, #libc

Spies: EricWF, libcxx-commits

Differential Revision: https://reviews.llvm.org/D137501

[libc++][math.h] Remove some code duplication

Reviewed By: ldionne, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D137500

[libc++][math.h] Remove __libcpp_<func> functions and instead call builtins directly

Reviewed By: ldionne, Mordante, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D13

[libc++][math.h] Remove __libcpp_<func> functions and instead call builtins directly

Reviewed By: ldionne, Mordante, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D137499

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[libc++] Assume that builtins for math.h functions are available

All supported compilers support the builtins, so this removes dead code and simplifies a lot of the functions through that.

Reviewed

[libc++] Assume that builtins for math.h functions are available

All supported compilers support the builtins, so this removes dead code and simplifies a lot of the functions through that.

Reviewed By: ldionne, #libc, EricWF

Spies: EricWF, michaelplatings, libcxx-commits

Differential Revision: https://reviews.llvm.org/D135781

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[libc++][math.h][NFC] Reformat functions

This is just to make to follow-up diffs simpler

Reviewed By: ldionne, #libc, EricWF

Spies: EricWF, libcxx-commits

Differential Revision: https://reviews.l

[libc++][math.h][NFC] Reformat functions

This is just to make to follow-up diffs simpler

Reviewed By: ldionne, #libc, EricWF

Spies: EricWF, libcxx-commits

Differential Revision: https://reviews.llvm.org/D137498

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[libc++] Only include_next C library headers when they exist

Some platforms don't provide all C library headers. In practice, libc++
only requires a few C library headers to exist, and only a few fu

[libc++] Only include_next C library headers when they exist

Some platforms don't provide all C library headers. In practice, libc++
only requires a few C library headers to exist, and only a few functions
on those headers. Missing functions that libc++ doesn't need for its own
implementation are handled properly by the using_if_exists attribute,
however a missing header is currently a hard error when we try to
do #include_next.

This patch should make libc++ more flexible on platforms that do not
provide C headers that libc++ doesn't actually require for its own
implementation. The only downside is that it may move some errors from
the #include_next point to later in the compilation if we actually try
to use something that isn't provided, which could be somewhat confusing.
However, these errors should be caught by folks trying to port libc++
over to a new platform (when running the libc++ test suite), not by end
users.

NOTE: This is a reapplicaton of 226409, which was reverted in 674729813
because it broke the build. The issue has now been fixed with
https://reviews.llvm.org/D138062.

Differential Revision: https://reviews.llvm.org/D136683

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Revert "[libc++] Only include_next C library headers when they exist"

This reverts commit 226409c62879bf5ff9928cd23a4255cd7c614fe0.
Breaks check-clang on mac, see comments on https://reviews.llvm.or

Revert "[libc++] Only include_next C library headers when they exist"

This reverts commit 226409c62879bf5ff9928cd23a4255cd7c614fe0.
Breaks check-clang on mac, see comments on https://reviews.llvm.org/D136683

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[libc++] Only include_next C library headers when they exist

Some platforms don't provide all C library headers. In practice, libc++
only requires a few C library headers to exist, and only a few fu

[libc++] Only include_next C library headers when they exist

Some platforms don't provide all C library headers. In practice, libc++
only requires a few C library headers to exist, and only a few functions
on those headers. Missing functions that libc++ doesn't need for its own
implementation are handled properly by the using_if_exists attribute,
however a missing header is currently a hard error when we try to
do #include_next.

This patch should make libc++ more flexible on platforms that do not
provide C headers that libc++ doesn't actually require for its own
implementation. The only downside is that it may move some errors from
the #include_next point to later in the compilation if we actually try
to use something that isn't provided, which could be somewhat confusing.
However, these errors should be caught by folks trying to port libc++
over to a new platform (when running the libc++ test suite), not by end
users.

Differential Revision: https://reviews.llvm.org/D136683

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[libc++][math.h] Remove unnecessary uses of __promote

Removes __promote when it's just the identity.

Reviewed By: ldionne, #libc

Spies: libcxx-commits, michaelplatings

Differential Revision: http

[libc++][math.h] Remove unnecessary uses of __promote

Removes __promote when it's just the identity.

Reviewed By: ldionne, #libc

Spies: libcxx-commits, michaelplatings

Differential Revision: https://reviews.llvm.org/D136868

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[libc++][NFC] Remove __lcpp prefix in math.h

Reviewed By: ldionne, #libc

Spies: libcxx-commits

Differential Revision: https://reviews.llvm.org/D135774