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[libc++] Add __pointer_int_pair
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‎libcxx/include/CMakeLists.txt

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@@ -877,6 +877,7 @@ set(files
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__utility/no_destroy.h
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__utility/pair.h
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__utility/piecewise_construct.h
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__utility/pointer_int_pair.h
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__utility/priority_tag.h
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__utility/private_constructor_tag.h
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__utility/rel_ops.h

‎libcxx/include/__utility/pointer_int_pair.h

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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___UTILITY_POINTER_INT_PAIR_H
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#define _LIBCPP___UTILITY_POINTER_INT_PAIR_H
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#include <__assert>
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#include <__bit/bit_log2.h>
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#include <__concepts/derived_from.h>
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#include <__config>
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#include <__cstddef/size_t.h>
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#include <__tuple/tuple_element.h>
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#include <__tuple/tuple_size.h>
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#include <__type_traits/is_integral.h>
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#include <__type_traits/is_pointer.h>
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#include <__type_traits/is_unsigned.h>
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#include <__type_traits/is_void.h>
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#include <__type_traits/remove_pointer.h>
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#include <__utility/swap.h>
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#include <cstdint>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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#if _LIBCPP_STD_VER >= 17
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// A __pointer_int_pair is a pair of a pointer and an integral type. The lower bits of the pointer that are free
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// due to the alignment requirement of the pointee are used to store the integral type.
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//
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// This imposes a constraint on the number of bits available for the integral type -- the integral type can use
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// at most log2(alignof(T)) bits. This technique allows storing the integral type without additional storage
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// beyond that of the pointer itself, at the cost of some bit twiddling.
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <class>
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struct _PointerLikeTraits;
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template <class _Tp>
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requires(!is_void_v<_Tp>)
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struct _PointerLikeTraits<_Tp*> {
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static constexpr size_t __low_bits_available = std::__bit_log2(alignof(_Tp));
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static _LIBCPP_HIDE_FROM_ABI uintptr_t __to_uintptr(_Tp* __ptr) { return reinterpret_cast<uintptr_t>(__ptr); }
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static _LIBCPP_HIDE_FROM_ABI _Tp* __to_pointer(uintptr_t __ptr) { return reinterpret_cast<_Tp*>(__ptr); }
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};
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template <class _Tp>
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requires is_void_v<_Tp>
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struct _PointerLikeTraits<_Tp*> {
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static constexpr size_t __low_bits_available = 0;
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static _LIBCPP_HIDE_FROM_ABI uintptr_t __to_uintptr(_Tp* __ptr) { return reinterpret_cast<uintptr_t>(__ptr); }
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static _LIBCPP_HIDE_FROM_ABI _Tp* __to_pointer(uintptr_t __ptr) { return reinterpret_cast<_Tp*>(__ptr); }
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};
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enum class __integer_width : size_t {};
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template <class _Pointer, class _IntType, __integer_width __int_bit_count>
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class __pointer_int_pair {
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using _PointerTraits = _PointerLikeTraits<_Pointer>;
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static constexpr auto __int_width = static_cast<size_t>(__int_bit_count);
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static_assert(__int_width <= _PointerTraits::__low_bits_available,
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"Not enough bits available for requested bit count");
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static_assert(is_integral_v<_IntType>, "_IntType has to be an integral type");
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static_assert(is_unsigned_v<_IntType>,
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"__pointer_int_pair doesn't work for signed types since that would require handling the sign bit");
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static constexpr size_t __extra_bits = _PointerTraits::__low_bits_available - __int_width;
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static constexpr uintptr_t __int_mask = static_cast<uintptr_t>(1 << _PointerTraits::__low_bits_available) - 1;
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static constexpr uintptr_t __ptr_mask = ~__int_mask;
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uintptr_t __value_ = 0;
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public:
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__pointer_int_pair() = default;
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__pointer_int_pair(const __pointer_int_pair&) = default;
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__pointer_int_pair(__pointer_int_pair&&) = default;
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__pointer_int_pair& operator=(const __pointer_int_pair&) = default;
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__pointer_int_pair& operator=(__pointer_int_pair&&) = default;
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~__pointer_int_pair() = default;
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_LIBCPP_HIDE_FROM_ABI __pointer_int_pair(_Pointer __ptr_value, _IntType __int_value)
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: __value_(_PointerTraits::__to_uintptr(__ptr_value) | (__int_value << __extra_bits)) {
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_LIBCPP_ASSERT_INTERNAL((__int_value & (__int_mask >> __extra_bits)) == __int_value, "integer is too large!");
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_LIBCPP_ASSERT_INTERNAL(
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(_PointerTraits::__to_uintptr(__ptr_value) & __ptr_mask) == _PointerTraits::__to_uintptr(__ptr_value),
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"Pointer alignment is too low!");
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}
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_LIBCPP_HIDE_FROM_ABI _IntType __get_value() const { return (__value_ & __int_mask) >> __extra_bits; }
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_LIBCPP_HIDE_FROM_ABI _Pointer __get_ptr() const { return _PointerTraits::__to_pointer(__value_ & __ptr_mask); }
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template <class>
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friend struct _PointerLikeTraits;
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};
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template <class _Pointer, __integer_width __int_bit_count, class _IntType>
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struct _PointerLikeTraits<__pointer_int_pair<_Pointer, _IntType, __int_bit_count>> {
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private:
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using _PointerIntPair = __pointer_int_pair<_Pointer, _IntType, __int_bit_count>;
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public:
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static constexpr size_t __low_bits_available = _PointerIntPair::__extra_bits;
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static _LIBCPP_HIDE_FROM_ABI uintptr_t __to_uintptr(_PointerIntPair __ptr) { return __ptr.__value_; }
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static _LIBCPP_HIDE_FROM_ABI _PointerIntPair __to_pointer(uintptr_t __ptr) {
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_PointerIntPair __tmp{};
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__tmp.__value_ = __ptr;
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return __tmp;
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}
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};
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// Make __pointer_int_pair tuple-like
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template <class _Pointer, class _IntType, __integer_width __int_bit_count>
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struct tuple_size<__pointer_int_pair<_Pointer, _IntType, __int_bit_count>> : integral_constant<size_t, 2> {};
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template <class _Pointer, class _IntType, __integer_width __int_bit_count>
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struct tuple_element<0, __pointer_int_pair<_Pointer, _IntType, __int_bit_count>> {
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using type = _Pointer;
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};
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template <class _Pointer, class _IntType, __integer_width __int_bit_count>
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struct tuple_element<1, __pointer_int_pair<_Pointer, _IntType, __int_bit_count>> {
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using type = _IntType;
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};
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template <size_t __i, class _Pointer, class _IntType, __integer_width __int_bit_count>
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_LIBCPP_HIDE_FROM_ABI auto get(__pointer_int_pair<_Pointer, _IntType, __int_bit_count> __pair) {
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if constexpr (__i == 0) {
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return __pair.__get_ptr();
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} else if constexpr (__i == 1) {
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return __pair.__get_value();
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} else {
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static_assert(__i == 0, "Index out of bounds");
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}
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}
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP_STD_VER >= 17
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#endif // _LIBCPP___UTILITY_POINTER_INT_PAIR_H

‎libcxx/include/module.modulemap

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module no_destroy { header "__utility/no_destroy.h" }
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module pair { header "__utility/pair.h" }
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module piecewise_construct { header "__utility/piecewise_construct.h" }
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module pointer_int_pair { header "__utility/pointer_int_pair.h" }
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module priority_tag { header "__utility/priority_tag.h" }
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module private_constructor_tag { header "__utility/private_constructor_tag.h" }
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module rel_ops { header "__utility/rel_ops.h" }

‎libcxx/test/libcxx/utilities/pointer_int_pair/assert.constructor.pass.cpp

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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// UNSUPPORTED: c++03, c++11, c++14
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// REQUIRES: has-unix-headers
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// REQUIRES: libcpp-hardening-mode=debug
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// XFAIL: availability-verbose_abort-missing
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#include "test_macros.h"
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TEST_DIAGNOSTIC_PUSH
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TEST_CLANG_DIAGNOSTIC_IGNORED("-Wprivate-header")
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#include <__utility/pointer_int_pair.h>
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TEST_DIAGNOSTIC_POP
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#include <cassert>
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#include "check_assertion.h"
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struct [[gnu::packed]] Packed {
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char c;
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int i;
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};
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int main(int, char**) {
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TEST_LIBCPP_ASSERT_FAILURE(
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(std::__pointer_int_pair<int*, size_t, std::__integer_width{1}>{nullptr, 2}), "integer is too large!");
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TEST_DIAGNOSTIC_PUSH
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TEST_CLANG_DIAGNOSTIC_IGNORED("-Waddress-of-packed-member") // That's what we're trying to test
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TEST_GCC_DIAGNOSTIC_IGNORED("-Waddress-of-packed-member")
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alignas(int) Packed p;
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TEST_LIBCPP_ASSERT_FAILURE(
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(std::__pointer_int_pair<int*, size_t, std::__integer_width{1}>{&p.i, 0}), "Pointer alignment is too low!");
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TEST_DIAGNOSTIC_POP
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return 0;
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}

‎libcxx/test/libcxx/utilities/pointer_int_pair/constinit.verify.cpp

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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// Ensure that __pointer_int_pair cannot be constant initialized with a value.
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// This would mean that the constructor is `constexpr`, which should only be
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// possible with compiler magic.
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// UNSUPPORTED: c++03, c++11, c++14
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// clang-format off
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#include <__utility/pointer_int_pair.h>
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#include <cstddef>
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template <class Ptr, class UnderlyingType>
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using single_bit_pair = std::__pointer_int_pair<Ptr, UnderlyingType, std::__integer_width{1}>;
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constinit int ptr = 0;
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constinit single_bit_pair<int*, size_t> continitiable_pointer_int_pair_values{&ptr, 0}; // expected-error {{variable does not have a constant initializer}}

‎libcxx/test/libcxx/utilities/pointer_int_pair/pointer_int_pair.pass.cpp

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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// UNSUPPORTED: c++03, c++11, c++14
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#include <__utility/pointer_int_pair.h>
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#include <cassert>
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#include <cstddef>
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template <class Ptr, class UnderlyingType>
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using single_bit_pair = std::__pointer_int_pair<Ptr, UnderlyingType, std::__integer_width{1}>;
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template <class Ptr, class UnderlyingType>
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using two_bit_pair = std::__pointer_int_pair<Ptr, UnderlyingType, std::__integer_width{2}>;
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constinit single_bit_pair<int*, size_t> continitiable_pointer_int_pair;
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int main(int, char**) {
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{ // __pointer_int_pair() constructor
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single_bit_pair<int*, size_t> pair = {};
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assert(pair.__get_value() == 0);
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assert(pair.__get_ptr() == nullptr);
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}
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{ // __pointer_int_pair(pointer, int) constructor
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single_bit_pair<int*, size_t> pair(nullptr, 1);
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assert(pair.__get_value() == 1);
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assert(pair.__get_ptr() == nullptr);
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}
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{ // pointer is correctly packed/unpacked (with different types and values)
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int i;
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single_bit_pair<int*, size_t> pair(&i, 0);
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assert(pair.__get_value() == 0);
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assert(pair.__get_ptr() == &i);
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}
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{
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int i;
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two_bit_pair<int*, size_t> pair(&i, 2);
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assert(pair.__get_value() == 2);
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assert(pair.__get_ptr() == &i);
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}
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{
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short i;
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single_bit_pair<short*, size_t> pair(&i, 1);
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assert(pair.__get_value() == 1);
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assert(pair.__get_ptr() == &i);
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}
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{ // check that a __pointer_int_pair<__pointer_int_pair> works
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int i;
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single_bit_pair<single_bit_pair<int*, size_t>, size_t> pair({&i, 1}, 0);
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assert(pair.__get_value() == 0);
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assert(pair.__get_ptr().__get_ptr() == &i);
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assert(pair.__get_ptr().__get_value() == 1);
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}
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{ // check that the tuple protocol is correctly implemented
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int i;
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two_bit_pair<int*, size_t> pair{&i, 3};
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auto [ptr, value] = pair;
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assert(ptr == &i);
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assert(value == 3);
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}
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{ // check that the (pointer, int) constructor is implicit
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int i;
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two_bit_pair<int*, size_t> pair = {&i, 3};
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assert(pair.__get_ptr() == &i);
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assert(pair.__get_value() == 3);
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}
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{ // check that overaligned types work as expected
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struct alignas(32) Overaligned {
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int i;
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};
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Overaligned i;
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std::__pointer_int_pair<Overaligned*, size_t, std::__integer_width{4}> pair = {&i, 13};
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assert(pair.__get_ptr() == &i);
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assert(pair.__get_value() == 13);
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}
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{ // check that types other than size_t work as well
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int i;
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single_bit_pair<int*, bool> pair = {&i, true};
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assert(pair.__get_ptr() == &i);
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assert(pair.__get_value());
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static_assert(std::is_same_v<decltype(pair.__get_value()), bool>);
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}
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{
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int i;
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single_bit_pair<int*, unsigned char> pair = {&i, 1};
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assert(pair.__get_ptr() == &i);
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assert(pair.__get_value() == 1);
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static_assert(std::is_same_v<decltype(pair.__get_value()), unsigned char>);
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}
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return 0;
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}

‎libcxx/test/libcxx/utilities/pointer_int_pair/static_asserts.verify.cpp

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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// UNSUPPORTED: c++03, c++11, c++14
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#include <__utility/pointer_int_pair.h>
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#include <cstddef>
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#include "test_macros.h"
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// expected-error@*:* {{Not enough bits available for requested bit count}}
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std::__pointer_int_pair<char*, size_t, std::__integer_width{2}> ptr1; // expected-note {{here}}
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// expected-error@*:* {{_IntType has to be an integral type}}
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std::__pointer_int_pair<int*, int*, std::__integer_width{2}> ptr2; // expected-note {{here}}
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// expected-error@*:* {{__pointer_int_pair doesn't work for signed types}}
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std::__pointer_int_pair<int*, signed, std::__integer_width{2}> ptr3; // expected-note {{here}}

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