v1/__memory/unique_temporary_buffer.h

0001 // -*- C++ -*-
0002 //===----------------------------------------------------------------------===//
0003 //
0004 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0005 // See https://llvm.org/LICENSE.txt for license information.
0006 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0007 //
0008 //===----------------------------------------------------------------------===//
0009
0010 #ifndef _LIBCPP___MEMORY_UNIQUE_TEMPORARY_BUFFER_H
0011 #define _LIBCPP___MEMORY_UNIQUE_TEMPORARY_BUFFER_H
0012
0013 #include <__assert>
0014 #include <__config>
0015
0016 #include <__cstddef/ptrdiff_t.h>
0017 #include <__memory/allocator.h>
0018 #include <__memory/unique_ptr.h>
0019 #include <__new/allocate.h>
0020 #include <__new/global_new_delete.h>
0021 #include <__type_traits/is_constant_evaluated.h>
0022
0023 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0024 #  pragma GCC system_header
0025 #endif
0026
0027 _LIBCPP_BEGIN_NAMESPACE_STD
0028
0029 template <class _Tp>
0030 struct __temporary_buffer_deleter {
0031   ptrdiff_t __count_; // ignored in non-constant evaluation
0032
0033   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __temporary_buffer_deleter() _NOEXCEPT : __count_(0) {}
0034   _LIBCPP_HIDE_FROM_ABI
0035   _LIBCPP_CONSTEXPR explicit __temporary_buffer_deleter(ptrdiff_t __count) _NOEXCEPT : __count_(__count) {}
0036
0037   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 void operator()(_Tp* __ptr) _NOEXCEPT {
0038     if (__libcpp_is_constant_evaluated()) {
0039       allocator<_Tp>().deallocate(__ptr, __count_);
0040       return;
0041     }
0042
0043     std::__libcpp_deallocate_unsized<_Tp>(__ptr);
0044   }
0045 };
0046
0047 template <class _Tp>
0048 using __unique_temporary_buffer _LIBCPP_NODEBUG = unique_ptr<_Tp, __temporary_buffer_deleter<_Tp> >;
0049
0050 template <class _Tp>
0051 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _LIBCPP_CONSTEXPR_SINCE_CXX23 __unique_temporary_buffer<_Tp>
0052 __allocate_unique_temporary_buffer(ptrdiff_t __count) {
0053   using __deleter_type       = __temporary_buffer_deleter<_Tp>;
0054   using __unique_buffer_type = __unique_temporary_buffer<_Tp>;
0055
0056   if (__libcpp_is_constant_evaluated()) {
0057     return __unique_buffer_type(allocator<_Tp>().allocate(__count), __deleter_type(__count));
0058   }
0059
0060   _Tp* __ptr = nullptr;
0061   const ptrdiff_t __max_count =
0062       (~ptrdiff_t(0) ^ ptrdiff_t(ptrdiff_t(1) << (sizeof(ptrdiff_t) * __CHAR_BIT__ - 1))) / sizeof(_Tp);
0063   if (__count > __max_count)
0064     __count = __max_count;
0065   while (__count > 0) {
0066 #if _LIBCPP_HAS_ALIGNED_ALLOCATION
0067     if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp))) {
0068       align_val_t __al = align_val_t(_LIBCPP_ALIGNOF(_Tp));
0069       __ptr            = static_cast<_Tp*>(::operator new(__count * sizeof(_Tp), __al, nothrow));
0070     } else {
0071       __ptr = static_cast<_Tp*>(::operator new(__count * sizeof(_Tp), nothrow));
0072     }
0073 #else
0074     if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp))) {
0075       // Since aligned operator new is unavailable, constructs an empty buffer rather than one with invalid alignment.
0076       return __unique_buffer_type();
0077     }
0078
0079     __ptr = static_cast<_Tp*>(::operator new(__count * sizeof(_Tp), nothrow));
0080 #endif
0081
0082     if (__ptr) {
0083       break;
0084     }
0085     __count /= 2;
0086   }
0087
0088   return __unique_buffer_type(__ptr, __deleter_type(__count));
0089 }
0090
0091 _LIBCPP_END_NAMESPACE_STD
0092
0093 #endif // _LIBCPP___MEMORY_UNIQUE_TEMPORARY_BUFFER_H