================ @@ -0,0 +1,545 @@ +//===----------------------------------------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// + +#ifndef _LIBCPP___VECTOR_LAYOUT_H +#define _LIBCPP___VECTOR_LAYOUT_H + +#include <__assert> +#include <__config> +#include <__debug_utils/sanitizers.h> +#include <__memory/allocator_traits.h> +#include <__memory/compressed_pair.h> +#include <__memory/pointer_traits.h> +#include <__memory/swap_allocator.h> +#include <__memory/uninitialized_algorithms.h> +#include <__split_buffer> +#include <__type_traits/is_nothrow_constructible.h> +#include <__utility/exchange.h> +#include <__utility/move.h> +#include <__utility/swap.h> + +#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) +# pragma GCC system_header +#endif + +_LIBCPP_PUSH_MACROS +#include <__undef_macros> + +_LIBCPP_BEGIN_NAMESPACE_STD + +/// Defines `std::vector`'s storage layout and any operations that are affected by a change in the +/// layout. +/// +/// `std::vector` can be represented in a variety of ways. Each representation strongly influences +/// the codegen when calling vector operations, which can significantly impact runtime performance +/// and memory utilisation. libc++ provides two alternative layouts for `std::vector`, although only +/// one can be active for an enitre binary: +/// +/// * pointer-based layout (stable ABI default) +/// * size-based layout (unstable ABI alternative) +// +/// We describe these layouts below. All vector representations have a pointer that points to where +/// the memory is allocated (called `__begin_`). +/// +/// **Pointer-based layout** +/// +/// The pointer-based layout uses two more pointers in addition to `__begin_`. The second pointer +/// (called `__end_`) points past the end of the part of the buffer that holds valid elements. +/// Another pointer (called `__capacity_`) points past the end of the allocated buffer. The original +/// libc++ `std::vector` implementation only provided the pointer-based layout. libc++ continues to +/// use the pointer-based layout, by default, in order to maintain binary compatibility with +/// existing software. +/// +/// The `__end_` pointer has three primary use-cases: +/// * to compute the size of the vector; and +/// * to construct the past-the-end iterator; and +/// * to indicate where the next element should be appended. +/// +/// The `__capacity_` is used to compute the capacity of the vector, which lets the vector know how +/// many elements can be added to the vector before a reallocation is necessary. +/// +/// __begin_ = 0xE4FD0, __end_ = 0xE4FF0, __capacity_ = 0xE5000 +/// 0xE4FD0 0xE4FF0 0xE5000 +/// v v v +/// +---------------+--------+--------+--------+--------+--------+--------+---------------------+ +/// | ????????????? | 3174 | 5656 | 648 | 489 | ------ | ------ | ??????????????????? | +/// +---------------+--------+--------+--------+--------+--------+--------+---------------------+ +/// ^ ^ ^ +/// __begin_ __end_ __capacity_ +/// +/// Figure 1: A visual representation of a pointer-based `std::vector<short>`. This vector has +/// four elements, with the capacity to store six. Boxes with numbers are valid elements within +/// the vector, and boxes with `xx` have been allocated, but aren't being used as elements right +/// now. +/// +/// This is the default layout for libc++. +/// +/// **Size-based layout** +/// +/// The size-based layout uses integers to track its size and capacity, and computes pointers to +/// past-the-end of the valid range and the whole buffer only when it's necessary. Programs using +/// the size-based layout have been measured to yield improved compute and memory performance over +/// the pointer-based layout. Despite these promising measurements, the size-based layout is opt-in, +/// to preserve ABI compatibility with prebuilt binaries. Given the improved performance, we +/// recommend preferring the size-based layout in the absence of such ABI constraints. +/// +/// __begin_ = 0xE4FD0, __size_ = 4, __capacity_ = 6 +/// 0xE4FD0 +/// v +/// +---------------+--------+--------+--------+--------+--------+--------+---------------------+ +/// | ????????????? | 3174 | 5656 | 648 | 489 | ------ | ------ | ??????????????????? | +/// +---------------+--------+--------+--------+--------+--------+--------+---------------------+ +/// ^ +/// __begin_ +/// +/// Figure 2: A visual representation of this a size-based layout. Blank boxes are not a part +/// of the vector's allocated buffer. +/// +/// **Class design** +/// +/// __vector_layout was designed with the following goals: +/// 1. to abstractly represent the buffer's boundaries; and +/// 2. to limit the number of `#ifdef` blocks that a reader needs to pass through; and +/// 3. given (1) and (2), to have no logically identical components in multiple `#ifdef` clauses. +/// +/// To facilitate these goals, there is a single `__vector_layout` definition. Users must choose +/// their vector's layout when libc++ is being configured, so there is no need to manage multiple +/// vector layout types (e.g. `__vector_size_layout`, `__vector_pointer_layout`, etc.). In doing so, +/// we reduce a significant portion of duplicate code. +template <class _Tp, class _Allocator> +class __vector_layout { +public: + using value_type _LIBCPP_NODEBUG = _Tp; + using allocator_type _LIBCPP_NODEBUG = _Allocator; + using __alloc_traits _LIBCPP_NODEBUG = allocator_traits<allocator_type>; + using size_type _LIBCPP_NODEBUG = typename __alloc_traits::size_type; + using pointer _LIBCPP_NODEBUG = typename __alloc_traits::pointer; + using const_pointer _LIBCPP_NODEBUG = typename __alloc_traits::const_pointer; +#ifdef _LIBCPP_ABI_SIZE_BASED_VECTOR + using _SplitBuffer _LIBCPP_NODEBUG = __split_buffer<_Tp, _Allocator, __split_buffer_size_layout>; + using __bound_type _LIBCPP_NODEBUG = size_type; +#else + using _SplitBuffer _LIBCPP_NODEBUG = __split_buffer<_Tp, _Allocator, __split_buffer_pointer_layout>; + using __bound_type _LIBCPP_NODEBUG = pointer; +#endif + + // Cannot be defaulted, since `_LIBCPP_COMPRESSED_PAIR` isn't an aggregate before C++14. + _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __vector_layout() + _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value) + : __capacity_() {} + + _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI explicit __vector_layout(allocator_type const& __a) + _NOEXCEPT_(is_nothrow_copy_constructible<allocator_type>::value) + : __capacity_(), __alloc_(__a) {} + + _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI explicit __vector_layout(allocator_type&& __a) + _NOEXCEPT_(is_nothrow_move_constructible<allocator_type>::value) + : __capacity_(), __alloc_(std::move(__a)) {} + + _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __vector_layout(__vector_layout&& __other) + _NOEXCEPT_(is_nothrow_move_constructible<allocator_type>::value); + + /// Returns a reference to the stored allocator. + [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI allocator_type& __alloc() _NOEXCEPT { + return __alloc_; + } + + [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI allocator_type const& + __alloc() const _NOEXCEPT { + return __alloc_; + } + + /// Returns a pointer to the beginning of the buffer. + /// + /// `__begin_ptr()` is not called `data()` because `vector::data()` returns `T*`, but `__begin_` + /// is allowed to be a fancy pointer. + [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI pointer __begin_ptr() _NOEXCEPT { + return __begin_; + } + + [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const_pointer __begin_ptr() const _NOEXCEPT { + return __begin_; + } + + /// Returns a built-in pointer to the beginning of the buffer. + [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI _Tp* __data() _NOEXCEPT { + return std::__to_address(__begin_); + } + + [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI _Tp const* __data() const _NOEXCEPT { + return std::__to_address(__begin_); + } + + /// Returns the value that the layout uses to determine the vector's size. + /// + /// `__bound_representation()` should only be used when directly operating on the layout from + /// outside `__vector_layout`. Its result must be used with type deduction to avoid compile-time + /// failures. + [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __bound_type + __bound_representation() const _NOEXCEPT; + + /// Returns how many elements can be added before a reallocation occurs. + [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type + __remaining_capacity() const _NOEXCEPT; + + /// Determines if a reallocation is necessary. + [[__nodiscard__]] _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI bool __is_full() const _NOEXCEPT; + + /// Sets the member pointing to the first element in the vector to `__new_begin`, the member used + /// to obtain the vector's bound to the equivalent of `__new_size`, and the member that represents + /// the vector's capacity to the equivalent to `__new_capacity`. + _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void + __set_layout(pointer __new_begin, size_type __new_size, size_type __new_capacity) _NOEXCEPT; + + /// Sets the member used to obtain the vector's bound to the equivalent of `__ptr`. + _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __set_bound_using_pointer(pointer __ptr) _NOEXCEPT; + + _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __reset_without_allocator() _NOEXCEPT; + _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __swap(__vector_layout& __other) _NOEXCEPT; + _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __swap_layouts(_SplitBuffer& __other) _NOEXCEPT; ---------------- ldionne wrote:
I think this is dead code (and also the two definitions). https://github.com/llvm/llvm-project/pull/155330 _______________________________________________ lldb-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
