================ @@ -0,0 +1,322 @@ +//===- llvm/ADT/PagedVector.h - 'Lazyly allocated' vectors --------*- C++ +//-*-===// +// +// 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 +// +//===----------------------------------------------------------------------===// +// +// This file defines the PagedVector class. +// +//===----------------------------------------------------------------------===// +#ifndef LLVM_ADT_PAGEDVECTOR_H +#define LLVM_ADT_PAGEDVECTOR_H + +#include "llvm/ADT/PointerIntPair.h" +#include "llvm/Support/Allocator.h" +#include <cassert> +#include <iostream> +#include <vector> + +namespace llvm { +// A vector that allocates memory in pages. +// Order is kept, but memory is allocated only when one element of the page is +// accessed. This introduces a level of indirection, but it is useful when you +// have a sparsely initialised vector where the full size is allocated upfront +// with the default constructor and elements are initialised later, on first +// access. +// +// Notice that this does not have iterators, because if you +// have iterators it probably means you are going to touch +// all the memory in any case, so better use a std::vector in +// the first place. +// +// Pages are allocated in SLAB_SIZE chunks, using the BumpPtrAllocator. +template <typename T, std::size_t PAGE_SIZE = 1024 / sizeof(T)> +class PagedVector { + static_assert(PAGE_SIZE > 0, "PAGE_SIZE must be greater than 0. Most likely " + "you want it to be greater than 16."); + // The actual number of element in the vector which can be accessed. + std::size_t Size = 0; + + // The position of the initial element of the page in the Data vector. + // Pages are allocated contiguously in the Data vector. + mutable std::vector<uintptr_t> PageToDataIdx; + // Actual page data. All the page elements are added to this vector on the + // first access of any of the elements of the page. Elements default + // constructed and elements of the page are stored contiguously. The order of + // the elements however depends on the order of access of the pages. + PointerIntPair<BumpPtrAllocator *, 1, bool> Allocator; + + constexpr static uintptr_t InvalidPage = SIZE_MAX; + +public: + using value_type = T; + + // Default constructor. We build our own allocator. + PagedVector() : Allocator(new BumpPtrAllocator, true) {} + PagedVector(BumpPtrAllocator *A) : Allocator(A, false) {} + + ~PagedVector() { + // If we own the allocator, delete it. + if (Allocator.getInt() == true) + delete Allocator.getPointer(); + } + + // Lookup an element at position i. + // If the associated page is not filled, it will be filled with default + // constructed elements. If the associated page is filled, return the element. + T &operator[](std::size_t Index) const { + assert(Index < Size); + assert(Index / PAGE_SIZE < PageToDataIdx.size()); + uintptr_t &PagePtr = PageToDataIdx[Index / PAGE_SIZE]; + // If the page was not yet allocated, allocate it. + if (PagePtr == InvalidPage) { + T *NewPagePtr = Allocator.getPointer()->template Allocate<T>(PAGE_SIZE); + // We need to invoke the default constructor on all the elements of the + // page. + for (std::size_t I = 0; I < PAGE_SIZE; ++I) + new (NewPagePtr + I) T(); + + PagePtr = reinterpret_cast<uintptr_t>(NewPagePtr); + } + // Dereference the element in the page. + return *((Index % PAGE_SIZE) + reinterpret_cast<T *>(PagePtr)); + } + + // Return the capacity of the vector. I.e. the maximum size it can be expanded + // to with the resize method without allocating more pages. + [[nodiscard]] std::size_t capacity() const { + return PageToDataIdx.size() * PAGE_SIZE; + } + + // Return the size of the vector. I.e. the maximum index that can be + // accessed, i.e. the maximum value which was used as argument of the + // resize method. + [[nodiscard]] std::size_t size() const { return Size; } + + // Expands the vector to the given NewSize number of elements. + // If the vector was smaller, allocates new pages as needed. + // It should be called only with NewSize >= Size. + void resize(std::size_t NewSize) { + // Handle shrink case: delete the pages and update the size. + if (NewSize < Size) { + std::size_t NewLastPage = (NewSize - 1) / PAGE_SIZE; + for (std::size_t I = NewLastPage + 1; I < PageToDataIdx.size(); ++I) { + uintptr_t PagePtr = PageToDataIdx[I]; + if (PagePtr == InvalidPage) + continue; + T *Page = reinterpret_cast<T *>(PagePtr); + // We need to invoke the destructor on all the elements of the page. + for (std::size_t J = 0; J < PAGE_SIZE; ++J) + Page[J].~T(); + Allocator.getPointer()->Deallocate(Page); + } + // Delete the extra ones in the new last page. + uintptr_t PagePtr = PageToDataIdx[NewLastPage]; + if (PagePtr != InvalidPage) { + T *Page = reinterpret_cast<T *>(PagePtr); + // If the new size and the old size are on the same page, we need to + // delete only the elements between the new size and the old size. + // Otherwise we need to delete all the remaining elements in the page. + std::size_t OldPage = (Size - 1) / PAGE_SIZE; + std::size_t NewPage = (NewSize - 1) / PAGE_SIZE; + std::size_t LastPageElements = + OldPage == NewPage ? Size % PAGE_SIZE : PAGE_SIZE; + for (std::size_t J = NewSize % PAGE_SIZE; J < LastPageElements; ++J) + Page[J].~T(); + } + PageToDataIdx.resize(NewLastPage + 1); + } + Size = NewSize; + // If the capacity is enough, just update the size and continue + // with the currently allocated pages. + if (Size <= capacity()) + return; + // The number of pages to allocate. The Remainder is calculated + // for the case in which the NewSize is not a multiple of PAGE_SIZE. + // In that case we need one more page. + std::size_t Pages = Size / PAGE_SIZE; + std::size_t Remainder = Size % PAGE_SIZE; + if (Remainder != 0) + Pages += 1; ---------------- zygoloid wrote:
I've added some suggested edits to demonstrate. https://github.com/llvm/llvm-project/pull/66430 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
