================ @@ -0,0 +1,133 @@ +//===- 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 <cassert> +#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. +template <typename T, int PAGE_SIZE = 1024 / sizeof(T)> class PagedVector { + // 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<int> Lookup; + // 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 oder of + // the elements however depends on the order of access of the pages. + mutable std::vector<T> Data; + +public: + // Lookup an element at position Index. + T &operator[](std::size_t Index) const { return at(Index); } + + // 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 &at(std::size_t Index) const { + assert(Index < Size); + assert(Index / PAGE_SIZE < Lookup.size()); + auto &PageId = Lookup[Index / PAGE_SIZE]; + // If the range is not filled, fill it + if (PageId == -1) { + int OldSize = Data.size(); + PageId = OldSize / PAGE_SIZE; + // Allocate the memory + Data.resize(OldSize + PAGE_SIZE); + // Fill the whole capacity with empty elements + for (int I = 0; I < PAGE_SIZE; ++I) { + Data[I + OldSize] = T(); + } + } + // Calculate the actual position in the Data vector + // by taking the start of the page and adding the offset + // in the page. + std::size_t StoreIndex = Index % PAGE_SIZE + PAGE_SIZE * PageId; + // Return the element + assert(StoreIndex < Data.size()); + return Data[StoreIndex]; + } + + // Return the capacity of the vector. I.e. the maximum size it can be expanded + // to with the expand method without allocating more pages. + std::size_t capacity() const { return Lookup.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 + // expand method. + 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 expand(std::size_t NewSize) { + // You cannot shrink the vector, otherwise + // one would have to invalidate contents which is expensive and + // while giving the false hope that the resize is cheap. + if (NewSize <= Size) { + return; + } + // If the capacity is enough, just update the size and continue + // with the currently allocated pages. + if (NewSize <= capacity()) { + Size = NewSize; + 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. + auto Pages = NewSize / PAGE_SIZE; + auto Remainder = NewSize % PAGE_SIZE; + if (Remainder) { + Pages += 1; + } + assert(Pages > Lookup.size()); + // We use -1 to indicate that a page has not been allocated yet. + // This cannot be 0, because 0 is a valid page id. + // We use -1 instead of a separate bool to avoid wasting space. + Lookup.resize(Pages, -1); + Size = NewSize; + } + + // Return true if the vector is empty + bool empty() const { return Size == 0; } + + /// Clear the vector, i.e. clear the allocated pages, the whole page + /// lookup index and reset the size. + void clear() { + Size = 0; + Lookup.clear(); + Data.clear(); + } + + /// Return the materialised vector. This is useful if you want to iterate + /// in an efficient way over the non default constructed elements. + /// It's not called data() because that would be misleading, since only + /// elements for pages which have been accessed are actually allocated. + std::vector<T> const &materialised() const { return Data; } ---------------- kuhar wrote:
I would expect this class to expose iterators/ranges. 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
