================ @@ -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; ---------------- ktf wrote:
I am not sure I understand the comment. PageId needs to be overridden in case it's -1, so that's effectively the closest to first use I think it can get to. 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
