Yi Kong | 7bf2a68 | 2019-04-18 17:30:49 -0700 | [diff] [blame] | 1 | //==- llvm/Support/ArrayRecycler.h - Recycling of Arrays ---------*- C++ -*-==// |
| 2 | // |
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | // See https://llvm.org/LICENSE.txt for license information. |
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | // |
| 7 | //===----------------------------------------------------------------------===// |
| 8 | // |
| 9 | // This file defines the ArrayRecycler class template which can recycle small |
| 10 | // arrays allocated from one of the allocators in Allocator.h |
| 11 | // |
| 12 | //===----------------------------------------------------------------------===// |
| 13 | |
| 14 | #ifndef LLVM_SUPPORT_ARRAYRECYCLER_H |
| 15 | #define LLVM_SUPPORT_ARRAYRECYCLER_H |
| 16 | |
| 17 | #include "llvm/ADT/SmallVector.h" |
| 18 | #include "llvm/Support/Allocator.h" |
| 19 | #include "llvm/Support/MathExtras.h" |
| 20 | |
| 21 | namespace llvm { |
| 22 | |
| 23 | /// Recycle small arrays allocated from a BumpPtrAllocator. |
| 24 | /// |
| 25 | /// Arrays are allocated in a small number of fixed sizes. For each supported |
| 26 | /// array size, the ArrayRecycler keeps a free list of available arrays. |
| 27 | /// |
| 28 | template <class T, size_t Align = alignof(T)> class ArrayRecycler { |
| 29 | // The free list for a given array size is a simple singly linked list. |
| 30 | // We can't use iplist or Recycler here since those classes can't be copied. |
| 31 | struct FreeList { |
| 32 | FreeList *Next; |
| 33 | }; |
| 34 | |
| 35 | static_assert(Align >= alignof(FreeList), "Object underaligned"); |
| 36 | static_assert(sizeof(T) >= sizeof(FreeList), "Objects are too small"); |
| 37 | |
| 38 | // Keep a free list for each array size. |
| 39 | SmallVector<FreeList*, 8> Bucket; |
| 40 | |
| 41 | // Remove an entry from the free list in Bucket[Idx] and return it. |
| 42 | // Return NULL if no entries are available. |
| 43 | T *pop(unsigned Idx) { |
| 44 | if (Idx >= Bucket.size()) |
| 45 | return nullptr; |
| 46 | FreeList *Entry = Bucket[Idx]; |
| 47 | if (!Entry) |
| 48 | return nullptr; |
| 49 | __asan_unpoison_memory_region(Entry, Capacity::get(Idx).getSize()); |
| 50 | Bucket[Idx] = Entry->Next; |
| 51 | __msan_allocated_memory(Entry, Capacity::get(Idx).getSize()); |
| 52 | return reinterpret_cast<T*>(Entry); |
| 53 | } |
| 54 | |
| 55 | // Add an entry to the free list at Bucket[Idx]. |
| 56 | void push(unsigned Idx, T *Ptr) { |
| 57 | assert(Ptr && "Cannot recycle NULL pointer"); |
| 58 | FreeList *Entry = reinterpret_cast<FreeList*>(Ptr); |
| 59 | if (Idx >= Bucket.size()) |
| 60 | Bucket.resize(size_t(Idx) + 1); |
| 61 | Entry->Next = Bucket[Idx]; |
| 62 | Bucket[Idx] = Entry; |
| 63 | __asan_poison_memory_region(Ptr, Capacity::get(Idx).getSize()); |
| 64 | } |
| 65 | |
| 66 | public: |
| 67 | /// The size of an allocated array is represented by a Capacity instance. |
| 68 | /// |
| 69 | /// This class is much smaller than a size_t, and it provides methods to work |
| 70 | /// with the set of legal array capacities. |
| 71 | class Capacity { |
| 72 | uint8_t Index; |
| 73 | explicit Capacity(uint8_t idx) : Index(idx) {} |
| 74 | |
| 75 | public: |
| 76 | Capacity() : Index(0) {} |
| 77 | |
| 78 | /// Get the capacity of an array that can hold at least N elements. |
| 79 | static Capacity get(size_t N) { |
| 80 | return Capacity(N ? Log2_64_Ceil(N) : 0); |
| 81 | } |
| 82 | |
| 83 | /// Get the number of elements in an array with this capacity. |
| 84 | size_t getSize() const { return size_t(1u) << Index; } |
| 85 | |
| 86 | /// Get the bucket number for this capacity. |
| 87 | unsigned getBucket() const { return Index; } |
| 88 | |
| 89 | /// Get the next larger capacity. Large capacities grow exponentially, so |
| 90 | /// this function can be used to reallocate incrementally growing vectors |
| 91 | /// in amortized linear time. |
| 92 | Capacity getNext() const { return Capacity(Index + 1); } |
| 93 | }; |
| 94 | |
| 95 | ~ArrayRecycler() { |
| 96 | // The client should always call clear() so recycled arrays can be returned |
| 97 | // to the allocator. |
| 98 | assert(Bucket.empty() && "Non-empty ArrayRecycler deleted!"); |
| 99 | } |
| 100 | |
| 101 | /// Release all the tracked allocations to the allocator. The recycler must |
| 102 | /// be free of any tracked allocations before being deleted. |
| 103 | template<class AllocatorType> |
| 104 | void clear(AllocatorType &Allocator) { |
| 105 | for (; !Bucket.empty(); Bucket.pop_back()) |
| 106 | while (T *Ptr = pop(Bucket.size() - 1)) |
| 107 | Allocator.Deallocate(Ptr); |
| 108 | } |
| 109 | |
| 110 | /// Special case for BumpPtrAllocator which has an empty Deallocate() |
| 111 | /// function. |
| 112 | /// |
| 113 | /// There is no need to traverse the free lists, pulling all the objects into |
| 114 | /// cache. |
| 115 | void clear(BumpPtrAllocator&) { |
| 116 | Bucket.clear(); |
| 117 | } |
| 118 | |
| 119 | /// Allocate an array of at least the requested capacity. |
| 120 | /// |
| 121 | /// Return an existing recycled array, or allocate one from Allocator if |
| 122 | /// none are available for recycling. |
| 123 | /// |
| 124 | template<class AllocatorType> |
| 125 | T *allocate(Capacity Cap, AllocatorType &Allocator) { |
| 126 | // Try to recycle an existing array. |
| 127 | if (T *Ptr = pop(Cap.getBucket())) |
| 128 | return Ptr; |
| 129 | // Nope, get more memory. |
| 130 | return static_cast<T*>(Allocator.Allocate(sizeof(T)*Cap.getSize(), Align)); |
| 131 | } |
| 132 | |
| 133 | /// Deallocate an array with the specified Capacity. |
| 134 | /// |
| 135 | /// Cap must be the same capacity that was given to allocate(). |
| 136 | /// |
| 137 | void deallocate(Capacity Cap, T *Ptr) { |
| 138 | push(Cap.getBucket(), Ptr); |
| 139 | } |
| 140 | }; |
| 141 | |
| 142 | } // end llvm namespace |
| 143 | |
| 144 | #endif |