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(Value: 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(Idx: 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(Idx: 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(Idx: Cap.getBucket(), Ptr); |
139 | } |
140 | }; |
141 | |
142 | } // end llvm namespace |
143 | |
144 | #endif |
145 | |