LLVM  3.7.0
ArrayRecycler.h
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1 //==- llvm/Support/ArrayRecycler.h - Recycling of Arrays ---------*- C++ -*-==//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the ArrayRecycler class template which can recycle small
11 // arrays allocated from one of the allocators in Allocator.h
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_SUPPORT_ARRAYRECYCLER_H
16 #define LLVM_SUPPORT_ARRAYRECYCLER_H
17 
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/Support/Allocator.h"
21 
22 namespace llvm {
23 
24 /// Recycle small arrays allocated from a BumpPtrAllocator.
25 ///
26 /// Arrays are allocated in a small number of fixed sizes. For each supported
27 /// array size, the ArrayRecycler keeps a free list of available arrays.
28 ///
29 template<class T, size_t Align = AlignOf<T>::Alignment>
31  // The free list for a given array size is a simple singly linked list.
32  // We can't use iplist or Recycler here since those classes can't be copied.
33  struct FreeList {
34  FreeList *Next;
35  };
36 
37  static_assert(Align >= AlignOf<FreeList>::Alignment, "Object underaligned");
38  static_assert(sizeof(T) >= sizeof(FreeList), "Objects are too small");
39 
40  // Keep a free list for each array size.
42 
43  // Remove an entry from the free list in Bucket[Idx] and return it.
44  // Return NULL if no entries are available.
45  T *pop(unsigned Idx) {
46  if (Idx >= Bucket.size())
47  return nullptr;
48  FreeList *Entry = Bucket[Idx];
49  if (!Entry)
50  return nullptr;
51  Bucket[Idx] = Entry->Next;
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  }
64 
65 public:
66  /// The size of an allocated array is represented by a Capacity instance.
67  ///
68  /// This class is much smaller than a size_t, and it provides methods to work
69  /// with the set of legal array capacities.
70  class Capacity {
71  uint8_t Index;
72  explicit Capacity(uint8_t idx) : Index(idx) {}
73 
74  public:
75  Capacity() : Index(0) {}
76 
77  /// Get the capacity of an array that can hold at least N elements.
78  static Capacity get(size_t N) {
79  return Capacity(N ? Log2_64_Ceil(N) : 0);
80  }
81 
82  /// Get the number of elements in an array with this capacity.
83  size_t getSize() const { return size_t(1u) << Index; }
84 
85  /// Get the bucket number for this capacity.
86  unsigned getBucket() const { return Index; }
87 
88  /// Get the next larger capacity. Large capacities grow exponentially, so
89  /// this function can be used to reallocate incrementally growing vectors
90  /// in amortized linear time.
91  Capacity getNext() const { return Capacity(Index + 1); }
92  };
93 
95  // The client should always call clear() so recycled arrays can be returned
96  // to the allocator.
97  assert(Bucket.empty() && "Non-empty ArrayRecycler deleted!");
98  }
99 
100  /// Release all the tracked allocations to the allocator. The recycler must
101  /// be free of any tracked allocations before being deleted.
102  template<class AllocatorType>
103  void clear(AllocatorType &Allocator) {
104  for (; !Bucket.empty(); Bucket.pop_back())
105  while (T *Ptr = pop(Bucket.size() - 1))
106  Allocator.Deallocate(Ptr);
107  }
108 
109  /// Special case for BumpPtrAllocator which has an empty Deallocate()
110  /// function.
111  ///
112  /// There is no need to traverse the free lists, pulling all the objects into
113  /// cache.
115  Bucket.clear();
116  }
117 
118  /// Allocate an array of at least the requested capacity.
119  ///
120  /// Return an existing recycled array, or allocate one from Allocator if
121  /// none are available for recycling.
122  ///
123  template<class AllocatorType>
124  T *allocate(Capacity Cap, AllocatorType &Allocator) {
125  // Try to recycle an existing array.
126  if (T *Ptr = pop(Cap.getBucket()))
127  return Ptr;
128  // Nope, get more memory.
129  return static_cast<T*>(Allocator.Allocate(sizeof(T)*Cap.getSize(), Align));
130  }
131 
132  /// Deallocate an array with the specified Capacity.
133  ///
134  /// Cap must be the same capacity that was given to allocate().
135  ///
136  void deallocate(Capacity Cap, T *Ptr) {
137  push(Cap.getBucket(), Ptr);
138  }
139 };
140 
141 } // end llvm namespace
142 
143 #endif
AlignOf - A templated class that contains an enum value representing the alignment of the template ar...
Definition: AlignOf.h:46
T * allocate(Capacity Cap, AllocatorType &Allocator)
Allocate an array of at least the requested capacity.
Recycle small arrays allocated from a BumpPtrAllocator.
Definition: ArrayRecycler.h:30
This file defines the MallocAllocator and BumpPtrAllocator interfaces.
The size of an allocated array is represented by a Capacity instance.
Definition: ArrayRecycler.h:70
bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const
Definition: SmallVector.h:57
unsigned getBucket() const
Get the bucket number for this capacity.
Definition: ArrayRecycler.h:86
size_t getSize() const
Get the number of elements in an array with this capacity.
Definition: ArrayRecycler.h:83
Allocate memory in an ever growing pool, as if by bump-pointer.
Definition: Allocator.h:135
Capacity getNext() const
Get the next larger capacity.
Definition: ArrayRecycler.h:91
void clear(AllocatorType &Allocator)
Release all the tracked allocations to the allocator.
static cl::opt< AlignMode > Align(cl::desc("Load/store alignment support"), cl::Hidden, cl::init(NoStrictAlign), cl::values(clEnumValN(StrictAlign,"aarch64-strict-align","Disallow all unaligned memory accesses"), clEnumValN(NoStrictAlign,"aarch64-no-strict-align","Allow unaligned memory accesses"), clEnumValEnd))
unsigned Log2_64_Ceil(uint64_t Value)
Log2_64_Ceil - This function returns the ceil log base 2 of the specified value, 64 if the value is z...
Definition: MathExtras.h:487
#define N
void clear(BumpPtrAllocator &)
Special case for BumpPtrAllocator which has an empty Deallocate() function.
void deallocate(Capacity Cap, T *Ptr)
Deallocate an array with the specified Capacity.
void resize(size_type N)
Definition: SmallVector.h:376