LLVM  4.0.0
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)> class ArrayRecycler {
30  // The free list for a given array size is a simple singly linked list.
31  // We can't use iplist or Recycler here since those classes can't be copied.
32  struct FreeList {
33  FreeList *Next;
34  };
35 
36  static_assert(Align >= alignof(FreeList), "Object underaligned");
37  static_assert(sizeof(T) >= sizeof(FreeList), "Objects are too small");
38 
39  // Keep a free list for each array size.
41 
42  // Remove an entry from the free list in Bucket[Idx] and return it.
43  // Return NULL if no entries are available.
44  T *pop(unsigned Idx) {
45  if (Idx >= Bucket.size())
46  return nullptr;
47  FreeList *Entry = Bucket[Idx];
48  if (!Entry)
49  return nullptr;
50  Bucket[Idx] = Entry->Next;
51  return reinterpret_cast<T*>(Entry);
52  }
53 
54  // Add an entry to the free list at Bucket[Idx].
55  void push(unsigned Idx, T *Ptr) {
56  assert(Ptr && "Cannot recycle NULL pointer");
57  FreeList *Entry = reinterpret_cast<FreeList*>(Ptr);
58  if (Idx >= Bucket.size())
59  Bucket.resize(size_t(Idx) + 1);
60  Entry->Next = Bucket[Idx];
61  Bucket[Idx] = Entry;
62  }
63 
64 public:
65  /// The size of an allocated array is represented by a Capacity instance.
66  ///
67  /// This class is much smaller than a size_t, and it provides methods to work
68  /// with the set of legal array capacities.
69  class Capacity {
70  uint8_t Index;
71  explicit Capacity(uint8_t idx) : Index(idx) {}
72 
73  public:
74  Capacity() : Index(0) {}
75 
76  /// Get the capacity of an array that can hold at least N elements.
77  static Capacity get(size_t N) {
78  return Capacity(N ? Log2_64_Ceil(N) : 0);
79  }
80 
81  /// Get the number of elements in an array with this capacity.
82  size_t getSize() const { return size_t(1u) << Index; }
83 
84  /// Get the bucket number for this capacity.
85  unsigned getBucket() const { return Index; }
86 
87  /// Get the next larger capacity. Large capacities grow exponentially, so
88  /// this function can be used to reallocate incrementally growing vectors
89  /// in amortized linear time.
90  Capacity getNext() const { return Capacity(Index + 1); }
91  };
92 
94  // The client should always call clear() so recycled arrays can be returned
95  // to the allocator.
96  assert(Bucket.empty() && "Non-empty ArrayRecycler deleted!");
97  }
98 
99  /// Release all the tracked allocations to the allocator. The recycler must
100  /// be free of any tracked allocations before being deleted.
101  template<class AllocatorType>
102  void clear(AllocatorType &Allocator) {
103  for (; !Bucket.empty(); Bucket.pop_back())
104  while (T *Ptr = pop(Bucket.size() - 1))
105  Allocator.Deallocate(Ptr);
106  }
107 
108  /// Special case for BumpPtrAllocator which has an empty Deallocate()
109  /// function.
110  ///
111  /// There is no need to traverse the free lists, pulling all the objects into
112  /// cache.
114  Bucket.clear();
115  }
116 
117  /// Allocate an array of at least the requested capacity.
118  ///
119  /// Return an existing recycled array, or allocate one from Allocator if
120  /// none are available for recycling.
121  ///
122  template<class AllocatorType>
123  T *allocate(Capacity Cap, AllocatorType &Allocator) {
124  // Try to recycle an existing array.
125  if (T *Ptr = pop(Cap.getBucket()))
126  return Ptr;
127  // Nope, get more memory.
128  return static_cast<T*>(Allocator.Allocate(sizeof(T)*Cap.getSize(), Align));
129  }
130 
131  /// Deallocate an array with the specified Capacity.
132  ///
133  /// Cap must be the same capacity that was given to allocate().
134  ///
135  void deallocate(Capacity Cap, T *Ptr) {
136  push(Cap.getBucket(), Ptr);
137  }
138 };
139 
140 } // end llvm namespace
141 
142 #endif
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:29
This file defines the MallocAllocator and BumpPtrAllocator interfaces.
The size of an allocated array is represented by a Capacity instance.
Definition: ArrayRecycler.h:69
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:60
unsigned getBucket() const
Get the bucket number for this capacity.
Definition: ArrayRecycler.h:85
size_t getSize() const
Get the number of elements in an array with this capacity.
Definition: ArrayRecycler.h:82
Allocate memory in an ever growing pool, as if by bump-pointer.
Definition: Allocator.h:138
Greedy Register Allocator
Capacity getNext() const
Get the next larger capacity.
Definition: ArrayRecycler.h:90
void clear(AllocatorType &Allocator)
Release all the tracked allocations to the allocator.
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:532
#define N
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:135
void clear(BumpPtrAllocator &)
Special case for BumpPtrAllocator which has an empty Deallocate() function.
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
void deallocate(Capacity Cap, T *Ptr)
Deallocate an array with the specified Capacity.
int * Ptr
void resize(size_type N)
Definition: SmallVector.h:352