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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204011 91177308-0d34-0410-b5e6-96231b3b80d8
145 lines
4.5 KiB
C++
145 lines
4.5 KiB
C++
//==- llvm/Support/ArrayRecycler.h - Recycling of Arrays ---------*- C++ -*-==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the ArrayRecycler class template which can recycle small
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// arrays allocated from one of the allocators in Allocator.h
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_ARRAYRECYCLER_H
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#define LLVM_SUPPORT_ARRAYRECYCLER_H
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Support/MathExtras.h"
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namespace llvm {
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class BumpPtrAllocator;
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/// Recycle small arrays allocated from a BumpPtrAllocator.
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///
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/// Arrays are allocated in a small number of fixed sizes. For each supported
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/// array size, the ArrayRecycler keeps a free list of available arrays.
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///
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template<class T, size_t Align = AlignOf<T>::Alignment>
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class ArrayRecycler {
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// The free list for a given array size is a simple singly linked list.
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// We can't use iplist or Recycler here since those classes can't be copied.
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struct FreeList {
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FreeList *Next;
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};
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static_assert(Align >= AlignOf<FreeList>::Alignment, "Object underaligned");
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static_assert(sizeof(T) >= sizeof(FreeList), "Objects are too small");
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// Keep a free list for each array size.
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SmallVector<FreeList*, 8> Bucket;
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// Remove an entry from the free list in Bucket[Idx] and return it.
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// Return NULL if no entries are available.
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T *pop(unsigned Idx) {
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if (Idx >= Bucket.size())
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return 0;
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FreeList *Entry = Bucket[Idx];
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if (!Entry)
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return 0;
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Bucket[Idx] = Entry->Next;
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return reinterpret_cast<T*>(Entry);
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}
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// Add an entry to the free list at Bucket[Idx].
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void push(unsigned Idx, T *Ptr) {
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assert(Ptr && "Cannot recycle NULL pointer");
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FreeList *Entry = reinterpret_cast<FreeList*>(Ptr);
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if (Idx >= Bucket.size())
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Bucket.resize(size_t(Idx) + 1);
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Entry->Next = Bucket[Idx];
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Bucket[Idx] = Entry;
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}
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public:
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/// The size of an allocated array is represented by a Capacity instance.
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///
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/// This class is much smaller than a size_t, and it provides methods to work
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/// with the set of legal array capacities.
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class Capacity {
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uint8_t Index;
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explicit Capacity(uint8_t idx) : Index(idx) {}
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public:
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Capacity() : Index(0) {}
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/// Get the capacity of an array that can hold at least N elements.
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static Capacity get(size_t N) {
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return Capacity(N ? Log2_64_Ceil(N) : 0);
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}
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/// Get the number of elements in an array with this capacity.
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size_t getSize() const { return size_t(1u) << Index; }
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/// Get the bucket number for this capacity.
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unsigned getBucket() const { return Index; }
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/// Get the next larger capacity. Large capacities grow exponentially, so
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/// this function can be used to reallocate incrementally growing vectors
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/// in amortized linear time.
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Capacity getNext() const { return Capacity(Index + 1); }
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};
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~ArrayRecycler() {
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// The client should always call clear() so recycled arrays can be returned
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// to the allocator.
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assert(Bucket.empty() && "Non-empty ArrayRecycler deleted!");
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}
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/// Release all the tracked allocations to the allocator. The recycler must
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/// be free of any tracked allocations before being deleted.
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template<class AllocatorType>
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void clear(AllocatorType &Allocator) {
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for (; !Bucket.empty(); Bucket.pop_back())
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while (T *Ptr = pop(Bucket.size() - 1))
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Allocator.Deallocate(Ptr);
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}
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/// Special case for BumpPtrAllocator which has an empty Deallocate()
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/// function.
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///
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/// There is no need to traverse the free lists, pulling all the objects into
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/// cache.
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void clear(BumpPtrAllocator&) {
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Bucket.clear();
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}
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/// Allocate an array of at least the requested capacity.
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///
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/// Return an existing recycled array, or allocate one from Allocator if
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/// none are available for recycling.
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///
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template<class AllocatorType>
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T *allocate(Capacity Cap, AllocatorType &Allocator) {
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// Try to recycle an existing array.
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if (T *Ptr = pop(Cap.getBucket()))
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return Ptr;
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// Nope, get more memory.
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return static_cast<T*>(Allocator.Allocate(sizeof(T)*Cap.getSize(), Align));
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}
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/// Deallocate an array with the specified Capacity.
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///
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/// Cap must be the same capacity that was given to allocate().
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///
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void deallocate(Capacity Cap, T *Ptr) {
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push(Cap.getBucket(), Ptr);
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}
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};
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} // end llvm namespace
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#endif
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