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//==- llvm/Support/ArrayRecycler.h - Recycling of Arrays ---------*- C++ -*-==//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines the ArrayRecycler class template which can recycle small
// arrays allocated from one of the allocators in Allocator.h
#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/MathExtras.h"
namespace llvm {
/// Recycle small arrays allocated from a BumpPtrAllocator.
/// Arrays are allocated in a small number of fixed sizes. For each supported
/// array size, the ArrayRecycler keeps a free list of available arrays.
template <class T, size_t Align = alignof(T)> class ArrayRecycler {
// The free list for a given array size is a simple singly linked list.
// We can't use iplist or Recycler here since those classes can't be copied.
struct FreeList {
FreeList *Next;
static_assert(Align >= alignof(FreeList), "Object underaligned");
static_assert(sizeof(T) >= sizeof(FreeList), "Objects are too small");
// Keep a free list for each array size.
SmallVector<FreeList*, 8> Bucket;
// Remove an entry from the free list in Bucket[Idx] and return it.
// Return NULL if no entries are available.
T *pop(unsigned Idx) {
if (Idx >= Bucket.size())
return nullptr;
FreeList *Entry = Bucket[Idx];
if (!Entry)
return nullptr;
__asan_unpoison_memory_region(Entry, Capacity::get(Idx).getSize());
Bucket[Idx] = Entry->Next;
__msan_allocated_memory(Entry, Capacity::get(Idx).getSize());
return reinterpret_cast<T*>(Entry);
// Add an entry to the free list at Bucket[Idx].
void push(unsigned Idx, T *Ptr) {
assert(Ptr && "Cannot recycle NULL pointer");
FreeList *Entry = reinterpret_cast<FreeList*>(Ptr);
if (Idx >= Bucket.size())
Bucket.resize(size_t(Idx) + 1);
Entry->Next = Bucket[Idx];
Bucket[Idx] = Entry;
__asan_poison_memory_region(Ptr, Capacity::get(Idx).getSize());
/// The size of an allocated array is represented by a Capacity instance.
/// This class is much smaller than a size_t, and it provides methods to work
/// with the set of legal array capacities.
class Capacity {
uint8_t Index;
explicit Capacity(uint8_t idx) : Index(idx) {}
Capacity() : Index(0) {}
/// Get the capacity of an array that can hold at least N elements.
static Capacity get(size_t N) {
return Capacity(N ? Log2_64_Ceil(N) : 0);
/// Get the number of elements in an array with this capacity.
size_t getSize() const { return size_t(1u) << Index; }
/// Get the bucket number for this capacity.
unsigned getBucket() const { return Index; }
/// Get the next larger capacity. Large capacities grow exponentially, so
/// this function can be used to reallocate incrementally growing vectors
/// in amortized linear time.
Capacity getNext() const { return Capacity(Index + 1); }
~ArrayRecycler() {
// The client should always call clear() so recycled arrays can be returned
// to the allocator.
assert(Bucket.empty() && "Non-empty ArrayRecycler deleted!");
/// Release all the tracked allocations to the allocator. The recycler must
/// be free of any tracked allocations before being deleted.
template<class AllocatorType>
void clear(AllocatorType &Allocator) {
for (; !Bucket.empty(); Bucket.pop_back())
while (T *Ptr = pop(Bucket.size() - 1))
/// Special case for BumpPtrAllocator which has an empty Deallocate()
/// function.
/// There is no need to traverse the free lists, pulling all the objects into
/// cache.
void clear(BumpPtrAllocator&) {
/// Allocate an array of at least the requested capacity.
/// Return an existing recycled array, or allocate one from Allocator if
/// none are available for recycling.
template<class AllocatorType>
T *allocate(Capacity Cap, AllocatorType &Allocator) {
// Try to recycle an existing array.
if (T *Ptr = pop(Cap.getBucket()))
return Ptr;
// Nope, get more memory.
return static_cast<T*>(Allocator.Allocate(sizeof(T)*Cap.getSize(), Align));
/// Deallocate an array with the specified Capacity.
/// Cap must be the same capacity that was given to allocate().
void deallocate(Capacity Cap, T *Ptr) {
push(Cap.getBucket(), Ptr);
} // end llvm namespace