Add an ArrayRecycler class.

This is similar to the existing Recycler allocator, but instead of
recycling individual objects from a BumpPtrAllocator, arrays of
different sizes can be allocated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171581 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 143 insertions, 0 deletions

diff --git a/include/llvm/Support/ArrayRecycler.h b/include/llvm/Support/ArrayRecycler.h
new file mode 100644
index 0000000000..0fbe79c5c5
--- /dev/null
+++ b/include/llvm/Support/ArrayRecycler.h
@@ -0,0 +1,143 @@
+//==- llvm/Support/ArrayRecycler.h - Recycling of Arrays ---------*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the ArrayRecycler class template which can recycle small
+// arrays allocated from one of the allocators in Allocator.h
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_ARRAY_RECYCLER_H
+#define LLVM_SUPPORT_ARRAY_RECYCLER_H
+
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/MathExtras.h"
+
+namespace llvm {
+
+class BumpPtrAllocator;
+
+/// 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>::Alignment>
+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;
+  };
+
+  // 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 0;
+    FreeList *Entry = Bucket[Idx];
+    if (!Entry)
+      return 0;
+    Bucket[Idx] = Entry->Next;
+    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");
+    assert(sizeof(T) >= sizeof(FreeList) && "Objects are too small");
+    assert(Align >= AlignOf<FreeList>::Alignment && "Object underaligned");
+    FreeList *Entry = reinterpret_cast<FreeList*>(Ptr);
+    if (Idx >= Bucket.size())
+      Bucket.resize(size_t(Idx) + 1);
+    Entry->Next = Bucket[Idx];
+    Bucket[Idx] = Entry;
+  }
+
+public:
+  /// 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) {}
+
+  public:
+    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))
+        Allocator.Deallocate(Ptr);
+  }
+
+  /// 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&) {
+    Bucket.clear();
+  }
+
+  /// 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
+
+#endif