Support: Stop using iplist in Recycler

Recycler just needs a singly-linked list, and it takes less (and
simpler) code to hand-roll one of those than to build up the equivalent
`iplist_traits`.  In theory, this should speed things up a bit too, but
this is really just a drive-by cleanup so I haven't measured.

llvm-svn: 249615

include/llvm/Support/Recycler.h

@@ -28,53 +28,36 @@ namespace llvm {
 ///
 void PrintRecyclerStats(size_t Size, size_t Align, size_t FreeListSize);
 
-/// RecyclerStruct - Implementation detail for Recycler. This is a
-/// class that the recycler imposes on free'd memory to carve out
-/// next/prev pointers.
-struct RecyclerStruct {
-  RecyclerStruct *Prev, *Next;
-};
-
-template<>
-struct ilist_traits<RecyclerStruct> :
-    public ilist_default_traits<RecyclerStruct> {
-  static RecyclerStruct *getPrev(const RecyclerStruct *t) { return t->Prev; }
-  static RecyclerStruct *getNext(const RecyclerStruct *t) { return t->Next; }
-  static void setPrev(RecyclerStruct *t, RecyclerStruct *p) { t->Prev = p; }
-  static void setNext(RecyclerStruct *t, RecyclerStruct *n) { t->Next = n; }
-
-  mutable RecyclerStruct Sentinel;
-  RecyclerStruct *createSentinel() const {
-    return &Sentinel;
-  }
-  static void destroySentinel(RecyclerStruct *) {}
-
-  RecyclerStruct *provideInitialHead() const { return createSentinel(); }
-  RecyclerStruct *ensureHead(RecyclerStruct*) const { return createSentinel(); }
-  static void noteHead(RecyclerStruct*, RecyclerStruct*) {}
-
-  static void deleteNode(RecyclerStruct *) {
-    llvm_unreachable("Recycler's ilist_traits shouldn't see a deleteNode call!");
-  }
-};
-
 /// Recycler - This class manages a linked-list of deallocated nodes
 /// and facilitates reusing deallocated memory in place of allocating
 /// new memory.
 ///
 template<class T, size_t Size = sizeof(T), size_t Align = AlignOf<T>::Alignment>
 class Recycler {
-  /// FreeList - Doubly-linked list of nodes that have deleted contents and
-  /// are not in active use.
-  ///
-  iplist<RecyclerStruct> FreeList;
+  struct FreeNode {
+    FreeNode *Next;
+  };
+
+  /// List of nodes that have deleted contents and are not in active use.
+  FreeNode *FreeList = nullptr;
+
+  FreeNode *pop_val() {
+    auto *Val = FreeList;
+    FreeList = FreeList->Next;
+    return Val;
+  }
+
+  void push(FreeNode *N) {
+    N->Next = FreeList;
+    FreeList = N;
+  }
 
 public:
   ~Recycler() {
     // If this fails, either the callee has lost track of some allocation,
     // or the callee isn't tracking allocations and should just call
     // clear() before deleting the Recycler.
-    assert(FreeList.empty() && "Non-empty recycler deleted!");
+    assert(!FreeList && "Non-empty recycler deleted!");
   }
 
   /// clear - Release all the tracked allocations to the allocator. The
@@ -82,8 +65,8 @@ public:
   /// deleted; calling clear is one way to ensure this.
   template<class AllocatorType>
   void clear(AllocatorType &Allocator) {
-    while (!FreeList.empty()) {
-      T *t = reinterpret_cast<T *>(FreeList.remove(FreeList.begin()));
+    while (FreeList) {
+      T *t = reinterpret_cast<T *>(pop_val());
       Allocator.Deallocate(t);
     }
   }
@@ -93,9 +76,7 @@ public:
   ///
   /// There is no need to traverse the free list, pulling all the objects into
   /// cache.
-  void clear(BumpPtrAllocator&) {
-    FreeList.clearAndLeakNodesUnsafely();
-  }
+  void clear(BumpPtrAllocator &) { FreeList = nullptr; }
 
   template<class SubClass, class AllocatorType>
   SubClass *Allocate(AllocatorType &Allocator) {
@@ -103,9 +84,8 @@ public:
                   "Recycler allocation alignment is less than object align!");
     static_assert(sizeof(SubClass) <= Size,
                   "Recycler allocation size is less than object size!");
-    return !FreeList.empty() ?
-           reinterpret_cast<SubClass *>(FreeList.remove(FreeList.begin())) :
-           static_cast<SubClass *>(Allocator.Allocate(Size, Align));
+    return FreeList ? reinterpret_cast<SubClass *>(pop_val())
+                    : static_cast<SubClass *>(Allocator.Allocate(Size, Align));
   }
 
   template<class AllocatorType>
@@ -115,14 +95,20 @@ public:
 
   template<class SubClass, class AllocatorType>
   void Deallocate(AllocatorType & /*Allocator*/, SubClass* Element) {
-    FreeList.push_front(reinterpret_cast<RecyclerStruct *>(Element));
+    push(reinterpret_cast<FreeNode *>(Element));
   }
 
-  void PrintStats() {
-    PrintRecyclerStats(Size, Align, FreeList.size());
-  }
+  void PrintStats();
 };
 
+template <class T, size_t Size, size_t Align>
+void Recycler<T, Size, Align>::PrintStats() {
+  size_t S = 0;
+  for (auto *I = FreeList; I; I = I->Next)
+    ++S;
+  PrintRecyclerStats(Size, Align, S);
+}
+
 }
 
 #endif