Add IteratorBase stub

ConflictSet.cpp

@@ -216,6 +216,9 @@ enum Type : int8_t {
 
 template <class T> struct NodeAllocator;
 
+// Make sure tag fits in low 4 bits
+static_assert(alignof(std::max_align_t) >= 16);
+
 struct TaggedNodePointer {
   TaggedNodePointer() = default;
   operator struct Node *() { return (struct Node *)withoutType(); }
@@ -271,11 +274,11 @@ struct TaggedNodePointer {
 
 private:
   TaggedNodePointer(struct Node *p, Type t) : p((uintptr_t)p) {
-    assert((this->p & 7) == 0);
+    assert((this->p & 15) == 0);
     this->p |= t;
     assume(p != 0);
   }
-  uintptr_t withoutType() const { return p & ~uintptr_t(7); }
+  uintptr_t withoutType() const { return p & ~uintptr_t(15); }
   uintptr_t p;
 };
 
@@ -317,7 +320,7 @@ TaggedNodePointer::TaggedNodePointer(Node *n)
 Type TaggedNodePointer::getType() {
   assert(p != 0);
   prefetch();
-  return Type(p & uintptr_t(7));
+  return Type(p & uintptr_t(15));
 }
 
 // copyChildrenAndKeyFrom is responsible for copying all
@@ -1882,6 +1885,59 @@ void downsize(Node *self, WriteContext *writeContext) {
   }
 }
 
+template <class T> struct Iterator;
+
+// Higher-level handle to a position in the tree
+struct IteratorBase {
+
+  explicit IteratorBase(Node *node) : node(node) {}
+
+  bool entryPresent() { return node->entryPresent; }
+  Entry getEntry() {
+    assert(node->entryPresent);
+    return node->entry;
+  }
+  void setEntry(Entry e) {
+    node->entryPresent = true;
+    node->entry = e;
+  }
+
+  bool operator==(const IteratorBase &other) const {
+    assert(!node->releaseDeferred);
+    assert(!other.node->releaseDeferred);
+    return node == other.node;
+  }
+
+  bool valid() { return node != nullptr; }
+
+  void followForwardingPointers() {
+    while (node->releaseDeferred) [[unlikely]] {
+      node = node->forwardTo;
+    }
+  }
+
+  Type getType() { return node->getType(); }
+
+  template <class T> Iterator<T> as() {
+    assert(getType() == T::kType);
+    return static_cast<Iterator<T>>(*this);
+  }
+
+  IteratorBase nextLogical();
+  IteratorBase nextPhysical();
+  InternalVersionT getMaxVersion();
+  InternalVersionT exchangeMaxVersion(InternalVersionT);
+  InternalVersionT setMaxVersion();
+  TrivialSpan partialKey();
+
+private:
+  Node *node;
+  // index into children array of particular leaf type
+  int index;
+};
+
+template <class T> struct Iterator : IteratorBase {};
+
 // Precondition: self is not the root. May invalidate nodes along the search
 // path to self. May invalidate children of self->parent. Returns a pointer to
 // the node after self. Precondition: `self->entryPresent`