More efficiently store SimpleHashMap with empty values

panda/src/pgraph/renderAttrib.cxx

@@ -389,7 +389,7 @@ return_unique(RenderAttrib *attrib) {
     // deleted while it's in it.
     attrib->ref();
   }
-  si = _attribs->store(attrib, Empty());
+  si = _attribs->store(attrib, nullptr);
 
   // Save the index and return the input attrib.
   attrib->_saved_entry = si;

panda/src/pgraph/renderAttrib.h

@@ -185,9 +185,7 @@ public:
 private:
   // This mutex protects _attribs.
   static LightReMutex *_attribs_lock;
-  class Empty {
-  };
-  typedef SimpleHashMap<const RenderAttrib *, Empty, indirect_compare_to_hash<const RenderAttrib *> > Attribs;
+  typedef SimpleHashMap<const RenderAttrib *, nullptr_t, indirect_compare_to_hash<const RenderAttrib *> > Attribs;
   static Attribs *_attribs;
 
   int _saved_entry;

panda/src/pgraph/renderAttribRegistry.cxx

@@ -93,7 +93,7 @@ register_slot(TypeHandle type_handle, int sort, RenderAttrib *default_attrib) {
       // If this attribute was already registered, something odd is going on.
       nassertr(RenderAttrib::_attribs->find(default_attrib) == -1, 0);
       default_attrib->_saved_entry =
-        RenderAttrib::_attribs->store(default_attrib, RenderAttrib::Empty());
+        RenderAttrib::_attribs->store(default_attrib, nullptr);
     }
 
     // It effectively lives forever.  Might as well make it official.

panda/src/pgraph/renderState.cxx

@@ -1338,7 +1338,7 @@ return_unique(RenderState *state) {
     // deleted while it's in it.
     state->cache_ref();
   }
-  si = _states->store(state, Empty());
+  si = _states->store(state, nullptr);
 
   // Save the index and return the input state.
   state->_saved_entry = si;
@@ -1865,7 +1865,7 @@ init_states() {
   // is declared globally, and lives forever.
   RenderState *state = new RenderState;
   state->local_object();
-  state->_saved_entry = _states->store(state, Empty());
+  state->_saved_entry = _states->store(state, nullptr);
   _empty_state = state;
 }
 

panda/src/pgraph/renderState.h

@@ -227,9 +227,7 @@ private:
   // cache, which is encoded in _composition_cache and
   // _invert_composition_cache.
   static LightReMutex *_states_lock;
-  class Empty {
-  };
-  typedef SimpleHashMap<const RenderState *, Empty, indirect_compare_to_hash<const RenderState *> > States;
+  typedef SimpleHashMap<const RenderState *, nullptr_t, indirect_compare_to_hash<const RenderState *> > States;
   static States *_states;
   static const RenderState *_empty_state;
 

panda/src/pgraph/transformState.cxx

@@ -1512,7 +1512,7 @@ return_unique(TransformState *state) {
     // deleted while it's in it.
     state->cache_ref();
   }
-  si = _states->store(state, Empty());
+  si = _states->store(state, nullptr);
 
   // Save the index and return the input state.
   state->_saved_entry = si;

panda/src/pgraph/transformState.h

@@ -253,9 +253,7 @@ private:
   // cache, which is encoded in _composition_cache and
   // _invert_composition_cache.
   static LightReMutex *_states_lock;
-  class Empty {
-  };
-  typedef SimpleHashMap<const TransformState *, Empty, indirect_equals_hash<const TransformState *> > States;
+  typedef SimpleHashMap<const TransformState *, nullptr_t, indirect_equals_hash<const TransformState *> > States;
   static States *_states;
   static CPT(TransformState) _identity_state;
   static CPT(TransformState) _invalid_state;

panda/src/putil/simpleHashMap.I

@@ -128,7 +128,7 @@ store(const Key &key, const Value &data) {
   }
   if (is_element(index, key)) {
     // This element is already in the map; replace the data at that key.
-    _table[index]._data = data;
+    set_data(index, data);
 #ifdef _DEBUG
     nassertr(validate(), index);
 #endif
@@ -151,7 +151,7 @@ store(const Key &key, const Value &data) {
       return index;
     }
     if (is_element(index, key)) {
-      _table[index]._data = data;
+      set_data(index, data);
 #ifdef _DEBUG
       nassertr(validate(), index);
 #endif
@@ -200,8 +200,7 @@ remove(const Key &key) {
 
     // Swap it with the last one, so that we don't get any gaps in the table
     // of entries.
-    _table[index]._key = move(_table[last]._key);
-    _table[index]._data = move(_table[last]._data);
+    _table[index] = move(_table[last]);
     index_array[(size_t)other_slot] = index;
   }
 
@@ -311,8 +310,8 @@ get_key(size_t n) const {
 template<class Key, class Value, class Compare>
 INLINE const Value &SimpleHashMap<Key, Value, Compare>::
 get_data(size_t n) const {
-  nassertr(n < _num_entries, _table[n]._data);
-  return _table[n]._data;
+  nassertr(n < _num_entries, _table[n].get_data());
+  return _table[n].get_data();
 }
 
 /**
@@ -323,8 +322,8 @@ get_data(size_t n) const {
 template<class Key, class Value, class Compare>
 INLINE Value &SimpleHashMap<Key, Value, Compare>::
 modify_data(size_t n) {
-  nassertr(n < _num_entries, _table[n]._data);
-  return _table[n]._data;
+  nassertr(n < _num_entries, _table[n].modify_data());
+  return _table[n].modify_data();
 }
 
 /**
@@ -336,7 +335,19 @@ template<class Key, class Value, class Compare>
 INLINE void SimpleHashMap<Key, Value, Compare>::
 set_data(size_t n, const Value &data) {
   nassertv(n < _num_entries);
-  _table[n]._data = data;
+  _table[n].set_data(data);
+}
+
+/**
+ * Changes the data for the nth entry of the table.
+ *
+ * @param n should be in the range 0 <= n < size().
+ */
+template<class Key, class Value, class Compare>
+INLINE void SimpleHashMap<Key, Value, Compare>::
+set_data(size_t n, Value &&data) {
+  nassertv(n < _num_entries);
+  _table[n].set_data(move(data));
 }
 
 /**

panda/src/putil/simpleHashMap.h

@@ -18,6 +18,52 @@
 #include "pvector.h"
 #include "config_util.h"
 
+/**
+ * Entry in the SimpleHashMap.
+ */
+template<class Key, class Value>
+class SimpleKeyValuePair {
+public:
+  INLINE SimpleKeyValuePair(const Key &key, const Value &data) :
+    _key(key),
+    _data(data) {}
+
+  Key _key;
+
+  ALWAYS_INLINE const Value &get_data() const {
+    return _data;
+  }
+  ALWAYS_INLINE Value &modify_data() {
+    return _data;
+  }
+  ALWAYS_INLINE void set_data(const Value &data) {
+    _data = data;
+  }
+  ALWAYS_INLINE void set_data(Value &&data) {
+    _data = move(data);
+  }
+
+private:
+  Value _data;
+};
+
+/**
+ * Specialisation of SimpleKeyValuePair to not waste memory for nullptr_t
+ * values.  This allows effectively using SimpleHashMap as a set.
+ */
+template<class Key>
+class SimpleKeyValuePair<Key, nullptr_t> {
+public:
+  INLINE SimpleKeyValuePair(const Key &key, nullptr_t data) :
+    _key(key) {}
+
+  Key _key;
+
+  ALWAYS_INLINE_CONSTEXPR static nullptr_t get_data() { return nullptr; }
+  ALWAYS_INLINE_CONSTEXPR static nullptr_t modify_data() { return nullptr; }
+  ALWAYS_INLINE static void set_data(nullptr_t) {}
+};
+
 /**
  * This template class implements an unordered map of keys to data,
  * implemented as a hashtable.  It is similar to STL's hash_map, but
@@ -28,6 +74,8 @@
  * (d) it allows for efficient iteration over the entries,
  * (e) permits removal and resizing during forward iteration, and
  * (f) it has a constexpr constructor.
+ *
+ * It can also be used as a set, by using nullptr_t as Value typename.
  */
 template<class Key, class Value, class Compare = method_hash<Key, less<Key> > >
 class SimpleHashMap {
@@ -55,6 +103,7 @@ public:
   INLINE const Value &get_data(size_t n) const;
   INLINE Value &modify_data(size_t n);
   INLINE void set_data(size_t n, const Value &data);
+  INLINE void set_data(size_t n, Value &&data);
   void remove_element(size_t n);
 
   INLINE size_t get_num_entries() const;
@@ -67,8 +116,6 @@ public:
   INLINE bool consider_shrink_table();
 
 private:
-  class TableEntry;
-
   INLINE size_t get_hash(const Key &key) const;
   INLINE size_t next_hash(size_t hash) const;
 
@@ -82,23 +129,8 @@ private:
   INLINE bool consider_expand_table();
   void resize_table(size_t new_size);
 
-  class TableEntry {
-  public:
-    INLINE TableEntry(const Key &key, const Value &data) :
-      _key(key),
-      _data(data) {}
-    INLINE TableEntry(const TableEntry &copy) :
-      _key(copy._key),
-      _data(copy._data) {}
-#ifdef USE_MOVE_SEMANTICS
-    INLINE TableEntry(TableEntry &&from) NOEXCEPT :
-      _key(move(from._key)),
-      _data(move(from._data)) {}
-#endif
-    Key _key;
-    Value _data;
-  };
-
+public:
+  typedef SimpleKeyValuePair<Key, Value> TableEntry;
   TableEntry *_table;
   DeletedBufferChain *_deleted_chain;
   size_t _table_size;