speed up DefaultItemInstanceManager

we can store the registered items in a map indexed by which-id, and
avoid most of the search cost

Change-Id: Ib3fbed436bc034e603819cfef8223dcc77eb7f06
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/169528
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

include/svl/poolitem.hxx

@@ -33,6 +33,7 @@
 #include <tools/long.hxx>
 #include <boost/property_tree/ptree_fwd.hpp>
 #include <unordered_set>
+#include <unordered_map>
 
 class IntlWrapper;
 
@@ -638,7 +639,7 @@ private:
 // that specific Item (see other derivations)
 class SVL_DLLPUBLIC DefaultItemInstanceManager : public ItemInstanceManager
 {
-    std::unordered_set<const SfxPoolItem*>  maRegistered;
+    std::unordered_map<sal_uInt16, std::unordered_set<const SfxPoolItem*>>  maRegistered;
 
 public:
     DefaultItemInstanceManager(const std::size_t aClassHash)

svl/source/items/poolitem.cxx

@@ -503,16 +503,25 @@ void listAllocatedSfxPoolItems()
 
 const SfxPoolItem* DefaultItemInstanceManager::find(const SfxPoolItem& rItem) const
 {
-    for (const auto& rCandidate : maRegistered)
-        if (rCandidate->Which() == rItem.Which() && *rCandidate == rItem)
+    auto it = maRegistered.find(rItem.Which());
+    if (it == maRegistered.end())
+        return nullptr;
+    for (const auto& rCandidate : it->second)
+        if (*rCandidate == rItem)
             return rCandidate;
 
     return nullptr;
 }
 
-void DefaultItemInstanceManager::add(const SfxPoolItem& rItem) { maRegistered.insert(&rItem); }
+void DefaultItemInstanceManager::add(const SfxPoolItem& rItem)
+{
+    maRegistered[rItem.Which()].insert(&rItem);
+}
 
-void DefaultItemInstanceManager::remove(const SfxPoolItem& rItem) { maRegistered.erase(&rItem); }
+void DefaultItemInstanceManager::remove(const SfxPoolItem& rItem)
+{
+    maRegistered[rItem.Which()].erase(&rItem);
+}
 
 ItemInstanceManager* SfxPoolItem::getItemInstanceManager() const { return nullptr; }