fastparser: avoid std::stack::top() - cache it's results.

amazingly std::stack::top() takes 146 pseudo-cycles to do not much,
so instead cache the result in a single pointer in lieu of burning
that code.

Change-Id: Ie326be47da6cbad0850e5f1026a1632bb840b6b8

sax/source/fastparser/fastparser.cxx

@@ -224,8 +224,8 @@ public:
 
     void pushEntity( const Entity& rEntity );
     void popEntity();
-    Entity& getEntity();
-    const Entity& getEntity() const;
+    Entity& getEntity()             { return *mpTop; }
+    const Entity& getEntity() const { return *mpTop; }
     void parse();
     void produce( CallbackType aType );
 
@@ -256,6 +256,8 @@ private:
     NamespaceMap                            maNamespaceMap;
 
     ParserData maData;                      /// Cached parser configuration for next call of parseStream().
+
+    Entity *mpTop;                          /// std::stack::top() is amazingly slow => cache this.
     ::std::stack< Entity > maEntities;      /// Entity stack for each call of parseStream().
     FastTokenLookup maTokenLookup;
 };
@@ -619,7 +621,9 @@ void Entity::saveException( const Exception &e )
 
 namespace sax_fastparser {
 
-FastSaxParserImpl::FastSaxParserImpl( FastSaxParser* pFront ) : mpFront(pFront)
+FastSaxParserImpl::FastSaxParserImpl( FastSaxParser* pFront ) :
+    mpFront(pFront),
+    mpTop(NULL)
 {
     mxDocumentLocator.set( new FastLocatorImpl( this ) );
 }
@@ -1038,21 +1042,13 @@ bool FastSaxParserImpl::consume(EventList *pEventList)
 void FastSaxParserImpl::pushEntity( const Entity& rEntity )
 {
     maEntities.push( rEntity );
+    mpTop = &maEntities.top();
 }
 
 void FastSaxParserImpl::popEntity()
 {
     maEntities.pop();
-}
-
-Entity& FastSaxParserImpl::getEntity()
-{
-    return maEntities.top();
-}
-
-const Entity& FastSaxParserImpl::getEntity() const
-{
-    return maEntities.top();
+    mpTop = &maEntities.top();
 }
 
 // starts parsing with actual parser !