- xpath.c include/libxml/xpath.h include/libxml/xpathInternals.h:

lot of optimization work, results in significant improvements
  when handling really complex XPath queries. Add a small optimizer
  for unions, improve [n] and [last()], avoid some costly ops.
Daniel

include/libxml/xpath.h

@@ -255,6 +255,7 @@ struct _xmlXPathParserContext {
 
     xmlXPathCompExprPtr comp;		/* the precompiled expression */
     int xptr;				/* it this an XPointer expression */
+    xmlNodePtr         ancestor;	/* used for walking preceding axis */
 };
 
 /**