Merge lp:~zorba-coders/zorba/gen-flwor-opt into lp:zorba

[Markos Zaharioudakis]

1, Implemented document-ordering elimination for general FLWOR.
2. No need to apply document ordering on the domain expression of a FOR clause, if the FOR clause is followed by an orderby or groupby clause.
3. Must apply document ordering on the domain expression of a FOR clause, if the FOR clause is followed by a sequential clause.
4. Applied count optimization to the return clause of general FLWORs

1, Implemented document-ordering elimination for general FLWOR.
2. No need to apply document ordering on the domain expression of a FOR clause, if the FOR clause is followed by an orderby or groupby clause.
3. Must apply document ordering on the domain expression of a FOR clause, if the FOR clause is followed by a sequential clause.
4 Applied count optimization to the return clause of general FLWORs

[lp:~zorba-coders/zorba/gen-flwor-opt]

10687. By Markos Zaharioudakis on 2013-05-22

No need to apply document ordering on the domain expression of a FOR clause, if the FOR clause is followed by an orderby or groupby clause

10688. By Markos Zaharioudakis on 2013-05-23

doc-ordering rules extended for general flwor

[Markos Zaharioudakis (markos-za)]

review: Approve

[Zorba Build Bot (zorba-buildbot)]

Validation queue starting for merge proposal.
Log at: http://zorbatest.lambda.nu:8080/remotequeue/gen-flwor-opt-2013-05-23T02-33-02.296Z/log.html

[Zorba Build Bot (zorba-buildbot)]

Validation queue job gen-flwor-opt-2013-05-23T02-33-02.296Z is finished. The final status was:

All tests succeeded!

=== modified file 'ChangeLog'
--- ChangeLog	2013-05-21 21:47:40 +0000
+++ ChangeLog	2013-05-23 02:29:28 +0000
@@ -7,11 +7,16 @@
 
 Optimizations:
   * Implemented hoisting optimization for general FLWOR.
+  * Implemented document-ordering elimination for general FLWOR.
   * Optimized implementation of fn:deep-equal
+  * No need to apply document ordering on the domain expression of a FOR clause
+    if the FOR clause is followed by an orderby or groupby clause.
 
 Bug Fixes/Other Changes:
   * Fixed bug in hoisting through try-catch expr
   * Fixed implementation of fn:deep-equal according to latest W3C spec.
+  * Must apply document ordering on the domain expression of a FOR clause, if
+    the FOR clause is followed by a sequential clause.
 
 
 version 2.9

=== modified file 'src/compiler/rewriter/rules/fold_rules.cpp'
--- src/compiler/rewriter/rules/fold_rules.cpp	2013-05-08 20:14:47 +0000
+++ src/compiler/rewriter/rules/fold_rules.cpp	2013-05-23 02:29:28 +0000
@@ -746,7 +746,8 @@
       }
     }
 
-    if (arg->get_expr_kind() == flwor_expr_kind)
+    if (arg->get_expr_kind() == flwor_expr_kind ||
+        arg->get_expr_kind() == gflwor_expr_kind)
     {
       bool modified = false;
       expr* newArg = partial_eval_return_clause(static_cast<flwor_expr*>(arg),
@@ -1021,7 +1022,8 @@
     }
   }
 
-  if (returnExpr->get_expr_kind() == flwor_expr_kind)
+  if (returnExpr->get_expr_kind() == flwor_expr_kind ||
+      returnExpr->get_expr_kind() == gflwor_expr_kind)
   {
     expr* newRet =
     partial_eval_return_clause(static_cast<flwor_expr*>(returnExpr),  modified, rCtx);

=== modified file 'src/compiler/rewriter/rules/nodeid_rules.cpp'
--- src/compiler/rewriter/rules/nodeid_rules.cpp	2013-04-24 01:35:58 +0000
+++ src/compiler/rewriter/rules/nodeid_rules.cpp	2013-05-23 02:29:28 +0000
@@ -183,20 +183,26 @@
   }
 
   case flwor_expr_kind:
+  case gflwor_expr_kind:
   {
     flwor_expr* flwor = static_cast<flwor_expr *>(node);
 
-    // no need to do anything for the where expr or the orderby exprs because
-    // they don't produce nodes.
+    expr* retExpr = flwor->get_return_expr();
 
     // The annotations for the return expr are the same as those of its
     // containing flwor expr.
-    pushdown_ignores_sorted_nodes(node, flwor->get_return_expr());
-    pushdown_ignores_duplicate_nodes(node, flwor->get_return_expr());
+    pushdown_ignores_sorted_nodes(node, retExpr);
+    pushdown_ignores_duplicate_nodes(node, retExpr);
 
     // apply the rule recursively on the return expr
     apply(rCtx, flwor->get_return_expr(), modified);
 
+    csize nextOrderingClause = 0;
+    csize nextSequentialClause = 0;
+
+    if (retExpr->is_sequential())
+      nextSequentialClause = flwor->num_clauses();
+
     // Process the clauses in reverse order so that by the time we reach the
     // definition of a LET var, we know if the LET var sequence must be in
     // doc order and/or without duplicates.
@@ -205,12 +211,17 @@
     {
       flwor_clause* clause = flwor->get_clause(i-1);
 
-      if (clause->get_kind() == flwor_clause::let_clause)
+      switch (clause->get_kind())
+      {
+      case flwor_clause::let_clause:
       {
         let_clause* lc = static_cast<let_clause*>(clause);
         expr* domainExpr = lc->get_expr();
         var_expr* var = lc->get_var();
 
+        if (domainExpr->is_sequential())
+          nextSequentialClause = i - 1;
+
         // The annotations for the domain expr are the same as those of its
         // associated LET var.
         domainExpr->setIgnoresSortedNodes(var->getIgnoresSortedNodes());
@@ -218,13 +229,17 @@
 
         // apply the rule recursively on the domainExpr
         apply(rCtx, domainExpr, modified);
+
+        break;
       }
-      else if (clause->get_kind() == flwor_clause::for_clause)
+      case flwor_clause::for_clause:
       {
         for_clause* fc = static_cast<for_clause*>(clause);
         expr* domainExpr = fc->get_expr();
         var_expr* posVar = fc->get_pos_var();
-        assert(posVar == NULL || posVar->get_kind() == var_expr::pos_var);
+
+        if (domainExpr->is_sequential())
+          nextSequentialClause = i - 1;
 
         // If a flwor expr does not need to care about producing nodes in doc
         // order, then the domain expr of a FOR variable does not need to care
@@ -234,7 +249,16 @@
         // to produce nodes in doc order as well.
         if (posVar == NULL)
         {
-          domainExpr->setIgnoresSortedNodes(flwor->getIgnoresSortedNodes());
+          if (nextOrderingClause > i-1 &&
+              (nextSequentialClause == 0 ||
+               nextSequentialClause > nextOrderingClause))
+          {
+            domainExpr->setIgnoresSortedNodes(ANNOTATION_TRUE);
+          }
+          else
+          {
+            domainExpr->setIgnoresSortedNodes(flwor->getIgnoresSortedNodes());
+          }
         }
         else if (rCtx.theIsInOrderedMode)
         {
@@ -243,15 +267,53 @@
 
         // apply the rule recursively on the domainExpr
         apply(rCtx, domainExpr, modified);
-      }
-      else if (clause->get_kind() == flwor_clause::where_clause)
+
+        break;
+      }
+      case flwor_clause::window_clause:
+      {
+        window_clause* wc = static_cast<window_clause*>(clause);
+        expr* domainExpr = wc->get_expr();
+
+        if (domainExpr->is_sequential())
+          nextSequentialClause = i - 1;
+
+        if (rCtx.theIsInOrderedMode)
+        {
+          domainExpr->setIgnoresSortedNodes(ANNOTATION_FALSE);
+          domainExpr->setIgnoresDuplicateNodes(ANNOTATION_FALSE);
+        }
+
+        // apply the rule recursively on the domainExpr and the condition exprs
+        apply(rCtx, domainExpr, modified);
+
+        flwor_wincond* startCond = wc->get_win_start();
+        flwor_wincond* stopCond = wc->get_win_stop();
+
+        if (startCond && startCond->get_expr())
+        {
+          apply(rCtx, startCond->get_expr(), modified);
+        }
+
+        if (stopCond && stopCond->get_expr())
+        {
+          apply(rCtx, stopCond->get_expr(), modified);
+        }
+
+        break;
+      }
+      case flwor_clause::where_clause:
       {
         // apply the rule recursively on the whereExpr
         where_clause* wc = static_cast<where_clause*>(clause);
         apply(rCtx, wc->get_expr(), modified);
+
+        break;
       }
-      else if (clause->get_kind() == flwor_clause::orderby_clause)
+      case flwor_clause::orderby_clause:
       {
+        nextOrderingClause = i-1;
+
         // apply the rule recursively on the orderby exprs
         orderby_clause* oc = static_cast<orderby_clause*>(clause);
 
@@ -261,6 +323,41 @@
         {
           apply(rCtx, oc->get_column_expr(i), modified);
         }
+
+        break;
+      }
+      case flwor_clause::groupby_clause:
+      {
+        nextOrderingClause = i-1;
+
+        // apply the rule recursively on the groupby exprs
+        groupby_clause* gc = static_cast<groupby_clause*>(clause);
+
+        var_rebind_list_t::const_iterator ite = gc->beginGroupVars();
+        var_rebind_list_t::const_iterator end = gc->endGroupVars();
+        for (; ite != end; ++ite)
+        {
+          apply(rCtx, (*ite).first, modified);
+        }
+
+        ite = gc->beginNonGroupVars();
+        end = gc->endNonGroupVars();
+        for (; ite != end; ++ite)
+        {
+          apply(rCtx, (*ite).first, modified);
+        }
+
+        break;
+      }
+      case flwor_clause::count_clause:
+      case flwor_clause::materialize_clause:
+      {
+        break;
+      }
+      default:
+      {
+        ZORBA_ASSERT(false);
+      }
       }
     }
     return NULL;
@@ -429,7 +526,6 @@
     break;
   }
 
-#ifdef ZORBA_WITH_JSON
   case json_object_expr_kind :
   {
     break;
@@ -448,7 +544,6 @@
     }
     break;
   }
-#endif
 
   case attr_expr_kind :
   case namespace_expr_kind :
@@ -459,7 +554,6 @@
 
   case extension_expr_kind :  // TODO
   case flowctl_expr_kind :    // TODO
-  case gflwor_expr_kind :     // TODO
   case name_cast_expr_kind :  // TODO
   case trycatch_expr_kind :   // TODO
   case validate_expr_kind :   // TODO

=== modified file 'src/compiler/rewriter/rules/type_rules.cpp'
--- src/compiler/rewriter/rules/type_rules.cpp	2013-02-07 17:24:36 +0000
+++ src/compiler/rewriter/rules/type_rules.cpp	2013-05-23 02:29:28 +0000
@@ -20,7 +20,6 @@
 #include "types/root_typemanager.h"
 #include "types/typeops.h"
 
-#include "compiler/expression/flwor_expr.h"
 #include "compiler/expression/expr_iter.h"
 #include "compiler/expression/expr.h"
 
@@ -445,46 +444,6 @@
       }
     }
   }
-#if 0
-  else if (node->get_expr_kind() == flwor_expr_kind ||
-           node->get_expr_kind() == gflwor_expr_kind)
-  {
-    flwor_expr* flworExpr = static_cast<flwor_expr*>(node);
-
-    bool modified = false;
-
-    csize numClauses = flworExpr->num_clauses();
-    for (csize i = 0; i < numClauses; ++i)
-    {
-      if (flworExpr->get_clause(i)->get_kind() == flwor_clause::order_clause)
-      {
-        orderby_clause* obc =
-        static_cast<orderby_clause*>(flworExpr->get_clause(i));
-
-        csize numColumns = obc->num_columns();
-        for (csize j = 0; j < numColumns; ++j)
-        {
-          expr* colExpr = obc->get_column_expr(j);
-          xqtref_t colType = colExpr->get_return_type();
-          const QueryLoc& colLoc = colExpr->get_loc();
-
-          if (!TypeOps::is_equal(tm, *colType, *rtm.EMPTY_TYPE, colLoc) &&
-              TypeOps::is_subtype(tm, *colType, *rtm.UNTYPED_ATOMIC_TYPE_STAR, colLoc))
-          {
-            expr* castExpr = rCtx.theEM->
-            create_cast_expr(sctx, udf, colLoc, colExpr, rtm.STRING_TYPE_QUESTION);
-
-            obc->set_column_expr(j, castExpr);
-            modified = true;
-          }
-        }
-      }
-    }
-
-    if (modified)
-      return node;
-  }
-#endif
 
   return NULL;
 }

=== modified file 'src/compiler/rewriter/tools/dataflow_annotations.cpp'
--- src/compiler/rewriter/tools/dataflow_annotations.cpp	2013-04-24 01:35:58 +0000
+++ src/compiler/rewriter/tools/dataflow_annotations.cpp	2013-05-23 02:29:28 +0000
@@ -365,13 +365,13 @@
 {
   default_walk(e);
 
-  if (! generic_compute(e) && !e->is_general())
+  if (! generic_compute(e))
   {
     flwor_expr::clause_list_t::const_iterator ite = e->clause_begin();
     flwor_expr::clause_list_t::const_iterator end = e->clause_end();
 
     const forletwin_clause* fc = NULL;
-    ulong numForClauses = 0;
+    csize numForClauses = 0;
 
     for (; ite != end; ++ite)
     {
@@ -398,9 +398,12 @@
       }
       case flwor_clause::let_clause:
       case flwor_clause::where_clause:
+      case flwor_clause::count_clause:
+      case flwor_clause::materialize_clause:
       {
         break;
       }
+      case flwor_clause::window_clause:
       case flwor_clause::orderby_clause:
       case flwor_clause::groupby_clause:
       {

=== modified file 'test/rbkt/ExpCompilerResults/IterPlan/zorba/hashjoins/gary1.iter'
--- test/rbkt/ExpCompilerResults/IterPlan/zorba/hashjoins/gary1.iter	2013-02-07 17:24:36 +0000
+++ test/rbkt/ExpCompilerResults/IterPlan/zorba/hashjoins/gary1.iter	2013-05-23 02:29:28 +0000
@@ -64,6 +64,25 @@
           </flwor::TupleStreamIterator>
         </ChildAxisIterator>
       </LetVariable>
+      <LetVariable name="$$opt_temp_4" materialize="true">
+        <CreateInternalIndexIterator name="xs:QName(,,tempIndex0)">
+          <flwor::FLWORIterator>
+            <ForVariable name="$$opt_temp_2">
+              <LetVarIterator varname="y"/>
+            </ForVariable>
+            <ReturnClause>
+              <GeneralIndexEntryBuilderIterator>
+                <ForVarIterator varname="$$opt_temp_2"/>
+                <FnDataIterator>
+                  <AttributeAxisIterator test kind="match_name_test" qname="xs:QName(,,unitid)" typename="*" nill allowed="0">
+                    <ForVarIterator varname="$$opt_temp_2"/>
+                  </AttributeAxisIterator>
+                </FnDataIterator>
+              </GeneralIndexEntryBuilderIterator>
+            </ReturnClause>
+          </flwor::FLWORIterator>
+        </CreateInternalIndexIterator>
+      </LetVariable>
       <ForVariable name="i">
         <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,inst)" typename="*" nill allowed="0">
           <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,institutions)" typename="*" nill allowed="0">
@@ -80,30 +99,23 @@
       </LetVariable>
       <LetVariable name="$$opt_temp_1" materialize="true">
         <HoistIterator>
-          <NodeSortIterator distinct="true" ascending="true">
-            <AttributeAxisIterator test kind="match_name_test" qname="*" typename="*" nill allowed="0">
-              <flwor::FLWORIterator>
-                <ForVariable name="$$context-item">
-                  <LetVarIterator varname="y"/>
-                </ForVariable>
-                <WhereClause>
-                  <CompareIterator>
-                    <FnDataIterator>
-                      <AttributeAxisIterator test kind="match_name_test" qname="xs:QName(,,unitid)" typename="*" nill allowed="0">
-                        <ForVarIterator varname="$$context-item"/>
-                      </AttributeAxisIterator>
-                    </FnDataIterator>
+          <AttributeAxisIterator test kind="match_name_test" qname="*" typename="*" nill allowed="0">
+            <flwor::FLWORIterator>
+              <ForVariable name="$$context-item">
+                <NodeSortIterator distinct="true" ascending="true">
+                  <ProbeIndexPointGeneralIterator>
+                    <SingletonIterator value="xs:QName(,,tempIndex0)"/>
                     <FnDataIterator>
                       <LetVarIterator varname="unitid"/>
                     </FnDataIterator>
-                  </CompareIterator>
-                </WhereClause>
-                <ReturnClause>
-                  <ForVarIterator varname="$$context-item"/>
-                </ReturnClause>
-              </flwor::FLWORIterator>
-            </AttributeAxisIterator>
-          </NodeSortIterator>
+                  </ProbeIndexPointGeneralIterator>
+                </NodeSortIterator>
+              </ForVariable>
+              <ReturnClause>
+                <ForVarIterator varname="$$context-item"/>
+              </ReturnClause>
+            </flwor::FLWORIterator>
+          </AttributeAxisIterator>
         </HoistIterator>
       </LetVariable>
       <ReturnClause>

=== modified file 'test/rbkt/ExpCompilerResults/IterPlan/zorba/index/match_veq_04.iter'
--- test/rbkt/ExpCompilerResults/IterPlan/zorba/index/match_veq_04.iter	2013-05-13 13:58:24 +0000
+++ test/rbkt/ExpCompilerResults/IterPlan/zorba/index/match_veq_04.iter	2013-05-23 02:29:28 +0000
@@ -219,11 +219,9 @@
               <LetVarIterator varname="id"/>
               <SingletonIterator value="xs:string(no session with the given uuid)"/>
             </TraceIterator>
-            <NodeSortIterator distinct="true" ascending="true">
-              <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,data)" typename="*" nill allowed="0">
-                <LetVarIterator varname="session"/>
-              </ChildAxisIterator>
-            </NodeSortIterator>
+            <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,data)" typename="*" nill allowed="0">
+              <LetVarIterator varname="session"/>
+            </ChildAxisIterator>
           </IfThenElseIterator>
         </ReturnClause>
       </flwor::FLWORIterator>

=== modified file 'test/rbkt/ExpCompilerResults/IterPlan/zorba/index/match_veq_05.iter'
--- test/rbkt/ExpCompilerResults/IterPlan/zorba/index/match_veq_05.iter	2013-05-13 13:58:24 +0000
+++ test/rbkt/ExpCompilerResults/IterPlan/zorba/index/match_veq_05.iter	2013-05-23 02:29:28 +0000
@@ -275,12 +275,14 @@
         <LetVariable name="session" materialize="true">
           <flwor::FLWORIterator>
             <ForVariable name="$$context-item">
-              <ProbeIndexPointValueIterator>
-                <SingletonIterator value="xs:QName(www.sessions.com,sessions,session-index)"/>
-                <UnhoistIterator>
-                  <LetVarIterator varname="$$opt_temp_0"/>
-                </UnhoistIterator>
-              </ProbeIndexPointValueIterator>
+              <NodeSortIterator distinct="false" ascending="true">
+                <ProbeIndexPointValueIterator>
+                  <SingletonIterator value="xs:QName(www.sessions.com,sessions,session-index)"/>
+                  <UnhoistIterator>
+                    <LetVarIterator varname="$$opt_temp_0"/>
+                  </UnhoistIterator>
+                </ProbeIndexPointValueIterator>
+              </NodeSortIterator>
             </ForVariable>
             <WhereClause>
               <CompareIterator>
@@ -306,11 +308,9 @@
               <LetVarIterator varname="id"/>
               <SingletonIterator value="xs:string(no session with the given uuid)"/>
             </TraceIterator>
-            <NodeSortIterator distinct="true" ascending="true">
-              <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,data)" typename="*" nill allowed="0">
-                <LetVarIterator varname="session"/>
-              </ChildAxisIterator>
-            </NodeSortIterator>
+            <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,data)" typename="*" nill allowed="0">
+              <LetVarIterator varname="session"/>
+            </ChildAxisIterator>
           </IfThenElseIterator>
         </ReturnClause>
       </flwor::FLWORIterator>

=== modified file 'test/rbkt/ExpCompilerResults/IterPlan/zorba/no-copy/hashjoin-gary1.iter'
--- test/rbkt/ExpCompilerResults/IterPlan/zorba/no-copy/hashjoin-gary1.iter	2013-02-07 17:24:36 +0000
+++ test/rbkt/ExpCompilerResults/IterPlan/zorba/no-copy/hashjoin-gary1.iter	2013-05-23 02:29:28 +0000
@@ -64,6 +64,25 @@
           </flwor::TupleStreamIterator>
         </ChildAxisIterator>
       </LetVariable>
+      <LetVariable name="$$opt_temp_4" materialize="true">
+        <CreateInternalIndexIterator name="xs:QName(,,tempIndex0)">
+          <flwor::FLWORIterator>
+            <ForVariable name="$$opt_temp_2">
+              <LetVarIterator varname="y"/>
+            </ForVariable>
+            <ReturnClause>
+              <GeneralIndexEntryBuilderIterator>
+                <ForVarIterator varname="$$opt_temp_2"/>
+                <FnDataIterator>
+                  <AttributeAxisIterator test kind="match_name_test" qname="xs:QName(,,unitid)" typename="*" nill allowed="0">
+                    <ForVarIterator varname="$$opt_temp_2"/>
+                  </AttributeAxisIterator>
+                </FnDataIterator>
+              </GeneralIndexEntryBuilderIterator>
+            </ReturnClause>
+          </flwor::FLWORIterator>
+        </CreateInternalIndexIterator>
+      </LetVariable>
       <ForVariable name="i">
         <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,inst)" typename="*" nill allowed="0">
           <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,institutions)" typename="*" nill allowed="0">
@@ -80,30 +99,23 @@
       </LetVariable>
       <LetVariable name="$$opt_temp_1" materialize="true">
         <HoistIterator>
-          <NodeSortIterator distinct="true" ascending="true">
-            <AttributeAxisIterator test kind="match_name_test" qname="*" typename="*" nill allowed="0">
-              <flwor::FLWORIterator>
-                <ForVariable name="$$context-item">
-                  <LetVarIterator varname="y"/>
-                </ForVariable>
-                <WhereClause>
-                  <CompareIterator>
-                    <FnDataIterator>
-                      <AttributeAxisIterator test kind="match_name_test" qname="xs:QName(,,unitid)" typename="*" nill allowed="0">
-                        <ForVarIterator varname="$$context-item"/>
-                      </AttributeAxisIterator>
-                    </FnDataIterator>
+          <AttributeAxisIterator test kind="match_name_test" qname="*" typename="*" nill allowed="0">
+            <flwor::FLWORIterator>
+              <ForVariable name="$$context-item">
+                <NodeSortIterator distinct="true" ascending="true">
+                  <ProbeIndexPointGeneralIterator>
+                    <SingletonIterator value="xs:QName(,,tempIndex0)"/>
                     <FnDataIterator>
                       <LetVarIterator varname="unitid"/>
                     </FnDataIterator>
-                  </CompareIterator>
-                </WhereClause>
-                <ReturnClause>
-                  <ForVarIterator varname="$$context-item"/>
-                </ReturnClause>
-              </flwor::FLWORIterator>
-            </AttributeAxisIterator>
-          </NodeSortIterator>
+                  </ProbeIndexPointGeneralIterator>
+                </NodeSortIterator>
+              </ForVariable>
+              <ReturnClause>
+                <ForVarIterator varname="$$context-item"/>
+              </ReturnClause>
+            </flwor::FLWORIterator>
+          </AttributeAxisIterator>
         </HoistIterator>
       </LetVariable>
       <ReturnClause>

=== added file 'test/rbkt/ExpCompilerResults/IterPlan/zorba/optim/doc_order_01.iter'
--- test/rbkt/ExpCompilerResults/IterPlan/zorba/optim/doc_order_01.iter	1970-01-01 00:00:00 +0000
+++ test/rbkt/ExpCompilerResults/IterPlan/zorba/optim/doc_order_01.iter	2013-05-23 02:29:28 +0000
@@ -0,0 +1,49 @@
+Iterator tree for main query:
+<flwor::FLWORIterator>
+  <ForVariable name="b">
+    <NodeDistinctIterator allow-atomics="false" check-only="false">
+      <DescendantAxisIterator test kind="match_name_test" qname="xs:QName(,,item)" typename="*" nill allowed="0">
+        <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,regions)" typename="*" nill allowed="0">
+          <DescendantAxisIterator test kind="match_name_test" qname="xs:QName(,,site)" typename="*" nill allowed="0">
+            <FnDocIterator>
+              <SingletonIterator value="xs:string(../xmark/auction.xml)"/>
+            </FnDocIterator>
+          </DescendantAxisIterator>
+        </ChildAxisIterator>
+      </DescendantAxisIterator>
+    </NodeDistinctIterator>
+  </ForVariable>
+  <OrderBySpec>
+    <FnDataIterator>
+      <FnZeroOrOneIterator>
+        <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,location)" typename="*" nill allowed="0">
+          <ForVarIterator varname="b"/>
+        </ChildAxisIterator>
+      </FnZeroOrOneIterator>
+    </FnDataIterator>
+  </OrderBySpec>
+  <ReturnClause>
+    <ElementIterator>
+      <SingletonIterator value="xs:QName(,,item)"/>
+      <AttributeIterator qname="xs:QName(,,name)">
+        <EnclosedIterator attr_cont="true">
+          <FnDataIterator>
+            <ChildAxisIterator test kind="match_text_test" qname="*" typename="*" nill allowed="0">
+              <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,name)" typename="*" nill allowed="0">
+                <ForVarIterator varname="b"/>
+              </ChildAxisIterator>
+            </ChildAxisIterator>
+          </FnDataIterator>
+        </EnclosedIterator>
+      </AttributeIterator>
+      <EnclosedIterator attr_cont="false">
+        <ChildAxisIterator test kind="match_text_test" qname="*" typename="*" nill allowed="0">
+          <ChildAxisIterator test kind="match_name_test" qname="xs:QName(,,location)" typename="*" nill allowed="0">
+            <ForVarIterator varname="b"/>
+          </ChildAxisIterator>
+        </ChildAxisIterator>
+      </EnclosedIterator>
+    </ElementIterator>
+  </ReturnClause>
+</flwor::FLWORIterator>
+

=== added file 'test/rbkt/ExpQueryResults/zorba/optim/doc_order_01.xml.res'
--- test/rbkt/ExpQueryResults/zorba/optim/doc_order_01.xml.res	1970-01-01 00:00:00 +0000
+++ test/rbkt/ExpQueryResults/zorba/optim/doc_order_01.xml.res	2013-05-23 02:29:28 +0000
@@ -0,0 +1,1 @@
+<item name="scarce brook ">Denmark</item><item name="duteous nine eighteen ">United States</item><item name="great ">United States</item><item name="lived unsur ">United States</item><item name="wine prevention ">United States</item><item name="waters derive ">United States</item><item name="subornation precepts laboured gentleman ">United States</item><item name="secure desires ">United States</item><item name="choughs stains ">United States</item><item name="shall ingenious ">United States</item><item name="heart ">United States</item><item name="lessens promise ">United States</item><item name="nearer conquerors over pays ">United States</item><item name="abominable confession greet heaven ">United States</item><item name="mole bonfires ">United States</item><item name="compact paper ">United States</item><item name="sake ">United States</item><item name="strive octavius seals happiness ">United States</item><item name="gaze wages proving english ">United States</item><item name="practice space commune women ">United States</item><item name="holds perhaps despair amorous ">United States</item><item name="abhorr execution beckon rue ">Uzbekistan</item>

=== added file 'test/rbkt/Queries/zorba/optim/doc_order_01.xq'
--- test/rbkt/Queries/zorba/optim/doc_order_01.xq	1970-01-01 00:00:00 +0000
+++ test/rbkt/Queries/zorba/optim/doc_order_01.xq	2013-05-23 02:29:28 +0000
@@ -0,0 +1,8 @@
+
+
+let $auction := doc("../xmark/auction.xml")
+return
+  for $b in $auction//site/regions//item
+  let $k := $b/name/text()
+  stable order by zero-or-one($b/location) ascending empty greatest
+  return <item name="{$k}">{$b/location/text()}</item>