[MOD] XQuery: optimizations on sequence functions

Author: ChristianGruen

basex-core/src/main/java/org/basex/query/func/fn/FnReverse.java

@@ -76,6 +76,8 @@ protected Expr opt(final CompileContext cc) throws QueryException {
     // reverse sequence
     if(expr instanceof RangeSeq) return ((RangeSeq) expr).reverse(cc.qc);
 
+    // reverse(reverse(E))  ->  E
+    if(REVERSE.is(expr)) return expr.arg(0);
     // reverse(tail(reverse(E))  ->  util:init(E)
     if(TAIL.is(expr) && REVERSE.is(expr.arg(0)))
       return cc.function(_UTIL_INIT, info, expr.arg(0).args());

basex-core/src/main/java/org/basex/query/func/fn/FnSort.java

@@ -135,6 +135,11 @@ protected Expr opt(final CompileContext cc) throws QueryException {
       final SeqType st = expr1.arg(0).seqType();
       if(st.zeroOrOne() && st.type.isSortable()) return expr1;
     }
+    if(REVERSE.is(expr1) || SORT.is(expr1)) {
+      final Expr[] args = exprs.clone();
+      args[0] = args[0].arg(0);
+      return cc.function(SORT, info, args);
+    }
     if(exprs.length == 3) {
       exprs[2] = coerceFunc(exprs[2], cc, SeqType.ANY_ATOMIC_TYPE_ZM, st1.with(Occ.EXACTLY_ONE));
     }

basex-core/src/main/java/org/basex/query/func/util/UtilDdo.java

@@ -46,6 +46,8 @@ protected Expr opt(final CompileContext cc) throws QueryException {
     if(type instanceof NodeType) {
       // util:ddo(util:replicate(*, 2))  ->  util:ddo(*)
       if(_UTIL_REPLICATE.is(expr) && ((UtilReplicate) expr).singleEval(false)) return expr.arg(0);
+      // util:ddo(reverse(*))  ->  util:ddo(*)
+      if(REVERSE.is(expr) || SORT.is(expr)) return cc.function(_UTIL_DDO, info, expr.arg(0));
       // util:ddo(/a/b/c)  ->  /a/b/c
       if(expr.ddo()) return expr;
       // adopt type of argument

basex-core/src/test/java/org/basex/query/func/FnModuleTest.java

@@ -834,7 +834,8 @@ public final class FnModuleTest extends QueryPlanTest {
 
     check(func.args(" (<_/>, ('a', 'b'))"),
         "b\na\n<_/>", empty(func));
-
+    check("(<a/>, <b/>)[. = ''] =>" + func.args() + " =>" + func.args(),
+        "<a/>\n<b/>", empty(func));
   }
 
   /** Test method. */

basex-core/src/test/java/org/basex/query/func/UtilModuleTest.java

@@ -227,7 +227,19 @@ public final class UtilModuleTest extends QueryPlanTest {
     final Function func = _UTIL_DDO;
     query(func.args(" <a/>"), "<a/>");
     query(func.args(" (<a/>, <b/>)"), "<a/>\n<b/>");
-    query(func.args(" reverse((<a/>, <b/>))"), "<b/>\n<a/>");
+
+    check(func.args(" util:replicate((<a/>, <b/>), 10)"), "<a/>\n<b/>",
+        empty(_UTIL_REPLICATE));
+    check(func.args(" util:replicate(<a/>, 2, true())"), "<a/>\n<a/>",
+        exists(_UTIL_REPLICATE));
+
+    check("(<a><b/></a> ! (., *)) => reverse() => " + func.args(),
+        "<a>\n<b/>\n</a>\n<b/>", empty(REVERSE));
+    check("(<a><b/></a> ! (., *)) => sort() => " + func.args(),
+        "<a>\n<b/>\n</a>\n<b/>", empty(SORT));
+    check("(<a><b/></a> ! (., *)) => sort() => reverse() => sort() => " + func.args(),
+        "<a>\n<b/>\n</a>\n<b/>", empty(SORT), empty(REVERSE));
+
     error(func.args(1), INVCONVERT_X_X_X);
   }