[optimize] Most predicates are not optimizable or only have a single optimizable expression

Author: adamretter

exist-core/src/main/java/org/exist/xquery/Optimizer.java

@@ -102,8 +102,8 @@ public void visitLocationStep(final LocationStep locationStep) {
             for (final Predicate pred : preds) {
                 final FindOptimizable find = new FindOptimizable();
                 pred.accept(find);
-                final List<Optimizable> list = find.getOptimizables();
-                if (list.size() > 0 && canOptimize(list)) {
+                @Nullable final Optimizable[] list = find.getOptimizables();
+                if (canOptimize(list)) {
                     optimize = true;
                     break;
                 }
@@ -215,8 +215,8 @@ private boolean hasOptimizable(List<Predicate> preds) {
         for (final Predicate pred : preds) {
             final FindOptimizable find = new FindOptimizable();
             pred.accept(find);
-            final List<Optimizable> list = find.getOptimizables();
-            if (list.size() > 0 && canOptimize(list)) {
+            @Nullable final Optimizable[] list = find.getOptimizables();
+            if (canOptimize(list)) {
                 return true;
             }
         }
@@ -337,7 +337,11 @@ public void visitVariableReference(final VariableReference ref) {
         }
     }
 
-    private boolean canOptimize(List<Optimizable> list) {
+    private boolean canOptimize(@Nullable final Optimizable[] list) {
+        if (list == null || list.length == 0) {
+            return false;
+        }
+
         for (final Optimizable optimizable : list) {
             final int axis = optimizable.getOptimizeAxis();
             if (!(axis == Constants.CHILD_AXIS || axis == Constants.DESCENDANT_AXIS ||
@@ -378,31 +382,44 @@ private Expression simplifyPath(Expression expression) {
      */
     public static class FindOptimizable extends BasicExpressionVisitor {
 
-        List<Optimizable> optimizables = new ArrayList<>();
+        private @Nullable Optimizable[] optimizables = null;
 
-        public List<Optimizable> getOptimizables() {
+        public @Nullable Optimizable[] getOptimizables() {
             return optimizables;
         }
 
-        public void visitPathExpr(PathExpr expression) {
+        @Override
+        public void visitPathExpr(final PathExpr expression) {
             for (int i = 0; i < expression.getLength(); i++) {
                 final Expression next = expression.getExpression(i);
                 next.accept(this);
             }
         }
 
-        public void visitGeneralComparison(GeneralComparison comparison) {
-            optimizables.add(comparison);
+        @Override
+        public void visitGeneralComparison(final GeneralComparison comparison) {
+            addOptimizable(comparison);
         }
 
-        public void visitPredicate(Predicate predicate) {
+        @Override
+        public void visitPredicate(final Predicate predicate) {
             predicate.getExpression(0).accept(this);
         }
 
-        public void visitBuiltinFunction(Function function) {
+        @Override
+        public void visitBuiltinFunction(final Function function) {
             if (function instanceof Optimizable) {
-                optimizables.add((Optimizable) function);
+                addOptimizable((Optimizable) function);
+            }
+        }
+
+        private void addOptimizable(final Optimizable optimizable) {
+            if (optimizables == null) {
+                optimizables = new Optimizable[1];
+            } else {
+                optimizables = Arrays.copyOf(optimizables, optimizables.length + 1);
             }
+            optimizables[optimizables.length - 1] = optimizable;
         }
     }