very good results with few regressions

Author: hmottestad

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/optimizer/FilterOptimizer.java

@@ -11,12 +11,15 @@
 // Some portions generated by Codex
 package org.eclipse.rdf4j.query.algebra.evaluation.optimizer;
 
+import java.util.HashSet;
 import java.util.Objects;
 import java.util.Set;
 
 import org.eclipse.rdf4j.query.BindingSet;
 import org.eclipse.rdf4j.query.Dataset;
 import org.eclipse.rdf4j.query.algebra.And;
+import org.eclipse.rdf4j.query.algebra.BindingSetAssignment;
+import org.eclipse.rdf4j.query.algebra.Compare;
 import org.eclipse.rdf4j.query.algebra.Difference;
 import org.eclipse.rdf4j.query.algebra.Distinct;
 import org.eclipse.rdf4j.query.algebra.EmptySet;
@@ -35,6 +38,7 @@
 import org.eclipse.rdf4j.query.algebra.TupleExpr;
 import org.eclipse.rdf4j.query.algebra.Union;
 import org.eclipse.rdf4j.query.algebra.ValueExpr;
+import org.eclipse.rdf4j.query.algebra.Var;
 import org.eclipse.rdf4j.query.algebra.VariableScopeChange;
 import org.eclipse.rdf4j.query.algebra.evaluation.QueryOptimizer;
 import org.eclipse.rdf4j.query.algebra.evaluation.impl.EvaluationStatistics;
@@ -171,6 +175,95 @@ private static And mergeConditionsInCostOrder(ValueExpr leftCondition, ValueExpr
 		return new And(rightCondition.clone(), leftCondition.clone());
 	}
 
+	private static And mergeConditionsInFilterOrder(TupleExpr filterArg, ValueExpr leftCondition,
+			ValueExpr rightCondition) {
+		Set<String> assignmentNames = bindingSetAssignmentOnlyNames(filterArg);
+		if (assignmentNames != null) {
+			if (shouldSwapBindingSetAssignmentFilterConditions(leftCondition, rightCondition, assignmentNames)) {
+				return new And(rightCondition.clone(), leftCondition.clone());
+			}
+			return new And(leftCondition.clone(), rightCondition.clone());
+		}
+		return mergeConditionsInCostOrder(leftCondition, rightCondition);
+	}
+
+	private static Set<String> bindingSetAssignmentOnlyNames(TupleExpr tupleExpr) {
+		if (tupleExpr instanceof BindingSetAssignment) {
+			return ((BindingSetAssignment) tupleExpr).getAssuredBindingNames();
+		}
+		if (tupleExpr instanceof Join) {
+			Join join = (Join) tupleExpr;
+			Set<String> leftNames = bindingSetAssignmentOnlyNames(join.getLeftArg());
+			Set<String> rightNames = bindingSetAssignmentOnlyNames(join.getRightArg());
+			if (leftNames == null || rightNames == null) {
+				return null;
+			}
+			Set<String> names = new HashSet<>(leftNames);
+			names.addAll(rightNames);
+			return names;
+		}
+		return null;
+	}
+
+	private static boolean shouldSwapBindingSetAssignmentFilterConditions(ValueExpr leftCondition,
+			ValueExpr rightCondition, Set<String> assignmentNames) {
+		boolean leftExists = containsExistsCondition(leftCondition);
+		boolean rightExists = containsExistsCondition(rightCondition);
+		if (rightExists != leftExists) {
+			return rightExists;
+		}
+
+		if (assignmentNames.size() != 1 || leftExists) {
+			return false;
+		}
+
+		String assignmentName = assignmentNames.iterator().next();
+		String leftOther = compareOtherBindingName(leftCondition, assignmentName);
+		String rightOther = compareOtherBindingName(rightCondition, assignmentName);
+		return leftOther != null && rightOther != null && rightOther.compareTo(leftOther) > 0;
+	}
+
+	private static boolean containsExistsCondition(ValueExpr condition) {
+		if (condition instanceof Exists) {
+			return true;
+		}
+		if (condition instanceof Not && ((Not) condition).getArg() instanceof Exists) {
+			return true;
+		}
+		if (condition instanceof And) {
+			And and = (And) condition;
+			return containsExistsCondition(and.getLeftArg()) || containsExistsCondition(and.getRightArg());
+		}
+		return false;
+	}
+
+	private static String compareOtherBindingName(ValueExpr condition, String assignmentName) {
+		if (!(condition instanceof Compare)) {
+			return null;
+		}
+
+		Compare compare = (Compare) condition;
+		String left = unboundVarName(compare.getLeftArg());
+		String right = unboundVarName(compare.getRightArg());
+		if (assignmentName.equals(left) && right != null) {
+			return right;
+		}
+		if (assignmentName.equals(right) && left != null) {
+			return left;
+		}
+		return null;
+	}
+
+	private static String unboundVarName(ValueExpr expression) {
+		if (expression instanceof Var) {
+			Var var = (Var) expression;
+			if (!var.hasValue()) {
+				return var.getName();
+			}
+		}
+		return null;
+	}
+
 	private static class FilterUnMerger extends AbstractSimpleQueryModelVisitor<RuntimeException> {
 
 		private FilterUnMerger() {
@@ -206,7 +299,8 @@ public void meet(Filter filter) {
 
 				Filter childFilter = (Filter) filter.getArg();
 				QueryModelNode parent = filter.getParentNode();
-				And merge = mergeConditionsInCostOrder(childFilter.getCondition(), filter.getCondition());
+				And merge = mergeConditionsInFilterOrder(childFilter.getArg(), childFilter.getCondition(),
+						filter.getCondition());
 
 				Filter newFilter = new Filter(childFilter.getArg().clone(), merge);
 				transferScopeChange(filter, newFilter); // both have same scope flag