Method optimizeEbv

basex-core/src/main/java/org/basex/query/expr/Arr.java:183–250

Tries to merge consecutive EBV tests. @param or union or intersection @param predicate predicate test @param cc compilation context @return true if evaluation can be skipped @throws QueryException query exception

(final boolean or, final boolean predicate, final CompileContext cc)

   * @throws QueryException query exception
   */
  final boolean optimizeEbv(final boolean or, final boolean predicate, final CompileContext cc)
      throws QueryException {

    final ExprList list = new ExprList(exprs.length);
    boolean pos = false;
    for(final Expr expr : exprs) {
      // pre-evaluate values
      if(expr instanceof Value && (!predicate || !expr.seqType().mayBeNumber())) {
        // skip evaluation: true() or $bool → true()
        if(expr.test(cc.qc, info, 0) == or) return true;
        // ignore result: true() and $bool → $bool
        cc.info(QueryText.OPTREMOVE_X_X, expr, (Supplier<?>) this::description);
      } else if(!pos && list.contains(expr) && !expr.has(Flag.NDT)) {
        // ignore duplicates: A[$node and $node] → A[$node]
        cc.info(QueryText.OPTREMOVE_X_X, expr, (Supplier<?>) this::description);
      } else {
        list.add(expr);
        // preserve entries after positional predicates
        if(predicate && !pos) pos = mayBePositional(expr);
      }
    }
    exprs = list.next();

    if(!(predicate && has(Flag.POS))) {
      final Class<? extends Arr> clazz = or ? And.class : Or.class;
      final QueryBiFunction<Boolean, Expr[], Expr> func = (invert, args) ->
        invert == or ? new And(info, args) : new Or(info, args);
      final Expr tmp = rewrite(clazz, func, cc);
      if(tmp != null) {
        exprs = new Expr[] { tmp };
        cc.info(QueryText.OPTREWRITE_X_X, (Supplier<?>) this::description, this);
      }
    }

    list.add(exprs);
    for(int l = 0; l < list.size(); l++) {
      for(int m = l + 1; m < list.size(); m++) {
        final Expr expr1 = list.get(l), expr2 = list.get(m);
        if(!expr1.has(Flag.NDT) && !(predicate && expr1.has(Flag.POS))) {
          // A or not(A) → true()
          // A[not(B)][B] → ()
          // empty(A) or exists(A) → true()
          if(contradict(expr1, expr2, true) || contradict(expr2, expr1, true)) return true;

          // 'a'[. = 'a' or . = 'b'] → 'a'[. = ('a', 'b')]
          // $v[. != 'a'][. != 'b'] → $v[not(. = ('a', 'b')]
          final Expr merged = expr1.mergeEbv(expr2, or, cc);
          if(merged != null) {
            cc.info(QueryText.OPTSIMPLE_X_X, (Supplier<?>) this::description, this);
            list.set(l, merged);
            list.remove(m--);
          }
        }
      }
    }
    exprs = list.next();

    // not($a) and not($b) → not($a or $b)