[CALCITE-4964] Reduce recursion when push predicate into CASE

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Ziwei Liu
• Reporter: Ziwei Liu
• Created: 24/Dec/21 10:17
• Updated: 30/Dec/21 01:25

Description

I think CaseShuttle do not need a loop of for(;; ).When a predicate is pushed into case, we only need to check the new RexCall whether need to push predicate into the child operand, not need to do a new recursion.

So I think CaseShuttle can be reduced like:

@Override public RexNode visitCall(RexCall call) {
   call = (RexCall) super.visitCall(call);
   if (call instanceof OdpsLambdaRexCall) {
      return call;
   }
   final RexCall old = call;
   call = ReduceExpressionsRule.pushPredicateIntoCase(call);
   if (call == old) {
     return call;
   } else {
      boolean containCase = false;
      List<RexNode> newOps = new ArrayList<>(call.getOperands().size());
      // call will be like case when c1 then f(x1 ...)
      // check whether need push f into x1
      for (int i = 0; i < call.getOperands().size(); i ++) {
         RexNode op = call.getOperands().get(i);
         RexNode newOp = op;
         if (i % 2 == 1 || i == call.getOperands().size() - 1) {
           if (op instanceof RexCall) {
             newOp = ReduceExpressionsRule.pushPredicateIntoCase((RexCall) op);
           }
         }
         if (op != newOp) {
           containCase = true;
         }
         newOps.add(newOp);
       }
       if (!containCase) {
         return call;
       } else {
         return call.clone(call.getType(), newOps);
       }
   }    
} 

Issue Links

• relates to: CALCITE-3630 Improve ReduceExpressionsRule