[CALCITE-2452] RexSimplify: avoid multiple similar optimization passes over the same nodes

• Type: Sub-task
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Assignee: Unassigned
• Reporter: Vladimir Sitnikov
• Created: 07/Aug/18 11:21
• Updated: 22/Feb/19 01:21

Description

simplifyAndTerms(List<RexNode> terms) has two loops and it calls simplify on each expression twice.

simplifyAnd(RexCall e) calls simplifyList (that walks all the tree down), then simplifyAnd2ForUnknownAsFalse calls simplify_ again.

It looks like just one pass should be sufficient for most of the cases, and the logic should probably be adjusted as follows:

simplify(RexNode node){
  // e.g. simplify the node with assumption that all the arguments were simplified, etc, avoid complicated checks
  node = simplifyTrivialCases(node); 

  // this walks over the tree, simplifies operands first then simplifies the call itself
  node = simplifyArgumentsThenSimplifyNode(node); 
  return node;
}

Method naming should clearly indicate that the method is heavy, so it would not accidentally be used.