julianhyde commented on a change in pull request #2253:
URL: https://github.com/apache/calcite/pull/2253#discussion_r543598582



##########
File path: 
core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java
##########
@@ -366,14 +368,18 @@ public JoinReduceExpressionsRule(Class<? extends Join> 
joinClass,
 
     @Override public void onMatch(RelOptRuleCall call) {
       final Join join = call.rel(0);
-      final List<RexNode> expList = Lists.newArrayList(join.getCondition());
+      final RexBuilder rexBuilder = join.getCluster().getRexBuilder();
+      final RexSimplify rexSimplify =
+          new RexSimplify(rexBuilder, RelOptPredicateList.EMPTY, EXECUTOR);
+      final RexNode condition = 
rexSimplify.eliminateCommonExprInCondition(join.getCondition());
+
+      final List<RexNode> expList = Lists.newArrayList(condition);

Review comment:
       I don’t like the idea of RexSimplify having “modes”. Something is either 
simple or it isn’t. If we can’t agree on what is simple, then it isn’t simple.
   
   I think the CNF/DNF rewrites are a better pattern to follow. 




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