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From jinfengni <...@git.apache.org>
Subject [GitHub] drill pull request: DRILL-3912: Common subexpression elimination
Date Tue, 03 Nov 2015 04:11:27 GMT
Github user jinfengni commented on a diff in the pull request:

    https://github.com/apache/drill/pull/189#discussion_r43714802
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/expr/EvaluationVisitor.java
---
    @@ -106,19 +177,30 @@ public HoldingContainer visitFunctionCall(FunctionCall call, ClassGenerator<?>
g
         @Override
         public HoldingContainer visitBooleanOperator(BooleanOperator op,
             ClassGenerator<?> generator) throws RuntimeException {
    +      HoldingContainer hc = getPrevious(op, generator.getMappingSet());
    --- End diff --
    
    You put the check whether it's common subexpression in EvalVisitor, when handling with
different expression. 
    
    I feel the code would be much cleaner, if we add a CSEFilter in a similar to ConstantFilter.
 The logic will go through ConstantFilter -> CSEFilter -> EvalVisitor.  The check of
common subexpression and adding to the Hashmap would be done solely in CSEFilter:visitiUnknow().
 In AbstractExrVisitor,  other methods will by default come to visitUnknow().  In this way,
there is no need to repeat the checking of common subexpression for different expression in
EvalVisitor; actually no change has to be done to EvalVisitor.
    
      


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