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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-3912) Common subexpression elimination in code generation
Date Tue, 03 Nov 2015 04:32:27 GMT

    [ https://issues.apache.org/jira/browse/DRILL-3912?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14986667#comment-14986667
] 

ASF GitHub Bot commented on DRILL-3912:
---------------------------------------

Github user jinfengni commented on the pull request:

    https://github.com/apache/drill/pull/189#issuecomment-153236066
  
    The revised code(adds MappingSet to ExpressionHolder) looks good to me.
    
      


> Common subexpression elimination in code generation
> ---------------------------------------------------
>
>                 Key: DRILL-3912
>                 URL: https://issues.apache.org/jira/browse/DRILL-3912
>             Project: Apache Drill
>          Issue Type: Improvement
>            Reporter: Steven Phillips
>            Assignee: Jinfeng Ni
>
> Drill currently will evaluate the full expression tree, even if there are redundant subtrees.
Many of these redundant evaluations can be eliminated by reusing the results from previously
evaluated expression trees.
> For example,
> {code}
> select a + 1, (a + 1)* (a - 1) from t
> {code}
> Will compute the entire (a + 1) expression twice. With CSE, it will only be evaluated
once.
> The benefit will be reducing the work done when evaluating expressions, as well as reducing
the amount of code that is generated, which could also lead to better JIT optimization.



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