[
https://issues.apache.org/jira/browse/DRILL-3912?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14964340#comment-14964340
]
ASF GitHub Bot commented on DRILL-3912:
---------------------------------------
Github user StevenMPhillips commented on the pull request:
https://github.com/apache/drill/pull/189#issuecomment-149390304
I actually have done some additional work on this branch to extend it to
work with other operators. But I ran into the Scalar Replacement bug that was
mentioned in the JIRA. So I didn't add the changes to the pull request.
The tests fail because the current PR assumes there is only a single
MappingSet, and thus the generated code is all going into the same methods. My
solution was to clear the evaluated expression cache whenever the
setMappingSet() method is called.
> Common subexpression elimination in code generation
> ---------------------------------------------------
>
> Key: DRILL-3912
> URL: https://issues.apache.org/jira/browse/DRILL-3912
> Project: Apache Drill
> Issue Type: Bug
> 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.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
