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https://issues.apache.org/jira/browse/DRILL-3912?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14947799#comment-14947799
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Jinfeng Ni commented on DRILL-3912:
-----------------------------------
I actually had one patch to remove the redundancy in run-time generated code.
https://issues.apache.org/jira/browse/DRILL-3754
The only failure with the patch is for it hit failure in scalar replacement
logic for case where same column appear twice in a HashJoin. The run-time code
seems valid, but the scalar replacement fails.
{code}
select t1.full_name from cp.`employee.json` t1, cp.`department.json` t2
where t1.department_id = t2.department_id and t1.position_id =
t2.department_id");
{code}
I just rebase on master branch. Can you check if the two patches address same
problem?
See: https://github.com/jinfengni/incubator-drill/tree/DRILL-3754
> 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.
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