[jira] [Commented] (SPARK-18376) Skip subexpression elimination for conditional expressions

["Apache Spark (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-18376?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15649779#comment-15649779 ] 

Apache Spark commented on SPARK-18376:
--------------------------------------

User 'viirya' has created a pull request for this issue:
https://github.com/apache/spark/pull/15824

> Skip subexpression elimination for conditional expressions
> ----------------------------------------------------------
>
>                 Key: SPARK-18376
>                 URL: https://issues.apache.org/jira/browse/SPARK-18376
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>            Reporter: Liang-Chi Hsieh
>
> We should disallow subexpression elimination for expressions wrapped in conditional expressions such as {{If}}.
> Because for an example like this:
> {code}
> if (isNull(subexpr)) {
>   ...
> } else {
>   AssertNotNull(subexpr)  // subexpr2
>   ....
>   SomeExpr(AssertNotNull(subexpr)) // SomeExpr(subexpr2)
> }
> {code}
> AssertNotNull(subexpr) will be recognized as  a subexpression and evaluate even the else branch is never run. Under such cases, it possibly causes not excepted exception and performance regression. 



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