[GitHub] [spark] viirya commented on pull request #27013: [SPARK-30356][SQL] Codegen support for the function str_to_map

[GitBox <gi...@apache.org>]

viirya commented on pull request #27013:
URL: https://github.com/apache/spark/pull/27013#issuecomment-705327777


   We don't support subexpression elimination in whole-stage codegen. It is not a problem for this PR specially.
   
   I added subexpression elimination to Hash Aggregation codegen. So currently Hash Aggregation is the only one operator supporting subexpression elimination in whole-stage codegen.
   
   Using the same code, it is not hard to support subexpression elimination in other operators such as ProjectExec.
   
   But we should notice that for ProjectExec, we don't evaluate all expressions in project list at once in ProjectExec. Instead we defer the evaluation because not all expressions will be evaluated. For subexpression elimination, we need to evaluate subexpressions in ProjectExec. That's said, we might evaluate expressions more early than current approach.
   
    


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