GitHub user davies opened a pull request:

    https://github.com/apache/spark/pull/11274

    [SPARK-13404] improve codegen

    ## What changes were proposed in this pull request?
    
    Right now, we create the variables in the first operator (usually 
InputAdapter), they could be wasted if most of rows after filtered out 
immediately.
    
    This PR change to defer that until they are used by following operators.
    
    This PR also change the `if` from 
    ```
    if (cond) {
      xxx
    }
    ```
    to 
    ```
    if (!cond) continue;
    xxx
    ```
    The new one could help to reduce the nested indents for multiple levels of 
Filter and BroadcastHashJoin.
    
    It also added some comments for operators.
    
    ## How was the this patch tested?
    
    Unit tests. Manually ran TPCDS Q78, without fixing column pruning, this PR 
could improve the performance 


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/davies/spark gen_defer

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/spark/pull/11274.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #11274
    
----
commit 37e5560a871c03f389af29f480c2159e0b60c134
Author: Davies Liu <[email protected]>
Date:   2016-02-19T08:11:17Z

    improve codegen

----


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