[jira] [Created] (DRILL-1854) reduce number of local variables in generated operators by reusing them

["Chris Westin (JIRA)" <ji...@apache.org>]

Chris Westin created DRILL-1854:
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             Summary: reduce number of local variables in generated operators by reusing them
                 Key: DRILL-1854
                 URL: https://issues.apache.org/jira/browse/DRILL-1854
             Project: Apache Drill
          Issue Type: Bug
          Components: Execution - Codegen
            Reporter: Chris Westin


Every time code gen inlines a function, it generates new temporaries for it to use. The number of locals is getting very large for some functions -- I've seen one case with about 300. But all of these locals are only referenced within a single block. It appears that the java compiler (at least Janino) does not reuse these (compare with a C/C++ compiler, which would reuse the same stack space across blocks). We can be smarter about not generating new temporaries, and just reusing compatible ones if they are already available by maintaining a pool (map of Type to variable name) of available variables, and borrowing from these during code generation as necessary.



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