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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