Steven Phillips created DRILL-3912:
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Summary: Common subexpression elimination
Key: DRILL-3912
URL: https://issues.apache.org/jira/browse/DRILL-3912
Project: Apache Drill
Issue Type: Bug
Reporter: Steven Phillips
Drill currently will evaluate the full expression tree, even if there are
redundant subtrees. Many of these redundant evaluations can be eliminated by
reusing the results from previously evaluated expression trees.
For example,
{code}
select a + 1, (a + 1)* (a - 1) from t
{code}
Will compute the entire (a + 1) expression twice. With CSE, it will only be
evaluated once.
The benefit will be reducing the work done when evaluating expressions, as well
as reducing the amount of code that is generated, which could also lead to
better JIT optimization.
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