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https://issues.apache.org/jira/browse/CALCITE-4711?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Julian Hyde reassigned CALCITE-4711:
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Assignee: Julian Hyde
> RexProgramBuilder should not simplify
> -------------------------------------
>
> Key: CALCITE-4711
> URL: https://issues.apache.org/jira/browse/CALCITE-4711
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
> Priority: Major
>
> {{RexProgramBuilder}} currently simplifies expressions even if no
> {{RexSimplifier}} instance is supplied in its constructor: the method
> {{registerInternal}} creates a {{RexSimplifier}}.
> This simplification used to be beneficial. For instance, as of
> [4ef9f467|https://github.com/apache/calcite/commits/4ef9f46757528d21c510eb8bd171fa04ba86e36d],
> {{RexProgramBuilder}} can simplify "x AND y AND x" to "x AND y". But now we
> have RexSimplifier, which is applied pretty much any time a RexNode is
> included in a RelNode via a RelBuilder method.
> Simplify is now called in too many places, and I suspect that the running
> time is multiplying. Consider: {{RexSimplify.simplifyCast}} calls
> {{RexExecutor.reduce}} to reduce constants. To do this, {{RexExecutor}} uses
> {{RexProgramBuilder}} to generate a program (which will then be executed to
> yield the reduced value), and the RexProgramBuilder calls simplify again. It
> is ridiculous to call simplify at so many levels. It's time that we reduced
> the responsibilities of {{RexProgramBuilder}} to just building programs.
> (It is possible that, once a {{RexProgram}} has been created, we can see some
> patterns in the flattened expressions that would not be apparent to
> {{RexSimplify}}. If this happens, we could have a simplify step that works on
> {{Calc}} after its program has been generated.)
> After this change, {{RexProgramBuilder}} will simplify only if a
> {{RexSimplify}} is passed in the constructor. {{RexProgramBuilder}} will no
> longer be able to simplify "x AND y AND x". We will add a test to ensure that
> {{RelBuilder.filter}} can do this.
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