Kimahriman opened a new pull request #34727:
URL: https://github.com/apache/spark/pull/34727
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### What changes were proposed in this pull request?
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This PR consolidates the code paths for subexpression elimination in whole
stage and non-whole stage codegen. Whole stage codegen seemed to be mostly a
superset of the non-whole stage subexpression elimination, just with whole
stage not using the codegen context to track subexpressions. Since
subexpression values are replaced with empty blocks when evaluated, the context
should be able to track the subexpressions across multiple operators. Not sure
if there's corner cases I'm missing though.
It shouldn't result in any functionality changes, but there are slight
differences in the generated code as a result of this:
- Subexpressions in whole stage always use mutable state for results instead
of inlining results to support code splitting in non-whole stage
- Non-whole stage now supports the same inlining subexpressions if small
enough as whole stage codegen
- Subexpressions are tracked across multiple physical operators in whole
stage. They are still only calculated in each operator, but if you happen to
have an expression in a later operator that was a subexpression in a previous
operator, it will be used in the later operator.
### Why are the changes needed?
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Currently, there are different code paths to handle subexpression
elimination in whole stage and non-whole stage codegen. This makes it harder to
add new capabilities to subexpression elimination having to deal with
independent code paths.
### Does this PR introduce _any_ user-facing change?
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No, just slight changes in generated code.
### How was this patch tested?
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Existing unit tests.
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