cloud-fan commented on a change in pull request #30790:
URL: https://github.com/apache/spark/pull/30790#discussion_r545307270
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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@@ -528,6 +528,28 @@ object SimplifyConditionals extends Rule[LogicalPlan] with
PredicateHelper {
}
+/**
+ * Push the foldable expression into (if / case) branches.
+ */
+object PushFoldableIntoBranches extends Rule[LogicalPlan] with PredicateHelper
{
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case q: LogicalPlan => q transformExpressionsUp {
+ case b @ BinaryComparison(i @ If(_, trueValue, falseValue), right) if
i.deterministic &&
+ right.foldable && trueValue.foldable && falseValue.foldable =>
+ i.copy(
+ trueValue = b.makeCopy(Array(trueValue, right)),
+ falseValue = b.makeCopy(Array(falseValue, right)))
+
+ case b @ BinaryComparison(c @ CaseWhen(branches, elseValue), right) if
c.deterministic &&
+ right.foldable && (branches.map(_._2) ++
elseValue).forall(_.foldable) =>
Review comment:
some more ideas:
1. I think it's helpful to pushdown foldables into branches as long as there
is at lease one foldable branche. To be conservative, we can do the pushdown if
the IF/CASE WHEN has at most one non-foldable branch, so that we never increase
the expression tree size, so is the generated code size.
2. I think it's also useful to pushdown expressions like Add, e.g.
`IF(cond, 1, 2) +1` -> `IF(cond, 2, 3)`. We can use `BinnaryExpression` instead
of `BinaryComparison`.
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