[SPARK-46632][SQL] Fix subexpression elimination when equivalent ternary expressions have different children

[zml1206]

What changes were proposed in this pull request?

Remove unexpected exception thrown in EquivalentExpressions.updateExprInMap(). Equivalent expressions may contain different children, it should happen expression not in map and useCount is -1.
For example, before this PR will throw IllegalStateException

Seq((1, 2, 3), (2, 3, 4)).toDF("a", "b", "c")
      .selectExpr("case when a + b + c>3 then 1 when c + a + b>0 then 2 else 0 end as d").show()

Why are the changes needed?

Bug fix.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

New unit test, before this PR will throw IllegalStateException: *** with use count: -1

Was this patch authored or co-authored using generative AI tooling?

No.

[zml1206]

cc @peter-toth @cloud-fan

[peter-toth]

Hmm, this is because ((1 + 2) + 3) semanticEquals to ((3 + 1) + 2) but their children are different. So when we compute the common elements between the above 2 here:

spark/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala

Lines 112 to 121 in 0d553d0

	var localEquivalenceMap = mutable.HashMap.empty[ExpressionEquals, ExpressionStats]
	updateExprTree(exprs.head, localEquivalenceMap)
	exprs.tail.foreach { expr =>
	val otherLocalEquivalenceMap = mutable.HashMap.empty[ExpressionEquals, ExpressionStats]
	updateExprTree(expr, otherLocalEquivalenceMap)
	localEquivalenceMap = localEquivalenceMap.filter { case (key, _) =>
	otherLocalEquivalenceMap.contains(key)
	}
	}

only ((1 + 2) + 3) remains in localEquivalenceMap but it's children don't. So later when we want to remove ((1 + 2) + 3) we can't find its children...

I think we could fix the above code that computes localEquivalenceMap, but the change in PR is simpler and doesn't seem to do any harm.

[zml1206]

cc @cloud-fan Do you have time to help take a look? Thank you.

[zml1206]

@peter-toth Can this PR be merged?