[SPARK-14627][SQL] Avoid shilfting encoder when delta is zero

[viirya]

What changes were proposed in this pull request?

JIRA: https://issues.apache.org/jira/browse/SPARK-14627

Every time we call TypedAggregateExpression.update method, we call encoder's shift method. As shift method will copy encoder and underlying BoundReference, we should prepare the shifted encoder in advance, instead of calling shift method every time.

BTW, we can also slightly improve encoder's shift method to return itself when shift delta is zero.

How was this patch tested?

Existing tests.

[SparkQA]

Test build #55804 has finished for PR 12387 at commit 05875ba.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[viirya]

A minor change. Should be straightforward. cc @marmbrus @cloud-fan @rxin

[cloud-fan]

Thanks for working on it! But unfortunately, we are rewriting TypedAggregateExpression to make it use expressions, see #12067, i.e. there will be no shifting stuff anymore, do you mind closing this PR? thanks.

[viirya]

ok. close it now.

[viirya]

Ah. But the change in encoder should not related to #12067, right?

[cloud-fan]

But shift in only used in TypedAggregateExpression ...

[viirya]

ha. got it.