pgsql: Avoid extra AggCheckCallContext() checks in ordered-set aggregat

Avoid extra AggCheckCallContext() checks in ordered-set aggregates.

In the transition functions, we don't really need to recheck this after the
first call. I had been feeling paranoid about possibly getting a non-null
argument value in some other context; but it's probably game over anyway
if we have a non-null "internal" value that's not what we are expecting.

In the final functions, the general convention in pre-existing final
functions seems to be that an Assert() is good enough, so do it like that
here too.

This seems to save a few tenths of a percent of overall query runtime,
which isn't much, but still it's just overhead if there's not a plausible
case where the checks would fire.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/847e46abc92333a5a948d8fa886604832c1db238

Modified Files
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src/backend/utils/adt/orderedsetaggs.c | 42 +++++++-------------------------
1 file changed, 9 insertions(+), 33 deletions(-)