pgsql: Skip unnecessary get_relids_in_jointree() when there are no PHVs

Skip unnecessary get_relids_in_jointree() when there are no PHVs

Commit 1df9e8d96 made remove_useless_result_rtes() compute the set of
baserels in the jointree, to pass down to the find_dependent_phvs()
checks. But those checks are no-ops when the query contains no PHVs,
since find_dependent_phvs() and find_dependent_phvs_in_jointree() both
return early in that case. So we can avoid the
get_relids_in_jointree() scan altogether when root->glob->lastPHId is
zero, leaving baserels as NULL.

Author: Richard Guo <guofenglinux(at)gmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/CAMbWs49H275KzgZr3Cd1Hy+6Lmwp35bZ+5PrVc62k3HDLj6hNQ@mail.gmail.com
Backpatch-through: 16

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/72457f1df803bba077b338d5ed3fb8418e69967d

Modified Files
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src/backend/optimizer/prep/prepjointree.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)