pgsql: Unify two isLogSwitch tests in XLogInsertRecord.

Unify two isLogSwitch tests in XLogInsertRecord.

An upcoming patch wants to introduce an additional special case in
this function. To keep that as cheap as possible, minimize the amount
of branching that we do based on whether this is an XLOG_SWITCH
record.

Additionally, and also in the interest of keeping the overhead of
special-case code paths as low as possible, apply likely() to the
non-XLOG_SWITCH case, since only a very tiny fraction of WAL records
will be XLOG_SWITCH records.

Patch by me, reviewed by Dilip Kumar, Amit Kapila, Andres Freund,
and Michael Paquier.

Discussion: http://postgr.es/m/CA+TgmoYy-Vc6G9QKcAKNksCa29cv__czr+N9X_QCxEfQVpp_8w@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/df9a3d4e99941f66f7a247eb01a48c1c2630625d

Modified Files
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src/backend/access/transam/xlog.c | 101 ++++++++++++++++++++++----------------
1 file changed, 58 insertions(+), 43 deletions(-)