pgsql: Introduce overflow-safe integer comparison functions.

Introduce overflow-safe integer comparison functions.

This commit adds integer comparison functions that are designed to
be as efficient as possible while avoiding overflow.  A follow-up
commit will make use of these functions in many of the in-tree
qsort() comparators.  The new functions are not better in all cases
(e.g., when the comparator function is inlined), so it is important
to consider the context before using them.

Author: Mats Kindahl
Reviewed-by: Tom Lane, Heikki Linnakangas, Andres Freund, Thomas Munro, Andrey Borodin, Fabrízio de Royes Mello
Discussion: https://postgr.es/m/CA%2B14426g2Wa9QuUpmakwPxXFWG_1FaY0AsApkvcTBy-YfS6uaw%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6b80394781c8de17fe7cae6996476088af3c319f

Modified Files
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src/include/common/int.h        | 75 +++++++++++++++++++++++++++++++++++++++--
src/include/lib/sort_template.h | 13 +++++++
2 files changed, 86 insertions(+), 2 deletions(-)