pgsql: Use memcpy instead of a byte loop in pglz_decompress

Use memcpy instead of a byte loop in pglz_decompress

The byte loop used in pglz_decompress() because of possible overlap may
be quite inefficient, so this commit replaces it with memcpy. The gains
do depend on the data (compressibility) and hardware, but seem to be
quite significant.

Author: Andrey Borodin
Reviewed-by: Michael Paquier, Konstantin Knizhnik, Tels
Discussion: https://postgr.es/m/469C9ED9-348C-4FE7-A7A7-B0FA671BEE4C@yandex-team.ru

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c60e520f6e0e8db9618cad042df071a6752f3c06

Modified Files
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src/common/pg_lzcompress.c | 52 ++++++++++++++++++++++++++++++++++++----------
1 file changed, 41 insertions(+), 11 deletions(-)