Horton

Re: Some optimisations for numeric division

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-02-25T18:30:33Z
Lists: pgsql-hackers 
Dean Rasheed <dean.a.rasheed@gmail.com> writes:
> And another update following feedback from the cfbot.

This patchset LGTM.  On my machine there doesn't seem to be any
measurable performance change for the numeric regression test,
but numeric_big gets about 15% faster.

The only additional thought I have, based on your comments about
0001, is that maybe in mul_var we should declare var1digit as
being NumericDigit not int.  I tried that here and didn't see
any material change in the generated assembly code (using gcc
8.5.0), so you're right that modern gcc doesn't need any help
there; but I wonder if it could help on other compiler versions.

I'll mark this RFC.

			regards, tom lane

Commits

  1. Optimise numeric division for one and two base-NBASE digit divisors.

  2. Simplify the inner loop of numeric division in div_var().

  3. Apply auto-vectorization to the inner loop of div_var_fast().

  4. Apply auto-vectorization to the inner loop of numeric multiplication.