Horton

Re: Auto-vectorization speeds up multiplication of large-precision numerics

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

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: Amit Khandekar <amitdkhan.pg@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2020-07-10T13:32:10Z
Lists: pgsql-hackers 
Peter Eisentraut <peter.eisentraut@2ndquadrant.com> writes:
> We normally don't compile with -O3, so very few users would get the 
> benefit of this.

Yeah.  I don't think changing that baseline globally would be a wise move.

> We have CFLAGS_VECTOR for the checksum code.  I 
> suppose if we are making the numeric code vectorizable as well, we 
> should apply this there also.

> I think we need a bit of a policy decision from the group here.

I'd vote in favor of applying CFLAGS_VECTOR to specific source files
that can benefit.  We already have experience with that and we've not
detected any destabilization potential.

(I've not looked at this patch, so don't take this as a +1 for this
specific patch.)

			regards, tom lane

Commits

  1. Use plain memset() in numeric.c, not MemSet and friends.

  2. Frob numeric.c loop so that clang will auto-vectorize it too.

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

  4. Split Makefile symbol CFLAGS_VECTOR into two symbols.