Date: Fri, 10 Jan 2025 14:46:45 -0600
From: Nathan Bossart <nathandbossart@gmail.com>
To: "Chiranmoy.Bhattacharya@fujitsu.com" <Chiranmoy.Bhattacharya@fujitsu.com>
Cc: "Devanga.Susmitha@fujitsu.com" <Devanga.Susmitha@fujitsu.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>,
	"Ragesh.Hajela@fujitsu.com" <Ragesh.Hajela@fujitsu.com>
Subject: Re: [PATCH] Hex-coding optimizations using SVE on ARM.
Message-ID: <Z4GHNfhRKuA0r_Wn@nathan>
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On Fri, Jan 10, 2025 at 09:38:14AM -0600, Nathan Bossart wrote:
> On Fri, Jan 10, 2025 at 11:10:03AM +0000, Chiranmoy.Bhattacharya@fujitsu.com wrote:
>> We tried auto-vectorization and observed no performance improvement.
> 
> Do you mean that the auto-vectorization worked and you observed no
> performance improvement, or the auto-vectorization had no effect on the
> code generated?

I was able to get auto-vectorization to take effect on Apple clang 16 with
the following addition to src/backend/utils/adt/Makefile:

	encode.o: CFLAGS += ${CFLAGS_VECTORIZE} -mllvm -force-vector-width=8

This gave the following results with your hex_encode_test() function:

    buf  | HEAD  | patch | % diff
  -------+-------+-------+--------
      16 |    21 |    16 |   24
      64 |    54 |    41 |   24
     256 |   138 |   100 |   28
    1024 |   441 |   300 |   32
    4096 |  1671 |  1106 |   34
   16384 |  6890 |  4570 |   34
   65536 | 27393 | 18054 |   34

This doesn't compare with the gains you are claiming to see with
intrinsics, but it's not bad for a one line change.  I bet there are ways
to adjust the code so that the auto-vectorization is more effective, too.

-- 
nathan