Feedback-ID: i0fe9450f:Fastmail
Date: Fri, 1 Nov 2024 16:14:09 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: David Rowley <dgrowleyml@gmail.com>,
	Peter Smith <smithpb2250@gmail.com>,
	Peter Eisentraut <peter@eisentraut.org>,
	Heikki Linnakangas <hlinnaka@iki.fi>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: define pg_structiszero(addr, s, r)
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On Fri, Nov 01, 2024 at 06:33:51AM +0000, Bertrand Drouvot wrote:
> We could try to write a more elaborate version of pg_memory_is_all_zeros(=
), but
> as it looks like there is only one use case, then it's probably better to=
 not
> implement (revert) this change here and "just" add a comment as to why pg=
_memory_is_all_zeros()
> should not be used here, thoughts?
>=20
> [0]: https://godbolt.org/z/xqnW4MPY5

Note that the two printf() calls make the code less optimized.

Anyway, I see the following from bufpage.s for these lines under -O2:

1) On HEAD at 07e9e28b56db:
=2ELVL306:
   .loc 3 201 23 is_stmt 1 discriminator 1 view .LVU547
   cmpq    $1024, %rbx <- Yep, that's wrong.
   jne     .L417

2) On HEAD at 49d6c7d8daba:
=2ELVL299:
   .loc 1 131 16 is_stmt 0 discriminator 1 view .LVU524
   cmpq    $8192, %rbx
   je      .L419

3) With the patch sent at [1]:
=2ELVL306:
   .loc 3 201 23 is_stmt 1 discriminator 1 view .LVU545
   cmpq    $8192, %rbx
   jne     .L417

So it does not matter one way or another for 2) or 3), does it?

[1]: https://www.postgresql.org/message-id/ZyR02ofHiWG1HmLI@paquier.xyz
--
Michael

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