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From: Michael Paquier <[email protected]>
To: Bertrand Drouvot <[email protected]>
Cc: David Rowley <[email protected]>
Cc: Peter Smith <[email protected]>
Cc: Peter Eisentraut <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Cc: [email protected]
Subject: Re: define pg_structiszero(addr, s, r)
Date: Fri, 1 Nov 2024 16:14:09 +0900
Message-ID: <[email protected]> (raw)
In-Reply-To: <ZyR2Tzdmj9c6E/[email protected]>
References: <[email protected]>
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	<ZyR2Tzdmj9c6E/[email protected]>

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?
> 
> [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:
.LVL306:
   .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:
.LVL299:
   .loc 1 131 16 is_stmt 0 discriminator 1 view .LVU524
   cmpq    $8192, %rbx
   je      .L419

3) With the patch sent at [1]:
.LVL306:
   .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/[email protected]
--
Michael


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