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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Bastien Roucariès <rouca@debian.org>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: Detection of hadware feature => please do not use signal
Date: Wed, 27 Nov 2024 14:57:03 -0500
Message-ID: <1909652.1732737423@sss.pgh.pa.us> (raw)
In-Reply-To: <1492578.1732574410@sss.pgh.pa.us>
References: <4496616.iHFcN1HehY@portable-bastien>
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	<1216860.1732491268@sss.pgh.pa.us>
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	<1229505.1732498033@sss.pgh.pa.us>
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	<1430419.1732557238@sss.pgh.pa.us>
	<1492578.1732574410@sss.pgh.pa.us>

I wrote:
> Early returns are that they're all picking the +simd option, and
> seem to be just as happy with that as they were without it.
> I wonder if we could just drop the "without" probe altogether.
> It'd save some configure cycles for other platforms (since they'll
> fruitlessly run through all of these tests).

Now that we have a nearly-complete census of the buildfarm,
the end result is that they are all happy with the +simd
spelling ... except for one.  "gull" rejects it:
  clang: error: unsupported argument 'armv8-a+crc+simd' to option '-march='
But without +simd it's okay, so removing the other spelling
would cause a performance regression on that machine.

I find this a bit surprising, because gull is using a reasonably
recent compiler (clang version 17.0.4).  We have much older
clang versions that accept +simd --- but they are all aarch64.
gull seems to be our only representative of clang on arm32.
So this seems like a gcc vs clang difference that we'll have
to put up with.

Anyway, I think this thread is now closed: nothing more to do
unless someone thinks of a platform we need more bespoke code
for.

			regards, tom lane





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