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From: Nathan Bossart <nathandbossart@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Devulapalli, Raghuveer <raghuveer.devulapalli@intel.com>
Cc: Shankaran, Akash <akash.shankaran@intel.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: Ants Aasma <ants.aasma@cybertec.at>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Amonson, Paul D <paul.d.amonson@intel.com>
Cc: Noah Misch <noah@leadboat.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org <pgsql-hackers@lists.postgresql.org>
Subject: Re: Popcount optimization using AVX512
Date: Tue, 30 Jul 2024 22:01:50 -0500
Message-ID: <ZqmpHjuDlJSjoZVT@nathan> (raw)
In-Reply-To: <20240731024308.xma56fxidkdydzlo@awork3.anarazel.de>
References: <PH8PR11MB82863AB8040AD090909DC18BFB0E2@PH8PR11MB8286.namprd11.prod.outlook.com>
	<20240418221358.GA3927188@nathanxps13>
	<20240423160207.GA841237@nathanxps13>
	<20240730210701.oyn2wr4zduu2efrg@awork3.anarazel.de>
	<Zqlb1_-BWlzVMbZv@nathan>
	<20240731004959.6ys24432n6xlgemk@awork3.anarazel.de>
	<ZqmRYh3iikm1Kh3D@nathan>
	<20240731014651.byn3exbu6n5v2yqa@awork3.anarazel.de>
	<Zqma-_guYhQmA9_A@nathan>
	<20240731024308.xma56fxidkdydzlo@awork3.anarazel.de>

On Tue, Jul 30, 2024 at 07:43:08PM -0700, Andres Freund wrote:
> On 2024-07-30 21:01:31 -0500, Nathan Bossart wrote:
>> The main purpose of the XSAVE compiler check is to determine whether we
>> need to add -mxsave in order to use _xgetbv() [0].  If that wasn't a
>> factor, we could probably skip it.  Earlier versions of the patch used
>> inline assembly in the non-MSVC path to call XGETBV, which I was trying to
>> avoid.
> 
> My point is that _xgetbv() is made available by -mavx512vpopcntdq -mavx512bw
> alone, without needing -mxsave:

Oh, I see.  I'll work on a patch to remove that compiler check, then...

-- 
nathan





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  Cc: nathandbossart@gmail.com, andres@anarazel.de, raghuveer.devulapalli@intel.com, akash.shankaran@intel.com, tgl@sss.pgh.pa.us, dgrowleyml@gmail.com, ants.aasma@cybertec.at, alvherre@alvh.no-ip.org, paul.d.amonson@intel.com, noah@leadboat.com, boekewurm+postgres@gmail.com, pgsql-hackers@lists.postgresql.org
  Subject: Re: Popcount optimization using AVX512
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