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From: Nathan Bossart <nathandbossart@gmail.com>
To: Amonson, Paul D <paul.d.amonson@intel.com>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Shankaran, Akash <akash.shankaran@intel.com>
Cc: Noah Misch <noah@leadboat.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
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: Mon, 18 Mar 2024 16:26:00 -0500
Message-ID: <20240318212600.GA655785@nathanxps13> (raw)
In-Reply-To: <BL1PR11MB53043A6B4224FDBC03D47B6EDC2D2@BL1PR11MB5304.namprd11.prod.outlook.com>
References: <BL1PR11MB53042473B7B53B96E43648A7DC292@BL1PR11MB5304.namprd11.prod.outlook.com>
	<20240315150611.GA3495582@nathanxps13>
	<CAApHDvrb7MJRB6JuKLDEY2x_LKdFHwVbogpjZBCX547i5+rXOQ@mail.gmail.com>
	<20240318152902.GA2850@nathanxps13>
	<BL1PR11MB5304070E33F7DD0520445B77DC2D2@BL1PR11MB5304.namprd11.prod.outlook.com>
	<20240318162018.GA204772@nathanxps13>
	<20240318173004.GA361138@nathanxps13>
	<CAApHDvqyMNGVgwpaOPtENdq5uEMR=vSkRJEgG1S+X7Vtk1-EnA@mail.gmail.com>
	<20240318210810.GA582529@nathanxps13>
	<BL1PR11MB53043A6B4224FDBC03D47B6EDC2D2@BL1PR11MB5304.namprd11.prod.outlook.com>

On Mon, Mar 18, 2024 at 09:22:43PM +0000, Amonson, Paul D wrote:
>> The only reason I left it out was because I couldn't convince myself that it
>> wasn't dead code, given we assume that popcntq is available in
>> pg_popcount64_fast() today.  But I don't see any harm in adding that just in
>> case.
> 
> I am not sure how to read this. Does this mean that for popcount32_fast
> and popcount64_fast I can assume that the x86(_64) instructions exists
> and stop doing the runtime checks for instruction availability?

I think my question boils down to "if pg_popcount_available() returns true,
can I safely assume I'm on a 64-bit machine?"

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com





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  Cc: nathandbossart@gmail.com, paul.d.amonson@intel.com, dgrowleyml@gmail.com, andres@anarazel.de, alvherre@alvh.no-ip.org, akash.shankaran@intel.com, noah@leadboat.com, tgl@sss.pgh.pa.us, boekewurm+postgres@gmail.com, pgsql-hackers@lists.postgresql.org
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