Horton

RE: Improve CRC32C performance on SSE4.2

Devulapalli, Raghuveer <raghuveer.devulapalli@intel.com>

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From: "Devulapalli, Raghuveer" <raghuveer.devulapalli@intel.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: John Naylor <johncnaylorls@gmail.com>, Andy Fan <zhihuifan1213@163.com>, Jesper Pedersen <jesperpedersen.db@gmail.com>, Tomas Vondra <tomas@vondra.me>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, "Shankaran, Akash" <akash.shankaran@intel.com>
Date: 2025-06-16T22:20:59Z
Lists: pgsql-hackers

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Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Include _mm512_zextsi128_si512() in AVX-512 configure probes.

  2. Properly fix AVX-512 CRC calculation bug

  3. Workaround code generation bug in clang

  4. Compute CRC32C using AVX-512 instructions where available

  5. Inline CRC computation for small fixed-length input on x86

  6. Be more paranoid in configure's checks for CRC and POPCNT intrinsics.

Great catch! From the intrinsic manual: 

Cast vector of type __m128i to type __m512i; the upper 384 bits of the result are undefined.

Replacing that with _mm512_zextsi128_si512 fixes the problem. 

> -----Original Message-----
> From: Nathan Bossart <nathandbossart@gmail.com>
> Sent: Monday, June 16, 2025 3:14 PM
> To: Devulapalli, Raghuveer <raghuveer.devulapalli@intel.com>
> Cc: John Naylor <johncnaylorls@gmail.com>; Andy Fan
> <zhihuifan1213@163.com>; Jesper Pedersen <jesperpedersen.db@gmail.com>;
> Tomas Vondra <tomas@vondra.me>; pgsql-hackers@lists.postgresql.org;
> Shankaran, Akash <akash.shankaran@intel.com>
> Subject: Re: Improve CRC32C performance on SSE4.2
> 
> On Mon, Jun 16, 2025 at 06:31:11PM +0000, Devulapalli, Raghuveer wrote:
> > Attached is a simple reproducer. It passes with clang v16 -O0, but
> > fails with 17 and 18 only when built with -O0..
> 
> I've just started looking into this, but the difference in code generated for
> _mm512_castsi128_si512() between gcc, clang 16, and clang 17 looks interesting.
> 
> --
> nathan