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Properly fix AVX-512 CRC calculation bug

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The problem that led to the workaround in f83f14881c7 was not in fact
a compiler bug, but a failure to zero the upper bits of the vector
register containing the initial scalar CRC value. Fix that and revert
the workaround.

Diagnosed-by: Nathan Bossart <nathandbossart@gmail.com>
Diagnosed-by: Raghuveer Devulapalli <raghuveer.devulapalli@intel.com>
Tested-by: Andy Fan <zhihuifan1213@163.com>
Tested-by: Soumyadeep Chakraborty <soumyadeep2007@gmail.com>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Raghuveer Devulapalli <raghuveer.devulapalli@intel.com>
Discussion: https://postgr.es/m/PH8PR11MB82866B07AA6758D12F699C00FB70A@PH8PR11MB8286.namprd11.prod.outlook.com
This commit is contained in:
John Naylor 2025-06-23 18:03:56 +07:00
parent 2c0d8b9508
commit 43da394304
2 changed files with 2 additions and 4 deletions
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2
src/port/pg_crc32c_sse42.c
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@ -123,7 +123,7 @@ pg_comp_crc32c_avx512(pg_crc32c crc, const void *data, size_t len)
__m512i k;
k = _mm512_broadcast_i32x4(_mm_setr_epi32(0x740eef02, 0, 0x9e4addf8, 0));
x0 = _mm512_xor_si512(_mm512_castsi128_si512(_mm_cvtsi32_si128(crc0)), x0);
x0 = _mm512_xor_si512(_mm512_zextsi128_si512(_mm_cvtsi32_si128(crc0)), x0);
buf += 64;
/* Main loop. */

4
src/port/pg_crc32c_sse42_choose.c
View File

@ -95,9 +95,7 @@ pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
__cpuidex(exx, 7, 0);
#endif
#if defined(__clang__) && !defined(__OPTIMIZE__)
/* Some versions of clang are broken at -O0 */
#elif defined(USE_AVX512_CRC32C_WITH_RUNTIME_CHECK)
#ifdef USE_AVX512_CRC32C_WITH_RUNTIME_CHECK
if (exx[2] & (1 << 10) && /* VPCLMULQDQ */
exx[1] & (1 << 31)) /* AVX512-VL */
pg_comp_crc32c = pg_comp_crc32c_avx512;