From 205737c56c7e49e8de25e6b4afca6a96abbb4e60 Mon Sep 17 00:00:00 2001 From: Nathan Bossart Date: Wed, 3 Aug 2022 09:49:04 -0700 Subject: [PATCH v7 1/2] Introduce optimized routine for linear searches through an array of integers. If SSE2 is available, this function uses it to speed up the search. Otherwise, it uses a simple 'for' loop. This is a prerequisite for a follow-up commit that will use this function to optimize [sub]xip lookups in XidInMVCCSnapshot(), but it can be used anywhere that might benefit from such an optimization. It might be worthwhile to add an ARM-specific code path to this function in the future. Author: Nathan Bossart Reviewed by: Andres Freund, John Naylor Discussion: https://postgr.es/m/20220713170950.GA3116318%40nathanxps13 --- src/include/port/pg_lfind.h | 73 +++++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 src/include/port/pg_lfind.h diff --git a/src/include/port/pg_lfind.h b/src/include/port/pg_lfind.h new file mode 100644 index 0000000000..27721490a6 --- /dev/null +++ b/src/include/port/pg_lfind.h @@ -0,0 +1,73 @@ +/*------------------------------------------------------------------------- + * + * pg_lfind.h + * Optimized linear search routines. + * + * Copyright (c) 2022, PostgreSQL Global Development Group + * + * + * IDENTIFICATION + * src/port/pg_lfind.h + * + *------------------------------------------------------------------------- + */ +#ifndef PG_LFIND_H +#define PG_LFIND_H + +#ifdef USE_SSE2 +#include "port/pg_bitutils.h" +#endif + +/* + * pg_lfind32 + * + * Returns the address of the first element in 'base' that equals 'key', or + * NULL if no match is found. + */ +static inline uint32 * +pg_lfind32(uint32 key, uint32 *base, uint32 nelem) +{ + uint32 i = 0; + + /* If possible, use SSE2 intrinsics to speed up the search. */ +#ifdef USE_SSE2 + __m128i keys = _mm_set1_epi32(key); /* load 4 copies of key */ + uint32 iterations = nelem & ~0xF; /* round down to multiple of 16 */ + + for (; i < iterations; i += 16) + { + /* load the next 16 values into __m128i variables */ + __m128i vals1 = _mm_loadu_si128((__m128i *) &base[i]); + __m128i vals2 = _mm_loadu_si128((__m128i *) &base[i + 4]); + __m128i vals3 = _mm_loadu_si128((__m128i *) &base[i + 8]); + __m128i vals4 = _mm_loadu_si128((__m128i *) &base[i + 12]); + + /* perform the comparisons */ + __m128i result1 = _mm_cmpeq_epi32(keys, vals1); + __m128i result2 = _mm_cmpeq_epi32(keys, vals2); + __m128i result3 = _mm_cmpeq_epi32(keys, vals3); + __m128i result4 = _mm_cmpeq_epi32(keys, vals4); + + /* shrink the results into a single variable */ + __m128i tmp1 = _mm_packs_epi32(result1, result2); + __m128i tmp2 = _mm_packs_epi32(result3, result4); + __m128i tmp3 = _mm_packs_epi16(tmp1, tmp2); + uint32 result = _mm_movemask_epi8(tmp3); + + /* see if there was a match */ + if (result != 0) + return &base[i + pg_rightmost_one_pos32(result)]; + } +#endif + + /* Process the remaining elements the slow way. */ + for (; i < nelem; i++) + { + if (key == base[i]) + return &base[i]; + } + + return NULL; +} + +#endif /* PG_LFIND_H */ -- 2.25.1