Use SSE2 intrinsics to speed up the search, where available. Otherwise,
use a simple 'for' loop. The motivation to add this now is to speed up
XidInMVCCSnapshot(), which is the reason only unsigned 32-bit integer
arrays are optimized. Other types are left for future work, as is the
extension of this technique to non-x86 platforms.
Nathan Bossart
Reviewed by: Andres Freund, Bharath Rupireddy, Masahiko Sawada
Discussion: https://postgr.es/m/
20220713170950.GA3116318%40nathanxps13
--- /dev/null
+/*-------------------------------------------------------------------------
+ *
+ * pg_lfind.h
+ * Optimized linear search routines.
+ *
+ * Copyright (c) 2022, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ * src/include/port/pg_lfind.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_LFIND_H
+#define PG_LFIND_H
+
+#include "port/simd.h"
+
+/*
+ * pg_lfind32
+ *
+ * Return true if there is an element in 'base' that equals 'key', otherwise
+ * return false.
+ */
+static inline bool
+pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
+{
+ uint32 i = 0;
+
+ /* Use SIMD intrinsics where available. */
+#ifdef USE_SSE2
+
+ /*
+ * A 16-byte register only has four 4-byte lanes. For better
+ * instruction-level parallelism, each loop iteration operates on a block
+ * of four registers. Testing has showed this is ~40% faster than using a
+ * block of two registers.
+ */
+ const __m128i keys = _mm_set1_epi32(key); /* load 4 copies of key */
+ uint32 iterations = nelem & ~0xF; /* round down to multiple of 16 */
+
+#if defined(USE_ASSERT_CHECKING)
+ bool assert_result = false;
+
+ /* pre-compute the result for assert checking */
+ for (i = 0; i < nelem; i++)
+ {
+ if (key == base[i])
+ {
+ assert_result = true;
+ break;
+ }
+ }
+#endif
+
+ for (i = 0; i < iterations; i += 16)
+ {
+ /* load the next block into 4 registers holding 4 values each */
+ const __m128i vals1 = _mm_loadu_si128((__m128i *) & base[i]);
+ const __m128i vals2 = _mm_loadu_si128((__m128i *) & base[i + 4]);
+ const __m128i vals3 = _mm_loadu_si128((__m128i *) & base[i + 8]);
+ const __m128i vals4 = _mm_loadu_si128((__m128i *) & base[i + 12]);
+
+ /* compare each value to the key */
+ const __m128i result1 = _mm_cmpeq_epi32(keys, vals1);
+ const __m128i result2 = _mm_cmpeq_epi32(keys, vals2);
+ const __m128i result3 = _mm_cmpeq_epi32(keys, vals3);
+ const __m128i result4 = _mm_cmpeq_epi32(keys, vals4);
+
+ /* combine the results into a single variable */
+ const __m128i tmp1 = _mm_or_si128(result1, result2);
+ const __m128i tmp2 = _mm_or_si128(result3, result4);
+ const __m128i result = _mm_or_si128(tmp1, tmp2);
+
+ /* see if there was a match */
+ if (_mm_movemask_epi8(result) != 0)
+ {
+#if defined(USE_ASSERT_CHECKING)
+ Assert(assert_result == true);
+#endif
+ return true;
+ }
+ }
+#endif /* USE_SSE2 */
+
+ /* Process the remaining elements one at a time. */
+ for (; i < nelem; i++)
+ {
+ if (key == base[i])
+ {
+#if defined(USE_SSE2) && defined(USE_ASSERT_CHECKING)
+ Assert(assert_result == true);
+#endif
+ return true;
+ }
+ }
+
+#if defined(USE_SSE2) && defined(USE_ASSERT_CHECKING)
+ Assert(assert_result == false);
+#endif
+ return false;
+}
+
+#endif /* PG_LFIND_H */
test_extensions \
test_ginpostinglist \
test_integerset \
+ test_lfind \
test_misc \
test_oat_hooks \
test_parser \
--- /dev/null
+# Generated subdirectories
+/log/
+/results/
+/tmp_check/
--- /dev/null
+# src/test/modules/test_lfind/Makefile
+
+MODULE_big = test_lfind
+OBJS = \
+ $(WIN32RES) \
+ test_lfind.o
+PGFILEDESC = "test_lfind - test code for optimized linear search functions"
+
+EXTENSION = test_lfind
+DATA = test_lfind--1.0.sql
+
+REGRESS = test_lfind
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = src/test/modules/test_lfind
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
--- /dev/null
+CREATE EXTENSION test_lfind;
+--
+-- These tests don't produce any interesting output. We're checking that
+-- the operations complete without crashing or hanging and that none of their
+-- internal sanity tests fail.
+--
+SELECT test_lfind();
+ test_lfind
+------------
+
+(1 row)
+
--- /dev/null
+CREATE EXTENSION test_lfind;
+
+--
+-- These tests don't produce any interesting output. We're checking that
+-- the operations complete without crashing or hanging and that none of their
+-- internal sanity tests fail.
+--
+SELECT test_lfind();
--- /dev/null
+/* src/test/modules/test_lfind/test_lfind--1.0.sql */
+
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_lfind" to load this file. \quit
+
+CREATE FUNCTION test_lfind()
+ RETURNS pg_catalog.void
+ AS 'MODULE_PATHNAME' LANGUAGE C;
--- /dev/null
+/*--------------------------------------------------------------------------
+ *
+ * test_lfind.c
+ * Test correctness of optimized linear search functions.
+ *
+ * Copyright (c) 2022, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ * src/test/modules/test_lfind/test_lfind.c
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "fmgr.h"
+#include "port/pg_lfind.h"
+
+PG_MODULE_MAGIC;
+
+PG_FUNCTION_INFO_V1(test_lfind);
+
+Datum
+test_lfind(PG_FUNCTION_ARGS)
+{
+#define TEST_ARRAY_SIZE 135
+ uint32 test_array[TEST_ARRAY_SIZE] = {0};
+
+ test_array[8] = 1;
+ test_array[64] = 2;
+ test_array[TEST_ARRAY_SIZE - 1] = 3;
+
+ if (pg_lfind32(1, test_array, 4))
+ elog(ERROR, "pg_lfind32() found nonexistent element");
+ if (!pg_lfind32(1, test_array, TEST_ARRAY_SIZE))
+ elog(ERROR, "pg_lfind32() did not find existing element");
+
+ if (pg_lfind32(2, test_array, 32))
+ elog(ERROR, "pg_lfind32() found nonexistent element");
+ if (!pg_lfind32(2, test_array, TEST_ARRAY_SIZE))
+ elog(ERROR, "pg_lfind32() did not find existing element");
+
+ if (pg_lfind32(3, test_array, 96))
+ elog(ERROR, "pg_lfind32() found nonexistent element");
+ if (!pg_lfind32(3, test_array, TEST_ARRAY_SIZE))
+ elog(ERROR, "pg_lfind32() did not find existing element");
+
+ if (pg_lfind32(4, test_array, TEST_ARRAY_SIZE))
+ elog(ERROR, "pg_lfind32() found nonexistent element");
+
+ PG_RETURN_VOID();
+}
--- /dev/null
+comment = 'Test code for optimized linear search functions'
+default_version = '1.0'
+module_pathname = '$libdir/test_lfind'
+relocatable = true
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