v14-0003-Improve-CRC32C-performance-on-x86_64.patch

From 98e0d9cf96cc9a5eb8ce1eac9517693bb078bfe2 Mon Sep 17 00:00:00 2001
From: John Naylor <john.naylor@postgresql.org>
Date: Wed, 12 Feb 2025 15:27:16 +0700
Subject: [PATCH v14 3/8] Improve CRC32C performance on x86_64

The current SSE4.2 implementation of CRC32C relies on the native
CRC32 instruction, which operates on 8 bytes at a time. We can get a
substantial speedup on longer inputs by using carryless multiplication
on SIMD registers, processing 64 bytes per loop iteration.

The PCLMULQDQ instruction has been widely available since 2011 (almost
as old as SSE 4.2), so this commit now requires that, as well as SSE
4.2, to build pg_crc32c_sse42.c.

The MIT-licensed implementation was generated with the "generate"
program from

https://github.com/corsix/fast-crc32/

Based on: "Fast CRC Computation for Generic Polynomials Using PCLMULQDQ
Instruction" V. Gopal, E. Ozturk, et al., 2009

Author: Raghuveer Devulapalli <raghuveer.devulapalli@intel.com>
Author: John Naylor <johncnaylorls@gmail.com>
Discussion: https://postgr.es/m/PH8PR11MB82869FF741DFA4E9A029FF13FBF72@PH8PR11MB8286.namprd11.prod.outlook.com
---
 src/include/port/pg_crc32c.h      | 30 ++++++++---
 src/port/pg_crc32c_sse42.c        | 88 +++++++++++++++++++++++++++++++
 src/port/pg_crc32c_sse42_choose.c | 26 ++++-----
 3 files changed, 124 insertions(+), 20 deletions(-)

diff --git a/src/include/port/pg_crc32c.h b/src/include/port/pg_crc32c.h
index b9f0a8c7cca..229f4f6a65a 100644
--- a/src/include/port/pg_crc32c.h
+++ b/src/include/port/pg_crc32c.h
@@ -37,6 +37,11 @@
 
 typedef uint32 pg_crc32c;
 
+/* WIP: configure checks */
+#ifdef __x86_64__
+#define USE_PCLMUL_WITH_RUNTIME_CHECK
+#endif
+
 /* The INIT and EQ macros are the same for all implementations. */
 #define INIT_CRC32C(crc) ((crc) = 0xFFFFFFFF)
 #define EQ_CRC32C(c1, c2) ((c1) == (c2))
@@ -80,6 +85,23 @@ pg_comp_crc32c_dispatch(pg_crc32c crc, const void *data, size_t len)
 		return pg_comp_crc32c_sse42(crc, data, len);
 }
 
+#elif defined(USE_SSE42_CRC32C_WITH_RUNTIME_CHECK)
+
+/*
+ * Use Intel SSE 4.2 or PCLMUL instructions, but perform a runtime check first
+ * to check that they are available.
+ */
+#define COMP_CRC32C(crc, data, len) \
+	((crc) = pg_comp_crc32c((crc), (data), (len)))
+#define FIN_CRC32C(crc) ((crc) ^= 0xFFFFFFFF)
+
+extern pg_crc32c pg_comp_crc32c_sb8(pg_crc32c crc, const void *data, size_t len);
+extern pg_crc32c (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len);
+extern pg_crc32c pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len);
+#ifdef USE_PCLMUL_WITH_RUNTIME_CHECK
+extern pg_crc32c pg_comp_crc32c_pclmul(pg_crc32c crc, const void *data, size_t len);
+#endif
+
 #elif defined(USE_ARMV8_CRC32C)
 /* Use ARMv8 CRC Extension instructions. */
 
@@ -98,7 +120,7 @@ extern pg_crc32c pg_comp_crc32c_armv8(pg_crc32c crc, const void *data, size_t le
 
 extern pg_crc32c pg_comp_crc32c_loongarch(pg_crc32c crc, const void *data, size_t len);
 
-#elif defined(USE_SSE42_CRC32C_WITH_RUNTIME_CHECK) || defined(USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK)
+#elif defined(USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK)
 
 /*
  * Use Intel SSE 4.2 or ARMv8 instructions, but perform a runtime check first
@@ -110,13 +132,7 @@ extern pg_crc32c pg_comp_crc32c_loongarch(pg_crc32c crc, const void *data, size_
 
 extern pg_crc32c pg_comp_crc32c_sb8(pg_crc32c crc, const void *data, size_t len);
 extern pg_crc32c (*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len);
-
-#ifdef USE_SSE42_CRC32C_WITH_RUNTIME_CHECK
-extern pg_crc32c pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len);
-#endif
-#ifdef USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK
 extern pg_crc32c pg_comp_crc32c_armv8(pg_crc32c crc, const void *data, size_t len);
-#endif
 
 #else
 /*
diff --git a/src/port/pg_crc32c_sse42.c b/src/port/pg_crc32c_sse42.c
index 22c2137df31..2001e69850b 100644
--- a/src/port/pg_crc32c_sse42.c
+++ b/src/port/pg_crc32c_sse42.c
@@ -15,6 +15,7 @@
 #include "c.h"
 
 #include <nmmintrin.h>
+#include <wmmintrin.h>
 
 #include "port/pg_crc32c.h"
 
@@ -68,3 +69,90 @@ pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len)
 
 	return crc;
 }
+
+#ifdef USE_PCLMUL_WITH_RUNTIME_CHECK
+
+/* Generated by https://github.com/corsix/fast-crc32/ using: */
+/* ./generate -i sse -p crc32c -a v4e */
+/* MIT licensed */
+
+#define clmul_lo(a, b) (_mm_clmulepi64_si128((a), (b), 0))
+#define clmul_hi(a, b) (_mm_clmulepi64_si128((a), (b), 17))
+
+pg_attribute_target("sse4.2,pclmul")
+pg_crc32c
+pg_comp_crc32c_pclmul(pg_crc32c crc, const void *data, size_t length)
+{
+	/* adjust names to match generated code */
+	pg_crc32c	crc0 = crc;
+	size_t		len = length;
+	const char *buf = data;
+
+	// This prolog is trying to avoid loads straddling
+	// cache lines, but it doesn't seem worth it if
+	// we're trying to be fast on small inputs as well
+#if 0
+	for (; len && ((uintptr_t) buf & 7); --len)
+	{
+		crc0 = _mm_crc32_u8(crc0, *buf++);
+	}
+	if (((uintptr_t) buf & 8) && len >= 8)
+	{
+		crc0 = _mm_crc32_u64(crc0, *(const uint64_t *) buf);
+		buf += 8;
+		len -= 8;
+	}
+#endif
+	if (len >= 64)
+	{
+		const char *end = buf + len;
+		const char *limit = buf + len - 64;
+
+		/* First vector chunk. */
+		__m128i		x0 = _mm_loadu_si128((const __m128i *) buf),
+					y0;
+		__m128i		x1 = _mm_loadu_si128((const __m128i *) (buf + 16)),
+					y1;
+		__m128i		x2 = _mm_loadu_si128((const __m128i *) (buf + 32)),
+					y2;
+		__m128i		x3 = _mm_loadu_si128((const __m128i *) (buf + 48)),
+					y3;
+		__m128i		k;
+
+		k = _mm_setr_epi32(0x740eef02, 0, 0x9e4addf8, 0);
+		x0 = _mm_xor_si128(_mm_cvtsi32_si128(crc0), x0);
+		buf += 64;
+		/* Main loop. */
+		while (buf <= limit)
+		{
+			y0 = clmul_lo(x0, k), x0 = clmul_hi(x0, k);
+			y1 = clmul_lo(x1, k), x1 = clmul_hi(x1, k);
+			y2 = clmul_lo(x2, k), x2 = clmul_hi(x2, k);
+			y3 = clmul_lo(x3, k), x3 = clmul_hi(x3, k);
+			y0 = _mm_xor_si128(y0, _mm_loadu_si128((const __m128i *) buf)), x0 = _mm_xor_si128(x0, y0);
+			y1 = _mm_xor_si128(y1, _mm_loadu_si128((const __m128i *) (buf + 16))), x1 = _mm_xor_si128(x1, y1);
+			y2 = _mm_xor_si128(y2, _mm_loadu_si128((const __m128i *) (buf + 32))), x2 = _mm_xor_si128(x2, y2);
+			y3 = _mm_xor_si128(y3, _mm_loadu_si128((const __m128i *) (buf + 48))), x3 = _mm_xor_si128(x3, y3);
+			buf += 64;
+		}
+
+		/* Reduce x0 ... x3 to just x0. */
+		k = _mm_setr_epi32(0xf20c0dfe, 0, 0x493c7d27, 0);
+		y0 = clmul_lo(x0, k), x0 = clmul_hi(x0, k);
+		y2 = clmul_lo(x2, k), x2 = clmul_hi(x2, k);
+		y0 = _mm_xor_si128(y0, x1), x0 = _mm_xor_si128(x0, y0);
+		y2 = _mm_xor_si128(y2, x3), x2 = _mm_xor_si128(x2, y2);
+		k = _mm_setr_epi32(0x3da6d0cb, 0, 0xba4fc28e, 0);
+		y0 = clmul_lo(x0, k), x0 = clmul_hi(x0, k);
+		y0 = _mm_xor_si128(y0, x2), x0 = _mm_xor_si128(x0, y0);
+
+		/* Reduce 128 bits to 32 bits, and multiply by x^32. */
+		crc0 = _mm_crc32_u64(0, _mm_extract_epi64(x0, 0));
+		crc0 = _mm_crc32_u64(crc0, _mm_extract_epi64(x0, 1));
+		len = end - buf;
+	}
+
+	return pg_comp_crc32c_sse42_inline(crc0, buf, len);
+}
+
+#endif
diff --git a/src/port/pg_crc32c_sse42_choose.c b/src/port/pg_crc32c_sse42_choose.c
index 65dbc4d4249..abea0f90eb3 100644
--- a/src/port/pg_crc32c_sse42_choose.c
+++ b/src/port/pg_crc32c_sse42_choose.c
@@ -30,8 +30,12 @@
 
 #include "port/pg_crc32c.h"
 
-static bool
-pg_crc32c_sse42_available(void)
+/*
+ * This gets called on the first call. It replaces the function pointer
+ * so that subsequent calls are routed directly to the chosen implementation.
+ */
+static pg_crc32c
+pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
 {
 	unsigned int exx[4] = {0, 0, 0, 0};
 
@@ -43,18 +47,14 @@ pg_crc32c_sse42_available(void)
 #error cpuid instruction not available
 #endif
 
-	return (exx[2] & (1 << 20)) != 0;	/* SSE 4.2 */
-}
-
-/*
- * This gets called on the first call. It replaces the function pointer
- * so that subsequent calls are routed directly to the chosen implementation.
- */
-static pg_crc32c
-pg_comp_crc32c_choose(pg_crc32c crc, const void *data, size_t len)
-{
-	if (pg_crc32c_sse42_available())
+	if ((exx[2] & (1 << 20)) != 0)	/* SSE 4.2 */
+	{
 		pg_comp_crc32c = pg_comp_crc32c_sse42;
+#ifdef USE_PCLMUL_WITH_RUNTIME_CHECK
+		if ((exx[2] & (1 << 1)) != 0)	/* PCLMUL */
+			pg_comp_crc32c = pg_comp_crc32c_pclmul;
+#endif
+	}
 	else
 		pg_comp_crc32c = pg_comp_crc32c_sb8;
 
-- 
2.48.1