Compute CRC32C using AVX-512 instructions where available

The previous implementation of CRC32C on x86 relied on the native
CRC32 instruction from the SSE 4.2 extension, which operates on
up to 8 bytes at a time. We can get a substantial speedup by using
carryless multiplication on SIMD registers, processing 64 bytes per
loop iteration. Shorter inputs fall back to ordinary CRC instructions.
On Intel Tiger Lake hardware (2020), CRC is now 50% faster for inputs
between 64 and 112 bytes, and 3x faster for 256 bytes.

The VPCLMULQDQ instruction on 512-bit registers has been available
on Intel hardware since 2019 and AMD since 2022. There is an older
variant for 128-bit registers, but at least on Zen 2 it performs worse
than normal CRC instructions for short inputs.

We must now do a runtime check, even for builds that target SSE
4.2. This doesn't matter in practice for WAL (arguably the most
critical case), because since commit e2809e3a1 the final computation
with the 20-byte WAL header is inlined and unrolled when targeting
that extension. Compared with two direct function calls, testing
showed equal or slightly faster performance in performing an indirect
function call on several dozen bytes followed by inlined instructions
on constant input of 20 bytes.

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

Co-authored-by: Raghuveer Devulapalli <raghuveer.devulapalli@intel.com>
Co-authored-by: Paul Amonson <paul.d.amonson@intel.com>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de> (earlier version)
Reviewed-by: Matthew Sterrett <matthewsterrett2@gmail.com> (earlier version)
Tested-by: Raghuveer Devulapalli <raghuveer.devulapalli@intel.com>
Tested-by: David Rowley <<dgrowleyml@gmail.com>> (earlier version)
Discussion: https://postgr.es/m/BL1PR11MB530401FA7E9B1CA432CF9DC3DC192@BL1PR11MB5304.namprd11.prod.outlook.com
Discussion: https://postgr.es/m/PH8PR11MB82869FF741DFA4E9A029FF13FBF72@PH8PR11MB8286.namprd11.prod.outlook.com

1 files changed, 29 insertions, 12 deletions

diff --git a/configure.ac b/configure.ac
index debdf165044..fc5f7475d07 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2116,17 +2116,21 @@ AC_SUBST(CFLAGS_CRC)
 
 # Select CRC-32C implementation.
 #
-# If we are targeting a processor that has Intel SSE 4.2 instructions, we can
-# use the special CRC instructions for calculating CRC-32C. If we're not
-# targeting such a processor, but we can nevertheless produce code that uses
-# the SSE intrinsics, compile both implementations and select which one to use
-# at runtime, depending on whether SSE 4.2 is supported by the processor we're
-# running on.
-#
-# Similarly, if we are targeting an ARM processor that has the CRC
-# instructions that are part of the ARMv8 CRC Extension, use them. And if
-# we're not targeting such a processor, but can nevertheless produce code that
-# uses the CRC instructions, compile both, and select at runtime.
+# There are three methods of calculating CRC, in order of increasing
+# performance:
+#
+# 1. The fallback using a lookup table, called slicing-by-8
+# 2. CRC-32C instructions (found in e.g. Intel SSE 4.2 and ARMv8 CRC Extension)
+# 3. Algorithms using carryless multiplication instructions
+#    (e.g. Intel PCLMUL and Arm PMULL)
+#
+# If we can produce code (via function attributes or additional compiler
+# flags) that uses #2 (and possibly #3), we compile all implementations
+# and select which one to use at runtime, depending on what is supported
+# by the processor we're running on.
+#
+# If we are targeting a processor that has #2, we can use that without
+# runtime selection.
 #
 # Note that we do not use __attribute__((target("..."))) for the ARM CRC
 # instructions because until clang 16, using the ARM intrinsics still requires
@@ -2174,7 +2178,7 @@ fi
 AC_MSG_CHECKING([which CRC-32C implementation to use])
 if test x"$USE_SSE42_CRC32C" = x"1"; then
   AC_DEFINE(USE_SSE42_CRC32C, 1, [Define to 1 use Intel SSE 4.2 CRC instructions.])
-  PG_CRC32C_OBJS="pg_crc32c_sse42.o"
+  PG_CRC32C_OBJS="pg_crc32c_sse42.o pg_crc32c_sse42_choose.o"
   AC_MSG_RESULT(SSE 4.2)
 else
   if test x"$USE_SSE42_CRC32C_WITH_RUNTIME_CHECK" = x"1"; then
@@ -2207,6 +2211,19 @@ else
 fi
 AC_SUBST(PG_CRC32C_OBJS)
 
+# Check for carryless multiplication intrinsics to do vectorized CRC calculations.
+#
+if test x"$host_cpu" = x"x86_64"; then
+  PGAC_AVX512_PCLMUL_INTRINSICS()
+fi
+
+AC_MSG_CHECKING([for vectorized CRC-32C])
+if test x"$pgac_avx512_pclmul_intrinsics" = x"yes"; then
+  AC_DEFINE(USE_AVX512_CRC32C_WITH_RUNTIME_CHECK, 1, [Define to 1 to use AVX-512 CRC algorithms with a runtime check.])
+  AC_MSG_RESULT(AVX-512 with runtime check)
+else
+  AC_MSG_RESULT(none)
+fi
 
 # Select semaphore implementation type.
 if test "$PORTNAME" != "win32"; then