v7-0001-Dispatch-CRC-computation-by-branching-rather-than.patch

From 1337d15dc73b247d8c35f2d8e22400d0c292ccc0 Mon Sep 17 00:00:00 2001
From: John Naylor <john.naylor@postgresql.org>
Date: Sat, 15 Feb 2025 19:18:16 +0700
Subject: [PATCH v7 1/3] Dispatch CRC computation by branching rather than
 indirect calls

---
 configure                                   |  2 +-
 configure.ac                                |  2 +-
 src/backend/postmaster/postmaster.c         |  4 ++
 src/bin/pg_basebackup/pg_basebackup.c       |  3 +
 src/bin/pg_basebackup/pg_createsubscriber.c |  3 +
 src/bin/pg_checksums/pg_checksums.c         |  3 +
 src/bin/pg_combinebackup/pg_combinebackup.c |  3 +
 src/bin/pg_controldata/pg_controldata.c     |  3 +
 src/bin/pg_ctl/pg_ctl.c                     |  3 +
 src/bin/pg_resetwal/pg_resetwal.c           |  3 +
 src/bin/pg_rewind/pg_rewind.c               |  3 +
 src/bin/pg_verifybackup/pg_verifybackup.c   |  3 +
 src/bin/pg_waldump/pg_waldump.c             |  3 +
 src/bin/pg_walsummary/pg_walsummary.c       |  4 ++
 src/include/port/pg_cpu.h                   | 23 ++++++
 src/include/port/pg_crc32c.h                | 78 +++++++++++++++------
 src/port/Makefile                           |  1 +
 src/port/meson.build                        |  4 ++
 src/port/pg_cpu.c                           | 54 ++++++++++++++
 src/port/pg_crc32c_armv8_choose.c           | 26 +------
 src/port/pg_crc32c_sse42_choose.c           | 26 +------
 21 files changed, 182 insertions(+), 72 deletions(-)
 create mode 100644 src/include/port/pg_cpu.h
 create mode 100644 src/port/pg_cpu.c

diff --git a/configure b/configure
index 0ffcaeb4367..41aad7b4d75 100755
--- a/configure
+++ b/configure
@@ -17352,7 +17352,7 @@ if test x"$USE_SSE42_CRC32C" = x"1"; then
 
 $as_echo "#define USE_SSE42_CRC32C 1" >>confdefs.h
 
-  PG_CRC32C_OBJS="pg_crc32c_sse42.o"
+  PG_CRC32C_OBJS="pg_crc32c_sse42.o pg_crc32c_sse42_choose.o"
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: SSE 4.2" >&5
 $as_echo "SSE 4.2" >&6; }
 else
diff --git a/configure.ac b/configure.ac
index f56681e0d91..efa8249360a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2110,7 +2110,7 @@ fi
 AC_MSG_CHECKING([which CRC-32C implementation to use])
 if test x"$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
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index bb22b13adef..c218f15f97e 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -99,6 +99,7 @@
 #include "pg_getopt.h"
 #include "pgstat.h"
 #include "port/pg_bswap.h"
+#include "port/pg_cpu.h"
 #include "postmaster/autovacuum.h"
 #include "postmaster/bgworker_internals.h"
 #include "postmaster/pgarch.h"
@@ -1951,6 +1952,9 @@ InitProcessGlobals(void)
 #ifndef WIN32
 	srandom(pg_prng_uint32(&pg_global_prng_state));
 #endif
+
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
 }
 
 /*
diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c
index dc0c805137a..8d4b3718b6e 100644
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -2405,6 +2405,9 @@ main(int argc, char **argv)
 	progname = get_progname(argv[0]);
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_basebackup"));
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	if (argc > 1)
 	{
 		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c
index 2d881d54f5b..04e550ef755 100644
--- a/src/bin/pg_basebackup/pg_createsubscriber.c
+++ b/src/bin/pg_basebackup/pg_createsubscriber.c
@@ -1906,6 +1906,9 @@ main(int argc, char **argv)
 	progname = get_progname(argv[0]);
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_basebackup"));
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	if (argc > 1)
 	{
 		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
diff --git a/src/bin/pg_checksums/pg_checksums.c b/src/bin/pg_checksums/pg_checksums.c
index e1acb6e933d..eb88aeedb53 100644
--- a/src/bin/pg_checksums/pg_checksums.c
+++ b/src/bin/pg_checksums/pg_checksums.c
@@ -453,6 +453,9 @@ main(int argc, char *argv[])
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_checksums"));
 	progname = get_progname(argv[0]);
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	if (argc > 1)
 	{
 		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
diff --git a/src/bin/pg_combinebackup/pg_combinebackup.c b/src/bin/pg_combinebackup/pg_combinebackup.c
index 5864ec574fb..ee24dba2315 100644
--- a/src/bin/pg_combinebackup/pg_combinebackup.c
+++ b/src/bin/pg_combinebackup/pg_combinebackup.c
@@ -166,6 +166,9 @@ main(int argc, char *argv[])
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_combinebackup"));
 	handle_help_version_opts(argc, argv, progname, help);
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	memset(&opt, 0, sizeof(opt));
 	opt.manifest_checksums = CHECKSUM_TYPE_CRC32C;
 	opt.sync_method = DATA_DIR_SYNC_METHOD_FSYNC;
diff --git a/src/bin/pg_controldata/pg_controldata.c b/src/bin/pg_controldata/pg_controldata.c
index cf11ab3f2ee..deb6b16ae65 100644
--- a/src/bin/pg_controldata/pg_controldata.c
+++ b/src/bin/pg_controldata/pg_controldata.c
@@ -112,6 +112,9 @@ main(int argc, char *argv[])
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_controldata"));
 	progname = get_progname(argv[0]);
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	if (argc > 1)
 	{
 		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
diff --git a/src/bin/pg_ctl/pg_ctl.c b/src/bin/pg_ctl/pg_ctl.c
index 8a405ff122c..7dc4da932e5 100644
--- a/src/bin/pg_ctl/pg_ctl.c
+++ b/src/bin/pg_ctl/pg_ctl.c
@@ -2226,6 +2226,9 @@ main(int argc, char **argv)
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_ctl"));
 	start_time = time(NULL);
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	/*
 	 * save argv[0] so do_start() can look for the postmaster if necessary. we
 	 * don't look for postmaster here because in many cases we won't need it.
diff --git a/src/bin/pg_resetwal/pg_resetwal.c b/src/bin/pg_resetwal/pg_resetwal.c
index ed73607a46f..52bcaadf69f 100644
--- a/src/bin/pg_resetwal/pg_resetwal.c
+++ b/src/bin/pg_resetwal/pg_resetwal.c
@@ -123,6 +123,9 @@ main(int argc, char *argv[])
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_resetwal"));
 	progname = get_progname(argv[0]);
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	if (argc > 1)
 	{
 		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c
index cae81cd6cb1..f6c755883c6 100644
--- a/src/bin/pg_rewind/pg_rewind.c
+++ b/src/bin/pg_rewind/pg_rewind.c
@@ -158,6 +158,9 @@ main(int argc, char **argv)
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_rewind"));
 	progname = get_progname(argv[0]);
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	/* Process command-line arguments */
 	if (argc > 1)
 	{
diff --git a/src/bin/pg_verifybackup/pg_verifybackup.c b/src/bin/pg_verifybackup/pg_verifybackup.c
index 7c720ab98bd..d44a87e83ad 100644
--- a/src/bin/pg_verifybackup/pg_verifybackup.c
+++ b/src/bin/pg_verifybackup/pg_verifybackup.c
@@ -144,6 +144,9 @@ main(int argc, char **argv)
 
 	memset(&context, 0, sizeof(context));
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	if (argc > 1)
 	{
 		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 51fb76efc48..10c529a5fac 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -835,6 +835,9 @@ main(int argc, char **argv)
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_waldump"));
 	progname = get_progname(argv[0]);
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	if (argc > 1)
 	{
 		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
diff --git a/src/bin/pg_walsummary/pg_walsummary.c b/src/bin/pg_walsummary/pg_walsummary.c
index cd7a6b147b2..a38565ea6d8 100644
--- a/src/bin/pg_walsummary/pg_walsummary.c
+++ b/src/bin/pg_walsummary/pg_walsummary.c
@@ -20,6 +20,7 @@
 #include "common/logging.h"
 #include "fe_utils/option_utils.h"
 #include "getopt_long.h"
+#include "port/pg_cpu.h"
 
 typedef struct ws_options
 {
@@ -69,6 +70,9 @@ main(int argc, char *argv[])
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_walsummary"));
 	handle_help_version_opts(argc, argv, progname, help);
 
+	/* detect CPU capabilities */
+	pg_cpucap_initialize();
+
 	/* process command-line options */
 	while ((c = getopt_long(argc, argv, "iq",
 							long_options, &optindex)) != -1)
diff --git a/src/include/port/pg_cpu.h b/src/include/port/pg_cpu.h
new file mode 100644
index 00000000000..45ce9d3c505
--- /dev/null
+++ b/src/include/port/pg_cpu.h
@@ -0,0 +1,23 @@
+/*-------------------------------------------------------------------------
+ *
+ * pg_cpu.h
+ *	  Runtime detection of CPU capabilities.
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ *	  src/include/port/pg_cpu.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_CPU_H
+#define PG_CPU_H
+
+#define PGCPUCAP_INIT           (1 << 0)
+#define PGCPUCAP_CRC32C         (1 << 1)
+
+extern uint32 pg_cpucap;
+extern void pg_cpucap_initialize(void);
+
+#endif							/* PG_CPU_H */
diff --git a/src/include/port/pg_crc32c.h b/src/include/port/pg_crc32c.h
index 65ebeacf4b1..db155d690e3 100644
--- a/src/include/port/pg_crc32c.h
+++ b/src/include/port/pg_crc32c.h
@@ -34,6 +34,7 @@
 #define PG_CRC32C_H
 
 #include "port/pg_bswap.h"
+#include "port/pg_cpu.h"
 
 typedef uint32 pg_crc32c;
 
@@ -41,52 +42,55 @@ typedef uint32 pg_crc32c;
 #define INIT_CRC32C(crc) ((crc) = 0xFFFFFFFF)
 #define EQ_CRC32C(c1, c2) ((c1) == (c2))
 
-#if defined(USE_SSE42_CRC32C)
+#if defined(USE_SSE42_CRC32C) || defined(USE_SSE42_CRC32C_WITH_RUNTIME_CHECK)
 /* Use Intel SSE4.2 instructions. */
 #define COMP_CRC32C(crc, data, len) \
+	((crc) = pg_comp_crc32c_dispatch((crc), (data), (len)))
+#define COMP_CRC32C_HW(crc, data, len) \
 	((crc) = pg_comp_crc32c_sse42((crc), (data), (len)))
 #define FIN_CRC32C(crc) ((crc) ^= 0xFFFFFFFF)
 
+#if defined(USE_SSE42_CRC32C)
+#define HAVE_CRC_COMPTIME
+#else
+#define HAVE_CRC_RUNTIME
+extern pg_crc32c pg_comp_crc32c_sb8(pg_crc32c crc, const void *data, size_t len);
+#endif
+
+extern bool pg_crc32c_sse42_available(void);
 extern pg_crc32c pg_comp_crc32c_sse42(pg_crc32c crc, const void *data, size_t len);
 
-#elif defined(USE_ARMV8_CRC32C)
+#elif defined(USE_ARMV8_CRC32C) || defined(USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK)
 /* Use ARMv8 CRC Extension instructions. */
 
 #define COMP_CRC32C(crc, data, len)							\
+	((crc) = pg_comp_crc32c_dispatch((crc), (data), (len)))
+#define COMP_CRC32C_HW(crc, data, len)						\
 	((crc) = pg_comp_crc32c_armv8((crc), (data), (len)))
 #define FIN_CRC32C(crc) ((crc) ^= 0xFFFFFFFF)
 
+#if defined(USE_ARMV8_CRC32C)
+#define HAVE_CRC_COMPTIME
+#else
+#define HAVE_CRC_RUNTIME
+extern pg_crc32c pg_comp_crc32c_sb8(pg_crc32c crc, const void *data, size_t len);
+#endif
+
+extern bool pg_crc32c_armv8_available(void);
 extern pg_crc32c pg_comp_crc32c_armv8(pg_crc32c crc, const void *data, size_t len);
 
 #elif defined(USE_LOONGARCH_CRC32C)
 /* Use LoongArch CRCC instructions. */
 
 #define COMP_CRC32C(crc, data, len)							\
+	((crc) = pg_comp_crc32c_dispatch((crc), (data), (len)))
+#define COMP_CRC32C_HW(crc, data, len)						\
 	((crc) = pg_comp_crc32c_loongarch((crc), (data), (len)))
 #define FIN_CRC32C(crc) ((crc) ^= 0xFFFFFFFF)
 
+#define HAVE_CRC_COMPTIME
 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)
-
-/*
- * Use Intel SSE 4.2 or ARMv8 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);
-
-#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
 /*
  * Use slicing-by-8 algorithm.
@@ -105,6 +109,36 @@ extern pg_crc32c pg_comp_crc32c_armv8(pg_crc32c crc, const void *data, size_t le
 
 extern pg_crc32c pg_comp_crc32c_sb8(pg_crc32c crc, const void *data, size_t len);
 
+#endif							/* end of CPU-specfic symbols */
+
+#if defined(HAVE_CRC_COMPTIME) || defined(HAVE_CRC_RUNTIME)
+/*
+ * Check if the CPU we're running on supports special
+ * instructions for CRC-32C computation. Otherwise, fall
+ * back to the pure software implementation (slicing-by-8).
+ */
+static inline pg_crc32c
+pg_comp_crc32c_dispatch(pg_crc32c crc, const void *data, size_t len)
+{
+	/*
+	 * If this is firing in a frontend program, first look if you forgot a
+	 * call to pg_cpucap_initialize() in main(). See for example
+	 * src/bin/pg_controldata/pg_controldata.c.
+	 */
+	Assert(pg_cpucap & PGCPUCAP_INIT);
+
+	{
+#if defined(HAVE_CRC_COMPTIME)
+		Assert(pg_cpucap & PGCPUCAP_CRC32C);
+		return COMP_CRC32C_HW(crc, data, len);
+#else
+		if (pg_cpucap & PGCPUCAP_CRC32C)
+			return COMP_CRC32C_HW(crc, data, len);
+		else
+			return pg_comp_crc32c_sb8(crc, data, len);
 #endif
+	}
+}
+#endif							/* HAVE_CRC_COMPTIME || HAVE_CRC_RUNTIME */
 
 #endif							/* PG_CRC32C_H */
diff --git a/src/port/Makefile b/src/port/Makefile
index 4c224319512..2ac79ecb0fd 100644
--- a/src/port/Makefile
+++ b/src/port/Makefile
@@ -44,6 +44,7 @@ OBJS = \
 	noblock.o \
 	path.o \
 	pg_bitutils.o \
+	pg_cpu.o \
 	pg_popcount_avx512.o \
 	pg_strong_random.o \
 	pgcheckdir.o \
diff --git a/src/port/meson.build b/src/port/meson.build
index 7fcfa728d43..02ae2067604 100644
--- a/src/port/meson.build
+++ b/src/port/meson.build
@@ -7,6 +7,7 @@ pgport_sources = [
   'noblock.c',
   'path.c',
   'pg_bitutils.c',
+  'pg_cpu.c',
   'pg_popcount_avx512.c',
   'pg_strong_random.c',
   'pgcheckdir.c',
@@ -83,12 +84,15 @@ replace_funcs_pos = [
   # x86/x64
   ['pg_crc32c_sse42', 'USE_SSE42_CRC32C'],
   ['pg_crc32c_sse42', 'USE_SSE42_CRC32C_WITH_RUNTIME_CHECK'],
+  # WIP sometime we'll need to build these based on host_cpu
+  ['pg_crc32c_sse42_choose', 'USE_SSE42_CRC32C'],
   ['pg_crc32c_sse42_choose', 'USE_SSE42_CRC32C_WITH_RUNTIME_CHECK'],
   ['pg_crc32c_sb8', 'USE_SSE42_CRC32C_WITH_RUNTIME_CHECK'],
 
   # arm / aarch64
   ['pg_crc32c_armv8', 'USE_ARMV8_CRC32C'],
   ['pg_crc32c_armv8', 'USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK', 'crc'],
+  ['pg_crc32c_armv8_choose', 'USE_ARMV8_CRC32C'],
   ['pg_crc32c_armv8_choose', 'USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK'],
   ['pg_crc32c_sb8', 'USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK'],
 
diff --git a/src/port/pg_cpu.c b/src/port/pg_cpu.c
new file mode 100644
index 00000000000..c9483357436
--- /dev/null
+++ b/src/port/pg_cpu.c
@@ -0,0 +1,54 @@
+/*-------------------------------------------------------------------------
+ *
+ * pg_cpu.c
+ *	  Runtime detection of CPU capabilities.
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ *	  src/port/pg_cpu.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "c.h"
+
+#include "port/pg_cpu.h"
+#include "port/pg_crc32c.h"
+
+
+/* starts uninitialized so we can detect errors of omission */
+uint32		pg_cpucap = 0;
+
+/*
+ * Check if hardware instructions for CRC computation are available.
+ */
+static void
+pg_cpucap_crc32c(void)
+{
+	/* WIP: It seems like we should use CPU arch symbols instead */
+#if defined(USE_SSE42_CRC32C) || defined(USE_SSE42_CRC32C_WITH_RUNTIME_CHECK)
+	if (pg_crc32c_sse42_available())
+		pg_cpucap |= PGCPUCAP_CRC32C;
+
+#elif defined(USE_ARMV8_CRC32C) || defined(USE_ARMV8_CRC32C_WITH_RUNTIME_CHECK)
+	if (pg_crc32c_armv8_available())
+		pg_cpucap |= PGCPUCAP_CRC32C;
+
+#elif defined(USE_LOONGARCH_CRC32C)
+	pg_cpucap |= PGCPUCAP_CRC32C;
+#endif
+}
+
+/*
+ * This needs to be called in main() for every
+ * program that calls a function that dispatches
+ * according to CPU features.
+ */
+void
+pg_cpucap_initialize(void)
+{
+	pg_cpucap = PGCPUCAP_INIT;
+
+	pg_cpucap_crc32c();
+}
diff --git a/src/port/pg_crc32c_armv8_choose.c b/src/port/pg_crc32c_armv8_choose.c
index ec12be1bbc3..e3654427c3f 100644
--- a/src/port/pg_crc32c_armv8_choose.c
+++ b/src/port/pg_crc32c_armv8_choose.c
@@ -1,12 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * pg_crc32c_armv8_choose.c
- *	  Choose between ARMv8 and software CRC-32C implementation.
- *
- * On first call, checks if the CPU we're running on supports the ARMv8
- * CRC Extension. If it does, use the special instructions for CRC-32C
- * computation. Otherwise, fall back to the pure software implementation
- * (slicing-by-8).
+ *	  Check if the CPU we're running on supports the ARMv8 CRC Extension.
  *
  * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -40,7 +35,7 @@
 
 #include "port/pg_crc32c.h"
 
-static bool
+bool
 pg_crc32c_armv8_available(void)
 {
 #if defined(HAVE_ELF_AUX_INFO)
@@ -106,20 +101,3 @@ pg_crc32c_armv8_available(void)
 	return false;
 #endif
 }
-
-/*
- * 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_armv8_available())
-		pg_comp_crc32c = pg_comp_crc32c_armv8;
-	else
-		pg_comp_crc32c = pg_comp_crc32c_sb8;
-
-	return pg_comp_crc32c(crc, data, len);
-}
-
-pg_crc32c	(*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;
diff --git a/src/port/pg_crc32c_sse42_choose.c b/src/port/pg_crc32c_sse42_choose.c
index 65dbc4d4249..f4d3215bc55 100644
--- a/src/port/pg_crc32c_sse42_choose.c
+++ b/src/port/pg_crc32c_sse42_choose.c
@@ -1,12 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * pg_crc32c_sse42_choose.c
- *	  Choose between Intel SSE 4.2 and software CRC-32C implementation.
- *
- * On first call, checks if the CPU we're running on supports Intel SSE
- * 4.2. If it does, use the special SSE instructions for CRC-32C
- * computation. Otherwise, fall back to the pure software implementation
- * (slicing-by-8).
+ *	  Check if the CPU we're running on supports SSE4.2.
  *
  * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -30,7 +25,7 @@
 
 #include "port/pg_crc32c.h"
 
-static bool
+bool
 pg_crc32c_sse42_available(void)
 {
 	unsigned int exx[4] = {0, 0, 0, 0};
@@ -45,20 +40,3 @@ pg_crc32c_sse42_available(void)
 
 	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())
-		pg_comp_crc32c = pg_comp_crc32c_sse42;
-	else
-		pg_comp_crc32c = pg_comp_crc32c_sb8;
-
-	return pg_comp_crc32c(crc, data, len);
-}
-
-pg_crc32c	(*pg_comp_crc32c) (pg_crc32c crc, const void *data, size_t len) = pg_comp_crc32c_choose;
-- 
2.48.1