From 2ffbc634839c94a7da1bae9ab3976937f46fb874 Mon Sep 17 00:00:00 2001
From: David Rowley <dgrowley@gmail.com>
Date: Mon, 10 Jul 2023 11:22:34 +0200
Subject: [PATCH 1/2] Add pg_prefetch_mem() macro to load cache lines.

Initially mapping to GCC/Clang and MSVC builtins.

Discussion: https://postgr.es/m/CA%2BhUKGKXZALJ%3D6aArUsXRJzBm%3Dqvc4AWp7%3DiJNXJQqpbRLnD_w%40mail.gmail.com
Discussion: https://postgr.es/m/CAEepm%3D2y9HM9QP%2BHhRZdQ3pU6FShSMyu%3DV1uHXhQ5gG-dketHg%40mail.gmail.com
---
 config/c-compiler.m4       | 17 ++++++++++++++++
 configure                  | 40 ++++++++++++++++++++++++++++++++++++++
 configure.ac               |  3 +++
 meson.build                |  1 +
 src/include/c.h            |  8 ++++++++
 src/include/pg_config.h.in |  3 +++
 6 files changed, 72 insertions(+)

diff --git a/config/c-compiler.m4 b/config/c-compiler.m4
index 10f8c7bd0a9..befd7c3b316 100644
--- a/config/c-compiler.m4
+++ b/config/c-compiler.m4
@@ -355,6 +355,23 @@ AC_DEFINE_UNQUOTED(AS_TR_CPP([HAVE$1]), 1,
                    [Define to 1 if your compiler understands $1.])
 fi])# PGAC_CHECK_BUILTIN_FUNC
 
+# PGAC_CHECK_BUILTIN_VOID_FUNC
+# -----------------------
+# Variant for void functions.
+AC_DEFUN([PGAC_CHECK_BUILTIN_VOID_FUNC],
+[AC_CACHE_CHECK(for $1, pgac_cv$1,
+[AC_LINK_IFELSE([AC_LANG_PROGRAM([
+void
+call$1($2)
+{
+    $1(x);
+}], [])],
+[pgac_cv$1=yes],
+[pgac_cv$1=no])])
+if test x"${pgac_cv$1}" = xyes ; then
+AC_DEFINE_UNQUOTED(AS_TR_CPP([HAVE$1]), 1,
+                   [Define to 1 if your compiler understands $1.])
+fi])# PGAC_CHECK_BUILTIN_VOID_FUNC
 
 
 # PGAC_CHECK_BUILTIN_FUNC_PTR
diff --git a/configure b/configure
index cfbd2a096f4..9d9ed38fe57 100755
--- a/configure
+++ b/configure
@@ -15546,6 +15546,46 @@ _ACEOF
 
 fi
 
+# Can we use a built-in to prefetch memory?
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __builtin_prefetch" >&5
+$as_echo_n "checking for __builtin_prefetch... " >&6; }
+if ${pgac_cv__builtin_prefetch+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+void
+call__builtin_prefetch(void *x)
+{
+    __builtin_prefetch(x);
+}
+int
+main ()
+{
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_link "$LINENO"; then :
+  pgac_cv__builtin_prefetch=yes
+else
+  pgac_cv__builtin_prefetch=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv__builtin_prefetch" >&5
+$as_echo "$pgac_cv__builtin_prefetch" >&6; }
+if test x"${pgac_cv__builtin_prefetch}" = xyes ; then
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE__BUILTIN_PREFETCH 1
+_ACEOF
+
+fi
+
 # We require 64-bit fseeko() to be available, but run this check anyway
 # in case it finds that _LARGEFILE_SOURCE has to be #define'd for that.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for _LARGEFILE_SOURCE value needed for large files" >&5
diff --git a/configure.ac b/configure.ac
index 67e738d92b1..e991e56613c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1781,6 +1781,9 @@ PGAC_CHECK_BUILTIN_FUNC([__builtin_popcount], [unsigned int x])
 # so it needs a different test function.
 PGAC_CHECK_BUILTIN_FUNC_PTR([__builtin_frame_address], [0])
 
+# Can we use a built-in to prefetch memory?
+PGAC_CHECK_BUILTIN_VOID_FUNC([__builtin_prefetch], [void *x])
+
 # We require 64-bit fseeko() to be available, but run this check anyway
 # in case it finds that _LARGEFILE_SOURCE has to be #define'd for that.
 AC_FUNC_FSEEKO
diff --git a/meson.build b/meson.build
index 5acf083ce3c..eecd8aa6f45 100644
--- a/meson.build
+++ b/meson.build
@@ -1707,6 +1707,7 @@ builtins = [
   'constant_p',
   'frame_address',
   'popcount',
+  'prefetch',
   'unreachable',
 ]
 
diff --git a/src/include/c.h b/src/include/c.h
index dc1841346cd..1cb191b02a4 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -425,6 +425,14 @@ typedef void (*pg_funcptr_t) (void);
 #define HAVE_PRAGMA_GCC_SYSTEM_HEADER	1
 #endif
 
+/* Do we have support for prefetching memory? */
+#if defined(HAVE__BUILTIN_PREFETCH)
+#define pg_prefetch_mem(a) __builtin_prefetch(a)
+#elif defined(_MSC_VER)
+#define pg_prefetch_mem(a) _m_prefetch(a)
+#else
+#define pg_prefetch_mem(a)
+#endif
 
 /* ----------------------------------------------------------------
  *				Section 2:	bool, true, false
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index f8d3e3b6b84..6f0b6a51417 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -546,6 +546,9 @@
 /* Define to 1 if your compiler understands __builtin_popcount. */
 #undef HAVE__BUILTIN_POPCOUNT
 
+/* Define to 1 if your compiler understands __builtin_prefetch. */
+#undef HAVE__BUILTIN_PREFETCH
+
 /* Define to 1 if your compiler understands __builtin_types_compatible_p. */
 #undef HAVE__BUILTIN_TYPES_COMPATIBLE_P
 
-- 
2.44.0