From 46219b20c12ad15a90100b4cf80b50c8cafb9548 Mon Sep 17 00:00:00 2001
From: Lukas Fittl <lukas@fittl.com>
Date: Sat, 31 Jan 2026 08:49:46 -0800
Subject: [PATCH v12 2/7] Check for HAVE__CPUIDEX and HAVE__GET_CPUID_COUNT
 separately

Previously we would only check for the availability of __cpuidex if
the related __get_cpuid_count was not available on a platform. But there
are cases where we want to be able to call __cpuidex as the only viable
option, specifically, when accessing a high leaf like VM Hypervisor
information (0x40000000), which __get_cpuid_count does not allow.

This will be used in an future commit to access Hypervisor information
about the TSC frequency of x86 CPUs, where available.

Note that __cpuidex is defined in cpuid.h for GCC/clang, but in intrin.h
for MSVC. Because we now set HAVE__CPUIDEX for GCC/clang when available,
adjust existing code to check for _MSC_VER when including intrin.h.

Author: Lukas Fittl <lukas@fittl.com>
Reviewed-by:
Discussion: https://www.postgresql.org/message-id/flat/20200612232810.f46nbqkdhbutzqdg%40alap3.anarazel.de
---
 configure             | 22 +++++++++++++---------
 configure.ac          | 30 +++++++++++++++++-------------
 meson.build           | 12 +++++++++---
 src/port/pg_cpu_x86.c | 10 +++++-----
 4 files changed, 44 insertions(+), 30 deletions(-)

diff --git a/configure b/configure
index 0d3f634abec..407f773e771 100755
--- a/configure
+++ b/configure
@@ -17746,7 +17746,8 @@ $as_echo "#define HAVE__CPUID 1" >>confdefs.h
   fi
 fi
 
-# Check for __get_cpuid_count() and __cpuidex() in a similar fashion.
+# Check for __get_cpuid_count() and __cpuidex() separately, since we sometimes
+# need __cpuidex() even if __get_cpuid_count() is available.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __get_cpuid_count" >&5
 $as_echo_n "checking for __get_cpuid_count... " >&6; }
 if ${pgac_cv__get_cpuid_count+:} false; then :
@@ -17779,21 +17780,25 @@ if test x"$pgac_cv__get_cpuid_count" = x"yes"; then
 
 $as_echo "#define HAVE__GET_CPUID_COUNT 1" >>confdefs.h
 
-else
-  # __cpuidex()
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for __cpuidex" >&5
+fi
+# __cpuidex()
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for __cpuidex" >&5
 $as_echo_n "checking for __cpuidex... " >&6; }
 if ${pgac_cv__cpuidex+:} false; then :
   $as_echo_n "(cached) " >&6
 else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-#include <intrin.h>
+#ifdef _MSC_VER
+    #include <intrin.h>
+    #else
+    #include <cpuid.h>
+    #endif
 int
 main ()
 {
-unsigned int exx[4] = {0, 0, 0, 0};
-    __cpuidex(exx, 7, 0);
+int exx[4] = {0, 0, 0, 0};
+  __cpuidex(exx, 7, 0);
 
   ;
   return 0;
@@ -17809,11 +17814,10 @@ rm -f core conftest.err conftest.$ac_objext \
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv__cpuidex" >&5
 $as_echo "$pgac_cv__cpuidex" >&6; }
-  if test x"$pgac_cv__cpuidex" = x"yes"; then
+if test x"$pgac_cv__cpuidex" = x"yes"; then
 
 $as_echo "#define HAVE__CPUIDEX 1" >>confdefs.h
 
-  fi
 fi
 
 # Check for XSAVE intrinsics
diff --git a/configure.ac b/configure.ac
index f8327a7020a..96674e8005b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2107,7 +2107,8 @@ else
   fi
 fi
 
-# Check for __get_cpuid_count() and __cpuidex() in a similar fashion.
+# Check for __get_cpuid_count() and __cpuidex() separately, since we sometimes
+# need __cpuidex() even if __get_cpuid_count() is available.
 AC_CACHE_CHECK([for __get_cpuid_count], [pgac_cv__get_cpuid_count],
 [AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <cpuid.h>],
   [[unsigned int exx[4] = {0, 0, 0, 0};
@@ -2117,18 +2118,21 @@ AC_CACHE_CHECK([for __get_cpuid_count], [pgac_cv__get_cpuid_count],
   [pgac_cv__get_cpuid_count="no"])])
 if test x"$pgac_cv__get_cpuid_count" = x"yes"; then
   AC_DEFINE(HAVE__GET_CPUID_COUNT, 1, [Define to 1 if you have __get_cpuid_count.])
-else
-  # __cpuidex()
-  AC_CACHE_CHECK([for __cpuidex], [pgac_cv__cpuidex],
-  [AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <intrin.h>],
-    [[unsigned int exx[4] = {0, 0, 0, 0};
-    __cpuidex(exx, 7, 0);
-    ]])],
-    [pgac_cv__cpuidex="yes"],
-    [pgac_cv__cpuidex="no"])])
-  if test x"$pgac_cv__cpuidex" = x"yes"; then
-    AC_DEFINE(HAVE__CPUIDEX, 1, [Define to 1 if you have __cpuidex.])
-  fi
+fi
+# __cpuidex()
+AC_CACHE_CHECK([for __cpuidex], [pgac_cv__cpuidex],
+[AC_LINK_IFELSE([AC_LANG_PROGRAM([#ifdef _MSC_VER
+    #include <intrin.h>
+    #else
+    #include <cpuid.h>
+    #endif],
+  [[int exx[4] = {0, 0, 0, 0};
+  __cpuidex(exx, 7, 0);
+  ]])],
+  [pgac_cv__cpuidex="yes"],
+  [pgac_cv__cpuidex="no"])])
+if test x"$pgac_cv__cpuidex" = x"yes"; then
+  AC_DEFINE(HAVE__CPUIDEX, 1, [Define to 1 if you have __cpuidex.])
 fi
 
 # Check for XSAVE intrinsics
diff --git a/meson.build b/meson.build
index 0a181909fab..d1208c747e2 100644
--- a/meson.build
+++ b/meson.build
@@ -2132,7 +2132,8 @@ elif cc.links('''
 endif
 
 
-# Check for __get_cpuid_count() and __cpuidex() in a similar fashion.
+# Check for __get_cpuid_count() and __cpuidex() separately, since we sometimes
+# need __cpuidex() even if __get_cpuid_count() is available.
 if cc.links('''
     #include <cpuid.h>
     int main(int arg, char **argv)
@@ -2143,11 +2144,16 @@ if cc.links('''
     ''', name: '__get_cpuid_count',
     args: test_c_args)
   cdata.set('HAVE__GET_CPUID_COUNT', 1)
-elif cc.links('''
+endif
+if cc.links('''
+    #ifdef _MSC_VER
     #include <intrin.h>
+    #else
+    #include <cpuid.h>
+    #endif
     int main(int arg, char **argv)
     {
-        unsigned int exx[4] = {0, 0, 0, 0};
+        int exx[4] = {0, 0, 0, 0};
         __cpuidex(exx, 7, 0);
     }
     ''', name: '__cpuidex',
diff --git a/src/port/pg_cpu_x86.c b/src/port/pg_cpu_x86.c
index 751f52f1e42..b1aa71b8887 100644
--- a/src/port/pg_cpu_x86.c
+++ b/src/port/pg_cpu_x86.c
@@ -17,12 +17,12 @@
 
 #if defined(USE_SSE2) || defined(__i386__)
 
-#if defined(HAVE__GET_CPUID) || defined(HAVE__GET_CPUID_COUNT)
-#include <cpuid.h>
-#endif
-
-#if defined(HAVE__CPUID) || defined(HAVE__CPUIDEX)
+#if defined(HAVE__CPUID) || defined(HAVE__GET_CPUID) || defined(HAVE__GET_CPUID_COUNT) || defined(HAVE__CPUIDEX)
+#if defined(_MSC_VER)
 #include <intrin.h>
+#else
+#include <cpuid.h>
+#endif							/* defined(_MSC_VER) */
 #endif
 
 #ifdef HAVE_XSAVE_INTRINSICS
-- 
2.47.1

