From 39b3a0abf937320458c84005a7faed0fd005e5d7 Mon Sep 17 00:00:00 2001
From: Lukas Fittl <lukas@fittl.com>
Date: Sat, 31 Jan 2026 08:49:46 -0800
Subject: [PATCH v4 1/3] 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.
---
 configure                         | 20 ++++++++++++--------
 configure.ac                      | 30 +++++++++++++++++-------------
 meson.build                       | 10 ++++++++--
 src/port/pg_crc32c_sse42_choose.c |  4 ++--
 src/port/pg_popcount_x86.c        |  4 ++--
 5 files changed, 41 insertions(+), 27 deletions(-)

diff --git a/configure b/configure
index a10a2c85c6a..38de88fcc50 100755
--- a/configure
+++ b/configure
@@ -17648,7 +17648,8 @@ $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 ${pgac_cv__get_cpuid_count+:} false; then :
@@ -17681,21 +17682,25 @@ if test x"$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);
+  __cpuidex(exx, 7, 0);
 
   ;
   return 0;
@@ -17711,11 +17716,10 @@ 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 814e64a967e..6e174cba328 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2098,7 +2098,8 @@ 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};
@@ -2108,18 +2109,21 @@ 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],
+  [[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
 
 # Check for XSAVE intrinsics
diff --git a/meson.build b/meson.build
index df907b62da3..2b106135869 100644
--- a/meson.build
+++ b/meson.build
@@ -2078,7 +2078,8 @@ 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)
@@ -2089,8 +2090,13 @@ 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};
diff --git a/src/port/pg_crc32c_sse42_choose.c b/src/port/pg_crc32c_sse42_choose.c
index f586476964f..7a75380b483 100644
--- a/src/port/pg_crc32c_sse42_choose.c
+++ b/src/port/pg_crc32c_sse42_choose.c
@@ -20,11 +20,11 @@
 
 #include "c.h"
 
-#if defined(HAVE__GET_CPUID) || defined(HAVE__GET_CPUID_COUNT)
+#if defined(HAVE__GET_CPUID) || defined(HAVE__GET_CPUID_COUNT) || (defined(HAVE__CPUIDEX) && !defined(_MSC_VER))
 #include <cpuid.h>
 #endif
 
-#if defined(HAVE__CPUID) || defined(HAVE__CPUIDEX)
+#if defined(HAVE__CPUID) || (defined(HAVE__CPUIDEX) && defined(_MSC_VER))
 #include <intrin.h>
 #endif
 
diff --git a/src/port/pg_popcount_x86.c b/src/port/pg_popcount_x86.c
index 245f0167d00..f8a20766f2d 100644
--- a/src/port/pg_popcount_x86.c
+++ b/src/port/pg_popcount_x86.c
@@ -14,7 +14,7 @@
 
 #ifdef HAVE_X86_64_POPCNTQ
 
-#if defined(HAVE__GET_CPUID) || defined(HAVE__GET_CPUID_COUNT)
+#if defined(HAVE__GET_CPUID) || defined(HAVE__GET_CPUID_COUNT) || (defined(HAVE__CPUIDEX) && !defined(_MSC_VER))
 #include <cpuid.h>
 #endif
 
@@ -22,7 +22,7 @@
 #include <immintrin.h>
 #endif
 
-#if defined(HAVE__CPUID) || defined(HAVE__CPUIDEX)
+#if defined(HAVE__CPUID) || (defined(HAVE__CPUIDEX) && defined(_MSC_VER))
 #include <intrin.h>
 #endif
 
-- 
2.47.1

