From 60364b439a80c217174e1830e0b7507d6f4538c4 Mon Sep 17 00:00:00 2001
From: liuhongt <hongtao.liu@intel.com>
Date: Fri, 4 Aug 2023 09:27:39 +0800
Subject: [PATCH 08/28] Workaround possible CPUID bug in Sandy Bridge.

Don't access leaf 7 subleaf 1 unless subleaf 0 says it is
supported via EAX.

Intel documentation says invalid subleaves return 0. We had been
relying on that behavior instead of checking the max sublef number.

It appears that some Sandy Bridge CPUs return at least the subleaf 0
EDX value for subleaf 1. Best guess is that this is a bug in a
microcode patch since all of the bits we're seeing set in EDX were
introduced after Sandy Bridge was originally released.

This is causing avxvnniint16 to be incorrectly enabled with
-march=native on these CPUs.

gcc/ChangeLog:

	* common/config/i386/cpuinfo.h (get_available_features): Check
	max_subleaf_level for valid subleaf before use CPUID.
---
 gcc/common/config/i386/cpuinfo.h | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/gcc/common/config/i386/cpuinfo.h b/gcc/common/config/i386/cpuinfo.h
index 28b2ff0b0..316ad3cb3 100644
--- a/gcc/common/config/i386/cpuinfo.h
+++ b/gcc/common/config/i386/cpuinfo.h
@@ -647,7 +647,9 @@ get_available_features (struct __processor_model *cpu_model,
   /* Get Advanced Features at level 7 (eax = 7, ecx = 0/1). */
   if (max_cpuid_level >= 7)
     {
-      __cpuid_count (7, 0, eax, ebx, ecx, edx);
+      unsigned int max_subleaf_level;
+
+      __cpuid_count (7, 0, max_subleaf_level, ebx, ecx, edx);
       if (ebx & bit_BMI)
 	set_feature (FEATURE_BMI);
       if (ebx & bit_SGX)
@@ -759,18 +761,21 @@ get_available_features (struct __processor_model *cpu_model,
 	    set_feature (FEATURE_AVX512FP16);
 	}
 
-      __cpuid_count (7, 1, eax, ebx, ecx, edx);
-      if (eax & bit_HRESET)
-	set_feature (FEATURE_HRESET);
-      if (avx_usable)
-	{
-	  if (eax & bit_AVXVNNI)
-	    set_feature (FEATURE_AVXVNNI);
-	}
-      if (avx512_usable)
+      if (max_subleaf_level >= 1)
 	{
-	  if (eax & bit_AVX512BF16)
-	    set_feature (FEATURE_AVX512BF16);
+	  __cpuid_count (7, 1, eax, ebx, ecx, edx);
+	  if (eax & bit_HRESET)
+	    set_feature (FEATURE_HRESET);
+	  if (avx_usable)
+	    {
+	      if (eax & bit_AVXVNNI)
+		set_feature (FEATURE_AVXVNNI);
+	    }
+	  if (avx512_usable)
+	    {
+	      if (eax & bit_AVX512BF16)
+		set_feature (FEATURE_AVX512BF16);
+	    }
 	}
     }
 
-- 
2.31.1