Speculative fix for AVX2 detection

source/libvpx/vpx_ports/x86.h

Index: source/libvpx/vpx_ports/x86.h
diff --git a/source/libvpx/vpx_ports/x86.h b/source/libvpx/vpx_ports/x86.h
index ae349fb84c631ea40a5cbbd084938fd56ef113f4..7d93710c4b0381ae0199172d2c57fa4e6232ce71 100644
--- a/source/libvpx/vpx_ports/x86.h
+++ b/source/libvpx/vpx_ports/x86.h
@@ -152,7 +152,7 @@ static INLINE int
 x86_simd_caps(void) {
   unsigned int flags = 0;
   unsigned int mask = ~0;
-  unsigned int reg_eax, reg_ebx, reg_ecx, reg_edx;
+  unsigned int max_cpuid_val, reg_eax, reg_ebx, reg_ecx, reg_edx;
   char *env;
   (void)reg_ebx;
 
@@ -168,9 +168,9 @@ x86_simd_caps(void) {
     mask = strtol(env, NULL, 0);
 
   /* Ensure that the CPUID instruction supports extended features */
-  cpuid(0, 0, reg_eax, reg_ebx, reg_ecx, reg_edx);
+  cpuid(0, 0, max_cpuid_val, reg_ebx, reg_ecx, reg_edx);
 
-  if (reg_eax < 1)
+  if (max_cpuid_val < 1)
     return 0;
 
   /* Get the standard feature flags */
@@ -193,10 +193,12 @@ x86_simd_caps(void) {
     if ((xgetbv() & 0x6) == 0x6) {
       flags |= HAS_AVX;
 
-      /* Get the leaf 7 feature flags. Needed to check for AVX2 support */
-      cpuid(7, 0, reg_eax, reg_ebx, reg_ecx, reg_edx);
+      if (max_cpuid_val >= 7) {
+        /* Get the leaf 7 feature flags. Needed to check for AVX2 support */
+        cpuid(7, 0, reg_eax, reg_ebx, reg_ecx, reg_edx);
 
-      if (reg_ebx & BIT(5)) flags |= HAS_AVX2;
+        if (reg_ebx & BIT(5)) flags |= HAS_AVX2;
+      }
     }
   }