Speculative fix for AVX2 detection

source/libvpx/vpx_ports/x86.h

 /*
  *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 134 matching lines @@
 #define HAS_AVX     0x40
 #define HAS_AVX2    0x80
 #ifndef BIT
 #define BIT(n) (1<<n)
 #endif
 
 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;
 
   /* See if the CPU capabilities are being overridden by the environment */
   env = getenv("VPX_SIMD_CAPS");
 
   if (env && *env)
     return (int)strtol(env, NULL, 0);
 
   env = getenv("VPX_SIMD_CAPS_MASK");
 
   if (env && *env)
     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 */
   cpuid(1, 0, reg_eax, reg_ebx, reg_ecx, reg_edx);
 
   if (reg_edx & BIT(23)) flags |= HAS_MMX;
 
   if (reg_edx & BIT(25)) flags |= HAS_SSE; /* aka xmm */
 
   if (reg_edx & BIT(26)) flags |= HAS_SSE2; /* aka wmt */
 
   if (reg_ecx & BIT(0)) flags |= HAS_SSE3;
 
   if (reg_ecx & BIT(9)) flags |= HAS_SSSE3;
 
   if (reg_ecx & BIT(19)) flags |= HAS_SSE4_1;
 
   // bits 27 (OSXSAVE) & 28 (256-bit AVX)
   if ((reg_ecx & (BIT(27) | BIT(28))) == (BIT(27) | BIT(28))) {
     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;
+      }
     }
   }
 
   return flags & mask;
 }
 
 #if ARCH_X86_64 && defined(_MSC_VER)
 unsigned __int64 __rdtsc(void);
 #pragma intrinsic(__rdtsc)
 #endif
@@ skipping 82 matching lines @@
 }
 
 
 extern void vpx_reset_mmx_state(void);
 
 #ifdef __cplusplus
 }  // extern "C"
 #endif
 
 #endif  // VPX_PORTS_X86_H_