Work around bug in xgetbv for Visual Studio.

source/cpu_id.cc

 /*
  *  Copyright 2011 The LibYuv 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 30 matching lines @@
 #else
 #define SAFEBUFFERS
 #endif
 
 // Low level cpuid for X86.
 #if (defined(_M_IX86) || defined(_M_X64) || \
     defined(__i386__) || defined(__x86_64__)) && \
     !defined(__pnacl__) && !defined(__CLR_VER)
 LIBYUV_API
 void CpuId(uint32 info_eax, uint32 info_ecx, uint32* cpu_info) {
-#if (defined(_MSC_VER) && !defined(__clang__)) && !defined(__clang__)
+#if defined(_MSC_VER) && !defined(__clang__)
 // Visual C version uses intrinsic or inline x86 assembly.
 #if (_MSC_FULL_VER >= 160040219)
   __cpuidex((int*)(cpu_info), info_eax, info_ecx);
 #elif defined(_M_IX86)
   __asm {
     mov        eax, info_eax
     mov        ecx, info_ecx
     mov        edi, cpu_info
     cpuid
     mov        [edi], eax
     mov        [edi + 4], ebx
     mov        [edi + 8], ecx
     mov        [edi + 12], edx
   }
-#else
+#else  // Visual C but not x86
   if (info_ecx == 0) {
     __cpuid((int*)(cpu_info), info_eax);
   } else {
     cpu_info[3] = cpu_info[2] = cpu_info[1] = cpu_info[0] = 0;
   }
 #endif
 // GCC version uses inline x86 assembly.
-#else  // (defined(_MSC_VER) && !defined(__clang__)) && !defined(__clang__)
+#else  // defined(_MSC_VER) && !defined(__clang__)
   uint32 info_ebx, info_edx;
   asm volatile (
 #if defined( __i386__) && defined(__PIC__)
     // Preserve ebx for fpic 32 bit.
     "mov %%ebx, %%edi                          \n"
     "cpuid                                     \n"
     "xchg %%edi, %%ebx                         \n"
     : "=D" (info_ebx),
 #else
     "cpuid                                     \n"
     : "=b" (info_ebx),
 #endif  //  defined( __i386__) && defined(__PIC__)
       "+a" (info_eax), "+c" (info_ecx), "=d" (info_edx));
   cpu_info[0] = info_eax;
   cpu_info[1] = info_ebx;
   cpu_info[2] = info_ecx;
   cpu_info[3] = info_edx;
-#endif  // (defined(_MSC_VER) && !defined(__clang__)) && !defined(__clang__)
+#endif  // defined(_MSC_VER) && !defined(__clang__)
 }
 #else  // (defined(_M_IX86) || defined(_M_X64) ...
 LIBYUV_API
 void CpuId(uint32 eax, uint32 ecx, uint32* cpu_info) {
   cpu_info[0] = cpu_info[1] = cpu_info[2] = cpu_info[3] = 0;
 }
 #endif
 
-// TODO(fbarchard): Enable xgetbv when validator supports it.
+// For VS2010 and earlier emit can be used:
+//   _asm _emit 0x0f _asm _emit 0x01 _asm _emit 0xd0  // For VS2010 and earlier.
+//  __asm {
+//    xor        ecx, ecx    // xcr 0
+//    xgetbv
+//    mov        xcr0, eax
+//  }
+// For VS2013 and earlier 32 bit, the _xgetbv(0) optimizer produces bad code.
+// https://code.google.com/p/libyuv/issues/detail?id=529
+#if defined(_M_IX86) && (_MSC_VER < 1900)
+#pragma optimize("g", off)
+#endif
 #if (defined(_M_IX86) || defined(_M_X64) || \
     defined(__i386__) || defined(__x86_64__)) && \
     !defined(__pnacl__) && !defined(__CLR_VER) && !defined(__native_client__)
 #define HAS_XGETBV
 // X86 CPUs have xgetbv to detect OS saves high parts of ymm registers.
 int GetXCR0() {
   uint32 xcr0 = 0u;
-#if (defined(_MSC_VER) && !defined(__clang__)) && (_MSC_FULL_VER >= 160040219)
+#if (_MSC_FULL_VER >= 160040219)
   xcr0 = (uint32)(_xgetbv(0));  // VS2010 SP1 required.
-#elif defined(_M_IX86) && defined(_MSC_VER) && !defined(__clang__)
-  __asm {
-    xor        ecx, ecx    // xcr 0
-    _asm _emit 0x0f _asm _emit 0x01 _asm _emit 0xd0  // For VS2010 and earlier.
-    mov        xcr0, eax
-  }
 #elif defined(__i386__) || defined(__x86_64__)
+  uint32 xcr0 = 0u;
   asm(".byte 0x0f, 0x01, 0xd0" : "=a" (xcr0) : "c" (0) : "%edx");
 #endif  // defined(__i386__) || defined(__x86_64__)
   return xcr0;
 }
 #endif  // defined(_M_IX86) || defined(_M_X64) ..
+// Return optimization to previous setting, which is off for debug.

[brucedawson, 2015/12/09 01:53:34]

I'd delete the ", which is off for debug." from the comment.

[fbarchard, 2015/12/09 02:13:21]

Done.

+#if defined(_M_IX86) && (_MSC_VER < 1900)
+#pragma optimize("g", on)
+#endif
 
 // based on libvpx arm_cpudetect.c
 // For Arm, but public to allow testing on any CPU
 LIBYUV_API SAFEBUFFERS
 int ArmCpuCaps(const char* cpuinfo_name) {
   char cpuinfo_line[512];
   FILE* f = fopen(cpuinfo_name, "r");
   if (!f) {
     // Assume Neon if /proc/cpuinfo is unavailable.
     // This will occur for Chrome sandbox for Pepper or Render process.
@@ skipping 152 matching lines @@
 // Note that use of this function is not thread safe.
 LIBYUV_API
 void MaskCpuFlags(int enable_flags) {
   cpu_info_ = InitCpuFlags() & enable_flags;
 }
 
 #ifdef __cplusplus
 }  // extern "C"
 }  // namespace libyuv
 #endif