Adding check for OS support to AVX

base/cpu.cc

Index: base/cpu.cc
diff --git a/base/cpu.cc b/base/cpu.cc
index d6976bab33b316aed50e3a133edf1a7e8a060a97..74513739f121ebc348e48a3b8f4cd0ed0cfefcf3 100644
--- a/base/cpu.cc
+++ b/base/cpu.cc
@@ -32,6 +32,7 @@ CPU::CPU()
     has_ssse3_(false),
     has_sse41_(false),
     has_sse42_(false),
+    has_avx_(false),
     cpu_vendor_("unknown") {
   Initialize();
 }
@@ -80,6 +81,17 @@ void __cpuidex(int cpu_info[4], int info_type, int info_index) {
 }
 
 #endif
+
+unsigned long long _xgetbv(unsigned int xcr) {
+  unsigned int eax, edx;
+  __asm__ volatile (
+    ".byte 0x0f, 0x01, 0xd0"
+    : "=a"(eax), "=d"(edx)
+    : "c" (xcr)
+  );
+  return static_cast<unsigned long long>(eax) ^
+         static_cast<unsigned long long>(edx) << 32;
+}
 #endif  // _MSC_VER
 #endif  // ARCH_CPU_X86_FAMILY
 
@@ -117,7 +129,7 @@ void CPU::Initialize() {
     has_ssse3_ = (cpu_info[2] & 0x00000200) != 0;
     has_sse41_ = (cpu_info[2] & 0x00080000) != 0;
     has_sse42_ = (cpu_info[2] & 0x00100000) != 0;
-    has_avx_ = (cpu_info[2] & 0x10000000) != 0;
+    has_avx_ = (cpu_info[2] & 0x10000000) != 0 && (_xgetbv(0) & 6) == 6;

[DaleCurtis, 2013/03/07 23:37:15]

I think this needs #include <immintrin.h> on Windows and that only works on
64-bit according to this bug:

https://code.google.com/p/libyuv/issues/detail?id=106

Perhaps that's fixed now? Have you done a Windows build with this?

[apatrick_chromium, 2013/03/08 00:39:41]

This says that it need Visual Studio 2010 SP1, which is a Chromium build
prerequisite.

http://insufficientlycomplicated.wordpress.com/2011/11/07/detecting-intel-adv...

It also suggests the need to check for XSAVE/XRSTOR support, bit 27 of
cpu_info[2].

[whunt, 2013/03/08 18:30:32]

XSAVE/XRSTOR are required for SSE to work at all and are supported by all OSes
we support.

On 2013/03/08 00:39:41, apatrick_chromium wrote:

[whunt, 2013/03/08 18:30:32]

<intrin.h> should include <immintrin.h>
I've only run the bots with it which I believe are 32 bit (I'm not aware of a
64bit windows build).

On 2013/03/07 23:37:15, DaleCurtis wrote:

   }
 
   // Get the brand string of the cpu.