What is the minimum version of OS X for use with AVX/AVX2?

Question

I have an image drawing routine which is compiled multiple times for SSE, SSE2, SSE3, SSE4.1, SSE4.2, AVX and AVX2. My program dynamically dispatches one of these binary var

Answer 1

For detecting instruction set features there are two source files I reference:

1. Mysticial's cpu_x86.cpp
2. Agner Fog's instrset_detect.cpp

Both of these files will tell you how to detect SSE through AVX2 as well as XOP, FMA3, FMA4, if your OS supports AVX and other features.

I am used to Agner's code (one source file for MSVC, GCC, Clang, ICC) so let's look at that first.

Here are the relevant code fragments from instrset_detect.cpp for detecting AVX:

iset = 0;                                              // default value
int abcd[4] = {0,0,0,0};                               // cpuid results
cpuid(abcd, 0);                                        // call cpuid function 0
//....
iset = 6;                                              // 6: SSE4.2 supported
if ((abcd[2] & (1 << 27)) == 0) return iset;           // no OSXSAVE
if ((xgetbv(0) & 6) != 6)       return iset;           // AVX not enabled in O.S.
if ((abcd[2] & (1 << 28)) == 0) return iset;           // no AVX
iset = 7;                                              // 7: AVX supported

with xgetbv defined as

// Define interface to xgetbv instruction
static inline int64_t xgetbv (int ctr) {    
#if (defined (_MSC_FULL_VER) && _MSC_FULL_VER >= 160040000) || (defined (__INTEL_COMPILER) && __INTEL_COMPILER >= 1200) // Microsoft or Intel compiler supporting _xgetbv intrinsic

    return _xgetbv(ctr);                                   // intrinsic function for XGETBV

#elif defined(__GNUC__)                                    // use inline assembly, Gnu/AT&T syntax

   uint32_t a, d;
   __asm("xgetbv" : "=a"(a),"=d"(d) : "c"(ctr) : );
   return a | (uint64_t(d) << 32);

#else  // #elif defined (_WIN32)                           // other compiler. try inline assembly with masm/intel/MS syntax

  //see the source file
}

I did not include the cpuid function (see the source code) and I removed the non GCC inline assembly from xgetbv to make the answer shorter.

Here is the detect_OS_AVX() from Mysticial's cpu_x86.cpp for detecting AVX:

bool cpu_x86::detect_OS_AVX(){
    //  Copied from: http://stackoverflow.com/a/22521619/922184

    bool avxSupported = false;

    int cpuInfo[4];
    cpuid(cpuInfo, 1);

    bool osUsesXSAVE_XRSTORE = (cpuInfo[2] & (1 << 27)) != 0;
    bool cpuAVXSuport = (cpuInfo[2] & (1 << 28)) != 0;

    if (osUsesXSAVE_XRSTORE && cpuAVXSuport)
    {
        uint64_t xcrFeatureMask = xgetbv(_XCR_XFEATURE_ENABLED_MASK);
        avxSupported = (xcrFeatureMask & 0x6) == 0x6;
    }

    return avxSupported;
}

Mystical apparently came up with this solution from this answer.

Notice that both source files do basically the same thing: check the OSXSAVE bit 27, check the AVX bit 28 from CPUID, check a result from xgetbv.

Answer 2

For AVX the answer is quite straightforward:

You need at least OS X 10.6.7

Please note that only build 10J3250 and 10J4138 would support it.

For AVX2 that would be 10.8.4 build 12E3067 or 12E4022