CODEWITHSUNDEEP
c++visual-studio-2015sseavxinstruction-set
user123443563
user123443563

Reputation: 271

Detecting SIMD instruction sets to be used with C++ Macros in Visual Studio 2015

So, here is what I am trying to accomplish. In my C++ project that has to be compiled with Microsoft Visual Studio 2015 or above, I need to have some code have different versions depending on the newest SIMD instrunction set available in the CPU of the user, among: SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2 and AVX512.

Since what I am look for at this point is compile-time CPU dispatching, my first guess was that it could be easily accomplished using compiler macros. However, to my astonishment, it has been quite hard to find information on how to achieve such CPU dispatching with macros in VS2015.

For instance, the former question "Detect the availability of SSE/SSE2 instruction set in Visual Studio" has information on how to detect SSE and SSE2 for x86 code, but not for x64 code. Although, they make a reference to this Microsoft's document: http://msdn.microsoft.com/en-us/library/b0084kay.aspx

There, we only have information on how to detect whether SSE, SSE2, AVX and AVX2 are enabled in the compiler - not exactly whether they are supported by CPU. Also, there is nothing at all about the other instrunction sets, like SSE3, SSSE3, SSE4.1, SSE4.2 and AVX512.

So, my question becomes: how can I detect whether the user's CPU supports those instrunction sets via macro, just like other compilers do, but with Microsoft Visual Studio 2015?

Upvotes: 3

Views: 4636

Answers (1)

MSalters
MSalters

Reputation: 179799

The problem you're facing is that Visual Studio historically is intended for software vendors. The idea that you compile your own software simply isn't in Microsoft's DNA.

The practical result is that Microsoft hardly cares about the processor of the build machine. That's unlikely to be the processor used to run the software.

On the upside, this also means that Microsoft doesn't suffer from the perennial Linux problem that the build system libraries are assumed to be present on the target machine. Building on Windows 10 for Windows 7 just works.

The compiler also doesn't allow you to enable up to SSE4.1, for example. You can only use /arch:avx or nothing. Also, that option only defines __AVX__, not the usual macros like __SSSE3__ that gcc/clang/icc define to indicate target support for previous instruction sets implied by AVX.

Upvotes: 1

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