[mxmlnkn]

Or simply require an AVX2-capable CPU. According to Steam survey, 90% have AVX2 support. That's not as nice as the 99.18% SSE4.2 support or the 100% SSE3 support, but for some use cases such as scientific libraries, requiring a CPU that is less than 8 years old makes sense to me. Some more helpful error message than "Illegal Instruction" would still be a good idea though. This does require runtime AVX2 detection but at least it avoids the pain of trying to compile "pristine" architecture-specific code, which seems only possible for C/C++ code that does not use any standard library function or by writing assembler directly.