Marko Mäkelä added a comment - 2020-08-27 15:18 - edited I would prefer to see something like this in the implementation. The approach was demonstrated in MDEV-20386 . For GCC 4, we must work around broken header files . #include <wmmintrin.h>   #ifdef __GNUC__ __attribute__((target( "sse4.2,pclmul" ))) #endif static unsigned crc32c_pclmul(unsigned crc32c, void *data, size_t size) { __m128i a,b,c; … c=_mm_clmulepi64_si128 (a,b,1); … } For GCC 4 (the oldest that we currently support is 4.8.2), some extra hoops are needed to replace the broken #include header: #include <string.h> #include <stdint.h>   #if defined __GNUC__ && !defined __clang__ && __GNUC__ < 5 # define _mm_clmulepi64_si128 __builtin_ia32_pclmulqdq128 typedef long long __attribute((vector_size(16))) __m128i; #else # include <wmmintrin.h> #endif   #ifdef __GNUC__ __attribute__((target( "sse4.2,pclmul" ))) #endif unsigned crc32c_pclmul(unsigned crc32c, void *data, size_t size) { __m128i a,b,c; c=_mm_clmulepi64_si128 (a,b,1); return 0; } I would find it risky to compile the entire compilation unit with something that enables many SIMD features that may not be available on the least common denominator (SSE2 for AMD64; Intel 80486 or possibly something newer for IA-32). We do not want the compiler to accidentally enable some exotic instructions for any ‘glue’ code that is supposed to run anywhere.

Vladislav Vaintroub added a comment - 2020-09-04 11:31 I do not see why anew feature and a workaround for the said feature will help code to be better. It only adds more code, we will need compiler options for clang-cl, and there are already compiler options for ARM etc. So, if anything, I would prefer not to add both attributes and GCC intrinsics for the broken attributes, to reduce complexity, and increase portability. I can't imagine that compiler will accidentially add pclmul in cpuid test (crc32_pclmul_enabled), which is single function in question in this particular compilation unit