O que é Compiler intrinsic, CPU feature dispatch?

A compiler intrinsic is a function the compiler knows and translates into one specific instruction (_mm256_cmpeq_epi8 into VPCMPEQB), letting a program use an instruction without writing assembly while the compiler still allocates registers and schedules around it. CPU feature dispatch selects at run time, from the features the processor reports, which of several compiled versions of a function to call.