I agree AVX-512 is not exactly widespread on client CPUs but as akelly mentions, it does exist (e.g. Icelake). What we do is dispatch to the best available ins

I agree AVX-512 is not exactly widespread on client CPUs but as akelly mentions, it does exist (e.g. Icelake). What we do is dispatch to the best available instruction set at runtime - that costs only an indirect branch, plus somewhat larger binary and longer compile time.