Unrolling on AVX-512, especially on Zen 4 with its double-pumped almost-everything, isn't particularly significant; the 512-bit store alone has a reciprocal throughput of 2 cycles/zmm, which gives a pretty comfortable best possible target of 2 cycles/iteration. With Zen 4 being 6-wide out of the op cache, that's fine for up to 12 instructions in the loop (and with separate ports for scalar & SIMD, the per-iteration scalar op overhead is irrelevant).

Interestingly enough, clang 16 doesn't unroll the intrinsics version, but trunk does, which'd make the entire point moot.

The benchmark in question, as per the article, tests over 1MB in blocks, so it'll be at L2 or L3 speeds anyway.

Clang downgrades to ymm, which'll handle a 32-byte tail, but after that it does a plain scalar loop, up to a massive 31 iterations. Whereas masking appears to be approximately free on Zen 4, so I'd be surprised if the scalar tail would be better at even, like, 4 bytes (perhaps there could be some minor throughput gained by splitting up into optional unmasked ymm and then a masked ymm, but even that's probably questionable just from the extra logic/decode overhead).

Also worth considering that in real-world usage the masking version could be significantly better just from being branchless for up to 64-byte inputs.