`vprolvd` is an almost 1:1 analog with this opcode and can be
conditionally emitted when the host supports AVX512{F,VL}.
Altivec docs say that `vrl{bhw}` masks the lower log2(n) bits of the
element-size.
[vprold](https://www.felixcloutier.com/x86/vprold:vprolvd:vprolq:vprolvq)
modulos the shift-value by the element size in bits, which is the same
as masking the lower log2(n) bits. So `vrlw` maps exactly to `vprold`.
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