benchmark and eventually support MOVDIRI/MOVDIR64B on Sapphire Rapids Xeon

[drossetti]

from Intel manuals:

Unlike WC stores and stores with non-temporal hint, direct-stores are eligible for immediate
eviction from the write-combining buffer, and thus not combined with younger stores (including direct-stores)
to the same address. Older WC and non-temporal stores held in the write-combing buffer may be combined with
younger direct stores to the same address. Direct stores are weakly ordered relative to other stores. Software that
desires stronger ordering should use a fencing instruction (MFENCE or SFENCE) before or after a direct store to
enforce the ordering desired.

[imaginary-person]

As of now, Sapphire Rapids Xeon is only available to select corporate Intel customers, and would be released in 2022.

[drossetti]

@pakmarkthub this might be fun :)