BMI2 instructions such as `pdep` and `pext` have been
known to be incredibly slow on AMD. But on Zen3
and newer, the performance of these instructions
are now much greater, but previous versions of AMD
architectures should still avoid BMI2.
On Zen 2, pdep/pext were 300 cycles. Now on Zen 3 it is 3 cycles.
This is a big enough improvement to allow BMI2 code to
be dispatched if available. The Zen 3 architecture is checked for
by detecting the family of the processor.
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