Looks like a VAX 11 thing: https://documentation.help/VAX11/op_POLY.htm

See also http://simh.trailing-edge.com/docs/vax_poly.pdf# and some HN discussion from 2015: http://simh.trailing-edge.com/docs/vax_poly.pdf#

This one is as infamous as it is useful. Modern CPUs have the same instruction, but without the built-in loop (fused multiply-add).

Likewise, modern CPUs have dedicated CRC instructions, ARM Thumb 2 famously has an instruction for case statements (jump tables, instructions TBB/TBH), and many more.

The VAX was way ahead of its time, but failed to deliver on performance due to not having a pipelined or out-of-order architecture as is industry standard today.

My other favorite instructions on the VAX: the CRC instruction, the CASE dispatch table operations, and, glory of all glories, the _3-parameter_ operand + operand + destination instructions.

Frankly, I tried to go into depth on this because it was really interesting. I am embarrassed to say it was tough to find sources outside Quora and Reddit. It's possible this HackerNews comment parent might become the canonical source :)