What instructions would you like to see added to x86 or ARM? Personally, I want an ADD3 or an add-and-accumulate SIMD operation. A lot of algorithms are dominated by additions, and getting two adds with one instruction could help a lot. The closest instruction is SABA (signed-absolute-difference-and-accumulate), so I'm assuming this would be practical. I also have AVX-512 embedded rounding (and exception) control envy, but idk if ARM can find the bits for that with fixed-size instructions.