register 31 - SP or XZR?

[skochinsky]

dougallj claims that 31 means XZR, but do any AMX operations make sense with an all-zero value? OTOH, using SP as GPR can be tricky/dangerous...

[corsix]

Most operations (other than loads/stores) have a perfectly rational interpretation of an all-zero operand, with this being clearest for something like fma64: all-zeroes there just does Z₀ += X₀ @ Y₀.

[skochinsky]

Thank you! I would suggest you to make this explicit in the encoding documentation