For any instruction, a list of constraints can be specified, like:

let Constraints = “$dst = $lhs” in

…

I checked the existing backends and I didn’t notice any complex constraints: basically “Constraints” keyword is used to force 1 operand register to be the same as another one.

I am wondering if there is any way to express more complicated constraints like for example:

- if $lhs is either r0,r1,r2,r3 then $dst should also be in the set {r0,r1,r2,r3}
- if $lhs is either r4,r5,r6,r7 then $dst should also be in the set {r4, r5, r6, r7}

…

Thank you !

Damien