Inter register constraints

[Denis Chertykov]

2013/7/5 Paulo Matos <pmatos@broadcom.com>
>
> Hi,
>
> I am convinced that what I am about to ask is not possible but I would like someone to confirm this.
>
> Can I define in an insn a register constraint that depends on another register value?
> So, for
> (set (match_operand:SI 0 "register_operand" "r")
>      (match_operand:SI 1 "register_operand" "r"))
>
> What I would like to represent is the fact that 0 and 1 are register pairs, so op0 is even and op1 is op0 + 1.
> I noticed that avr defines register pair constraints but only for specific registers. If you have 64 registers that will give you 22 pairs. I could, of course, create all of these by hand by defining 23 classes and define a single constraint that matches these classes but I would like to know if there's another way.

You can try to play with DImode register and two SImode subregs of it.

Denis.