Controlling what kind of value ends in a register

[Alexandre Courbot <Alexandre dot Courbot at lifl dot fr>]

Hello everybody,

My machine definition requires that one kind of register class (named 
POINTER_REGS) is exclusively used to hold addresses. In other words, whenever 
an address must be stored into a register, this class must be used. In no way 
should an address finish in a register that doesn't belong to this class.

My problem is that I don't know how to direct the register allocator to select 
the correct register class. Using reloading doesn't help here, as the value 
will eventually be copied into the register chosen by the allocator (of wrong 
class) after being copied in a register of the right class. I had a look at 
regclass.c and couldn't find anything else but costs to direct the allocator. 
Costs are unfortunately only a direction and not a requirement.

Is there a way to direct the register allocator to chose a certain class of 
registers (that doesn't belong to GENERAL_REGISTERS) from what's being copied 
into that reg? I'd bet there is and it is quite obvious, but so far I missed 
it. Any pointer would be greatly appreciated.

Thanks,
Alex.