Re: Constrainst for individual registers

[Georg-Johann Lay <avr at gjlay dot de>]

> Hi,
> I'm doing some modifections to the avr backend to suit my needs.
>
> I would like to add new constrainst for individual registers to use in
> inline assembly blocks and i was wondering what is the correct way of
> doing this?

Not on topic: You can have a look at GCC's "Specifying Registers for 
Local Variables" feature:
http://gcc.gnu.org/onlinedocs/gcc/Local-Reg-Vars.html#Local-Reg-Vars

For example, this enables you to interface non-ABI assembler functions 
with C code without patching the compiler.

Moreover, introducing individual register classes will result in a zoo 
of constraints for 8-bit, 16-bit, 32-bit registers.

> in gcc-4.5, i've added a new class for each register to reg_class,
> REG_CLASS_NAMES and REG_CLASS_CONTENTS, made a need constrainst for
> each register using its class and it worked as expected.
>
> i tried to do the same in gcc-4.7 and i got:
> internal compiler error: in find_costs_and_classes, at ira-costs.c:1704.

You will have to debug the compiler proper.

Notice that hooks like HARD_REGNO_MODE_OK put additional restrictions on 
registers/mode combinations.

> So i was wondering whether i did the wrong thing or just forgot to
> update some target hook.
>
> Thanks,
> Ilya.