Re: Porting GCC to Zilog z80

[Jim Wilson <wilson at tuliptree dot org>]

Alexander Aganichev wrote:
> I'm playing with the gcc patches made by Brahmaiah Vallabhane. I have ported them to gcc 3.2.3 and cleaned up. I'm aware of copyright problem, but this is not currently
> an issue since I plan to rewrite them once the GCC architecture will be clear to me.

If you are basing your port on an earlier one, then your port will be a 
derivitive work, and we would still need copyright assignments for the 
earlier port.  Rewriting the port helps, but you need to be careful not 
to copy anything from the earlier port.  You need to start from scratch 
with your own port.

> So, the question: should BC, DE, and HL registers be defined for the compiler as
> 16-bit or as splitted 8-bit?

I think they need to be 8-bit registers, accessed as pairs for 16-bit 
values.  gen_highpart will give you a subreg that refers to the high 
part of a register, but it is uncommon to use this as an operand.  There 
is also the problem that gen_highpart is allowed to emit RTL.  It isn't 
a function for accessing the high part of a register.  It is a function 
for emitting code to access the value in the high part of a register 
which is not quite the same thing.  If you must have the B register, 
then gen_highpart (BC) isn't safe.  gen_highpart might move the value 
someplace else before returning it to you.

Jim