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Re: Adding soft-registers
- From: <tm_gccmail at kloo dot net>
- To: Stephane Carrez <stcarrez at nerim dot fr>
- Cc: James Dessart <james at skwirl dot ca>,Eric Botcazou <ebotcazou at libertysurf dot fr>, gcc at gcc dot gnu dot org
- Date: Thu, 8 Jan 2004 14:55:40 -0800 (PST)
- Subject: Re: Adding soft-registers
On Thu, 8 Jan 2004, Stephane Carrez wrote:
>
>
> tm_gccmail@kloo.net wrote:
> >
> > It sounds like the 6809 direct page differs from the 65816 direct page
> > because the 65816 direct page is settable on a byte boundary. This allowed
> > it be used as the frame pointer, and we generally accessed the locals on
> > the stack via the direct page.
> >
>
> Interesting! It must be changed to a 16-bit register then does it?
> If you have this your task is easier in gcc because you don't fall in the
> reload nightmare (or reduce it).
>
> Stephane
Yes, the DP and SP registers are 16 bits on the 65816.
The 65816 address space, however, is 24 bits, so the stack is limited
to the first 64k. This wasn't too terrible a restriction as long
as people didn't try to alloca() large amounts of memory.
Toshi