This is the mail archive of the
mailing list for the GCC project.
Re: Backend Programming
- From: Dave Hudson <dave at cyclicode dot net>
- To: Eric Robert <eric dot robert at videotron dot ca>
- Cc: gcc at gcc dot gnu dot org
- Date: Mon, 19 Aug 2002 17:54:28 +0100
- Subject: Re: Backend Programming
- References: <000701c24787$d0ca9690$0200a8c0@cortex>
Eric Robert wrote:
The "very few instructions" and "very few registers" will actually be
the major problem here. I've spent a great deal of time working on the
backend of the IP2022 in the last 18 months and this has some PIC-like
characteristics (e.g. one accumulator register and only 3 pointer
registers) and the lack of pointers creates major headaches.
I would like to use GCC to program some types of microcontrollers -
Microchip's PIC if it's of any interest - and I would like to know the
amount of work involved in writing a backend for this very small chip?
It has very few instructions and very few registers.
With the IP2022 the only way to have a chance to get things to work
correctly was to essentially hide the W register (accumulator)
throughout almost all of the code generation (exposing it only right at
the end in the machine-dependent reorg in order to get better code
generation - much of this has not yet been merged into the FSF sources).
Similarly the reload pass causes major problems w.r.t. pointer handling.
Some of the bigger PICs may now make things a little easier (I'm not
sure) but I suspect that getting good code generation will take quite a
significant amount of work.
I'd suggest deciding which processor you wish to support first and then
look to see what similarities it has with the 3 contributed 8-bit ports
(AVR, 68HC11 and IP2022) and then look to see what has been required for
each. The AVR is probably the easiest fit for gcc because it's a very
conventional RISC processor, just 8 bits wide. The IP2022 is by far the
most difficult fit although in fact we have now started to get very good
code generation (gcc is the sole production compiler for the processor).
2. Any pointers to what I have to do?