Re: Backend for PicoBlaze

[Ian Lance Taylor <iant at google dot com>]

"Armin Vogl" <Armin.Vogl@gmx.net> writes:

> I would like to ask if it would be possible to write a gcc backend for the
> Xilinx PicoBlaze soft processor.

Porting gcc to an 8-bit microcontroller is not completely impossible,
but it is not easy.  gcc was written to generate code for 32-bit
processors, and tends to get in a register crunch on very small
processors.  While I didn't look at the PicoBlaze docs at all, small
processors also tend to have specialized addressing modes which tend
to confuse gcc.  Fixing these problems in a gcc port tends to put you
into the most complex part of the compiler, which is reload.

> As I have never programmed anything like a compiler and am
> not familiar with gcc, I would like to ask how much time it would
> need to implement a backend. Is it realistic to do it myself or is
> there a place to request the addition of a backend.
> 
> Is it realistic for somebody with zero gcc experience to implement a backend
> in a reasonable time (whatever that may mean :) ?

It's obviously hard to say.  There is fairly decent documentation and
there are plenty of existing examples.  One advantage of a small
processor is that there isn't all that much to implement--it's mostly
debugging.  An excellent programmer could probably get up to speed and
do the backend port in a few months.  (For comparison, I've written a
few gcc backend ports already, and last year I did a port to a 16-bit
microcontroller in less than a month, but the chip had the advantage
of having 16 registers and only one addressing mode (register
indirect)).

There is no place to request a backend port, other than the e-mail you
sent.  Most such requests go unanswered.  A backend port is hard
enough that most people wouldn't do one without a good reason.

Ian