[Coco] [Color Computer] SDCC

[Michael Wayne Harwood]

Conversion from .djvu to .pdf is currently possible by using a .pdf printer
- both Windows and Unix have a system for sending print jobs to a .pdf based
printer.  The searchable text layers would not go across with this method,
but you would get the images.

Regards,
Michael Harwood 


-----Original Message-----
From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] On
Behalf Of James Diffendaffer
Sent: Monday, July 18, 2005 2:34 PM
To: ColorComputer at yahoogroups.com
Subject: Re: [Coco] [Color Computer] SDCC

--- In ColorComputer at yahoogroups.com, "John R. Hogerhuis"
<jhoger at p...> wrote:
> On Mon, 2005-07-18 at 14:17 +0000, James Diffendaffer wrote:

> What I had done was replicate the source files and build stuff to add 
> a copy of the hc08 module an rename it mc6809. What James had done was 
> some of the register allocator.

I'm already past that so it's no big deal.

> > I won't know if everything is right until I start testing but it 
> > looks like the changes are pretty obvious the more familiar I am
with it.
> > 
> 
> Good on you. I found the sdcc register allocator and code generator a 
> bit of a mess.

It has flags for special purpose registers so it knows what they can be used
for and it just searches through the register structure array till in finds
the first free register of the proper type or size.  At least that's what it
looks like it's doing.  I'm not sure how smart it will be for the combined
registers though.  I'll have to worry about that later.  The 32 bit register
will almost be of no use to the code generator.  It *might* be usefull to
the peephole optimizer... I'll have to look at it's functionality closer.
Loading up to 4 parameters into registers at one time could be usefull.

There seems to be one issue with the hc08 compiler that should be fixed.
Since the condition code register wasn't placed at the end of the register
structure array and the size reduced by one like the Z80 compiler, the
allocator/deallocator routines always run an extra loop each time once the
previous registers are all allocated.  That slows down the compiler.  It
makes no difference to the code generated though.

Since register allocation seems to start at the bottom and works it's way to
the top of the array, the compiler may not produce the most stack efficient
code.  I had some deep discussion about this in another group... it might be
more theory than practice though.  

I'm planning on using the user stack pointer by default for stack operations
but a compiler directive (#pragma?) that lets you chose which one for a
section of code could prove usefull.  I'd call that a want list item.

As for OS-9 code, I think a smart assembler could generate PC relative code
even if the compiler doesn't.  I'm sure there's more to worry about but I
pretty much missed the OS-9 part of the CoCo's life so I'm no expert.

> Add to that I've never worked on compilers, poor vocabulary and 
> abbeviation choices in the comments and I couldn't tell what the 
> authors were attempting to accomplish in several places.

You aren't kidding!  I had to look around a lot to figure out what some of
the variables are.  The good news is that you don't need wo worry about most
of them.  The bad news may be that I may miss one that I do need to worry
about!

> But there was an interesting Q&Q on the internals at the mailing
list. The
> developer of the hc08 module will respond to questions if you have 
> any, he (at least was) talking to us on the cc6809 list.
>
> -- John.

I haven't hit any dead ends yet but you never know.  When I start testing
his assistance may be usefull.

I haven't done a lot of compiler work.  I looked at a lot of assembly output
when I was doing a lot of embedded systems work.  I had to mix a lot of C
and assembly writing device drivers and OS Kernels.
I did write a 64180 peephole optimizer for the Z-World Z80/64180 C compiler
and a 680x0 peephole optimizer for a free Pascal on the Amiga in the early
90's.  Plus compiler construction is a requirement for a Computer Science
Major at the University I attended.





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