Re: AVR: CC0 to CCmode conversion

[Denis Chertykov <denisc at overta dot ru>]

Paul Schlie <schlie@comcast.net> writes:

> > Denis wrote:
> > I have converted the AVR port from CC0 to CCmode.
> > But may be I have converted the port in wrong way.
> > (It's because I was interested in *this* way.)
> > 
> > I have used CCmode register and havn't added the
> > '(clobber (reg:QI CC_REGNUM))' to any insn that really clobber the
> > CC_REGNUM just because AVR is'n needed in scheduling.
> > I think that sequence of compare + cond-jump will exists in any
> > compiler pass.
> > The port was successfully tested without new regressions.
> > What do you (MAINTAINERS) think about this ?
> 
> Interesting:
> 
> - might you be able to post the resulting port files for review?

patch against cvs:
http://home.overta.ru/users/denisc/cc0-ccmode/cc0-ccmode.patch.gz
new port:
http://home.overta.ru/users/denisc/cc0-ccmode/avr.tgz

> - are you proposing that all conditional branches then required to be
>   explicitly paired with a corresponding immediately previous compare
>   instruction?

I founded that GCC isn't break cmp+jump sequences.
(My port havn't scheduling.)

>   (if so, how is this a good thing observing that it's fairly typical
>   for most conditional branches to be naturally based on comparisons
>   against 0 resulting from the immediately preceding operation, which
>   would have otherwise not required an explicit compare?)

I think that it's not good.

Denis.