Re: Suggestion for a fix to Bug middle-end/20177

[Steven Bosscher <stevenb at suse dot de>]

On Mar 16, 2005 05:11 PM, Mostafa Hagog <MUSTAFA@il.ibm.com> wrote:

> 
> 
> 
> 
> kenner@vlsi1.ultra.nyu.edu (Richard Kenner) wrote on 16/03/2005 17:27:59:
> 
> >     REG_NOTE (NONNEG)
> >     REG_NOTE (NO_CONFLICT)
> >     REG_NOTE (UNUSED)
> >        mustn't be copied
> >        describe a fact about other instructions so this
> >        may change if copied.
> >
> > Tricky.  Often UNUSED means that we're allocating a psuedo for some
> temporary
> > which we know isn't used.
> 
> I suppose this is a function level information - meaning: the rgister is
> not used all over the
> function-  so we can (and should) copy it.
> 
> >
> >     REG_NOTE (CC_SETTER)
> >     REG_NOTE (CC_USER)
> >       I suppose that using CC0 is possible only in branch
> > instructions (correct
> >     me if I am wrong)
> >
> > It can also be used in "scc" insns.
> 
> This is interesting, so there could be cases were want to copy CC register
> when doing SMS.  what happens if we want to move the set of a CC to
> another iteration of the loop ? or the use of the CC ?
> but usually this is couldn't happen in a simple loop, right? the use of CC
> is
> eventually used in a branch, or there is something that I am missing ?

IIRC these notes are for CCO, and you have to move the CC setter
and user together.

Actually I think SMS for CC0 targets is Just Silly to do at all ;-)

Gr.
Steven


the CC setter is always th