Compare-elim pass (was: Re: [PATCH] Fix PR 61225)

[Jakub Jelinek]

On Sun, Jan 18, 2015 at 05:28:39PM -0600, Segher Boessenkool wrote:
> On Sat, Jan 17, 2015 at 01:18:44PM -0500, Hans-Peter Nilsson wrote:
> > The current cc-first order happened more of an accidental
> > opinion than an architectural decision as I vaguely recall, when
> > asking.  We also have the canonical location of a *cc clobber*,
> > i.e. last in a parallel.  For that reason, it then makes sense
> > to have the *cc-setting* last.  Changing rebelling ports doesn't
> > solve that inconsistency.
> 
> Except you also have the variant of the insn pattern where the CC is
> set and the GPR is clobbered (on PowerPC we have one of those for
> every insn, and only a few where CC is clobbered).
> 
> > So, my vote for canonically declaring the order non-canonical
> > *and* automatically generating/matching both orders.
> 
> It would be nice to only have to write the set+set version, and do
> some markup to say which of the clobber variants should be generated,
> yes.

define_subst should be able to do that.

	Jakub