Re: fix jump threading with liveness

[Jan Hubicka <jh at suse dot cz>]

> On Tue, Mar 05, 2002 at 07:22:14PM +0100, Jan Hubicka wrote:
> > This can be handled by anding with the liveness of edge destination.
> 
> Err, why isn't it _just_ the liveness of the destination?

Thats what I meant :)
> 
> > Other case is problem with different CC flags - basically different
> > comparions have different CCmodes and the jump threading may fail just
> > because of different modes.  I believe this can be handled by trying
> > to canonicalize the condtional if former does not match.
> 
> Maybe.
> 
> > By adding trivial conditional simplifier proving that condition A implies
> > (negation of) condtiion B.  Is there something similar present already?  It
> > would help loop unswitching as well.
> 
> Not as such, but perhaps you could put simplify-rtx to use.
> I think most of the bits for this would have come in via
> John Wehle's VRP pass.

True.  In case it is expectable for it to come in 3.2 period, I should
probably hold the issue to see how much VRP obsolettes such step.
It is possible to think of cases that VRP can't do, like my teastcase
with testing to inequivalency that don't represent as interval.
Interestingly enought our CSE does simplify it somewhere, I duno
where at the moment.

Honza