[PATCH] ccp for V_MUST_DEF operands

[Brian Booth]

On Fri, 2004-07-16 at 11:21, Diego Novillo wrote: 
> On Fri, 2004-07-16 at 10:26, Brian Booth wrote:
> > On Thu, 2004-07-15 at 09:18, Diego Novillo wrote:
> > > Could you add a test case?  Something like this should suffice:
> > > 
> > > --
> > > int G;
> > > 
> > > foo (int i)
> > > {
> > >    if (i > 0)
> > >      G = 3;
> > >    else
> > >      G = 3;
> > >    if (G != 3)
> > >      link_error ();
> > > }
> > > 
> > > main ()
> > > {
> > >    foo (0);
> > >    return 0;
> > > }
> > > --
> > 
> > I'm withdrawing this patch for the time being because it does not
> > propagate G in the testcase above. The problem has to do with performing
> > a meet operation on UNKNOWN_VAL. More specifically, the case CONSTANT M
> > UNKNOWN_VAL = VARYING is causing G not to be propagated since the PHI
> > node for G is simulated before one of the assignments to G in the
> > if-else block. This is causing the PHI node to be marked as VARYING and
> > ensures that it is not simulated again.
> > 
> What about initially setting phi_val to UNDEFINED if 
> get_value (PHI_RESULT (phi)) returns UNKNOWN_VAL?

That's exactly what I'm working on right now. We just have to be careful
as to avoid a UNKNOWN_VAL->UNDEFINED state transition inadvertently
being saved because of this.

Brian