PRE (sometimes) confuses ivopts/scev?

[Ulrich Weigand]

Daniel Berlin wrote:

> > Unfortunately your patch doesn't change this because the variables
> > fail the
> >
> >      if (firstinsideloop ^ secondinsideloop
> >          && is_gimple_min_invariant (avail[outsideloopblock->index])
> >          && !is_gimple_min_invariant (avail[insideloopblock->index]))
> >
> > test -- the outsideloop value is not invariant (because it varies
> > with the next outer loop).
> 
> > Why is this test required in the first place?
> 
> Because induction variables should be 2 argument phi nodes with the 
> following property:
> 
> 1. Edge incoming to loop doesn't change in the loop

Well, but "doesn't change in the loop" is quite something else
than is_gimple_min_invariant!

Maybe I'm missing something here, but how *could* the *incoming*
value change in the loop?  Its definition is outside the loop ...

>   If I remove it,
> 
> Remove what?

The two is_gimple_min_invariant checks.

> If you remove the test and replace it with 1, it'll never PRE anything.

I did leave in the 
   if (firstinsideloop ^ secondinsideloop)


Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  Linux on zSeries Development
  Ulrich.Weigand@de.ibm.com