[Bug tree-optimization/68234] tree-vrp pass need to be improved when handling ASSERT_EXPR

[jiwang at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68234

--- Comment #4 from Jiong Wang <jiwang at gcc dot gnu.org> ---
(In reply to rguenther@suse.de from comment #3)
> On Mon, 9 Nov 2015, jiwang at gcc dot gnu.org wrote:
> 
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68234
> > 
> > Jiong Wang <jiwang at gcc dot gnu.org> changed:
> > 
> >            What    |Removed                     |Added
> > ----------------------------------------------------------------------------
> >             Summary|tree-vrp pass need to be    |tree-vrp pass need to be
> >                    |improved when handling      |improved when handling
> >                    |ASSERT/PLUS/MINUS/_EXPR and |ASSERT_EXPR
> >                    |Phi node                    |
> > 
> > --- Comment #2 from Jiong Wang <jiwang at gcc dot gnu.org> ---
> > (In reply to Richard Biener from comment #1)
> > 
> > > I think the issue is that we insert the assert in the first place or
> > > that we intersect to a symbolic range this causes us to not use SCEV / loop
> > > analysis to get at the range for c_1.  That is, in vrp_visit_phi_node
> > > the early outs to varying: shouldn't skip
> > > 
> > >       /* If we dropped either bound to +-INF then if this is a loop
> > >          PHI node SCEV may known more about its value-range.  */
> > >       if ((cmp_min > 0 || cmp_min < 0
> > >            || cmp_max < 0 || cmp_max > 0)
> > >           && (l = loop_containing_stmt (phi))
> > >           && l->header == gimple_bb (phi))
> > >         adjust_range_with_scev (&vr_result, l, phi, lhs);
> > > 
> > > sth like
> > > 
> > > Index: gcc/tree-vrp.c
> > > ===================================================================
> > > --- gcc/tree-vrp.c      (revision 229804)
> > > +++ gcc/tree-vrp.c      (working copy)
> > > @@ -8827,6 +8805,24 @@ update_range:
> > >  
> > >    /* No match found.  Set the LHS to VARYING.  */
> > >  varying:
> > > +
> > > +  /* If we dropped either bound to +-INF then if this is a loop
> > > +     PHI node SCEV may known more about its value-range.  */
> > > +  if ((l = loop_containing_stmt (phi))
> > > +      && l->header == gimple_bb (phi))
> > > +    {
> > > +      adjust_range_with_scev (&vr_result, l, phi, lhs);
> > > +
> > > +      /* If we will end up with a (-INF, +INF) range, set it to
> > > +        VARYING.  Same if the previous max value was invalid for
> > > +        the type and we end up with vr_result.min > vr_result.max.  */
> > > +      if (!((vrp_val_is_max (vr_result.max)
> > > +            && vrp_val_is_min (vr_result.min))
> > > +           || compare_values (vr_result.min,
> > > +                              vr_result.max) > 0))
> > > +       goto update_range;
> > > +    }
> > > +
> > >    set_value_range_to_varying (lhs_vr);
> > >    return SSA_PROP_VARYING;
> > >  }
> > > 
> > > which ends up with
> > > 
> > > Value ranges after VRP:
> > > 
> > > c_1: [0, +INF]
> > > 
> > > as desired.  Maybe you can take the above and put it to testing.
> > 
> > Thanks for the explanation on those issues.
> > 
> > The "if" check needs to be guarded by vr_result.type == VR_RANGE, otherwise
> > above draft patch passed my testing. bootstrapping on x86-64 and AArch64 OK. no
> > regresson on both.
> 
> Great.  Can you add a testcase and post the patch?

OK.

now I understand this patch actually done the range correction not in vrp1 but
in vrp2, as after vrp1 those trouble maker ASSERT_EXPR are removed, then in
vrp2, the tree is quite simplified that we invoke the scalar evolution to do a
final calculation to make sure we find as accurate information as possible. I
feel this is what we should have done originally, it is a general improvement
to range info calcuation.

Will combine this block of code with above similar code then send out the patch
with testcase.