Re: Problems in IPA passes

[Kugan Vivekanandarajah <kugan dot vivekanandarajah at linaro dot org>]

Hi Jeff,

On 28 October 2017 at 18:28, Jeff Law <law@redhat.com> wrote:
>
> Jan,
>
> What's the purpose behind calling vrp_meet and
> extract_range_from_unary_expr from within the IPA passes?

This is used such that when we have an argument to a function and this
for which we know the VR and this intern is passed as a parameter to
another. For example:

void foo (int i)
{
...
  bar (unary_op (i))
...
}

This is mainly to share what is done in tree-vrp.
>
> AFAICT that is not safe to do.  Various paths through those routines
> will access static objects within tree-vrp.c which may not be
> initialized when IPA runs (vrp_equiv_obstack, vr_value).

IPA-VRP does not track equivalence and vr_value is not used.

Thanks,
Kugan

>
> While this seems to be working today, it's a failure waiting to happen.
>
> Is there any way you can avoid using those routines?  I can't believe
> you really need all the complexity of those routines, particularly
> extract_range_from_unary_expr.  Plus it's just downright fugly from a
> modularity standpoint.
>
>
> ?
>
> Jeff