Problems in IPA passes

[Jeff Law]

On 10/29/2017 03:54 PM, Kugan Vivekanandarajah wrote:
> 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.
Presumably you never have equivalences or anything like that, which
probably helps with not touching vrp_bitmap_obstack which isn't
initialized when you run the IPA bits.

>>
>> 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.
But there's no enforcement and I'd be hard pressed to believe that all
the paths through the routines you use in tree-vrp aren't going to touch
vr_value, or vrp_bitmap_obstack.  vrp_bitmap_obstack turns out to be
incredibly tangled into the implementations within tree-vrp.c :(