Hi Jeff,
On 31 October 2017 at 14:47, Jeff Law <[email protected]> wrote:
> On 10/29/2017 03:54 PM, Kugan Vivekanandarajah wrote:
>> Hi Jeff,
>>
>> On 28 October 2017 at 18:28, Jeff Law <[email protected]> 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 :(
>
I looked into the usage and it does seem to be not using vr_value
unless I am missing something. There are two overloaded functions
here:
extract_range_from_unary_expr (value_range *vr,
enum tree_code code, tree type,
value_range *vr0_, tree op0_type)
is safe as this works with value_range and does not use
get_value_range to access vr_value.
extract_range_from_unary_expr (value_range *vr, enum tree_code code,
tree type, tree op0)
This is not safe as this takes tree as an argument and gets
value_range by calling get_value_range. May be we should change the
names to reflect this.
Thanks,
Kugan
