On October 31, 2017 10:49:51 AM GMT+01:00, Kugan Vivekanandarajah <[email protected]> wrote: >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.
At some point I wanted to isolate those functions not relying on global state but I never came to do this. Those are the building blocks alternative range propagation stuff like Andrew's could use. With C++ using a namespace like wide_int does would work I guess. And yes, equivalences are ugly... Ideally we'd have a base value-range class without them used by IPA and VRP (non-early) would use a derived class. Richard. Richard. >Thanks, >Kugan
