On Thu, 27 Apr 2017, Richard Biener wrote:
> On April 27, 2017 4:06:48 PM GMT+02:00, "Bin.Cheng" <amker.ch...@gmail.com>
> wrote:
> >On Thu, Apr 27, 2017 at 2:49 PM, Richard Biener <rguent...@suse.de>
> >wrote:
> >>
> >> The following makes intersecting [-INF, +10] and [a + -1, +INF]
> >> to [10, a + -1] possible with the chance that for a <= 10 the
> >> resulting range will be empty (but not trivially visible as so).
> >Hi,
> >I noticed operand_less_p is quite simple, so does
> >fold_binary_to_constant take range information into consideration? In
> >this case, it is a's range information to be considered. Otherwise it
> >can't tell between "a + -1" and 10.
>
> I think we can get away without knowing
> Given the constraints on the other ends of the ranges. So it's really just a
> special case that came up with testing another patch.
So actually the patch causes [k_3(D), +INF] intersected with
[10, +INF] to become [k_3(D), +INF]. That's not a win IMHO.
Thus retracted for now.
Richard.
> Richard.
>
> It is good to have [10, a+-1] in
> >this case if we can do it (by using compare_values or similar
> >interface), but I remember there are quite lots of fallouts in
> >handling symbolic ranges, which could result in worse range
> >information overall in the end. It is PR71437 when I found out this
> >in VRP. I had some patches improving symbolic range handling, but
> >gave up last time because keep running into new cases.
> >
> >Thanks,
> >bin
> >>
> >> Bootstrap / regtest running on x86_64-unknown-linux-gnu.
> >>
> >> I'll add a testcase later.
> >>
> >> Richard.
> >>
> >> 2017-04-27 Richard Biener <rguent...@suse.de>
> >>
> >> * tree-vrp.c (intersect_ranges): Better handle partly
> >> symbolic ranges.
> >>
> >> Index: gcc/tree-vrp.c
> >> ===================================================================
> >> --- gcc/tree-vrp.c (revision 247334)
> >> +++ gcc/tree-vrp.c (working copy)
> >> @@ -8989,6 +8989,28 @@ intersect_ranges (enum value_range_type
> >> else
> >> gcc_unreachable ();
> >> }
> >> + else if (operand_less_p (*vr0min, vr1max) == 1
> >> + && operand_less_p (*vr0min, vr1min) == 1
> >> + && operand_less_p (*vr0max, vr1max) == 1
> >> + && operand_less_p (vr1min, *vr0max) == -2)
> >> + {
> >> + /* [ (] ) with ] and ( being unordered as (partly) symbolic.
> >> + This can result in ranges that are effectively empty. */
> >> + if (*vr0type == VR_RANGE
> >> + && vr1type == VR_RANGE)
> >> + *vr0min = vr1min;
> >> + }
> >> + else if (operand_less_p (vr1min, *vr0max) == 1
> >> + && operand_less_p (vr1min, *vr0min) == 1
> >> + && operand_less_p (vr1max, *vr0max) == 1
> >> + && operand_less_p (*vr0min, vr1max) == -2)
> >> + {
> >> + /* ( [) ] with ] and ( being unordered as (partly) symbolic.
> >> + This can result in ranges that are effectively empty. */
> >> + if (*vr0type == VR_RANGE
> >> + && vr1type == VR_RANGE)
> >> + *vr0max = vr1max;
> >> + }
> >>
> >> /* As a fallback simply use { *VRTYPE, *VR0MIN, *VR0MAX } as
> >> result for the intersection. That's always a conservative
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
