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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/104356] [12 Regression] divide by zero trap
 incorrectly optimized away
Date: Fri, 04 Feb 2022 07:08:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104356

--- Comment #40 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 3 Feb 2022, amacleod at redhat dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104356
>=20
> --- Comment #37 from Andrew Macleod <amacleod at redhat dot com> ---
> (In reply to Jakub Jelinek from comment #35)
> > I meant something like:
> >   return Z / X;
>=20
> > and there evrp does with -O2 -gnatp optimize away the division.
> > Though that is likely the X / boolean_range_Y case which you've disable=
d.
> > In any case, I think you want to hear from Andrew/Aldy where exactly do=
es
> > VRP/ranger assume UB on integer division by zero.
>=20
> That divide is remove by the simplifier because it determines that X has a
> range of [0,1] and I believe the simplifer chooses to ignore the 0 under
> various circumstances.
>=20
> As for ranger, range-ops will return UNDEFINED for the range if x is know=
n to
> be [0,0].  This can be propagated around, and depending on how it ends up=
 being
> used as to what happens with it.=20

I think that's OK as outgoing range (on the non-exceptional path - on the
exeptional path the result isn't computed).  That just may not be used
to simplify the stmt producing the range itself of course.=