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From: "aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/96564] [11/12/13/14/15 Regression] New maybe use of
 uninitialized variable warning since r11-959
Date: Thu, 16 May 2024 14:27:52 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96564

--- Comment #19 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #17)
> Handling pointer-vs-pointer in ptrs_compare_unequal isn't enough since we
> have
>=20
>   # PT =3D nonlocal null
>   unsigned int * x_7(D) =3D x;
> ...
>   # PT =3D null { D.2785 }
>   a_9 =3D malloc (_2);
>   if (a_9 =3D=3D 0B)=20
>     goto <bb 7>; [0.04%]
>   else
>     goto <bb 3>; [99.96%]
>=20
>   <bb 7> [local count: 429496]:
>   goto <bb 6>; [100.00%]
>=20
>   <bb 3> [local count: 1073312328]:
>   if (x_7(D) !=3D a_9)
>=20
> so querying points-to only has to consider both pointers being NULL.  Now,
> I'm not sure how prange handles the above and whether or how it integrates
> knowledge from flow-insensitive points-to analysis.

prange currently does nothing different than what irange did.  It's a first
step in providing points-to and propagating the information through the CFG
like we do for integer ranges.  Or more precisely, prange is meant to be
nothing more than a pair of integer end points (not unlimited like
int_range_max), plus a value/mask pair.

>=20
> Aldy might know.
>=20
> I'm testing a patch enhancing ptrs_compare_unequal right now, also filling
> in a missing bit in points-to info.=