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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102381] unexpected -Wmaybe-uninitialized
Date: Fri, 17 Sep 2021 04:00:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102381

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-09-17

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

....

[AFTER NORMALIZATION -- [DEF]:
ipp_28 =3D PHI <ipp_23(17), ipp_11(D)(15)>
is guarded by :

i2.2_26 > 0 (.AND.) i1_10(D) !=3D 0

....

[AFTER NORMALIZATION -- [USE]:
ipp_27 =3D PHI <ipp_28(21), ipp_23(18)>
is guarded by :

i1_10(D) !=3D 0 (.AND.)  (.NOT.) i4_17 < prephitmp_25 (.AND.) _2 =3D=3D 0
(.OR.)
i1_10(D) !=3D 0 (.AND.)  (.NOT.) i4_17 < prephitmp_25 (.AND.) i3.0_1 & 1

...
  _2 =3D i3.0_1 & 1;

So there is a missing simplification
It should have been:

i1_10(D) !=3D 0 (.AND.)  (.NOT.) i4_17 < prephitmp_25

prephitmp_25 is defined as:
  # prephitmp_25 =3D PHI <i2.2_26(17), i2.2_21(15)>
So i2.2_26 (as i2.2_21 is the one on the branch which would have been
uninitialized).
So we are down to:
i1_10(D) !=3D 0 (.AND.)  (.NOT.) i4_17 < i2.2_26

i4_17 is the loop IV so it should be discarded.=