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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113119] ICE: verify_ssa failed: definition in
 block 18 does not dominate use in block 4 at -O1 with _BitInt
Date: Fri, 22 Dec 2023 21:04:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113119

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Without the second redundant __builtin_add_overflow, we get
  a.0_1 =3D a;
  _7 =3D .ADD_OVERFLOW (a.0_1, 0);
  _2 =3D REALPART_EXPR <_7>;
  _3 =3D IMAGPART_EXPR <_7>;
  _4 =3D (_Bool) _3;
  c =3D _4;
  _5 =3D (_BitInt(8)) _2;
  b =3D _5;
before bitint lowering and lower it well, but the redundant call results in
  a.0_1 =3D a;
  _7 =3D .ADD_OVERFLOW (a.0_1, 0);
  _2 =3D IMAGPART_EXPR <_7>;
  _3 =3D (_Bool) _2;
  c =3D _3;
  _4 =3D REALPART_EXPR <_7>;
  _5 =3D (_BitInt(8)) _4;
  b =3D _5;
and optimizable_arith_overflow doesn't flag that as non-optimizable, so
the bitint lowering of .ADD_OVERFLOW happens in that case on the REALPART_E=
XPR
stmt.
optimizable_arith_overflow checks if both REALPART_EXPR and IMAGPART_EXPR
appear in the same bb (and that there are no other uses), but doesn't check
that REALPART_EXPR is first.  Either it should check that or perhaps allow =
it
first but require that it is not used in statements before the REALPART_EXP=
R.=