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From: "aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/103690] [12 Regression] ICE: in build2, at
 tree.c:4985 with -g -O2 -fno-tree-dce -fno-tree-dse -fno-tree-fre
 --param=max-jump-thread-duplication-stmts=94 since r12-2591-g2e96b5f14e402569
Date: Thu, 16 Dec 2021 17:17:16 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103690

--- Comment #5 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> (gdb) p debug_gimple_stmt(stmt)
> _67 =3D _14 + _66;
>=20
>=20
> Before pre had:
>   intD.9 * __trans_tmp_1D.2946;
> ....
>   # RANGE [1, 9223372036854775807] NONZERO 9223372036854775804
>   _66 =3D (long unsigned intD.16) _17;
>   # PT =3D nonlocal escaped
>   # ALIGN =3D 4, MISALIGN =3D 0
>   _67 =3D __trans_tmp_1_14 + _66;
>=20
> But after:
>   # RANGE [1, 9223372036854775807] NONZERO 9223372036854775804
>   _66 =3D (long unsigned intD.16) _17;
>   # PT =3D nonlocal escaped
>   # ALIGN =3D 4, MISALIGN =3D 0
>   _67 =3D _14 + _66;
>=20
> We already removed the definition of _14 too:
> Removing dead stmt __trans_tmp_1_14 =3D _24 + 4;
>=20
> So it is the order of the removal which is causing issues.

Why is PRE removing the DEF of _14 when there are still uses?

  <bb 5> [local count: 69834]:
  __count.1_62 =3D (long unsigned int) _11;
  __builtin_memmove (_14, _9, __count.1_62);
  _66 =3D (long unsigned int) _17;
  _67 =3D _14 + _66;
...=