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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110131] [12/13/14 Regression] Missed Dead
 Code Elimination when using __builtin_unreachable since r12-6924-gc2b610e7c6c
Date: Fri, 15 Sep 2023 19:51:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110131

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #8)
> With https://gcc.gnu.org/pipermail/gcc-patches/2023-September/629128.html=
 we
> get:
>   _34 =3D (int) _13;
>   _30 =3D (unsigned int) _13;
>   _22 =3D _30 =3D=3D 4294967295;
>   _35 =3D _22 ? _34 : 0;

Maybe:
(simplify
 (cond (eq (convert1?@4 @0) INTEGER_CST@1)
  (convert2? @0) INTEGER_CST@3)
  (if (type is a nop_conversion type from @1)
   (cond! @4 (convert @1) @3)))

This should give:
_30 =3D (unsigned int) _13;
_22 =3D _30 =3D=3D 4294967295;
_35 =3D _22 ? -1 : 0;
if (_35 !=3D 5)

_35 will -(convert)_22 really.
Anyways VRP will notice that _35 can't be 5 and optimize it out.=