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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/100162] missed optimization for dead code
 elimination at -O3 (vs. -O2)
Date: Fri, 05 May 2023 10:16:56 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100162

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> FRE is no longer able to optimize _7 to 2 in GCC 13+:
>   c[0][b.1_1] =3D 2;
>   c[1][b.1_1] =3D 2;
>   c[2][b.1_1] =3D 2;
>   c[3][b.1_1] =3D 2;
>   c[4][b.1_1] =3D 2;
>   a =3D 5;
>   _5 =3D b.1_1 !=3D 0;
>   _6 =3D (int) _5;
>   _7 =3D c[0][0];

That's PR108355.  The "magic" special-casing of single element arrays went
away (or rather now triggers more unreliably).=