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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/111151] [12/13/14 Regression] Wrong code at -O0 on
 x86_64-pc-linux-gnu
Date: Mon, 25 Mar 2024 07:23:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111151

--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #11)
> Perhaps
> --- fold-const.cc.jj8	2024-03-11 22:37:29.000000000 +0100
> +++ fold-const.cc	2024-03-22 19:31:44.189686120 +0100
> @@ -7104,6 +7104,27 @@ extract_muldiv_1 (tree t, tree c, enum t
>        if (TYPE_UNSIGNED (ctype) !=3D TYPE_UNSIGNED (type))
>  	break;
>=20=20
> +      /* Punt for multiplication altogether.
> +	 MAX (1U + INT_MAX, 1U) * 2U is not equivalent to
> +	 MAX ((1U + INT_MAX) * 2U, 1U * 2U), the former is
> +	 0U, the latter is 2U.
> +	 MAX (INT_MIN / 2, 0) * -2 is not equivalent to
> +	 MIN (INT_MIN / 2 * -2, 0 * -2), the former is
> +	 well defined 0, the latter invokes UB.
> +	 MAX (INT_MIN / 2, 5) * 5 is not equivalent to
> +	 MAX (INT_MIN / 2 * 5, 5 * 5), the former is
> +	 well defined 25, the latter invokes UB.  */
> +      if (code =3D=3D MULT_EXPR)
> +	break;
> +      /* For division/modulo, punt on c being -1 for MAX, as
> +	 MAX (INT_MIN, 0) / -1 is not equivalent to
> +	 MIN (INT_MIN / -1, 0 / -1), the former is well defined
> +	 0, the latter invokes UB (or for -fwrapv is INT_MIN).
> +	 MIN (INT_MIN, 0) / -1 already invokes UB, so the
> +	 transformation won't make it worse.  */
> +      else if (tcode =3D=3D MAX_EXPR && integer_minus_onep (c))
> +	break;
> +
>        /* MIN (a, b) / 5 -> MIN (a / 5, b / 5)  */
>        sub_strict_overflow_p =3D false;
>        if ((t1 =3D extract_muldiv (op0, c, code, wide_type,
> ?

I think that looks reasonable.=