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From: "jakub 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: Fri, 22 Mar 2024 17:41:25 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111151

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #8)
> (In reply to Richard Biener from comment #5)
> > but even when overflow is undefined we don't know whether we introduce
> > additional overflow then.  Consider MAX (INT_MIN, 0) * -1 where we comp=
ute
> > 0 * -1 (fine) but after the transform we'd do MIN (INT_MIN * -1, 0)
> > which isn't valid.
> >=20
> > And when overflow wraps consider MAX (UINT_MAX, 1) * 2 which
> > will compute UINT_MAX * 2 =3D=3D 0 while MAX (UINT_MAX * 2, 1 * 2) will=
 compute
> > 2.
> >=20
> > Unless I'm missing something.
>=20
> You're right.  So perhaps punt on this optimization for code =3D=3D MULT_=
EXPR
> altogether.

Although, even for MULT_EXPR when TYPE_OVERFLOW_UNDEFINED, if the only
problematic
cases are when one of the multiplication operand is -1 and the other is sig=
ned
minimum,
because we know one of those operands (c), we could just punt if
integer_minus_onep (c) or if c is TYPE_MIN_VALUE.=