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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/104526] [12 Regression] Dead Code Elimination
 Regression at -O3 (trunk vs. 11.2.0)
Date: Mon, 14 Feb 2022 22:14:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104526

--- Comment #3 from Andrew Macleod <amacleod at redhat dot com> ---
(In reply to Jakub Jelinek from comment #2)

> and evrp properly figured out those ranges, that 1 / int is [-1, 1] and
> that 2 >> [-1, 1] is [1, 2].
> But since r12-6924 the IL is:
>   c.0_1 =3D c;
>   _2 =3D *c.0_1;
>   _11 =3D (unsigned int) _2;
>   _12 =3D _11 + 1;
>   _13 =3D _12 <=3D 2;
>   _3 =3D _12 <=3D 2 ? _2 : 0;

> So, Andrew/Aldy, how hard would it be to improve ranger COND_EXPR handlin=
g,
> so that it essentially does what we do for the PHI cases?  I.e. from the
> COND_EXPR condition, compute "assertion" if condition is true or if
> condition is false, and use that on the COND_EXPR's second and third
> argument.
> So for the
>   _3 =3D _12 <=3D 2 ? _2 : 0;
> comparison, for second argument the condition must be true which implies =
that
> _2 must be there [-1, 1], while for the third argument the condition must=
 be
> false, but the argument is constant 0, so range is [0, 0], then just union
> those 2 ranges.
>=20
> As this is a P1 regression, if we can fix it, would be nice to get it into
> GCC 12.

I'm having a look. The bits are all there. Most of gori is stmt oriented, b=
ut I
may be able to invoke the components such that we evaluate the 2nd and 3rd
arguemnts as if they were on true/false edges to improve the results..=