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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/108341] argument to `__builtin_ctz` should be
 assumed non-zero when  CTZ_DEFINED_VALUE_AT_ZERO says it is undefined
Date: Mon, 09 Jan 2023 18:49:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108341

--- Comment #5 from Andrew Macleod <amacleod at redhat dot com> ---
(In reply to Aldy Hernandez from comment #2)
> (In reply to Martin Li=C5=A1ka from comment #1)
> > May be an opportunity for Ranger?
>=20
> Hmmm... I don't think so:
>=20
>     <bb 2> :
>     value.0_1 =3D (unsigned int) value_4(D);
>     _2 =3D __builtin_ctz (value.0_1);
>     r =3D _2;
>     _3 =3D value_4(D) !=3D 0;
>     _7 =3D (int) _3;
>     return _7;
>=20
> We could add an op1_range operator to class cfn_clz to return nonzero for
> op1, but that would only work if we knew _2 to be anything...and have no
> info on _2.

Seems more like a candidate for gimpe_infer::gimple_infer (gimple *s).

THe side effect to register would be to check if 's' is a builtin_ctz and if
so, call add_nonzero (operand1) if whatever those other conditions are are
matched which make it true.

That should register a non-zero inferred range on value.0_1 after the
assignment of _2.


=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D BB 2 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Partial equiv (value.0_1 pe32 value_4(D))
    <bb 2> :
    value.0_1 =3D (unsigned int) value_4(D);
    _2 =3D __builtin_ctz (value.0_1);
    r =3D _2;
    _3 =3D value_4(D) !=3D 0;
    _7 =3D (int) _3;
    return _7;

I see ranger also registers a 32 bit equivalence between value.0_1 and valu=
e_4,
so in theory we would then be able to determine that value_4 is also non-ze=
ro
for the comparison.=