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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/98028] [8/9/10/11 Regression]
 __builtin_sub_overflow_p not folded to const when some constraints are known
Date: Thu, 14 Jan 2021 14:23:41 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98028

--- Comment #2 from Andrew Macleod <amacleod at redhat dot com> ---
I see
=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
    <bb 2> :
    if (j_3(D) > i_4(D))
      goto <bb 3>; [INV]
    else
      goto <bb 4>; [INV]
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D BB 3 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
    <bb 3> :
    __builtin_unreachable ();
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D BB 4 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
j_3(D)  unsigned int VARYING
i_4(D)  unsigned int VARYING
    <bb 4> :
    _5 =3D .SUB_OVERFLOW (i_4(D), j_3(D));
    _1 =3D IMAGPART_EXPR <_5>;
    _2 =3D (_Bool) _1;
    _8 =3D _1;
    return _8;

gimple_range_adjustment currently recognizes the SUB_OVERFLOW/IMAGPART_EXPR
pattern and marks _1 as having range [0,1].

Once we can query if i_4 >=3D j_3, it should be pretty straightforward to c=
hange
the range of _1 to [0,0] or [1,1] as appropriate, which should then propaga=
te
to the return.=