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From: "aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/24021] VRP does not work with floating points
Date: Mon, 01 Aug 2022 14:30:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D24021

--- Comment #26 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
(In reply to Andrew Macleod from comment #19)
> We can use the original testcase as the litmus test for basic support if =
we
> compile it with
>=20
> -O2  -fno-tree-fre  -fno-tree-dominator-opts
>=20
> The unroller will unroll the loop and the VRP2 pass will be presented wit=
h:
>=20
>  <bb 2> [local count: 97603129]:
>  i_1 =3D 1.1000000149011611438876201418679556809365749359130859375e-1;
>  i_17 =3D i_1 + 1.00000001490116119384765625e-1;
>  i_22 =3D i_17 + 1.00000001490116119384765625e-1;
>  i_27 =3D i_22 + 1.00000001490116119384765625e-1;
>  i_32 =3D i_27 + 1.00000001490116119384765625e-1;
>  i_37 =3D i_32 + 1.00000001490116119384765625e-1;
>  i_42 =3D i_37 + 1.00000001490116119384765625e-1;
>  i_47 =3D i_42 + 1.00000001490116119384765625e-1;
>  i_52 =3D i_47 + 1.00000001490116119384765625e-1;
>  if (i_52 =3D=3D 0.0)
>    goto <bb 4>; [50.00%]
>  else
>    goto <bb 3>; [50.00%]
>=20
>  <bb 3> [local count: 48801565]:
>=20
>  <bb 4> [local count: 97603129]:
>  # lastPoint_12 =3D PHI <i_52(2), 2.0e+0(3)>
>  return lastPoint_12;
>=20
> Which is we can track floating point ranges in VRP and simplification,
> recognize that i_52 !=3D 0.0 and VRP2 should be able to resolve this to=20
>=20
> return 2.0e+0;

Errr, just saw this.  I if we let the unroller do it's thing, we can catch =
this
at VRP2, and continue using this testcase.

And sure enough, my current work catches this:

Folding statement: i_5 =3D
1.1000000149011611438876201418679556809365749359130859375e-1;
Queued stmt for removal.  Folds to:
1.1000000149011611438876201418679556809365749359130859375e-1
Folding statement: i_17 =3D i_5 + 1.00000001490116119384765625e-1;
Queued stmt for removal.  Folds to:
2.100000029802322476513154470012523233890533447265625e-1
...
...
...
Folding statement: if (i_52 =3D=3D 0.0)
gimple_simplified to if (0 !=3D 0)
gimple_simplified to if (0 !=3D 0)
Folded into: if (0 !=3D 0)=