[Bug tree-optimization/24021] VRP does not work with floating points

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=24021

--- 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
> 
> -O2  -fno-tree-fre  -fno-tree-dominator-opts
> 
> The unroller will unroll the loop and the VRP2 pass will be presented with:
> 
>  <bb 2> [local count: 97603129]:
>  i_1 = 1.1000000149011611438876201418679556809365749359130859375e-1;
>  i_17 = i_1 + 1.00000001490116119384765625e-1;
>  i_22 = i_17 + 1.00000001490116119384765625e-1;
>  i_27 = i_22 + 1.00000001490116119384765625e-1;
>  i_32 = i_27 + 1.00000001490116119384765625e-1;
>  i_37 = i_32 + 1.00000001490116119384765625e-1;
>  i_42 = i_37 + 1.00000001490116119384765625e-1;
>  i_47 = i_42 + 1.00000001490116119384765625e-1;
>  i_52 = i_47 + 1.00000001490116119384765625e-1;
>  if (i_52 == 0.0)
>    goto <bb 4>; [50.00%]
>  else
>    goto <bb 3>; [50.00%]
> 
>  <bb 3> [local count: 48801565]:
> 
>  <bb 4> [local count: 97603129]:
>  # lastPoint_12 = PHI <i_52(2), 2.0e+0(3)>
>  return lastPoint_12;
> 
> Which is we can track floating point ranges in VRP and simplification,
> recognize that i_52 != 0.0 and VRP2 should be able to resolve this to 
> 
> 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 =
1.1000000149011611438876201418679556809365749359130859375e-1;
Queued stmt for removal.  Folds to:
1.1000000149011611438876201418679556809365749359130859375e-1
Folding statement: i_17 = i_5 + 1.00000001490116119384765625e-1;
Queued stmt for removal.  Folds to:
2.100000029802322476513154470012523233890533447265625e-1
...
...
...
Folding statement: if (i_52 == 0.0)
gimple_simplified to if (0 != 0)
gimple_simplified to if (0 != 0)
Folded into: if (0 != 0)