[Bug tree-optimization/26731] Jump threading gets in the way of loops

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26731

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #5)
> In GCC 9 and above we get:
>   _2 = x_6(D) + 1;
>   _7 = (unsigned int) n_1;
>   _11 = _7 + 4294967295;
>   _15 = (int) _11;
>   _16 = n_1 > 0 ? _15 : 0;
>   x_3 = _2 + _16;
> 
> Which is okish, the loop has been removed but the above should be able to
> reduce further:
>   # RANGE [1, 2147483647] NONZERO 2147483647
>   # n_1 = PHI <a_5(D)(3), 4(2)>
>   # RANGE [-2147483647, 2147483647]
>   _2 = x_6(D) + 1;
>   # RANGE [1, 2147483647] NONZERO 2147483647
>   _7 = (unsigned int) n_1;
>   # RANGE [0, 2147483646] NONZERO 2147483647
>   _11 = _7 + 4294967295;
>   # RANGE [0, 2147483646] NONZERO 2147483647
>   _15 = (intD.9) _11;
>   # RANGE [0, 2147483646] NONZERO 2147483647
>   _16 = n_1 > 0 ? _15 : 0;
>   x_3 = _2 + _16;
> 
> The COND_EXPR should just converted into _15 but we don't ...
> VRP should have done that ....

That was fixed in GCC 13 by not have the COND_EXPR have the comparison in the
first operand (I don't have the revision offhand).

We now get at optimization:
  <bb 2> [local count: 118111600]:
  if (t_4(D) != 0)
    goto <bb 3>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 3> [local count: 59055800]:
  if (a_5(D) > 0)
    goto <bb 4>; [66.92%]
  else
    goto <bb 5>; [33.08%]

  <bb 4> [local count: 105119324]:
  # n_1 = PHI <a_5(D)(3), 4(2)>
  _2 = x_6(D) + 1;
  _11 = (unsigned int) n_1;
  _15 = _11 + 4294967295;
  _16 = (int) _15;
  x_3 = _2 + _16;

  <bb 5> [local count: 118111600]:
  # x_13 = PHI <x_3(4), x_6(D)(3)>
  return x_13;

}