On Mon, Sep 19, 2022 at 10:14 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Mon, Sep 19, 2022 at 9:59 AM Aldy Hernandez <aldyh@redhat.com> wrote:
> >
> > ISTM that a specifically nonnegative range should not contain -NAN,
> > otherwise signbit_p() would return false, because we'd be unsure of the
> > sign.
> >
> > Do y'all agree?
>
> what tree_expr_nonnegative_p actually means isn't 100% clear.  For REAL_CST
> it actually looks at the sign-bit but we have
>
> (simplify
>  /* copysign(x,y) -> fabs(x) if y is nonnegative.  */
>  (COPYSIGN_ALL @0 tree_expr_nonnegative_p@1)
>  (abs @0))
>
> is abs (@0) OK for sNaNs and -NaN/+NaN?

At least for real_value's, ABS_EXPR works on NAN's.  There's no
special code dealing with them.  We just clear the sign bit:

real_arithmetic:
    case ABS_EXPR:
      *r = *op0;
      r->sign = 0;
      break;

>
> And we have
>
> /* Convert abs[u] (X)  where X is nonnegative -> (X).  */
> (simplify
>  (abs tree_expr_nonnegative_p@0)
>  @0)
>
> where at least sNaN -> qNaN would be dropped?
>
> And of course
>
> (simplify
>  /* signbit(x) -> 0 if x is nonnegative.  */
>  (SIGNBIT tree_expr_nonnegative_p@0)
>  { integer_zero_node; })
>
> that is, is tree_expr_nonnegative_p actually tree_expr_sign or
> does tree_expr_nonnegative (x) mean x >= (typeof(X)) 0
> or !(x < (typeof(X))0)?

I have no idea, but I'm happy to have frange::set_nonnegative() do
whatever you agree on.

Actually TBH, ranger only uses set_nonnegative for call's, not much else:

  if (range_of_builtin_call (r, call, src))
    ;
  else if (gimple_stmt_nonnegative_warnv_p (call, &strict_overflow_p))
    r.set_nonnegative (type);
  else if (gimple_call_nonnull_result_p (call)
       || gimple_call_nonnull_arg (call))
    r.set_nonzero (type);
  else
    r.set_varying (type);

but I guess it's good we do the right thing for correctness sake, and
if it ever gets used by someone else.

>
> That said, 'set_nonnegative' could be interpreted to be without
> NaNs?

Sounds good to me.  How's this?

Aldy