On Thu, Feb 29, 2024 at 02:08:19PM +0100, Richard Biener wrote:
> > So, wouldn't it be better to outline what you have above + POLY_INT_CST
> > handling into a helper function, which similarly to get_range_pos_neg
> > returns a bitmask, but rather than 1 bit for may be [0, max] and another
> > bit for
> > may be [min, -1] you return 3 bits, 1 bit for may be [1, max], another for
> > may be [0, 0] and another for may be [min, -1]?
> > Also, I bet you actually want to handle TREE_UNSIGNED just as [0, 0]
> > and [1, max] ranges unlike get_range_pos_neg.
>
> I'm just lazy and given TYPE_OVERFLOW_WRAPS (and thus unsigned) doesn't
> ever get here and I special-case integer_zerop it doesn't really matter
> that in these cases get_range_pos_neg isn't exactly what's wanted - I'm
> asking it only for those cases where it works just fine.
Just handling integer_zerop doesn't cover the case where the chrec
operand isn't INTEGER_CST, just includes zero in its range. And I'd think
that is something quite common (sure, INTEGER_CST chrec operands are likely
more common than that) that we know that something isn't negative, or isn't
positive, or is non-negative, or is non-positive etc.
> > So perhaps
> > int ret = 7;
> > if (TYPE_UNSIGNED (TREE_TYPE (arg)))
> > ret = 3;
> > if (poly_int_tree_p (arg))
> > {
> > poly_wide_int w = wi::to_poly_wide (arg);
> > if (known_lt (w, 0))
> > return 4;
> > else if (known_eq (w, 0))
> > return 2;
> > else if (known_gt (w, 0))
> > return 1;
> > else
> > return 7;
> > }
> > value_range r;
> > if (!get_range_query (cfun)->range_of_expr (r, arg)
> > || r.undefined_p ())
> > return ret;
> > if (r.nonpositive_p ())
> > ret &= ~1;
> > if (r.nonzero_p ())
> > ret &= ~2;
> > if (r.nonnegative_p ())
> > ret &= ~4;
> > return ret;
And the above should be short/simple enough to be added even if it
just has a single user (ok, 2 in the same stmt).
Could be even just a lambda if there are no other uses for it,
so you would need to care less how to name it/where to declare etc.
> > I doubt POLY_INT_CST will appear on what the function is being called on
> > (types with scalar integral modes, mainly in .*_OVERFLOW expansion or say
> > division/modulo expansion, but maybe my imagination is limited);
> > so, if you think this is a good idea and the poly int in that case somehow
> > guarantees the existing behavior (guess for signed it would be at least when
> > not -fwrapv in action UB if the addition of the first POLY_INT_CST coeff
> > and the others multiplied by the runtime value wraps around, but for
> > unsigned is there a guarantee that if all the POLY_INT_CST coefficients
> > don't have msb set that the resulting value will not have msb set either?
>
> I hope so, but ...
Let's wait for Richard there.
Anyway, if for the chrec case it only uses it on non-wrapping signed,
then the POLY_INT_CST handling is fine in there...
Jakub
