Aldy Hernandez <al...@redhat.com> writes:
> On 10/11/19 10:42 AM, Richard Sandiford wrote:
>> The range-tracking code has a pretty hard-coded assumption that
>> is_gimple_min_invariant is equivalent to "INTEGER_CST or invariant
>> ADDR_EXPR". It seems better to add a predicate specifically for
>> that rather than contiually fight cases in which it can't handle
>> other invariants.
>
> I was going to suggest we normalize ranges to numerics completely before
> folding. That is, replacing normalize_addresses() here:
>
> *vr = op->fold_range (expr_type,
> vr0.normalize_addresses (),
> vr1.normalize_addresses ());
>
> ...into normalize_symbolics(). But I suppose getting the gate correct
> is even better. Thanks for taking the care of this extensive and manual
> change.
>
> The patch looks good to me. However, I do wonder if VRP and
> subsidiaries can't handle non-integer invariants, if we shouldn't
> disallow them from the setters as well:
>
> void
> value_range_base::set (tree val)
> {
> gcc_assert (TREE_CODE (val) == SSA_NAME || is_gimple_min_invariant
> (val));
> if (TREE_OVERFLOW_P (val))
> val = drop_tree_overflow (val);
> set (VR_RANGE, val, val);
> }
>
> void
> value_range::set (tree val)
> {
> gcc_assert (TREE_CODE (val) == SSA_NAME || is_gimple_min_invariant
> (val));
> if (TREE_OVERFLOW_P (val))
> val = drop_tree_overflow (val);
> set (VR_RANGE, val, val, NULL);
> }
>
> This would still allow setting of VARYING and UNDEFINED, but disallow
> poly-ints, etc from a range.
>
> Was this a small oversight, or was there a reason you left those in?
Yeah, this was intentional. The patch is effectively treating
POLY_INY_CST as symbolic rather than constant. (It's really somewhere
in the middle: it's at least a function invariant, but the invariant
depends on a runtime target property.) So places like here that
can handle both symbolics and constants should be able to handle
POLY_INT_CST wihout problems. We just need to make sure that
POLY_INT_CSTs aren't treated as constants for range tracking,
because they're not "constant enough" there.
Thanks,
Richard
