On 02/06/2017 01:11 AM, Richard Biener wrote:
On Sat, Feb 4, 2017 at 3:52 PM, Jeff Law <l...@redhat.com> wrote:
This is the first of a 4 part series to address the issues around 79095.
This patch addresses improvements in determining ranges of binary
expressions in three ways.
First if we are otherwise unable to find a range for the result of a
MINUS_EXPR, if we know the arguments are not equal, then we know the
resultant range is ~[0,0].
Second, for EXACT_DIV_EXPR, if the numerator has the range ~[0,0], then
resultant range is currently [TYPE_MIN/DENOM,TYPE_MAX/DENOM]. That is
rarely a useful range. A resultant range of ~[0,0] is actually more useful
since it often tells us something important about the difference of two
pointers.
Finally, when vrp2 discovers an updated range for an object that had a range
discovered by vrp1, if the new range is ~[0,0], prefer that new range in
some cases. This is needed to avoid losing the newly discovered ~[0,0]
range for EXACT_DIV_EXPR.
Bootstrapped and regression tested with the other patches in this series.
OK for the trunk?
Jeff
* tree-vrp.c (extract_range_from_binary_expr): For EXACT_DIV_EXPR,
if the numerator has the range ~[0,0] make the resultant range
~[0,0]. For MINUS_EXPR with no derived range, if the operands are
known to be not equal, then the resulting range is ~[0,0].
(intersect_ranges): In some cases prefer ~[0,0].
commit b7baf46ab62e28d2dbc22e9dcd4404926d59df18
Author: Jeff Law <l...@torsion.usersys.redhat.com>
Date: Fri Feb 3 15:45:58 2017 -0500
Improved ranges
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index b429217..3338d8b 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -3298,6 +3298,37 @@ extract_range_from_binary_expr (value_range *vr,
extract_range_from_binary_expr_1 (vr, code, expr_type, &n_vr0, &vr1);
}
+
+ /* EXACT_DIV_EXPR is typically used for pointer subtraction;
+ as a result a ~[0,0] may be better than what has already
+ been computed.
+
+ In particular if numerator has the range ~[0,0], then the
+ result range is going to be something like
+ [MININT/DIVISOR,MAXINT/DIVISOR], which is rarely useful.
+
+ So instead make the result range ~[0,0]. */
+ if (code == EXACT_DIV_EXPR
+ && TREE_CODE (op0) == SSA_NAME
+ && vr0.type == VR_ANTI_RANGE
+ && vr0.min == vr0.max
+ && integer_zerop (vr0.min))
+ set_value_range_to_nonnull (vr, TREE_TYPE (op0));
The above belongs in extract_range_from_binary_expr_1, in principle the
cases below as well (though there's pre-existing VARYING result handling).
Do you want those existing cases moved, it's easy enough to do.
The _1 ones are supposed to be the actual range computations while
the routine you patched is responsible for interfacing with a lattice. The
_1 routines can be used from code outside of VRP.
OK. Good to know.
/* Extract range information from a unary operation CODE based on
@@ -8620,6 +8651,12 @@ intersect_ranges (enum value_range_type *vr0type,
else if (vrp_val_is_min (vr1min)
&& vrp_val_is_max (vr1max))
;
+ /* Choose the anti-range if it is ~[0,0], that range is special
+ enough to special case. */
+ else if (*vr0type == VR_ANTI_RANGE
+ && *vr0min == *vr0max
+ && integer_zerop (*vr0min))
+ ;
Huh. If I spotted the place of the change correctly then we cannot arrive
here with vr0 == ~[0,0] as *vr0type is VR_RANGE. In the case covered
we'd have the only case intersecting [-1, 1] and ~[0,0] that you'd change
to ~[0,0] instead of [-1,1] which generally would be a bad choice (apart
from your implementation error as vr1 is the anti-range here).
Nope. It's in the right place. We have a ~[0,0] for vr0 and vr1 is
typically going to be [4,4] or [8.8]. Thus we're in this case:
else if ((maxeq || operand_less_p (*vr0max, vr1max) == 1)
&& (mineq || operand_less_p (vr1min, *vr0min) == 1))
{
/* ( [ ] ) or ([ ] ) or ( [ ]) */
mineq and maxeq are both false. So neither of these subcases apply:
/* Choose the right gap if the left is empty. */
if (mineq)
[ ... ]
/* Choose the left gap if the right is empty. */
else if (maxeq)
This doesn't apply either:
/* Choose the anti-range if the range is effectively varying. */
else if (vrp_val_is_min (vr1min)
&& vrp_val_is_max (vr1max))
Even if vr1 is something larger, we're almost never going to derive
anything useful from vr1 because vr0 is ~[0,0].
