It seems most of the remaining anti range code in
extract_range_from_unary_expr for CONVERT_EXPR_P is actually dealing
with non-nullness in practice.
Anti-range handling is mostly handled by canonicalizing anti-ranges into
its two set constituents (~[10,20] => [MIN,9] U [21,MAX]) and dealing
with them piece-meal. For that matter, the only way we can reach the
conversion code in extract_range_from_unary_expr with an anti-range is
either with a pointer (because pointers are ignored from
ranges_from_anti_range on purpose), or when converting integers of the
form ~[SSA, SSA]. I verified this with a bootstrap + tests with some
specially placed asserts, BTW.
So... if we special handle pointer conversions (both to and fro, as
opposed to just to), we get rid of any anti-ranges with the exception of
~[SSA, SSA] between integers. And anti-ranges of unknown quantities
(SSAs) will be handled automatically already (courtesy of
extract_range_into_wide_ints).
I propose we handle pointers at the beginning, and everything else just
falls into place, with no special code.
As commented in the code, this will pessimize conversions from (char
*)~[0, 2] to int, because we will forget that the range can also not be
1 or 2. But as Jeff commented, we really only care about null or
non-nullness. Special handling magic pointers with constants IMO is a
wasted effort. For that matter, I think it was me that added this
spaghetti a few weeks ago to make sure we handled ~[0,2]. We weren't
even handling it a short while back :-). Furthermore, in a bootstrap, I
think we only triggered this twice. And I'm not even sure we make
further use of anything null/not-null for pointers later on.
This patch simplifies the code, and removes more special handling and
cryptic comments related to anti-ranges.
Tested with all languages including Ada and Go.
OK for trunk?
commit 10406735080ebba81f31b9e7b36247446e07fb69
Author: Aldy Hernandez <al...@redhat.com>
Date: Mon Sep 17 11:05:57 2018 +0200
* tree-vrp.c (extract_range_from_unary_expr): Special case all
pointer conversions.
Do not do anything special for anti-ranges.
diff --git a/gcc/tree-vrp.c b/gcc/tree-vrp.c
index 622ccbc2df7..3e12d1d9bda 100644
--- a/gcc/tree-vrp.c
+++ b/gcc/tree-vrp.c
@@ -1842,9 +1842,14 @@ extract_range_from_unary_expr (value_range *vr,
tree inner_type = op0_type;
tree outer_type = type;
- /* If the expression evaluates to a pointer, we are only interested in
- determining if it evaluates to NULL [0, 0] or non-NULL (~[0, 0]). */
- if (POINTER_TYPE_P (type))
+ /* If the expression involves a pointer, we are only interested in
+ determining if it evaluates to NULL [0, 0] or non-NULL (~[0, 0]).
+
+ This may lose precision when converting (char *)~[0,2] to
+ int, because we'll forget that the pointer can also not be 1
+ or 2. In practice we don't care, as this is some idiot
+ storing a magic constant to a pointer. */
+ if (POINTER_TYPE_P (type) || POINTER_TYPE_P (op0_type))
{
if (!range_includes_zero_p (&vr0))
set_value_range_to_nonnull (vr, type);
@@ -1855,15 +1860,12 @@ extract_range_from_unary_expr (value_range *vr,
return;
}
- /* We normalize everything to a VR_RANGE, but for constant
- anti-ranges we must handle them by leaving the final result
- as an anti range. This allows us to convert things like
- ~[0,5] seamlessly. */
- value_range_type vr_type = VR_RANGE;
- if (vr0.type == VR_ANTI_RANGE
- && TREE_CODE (vr0.min) == INTEGER_CST
- && TREE_CODE (vr0.max) == INTEGER_CST)
- vr_type = VR_ANTI_RANGE;
+ /* The POINTER_TYPE_P code above will have dealt with all
+ pointer anti-ranges. Any remaining anti-ranges at this point
+ will be integer conversions from SSA names that will be
+ normalized into VARYING. For instance: ~[x_55, x_55]. */
+ gcc_assert (vr0.type != VR_ANTI_RANGE
+ || TREE_CODE (vr0.min) != INTEGER_CST);
/* NOTES: Previously we were returning VARYING for all symbolics, but
we can do better by treating them as [-MIN, +MAX]. For
@@ -1886,7 +1888,7 @@ extract_range_from_unary_expr (value_range *vr,
{
tree min = wide_int_to_tree (outer_type, wmin);
tree max = wide_int_to_tree (outer_type, wmax);
- set_and_canonicalize_value_range (vr, vr_type, min, max, NULL);
+ set_and_canonicalize_value_range (vr, VR_RANGE, min, max, NULL);
}
else
set_value_range_to_varying (vr);
