On Dec 19, 2018, Alexandre Oliva <aol...@redhat.com> wrote:
> + op1 = x;
> + code = (code == LT_EXPR || code == LE_EXPR) ? LE_EXPR : GT_EXPR;
So... I've done some more testing, and this alone seems to overlap
nicely with what's in the trunk ATM, with a few exceptions:
- for some reason, LE/GT do not get us some simplifications that EQ/NE
do when x is zero, despite the unsigned type for op0, that ought to
make them equivalent. That could probably be improved elsewhere, but
it's easy enough to remedy with:
if (integer_zerop (x))
code = (code == LT_EXPR || code == LE_EXPR) ? EQ_EXPR : NE_EXPR;
else
code = (code == LT_EXPR || code == LE_EXPR) ? LE_EXPR : GT_EXPR;
- other differences I observed involved other case we currently
transform to equality, namely, if x is (u)max-1, we test op1 against
zero. The transformation quoted above does better than this in at
least 3 situations: a selftest in vec.c, cp_genericize_r in
cp/cp-gimplify.c, and cp_maybe_mangle_decomp in cp/decl.c. In these
cases, op0 has a known range from 0 to INT_MAX or INT_MAX-1, so a
compare of op0 vs 2u*INT_MAX can be folded to a constant, but the
compare of op1 vs 0 we currently use cannot.
- the fact that in some cases a test against one of the overflow-related
variables can be optimized when a test against the other can't
surprised me; I would have expected the ranges and equivalences and
whatnot to be such that this would never happen, but it does. It
suggests we could get some additional folding out of trying op1 vs
max-x when op0 vs x fails to resolve to a constant.
FTR, here's the patchlet (-b) I've used to look for differences.
commit 2fe0b2784815882c3e2821b171979b54c3ffdc55
Author: Alexandre Oliva <aol...@redhat.com>
Date: Sat Dec 29 00:21:42 2018 -0200
[PR86153/83239] identify vrp overflow simplification differences to
investigate
diff --git a/gcc/vr-values.c b/gcc/vr-values.c
index d71a703ab550..a40c41e4d139 100644
--- a/gcc/vr-values.c
+++ b/gcc/vr-values.c
@@ -2296,7 +2296,6 @@ vr_values::vrp_evaluate_conditional_warnv_with_ops (enum
tree_code code,
bool *strict_overflow_p,
bool *only_ranges)
{
- tree ret;
if (only_ranges)
*only_ranges = true;
@@ -2316,6 +2315,40 @@ vr_values::vrp_evaluate_conditional_warnv_with_ops (enum
tree_code code,
tree x;
if (overflow_comparison_p (code, op0, op1, use_equiv_p, &x))
{
+ tree ret1 = ovrflow_vrp_evaluate_conditional_warnv_with_ops (code, op0,
op1, x,
+ use_equiv_p,
+
strict_overflow_p,
+ only_ranges);
+
+ op1 = x;
+ if (integer_zerop (x))
+ code = (code == LT_EXPR || code == LE_EXPR) ? EQ_EXPR : NE_EXPR;
+ else
+ code = (code == LT_EXPR || code == LE_EXPR) ? LE_EXPR : GT_EXPR;
+
+ tree ret2 = rest_of_vrp_evaluate_conditional_warnv_with_ops (code, op0,
op1,
+ use_equiv_p,
+
strict_overflow_p,
+ only_ranges);
+ gcc_assert (ret1 == ret2
+ || (ret1 && ret2 && operand_equal_p (ret1, ret2, 0)));
+
+ return ret2;
+ }
+ else
+ return rest_of_vrp_evaluate_conditional_warnv_with_ops (code, op0, op1,
+ use_equiv_p,
+ strict_overflow_p,
+ only_ranges);
+}
+
+tree vr_values::
+ovrflow_vrp_evaluate_conditional_warnv_with_ops (enum tree_code code,
+ tree op0, tree op1, tree x,
+ bool use_equiv_p,
+ bool *strict_overflow_p,
+ bool *only_ranges)
+{
wide_int max = wi::max_value (TYPE_PRECISION (TREE_TYPE (op0)), UNSIGNED);
/* B = A - 1; if (A < B) -> B = A - 1; if (A == 0)
B = A - 1; if (A > B) -> B = A - 1; if (A != 0)
@@ -2369,7 +2402,21 @@ vr_values::vrp_evaluate_conditional_warnv_with_ops (enum
tree_code code,
if (vri.undefined_p ())
return boolean_true_node;
}
- }
+
+ return rest_of_vrp_evaluate_conditional_warnv_with_ops (code, op0, op1,
+ use_equiv_p,
+ strict_overflow_p,
+ only_ranges);
+}
+
+tree vr_values::
+rest_of_vrp_evaluate_conditional_warnv_with_ops (enum tree_code code,
+ tree op0, tree op1,
+ bool use_equiv_p,
+ bool *strict_overflow_p,
+ bool *only_ranges)
+{
+ tree ret;
if ((ret = vrp_evaluate_conditional_warnv_with_ops_using_ranges
(code, op0, op1, strict_overflow_p)))
diff --git a/gcc/vr-values.h b/gcc/vr-values.h
index 6785cb68fa76..e30719e82599 100644
--- a/gcc/vr-values.h
+++ b/gcc/vr-values.h
@@ -85,6 +85,17 @@ class vr_values
tree vrp_evaluate_conditional_warnv_with_ops (enum tree_code,
tree, tree, bool,
bool *, bool *);
+ tree rest_of_vrp_evaluate_conditional_warnv_with_ops (enum tree_code code,
+ tree op0, tree op1,
+ bool use_equiv_p,
+ bool *strict_overflow_p,
+ bool *only_ranges);
+ tree ovrflow_vrp_evaluate_conditional_warnv_with_ops (enum tree_code code,
+ tree op0, tree op1,
tree x,
+ bool use_equiv_p,
+ bool *strict_overflow_p,
+ bool *only_ranges);
+
void extract_range_from_assignment (value_range *, gassign *);
void extract_range_from_assert (value_range *, tree);
void extract_range_from_ssa_name (value_range *, tree);
--
Alexandre Oliva, freedom fighter https://FSFLA.org/blogs/lxo
Be the change, be Free! FSF Latin America board member
GNU Toolchain Engineer Free Software Evangelist
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