This patch enhances processing of OP_MINUS to show how we can utilize
relations between op1 and op2 to produce a better result. Given:
a_3 = b_4 - d_1
if we know b_4 > d_1, on top of whatever other range calculations we can
do with the actual ranges, we can apply the knowledge that the result
must also be in the range [1, +INF] as well.
likewise, if we know b_4 == d_1, we know the result is [0,0]
This provide a sample of how applying a relation between 2 operands is
implemented.
Bootstraps on x86_64-pc-linux-gnu with no regressions. Pushed.
Andrew
>From ae6b830f31a47aca7ca24c4fea245c29214eef3a Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <amacl...@redhat.com>
Date: Thu, 17 Jun 2021 13:38:03 -0400
Subject: [PATCH 5/7] Add relation effects between operands to MINUS_EXPR.
* range-op.cc (operator_minus::op1_op2_relation_effect): New.
---
gcc/range-op.cc | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)
diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index a7698f21b0d..ec4816d69fa 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -1279,6 +1279,11 @@ public:
const wide_int &lh_ub,
const wide_int &rh_lb,
const wide_int &rh_ub) const;
+ virtual bool op1_op2_relation_effect (irange &lhs_range,
+ tree type,
+ const irange &op1_range,
+ const irange &op2_range,
+ relation_kind rel) const;
} op_minus;
void
@@ -1293,6 +1298,45 @@ operator_minus::wi_fold (irange &r, tree type,
value_range_with_overflow (r, type, new_lb, new_ub, ov_lb, ov_ub);
}
+// Check to see if the relation REL between OP1 and OP2 has any effect on the
+// LHS of the epxression. If so, apply it to LHS_RANGE.
+
+bool
+operator_minus::op1_op2_relation_effect (irange &lhs_range, tree type,
+ const irange &op1_range ATTRIBUTE_UNUSED,
+ const irange &op2_range ATTRIBUTE_UNUSED,
+ relation_kind rel) const
+{
+ if (rel == VREL_NONE)
+ return false;
+
+ int_range<2> rel_range;
+ unsigned prec = TYPE_PRECISION (type);
+ signop sgn = TYPE_SIGN (type);
+
+ switch (rel)
+ {
+ // op1 > op2, op1 - op2 can be restricted to [1, max]
+ case GT_EXPR:
+ rel_range = int_range<2> (type, wi::one (prec),
+ wi::max_value (prec, sgn));
+ break;
+ // op1 >= op2, op1 - op2 can be restricted to [0, max]
+ case GE_EXPR:
+ rel_range = int_range<2> (type, wi::zero (prec),
+ wi::max_value (prec, sgn));
+ break;
+ // op1 == op2, op1 - op2 can be restricted to [0, 0]
+ case EQ_EXPR:
+ rel_range = int_range<2> (type, wi::zero (prec), wi::zero (prec));
+ break;
+ default:
+ return false;
+ }
+ lhs_range.intersect (rel_range);
+ return true;
+}
+
bool
operator_minus::op1_range (irange &r, tree type,
const irange &lhs,
--
2.17.2
