On 11/17/20 11:01 PM, Andrew MacLeod wrote:
PR 91029 observes when
a % b > 0 && b >= 0,
then a has an implied range of a >=0. likewise
Shouldn't that be && b > 0? b == 0 is undefined.
a % b < 0 implies a range of a <= 0.
This patch is a good example of how range-ops can be leveraged to solve
problems. It simply implements operator_trunc_mod::op1_range() to solve
for 'A' when the LHS and 'b' are known to be within the specified
ranges. I also added a a test case to show folding of conditions
based on that.
Bootstrapped on x86_64-pc-linux-gnu, no regressions. pushed.
Andrew
diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index d0adc95527a..f37796cac70 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -2634,6 +2634,9 @@ public:
const wide_int &lh_ub,
const wide_int &rh_lb,
const wide_int &rh_ub) const;
+ virtual bool op1_range (irange &r, tree type,
+ const irange &lhs,
+ const irange &op2) const;
} op_trunc_mod;
void
@@ -2680,6 +2683,31 @@ operator_trunc_mod::wi_fold (irange &r, tree type,
value_range_with_overflow (r, type, new_lb, new_ub);
}
+bool
+operator_trunc_mod::op1_range (irange &r, tree type,
+ const irange &lhs,
+ const irange &op2) const
+{
+ // PR 91029. Check for signed truncation with op2 >= 0.
+ if (TYPE_SIGN (type) == SIGNED && wi::ge_p (op2.lower_bound (), 0, SIGNED))
+ {
+ unsigned prec = TYPE_PRECISION (type);
+ // if a & b >=0 , then a >= 0.
Shouldn't comment be %, not & ??.
+ if (wi::ge_p (lhs.lower_bound (), 0, SIGNED))
+ {
+ r = value_range (type, wi::zero (prec), wi::max_value (prec, SIGNED));
+ return true;
+ }
+ // if a & b < 0 , then a <= 0.
Similarly here.
+ if (wi::lt_p (lhs.upper_bound (), 0, SIGNED))
+ {
+ r = value_range (type, wi::min_value (prec, SIGNED), wi::zero (prec));
+ return true;
+ }
+ }
+ return false;
+}
+
Thanks for doing this BTW.
Aldy
