| Message ID | e6e36e5c-0f4f-5edf-a4f1-2dea74bfedd7@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | recognize implied ranges for modulo. | expand |
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
On 11/18/20 3:35 AM, Aldy Hernandez wrote: > > > 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. > > If you were folding, sure, but I think its OK for equation solving.. whats important is that b is not negative. I can easily imagine having a positive LHS and an unknown unsigned value for b.. we could still conclude that 'a' is positive even though 0 is in the "possible ranges" for 'b' Andrew
commit 1e27e7a582a9b86bcf86f5c103cd947672746e97
Author: Andrew MacLeod <amacleod@redhat.com>
Date: Tue Nov 17 14:47:58 2020 -0500
recognize implied ranges for modulo.
implement op1_range for modulo with implied positive and negative ranges.
gcc/
PR tree-optimization/91029
* range-op.cc (operator_trunc_mod::op1_range): New.
gcc/testsuite/
* gcc.dg/pr91029.c: New.
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.
+ 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.
+ 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;
+}
+
class operator_logical_not : public range_operator
{
diff --git a/gcc/testsuite/gcc.dg/pr91029.c b/gcc/testsuite/gcc.dg/pr91029.c
new file mode 100644
index 00000000000..8a4134c5d96
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr91029.c
@@ -0,0 +1,47 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-evrp" } */
+
+void kill (void);
+int xx;
+
+void f1 (int i)
+{
+ if ((i % 7) == 3)
+ {
+ xx = (i < 0);
+ if (xx)
+ kill ();
+ }
+}
+
+void f2 (int i)
+{
+ if ((i % 7) >= 0)
+ {
+ xx = (i < 0);
+ if (xx)
+ kill ();
+ }
+}
+
+void f3 (int i)
+{
+ if ((i % 7) == -3)
+ {
+ xx = (i > 0);
+ if (xx)
+ kill ();
+ }
+}
+
+void f4 (int i)
+{
+ if ((i % 7) < 0)
+ {
+ xx = (i > 0);
+ if (xx)
+ kill ();
+ }
+}
+
+/* { dg-final { scan-tree-dump-not "kill" "evrp" } } */