range-op-float: Fix up multiplication and division reverse operation [PR107879]

While for the normal cases it seems to be correct to implement
reverse multiplication (op1_range/op2_range) through division
with float_binary_op_range_finish, reverse division (op1_range)
through multiplication with float_binary_op_range_finish or
(op2_range) through division with float_binary_op_range_finish,
as e.g. following testcase shows for the corner cases it is
incorrect.
Say on the testcase we are doing reverse multiplication, we
have [-0., 0.] range (no NAN) on lhs and VARYING on op1 (or op2).
We implement that through division, because x from
lhs = x * op2
is
x = lhs / op2
For the division, [-0., 0.] / VARYING is computed (IMHO correctly)
as [-0., 0.] +-NAN, because 0 / anything but 0 or NAN is still
0 and 0 / 0 is NAN and ditto 0 / NAN.  And then we just
float_binary_op_range_finish, which figures out that because lhs
can't be NAN, neither operand can be NAN.  So, the end range is
[-0., 0.].  But that is not correct for the reverse multiplication.
When the result is 0, if op2 can be zero, then x can be anything
(VARYING), to be precise anything but INF (unless result can be NAN),
because anything * 0 is 0 (or NAN for INF).  While if op2 must be
non-zero, then x must be 0.  Of course the sign logic
(signbit(x) = signbit(lhs) ^ signbit(op2)) still holds, so it actually
isn't full VARYING if both lhs and op2 have known sign bits.
And going through other corner cases one by one shows other differences
between what we compute for the corresponding forward operation and
what we should compute for the reverse operations.
The following patch is slightly conservative and includes INF
(in case of result including 0 and not NAN) in the ranges or
0 in the ranges (in case of result including INF and not NAN).
The latter is what happens anyway because we flush denormals to 0,
and the former just not to deal with all the corner cases.
So, the end test is that for reverse multiplication and division
op2_range the cases we need to adjust to VARYING or VARYING positive
or VARYING negative are if lhs and op? ranges both contain 0,
or both contain some infinity, while for division op1_range the
corner case is if lhs range contains 0 and op2 range contains INF or vice
versa.  Otherwise I believe ranges from the corresponding operation
are ok, or could be slightly more conservative (e.g. for
reverse multiplication, if op? range is singleton INF and lhs
range doesn't include any INF, then x's range should be UNDEFINED or
known NAN (depending on if lhs can be NAN), while the division computes
[-0., 0.] +-NAN; or similarly if op? range is only 0 and lhs range
doesn't include 0, division would compute +INF +-NAN, or -INF +-NAN,
or (for lack of multipart franges -INF +INF +-NAN just VARYING +-NAN),
while again it is UNDEFINED or known NAN.

Oh, and I found by code inspection wrong condition for the division's
known NAN result, due to thinko it would trigger not just when
both operands are known to be 0 or both are known to be INF, but
when either both are known to be 0, or at least one is known to be INF.

2022-12-05  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/107879
	* range-op-float.cc (foperator_mult::op1_range): If both
	lhs and op2 ranges contain zero or both ranges contain
	some infinity, set r range to zero_to_inf_range depending on
	signbit_known_p.
	(foperator_div::op2_range): Similarly for lhs and op1 ranges.
	(foperator_div::op1_range): If lhs range contains zero and op2
	range contains some infinity or vice versa, set r range to
	zero_to_inf_range depending on signbit_known_p.
	(foperator_div::rv_fold): Fix up condition for returning known NAN.

diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index ee88511eba0b4b02425c936b38a3406d97426bae..e9455a929ae7a4b2267d55a4792f013e44596bf0 100644 (file)
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -2143,8 +2143,30 @@ public:
     range_op_handler rdiv (RDIV_EXPR, type);
     if (!rdiv)
       return false;
-    return float_binary_op_range_finish (rdiv.fold_range (r, type, lhs, op2),
-                                        r, type, lhs);
+    bool ret = rdiv.fold_range (r, type, lhs, op2);
+    if (ret == false)
+      return false;
+    const REAL_VALUE_TYPE &lhs_lb = lhs.lower_bound ();
+    const REAL_VALUE_TYPE &lhs_ub = lhs.upper_bound ();
+    const REAL_VALUE_TYPE &op2_lb = op2.lower_bound ();
+    const REAL_VALUE_TYPE &op2_ub = op2.upper_bound ();
+    if ((contains_zero_p (lhs_lb, lhs_ub) && contains_zero_p (op2_lb, op2_ub))
+       || ((real_isinf (&lhs_lb) || real_isinf (&lhs_ub))
+           && (real_isinf (&op2_lb) || real_isinf (&op2_ub))))
+      {
+       // If both lhs and op2 could be zeros or both could be infinities,
+       // we don't know anything about op1 except maybe for the sign
+       // and perhaps if it can be NAN or not.
+       REAL_VALUE_TYPE lb, ub;
+       int signbit_known = signbit_known_p (lhs_lb, lhs_ub, op2_lb, op2_ub);
+       zero_to_inf_range (lb, ub, signbit_known);
+       r.set (type, lb, ub);
+      }
+    // Otherwise, if op2 is a singleton INF and lhs doesn't include INF,
+    // or if lhs must be zero and op2 doesn't include zero, it would be
+    // UNDEFINED, while rdiv.fold_range computes a zero or singleton INF
+    // range.  Those are supersets of UNDEFINED, so let's keep that way.
+    return float_binary_op_range_finish (ret, r, type, lhs);
   }
   virtual bool op2_range (frange &r, tree type,
                          const frange &lhs,
@@ -2271,9 +2293,27 @@ public:
   {
     if (lhs.undefined_p ())
       return false;
-    return float_binary_op_range_finish (fop_mult.fold_range (r, type, lhs,
-                                                             op2),
-                                        r, type, lhs);
+    bool ret = fop_mult.fold_range (r, type, lhs, op2);
+    if (!ret)
+      return ret;
+    const REAL_VALUE_TYPE &lhs_lb = lhs.lower_bound ();
+    const REAL_VALUE_TYPE &lhs_ub = lhs.upper_bound ();
+    const REAL_VALUE_TYPE &op2_lb = op2.lower_bound ();
+    const REAL_VALUE_TYPE &op2_ub = op2.upper_bound ();
+    if ((contains_zero_p (lhs_lb, lhs_ub)
+        && (real_isinf (&op2_lb) || real_isinf (&op2_ub)))
+       || ((contains_zero_p (op2_lb, op2_ub))
+           && (real_isinf (&lhs_lb) || real_isinf (&lhs_ub))))
+      {
+       // If both lhs could be zero and op2 infinity or vice versa,
+       // we don't know anything about op1 except maybe for the sign
+       // and perhaps if it can be NAN or not.
+       REAL_VALUE_TYPE lb, ub;
+       int signbit_known = signbit_known_p (lhs_lb, lhs_ub, op2_lb, op2_ub);
+       zero_to_inf_range (lb, ub, signbit_known);
+       r.set (type, lb, ub);
+      }
+    return float_binary_op_range_finish (ret, r, type, lhs);
   }
   virtual bool op2_range (frange &r, tree type,
                          const frange &lhs,
@@ -2282,8 +2322,26 @@ public:
   {
     if (lhs.undefined_p ())
       return false;
-    return float_binary_op_range_finish (fold_range (r, type, op1, lhs),
-                                        r, type, lhs);
+    bool ret = fold_range (r, type, op1, lhs);
+    if (!ret)
+      return ret;
+    const REAL_VALUE_TYPE &lhs_lb = lhs.lower_bound ();
+    const REAL_VALUE_TYPE &lhs_ub = lhs.upper_bound ();
+    const REAL_VALUE_TYPE &op1_lb = op1.lower_bound ();
+    const REAL_VALUE_TYPE &op1_ub = op1.upper_bound ();
+    if ((contains_zero_p (lhs_lb, lhs_ub) && contains_zero_p (op1_lb, op1_ub))
+       || ((real_isinf (&lhs_lb) || real_isinf (&lhs_ub))
+           && (real_isinf (&op1_lb) || real_isinf (&op1_ub))))
+      {
+       // If both lhs and op1 could be zeros or both could be infinities,
+       // we don't know anything about op2 except maybe for the sign
+       // and perhaps if it can be NAN or not.
+       REAL_VALUE_TYPE lb, ub;
+       int signbit_known = signbit_known_p (lhs_lb, lhs_ub, op1_lb, op1_ub);
+       zero_to_inf_range (lb, ub, signbit_known);
+       r.set (type, lb, ub);
+      }
+    return float_binary_op_range_finish (ret, r, type, lhs);
   }
 private:
   void rv_fold (REAL_VALUE_TYPE &lb, REAL_VALUE_TYPE &ub, bool &maybe_nan,
@@ -2296,7 +2354,7 @@ private:
   {
     // +-0.0 / +-0.0 or +-INF / +-INF is a known NAN.
     if ((zero_p (lh_lb, lh_ub) && zero_p (rh_lb, rh_ub))
-       || (singleton_inf_p (lh_lb, lh_ub) || singleton_inf_p (rh_lb, rh_ub)))
+       || (singleton_inf_p (lh_lb, lh_ub) && singleton_inf_p (rh_lb, rh_ub)))
       {
        real_nan (&lb, "", 0, TYPE_MODE (type));
        ub = lb;

diff --git a/gcc/testsuite/gcc.c-torture/execute/pr107879.c b/gcc/testsuite/gcc.c-torture/execute/pr107879.c
new file mode 100644 (file)
index 0000000..2aabe8e
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr107879.c
@@ -0,0 +1,25 @@
+/* PR tree-optimization/107879 */
+
+__attribute__((noipa)) static double
+foo (double *y)
+{
+  volatile int ph = 0;
+  volatile double vf = 1.0;
+  double factor = vf;
+  double x = - (double) ph * factor;
+  if (x == 0)
+    *y = 1.0;
+  else
+    *y = 1.0 / x;
+  double w = 2.0 * x / factor;
+  double omww = 1 - w;
+  return omww > 0.0 ? omww : 0.0;
+}
+
+int
+main ()
+{
+  double y = 42.0;
+  if (foo (&y) != 1.0)
+    __builtin_abort ();
+}