range-op: Implement op[12]_range operators for {PLUS,MINUS,MULT,RDIV}_EXPR

On Wed, Nov 09, 2022 at 04:43:56PM +0100, Aldy Hernandez wrote:
> On Wed, Nov 9, 2022 at 3:58 PM Jakub Jelinek <jakub@redhat.com> wrote:
> >
> > On Wed, Nov 09, 2022 at 10:02:46AM +0100, Aldy Hernandez wrote:
> > > We can implement the op[12]_range entries for plus and minus in terms
> > > of each other.  These are adapted from the integer versions.
> >
> > I think for NANs the op[12]_range shouldn't act this way.
> > For the forward binary operations, we have the (maybe/known) NAN handling
> > of one or both NAN operands resulting in VARYING sign (maybe/known) NAN
> > result, that is the somehow the case for the reverse binary operations too,
> > if result is (maybe/known) NAN and the other op is not NAN, op is
> > VARYING sign (maybe/known) NAN, if other op is (maybe/known) NAN,
> > then op is VARYING sign maybe NAN (always maybe, never known).
> > But then for + we have the -INF + INF or vice versa into NAN, and that
> > is something that shouldn't be considered.  If result isn't NAN, then
> > neither operand can be NAN, regardless of whether result can be
> > +/- INF and the other op -/+ INF.
>
> Heh.  I just ran into this while debugging the problem reported by Xi.
>
> We are solving NAN = op1 - VARYING, and trying to do it with op1 = NAN
> + VARYING, which returns op1 = NAN (incorrectly).
>
> I suppose in the above case op1 should ideally be
> [-INF,-INF][+INF,+INF]+-NAN, but since we can't represent that then
> [-INF,+INF] +-NAN, which is actually VARYING.  Do you agree?
>
> I'm reverting this patch as attached, while I sort this out.

Here is a patch which reinstalls your change, add the fixups I've talked
about and also hooks up reverse operators for MULT_EXPR/RDIV_EXPR.

2022-11-12  Aldy Hernandez  <aldyh@redhat.com>
	    Jakub Jelinek  <jakub@redhat.com>

	* range-op-float.cc (float_binary_op_range_finish): New function.
	(foperator_plus::op1_range): New.
	(foperator_plus::op2_range): New.
	(foperator_minus::op1_range): New.
	(foperator_minus::op2_range): New.
	(foperator_mult::op1_range): New.
	(foperator_mult::op2_range): New.
	(foperator_div::op1_range): New.
	(foperator_div::op2_range): New.

	* gcc.c-torture/execute/ieee/inf-4.c: New test.

2 files changed, 157 insertions, 0 deletions

diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index 91185c5..4472337 100644
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -1861,6 +1861,39 @@ foperator_unordered_equal::op1_range (frange &r, tree type,
   return true;
 }
 
+// Final tweaks for float binary op op1_range/op2_range.
+// Return TRUE if the operation is performed and a valid range is available.
+
+static bool
+float_binary_op_range_finish (bool ret, frange &r, tree type,
+			      const frange &lhs)
+{
+  if (!ret)
+    return false;
+
+  // If we get a known NAN from reverse op, it means either that
+  // the other operand was known NAN (in that case we know nothing),
+  // or the reverse operation introduced a known NAN.
+  // Say for lhs = op1 * op2 if lhs is [-0, +0] and op2 is too,
+  // 0 / 0 is known NAN.  Just punt in that case.
+  // Or if lhs is a known NAN, we also don't know anything.
+  if (r.known_isnan () || lhs.known_isnan ())
+    {
+      r.set_varying (type);
+      return true;
+    }
+
+  // If lhs isn't NAN, then neither operand could be NAN,
+  // even if the reverse operation does introduce a maybe_nan.
+  if (!lhs.maybe_isnan ())
+    r.clear_nan ();
+  // If lhs is a maybe or known NAN, the operand could be
+  // NAN.
+  else
+    r.update_nan ();
+  return true;
+}
+
 // True if [lb, ub] is [+-0, +-0].
 static bool
 zero_p (const REAL_VALUE_TYPE &lb, const REAL_VALUE_TYPE &ub)
@@ -1955,6 +1988,30 @@ zero_to_inf_range (REAL_VALUE_TYPE &lb, REAL_VALUE_TYPE &ub, int signbit_known)
 
 class foperator_plus : public range_operator_float
 {
+  using range_operator_float::op1_range;
+  using range_operator_float::op2_range;
+public:
+  virtual bool op1_range (frange &r, tree type,
+			  const frange &lhs,
+			  const frange &op2,
+			  relation_trio = TRIO_VARYING) const final override
+  {
+    if (lhs.undefined_p ())
+      return false;
+    range_op_handler minus (MINUS_EXPR, type);
+    if (!minus)
+      return false;
+    return float_binary_op_range_finish (minus.fold_range (r, type, lhs, op2),
+					 r, type, lhs);
+  }
+  virtual bool op2_range (frange &r, tree type,
+			  const frange &lhs,
+			  const frange &op1,
+			  relation_trio = TRIO_VARYING) const final override
+  {
+    return op1_range (r, type, lhs, op1);
+  }
+private:
   void rv_fold (REAL_VALUE_TYPE &lb, REAL_VALUE_TYPE &ub, bool &maybe_nan,
 		tree type,
 		const REAL_VALUE_TYPE &lh_lb,
@@ -1980,6 +2037,31 @@ class foperator_plus : public range_operator_float
 
 class foperator_minus : public range_operator_float
 {
+  using range_operator_float::op1_range;
+  using range_operator_float::op2_range;
+public:
+  virtual bool op1_range (frange &r, tree type,
+			  const frange &lhs,
+			  const frange &op2,
+			  relation_trio = TRIO_VARYING) const final override
+  {
+    if (lhs.undefined_p ())
+      return false;
+    return float_binary_op_range_finish (fop_plus.fold_range (r, type, lhs,
+							      op2),
+					 r, type, lhs);
+  }
+  virtual bool op2_range (frange &r, tree type,
+			  const frange &lhs,
+			  const frange &op1,
+			  relation_trio = TRIO_VARYING) const final override
+  {
+    if (lhs.undefined_p ())
+      return false;
+    return float_binary_op_range_finish (fold_range (r, type, op1, lhs),
+					 r, type, lhs);
+  }
+private:
   void rv_fold (REAL_VALUE_TYPE &lb, REAL_VALUE_TYPE &ub, bool &maybe_nan,
 		tree type,
 		const REAL_VALUE_TYPE &lh_lb,
@@ -2030,6 +2112,30 @@ protected:
 
 class foperator_mult : public foperator_mult_div_base
 {
+  using range_operator_float::op1_range;
+  using range_operator_float::op2_range;
+public:
+  virtual bool op1_range (frange &r, tree type,
+			  const frange &lhs,
+			  const frange &op2,
+			  relation_trio = TRIO_VARYING) const final override
+  {
+    if (lhs.undefined_p ())
+      return false;
+    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);
+  }
+  virtual bool op2_range (frange &r, tree type,
+			  const frange &lhs,
+			  const frange &op1,
+			  relation_trio = TRIO_VARYING) const final override
+  {
+    return op1_range (r, type, lhs, op1);
+  }
+private:
   void rv_fold (REAL_VALUE_TYPE &lb, REAL_VALUE_TYPE &ub, bool &maybe_nan,
 		tree type,
 		const REAL_VALUE_TYPE &lh_lb,
@@ -2137,6 +2243,31 @@ class foperator_mult : public foperator_mult_div_base
 
 class foperator_div : public foperator_mult_div_base
 {
+  using range_operator_float::op1_range;
+  using range_operator_float::op2_range;
+public:
+  virtual bool op1_range (frange &r, tree type,
+			  const frange &lhs,
+			  const frange &op2,
+			  relation_trio = TRIO_VARYING) const final override
+  {
+    if (lhs.undefined_p ())
+      return false;
+    return float_binary_op_range_finish (fop_mult.fold_range (r, type, lhs,
+							      op2),
+					 r, type, lhs);
+  }
+  virtual bool op2_range (frange &r, tree type,
+			  const frange &lhs,
+			  const frange &op1,
+			  relation_trio = TRIO_VARYING) const final override
+  {
+    if (lhs.undefined_p ())
+      return false;
+    return float_binary_op_range_finish (fold_range (r, type, op1, lhs),
+					 r, type, lhs);
+  }
+private:
   void rv_fold (REAL_VALUE_TYPE &lb, REAL_VALUE_TYPE &ub, bool &maybe_nan,
 		tree type,
 		const REAL_VALUE_TYPE &lh_lb,
diff --git a/gcc/testsuite/gcc.c-torture/execute/ieee/inf-4.c b/gcc/testsuite/gcc.c-torture/execute/ieee/inf-4.c
new file mode 100644
index 0000000..119775d
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/ieee/inf-4.c
@@ -0,0 +1,26 @@
+__attribute__((noipa)) int
+foo (double a, double b)
+{
+  double c = a - b;
+  if (!__builtin_isfinite (c))
+    {
+      if (__builtin_isnan (c))
+	{
+	  if (!__builtin_isnan (a) && !__builtin_isnan (b))
+	    return 1;
+	}
+      else if (__builtin_isfinite (a) && __builtin_isfinite (b))
+	return 2;
+    }
+  else if (c == 0 && a != b)
+    return 3;
+  return 4;
+}
+
+int
+main ()
+{
+  double a = __builtin_inf ();
+  if (foo (a, a) != 1)
+    __builtin_abort ();
+}