[PATCH] Implement range-op entry for __builtin_copysign.

[Aldy Hernandez <aldyh@redhat.com>]

[Jakub, while we're on the subject of signed zeros and copysign, does
this look OK to you?]

copysign(MAGNITUDE, SIGN) is implemented as the absolute of MAGNITUDE,
with SIGN applied.  If the sign of "SIGN" cannot be determined, we
return a range of [-MAGNITUDE, +MAGNITUDE].

gcc/ChangeLog:

	* gimple-range-op.cc (class cfn_copysign): New.
	(gimple_range_op_handler::maybe_builtin_call): Add
	CFN_BUILT_IN_COPYSIGN*.
---
 gcc/gimple-range-op.cc | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/gcc/gimple-range-op.cc b/gcc/gimple-range-op.cc
index 527893f66af..8137308f32e 100644
--- a/gcc/gimple-range-op.cc
+++ b/gcc/gimple-range-op.cc
@@ -342,6 +342,38 @@ public:
   }
 } op_cfn_signbit;
 
+// Implement range operator for CFN_BUILT_IN_COPYSIGN
+class cfn_copysign : public range_operator_float
+{
+public:
+  using range_operator_float::fold_range;
+  virtual bool fold_range (frange &r, tree type, const frange &lh,
+			   const frange &rh, relation_kind) const override
+  {
+    frange neg;
+    range_op_handler abs_op (ABS_EXPR, type);
+    range_op_handler neg_op (NEGATE_EXPR, type);
+    if (!abs_op || !abs_op.fold_range (r, type, lh, frange (type)))
+      return false;
+    if (!neg_op || !neg_op.fold_range (neg, type, r, frange (type)))
+      return false;
+
+    bool signbit;
+    if (rh.signbit_p (signbit))
+      {
+	// If the sign is negative, flip the result from ABS,
+	// otherwise leave things positive.
+	if (signbit)
+	  r = neg;
+      }
+    else
+      // If the sign is unknown, keep the positive and negative
+      // alternatives.
+      r.union_ (neg);
+    return true;
+  }
+} op_cfn_copysign;
+
 // Implement range operator for CFN_BUILT_IN_TOUPPER and CFN_BUILT_IN_TOLOWER.
 class cfn_toupper_tolower : public range_operator
 {
@@ -762,6 +794,13 @@ gimple_range_op_handler::maybe_builtin_call ()
       m_valid = true;
       break;
 
+    CASE_FLT_FN (CFN_BUILT_IN_COPYSIGN):
+      m_op1 = gimple_call_arg (call, 0);
+      m_op2 = gimple_call_arg (call, 1);
+      m_float = &op_cfn_copysign;
+      m_valid = true;
+      break;
+
     case CFN_BUILT_IN_TOUPPER:
     case CFN_BUILT_IN_TOLOWER:
       // Only proceed If the argument is compatible with the LHS.
-- 
2.37.3