Add op1_range for __builtin_signbit.

This is the op1_range range-op entry for __builtin_signbit.  It allows
us to wind back through a call to signbit.

For example, on the true side of if (__builtin_signbit(x_5) != 0) we
can crop down the range of x_5 to:

	[frange] float [-Inf, -0.0 (-0x0.0p+0)] -NAN

Similarly on the false side, we can crop to:

	[frange] float [0.0 (0x0.0p+0), +Inf] +NAN

Tested on x86-64 Linux.

gcc/ChangeLog:

	* gimple-range-op.cc: Add op1_range entry for __builtin_signbit.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/vrp-float-signbit-3.c: New test.

2 files changed, 35 insertions, 0 deletions

diff --git a/gcc/gimple-range-op.cc b/gcc/gimple-range-op.cc
index 42ebc7d..abc33e7 100644
--- a/gcc/gimple-range-op.cc
+++ b/gcc/gimple-range-op.cc
@@ -306,6 +306,7 @@ class cfn_signbit : public range_operator_float
 {
 public:
   using range_operator_float::fold_range;
+  using range_operator_float::op1_range;
   virtual bool fold_range (irange &r, tree type, const frange &lh,
 			   const irange &, relation_kind) const
   {
@@ -320,6 +321,25 @@ public:
       }
    return false;
   }
+  virtual bool op1_range (frange &r, tree type, const irange &lhs,
+			  const frange &, relation_kind) const override
+  {
+    if (lhs.zero_p ())
+      {
+	r.set (type, dconst0, frange_val_max (type));
+	r.update_nan (false);
+	return true;
+      }
+    if (!lhs.contains_p (build_zero_cst (lhs.type ())))
+      {
+	REAL_VALUE_TYPE dconstm0 = dconst0;
+	dconstm0.sign = 1;
+	r.set (type, frange_val_min (type), dconstm0);
+	r.update_nan (true);
+	return true;
+      }
+    return false;
+  }
 } op_cfn_signbit;
 
 // Implement range operator for CFN_BUILT_IN_TOUPPER and CFN_BUILT_IN_TOLOWER.
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c
new file mode 100644
index 0000000..182a33f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/vrp-float-signbit-3.c
@@ -0,0 +1,15 @@
+// { dg-do compile }
+// { dg-options "-O2 -ffinite-math-only -fdump-tree-evrp" }
+
+void link_error();
+
+void foo(float x)
+{
+  if (__builtin_signbit (x))
+    {
+      if (x > 0.0)
+	link_error();
+    }
+}
+
+// { dg-final { scan-tree-dump-not "link_error" "evrp" } }