fill_constant op supports NINF (#28270)

paddle/fluid/operators/fill_constant_op.h

@@ -50,6 +50,8 @@ class FillConstantKernel : public framework::OpKernel<T> {
       // handle NaN/Inf first, which cannot be read from stream.
       if (str_value == "inf") {
         value = static_cast<T>(std::numeric_limits<double>::infinity());
+      } else if (str_value == "-inf") {
+        value = static_cast<T>(-std::numeric_limits<double>::infinity());
       } else if (str_value == "nan") {
         value = static_cast<T>(std::numeric_limits<double>::quiet_NaN());
       } else {

python/paddle/fluid/tests/unittests/test_fill_constant_op.py

@@ -340,6 +340,12 @@ class TestFillConstantImperative(unittest.TestCase):
             res = fluid.layers.fill_constant([1], 'float32', np.inf)
             self.assertTrue(np.isinf(res.numpy().item(0)))
 
+    def test_ninf(self):
+        with fluid.dygraph.guard():
+            res = fluid.layers.fill_constant([1], 'float32', np.NINF)
+            self.assertTrue(np.isinf(res.numpy().item(0)))
+            self.assertEqual(np.NINF, res.numpy().item(0))
+
 
 class TestFillConstantOpError(unittest.TestCase):
     def test_errors(self):